[gtofreek]

It depends on the alloy of the piston. 2618 material needs .004"-.005" clearance for these bore sizes. This material is stronger and expands more. This is what JE, CP, Icon Race-Tec and many other pistons are made of.

4032 material has less expansion than 2618. They typically set up at .002"-.003" clearance. This is used for SRP non-dome pistons and many other street type forged pistons. It is not as strong as 2618.

If you hone a block with only .002" clearance for a 2618 piston, you will have issues.

I have built many street engines with 2618 pistons, and NO they don't wear out in a month. Many have been running for 10 years or more now. They expand at temp so they are not flopping around in the cylinder, just when cold, which is why you don't go raving the piss out of it when it's cold.

[72LuxuryLeMansLa.]

Originally Posted by gtofreek

You need to keep in mind also what the piston to cylinder clearance is. The more clearance, the more piston rock at TDC, and the more likely you are to hit. The Race-Tec pistons probably want .004-.005" clearance. I'm guessing if you run it that way for a while, and you pull the heads, you will see where the carbon on the piston would be smacking the head. I have seen engines with the carbon hitting the head, sound like a rod knock.

At EMC challenge, John Kaase ran .025" quench and from just the dyno pulls, there were impressions on his heads and pistons where they were barely hitting.

The RaceTec spec sheet calls for .003" and I told my machinist that .0025 would not hurt my feelings. I'll know what it is when I assemble and measure but if they are .004"-.005" I will not be happy. The spec sheet also says "AutoTec Shelf" for the piston design so that may be the "Race" pistons that need .004"-.005" clearance....

[72LuxuryLeMansLa.]

Originally Posted by gtofreek

It depends on the alloy of the piston. 2618 material needs .004"-.005" clearance for these bore sizes. This material is stronger and expands more. This is what JE, CP, Icon Race-Tec and many other pistons are made of.

4032 material has less expansion than 2618. They typically set up at .002"-.003" clearance. This is used for SRP non-dome pistons and many other street type forged pistons. It is not as strong as 2618.

If you hone a block with only .002" clearance for a 2618 piston, you will have issues.

I have built many street engines with 2618 pistons, and NO they don't wear out in a month. Many have been running for 10 years or more now. They expand at temp so they are not flopping around in the cylinder, just when cold, which is why you don't go raving the piss out of it when it's cold.

RaceTec uses 4032 for their pistons.

[gtofreek]

They actually use both, but yours apparently are the street versions. They will set up a little tighter.

[gtofreek]

Originally Posted by 72LuxuryLeMansLa.

The RaceTec spec sheet calls for .003" and I told my machinist that .0025 would not hurt my feelings. I'll know what it is when I assemble and measure but if they are .004"-.005" I will not be happy. The spec sheet also says "AutoTec Shelf" for the piston design so that may be the "Race" pistons that need .004"-.005" clearance....

Yes, the race pistons use 2618 and need the .004"-.005".

By the way, .004"-.005" clearance on a street engine is not a problem at all, as long as it's on a piston that requires it. The problem would be if you had .004"-.005" clearance on a piston that needs .002"-.003". That's when you would have a problem.

Karl, you'll be fine at .0025" and could probably have gotten away with .002", especially if you had it honed with a torque plate. We all have to keep in mind that the cylinder is also growing as the piston is. Some engines with stock replacement pistons I have done call for as little as .0005" clearance. My air cooled Honda 350 ATC engine called for .0005"-.0012" clearance max. It's all in the piston design and material being used.

I gave the pistons in my 87 S-10 2.8 v-6 .0012" clearance and proceeded to drive it into the mountains and tow my Moms car back home 200 miles, when I had less than 200 miles on it. That engine now has 135,000 miles on it and still runs like new.

[BLANK1]

I use the Mr. Gasket Ultra Seal part#5810G on my 461(030 over 400). They have a 4.205 bore and .038 thickness. Summit has them for about 38.00 a piece.

[my72lemans]

just measured my new set of vr head gaskets and i come up with .046-.047. the machine shop i use bought the whole set for me after all the machining was done .030over and decking etc. they knew which pistons, rods etc. i personally like the way these gaskets look. 3398vr is the whole gasket set. fwiw

[72LuxuryLeMansLa.]

Originally Posted by my72lemans

just measured my new set of vr head gaskets and i come up with .046-.047. the machine shop i use bought the whole set for me after all the machining was done .030over and decking etc. they knew which pistons, rods etc. i personally like the way these gaskets look. 3398vr is the whole gasket set. fwiw

I don't know how the hell I made that big an error reading a micrometer! You are correct the gasket is not .026" I have measured again and the measurement I get now is .046" .
This is not good. I certainly don't want more than .039" quench. Now I'm back to needing the expensive Cometic gaskets!

