New Turbo Motor: 200 or 250 ?

[Anonymous]

I have been reading posts in this and other forums for over a month now and have some questions. Taking a clean sheet of paper I would like input on my decision from some experienced people.

Vehicle: 67 Mustang

Engine: 200ci or 250ci?

Induction: Turbocharger !!!!

Fuel: Carb?, MPFI?, CFI(TBI)?

Transmission: ????

I read the FAQ on the 250 upgrade on FordSix and it suprised me. There will be some issues there. My question and dilemna is, will it be worth it. No replacement for displacement! But,,,

250 pro's

+ 50 cubes
V-8 bell housing pattern
low mount starter (clearance)

200 pro's

It fits already
easier to find
lots of experience out there
Turbo's are displacement

I have read Lincs200 post a dozen times and am amazed at the results he has achieved. Does10's also has accomplished much.

This car is and will continue to be a daily driver. I need to leave it an automatic so my wife can drive it. I have never ridden in a car with an altered stall converter, but I can see how one might be desireable for off the line performance. Are they difficult to deal with on the street,i.e. stop and go traffic? I am sure an auxillary cooler would be called for at the least. I would prefer an AOD for mileage(score one for the 250), but with 20mpg a C4 ain't that bad.

About headers. After reading the equal length header posts it seems to me the way to go is a J pipe on a stock log. I haven't seen anyone justify the gains to be had on a street motor justifying the effort involved in building a header. Tell me why I'm wrong.

Lincs car is doing extremely well on a 1-barrell, but running alchohol injection and 20psi on the street doesn't sound reasonable. Blowing through a carb at 6-10 psi with pump gas would be the cheapest way out initially. But according to what I have read on the MegaSquirt site you can run a closed loop, thereby controlling A/f ratio. This is somewhat more expensive, with a CFI(TBI). I saw the mod's made to the log head by drag 200stang for MPFI, and agree this would be the best way to go, but the cost in machine work just makes this prohibitive.

Ford has a dual injector TB on some 5.0's that fits a 2100 pattern. The only concern here is boost leakage ( no solid floats, no fuel pressure control problems, no air bleeds or jets, etc.). Would the injectors on this unit be big enough? Not sure of the lbs/hr required on either a 200/250 on boost. Tell me why not.

I am so excited to have such a group of scientist's, mechanic's, philospher's, and plain old engineer's to fall back on. I've been daydreaming on this project for two plus years, and feel it closing in. I've already scored a 74 250 and have 2 200's available. Help me make up my mind !

 

[Does10s]

Howard,
I had no problems putting a 250 into a '63 Falcon. It just bolted right in. In a '67 Mustang it should be easy. The only problem might be with hood clearance. But if you get the right carb hat it shouldn't be an issue.
Both engines are great to turbo! Since you mentioned an AOD, get the 250 and stick a turbo on it. You could put in 4.11s in the rear and still get good gas mileage. Although turbos like higher gears. We've got 3.50s in Kelly's Falcon!
A 250 will easily out-torque a 200 in turbo trim. Kelly's Falcon made 320.9 lb/ft. at 2450rpm with a very rich tune up (10:1 A/F). So on the street it makes for a very easy drive. You can also destroy almost anything from a stoplight!
I also prefer a blow thru carb. EFI is great, I had it on my turbo'd 5.0 in my '86 Stang. I just like the simplicity and cost savings of the old school carb. I think I've got $60 invested into Kelly's 350cfm Holley.
Hope that helps a little.
Will

 

[Anonymous]

Thx for all the props...


I am pushing the envelope very hard because I am a little too eager to find out where the engine's weaknesses are, and am actually TRYING to break the engine (that's one tough little sucker, even with CAST rods!)
AND.....I am not done with it yet!

I think you could very easily duplicate my set up for the street with:

1) a used T-3 from a Buick GN, or small TO4B like me

2) blow through carb
(the 1946 Holley has a lot of merits to its design, I am going to see how far I can push it)
and a boost referenced machanical diaphragm pump.
A very cheap and easy set -up.

3) J pipe with manifold is cheap and easy

4) stay under 8-10 psi, intercooler is optional

5) You can always add a small, simple alcohol injection kit (if you need details, ask!) that is only used over, say.... 4-6 psi on pump gas.
If you never get into boost you will nveer need to spray it.

6) stock low-compression cast pistons are obviously good enough if you don't detonate them to smithereens like I did.

7) stock cam, stock head, stock everything else

I don't know a lot about small bell 200's - I think the ring gear is on the TQ converter? My Big Bell (80-82) 200 is closer to a v-8 pattern, so it was easier for me to do a different trans/converter swap. You could also consider a Big Bell 200 if you are set on an AOD. They are pretty easy to find.

