250 six RPM question

[Anonymous]

: : I have a 250 six with a c4 trans and a 2.73 rear end in my 72 Maverick. I have read alot of posts and info that say it should go to around 4000 rpm before it maxes out HP. My car shifts auto at 3000, and when i do it with the gear shift, it goes to about 3500 and sound like its about to go byebye. it is totally stock, but from what i have seen on this website it should go higher than that. If someone couldexplain this to me i would greatly appreciate it.

 

[Anonymous]

You'll start to run out of breath far before 4000 RPM, even with the 250.

What's your setup look like?

 

[Anonymous]

Well my set up is stock from 1972, and I am looking for some way to get it beefed up. I have a 302 sitting in the garage, but I am almost wanting more now to have some fun and get the 6 to beat up up on some 8's at the track. I tried cliffords website but its down right now. my car runs 17.8 at 73 the way it is now, and I am just getting tired of honda's beating me. any suggestions?

 

[Anonymous]

The 1972 250 was rated 99 hp @ 3600 rpm. 1972 was the first year, as I recall, the the manufacturers rated HP and Torque with the engines in the car, i.e., a real would number. This same engine was rated 155 @ 4400 the year before. 200 engines went from 120 @ 4400 to 85 @ 3600. These are not efficient engines in their stock condition. However, a 250 would require 230 cfm of air flow at 4000 rpm, 260 at 4500. The stock Carter RBS used on the 250 in 1972 had a flow rating of 215. Go figure?? On the plus side, your '72 250 has more intake volume than a 200 of the same period so you should be able to take better advantage of more flow than us early 200 guys. No suprise to many members I am a fan of the Holley-Weber / Weber series of carbs. The 26/27 Holley 5200 flows 270 cfm. Probably light for you need. The 32/36 Weber flows 320 cfm. The 38/38 flows 350 cfm. I would probable go with the 32/36 because it is progressive and will give you more bottom end torque (better around town) than the 38/38. If you ultimately get your usable RPM range to 5000 or more through cam and head changes you can alway go to the 38/38 later.

If you do this go with the Clifford adapter and please let us all know what happens to you 1/4 mile numbers.

Buy the way, I assume your car has a dual advance distributor. A dual vac won't work with the carbs I am suggesting. Actually, it won't work with any of the carb choices out there.

For ignition I like the Pertronix Ignitor II with the recommended coil. This system eliminates the ballast resistor in the coil circut and includes a built in mico-processor to manage dwell. You get a 12 volt coil, 45000 volt spark, 20 min install and no worry about the unreliable Ford control module, i.e., no need to consider a $180 MSD unit to replace the Ford. Bet I have insulted some people here, but opinion is want make the worlf d go 'round.

Good luck. Let us know the outcome.

 

[CZLN6]

Howdy Afxtreme03:

Make sure you are getting the most from your stock set up by;
1. Making sure you throttle linkage is properly adjusted to get full throttle. This is a two person job, that only requires adjusting the linkage.
2. Increase your stock initial advance setting by another 5 degrees. Listen carefully for knock under load. If you hear none, enjoy. If you do, retard 2 degrees at a time til it's gone, or use a higher octane gas.
3. Install a set of fresh plugs gapped at .040".
4 make sure all of your tires are aired up to the max and that you're not carrying any extra junk (weight) around with you.
5. Make sure your carbs low speed system is tuned to draw maximum vacuum.

What is the status of your exhaust system?

You may find some advantage by using the smallest diameter, lowest profile rear tire possible to improve you acceleration gear ratio.

Are you preloading the torque converter on your drag strip launches? If so, what rpm?

If you must compare your Maverick to a Honda, find one that's also 30 years old, that can carry 4 people comfortably, and can survive a 5 mph crash. You have something quite different from a Honda. Enjoy it for what it is.

Adios, David

 

[Anonymous]

"The 1972 250 was rated 99 hp @ 3600 rpm"

Just out of curiosity, if it is rated at 99 hp at 3600 rpm, then why does mine shift at 3000 and sound like its gonna blow at 3450 to 3500?

My exauhst is nice and stock, nothing fancy, although I was looking into changing that.

And when I drag, I normally power brake to about 1600 before I launch. any less and its slower, any more and the tires spin.

 

[Anonymous]

The short answer is that you are not going to get more out of the stock set-up. If it is tuned as per David's response, there is no more. You simply run out of carburation at approx 3500 - 3600 rpm. This is why the factory max HP spec is 99 @ 3600. I would say you are getting that.

 

[Anonymous]

I have been thinking about some good modifications i could do to my 6, and I was thinking if i went with the 32/38 carb, a comp cam, and about a 3.00 to a 3.10 rear end. Would this be a good combo to try out?

