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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.
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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.
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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.
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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.
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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.
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why would you want to swap from the ones you have?
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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.
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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.
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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.
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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. :) |
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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... |
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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.
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This is exactly what I went through when building the 400 for my '69 GTO several years ago. Eventually ended up going with the 670's with TRW Powerforged flat top pistons. 8 valve reliefs with beveled edge.
These would seem to be the modern equivalent : http://store.summitracing.com/partde...5&autoview=sku Final compression was about 10:1. Which was managable with 93-94 octane with some timing adjusments. Cam overlap surely affected this as well. This is not to say that I didn't have some detonation going on like Skip said in post #12. Never had my engine Dyno tested. |
While my stock original 400 WT with 670's was running seemingly fine on 91 octane plus 100 octane (50/50, sometimes even 25:75 mix to get 93-95 octane), I'm not taking a chance with my rebuild. Having Dave at SD work his chamber mod and then I'm looking for anywhere from 5-9cc's to come from a piston dish. Lastly I'm going to get the block zero-decked.
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I just purchased ROSS pistons through Butler, dished 10cc for a 9:5 compression in a 67 WS engine with 670 heads for my original H.O. four speed car. Jim told me this will be fine for a street driven car on pump gas, he will be receiving the 670 heads this winter for flow and port work, nothing exotic just upgrading for the street. My car is a 13 second car in the 1/4 mile so it is not setting any land speed records but it will be a robust engine for the street without any spark knock. The ROSS pistons are a work of art, just beautiful ! and another plus was they (pistons) were 200 grams lighter than stock each so I now have 1,600 grams less rotational weight on the crank which is a huge benefit for wear and tear on the bottom end. I also went with Eagle H beam connecting rods and total seal piston rings (file fit). Everything will be balanced (rotating assembly). Block square decked as well.
Tim john--- |
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I know someone running a 455 + .030, flat top pistons, mild cam,and 670 heads. He runs fine on pump gas. His secret.........water injection. He swears by it.
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Open those chambers up a bit - PROPERLY. Zero deck the block. Have someone help select a PROPER camshaft. Careful tuning, including advance curve and carburetor and it'll run fine on 93 octane with no spark knock or detonation.
My advice is NOT to used bevel edged or eight valve relief pistons. More downsides to those than benefits, such as reduced quench, more edges to hold carbon (hot spots) and poor burn patterns. Most efficient would be custom, two valve relief flat tops or reverse deflector deals, but those are custom, made to order and big $$$. Once again - ZERO deck that dude and do NOT use a thicker head gasket, |
I have an original Edelbrock water injection unit from the mid-70's called "Vara-jection. I removed this back from my car in about 1979 or 80 and it is currently up in the barn loft, it did work but I was not a fan of putting water into the cylinders, I was paranoid of hurting my pistons but no damage ever occured and I ran it for two summers. I ran the water line into my center tri power carburetor through the chrome lid, it just killed me to drill a hole in that original lid even back then. I just had AIH chrome in Iowa fix the hole and re-plate this very same lid last month after all these years. I am going with dished pistons now as stated above, back then I was looking for an easy, cheap way out to stop the spark knock, parts and cars are too hard to come by today for gadgets so I will pay the price for quality ...gladly.
Tim john--- |
I have done a little research about water injection and have found nothing bad about it as long as it's done properly. Some say they have taken the engine apart after years of using it and it looked like it had just been steam cleaned. It needs to be a fine mist. You have to use the correct pressure and nozzles. I'm not recommending it, I haven't tried it myself (although I'm thinking about it), it's just another idea. fwiw.
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Feel I need to clarify my last post .... my intention was to point out a possible solution for those without the funds or means to get custom pistons, or have the chambers on their 670 heads machined. With above said ... for my next 400 build I will probably open up the 72cc chambers on my 061 heads and use a proper set of flat tops. For those who don't know, the 061 are basically 670's with open chambers. If you see a pair of these rare heads grab them! Most likely they will be going cheap because of the press-in studs. Very easy fix for a competent shop. |
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Refresh my memory - the 061 castings are what - '67 big car heads? |
Opening the 670 Chamber
[QUOTE=Skip Fix]
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 have heard of this process, I have a set of 670's that I would like to have this done. Can the process be done on heads that are assembled or at least already have guides. Do you have any more info, Location, Cost, Contact info, Web site ? Thanks JK |
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CORRECTION--www.wilhiteauto.net
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Finding info on these heads is difficult. Found more info in these forums than everywhere else combined. Member Will has a ported set & has submitted some good posts on the 061 heads. Quote:
Most sources I see list the 061 as small valve heads, but they obviously are not. Probably another reason they are so rare. Know I have seen a couple sets in swap meets that never sold because most see the press-in studs & keep on going. |
I've also got a set of 061s that I took off a 400 motor. Originally from a '67 Cat with 400 and 2bbl. Big valves, have all exhaust bolt holes, early accy bolt system, no EGR, push-in studs,etc. Approx 72-75 CC open chambers. Great heads as far as I can tell. Since I had a set of 670s I used them instead. Still have the 061s in storage. I think they are often confused with the '67 143 heads, which were used on the same cars and MAY have been small valve heads.
And Ive mentioned this before, I wouldnt modify a set of 670s if I didnt absolutely have to. They're a one-year only head with the 400 big valve size and later valve angle and closed chambers. As more people cut them to open chamber, an unmolested set will get very rare. chip |
Hi Chip. If you ever want to sell the 061's let me know ... < wink > :biggerGri
Sounds like you were in the same boat as me. I traded these 061's for a set of 6X-4's with customer (more on that in my other thread). Was tweeking them in my spare time at work when the 670's came along. The 061 have been sitting in storage half done ever since. Hopefully I will be able to finially use them soon. |
Yeah, since I was building a pump-gas 400, I used Ross pistons to drop compression with the 670s. Now in the low 9 area with static comp. But the engine revvs so freely with the long rods and lightweight internals. I'm using the SBC 400 1/16" ring pack relocated downwards on piston. In the future I can spray the motor and not worry about melting a slug or butting a ring.
chip |
You could also do it with a die grinder, but it would be moderate work. I would bet that would open them up just about right for pump gas and flat tops.
Mr. Wilhite has some pretty awesome old Pontiacs he and his wife race, one with an EFI Victor on it! |
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