670 heads and pump gas
 

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!

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

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.

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.

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.

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.

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

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.

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

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.

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.

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!

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

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. :)

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.

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.

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.

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...

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

http://www.flatlanderracing.com/

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.