Howdy. I have a mid 70's Pontiac 400 I was thinking of rebuilding. It came with the 4x heads, and not a very good compression ratio. I also have a 350 from a 74 GTO. From the little bit of research I've done, I think I can boost the compresion up into nines with the GTO heads. Would there be any valvetrain clearance issues? The motor will be going in a 69 Grand Prix. Wish I had the original 400. Let me know your thoughts. Thanks.
2007-04-27 17:02:13 · 13 answers · asked by jonathan727 1 in Cars & Transportation ➔ Car Makes ➔ Pontiac
heads from the 350 are #46
2007-04-30 16:38:29 · update #1
yes they will work. i have read some articles in high performance pontiac about them getting some good flow numbers out of the 70's heads (ie 6X) .. edlebrock, wenzler, kaufman racing equip, all make aftermarket heads if you wish to go that route. and either Ames or OPG makes repo RAM AIR IV heads.
2007-04-28 02:21:23 · answer #1 · answered by turkey 6 · 0⤊ 2⤋
First off - 350 Pontiac heads will fit a 400 and 455 Pontiac V8. All Pontiac V8s the same dimensions. A small block GM is a chevrolet.
Second - Less cc's in the head give you a higher compression ratio (CR) - More cc's give you less CR. Then 1974 8:1 heads will give you 8.72:1 on a 400. The 4Xs 8:1, the 6x's between 8:1 to 8.37:1.
The 4x heads flow about the same as or better than the 6x - Some 4X are the small combustion chamber heads from a 400 - some are large from a 455. The combustion chamber sizes between a 6X and 4x -7H (the 400) are pretty close. Look for a 7H stamping on the head - that gives you big valves and small combustion chamber. Check old issues of High Performance Pontiac (HPP) for more info on that. My 4x's came from a 1974 grand am (400 cu in). cc the heads to be sure - If they are over 100 cc's you have the 455 heads. If you have the good 4X - save your money. The best 6X heads have is a 91 cc Combustion chamber - the 4X-7H had 98cc. Note - Most 6X's had 98 too - the 91's are harder to find. In either case you can mill them to get what you want. The 4x and 6X are a hot low $ setup for a 455.
The second thing to check is how your 350 heads will flow vs. the 4X's - a tenth of a point of compression ratio won't mean much if the flow is down. Check the valve sizes - The intake is sometimes smaller on the 350 heads than 400 - the exhaust should be the same.
Your 350 heads should be either a 4C or 46 casting. 46 had the small intake valves (1.96) and 4C had the 2.11s. Per the link below the small valves actually flow better than the larger (and 4X/6xs) - go figure.
Good luck - If it was me - clean up the 350s, check they flow better than the 4Xs, port match the intake and exhaust, multi-angle the seats, bolt them on with a good set of headers and have fun. The valvetrains will be OK - but if the heads are off - open up the pushrod holes - that gives you an option later to run 1.65 rockers for more lift and effective duration without swapping cams. I didn't do this and am kicking myself now.
2007-05-05 13:56:11 · answer #2 · answered by Bill c 3 · 0⤊ 0⤋
This Site Might Help You.
RE:
Can I swap heads from a 74 Pontiac GTO motor (350) to a 400 motor?
Howdy. I have a mid 70's Pontiac 400 I was thinking of rebuilding. It came with the 4x heads, and not a very good compression ratio. I also have a 350 from a 74 GTO. From the little bit of research I've done, I think I can boost the compresion up into nines with the GTO heads. Would there...
2015-08-07 19:28:03 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Pontiac 400 Heads
2016-12-14 04:11:30 · answer #4 · answered by ? 4 · 0⤊ 0⤋
recommend'55-79 heads can be swapped, can you give me more info, castings numbers off the heads & block and I can tell you the compression ration.
UPDATE: My books shows 4C (casting #s) heads on your '74 and around 90cc. Unless you bore the block 60 over, witch I do not recommend but I can recommend other heads, 62, 16, 12 &13 and 48 and these are the casting numbers witch are found on the center of the exhaust ports.
What are you looking for, an extra 100hp, cam & intake change, etc.
Those 4X or 4C heads are not a good choice for performance and I don't think your cr points will go up at all.
Second UPDATE: The 46 casting heads off your 350 '74 GTO motor are 89cc.
Larger volume cc heads will lower your compression ratio. A 6X head can be 100-110cc and that just depends upon the motor they came off.
2007-04-28 17:45:30 · answer #5 · answered by gretsch16pc 6 · 0⤊ 0⤋
Pontiac Heads
2016-09-28 00:11:34 · answer #6 · answered by Anonymous · 0⤊ 0⤋
Yes, you can. The heads are the same. Ideally though, look for ones with a casting on the side with "6X". These offer the best flow, unless you happen upon some RAIII or IV heads. The good thing about Pontiac engines are the heads amongst the three major offerings of the period (350, 400, and 455) are they are interchangeable, with no valve clearance problems.
2007-04-27 23:32:46 · answer #7 · answered by Darwin K 2 · 2⤊ 3⤋
As others have stated they will infact interchange. If you're looking for the best stock heads to work that are cheap search the junknyards for a set of 6X. They will work much better. Ram air would be ideal but you're not going to find those cheap anywhere. Check those casting numbers to make sure of what you have though before you do anything.
2007-05-03 04:09:10 · answer #8 · answered by RED FIVE O 2 · 0⤊ 1⤋
you can but i wouldn't recommend it . i think that the 400 heads will give a 350 a boost but not 350 heads on a 400. clearance will probably be fine,are the gto heads stock ?
2007-04-27 17:20:57 · answer #9 · answered by KC 2 · 1⤊ 3⤋
You motorheads realize that the Pontiac 400 was a big block, right? You want to put small block heads on a big block?
2007-05-05 07:26:04 · answer #10 · answered by mrknositall 6 · 0⤊ 6⤋