# Need power improving tips!



## pontiacsniper (Jan 20, 2012)

The 400 in my car is out of a 75 Firebird and needs more power. It's been rebuilt from prior owner and runs great. According to what I've found it's rated at less than 200 horsepower and less than 9:1 c/r. It feels more powerful than that but needs more power. It has a ram air cam with stock 6x heads, edelbrock performer intake and 650 carb. The trans is a 400 with a 2000 stall. Would switching to a q-jet and better heads be a huge improvement? Any recommendations would be great!


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## BearGFR (Aug 25, 2008)

First order of business is to identify exactly which heads you have, 6x-4's or 6x-8's. (Google "Pontiac head codes" for a plethora of sites that will show you how to figure this out). After that, you need to know exactly which cam you have and what it's specs are. 650 is a little on the small side for a strong running 400, but a carb change and/or manifold change isn't going to make the "huge improvement" you're looking for. It wouild also help to have some sort of idea about how deep your pockets are for this project. To quote famous race driver/owner A.J. Foyt: "Speed costs money. How fast do you want to go?"
For the street, the best "bang for your buck" so to speak would be to build that 400 into a "stroker motor" of 460+ cubic inches. Doing that means rebuilding it using a new crank, rods, and pistons, plus the cost of having the block machined (bored) for the larger pistons. Then to get the best advantage of that you might also need better heads, bigger/better carb/intake to let it breathe, better exhaust, etc... 
There are such engines "out there" making above 500 HP, some more than 600... but they're not cheap to build.

Bear


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## geeteeohguy (Feb 2, 2008)

If it's been rebuilt and runs great as you say, I wouldn't tear it apart. I would look at upgrading to the stock intake and carb (Q jet) and decent exhaust manifolds and system. You also might want to change out the camshaft to a Comp Cams XE262 or XE268 grind, which will work great with your low compression. High compression isn't everything....and it won't work on today's gas without a lot of tuning and know how. It's all about the flow of fuel/air thru the engine. For under 1k, you should be able to make a significant improvement with just these bolt ons......


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## leeklm (Mar 11, 2012)

Hey Guys,

Dont mean to hijack this thread, but I have been keeping tabs on discussion threads like this as I prepare to beef up my 400 next winter. I picked up the Pontiac Performance book by Jim Hand, which of course has lots of good info. The info from the two of you and others like Lars is also very helpful!

I will try to use as much as I can from my 1972 smogger 400 block with 1975/5c heads, but am curious about my intake & carb. I have a Holley 650 dbl pump and stock aluminum manifold from a 79 firebird with egr blocked off. Can either of these support a "mild" 460 stroker with Ram Air exhaust manifolds?

Similar to sniper, my engine runs well with ok power, but even with my 4spd, I have to "try" to spin my single 255/60/15 tire with 3:36 gears. Just not right for a Pontiac!! I mean come on, those Goodyear GTs dont provide that much traction!!

On edit, I really would not mind needing to add a posi carrier. Would be a waste of money right now unless I am dumping the clutch while mashing the throttle!


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## Instg8ter (Sep 28, 2010)

stock manifold is fine you will need to move the carb up to around 800CFM especially if you get any flow work done on the heads when you build the stroker, you have a few options....Tri-power (original)....bigger four barrel (Quads will go up too 800 cfm) or something like this....LOL, i like the wow factor


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## BearGFR (Aug 25, 2008)

A 650 is going to be pretty stretched to feed even a healthy 400, much less anything bigger. There are things to be understood about carburetors and CFM ratings that aren't readily apparent to the casual observer. First of all, carb manufacturers rate flow when measured at a _certain amount of manifold vacuum_. Now think about this: if manifold vacuum is anywhere more than "zero", it means that whatever's pulling on it is already wanting more air than it can get - otherwise, you wouldn't have a vaccum, right? 