My buddy Joe (with the turbo 4-banger mustang) was loooking at the 2- bbl CFI from the ol' V-6, and said they were 86 lb per hour injectors. (I think) That should be good to about 300 HP.

what amount do you have budgeted for this project?
Do you have: Tools? Shop ? Welder? Knowledge?

 

[Anonymous]

oh yeah, with just the wastegate spring only (no boost controller) I see 8 psi, which is still good for low and mid 15's, even with a crappy launch. That;s what my 302 Ranger runs in the 1/4.

 

[Anonymous]

Okay !

I thank you for the response. I hope to get more input on this.

The question in my mind is still 200 over 250. The 250 has the advantages of more cubes. small block V8 dimensions for flex plate and bell housing, and low mount starter.

The problems I see are the overall length, and having to source new brackets for PS & A/C. The 200 in place right now with a 1.5 inch fan spacer puts the fan @ 1/2 inch from the radiator, and if I've read correctly the 250 will be about 1.5 inches longer. I've got a Shelby hood on the car and it gives @ 1.5 inches of extra clearance.

The 200 would be a straight drop in. Giving up a 25% increase in cubes may be worth it if I can still get a AOD behind it. I have not seen any info at all on a "big bell" 200. Can you tell me where to look for this( vehicle type and year) and what the difference is ?

At first I was not sure about an I/C, then I was convinced I should have one, and now you tell me a may not need one. I know a lot of factory cars came without them. The major advantage I see is a denser,cooler air charge resulting in more power and reducing detonation potential. Boy it would be nice to do away with all that plumbing. I can tell myself I'll keep my foot out of it for lot's of reason's, but we all know what will happen. The ol' 200 is about worn out. I need more than anything passing gear and to climb these Ozark hills at a steady pace. My ego wants the car to perform as good as it looks.

I am going to get a T4/S3-T4/O .58 unit. This appears to be a close fit according to the selection guide for either 200/250. I'm thinking lag will be the defecit and RPM the result, so cam selection will be critical. There are two turbo rebuilders in my neighborhood with warehouses FULL of cores for $75 a piece. Rebuild kits at $90 make this a bargain.

Sound's like the J-pipe it is. I should probably fab up a support bracket of some kind eh ? Will standard exhaust tubing be sufficient or should I use schedule 40?

You've just about talked me into the carb. Running cost for EFI will be $600+. My main reason for looking at EFI is tuning. I am not strong in this area, and really like the idea of closed loop computer control. I want to be able to get in the car and go. Maybe I am overly concerned about this whole A/F ratio for a moderate street motor. "IF" I keep C/R around 8:1, limit boost to 10 psi, water or alchohol injection over 8psi, boost referenced fuel pump, maybe forged pistons, will lean condition be much of an issue ? I suppose an A/F gauge would be a good investment considering the savings over EFI.

Overall I'd say I'm a lucky man. Kid's all grown so money is not so much of a problem (although I still have a wife), good sized shop (pole barn), hand,air,power tools, welder(not much skill here) fairly good fab skills, and an oversized imagination. I know what I don't know, but not afraid to try something or ask questions. Measure thrice cut once!

One last note. I called the folk's at C******D about 2 years ago and they told me I'd be wasting my time to turbo my 200 ! Guess my business will be going to someone who has some real world experience!!

 

[CobraSix]

Okay !
One last note. I called the folk's at C******D about 2 years ago and they told me I'd be wasting my time to turbo my 200 ! Guess my business will be going to someone who has some real world experience!!

It is a waste...but that's not why we do it! LOL

Slade

 

[Anonymous]

1) I have not seen any info at all on a "big bell" 200. Can you tell me where to look for this( vehicle type and year) and what the difference is ?

2) At first I was not sure about an I/C, then I was convinced I should have one, and now you tell me a may not need one.

3) I need more than anything passing gear and to climb these Ozark hills at a steady pace. My ego wants the car to perform as good as it looks.

4) I am going to get a T4/S3-T4/O .58 unit. This appears to be a close fit according to the selection guide for either 200/250.

5) I'm thinking lag will be the defecit and RPM the result, so cam selection will be critical.

6) Sound's like the J-pipe it is. I should probably fab up a support bracket of some kind eh ? Will standard exhaust tubing be sufficient or should I use schedule 40?

7) "IF" I keep C/R around 8:1, limit boost to 10 psi, water or alchohol injection over 8psi, boost referenced fuel pump, maybe forged pistons, will lean condition be much of an issue ? I suppose an A/F gauge would be a good investment considering the savings over EFI.

