Running it a little fat will help. Not eye burner fat. Another thing that can be done is to water spray it or methanol spray it. You could go extreme but all you really need it a vac sensitive switch and some sort of a spray bar either under of over the carb, a NOS plate or cheater system sprayer actually works really well. You switch works when the vacuum drops and you begin spraying it. the only time you really have a pre-detonation problem is when you are under load and that is when your vacuum drops. Either water or methanol will work, water is cheaper.
Reminds me of a blind date I had once. I run 11:1 compression on a street driven Olds 455 that has no issues on pump fuel. I do like the clear stuff when I can find it but 92 octane with a side of corn doesn't seem to bother her.
You guys must not have ever torn down a Pontiac, the chambers are fully machined and smooth. I’m not sure what you could polish on a smooth surface but if you want to try for a mirror finish be my guest. The fully machined Pontiac chamber won’t be exact but it for sure will CC closer than any as cast chamber. Now if the statement was to take a grinding stone, or a carbide burr and hog out some material that’s a different story. The SBC chambers were often polished by head porters BITD but those were “as cast.” There’s that phrase again, they were cast and have that rough cast iron texture unless Chevrolet machined the intake area of the chamber to unshroud the valve. The Pontiac guys here know what I’m talking about.
Never mind there is a reason I have not been on the HAMB much lately and it has to do with my not wanting to be an ass. Believe what you want and you'll be a happy camper for along time.
Dad and I have been building Pontiac's for years, you can do some chamber work without hurting the performance and still lower the compression. You need to work around the intake valve and remove all the over hang, part of the un-shrouding process. You can gain 3-4 cc's if you really try, the air flow will improve and you lower compression. Remove all sharp edges from the chamber area and polish the valve edges, anything that could be a potential hot spot. You still haven't mentioned what head you are using, so I can't give any advise other then general work. The " 041 " Ram Air cam is pretty aggressive, so be aware the idle will be rough. Pontiac only sold the Ram Air VI with 3.90 - 4.10 rear axles and no A/C, and mostly manual transmission cars for a reason, this is the same cam modified from the early 421 engines used on the Nascar tracks. Rhoads lifters will go along way to improve the idle. Here is one of dad's articles on camshafts, http://www.silverstatepontiacs.com/jharticles/jharticles5.html
I read the article, I remember you and your Dad, and based on that, Joe H knows what he's talking about. Those Pontiacs were bad ass. I was running a turbocharged 240z back then, ran your Dad's wagon many times. If I recall you had a silver blue GTO?
Quench is very important I had a 1971 351C four barrel @ 10.7 ratio a buddies 400 ford open chamber motor @ 9.2 was more prone to ping than my 351 on the same fuel. We finely installed water injection on his 400.
I have doubled head gaskets on a 239 flathead. I hand machined the combustion area in the heads after installing domed pistons and new rings. I "foiled" to check clearances and still wanted a bit more. Can' t remember the numbers, too long ago. I used RTV sealer between the gaskets, no problem. Do recall 135# compression after the fix. Chap
My car was a maroon '67 Lemans, dad's wagon was red, and his '67 GTO was a silver blue convertable. Going through dad's record keeping, his old wagon has made over 2500 runs since 'late 80's.
Some where I have pictures of my Z racing your Dad's wagon, good memories from KCIR. Those were good times.
Check Cometic MLS.. I saw them listed up to .120" and .140" on Jegs. I lowered the comp on a SBC with some. The surface needs so be pretty smooth. so I stoned them. ran engine on a dyno with no problems.. don't go with 2... just use the right one. don't guess on comp. ratio either. I use the calculator on the KB piston website..
Dished pistons would be a better choice, than double gaskets. Quench clearance is important. Too much = bad.
Paralleling from other responses.... Too much quench can actually lead to detonation, although the compression may be reduced. This may sound backwards at first but if the squish volume is too great, this reduces turbulence and slowing the burn rate, potentially leading to leftover fuel. For street motors: .040- .060 is a common target (w/ head gasket)
You commented about the water passages not lining up in the heads and block, there is a reason for that, and if you open them up, the back of the block will run hot. The front half of the block deck has smaller holes then the back half, this forces more water to the back, open the fronts up and the engine will run hot. The heads have pretty rough cast holes, about all they need is a good chamfer and the really ugly casting removed, the holes them selfs are plenty big.
