Hoping to get a little help verifying some information. I have a 350 that I built a while back using mostly on hand parts and I am now looking to perform a few upgrades. The basics are: Standard 4.00 bore, 5.7" rods, 3.48 stroke, .018 comp head gasket, 64cc L98 iron heads and I am assuming a standard 0.20 deck height as I know the block is untouched from the factory. I installed speedpro H631CP pistons and this is where I have some questions, the Summit site lists them as +5cc cylinder head volume. I called them and was told that this indicates the complete volume of both valve reliefs. I could be wrong here, quite possible, but I thought that seemed low.

In using some of the online compression calculators my compression is indicated to be higher than I think it is. The engine runs great even on the occasional tank of 87 and using the info above I get a compression of 10.3 which i would not expect to run well on the 87 octane. Either I am missing something here or the specs for these pistons are not what the summit site indicates. Any help is appreciated.

Thanks
Mark

Hoping to get a little help verifying some information. I have a 350 that I built a while back using mostly on hand parts and I am now looking to perform a few upgrades. The basics are: Standard 4.00 bore, 5.7" rods, 3.48 stroke, .018 comp head gasket, 64cc L98 iron heads and I am assuming a standard 0.20 deck height as I know the block is untouched from the factory. I installed speedpro H631CP pistons and this is where I have some questions, the Summit site lists them as +5cc cylinder head volume. I called them and was told that this indicates the complete volume of both valve reliefs. I could be wrong here, quite possible, but I thought that seemed low.

In using some of the online compression calculators my compression is indicated to be higher than I think it is. The engine runs great even on the occasional tank of 87 and using the info above I get a compression of 10.3 which i would not expect to run well on the 87 octane. Either I am missing something here or the specs for these pistons are not what the summit site indicates. Any help is appreciated.

Thanks
Mark

Most small block flat top 2 VR pistons are around about +5cc's.....those cc's being the valve relief.

With all of your measurements, I come up with the same thing you did.

I will agree with you on the 87 octane as well. It will most likely clatter under a load with that amount of compression......unless you have a really good fuel system which could introduce the fuel to the chamber a really efficient way......or you have a cam with alot of overlap......or you arent running enough timing.

How much timing are you running? How does it run? Do you hear any clatter (pre-ignition)?

Joe

Try this. http://members.uia.net/pkelley2/crc.htm

You need to determine how much your piston is in the hole at TDC. This can be done to get a ball park average , straight edge across block and stick some feeler gauges until you close the gap unless your have a depth mic.
Shoot for .035-.045 quench, if you are .020 in the hole all way across, then the .018 will work. Doing the best with what you got. Yes, 5cc on the piston is about right, my 2256 4 relief pistons were 6.

How much timing are you running? How does it run? Do you hear any clatter (pre-ignition)?

Joe

The timing is one thing I'm not sure on, I don't have a timing light at the moment and don't recall exactly where I set it as it's been a while. Runs great, well it does have a bit of a flat spot in the power around 3200-3800 not that it's bad just seems to have more both below and above that range. I don't hear any clatter at all.

To be a little more specific on the 87 octane it is rare that I run it but if I have a partial tank of 93 or 89 and I am taking a highway trip I will top off with 87.

Try this. http://members.uia.net/pkelley2/crc.htm

You need to determine how much your piston is in the hole at TDC. This can be done to get a ball park average , straight edge across block and stick some feeler gauges until you close the gap unless your have a depth mic.
Shoot for .035-.045 quench, if you are .020 in the hole all way across, then the .018 will work. Doing the best with what you got. Yes, 5cc on the piston is about right, my 2256 4 relief pistons were 6.

I will be pulling the heads in the next couple of days so I can verify they are .020 in as I expect they are. Thanks For the info guys.

The cam has alot to do with how a high comp engine runs on 87 also.
If there is more overlap, it will bleed off some compression.

An old L-48, 295 and 300hp/350 engine stock is generally right at 10 to 1 w/ 4-notch true flat-tops, .020" thick shim headgaskets and about 64 cc medium valved double-hump heads so you are close.

Cam is the old -929 jobber at 195/202, 112/108, .390"/.410" lift.

Sucker's pulled like a freight train but ran out of breath early on even if they would go above 5,000 back then.

I added the good old 350hp/327, -151 cam to mine, 1200 miles from new and it woke it right up!! No more running out of breath up top and it still pulled like a freight train from the bottom of 2nd to the top of 3rd and on over into 4th w/ my M-20, 3.31 posi and bigger stires back then.

And this was timing it by the old "turn her 'till the starter kick's back and back her off a schosh" and go!!

pdq67