85 Grand Prix LE with a pontiac 400

[gto78]

So your saying the 4 tube headers for a 68-72 GTO should fit? I currently have a set of 4 tubes but I don't know what model they were built for, and when they're worn out I want some that fit right in place. I used to have stock 301 manifolds on the car when I originally dropped in the 400 since they bolted right up to the engine and I already had dual exhaust. Then I tried firebird headers which were impossible to fit. Then someone gave me some 3 tube headers, one side fit easily and the other side had to have 2 pipes replaced at the muffler shop in order to fit my chassis. Eventually a friend gave me a set of 4 tube headers that fit really well with some minor hammering here and there, and trimming of the lower A arm outer edges.

I used the stock 301 engine mounts on my first 400. Then we had a 428 which required special mounts, something was different about that block. After that dropped a valve we got another 400 block but it's older style and wouldn't fit my car without using the special 428 engine mount brackets.

I'm really interested in factory headers. They're cast iron right? How do they perform in comparison to the standard 4 tubes? I'm slowly making this car more street friendly/reliable and want a decent exhaust system that doesn't leak. Header gaskets seem to constantly blow out, and headers rust pretty easily.

 

[MrHarley123]

Early 4 tube headers for late 60's models lemans/gto's fit with some banging and 3 tube headers also work from the a body cars. Firebird headers will not work so don't waste time with those. The 428 is a pre-1970 engine which does not have all 5 mounting bosses that blocks after 70 have. Butler Performance sells the adaptors for around 20 dollars or you can make your own. Manifolds from the 350 and up flow alot better than a set from a 301. The factory headers that are being reproduced are cast or aluminum. Price is the major deciding factor for them. They are availible from Ram Air Restorations. http://www.ramairrestoration.com/catalo ... th=31_2_21
What type of set up are you using for your engine. What are your goals for your engine? What cam, intake, valve train components because you may not even need headers. SD Performance did a write up on the benefits of using headers over ram air manifolds and the results may surprise you. http://www.sdperformance.com/moreTech.php?newsID=39

 

[MrHarley123]

If you are set on getting headers for the poncho then here is the price on a very good custom set of headers for the g body swap.http://forums.performanceyears.com/foru ... dy+headers

 

[84GP455]

You don't need headers, they are grossly overrated in my opinion! They rust, leak and get banged up when going over simple speed bumps and what not. I have run a set of factory Pontiac cast iron headers on my car since 1991 and only changed the gasket once! Try that with a pair of headers! IMO they are better than headers because they are basically maintenance free. How much extra horsepower do you really get from them anyways? 25-30hp maybe?? I don't really know but i blow by cars with headers all the time so do they really make that much of a difference?? Get the Ram Air headers and they flow just as good as headers if not better.

 

[gto78]

This car used to be a 1/4 mile drag car only. My dad and I got tired of the race scene because of the constant risk of blowing stuff up, and only getting to drive once a week. So now I've been in the process of converting it to a weekend driver car. I want it to be reliable but still don't want to throw away HP by using stock manifolds. I'd get the factory cast headers if I could afford them, they're better than manifolds and still reliable. Those headers from the Performance Years forum link look really nice, especially the 2" primaries- but $725 is out of my price range.

I'm running a 400, stock pistons/crank, Lunati 292 cam (490 lift, 230 duration), holley 750 square DP, HEI ignition, 3.73 gears, Super T-10, #670 GTO heads, 2.11 intakes/1.77 exhausts, 10.3 compression, hydraulic lifters, and stock windage tray etc. The cam is made for 1800-5800 rpm range if installed straight up (which it is). I have a used set of triple valve springs a friend gave me, it's been so long that I honestly don't even know what pressure they are or what height I installed them. They probably should be replaced if I ever go back to racing. But basically that's the engine, nothing special, just a few mods.