And that is what can cause a misalignment issue. Of course this isn't normally a problem, where it occurred for me was on a 421 that had the top of the cylinder in the block chamfered to unshroud the intake valve. It looked good on the block, in the head not so much. At some point I plan to plug the big holes in the head and then drill them the same size and position as the holes in the block; that way I have the maximum amount of gasket between the water hole and the cylinder. But that is another engine for another day.
Jegs has a Cometic 455 gasket .070 $86 ea, but you will also need thicker intake gaskets because you are also spreading the heads out with a thicker head gasket because it does not fall in intake tollerence
Exactly that's what many folks don't realize is when you deck the block or mill the heads and even using thicker or thinner head & double gaskets it often will change intake alignment.
Thank you, I didn't think of that aspect and will check the port alignment. I already gasket matched the ports and it would be a shame to have them not line up. Another thing that I am wondering about is the valve train geometry. It seems to me that moving the head up is the same as shortening the push rods, something else to check. This is the typical "push over the first domino" kinda thing.
I discovered that I missed several responses and so I will try to address those comments/questions. The heads have the cast in number 16 on the exhaust port area. They are alleged to be Ram Air III heads off of a '68 GTO. Of course just like all SBC heads came off of a Corvette I took that with a grain of salt. The casting date is A178 that I translate to January 17, 1968. The heads have the big valves, 2.11 intake and I think 1.96 exhaust. The combustion chambers were "mostly" machined although some of the machining was pretty rough. I am not the first pilgrim through these heads. The valve guides had been replaced and it looked like they had been milled. How much was taken off, who knows? The heads came to me with recent double valve springs. I did check the springs at .550" lift and found no coil bind. I have issues believing what the factory or other previous owners say about combustion chamber size, etc. I have found that as a general rule GM heads are around 1/2 point lower in compression than advertised. As a result I measured the chambers. What I found was that the chambers were 75CC plus or minus one CC. The large intake valves were pretty seriously shrouded on the outer side, I think that reduced the benefit of the larger valves. I unshrouded the intake and exhaust valves and removed material from around the spark plug. All of this resulted in combustion chambers that are 80CC within 1/2 CC chamber to chamber. By the way, removing 5CC of cast iron is a lot of work. In honor of "as long as we are here" I cleaned up the valve pockets. The intake passages didn't take much but the exhausts were pretty ugly. When I had the crankshaft journals turned I had the crank stroked. This resulted in a stroke of 4.24 and the pistons are .015" above the block deck. All of this resulted in a MEASURED compression ratio of 10.88 to 1. The question is if that is going to annoy me when driving to the burger palace. I ran a 421 with 10.1:1 at sea level with no detonation problems. How much difference will the extra compression make? Of course that was a different engine with a different cam, etc. Apples to oranges I guess. I have done the "add some high octane fuel" thing. That is a pain and it is difficult to get the same mix from fill up to fill up. I have also done water/methional injection and found it complicated and troublesome. I also tended to run out of fluid at inopportune moments. It was mentioned that the RAIV cam would result in a poor idle. You say that like it is a bad thing! Real hot rods go rumpity rump. Thanks to everyone who took the time to comment on my issue. Now that I have more information I can go out, do the wrong thing and you can say "I told you so"!
Update: I finally did the dynamic compression calculation. I wasn't able to do it before because I didn't have the specs on the cam. I bought the cam NOS at a swap meet and all it said was RA IV. After an internet search I discovered the cam is obsolete, no specs to be found. I guess that is no surprise. I broke out my degree wheel and dial indicator and after a couple of frustrating hours came up with the cam specs. Interestingly the valve timing is very close to what I have found listed for the factory RA IV cam but the lift is somewhat less. After plugging the proper information into the wallace racing calculator I came up with 9.99:1 compression. I think I'll say that is 10 to 1 and call it a day. The explanation on wallace web site is great. I finally understand dynamic compression although I think that the word "dynamic" is a bit of a misnomer. I'm thinking that "effective" compression ratio would be a more accurate term. Thanks to all who participated in my little adventure, stay tuned I'm sure that I will find something else to worry about before I'm done with this engine.
Yes porknbeaner the heads are cast but all Pontiac V-8 engines the combustion chamber is machined, therefore doesn't have the cast appearance anymore, they have a smooth surface. You can polish them and cc them as the heads aren't CC'd from the factory
It's always been my experience when there is a double gasket situation, the seal will fail in between the two gaskets. Gaskets are designed to seal against a mating surface, not against another gasket.
The Jalopy Journal