 

[Duane]

I've wondered this rpm thing for years too. My old 200's would shift at 4500, and run past 5,000+. Now I have had two different 250's in the Maverick, and both won't hardly hit 3500, shifts at 3200 for second, 3000 for third. And the 250 has had both Carters on it, no difference. They seem to ET the same, 1/8 miles in the 11.15 @ 60 range. I have not juiced the 250 yet, my plate is for the 200 adapter, but it may go faster, being it has more low end. Maybe the bore/stroke combo makes the 250 not want to rev? I can't see only 50ci making that much more need for carburetion size. I tried that Clifford 2-1 with a motorcraft 2BBl about 15 years ago, no et gains, but it may help the 250. I have 460 in a 69 Mustang, so the Maverick performance is not real important right now, but my daughter will most likely race it next year when she quits driving Jr dragsters, so being her "little" Briggs can run 9.'s, she won't like running low 11.'s!

 

[MustangSix]

The Ford six is so short of carb and cam that replacing those makes a big difference in the way they rev.

It's surprising that the 200 and 250 use basically the same cam and carb in spite of the additional inches. If you do the math you'll see that a 250 with 80%VE at 4500 needs around 400 cfm. A 200 only needs just over 300 cfm. The stock carbs only flow about 200 cfm or less.

A bigger carb will make more power, but unless you swap cams, it will come in at the same rpm, around 4000. Switching to a Comp, Clifford, Isky, or other cam in the 252-to 260 range will wake it up considerably.

 

[Anonymous]

I run a solid lifter Crane cam a 272 if i remember right. It has a 170 head milled .060 ported a bit CC'ed and a 500 CFM 3205 Holley on a 250. To the best of my knowlege the 170 heads out flow the newer ones. The 250 isnt broken in yet and in the last 15 years is only started up and run once in a while. But a few years back I installed the head from it on a 200 in a 81 mustang. A mild Clifford solid cam and the engine buzzed an easy 7000 RPM. Carbs tried a 350 2305 Holley , Pinto 2300 carb, 500 CFM Holley with one bore blocked, A 350 2300 Holley. My favorite set up was the carb off the 2300 Pinto. Got me an easy 29 to 32 MPG even though I never could get the jetting quite right.
Usally ran the timing up to about 20 degrees initall and modified the stops in the distributor to advance the timing to 35 to 40 total. Now I could get into the motorcycle carbs I have used also.

 

[Anonymous]

The older 250 s had a bit hotter cam than the 200 s if you got one around the swap is worth a bit.

 

[CZLN6]

Howdy All:

Turbo 2256- please share your source for your statement, "To the best of my knowlege the 170 heads out flow the newer ones." We've heard that myth for years and cannot substantiate its source. Best we can come up with is an old, from the 60s, statement in Hot Rod comparing the, then new, 170 head to the 144.

The pre-70 170 head had smaller valves and ports than a late model D7 or later head. It does have a smaller combustion chamber in the head for a slightly smaller cc and, consequently a little higher CR and a slightly better squench to bore ratio.

If you have data supporting your belief please share it. And thanks in advance. I hope this is not coming accross as confrontational. That is not my intent. I am just really curious about the origin of this widely held myth.

Afxtreme03- Add a turbo type muffler to your proposed plan.

Adios, David

 

[Anonymous]

www.claysmithcams.com

This hombre Goerge is one kewl cat and will help you figure things out quick. He's a master cam grinder and enough said!

I'm running a (hydraulic) high torque cam but with a twist....The Mistro worked his magic and ground the intake lobes with a late closing and as some of you know, that makes big power upstairs! When this L6 hits 3,000 it kicks into hyperchampion and that be THE TRUFF! It pulls SUPER STRONG from 3000-5000, although "MASTER G" mentioned that running the motor to many times at 5500(maximum) would eventually spit the cam out the side!!! I have taken it to 4800-5000(not sure, the peg stopped at 4800 with the engine still climbing upstairs at a frantic pace

Give the vato a call if yer gonna race the L6....just my 2 pesos worth...

CHEVYTOWN and the

 

[Anonymous]

As soon as clifford performance's website comes back up, I am going t look into some of the suggestions I have seen here. I don't know exactly what all i will be able to do in my budget, but i know that 302 sitting in the garage with 200 HP is looking mighty good right now. I am hoping I don't give in though and keep my car unique but fast!