You'll find folks who go to the trouble to "calculate" an engine's CFM needs based on rpm, cubic inch displacement, volumetric efficiency, etc. --- but they forget this little item. Second, not all carb manufacturers necessarily use the same "vacuum point" to measure CFM flow, so when you compare say a QJet to a Holley 750 to some other 750, that doesn't mean that all 3 are going to perform the same on an engine. So, if you "calculate" that a 455 needs 658 cfm at 5000 rpm (assuming 100% VE - which is a fantasy), don't think that it's going to be happy with a carb rated at 700 cfm. In order to supply the engine an honest 700 CFM _without forcing it to pull a significant vacuum_ you might need a carb "rated" at something on the order of 800, 900 or even more. That need gets bigger as rpm goes up from there.

Carb sizing is something of an art though. You can't use the "bigger is better" logic and do something like put an 1100 Dominator on a Pontiac 350 and think that it'll be good because the motor will never have to work hard to get air. That doesn't work either because carburetors depend on a certain air flow velocity in order to function properly. They "need" at least SOME vacuum to get the air moving and cause their various metering circuits to operate. This is another one of those areas where experience pays off - you've got to hit the "happy area" that's right in the center of "big enough" but not "too big".

(If it was easy, it'd be a Chevy... )

Bear


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## NorwalkNugget (Aug 5, 2011)

Well from my own experiences... depends on your pockets $$$ and amount of down-time you're prepared for. For pure power like everyone is stating... q-jet and stock manifolds. I regret not keeping them when I bought this engine 2nd hand. But no matter, air is big deal so get some good stock manifold or headers and definitely exhaust sytem. If it can't breath right, it's not gonna go fast.


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## pontiacsniper (Jan 20, 2012)

Thanks for all the posts! My pockets are thin right now. Do you think a Q-jet or 750 Holley is better? I have to check my heads and report back. I have repop ram-air manifolds and 2.5 exhaust on it now. I believe the cam is the ram-air cam with .470 lift. It sounds good. It runs out of steam fast and doesn't feel like it kicks down when I stomp on it. One more question, what carb came on a 75' TransAm with a 400?


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## BearGFR (Aug 25, 2008)

Qjet all the way. (Disclaimer: I am -not- unbiased  ) Reason? even a garden variety QJet also flows 750 cfm, and it has the advantage of giving you much "finer" control over the various modes of operation from idle, to easy cruise, to highway, to WOT - all because of the design that employs metering rods and uses manifold vacuum to sense engine load to adjust fuel flow accordingly. With a Holley, you get fuel mixtures determined by idle - primary and secondary jet size - and power valve - that's it. Holley's are simple - that's what makes them popular with racers who are either idleing in the pits or at WOT going down the track, but that simplicity also shows itself in other ways. A perfectly tuned and dialed in Holley isn't going to deliver the part-throttle transition smoothness nor the fuel mileage that a correctly setup QJet will, it just doesn't have enough fine/gradual control over the fuel mixture due to its design.

A friend of mine says, "The main problem with a QJet is usually the last person who worked on it.", and there's a lot of truth to that. There's a lot of misinformation and "trick of the month club" stuff out there about them that in truth very often just messes them up. You've got to be pretty careful who you trust.

Bear


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## NorwalkNugget (Aug 5, 2011)

BearGFR said:


> Qjet all the way. (Disclaimer: I am -not- unbiased  ) Reason? even a garden variety QJet also flows 750 cfm, and it has the advantage of giving you much "finer" control over the various modes of operation from idle, to easy cruise, to highway, to WOT - all because of the design that employs metering rods and uses manifold vacuum to sense engine load to adjust fuel flow accordingly. With a Holley, you get fuel mixtures determined by idle - primary and secondary jet size - and power valve - that's it. Holley's are simple - that's what makes them popular with racers who are either idleing in the pits or at WOT going down the track, but that simplicity also shows itself in other ways. A perfectly tuned and dialed in Holley isn't going to deliver the part-throttle transition smoothness nor the fuel mileage that a correctly setup QJet will, it just doesn't have enough fine/gradual control over the fuel mixture due to its design.
> 
> A friend of mine says, "The main problem with a QJet is usually the last person who worked on it.", and there's a lot of truth to that. There's a lot of misinformation and "trick of the month club" stuff out there about them that in truth very often just messes them up. You've got to be pretty careful who you trust.
> 
> Bear


But for those who are on a budget and looking for ease of install and manitainence what would you recommend? Edelbrock or Holley?