8) I called the folk's at C******D about 2 years ago and they told me I'd be wasting my time to turbo my 200 !!

1) I think casting number E0xx is the first year (1980) but could possibly have come out in 79. Lasted until the ax fell on the 200 six program.

2) this really comes down to compressor efficency, not psi like I stated before. If you have a better quality/newer tech turbo that makes it s boost at 78% efficiency (that's pretty high) then the need for an intercooler is reduced. I think the worst efficiency (part of "islands" on a compressor map) of my S-3 is around 64% at full boogey, so I definitely need the intercooler to kill some heat.

3) Turbo will fix all that.

4) Good choice. I have a .68 A/R housing on mine, and a .58 would spool even a little quicker. Mine spools quick enough for what I need to do with it. If you spool quicker, the more the need for a good wastegate. Some of the common T-3's have wastegates built in. Also, take a look at the Holset HY-35 from dodge cummins diesel trucks. (HX 35 and HX 40 might be a little too big) These are good to about 300 HP on a 2.3 liter 4 cyl (turboford.org) so should work fine on a 3.3 liter (but don't know what spool up would be at)

5) not critical, stay around 214*/214* at .050", like the CSC-264-12-SHS
CSC-264 (112*) from FSPP

Or just use the stock cam.

6) a bracket would be a very nice touch. I used very thick stainless tubing from a Ford Explorer for mine (pre-cat), it looks to be about .060" wall thickness. Be very careful to stay away from the thinwall stuff. Schedule 40 is pretty thick, maybe Sched 10 is a better choice if it is available. All my tubing (and I do mean ALL of it!!) came from the scrap pile.

7) YES.
The carb tune will be up to you to get right. It will take some patience to get "right" and will constitute a fair amount of time to the conversion. This will also depend on what you know about carbs. If you are willing to learn a bit you might get the confidence to try to mod any carb - but some will work better than others by design.

A) You will need a solid float. A hollow brass float will get crushed by x pounds of boost (it varies by design)
B) Something with available jets in different sizes helps.
C) other design "stuff" like how the air cleaner stud is held, Power valve design and function, needle and seat design, annular venturis or not, ability to get inside to drill and modify, etc.


Some folks are even crazy enough to try to modify and blow through a 1 barrel carb.
It's a good thing those idiots don't hang out around here, because we don't need the likes of them polluting this website.


A little time on a chassis dyno would be well worth it if it is available to you.
Forget the forged pistons, the cast seem to be fine for me and "Does10s".
Even at 20+ psi. (WITHOUT detonation, mind you...)


8) Good thing I never talked to the folks at Clifford.
Who knows what kind of effect that would have had on my life.

They might have even suggested I try to blow through a 1 barrel, HEAVEN FORBID the thought !!!!

 

[Anonymous]

I forgot:

"Adapt a V8 Bellhousing"

http://fordsix.com/tech/engine/bigbell.php

Will work only on the Big Bell 200, or a 250 with no mods. (but you already knew that)

 

[Anonymous]

Some folks are even crazy enough to try to modify and blow through a 1 barrel carb.
It's a good thing those idiots don't hang out around here, because we don't need the likes of them polluting this website.


They might have even suggested I try to blow through a 1 barrel, HEAVEN FORBID the thought !!!!

I've heard about a guy whose been trying to do just that. The dam fool just refuses to give up. Seems to think that by experimenting he may be able to find out what is possible. People should just conform and be normal!

 

[Anonymous]

The dam fool just refuses to give up. Seems to think that by experimenting he may be able to find out what is possible.

People like that scare the bejeezus out of me.
They shouldn't let folks like that out in public unsupervised, if you ask me!

 

[addo]

Maybe "exile" them... Siberia?

 

[Anonymous]

Maybe "exile" them... Siberia?

That doesn't sound like "punishment" !!

 

[xctasy]

I've had three 250 powered cars, and they out torque a 200 by well over 29%. Something happens when the little 200 gets an extra 3/4" of stroke to become a 250 Ford. It seams to provide more torque than the sum of its capacity increase for some reason.

I've analysed the power and torque curve of a 200, and the weight cost of a 250 is 3% to 5% when you factor in the transmission and diff upgrades required to deal with its immense torque. If you are going to turbo an engine in the US, the 200 is the one to do it to, becasue its much softer on the drive train, and lighter and easier to get parts for tha the 250. The mass of the engine is down to 385 pounds, while the 250 is above 460 pounds. Its 21% taller, and 21% heavier

Regarding power, any 250 engine yields less than half the power a 25% capacity increase should. In most instances, you only go up 9%, despite what Fords factory ratings gave (155hp gross vs 125hp gross in the late 60's, 93hp net verses 83hp net in the early 80's). The whole car with a 250 combo is 5% heavier with a C4 and the mandatory 50 to 60 pound heavier 9 or 8.8" diff it will have to use to survive the torque loads. The cost of an extra 25% more torque in a stock 200 Falcon or Fairmont or Mustang is nothing.