 

[Anonymous]

CZLN6,

The info is in a very old article done on hopping up the 200 six. Back then I didnt have axcess to a flow bench few did back then. The article could be wrong. But after doing flow bench work here is my guess. There are a number of head changes on the 200 series engines. The 144 with round log intake small chambers and valves, the 170 head round log intake big valves small chamber and a 170 head big valves big chamber, then came the 200 oval log big valve and a bigger chamber, the 250 is very much the same as the 200. Also I have heard of a truck head that was even better usd in Bronco's but have never seen one. I believe anyway the 170 heads were the best. The bigger log on the later engines from my guess has increased port volume and reduced air speed over the round style I do like the bigger carb mounting hole in the later heads. At the same time they never changed the exhaust porting over the years so even if the intake works better in the newer heads the exhaust wouldnt support it. My guess is this provided a form of EGR. Another note here throttle plate orentation seems to make a differance in fuel distribution in the log manifold. Anyway I have access to a bench now and havent had the opertunity to do any work on the "small" 6 cyl heads. The article said there is 20 percent better flow in the older heads. If anyone would like some heads ported let me know I have a great shop I work with and prices are good.

 

[Anonymous]

hi, peoples,been a while. turbo2256,your 170 head thinking is right on. my set up is,'75-250-6cyl...'70-170-head with small valves, 3 angle valve job,ported & polished. port divider. adj. rockers. head milled .010. one bbl. carb.6-1 header. block decked. comp.hydraulic towing cam. 2.5in. exhuast pipes. flo master muff. 2.79 rear end. auto. c 4-stock floor shifter.... this set up runs and sounds great.this is one bad bottom end motor. all is new so i don't have any times but will in the near future... was wondering if there are roller rockers for this head...this is in a '71 maverick grabber-c..thanks for any info on the rockers...frank..

 

[addo]

Check out AzCoupe's "shop" site for the Roller Rockers. They are a mod you won't regret.

 

[Anonymous]

M7A1V,
when you run your tiems with that engine, please post them on the board. I would love to know what kind of times you run.

I am guessing since it's getting colder and colder I might as well wait till next spring before I do anymore major work to my car. I hope all of these suggestions help give me a kick but 6. If not, the 302 in the garage is begging to be put in.

 

[LEROY POLL]

HELLO AFXTREME03

I HAVE A FRIEND, WHO IN 1983 HAD THE SAME 250. IT WAS A 1972 MAV. IT HAD GOOD LOW END BUT WOULD NOT GO ABOVE 31 MPH IN LOW GEAR (STD). WE GOT A BIGGER CARB, BETTER EXHAUST,....BUT WOULD SLOW DOWN AT 32 MPH, FOR NO REAL GAIN. THE CAR COULD GO HIGHER BUT SLOWY??? IT WAS CHOAKING. HE LIVED WITH IT FOR TWO YEARS AND BOUGHT ANOTHER CAR AND THAT ONE SAT!!

AFTER ONE SUMMER DRIVE HE WENT BACK TO IT AND SAID HE WOULD TRY JUST ONE MORE THING AND THEN SELL IT. HE GOT A SMALL CAM FROM J.C. WHITNEY FOR $60.00. I BELIEVE HIS TAG SAID IT WAS A 256* CAM. HE WANTED ME TO PUT IT IN. I TOLD HIM ABOUT THE WORK IT WOULD TAKE AND HE TOOK IT TO FATADOS, A ENG. BUILDER IN TOWN. COST HIM $145.00 + PARTS.

WITH NO OTHER CHANGE THE CAR WENT RIGHT UP TO 38 MPH WITH NO SLOW DOWN. HE HAD IT OVER 40 MPH, BUT SOUNDED BAD. THE CAR WAS MUCH MORE FUN TO DRIVE IN SECOND GEAR. IT WAS A GOOD PASSING GEAR. THERE WERE MANY THING DONE TO THE MOTOR BEFORE THE CAM. BUT THE BOTTOM LINE IS WE STILL COULDN'T GET THE CAR TO REV. THIS WAS A CALIF. TYPE CAR. TO ME IT WAS NOT AS GOOD THE OTHER 49 STATES.

SO WE BELIEVED THE CAM IS THE LIMITING PART OF THE REV PROBLEM. IT COULD HAVE HAD A LOOSE CHAIN OR SOME THING ELSE WRONG WITH THE CAM. THIS MIGHT HAVE BEEN JUST THIS MOTOR, BUT TO ME IT SOUNDS JUST LIKE YOURS. THE PRICES WERE IN 1985 SO YOU WILL PAY MORE IF YOU WANT TO CHANGE A CAM.

HE SOLD THAT CAR TO AS KID WHO REALLY WANT IT. I LOVED THE CHANGE SO MUCH THAT I GOT A CAM FOR MY CAR.

LOL....LOTS OF LUCK.

LIVE IN GRACE

LEROY POLL