[Cliff R]

I have the JE full race pistons in my 455 at .002" final honed with a plate and the engine has been trouble free and effectively sealed up for quite a few years. To run that tight you absolutely MUST have the bores dead on the money. Quite a few years back we tried a few at .004-.005" and they "rattled" way too much for my liking till the engine was fully warmed up.

I'm not recommending anyone else run the "race" pistons that tight, as I'm sure one will lock-up in the bore or yank all the material off the skirts and then I'll have to hear all about it.

For the street engines it's gonna be a better deal all the way around to step up to pistons that don't expand as much and designed to run tighter clearances. Just stay as far away from the hypereutectic pistons as you can, they are NOT a gap or stepping stone between plain old cast pistons and a good forging, IMHO. I've seen just enough tops yanked off them to avoid them at any power level, and who wants to run HUGE top ring gaps waiting on them to heat up and expand to close down the leakage?

After putting quite a few street engines out of here over the years I would not under any circumstances run over .040" quench. The benefits of tight quench, especially with the flat chamber floor factory type heads go far beyond the obvious of being able to run a little less timing to make the same peak HP. It's a mandatory part of the needed "recipe" to come up with a good end result.....IMHO......Cliff

[Skip Fix]

That 455 I mentioned used Venolias which take a lot of clearance and could rock and change the deck by 0.008 out so darned near 0.027 up when rocked-drops the clearance oan a 0.039 gasket a lot.

[72LuxuryLeMansLa.]

Originally Posted by Cliff R

For the street engines it's gonna be a better deal all the way around to step up to pistons that don't expand as much and designed to run tighter clearances.

After putting quite a few street engines out of here over the years I would not under any circumstances run over .040" quench. The benefits of tight quench, especially with the flat chamber floor factory type heads go far beyond the obvious of being able to run a little less timing to make the same peak HP. It's a mandatory part of the needed "recipe" to come up with a good end result.....IMHO......Cliff

The reason I went to RaceTec is the 4032 having a low expansion rate and the 1.5mm, 1.5mm, 3mm ring pack. As far as the head gasket goes, I will wait to assemble the short block and see where my pistons rest at TDC. If they are out of the hole I think I will use the .030" or .036" depending on how far out they are. If it is exactly zero decked as I asked for then I will buy the Cometics .027" gasket. Cometics has a 4.16" bore and the next largest is 4.20". For guys that run Cometics, does the 4.16" bore fit a 4.15" 400 block well or is the 4.2" required. I want as little dead space as I can get to go along with the tight quench.

[72LuxuryLeMansLa.]

Originally Posted by Skip Fix

That 455 I mentioned used Venolias which take a lot of clearance and could rock and change the deck by 0.008 out so darned near 0.027 up when rocked-drops the clearance oan a 0.039 gasket a lot.

.008" seems like a huge rock to me but I am no expert on this. Was that a fairly noisy set up?

[67drake]

"For guys that run Cometics, does the 4.16" bore fit a 4.15" 400 block well or is the 4.2" required. I want as little dead space as I can get to go along with the tight quench."

Mine are listed as 4.185". My 400 is .030" over. FWIW

[BLANK1]

I'm using the Mr. Gasket Ultra Seal 5810G gaskets on my 461. It's a 400 stroked with a 4.155 bore. They have a 2.05 bore and a compressed thickness of .038. They fit the bores pretty tight. A little wiggle room there but not much. I have ROSS pistons and they are .005 in the hole. My compression is at 10.8 with the E-heads. Haven't had any problems with them. Don't know the horsepower but my 68 GTO has run a best 10.98 @ 122 mph with a 3785# race weight. Do a lot of street driving too. They are $37.97 a piece through Summit.

[gtofreek]

Originally Posted by 72LuxuryLeMansLa.

I don't know how the hell I made that big an error reading a micrometer! You are correct the gasket is not .026" I have measured again and the measurement I get now is .046" .
This is not good. I certainly don't want more than .039" quench. Now I'm back to needing the expensive Cometic gaskets!

For one, that gasket will crush some. Also, even if it didn't, an extra .007" is not the end of the world. You start loosing your quench benefits when you start getting .060" or more away. As long as you have less than .050" and closer to .040", you're fine.

I wouldn't make a big deal out of it as you'll probably be around .043-.044" when torqued down.

[tom s]

I agree with Paul,you can get too anal over trying to get exact.Tom