Talking stock, unsupercharged 250 verses 200's. You'll never break a diff or transmission going up from 150 flywheel net lb-ft at 2400 rpm to 190 flywheel net lb-ft at 1600 rpm. When you add 9 or 12 pounds of boost, however, your 190 lb-ft 250 goes up to 310 to 345 lb-ft at the flywheel. That's more than a good 351 Windsor 4-bbl or 351 Cleveland, enough to tear stones out of cement!

Does 10's and his wife are professional racers now, and know all about great gearboxes and differentials. If you are going 250, you'll have to get a shortened 9", a set of great gears and axles, a locked Limited slip, ARB, or Detroit locker, and a fully worked C4 or AOD. Reworking the C4 is cheap. The AOD is able to be upgraded, but its a little more expensive because the torque of a turbo 250 will try to rip the 3 element torque converter shaft appart.

Since power is what wins at drag races, then the extra 25% torque is a waste of money spent on upgrading the transmission and diff. You don't see 25% more power, you see 9% when the head is the limiting factor.

I'd look at the easier to find parts of the 200, and easier to get C4 and C5 bits form a late model Big Bell 200 found in a junked 81-84 Fairmont or Cougar or 80-82 Poverty Pack Tbird (some had sixes).

An 8" diff from a Maverick or Granada has 2.79:1 gears, but you can find good sets of limited slips with 3.55's from Summit for small money. I'd just look for something you can get quickly, and look at upgrading the C5 gearbox with a shift kit and C4 truck bits, and look at an AOD from a 5.0 Mustang if your going to do street and strip duty. There are good input shafts, 2350 torque converters, and there is an upgrade availabe to raise the full throttle shift points from 3800 rpm to over 5200 rpm if you use a shift kit.

Looking at the theory, a Mini Does 10's 200 or a 2-bbl Linc 200, with a 264 cam and D8 head with direct mount 350 or 500 is in theory a 150 hp at 5000 rpm engine if its matched properly, before its turboed. Plenty of guys here have gotten close to or above that figure with a 200 and log head. Add a 12 psi turbo and charge cooler, you have 260 odd hp at 5000 rpm already. A 150 hp engine has about 200 lb-ft of torque at 3200 rpm. Add a turbo, and you are at 365 lb-ft already. An 8" will cope with that.

I'd look at taking 200 cube baby steps. Look at

Add 260 flywheel hp via a 12 pound boost 200, divide off 1.33 for gearbox and diff losses, and you have 195 hp at the rear wheels. In a 3000 pound car, there is 14.8 second quarter mile at 90 something mph. You'd need 3.9:1 gears and a good C4

With a 283 hp 250, and an extra 150 pounds from the engine and diff, you get 14.3 second quarters at 95 mph with 12 pounds of boost. Same 3.9:1 gears.

The extra 23 hp comes with a 150 pound penalty. Adding just another 10 hp via 14 psi of boost to your 200 will close the gap.

Doing the calcs with 270 hp in a 3000 pound car gives 14.3 seconds, still with 3.9:1 gears.

I doubt you'd get 100 miles at 75 mph. Either turbo 200 or 250 car would be doing 4110 rpm at that speed. You'd have to have an AOD to run it on the highway. A T5 would be in little pieces after drag racing, and are no good at drag races unless you are very consistant.

Summary is this. Torque doesn't win at drags. It has no bearing at on on your quarter mile time. Weight to power does. Since a 250 doesn't produce proportional power gains with its increased capacity, it is money wasted. Sort of like comparing a Boss 302 to a Boss 351, or a Boss 351 to a Boss 429. Mustangs running the bigger engines simply were not that much faster, and the cost in component breakage and fuel was significant.

The old maxim of "For staight line power, go cubic inches" is true only if the bigger engine has a much bigger bore. Like a 402 Big Block Chev verses a 400 Small BlockChev, or a 460 Ford verses a 455 Pontiac. Stroker engine combinations on narrow bore engines don't yield proportional power increased, and its the same rules apply with big and small turbo engines.


Deano

 

[Anonymous]

I've had three 250 powered cars, and they out torque a 200 by well over 29%. Something happens when the little 200 gets an extra 3/4" of stroke to become a 250 Ford. It seams to provide more torque than the sum of its capacity increase for some reason.

