opinion on possible 250 power gains

[bigblue91]

after planning a stock rebuild for this summer I've been reading through everybody's pages/articles and I think I want to get a little more power from my 250, but don't know if the gains I've be seeing are the real deal.

i found a machine shop here to mill the head down and perform a 3 angle valve job for me.

what kind of power will a 250 put out (from an educated guess) with
-9:1 compression
-3 angle valve job
- port divider (I've heard varying opinions on this...so ???), and I really like CI's stainless steel headers
-264/274 :112 cam
- i want to just do an adapter plate and a 2 barrel but does the offy triple carb setup pay for itself in looks and gains?


---ive heard great things about classic inlines headers. has anyone used stainless steel headers, how well do they hold up?


Would anyone recommend any other idea's, I'm still leaning towards a stock build but these additions do sound like fun..

 

[CobraSix]

You will see gains. Can't really say that you'll get X amount of HP, but you'll feel the difference.

1) CR helps power. But not sure where you are at now, so it may not be a gain of much.
2) This is just a good thing to do. Helps the breathing, which is the biggest limit of these engines.
3) Port divider. hmmm...Honestly, I've run with and without it. Didn't notice any difference except in the exhaust note (not bad). If you are having the head pulled off, it won't hurt to put it in. But I wouldn't pull the head just to install it.
4) The cam will be the biggest improvement and IMHO, is the best bang for buck you'll get. It's cheap to do, and not that difficult. The best part of the cam is the increased lift, which increases breathing of the engine.

http://www.kastang.info/camshaftreview.html

5) Depends on how you mean "pays for itself in looks and gains". In looks, IMHO, nothing can beat the appearance of the Offy set up. Performance, well it is a cure for the asthmatic log head. Kits can be found without too much expense if you are patient. It is also IMO one of the cheaper, high power modifications that can be done. That said, it isn't all sugar and bubble gum. It will require more tuning and tinkering.

http://www.kastang.info/offenhauserreview.html
http://www.kastang.info/offenhausermod.html


Other things to consider first:
1) Electronic ignition. This is a cheap modification, and one that will increase mileage, power, and overall performance (smoother idle, etc). Yes, it is a 'miracle' modification. TO me at least, it is the first one people who are looking to get more performance out of the engine should do. Here is my comparison of the two cheaper systems out there right now. I haven't tested Mikes DUI system.

http://www.kastang.info/pertvds2.html

2) Paired with #1, get a 40kV coil. Increase your plug gap and make it past a few gas stations. With the 200 with a 1V carb in my 65, even with the upgraded comp cam, I was able to get around 27-28MPG on the highway (with a 5 speed transmission though). If I recall, I got about 2-3 more MPG from the electronic ignition, hotter coil, and opening the plug gap to .055.


In my reasonably educated guess, as I've run a 200 with cam, 9.1:1 CR, and Offy, I think you'd probably easily see gains of 50-60% over stock with a set up like that (and I'm being conservative). My Offy set up pulled better on the high end (by my butt-o-meter) than my current Oz250 head does, which dyno'd around 141 RWHP (and what, 60RWHP was stock for a 200?). Eventually, I gotta find that slip.

 

[bigblue91]

sounds good

thanks for showing me those reviews they were informative.

the triple carb head does look good and you mentioned great gains but the tuning side turned me off, i would end up playing/tuning with the carb everyday here with the weather, haha. i saw on classic inlines that the adapter plate and 2 barrel saw a 5hp gain, I'll probably run this more conservative route and go with that setup over the offy but at least I'll see some gains over the 1 barrel.


---compression I'm not sure what I'm at I'll have to test it when it warms up but since the engines a 75' im pretty sure its 8:0 or something low since most engines saw compression losses in the mid/late seventies.
--- if i run headers i may just skip on the port divider,
clifford 6=8 says that you may see gains of 10% using it, but you and many others have wrote of no-minimal improvements so I'll pass on the divider.

