[az67goat]

I have a 67 GTO with a 69 400 in it with 4x-7h heads. Not the fastest 67 GTO on the road but it runs great on 91 octane. I'm going to try some 87 when I get back on the road soon after a year and a half of body work.
I have been thinking about going to 670 heads. I have heard conflicting stories about running pump gas with these heads due to the higher compression.

Can you run 91 octane with 670 heads or not? Anyone doing this?
Thanks!

[BILTIT]

If you do a search you will find some threads on this.

[tc]

It all depends on what the compression ratio is. I have 670 heads and am probably pushing it with pump gas ( 91 octane )at 9.9 to 1 compression.

[BILTIT]

I ran them on my old 400 at about 10.4:1 and 91-93 octane. Had lots of overlap in cam, only thing that saved me i think, and i ran fairly rich.

[Midnight Goat]

I have a 67 with 670 heads not sure of my compression ratio but i havent noticed any pinging due to the gas. I put mobil 93 in the tank.

[az67goat]

I did some searching and found some conficting info so I started this thread. Some say you need dished pistons, some say they run fine with 93. I thought I'd just try to develop a thread where everyone could weigh in on this ? specifically. Thanks for the replys.

[BVR421]

why would you want to swap from the ones you have?

[bobbyj1]

Before my rebuild my basically stock 67 400 with 670 heads and the 068 cam required me to mix 110 50/50 with 93 in order to stop pinging. I have since rebuilt and have a small dish in the pistons as well as some mild porting to get the chamber to around 98cc and 9.5 to 1 compression. I have been running well on straight 93 octane now.

[6567GTO]

Originally Posted by BILTIT

I ran them on my old 400 at about 10.4:1 and 91-93 octane. Had lots of overlap in cam, only thing that saved me i think, and i ran fairly rich.

That's what I've found to be true as well. I'm running some 670's on my 455. Last cam it pinged like the dickens, a street/strip hyd. This cam, a solid drag race comp cam with lots of overlap, I'm finding that I can use 93 when needed to get home from a far away show, for example. I don't do it regularly but can get away with it when needed. It has 12.1 compression too! I really need to fatten up my carb again, now that it's driven more on the street these days.

Phil

[Brian D'Amico]

When I ran my 67 (670's) GTO last year, I ran Sunoco 94 in it and it ran just fine. I never tried 91 though. Now, with my rebuild, I bought the TRW L2440 (beveled edge piston) and it should get me down to 9.5:1. I'll feel a bit more comfortable running at 9.5 instead of 10:1.

[PONTIAC DUDE]

Depends on the piston. Most cast pistons have the 8 eyebrow deal and the compression is Ok with 670's. But modify the head chamber for less chance of detonation.
Forged flat top is another story.

I preferr 9.5 to 9.8-1 max compression and pump gas.

[Skip Fix]

My RAIV heads on a 400 had not audible ping/detonation on the dyno, and was using muffler on it.Picked up 5-7 hp on race gas over 93 octane so HAD detonation going on.

Dish!

[6567GTO]

Inaudible detonation is definately a concern of mine which is why I still mix 110 and 93.

[gearbanger]

I had a .040 over 400 that had 670's with 72cc (verified) chambers. I had inaudible detonation and destroyed the bearings 3 times. I first had a pretty big cam, something like a 302-310 duration. It lasted the longest, Then I went with like a 290 cam when I rebuilt it. I lasted less time. The last time, I had a 278-284 comp cam, and switched to a set of 62's with a 74 cc (verified) chamber. It lasted the least of all. I have been the poster child for detonation I think. But I was dumb about that stuff back then and that was before I found these forums. I also always had hot running problems that sort of acted up at idle in traffic. Don't know if the two are related, but I now have a stroked 400 with KRE heads putting out about 550-600 hp and I have zero hot running issues. It will run 170 all day in stopped traffic on a 90 degree day.

That makes me smile.

[67TIGER]

Originally Posted by Brian D'Amico

I bought the TRW L2440 (beveled edge piston) and it should get me down to 9.5:1. I'll feel a bit more comfortable running at 9.5 instead of 10:1.

Where did you get a set of the TRW L2440 pistons from? I can't seem to find anyone who carries them around here.
I would really like to lower the compression ratio but keep the outside appearance looking stock with the 670 heads.

[PONTIAC DUDE]

TRW is no longer in business. Bought out and changed to Federal Mogul.

You then can have then dished to the compression ratio your want.

[Skip Fix]

Many guys post here their car is running fine on pump gas my RAIV had a moderate amount of overlap also. I'd bet a dyno test with race gas they would see a need for more octane.

Dish options-custom from Ken etc, in whatever size you want. KB hypereutectic-be sure to gap the top ring EXACTLYto thier specs or break ring lands., Get a F-M(TRW) forged 2262 machine a 2.8x0.100 dish on the lathe -the old HO dished Ken Crocie used to sell., I think that figures around a 9.9cc dish. Bet by the time you add the machine work Ken can get you a better deal.

Other option is opening the 670s chamber closer to a later 68 and up chambers. Tom Wilhite has a special Bridgeport cutter for this. That should get you the 10cc easy if you don't need a fresh rebuild. I always thought opening them to copy a late model Fast Burn SBC chamber(biased toward the exhaust) and keeping some of the quench would be a good thing to try on 670s and drop the compression.

[az67goat]

Sorry...just got back to the forum.
I wanted to go to the 670s to get more power and look stock.
From what I'm seeing here, I will probably just stick with the 4x-7hs for now. I just got done with alot of GTO down time for body work.
My dream would be to have a 67 400 block with 670 heads and a stroker crank. I have also heard that you can't run dished pistons with the 462 stroker crank, so I guess I'd have to modify the heads to increase the chamber size.
Tahnks again...

[Brian D'Amico]

Originally Posted by 67TIGER

Where did you get a set of the TRW L2440 pistons from? I can't seem to find anyone who carries them around here.
I would really like to lower the compression ratio but keep the outside appearance looking stock with the 670 heads.

I bought them thru a PY member but you can get them here:

http://www.flatlanderracing.com/

[Skip Fix]

Ross,JE or BRC can make any dish you want for any stroke. I have 20cc dish on my 72cc E head 455 punmp gas motor. It didn't need more octane on the dyno.