This should be obvious but is not. Your experience with both engines is just what this thread is supposed to help us with. That said let's look at this.

I've analysed the power and torque curve of a 200, and the weight cost of a 250 is 3% to 5% when you factor in the transmission and diff upgrades required to deal with its immense torque. If you are going to turbo an engine in the US, the 200 is the one to do it to, becasue its much softer on the drive train, and lighter and easier to get parts for tha the 250. The mass of the engine is down to 385 pounds, while the 250 is above 460 pounds. Its 21% taller, and 21% heavier

The only info I have on the US 250 states that it is 1" taller and 1" longer than the 200. Even stretching it I'll give you 30lbs there. I can only venture a guess that a C4(I6) vs C4(V8) differ by another 40lbs. If there is a 29% increase in torque available in stock form this should surely offset the added weight penalty. The only part I would normally add to a performance build I can't seem to find is a double row timing set.

Regarding power, any 250 engine yields less than half the power a 25% capacity increase should. In most instances, you only go up 9%, despite what Fords factory ratings gave (155hp gross vs 125hp gross in the late 60's, 93hp net verses 83hp net in the early 80's). The whole car with a 250 combo is 5% heavier with a C4 and the mandatory 50 to 60 pound heavier 9 or 8.8" diff it will have to use to survive the torque loads. The cost of an extra 25% more torque in a stock 200 Falcon or Fairmont or Mustang is nothing.

Talking stock, unsupercharged 250 verses 200's. You'll never break a diff or transmission going up from 150 flywheel net lb-ft at 2400 rpm to 190 flywheel net lb-ft at 1600 rpm. When you add 9 or 12 pounds of boost, however, your 190 lb-ft 250 goes up to 310 to 345 lb-ft at the flywheel. That's more than a good 351 Windsor 4-bbl or 351 Cleveland, enough to tear stones out of cement!

Speaking from experience I have found the stock 8" diff to be quite strong. I have a '66 Mustang with a 365hp 302 and 4 speed. It has a limited slip 3.80:1 8" that has been abused thoroughly. I recently rebuilt it and found no evidence of wear or damage. I think part of this may be due to poor traction as my best 60' time has been a 2.60.

Does 10's and his wife are professional racers now, and know all about great gearboxes and differentials. If you are going 250, you'll have to get a shortened 9", a set of great gears and axles, a locked Limited slip, ARB, or Detroit locker, and a fully worked C4 or AOD. Reworking the C4 is cheap. The AOD is able to be upgraded, but its a little more expensive because the torque of a turbo 250 will try to rip the 3 element torque converter shaft appart.

Since power is what wins at drag races, then the extra 25% torque is a waste of money spent on upgrading the transmission and diff. You don't see 25% more power, you see 9% when the head is the limiting factor.

The end result of this project would be to put between 250 to 300hp to the rear wheels. With an automatic the torque converter will absorb a great deal of the stresses involved as opposed to a manual. Drag type launches are not what I am looking for. In fact I would probably go to the dragstrip for one night just to satisfy my curiosity. I expect roll in's would be far more common. I would like to hear from anyone who has actually broken an 8" diff with an automatic, and what gave.

As for the head, that is the $64,000 dollar question. How in hell can you size a turbo system to work around all the restrictions involved? We've all seen what these guy's are doing, some blowing thru a 1 bbl !!! I am amazed and humbled. It may be like blowing through a straw but it seems to be working.

I'd look at the easier to find parts of the 200, and easier to get C4 and C5 bits form a late model Big Bell 200 found in a junked 81-84 Fairmont or Cougar or 80-82 Poverty Pack Tbird (some had sixes).

An 8" diff from a Maverick or Granada has 2.79:1 gears, but you can find good sets of limited slips with 3.55's from Summit for small money. I'd just look for something you can get quickly, and look at upgrading the C5 gearbox with a shift kit and C4 truck bits, and look at an AOD from a 5.0 Mustang if your going to do street and strip duty. There are good input shafts, 2350 torque converters, and there is an upgrade availabe to raise the full throttle shift points from 3800 rpm to over 5200 rpm if you use a shift kit.

Looking at the theory, a Mini Does 10's 200 or a 2-bbl Linc 200, with a 264 cam and D8 head with direct mount 350 or 500 is in theory a 150 hp at 5000 rpm engine if its matched properly, before its turboed. Plenty of guys here have gotten close to or above that figure with a 200 and log head. Add a 12 psi turbo and charge cooler, you have 260 odd hp at 5000 rpm already. A 150 hp engine has about 200 lb-ft of torque at 3200 rpm. Add a turbo, and you are at 365 lb-ft already. An 8" will cope with that.