--is that a reasonable cam? thats what was recommended for me when i posted several weeks ago about the 250

thanks for the info

 

[rbohm]

8) slade put up good advice. the cam you want is an excellent street cam, one thing though dont push the static compression ratio too high with that cam, stay between 9 and 9.5:1. that way you can run 87 octane with out running into detonation. the wider lobe separation angle will raise the dynamic compression ratio. as for the port divider, clifford claims a 10% gain, and others indicate very little if any gains that they can feel. i seriously doubt that the port divider will add 15hp on a 150hp engine, more like 3-5 at best. like slade indicated though if you feel you want to use it, then put it in when you have the head off for other things, other wise save your money.

a three angle valve job will encourage better flow through the valves, but you also want to do some pocket porting on the intake side. clean up the valve bowl area, and smooth out the port as far back as you can go. on the exhaust side you want to open up the ports as well as clean up the bowls.

as for what fuel system to use, as you noted the triple carb system can be a tuning nightmare to get right. as for using the 2bbl to 1bbl carb adapter, not a bad choice, i used one on my old 66 falcon to adapt a 2100 autolite carb to the 170 and it worked fine. there was a small gain in power. if you are going to do all the other work on the head though i would suggest getting the 2bbl adapter plate that allows you to direct mount the 2bbl carb instead. yes it takes a bit of machine work, but in the end you will feed the engine better in that manner.

 

[powerband]

after planning a stock rebuild for this summer I've been reading through everybody's pages/articles and I think I want to get a little more power from my 250, but don't know if the gains I've be seeing are the real deal.

i found a machine shop here to mill the head down and perform a 3 angle valve job for me.
what kind of power will a 250 put out (from an educated guess) with
-9:1 compression
-3 angle valve job
- port divider (I've heard varying opinions on this...so ???), and I really like CI's stainless steel headers
-264/274 :112 cam
- i want to just do an adapter plate and a 2 barrel but does the offy triple carb setup pay for itself in looks and gains?

---ive heard great things about classic inlines headers. has anyone used stainless steel headers, how well do they hold up?

Would anyone recommend any other idea's, I'm still leaning towards a stock build but these additions do sound like fun..

You don't need to add too much money to a stock build for power gains, a simple approach will work. You seem to have an idea of target CR and degree of build complexity. If you can live with needing higher octane, CR boost with typical valve job-head milling and/or block decking will add effective power. The complementing cam choice is big MPG and drivability variable.. Port divider is easy addition at @ $20.oo adding to confidence of cool looking and useful headers. The Offy vs 2Bbl setup can not be easily compared. As you mention the Offy looks if not the gains have unique value. I run an Offy 3X1 setup on a 250 (272 cam) and have also tried H/W progressive and 350 CFM 2300 2bbl series. Tuning the 3X1 is worth hours more fun than single 2bbl. With the 250, most H/W 5200's are too small CFM, the single 350 CFM 7448 through a 2BBl adapter in center carb position gave great performance but with the 3 Holley singles, when the outer carbs snap open to WOT, it's a more dramatic kick in the pants switch ( may also have to do with outer carb ports short runner into valves?) ....

I also have a daily driver '63 170/T5 with stock cam, H/W 2bbl progressive carb and Dual headers. It has full tilt head mods running @ 9.5:1 CR. . It needs 93 octane but with stock cam gets great mileage and cruises at low RPM-high MPH with OD tranny with ease. Headers help breathing to spin up RPM and power when the progressive 2bbl opens up ... .

Have Fun

Powerband

 

[bigblue91]

thanks for the feedback/advice.

what carbs would you guys recommend as the outside secondaries?

 

[MustangSix]

More than anything, you need to port the head for more flow. That's the biggest limitation on getting a 250 to perform.

 

[bigblue91]

After looking into it I think I will just do a direct 2BBl bolt on.
Use the 264/274:112 cam
I will stick with the 3 angle and try the head porting myself.

- as far as the headers go I like Classic Inlines stainless steel header and Clifford has a shorty header in their online catalog I like.
How well does stainless hold up or will they eventually rust like others?

Which would you guys recommend the clifford shorty or the CI header :

 

[rbohm]

After looking into it I think I will just do a direct 2BBl bolt on.
Use the 264/274:112 cam
I will stick with the 3 angle and try the head porting myself.

good choices. regarding head porting, all you want to do is clean up the bowls as far back on the intake side as possible. blend the sharp edges as smoothly as possible. on the exhaust side use the gasket to set the size of the ports, and blend back into the port about 3/4". avoid changing the shape of the port unless you have a good flow bench to determine how much flow you are getting through each port.