 

[79GP6.6L]

Do it, it is the way GM should have offered these cars I the first place! Yes, I know why they didn't/couldn't, but you can. My 79 has had a 400 under the hood since I yanked the 301 in 1994.

I run Hedman shorty headers on mine, with 3" downpipes. Outstanding ground clearance. The drivers side header required collector modification to fit (with a welder, not a hammer).

 

[MrHarley123]

Nice set up gto78. With a 10.3 to 1 compression it is not going to be very good on just pump gas. Pontiac iron headed motors tend to detonate at that level. My set up is a 400 stroker(461), ram air 4 cam( 308,320, 230,240 at about 520 lift. It also has a performer rpm intake with 6x heads at 9.2 to 1 compression. Have your heads been ported? If not the guys at butler performance do good head porting starting at around 600 dollars and up. They are in tennessee. With some head work you could be in the mid 11's on motor. My next upgrade is either kre or edel aluminum heads.

 

[gto78]

Nice set up gto78. With a 10.3 to 1 compression it is not going to be very good on just pump gas. Pontiac iron headed motors tend to detonate at that level. My set up is a 400 stroker(461), ram air 4 cam( 308,320, 230,240 at about 520 lift. It also has a performer rpm intake with 6x heads at 9.2 to 1 compression. Have your heads been ported? If not the guys at butler performance do good head porting starting at around 600 dollars and up. They are in tennessee. With some head work you could be in the mid 11's on motor. My next upgrade is either kre or edel aluminum heads.

On my 78 Grand Am I had the #670 heads and the same RA IV cam your running. I drove it on the street for years on pump gas and had no problems. On that car I decided to donate the #670 heads back to the guy who gave them to me in the first place, he was trying to make a nice 67 GTO and needed the heads to get the engine built right. He gave me a great set of 6X which I then milled .050 and cc'd around 88CC. That engine never had the same power as it did with the #670's. I pulled the engine and moth balled it in my garage when I junked that car. My current car/engine has #670's in it also. We didn't really port it but we did gasket match and do my own half *ss version of a port job with a dremel to just smooth out the runners and get rid of the messy mold marks from the factory.

I've heard that although aluminum heads flow better and overall make better power than any old school heads, the aluminum heads supposedly have to run at least one point higher compression ratio to make equal power as the equivalent iron heads. In other words two identical heads, one aluminum and one iron, the aluminum head won't hold the heat inside the cylinder and therefore allegedly loses some power. I don't know if that means anything or even matters, but supposedly you have to run higher c/r to get the same power.

I think I'd still want aluminum just to save a ton of weight.

 

[MrHarley123]

Yeah I see why you were not happy with the 6x heads on your 400. Even with the .50 mill on those heads the compression was in the mid to high 8's instead of the low 10's you where getting with the 670's. D port heads all flow about the same so your compression just was not high enough to get you back where you where. The reason that everyone leans more toward the aluminum heads is because of the potential for more. Even the best ported iron heads will only flow around 260-270 after about 2000 in port work, yet you can buy kre heads that flow that much stock for the same price, and the edelbrock's flow even closer to 300cfm standard. Bolting on either one of those heads gives you 500ftlbs at around 2200 to 2800rpms easy. Hope you are enjoying teaching the chevy boys what a poncho powered car can do. I am from the augusta, ga area where everyone thinks that the 350 is the best motor in the world and nothing can beat it. We raced at Jackson Drag Strip also known as the house of hook.

 

[gto78]

As far as needing to flow 300 cfm, do you think that makes any difference when running an 1800-5800 cam? I can see using a head that has a better combustion chamber and better quench, better heat disipation, nice solid valve train, and making it as efficient as possible. But I wonder if needing that much more flow would really make a difference on a setup that doesn't go beyond 6K rpms. I'm real picky about what mods to use and only use the ones that actually seem to make a difference, since I have an extremely low budget. So far we've been pretty successful in reaching our goals of keeping a mid 12's car with not too much breaking down. If I could afford it I'd go for those heads.