I have to agree the 200 has advantages in availability, but performance oriented parts will interchange except for the above mentioned timing chain. Thank's for the faith in my beloved 8" rear !
I agree with your theory on on the above combo's, but lets say we combine the best of both in a 250; 264 cam, 350-390 cfm carb, modest c/r, intercooler, etc,...

Turbo selection would seem to be the biggest obstacle depending on where you want your torque curve to start vs horsepower. For a daily driver in an automatic ( Oh God an AOD with 4:11's or a C4 with 3:10's)
it would seem to me you would want to have your grunt at no less than 2000 rpm. Where would you peak at on horsepower?

Summary is this. Torque doesn't win at drags. It has no bearing at on on your quarter mile time. Weight to power does. Since a 250 doesn't produce proportional power gains with its increased capacity, it is money wasted. Sort of like comparing a Boss 302 to a Boss 351, or a Boss 351 to a Boss 429. Mustangs running the bigger engines simply were not that much faster, and the cost in component breakage and fuel was significant.

Please correct me if I am wrong. Torque is the significant factor in acceleration, horsepower is for top speed. That may be oversimplifying and may be just wrong, but is essentially what I've read for over 20 years. When it comes to weight to power I think typically we use peak horsepower numbers. But when for instance a serious drag racer selects a flash speed for a torque converter, he is using his peak torque rpm. This is why I feel that actual torque numbers are more important in figuring for your system approach to engine building for a specific purpose.

 

[addo]

I agree with that last paragaraph! If the FTF isn't leaning hard on his motor's torque characteristics, where the heck is he getting his times from? I've never drag raced, never built a turbo six but what I have seen is a different approach compared to building quick eights. One of the big differences is in gearing. Again, this has to be related to torque.

The eight and six C4s would only differ by a few ounces weight. Both run similar enough cast alloy bells, one has a few less plates (from memory) and a smaller front servo under the same cover. So any weight differences are really in the block and crank. I expect the 250 timing set supply issues will be resolved soon enough by AzCoupe.

A thought or two on diffs. This actually came from a guy known as "jmac", a few years ago. Like X, he pondered things and also he'd got a modest amount of racing background to back things up. He suggested that the main benefit of a 9" was in drags. It added a gyroscopic effect that helped traction and stability if the chassis tuning was right. For all other applications, as light a diff as possible, was the key.

Back then I offered a case of beer to anyone who could prove they'd broken a smaller diff that had been professionally set up - nobody came forward. Suddenly the "gotta getta nine" cheer squad had fallen silent. The big benefit of a 9" to people in the US is supply of parts; new and used.

Anyhow, just a few thoughts!

Cheers, Adam.

 

[xctasy]

Some ground rules, citing the example of

Case 1) a 125hp 12A Mazda RX-7. An RX-7 has 109 lb-ft of torque at 4000 rpm, 125 hp flywheel hp at 6000 rpm, and weighs 2400 pounds.

Case 2) a 65 Mustang 200 fastback with a good 350 or 500 cfm carb, automatic and some moderate mods, verses A 200 may have 125 flywheel hp at 4600 rpm, 182 lb-ft at 3200 rpm, and also weigh 2400 pounds.

Case 3) a 65 Mustang with a Smog 1980 302 with 125 hp at 4200 rpm and 216 lb-ft at 1800 rpm to the Mustang and kept weight at 2400 pounds.

Weight to Power is the only thing which affects the rate of acceleration.

The only time torque comes into it is the impules off the line, when it helps the net thrust at the wheel. For about 33 feet. Past that point, the power takes over. Power is the rate at which work is done, torque is the force applied. I can out torque a 200 six right now, by adding my body weight to a a 1 foot steel rod, and dangling off the end of the crank shaft. 182 ft pounds over 1 foot. I win.

The rate of acceleration is power. 182 lb-ft at 3200 rpm is 111 hp.

I can't do 111 hp at 2400 rpm, let alone 125 hp at 4600 rpm.


Top speed, given enough road, its not related to the weight of a car. If its 1500, 3000 or 6000 pounds, and has the same frontal area, tire drag, and drive train losses, a 260 hp engine will yield the same top speed, given enough road.

(Km/h to the power of three) = (Flywheel kW/1.333)-(Tire drag in kW)-(drag factor X frontal area in m2)
. . . >>>>>>>>>>>>>>>>>>>. .........................................76719


Weight is definately not a factor in top speed as long as the rolling resistance in the tire is the same.