- as far as the headers go I like Classic Inlines stainless steel header and Clifford has a shorty header in their online catalog I like.
How well does stainless hold up or will they eventually rust like others?

Which would you guys recommend the clifford shorty or the CI header :

personally i would go with the classicinlines header. i think mikes customer service is much better than cliffords is.

 

[bigblue91]

thanks

 

[Thanimal]

I would definitely go with the CI Headers, I have a set of them myslef on my 1970 Maverick, and it does great. I also have the same cam with a 109 lobe, and it makes it sound nice,I have done quite a bit to my 250 but the headers made some of the biggest difference(s). A bigger better carb is about the only thing I can do at this point before I buy a new aluminum head and intake,.. and when that happens my auto to manual 250 sweetness will roar louder and faster then it ever has,... already dusted a 73 Camero and a couple imports. If you want to know what I have done you can email me at thanimal05@gmail.com, I'd be happy to answer questions, and since your going to swap out the cam, if your feelin ambitious, use pistons from a 255 V8, they are .085 taller and it will take your compression up one whole point e.g. (8:1 to 9:1), just buy swapping them out. that helps make up for thicker gaskets and you wont have to deck or mill the block or head if you dont want to. (but if you do then make sure you check your spacing BEFORE you do that)

 

[MustangSix]

a three angle valve job will encourage better flow through the valves, but you also want to do some pocket porting on the intake side. clean up the valve bowl area, and smooth out the port as far back as you can go. on the exhaust side you want to open up the ports as well as clean up the bowls.

Good advice. The are under the bowls are the worst. Bad transitions, lots of flash, lots of room for improvement, esp on the exhaust side. There's at least a 2-5% improvement in power just doing this.

 

[bigblue91]

on the port and polish my friend emailed me saying
-It will increase your airflow through the head and give you more top end power. But, it will cost you the good fuel atomization characteristics that a stock intake port offers
-the rough casting breaks up the fuel into smaller dropplets as it passes through the intake ports and allows for a more even spread while entering the combustion chamber past the valves. With the fuel more finely atomized you will use slightly less fuel and will have a slight boost in low end torque when compared to a ported head because of the smoother and slightly leaner burn

sounds about right but does the porting hurt these heads in any way, i know these heads need help breathing but are there short falls to porting/polish.

 

[gb500]

getting the right shape is the most important .

the wisdom in the 60's(70's?) was to polish the ports -now its leave it rough

if you do a web search, the porters leave the inlets ports rough by doing a cartridge roll (not sure what grit number) smoothing after the actual porting.

but IMHO the differences (between polish and left rough) would be small on theses old tech engines with the shape of the bowls etc being the most important


read the 6 performance handbook - gives a diagram on the shape to achieve

brett

 

[rbohm]

8) when porting the heads, the big thing is getting rid of as much flow disruption as possible. get rid of the casting flash, sharp edges, narrow the valve guide, etc. anything that sticks up more than .030" needs to be knocked down. .030" by the way is the typical boundary layer for airflow. anything smaller than .030 has little if any effect on airflow. as for polishing, that is a big nono on a street engine, and even on a race engine. the reason is that the roughness on the ports causes turbulent airflow and keeps the fuel in suspension in the air. i realize that this sounds like a contradiction where i say get rid of some things to improve airflow then tell you to not polish the same area, but there is a difference between turbulent airflow and blocking airflow.

case in point, one of my old college teachers, david vizard in fact, mentioned that when he was building race engines in england, he would port the heads to get the shape he wanted to make power, then he would take his cutting tool and let it rattle around in the port. when he was asked why he did that he said that on the dyno the rougher port walls made 5 more horsepower than when the port walls were smooth(though not polished).

 

[bigblue91]

alright thanks for letting me know the fundamentals for porting .my friend emailed me that and i just wanted to be sure of the pros and cons, but no i haven't picked up the falcon six handbook yet. i will purchase before i sit in on my build for the information.