I also thought that Edelbrocks were essentially qjet carbs?!?!


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## BearGFR (Aug 25, 2008)

I don't recommend Edelbrock carbs - at all. So if those are my only two options I'd pick the H-bomb. I still like a real QJet better than both of them though. 

Bear


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## pontiacsniper (Jan 20, 2012)

Well it looks like I have mismatched heads. Both are 6X but one has a 4 and one has an 8. Where is the best place to buy a good Q-jet???


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## Instg8ter (Sep 28, 2010)

that may be a problem as the 4 and 8's were different volume 

1976 thru 1979	6X	350(4)/400(8)/455(11) cu.in.
D-PORT	2.11	1.66	92 thru 114 CC depending on cu.in.


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## pontiacsniper (Jan 20, 2012)

Supposedly the heads were rebuilt with the engine. Is it possible they rebuilt the one volume to match the other? Like I said, it runs great but needs a little more punch.


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## BearGFR (Aug 25, 2008)

pontiacsniper said:


> Supposedly the heads were rebuilt with the engine. Is it possible they rebuilt the one volume to match the other? Like I said, it runs great but needs a little more punch.


To match the volumes that one head would have had to have been milled by about .050 or so (.060 is the max) and the other left untouched. That would have left the heads at different heights and probably made it difficult if not impossible to mount the intake manifold and get it to seal. So.... maybe possible but highly unlikely. The only way to tell for sure would be to pull both heads and measure the chambers yourself.

Bear


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## pontiacsniper (Jan 20, 2012)

Thanks, I agree,highly unlikely. Can anything bad happen with two different heads? I may just leave those alone for now and look for a new quadrajet for the punch I'm missing and start saving for a new motor. Who sells the best q-jet?


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## BearGFR (Aug 25, 2008)

pontiacsniper said:


> Thanks, I agree,highly unlikely. Can anything bad happen with two different heads? I may just leave those alone for now and look for a new quadrajet for the punch I'm missing and start saving for a new motor. Who sells the best q-jet?


I don't think it would damage anything, other than folks' sensibilities for having such a mismatched Frankenstein situation 

You should with some effort be able to find either another 6x-4 or some other matched pair of big valve heads for not a whole lot of coin.

Best Qjet? "Best" is a relative term. If you don't mind getting your hands dirty what I'd do would be to hit all the local salvage yards looking for both a 67-71 Pontiac cast iron intake and a "big car big inch" Qjet off of say a 455 Olds, Buick, or Pontiac... there's a decent chance you could get lucky and get one that's 800 cfm instead of the normal 750. 
Cliff Ruggles is 'the guy' that most people think of when they think QJets, but he's almost always backlogged with work up past his eyeballs and you can wait upwards of a year or more for him to rework a carb for you. There are others around (like Lars on here) who are also authorities on them. If you're reasonably skilled and can follow instructions, you can rebuild it yourself using equal measures of common sense and information from Cliff's book on the subject.

Bear


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## pontiacsniper (Jan 20, 2012)

Thanks again Bear! You are a great assett to this forum as well as the others who have posted answers to my question. I am going to buy a new q-jet online because i want it to look new.


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## BearGFR (Aug 25, 2008)

Well, it's not hard at all to clean up a used one to the point where it looks new, and most of the time it's going to be covered up by the air cleaner anyway.... but, whatever floats your boat 

Bear


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## geeteeohguy (Feb 2, 2008)

Here's my advice, for a quick and dirty diagnosis: do a compression check side to side. If both sides are within 15 psi compression of each other, you are ok. If one side is 185, and the other is 160, you need to get a matched set of heads. Years ago, the shop I worked at put a reman engine from a local volume builder in a Chrysler Imperial...a 440. The tech couldn't get it to run right....I was called in to check it out (I was the tune up guy), and I found that it had a mid '60's high compression head (about 10.5:1) on one bank, and a 70's smogger head on the other bank....about 8:1, with different valves and everything else. It ran like crap, of course. Even compression on all 8 is very important for a good running and balanced engine. X2 on the Edelbrock carbs.....not a fan, at ALL.


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