Example of a 1968 Mustang 200 notchback

estimated 125hp net at flywheel (93 kW), C4 automatic and 7.25" diff (1.333 power loss from flywheel to wheels, means there is only 94 rear wheel hp), 3.55:1 rear, P215/60-15 tires loose 10.46 hp at 112 mph (5.8 kW loss at 180 km/h), 0.44cd, frontal area 22.06 Sq ft (2.06 m2).

Given gearing, mph at 1000 rpm is 20.6, so 75 mph is 3640 rpm

Weight is 2400 pounds all up, but its irrelevent when assessing speed if the road is long enough.

Tire hp loss is 5.8 kw with 2400 pounds, or about 7.85 hp at 112 mph.

*Top speed 112 mph @ 5435 rpm if it had that estimated 125 hp at that rpm. As it will be, if power is at 4600 rpm, you'd only get about 95 mph or so. At 5400 rpm, all the power would have tailed off long ago.

Gearing is *20.63 mph @ 1000 rpm in top with C4. Raising the gearing above a certain amount hurts acceleration because the torque multiplication drops as the gearing is raised

*Standing Quarter Mile is 17.17 sec Mph at end of 1320 feet should be 75 mph, using

*Rpm at end of I/4 mile (1320 ft) = 5400 rpm in second gear

For the other 660, 330 and 60 feet accelerations, you calculate them like this :-

Standing 1/8 Mile Formulae (0-660 feet):-

ET=([Weight/hp]*198)^0.289 , = 11.76 secs

Standing 1/16 Mile Formulae (0-330 feet):-

ET=([Weight/hp]*198)^0.240, = 7.74 secs

Standing 1/88 Mile Formulae (0-60 feet):-

ET=([Weight/hp]*0.54)^0.450, = 3.26 secs

Summary


None of these inputs are related at all to torque. Not one.


In the final analysis, a 125hp 12A Mazda RX-7 , a 125 hp 200 Mustang, or a 125 hp 302 Mustang will accelerate at the same rate if they are the same weight.


Even if one has only 109 lb-ft at 4000 rpm, and the other has 182 lb-ft at 3200 rpm, and the 302 has 216 lb-ft at 1800 rpm.


The 60 ft, 330 ft, 660 ft, 1320 ft and top speed figures would be no different despite the torque raitng, becasue the torque and engine has isn't a measure of its ability to do work.

Despite the 302 Mustang with smog engine having 100% more torque than an RX-7, and 19% more than our worked 200, there is no difference in acceleration.

An accelerating RX-7, 200 Mustang or 302 Mustang never sees less than 3000 rpm on take-off or even during gear changes, so the low end torque is totally irrelevent.

Getting back to the turbo situation, most T03 and TO4 turbos can be tuned to work with a 200 or 250, a carb of about 200 cfm at 3" Hg, like the 1946 Holley 1-bbl, or 350 cfm at 3"Hg, like the 2-bbl #7448 , or 500 cfm at 3" Hg, like the 2-bbl #4412 Holley. What turbo guys find is that a restrictive carb and head brings on the boost later than a free breathing head with the same turbo. An engines volumetric efficiency drops if a restrictive head, longer stroke, or smaller carb is added. So people here who run log heads and 200 cube engines with small carbs have to wait a few more revs for the turbo to kick in. A 500 cfm carb 2v head 200 will come on the turbo sooner than a 1-bbl log head 200 will with the same turbo. If the turbo characteristics are not suitable, the owner just adds a different stall ratio converter or a different profile turbine to suit.

Becasue turbos make boost, a 1-bbl carb can out do a 2-bbl 200 if the turbine and converter are suitable. All that is important is the peak power. If a 200 1-bbl needs 16 psi to do the job of a 12 psi 200 with a 2-bbl, and its tuned to operate properly, then who cares?

Linc 200 and Does10's are smart enough to make the turbo do all the work, and don't care what the CFM rating on there carb is. As long as the engine makes the peak power they want given the wieght of the car, then they have achieved there objective.

That's what we should focus on. Getting the power level we can afford.


Last point. The 250 I6 is 1.677" taller than a 200 I6, and is about 82 pounds heavier. 462 pounds verses about 380 lb, dressed to run. It is in fact almost as heavy as a 240 or 300 I6 becasue it runs the huge 6-bolt V8 bell mount, and, unlike the 240/300, has no weight saving by having a side plate in the side of the block, or alloy intkae manifold, both which save a heck of a lot of weight.

