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Old 02-01-2004, 09:19 AM
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Help on a Pontiac 400 dirt track motor

I am trying this again to get better attention on the topic.

ok, I dont know much about Pontiac, and we are building a motor for circle track. we cant use chevy parts or cars, so we have a 79 firebird and a stock 73' 400 (we use to run a 80' 301). we want about 9.5-1 compression, it already has flattops with the 4 valve spaces. the motor is suppose to have I believe 7.5-1 compression. The heads say 4X on them. Alot of cc space in there, ALOT. What heads do I need to get more compression, less cc, and keep the torque.

The rules say motor must APPEAR stock. We can't have more than 9.5-1 compression. Has to be Brand to brand IE. Pontiac to pontiac, ford to ford. NOT ford motor in chrysler and so on.

We can't have alot of lope, must sound very close to stock unless motor was built with a slight lope, just maybe enough to notice a bit. 455 lift should be max. Shift for us should be about 4,600rpm.

The rules say stock motor specs, but they have a gray area, they didnt say match year of car to motor, and in 69 they had a 400 with 10.75-1 compression and 380 hp. Then in 81 it was 180hp. and 8.1. Makes little sense to me, they should of said year of car to match year to motor. They dont, just brand.

Like i said, 9.5-1 compression, little lope with 455 lift cam, no aluminum high rise, cast iron intake with maybe a slight little high rise if not to noticeable, OH, and we can only run a 500 Motorcraft 2 barrel.

another great night for us.
http://pic7.picturetrail.com/VOL192...68/37537472.jpg

OH, and if you can, email me any specs that you might know, I dont have anything to go on at the moment. THanks


Last edited by ridlenracing on 01-31-2004 at 07:50 PM

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Old 02-01-2004, 09:44 AM
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the reason the horsepower and compression ratings make no sense is because in the early seventies hp. ratings were revised to reflect a more correct power rating with all components on the vehicle. For heads try something like 670 heads or early (pre 71) heads. Most Pontiac cams use limited lift anyhow because of the short valve springs and limited rpm range
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Old 02-01-2004, 11:18 AM
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I would find something like this intake or this intake and hack it up to have an open plenum so that you get as much out of the tiny carb. You could probably find one without an EGR pretty easy too.


For a cam I would run 0608 or this. Youre kind of stuck with a custom grind if you want something bigger because of the lift being limited.


For heads I would heads either use a set of 6x from a 350 or something from late 60s but I dont know casting numbers. Heres a little info on cyl heads.

The only guy I know who is a Pontiac freak isnt into computers or Id have him try to help.
How are they checking compression?
Are you allowed to do any porting?
Sounds like a lot of leeway to get creative with the rules.
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Old 02-01-2004, 12:04 PM
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THey usally check it by pulling a plug and turning it over with a pounds meter or something of that sort, no porting allowed.

What are these heads, any good. F232 4X, thats is whats on the motor. where would I look for some 6x.

What do you mean cut up the intake? Like I said, no porting or polishing. I WISH.
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Old 02-01-2004, 01:14 PM
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Are these intakes anything special. I looked at the cams and heads codes, THANK YOU. That was a huge help. I believe I need to find better heads, that is for sure, less cc. What head do you recomend? AGAIN, thanks for the info.
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Old 02-02-2004, 06:11 PM
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Set of those 13, 16, or 62 look pretty good I think they're fairly common. People get big bucks for the 670 castings.

On the intake you would grind down the center divider it would still have the runner layout of a dual plane intake but have an open plenum right under carburetor.
A dual plane intake has each bore of carb feeding only one side of motor, on a intake with open plenum both venturis are exposed to all cylinders.

This is hard for me to explain.
When all cylinders have access to both venturis they will draw more air into the motor even though the carb would be the same size.

Something to think about. With a carb that small will you start to pull enough vacuum at full throttle that power valve will shut?
Where is a carb genius when you need one?

Last edited by Greg Latvala; 02-02-2004 at 06:20 PM.
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Old 02-02-2004, 08:43 PM
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I would personally use the # 16,62,12,13 heads these are great heads to choose from and flow pretty good I would turn to comp cams for a good cam


Thad
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Old 02-02-2004, 10:07 PM
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All the previous heads are 72 cc from the factory, and all will produce about 10.5:1 compression. There are two different 4X heads, one has 98 cc chambers and came on the 400, and the other has 114 cc chambers and only came on the 455. You should have the smaller chamber head. Both of these 4X heads have the smaller 1.66" exhaust valves. Not the end of the world, and you could substitute the larger valve with suitable bowl work if you can get away with it. While I'm not a fan of the smaller valve, Edelbrock saw fit to use the 1.66" valve on their aluminum heads. Your 4X's should be okay with enough material milled off to arrive at the 9.5:1 ratio you desire.

Other acceptable cast numbers are 64 and 96 because of the larger 1.77" exhaust valves. Both can be milled to get down to a 9.5:1 compression ratio without problem.

Pontiac cams came with more duration on the exhaust port, and whatever cam you choose, I'd probably stay with a split duration cam. As mentioned earlier, the stock 068 cam is surprisingly good with a wide power band. Only thing it lacks is lift at .406".

Pontiac manifolds are hard to beat, but I'm not too sure about removing more than about an inch of the spacer plate. The dual plane should produce more torque, and removing too much could kill your bottom end and midrange.

If cost was no object (and you could get away with it), you could go for a 4.25" stroker crank with the 3" mains with a .060 bore, and get it out to about 468 cu. in. and by using the 4x unmilled, you would be right where you need to be on compression ratio.
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Old 02-28-2004, 10:32 AM
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need some

I am looking for some heads with 76cc for a 73' 400 pontiac.. If you have any that are good and ready to go, let me know please.
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Old 06-16-2007, 10:26 PM
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Pontiac Motor

Talk to the Dude at zKuffmanRacing E-Mail is kre@ecr.net. they helped me out a lot for I dont know a lot bout the pontia. And that is all they do is Pontiac.
John Martin
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