Author Topic: 6X Pontiac Heads (Read 8174 times)

LANCER · « **on:** December 30, 2006, 05:03:08 PM »

I have a quick question. I have 6X 8 heads on my 1977 Trans Am with a 400 engine. I am going to go threw the engine soon. Should I rebuild these or should I be looking for 6X 4 heads? If the 6X 8 will work what should be doen to these to make them perform? I am trying to achieve a motor that has 250 HP instead of the stock 180HP. Thanks Lance

Tin Indians Rule · « **Reply #1 on:** December 30, 2006, 06:47:03 PM »

lancer, i'm not sure that swiching to the 6X4 heads would really be worth the investment. They would certainly lower your compression by a few points but I think your goal can be acheived easily without the added expense of buying 6X4 heads.

A good quality rebuild with a high performance camshaft/intake/carb on a 400 with a properly tuned distributor would easily net you the 250 ponies that your looking for.

I'm sure there are guy on here that can provide you with specific cam grinds, intakes, etc to acheive your goal. Also, most cam manufacturers will guide you to the cam thats right for your application. Consider installed options such as A/C, rear gear and idle quality before choosing.

LANCER · « **Reply #2 on:** December 30, 2006, 06:57:50 PM »

So far I have purchased a Edelbrock Performer intake and a 750 Edelbrock #1411 Carb. When I pull the engine I am going to have it cleaned and cooked. should I do these things?New pistons,bore it, deck it ?I would greatley appreciate a few members of this board giving me there input or experiences in achieving more HP with out breaking the bank. Thanks

Tin Indians Rule · « **Reply #3 on:** December 30, 2006, 11:46:10 PM »

Lancer, Some of those questions are best answered by your machine shop. As far as vatting the block, heads, etc, you'll have to do that to get everything clean enough to check tolerances.

Do you plan to rebuild the engine yourself or will you hire it done? Regardless, you'll know if the block needs to be bored after you mic the cylinders. Chances are good it'll need some amount of overbore unless it's recently been done. I never cut corners on an engine that I have no previous personal knowledge of. Everything gets checked, magnafluxed, mic'd, replaced or reconditioned to spec. Spend the extra money and find a machine shop that can pressure check your heads and block. Don't skip that part, it's money well wasted.

Your machine shop can tell you if you need to deck the block or mill the heads. Just remember that too much compression creates detonation. And detonation eats engines. If you do deck or mill you'll need to cut the intake as well so it'll seal against the heads. You're changing height when you're milling and decking which will also have affect on valve train items depending on how much you mill or deck.

It seems like a nightmare but find yourself a good machine shop that knows something about pontiac engines and then share with them your horsepower goal and budget. What kind of budget are you on? You may need to rebuild small now but keep in mind bolt on stuff for down the road as money surfaces.

LANCER · « **Reply #4 on:** December 31, 2006, 10:07:45 AM »

I have about $2,000 to spend at this point. I have found a set of 6X 4 and 4X heads. Not sure if one is better than the other. When I pick one of those heads up I am going to take it to our local macnine shop and completely have them goen threw. My brother inlaw will be doing the assembly, he use to race at Brainerd International Speedway, so he is pretty sharp in this catagory.The block will be striped down and checked out for cracks or any other problems. So maybe pistons might be in the near future. The air conditioning is goen but will be kept for future so it can be put back to original if needed. Not sure about exhaust, what is best , manifolds, headers not really sure.

bad76 · « **Reply #5 on:** January 03, 2007, 09:57:31 AM »

Have the heads you have now rebuilt and ported. I am useing a set of these on a 455 and It turns out almost 550 horse.

Chewey · « **Reply #6 on:** January 05, 2007, 03:13:17 PM »

The bad thing about the -8 heads is they leave your compression around 7.6 on a 400 while on a typical 455 they'll produce around 9.5. If you keep those heads, you'll have to find a cam that produces a lot of dynamic cylinder pressure as the static pressure is so low. I tried using a RAIII 068 cam with the stock heads and the engine had less get up and go than the stock cam. You'll hear over and over about how every component on the engine has to be matched to work well togther. Just replacing one component won't give you instant horsepower if the other components don't support it, no matter what Car Craft says. There is a rather lengthy post on TAC where I went through this that I'll post a link to when TAC comes back up.

I would suggest going with the 6X-4s (I don't know much about the 4X heads) as you should be able to pick up a set fairly cheaply...like around $150-$200 and then spend the money on them instead of the 6X-8s. That's what I did.

phishfud · « **Reply #7 on:** January 05, 2007, 04:38:48 PM »

There really isn't a whole bunch of difference between the 6x-8 and the 4x. the -8 is roughly 101cc and the 4x is 98 or so, IIRC. Either of those on your 400 is gonna net some low compression. Now the 6x-4 is about a 92cc, which if memory serves, was roughly 8:1 on a 400. I know the 4x's I was running yielded me 7.6:1, but this was on a .060 400 with a block that was not zero decked, and my psitons have an 11cc dish in them. I think I spent about $250 for the #62's I have, which after taking all the measurements, will get me to around 9.2:1. If I had flattops and a zero deck, my comp ratio would be really high with the 62's. For what you wanna achieve, the 6x-4's sound like a good bet.