In a Mustang, you'd then need to add another 55 pounds for power steering, or go work out in a gym, to cover off the added wieght of the engine on the steering forces. In a 2400 pound Mustang, it could end up being a 137 pound weight penalty, which is a 5.7% weight gain in a 2400 pound car. If the six only yields another 9% more power, and forces you to add 5.7% more weight, then your 250 has only addded 3.1% more power.


A turbo on a 200 will provide all the power you can use. The extra cubic inches of a 250 engine are not effective in making more power for every pound of weight.

 

[Anonymous]

The big benefit of a 9" to people in the US is supply of parts; new and used.

That's about it .

Otherwise, it is just too heavy and draggy for anything other than the most serious of racers.

 

[Anonymous]

interesting discussion, execute.

I would like to see both engines performing real world to see if practice matches up with theory.

One reason I have never bothered with a 250 is they are getting rare. I have never had the opportunity to buy one. I never see them at the wreckers or in people's backyards. On the other hand, people are ginving me 200 engines for free.

Howard, you really opened a can of worms, here!

IMHO, if you do decide to go with a turbo, go with a 200. Power will be more than adeqaute if done right. Parts for 200's seem to be easier to find, and I think a log head on a 200 is restrictive enough without trying to make it flow well on a larger 250.

On the street, torque is king. A 250 will be more fun to drive "off of the light" because the torque is right there. But, I can break the tires loose (both, I have trac loc) with a 200 (no boost) so a 250's torque would be excessive.

A turbo 200 is lacking for a little bit until boost arrives, then will eat the 250. My 200 is actuallly torquey enough before boost (burnouts are no problem) that I do not complain.

A turbo 250 would be a great, torquey combo because the turbo takes over right when the head gets restrictive. It will also have more power to deal with the AOD trans.

It all depends on how much power you really need. Or the wife wants.

 

[Anonymous]

Linc you hit the nail on the head. A great big can of worms. This is just what I wanted to see.

If there were as many 2v heads out there as 250 I6's everyone would have one, right?

All things considered my main concerns deal with the fact that from the crank back I would have the stronger V* tranny as a bolt in. I know there are some other issues to address with that such as mounts, TV cables, driveshaft and such, but no adapter plates or block mods. Call me lazy.

And I think we can all agree a 250 will out torque a 200 for a few RPM anyway.

When it comes to feeding pressurized air the head and carb become the issues.

xecute is without a doubt the magic formula man. Do any of you have actual flow numbers on a factory log head? With all the variations I know these numbers would be arbitrary. There is where you have to look at experience. Does 10's thinks the 250 is the way to go. He is getting better performance than my 6500rpm 302. Linc's is just getting started probing the potetial of his 1bbl 200. Air flow has not really been a limiting factor yet in power production.

So, to address execute's statement, focusing on getting the power we can afford.

Given the mod's most of you agree are the best:

Blow thru carb: probably a 350 holley 2v
Stock pistons, cam and valvetrain
TO4 turbo

Why give up the extra 50 cubes?

Weight
Rarity
Negligible increase in HP

The strategy of this engine is to drive it to work, weekend trips, get groceries, and suprise 5.0's

I want to build it once, get the tune right, and drive the s**t out of it.
I've reached the stage where tinkering has lost a lot of it's magic. I prefer to make it right and be done. Making it right the first time out is the hard part. If Does 10's can make 320 lb ft I think I could easily live with his combo. Then I can live vicariously through Linc's and glory in his acheivments.

That is why I posted this thread. I can't believe I'm the only one contemplating a decision like this for this very reason.

In my dreams I'd build the short stroke 200, cam the crap out of it, MPFI, blow it to 22 psi, turn 7000 rpm at peak and scare the crap out of myself and everyone around. Great drag car or road racer, bad grocery getter.

The other side is to build the long stroke 250, rely on the hairdryer to make outstanding power to maybe 5000 rpm, and smile while I sit at a stoplight to gently roll away knowing the whole time I could punch it and launch like a rocket.

 

[6bangerwanab]

very interesting read guys, might have to go through it twice to make sure i caught it all!

sorry howard i dont have anything to add to your situation.

but it has gotten me thinking, my 61 falcon, that i intend to do more autocrossing with than dragracing that a 200 would be better for me since it will reduce weight over the front tires, helping with handling, and on a drag car, weight transfer (correct me if im wrong there) plus its packadging will allow it to fit better under my smaller hood.

also a note on torque: your not going anywhere very fast if you spinning tires that have been overcome with power.

im fixing on starting with a carb and progressing onto a megasquirt fuelie setup, but just so you are aware i just removed a cfi system from an 84 mercury capri (3.8 v6) and it should be very simple to transfer to a different vehicle.