I did some calculations for CR today on my new motor. It turns out to be in the neighborhood of 12:1:eek: That's a little steep as I'd have to run pure race gas. What would y'all do to lower the compression?

Keep in mind, I'm shopping for some suggestions based on my best guess of CR. I should have some accurate measurements later this week.

What's your dynamic compression with that cam Mark?

Going to the boat cam lowered my dynamic to the point that with 11:1 static I'm able to run pump 92. I'm still going to add booster on race days.

How deep are your pistons in the hole? Can you go with a thicker head gasket?

I guess I havent been following the build much but how did this just happen? What pistons and what heads? Choose your head gasket to get ideal quench, not compression ratio. With that much compression and assuming you want it around 10.5:1, I would either change heads or pistons. Definitely get on a compression calculator and get some more exact numbers before you do anything.

I'm know for a fact that the L2268F pistons and '101cc nominal Closed Chamber heads' are a lot of CR!!!!
This is exactly why I went from 063 closed chamber heads to 781 open chamber heads on the Vette.... The difference between 12.3:1 and 10.55:1


I have mentioned this exact early Vette combo many times yet I failed to catch Mark going in that direction. Seems Doc and Kevin too. Somehow I kept thinking you had some 049s 0r 781s. As the rotating assembly is balanced....installed....best course of action is to get some open chamber heads

http://kb-silvolite.com/calc.php?action=comp
Use this calculator, get your cam card out and do the Dynamic Compression Ratio calculation.

Trying to lower the CR with a fat head gasket would only reduce the quench effect and make it more ping-prone.

I'm suprised none of you said just fill it up with race gas and run the nuts off it:D

The key piece of data I'm missing right now is the deck clearence, should have that tonight as I'm installing the pistons. The thickest I'd go with a gasket is .051. I may have to enlarge the combustion chambers too if the piston hits the exhaust side of the heads. We'll see.

Darryl knew it'd be high and I was gonna keep it a secret but what the hell. As I said, I'm just shopping for ideas just in case.

Or, I could just run it on 110 and whoop ass:thumbsup:

As large as your cam is, your dynamic CR would be low-enough for UL-Premium and booster for street use. Get a few cases of Kemco and let fly!

Why not just run race gas? You probably dont drive it that much and if you can afford it...

Interesting....

I'd say fix it to where you can drive it normally, obviously that may mean changing heads depending on your piston to deck height measurement. While running race gas or premium w/booster may sound fun, I'm guessing you'd want to take it for more than just a jaunt to the corner store, and that Kemco seems somewhat expensive for all-the-time use from what I've seen.

Not to mention why have a 5 speed car that only runs race gas? Somehow that doesn't make sense to me.

Nos!!!!!!!!!!!!!!!!!!!!!

Well, the pistons aren't going in tonight. My ring expander is too small:mad: Its too late to run and get one now, so I'll have to put in some extra hours tomorrow night on it. I was really hoping to get the deck clearance measured tonight. DAMN IT:mad:

Well, the pistons aren't going in tonight. My ring expander is too small:mad: Its too late to run and get one now, so I'll have to put in some extra hours tomorrow night on it. I was really hoping to get the deck clearance measured tonight. DAMN IT:mad:

your hands are too small? all ive worked on is small block are big block pistons that big :D

your hands are too small? all ive worked on is small block are big block pistons that big :D

A direct quote from the directions: DO NOT SPIRIAL IRON RINGS, USE RING EXPANDER! And yes, big block pistons are THAT BIG:D

Mark

I was told don't run much more quench than about .045-.050. Yes you will lower you compression with more but your chances of detonation are insane. best idea would be get an open chamber head to lower the comp.

What would I do. run the 12:1 (like i will be doing) and have fun with it

Mark,
If just checking clearances, Install one piston, or several without rings....will take seconds. This way you know tonight!
Rotate the piston to it's TDC. Then place a straight-edge, narrow end down, across the deck. See what kinda feeler gauge fits under there...... Measure at a few places. Takes seconds.

Take out the pistons when done so none are permanent w/o rings.

Huh, I always thought you'd risk breaking a ring by not spiraling them down:confused: I would think a ring expander would stress the rings more than using the usual method of spiraling them down. By applying the most pressure at the exact opposite center of the gap, wouldn't this be true?

Just looking for thoughts, anybody have a hypothesis?

Not to mention why have a 5 speed car that only runs race gas? Somehow that doesn't make sense to me.

Good point..........................

Maybe its time for a Lenco or a Jerico;)

Good point..........................

Maybe its time for a Lenco or a Jerico;)

I've found some on a few sites for $1,500 used....may be worth a look if you're interested. I have the sites in my favorites if you want them to peruse.

I'm suprised none of you said just fill it up with race gas and run the nuts off it:D
Or, I could just run it on 110 and whoop ass:thumbsup:

That's because I just got home and sat down to look.:D You know where I'm at on this one.

I vote to put it together, mix your fuel 50/50 pump gas/110 and run the snot out of it:D

To me thats alot of compression for iron heads. You will def need to run high octane fuel.
With my 115CC heads, same pistons you have, 0 deck Im at 10.97 CR with a dynamic of 10.02

Again, I did run this on the mean streets of Columbus, GA and a three years of the dry season up here in WA. Not a lotta fun for a street car...but RIGHT-ON for a go-fast race car or a FRI NIGHT PICK A FIGHT car. Had I known about Kemco, I'd have probably never done the heads swap. IMHO, the Vette was a bit meaner with the extra CR and small valves vs less CR and big valves.

http://kb-silvolite.com/calc.php?action=comp
Use this calculator, get your cam card out and do the Dynamic Compression Ratio calculation.



12.3 static/10.1 dynamic. This is with a SWAG of .005 for the deck clearance. I'll know for sure tomorrow when I get the pistons in.

You didn't put a few pistons in w/out rings to test the deck height? Shame!

That's because I just got home and sat down to look.:D You know where I'm at on this one.

Me too. :)

Run some good fuel through it, and run the ever lovin' bag off it. ;)

Well, if you put it together that way, I'm voting for the Lenco or Jerico:yes:. Then you have no excuse:D

Kemco is roughly $10/quart.

At a dynamic compression of 9.1:1 I was adding a 1/2 qt to 10 gallons of 92.
On race days a full qt per 16 gals.

You might want to run a full qt with every tank... $40 92 oct +$10 kemco= 97.5-98 octane.:thumbsup: