Well, the 498 is moving along.
After deciding to go with .051 head gaskets and doing some relief grinding on the tops of the bores to help with valve unshrouding, we are at 9.4:1 for compression ratio. Should be a true pump gas friendly engine.
I was counting on right at 10:1 with the parts I had chosen.
My engine builder insists that a few tenths of a point one way or the other doesn't make much difference. Mostly in the mid range torque....which we agree I'll have plenty of.
According to AFR, flat milling the head gives a 1cc reduction for each .006" matertial removed. So to move the ratio higher would require quite a cut, and that just opens up a whole other can of worms. Manifold won't fit, valve to piston decreases and the push rod length will change.
I hope we did the right thing by relief grinding the tops of the bores....this added about 5cc to the chamber volume..........

Here are the numbers:
Bore 4.32
Stroke 4.25
Piston-deck .000
Gasket Bore 4.54
Gasket Thickness .051 (13.7CC)
Chamber 121cc + 5cc for bore work
Dome 18cc

Comments?

Should be on the dyno within a month.

Ron

I installed Mr. Gasket, .020" steel shims on my 496 with Merlin Ovals.

I ordered 9.5CR. pistons from ROSS by telling them what I wanted and they sent me their recommendation.

I started out with the "blue", .039" thick composite headgaskets and then the dreaded, "more power, Scottie", bug bit me so I never installed them and instead put on the shims to put me right at 9.8 to 1 or so CR..

Please go over to the ROSS Racing Pistons site and run your spec's through their compression ratio calculator b/c maybe you can gain the CR. you want by just using shims like I did?

pdq67

Because he torque plated the bores with the Felpro Gasket, we can't change. The bore distortion he assures me is quite different with anything other than what he used while machining.
We went to the .051" gasket because the pistons were at .000 to +.007 above the deck. And due to the long stroke, he felt that we needed the added clearance......don't want the pistons hitting the head at high rpm.
Ron

Ron,
I would cut the heads to the minimum with a flat mill which is 114 & is only about 42thou.
If the intake seat will allow I would cut more.
Cut the intake side of the head the same & you will have no problems with intake fit.
This will give you 9.85.
You are at 9.35 now.
Only thing you may need to address is pushrod length.
You should have plenty of p/v clearance unless you went crazy with a cam ;)
I don't recall but I thought it was mid 250's on a 110??

Hi Mike,
So in the real world, how much power is an increase of .5 in the compression ratio worth?
Ron

Yeah not much if the cam is big enough to schootch it over a few more degrees advanced.

Originally posted by Ron454:
Hi Mike,
So in the real world, how much power is an increase of .5 in the compression ratio worth?
Ron =
Not much but with a 250+ degree intake lobe I would take all I could get & it's basicly free ;)
Probably about 2% to 3% max from 9.3 to 9.8

You normally should see a much bigger gain going from say 8 to to 10 than from say 11 to 13.
The gains become less as you go up in compression but you should see 3 or 4% per point at the lower ratios & a couple more as you get higher.

And if you stick a big dome in front of the spark plug like in a small block you could lose 50HP while raising the compression :D

Several guys here tried to build low ( 9.5-10 to 1) compression big block motors and all were slow, even at over 500 cubic inches. It seems that at about 11-1 compression and above they start to run. Wolfy is right about how to gain the compression, a 114 or 115 chamber is the way to go.

Well, w/o swapping pistons, this engine will not be able to get to 11:1. 11:1 seems to be a tweener CR anyway. When shopping for pistons, you either choose around 10:1 or 12.5:1 and up.
This whole engine project has obviously turned out to be a tweener. Not really a street engine and not really a race engine.
I chose to do this project so I could go play with the 10" tire street legal croud at the local drags. Well, I missed the whole season, and the whole boat aparrantly. They all run loads of nitrous and in the low 9's. The "all motor" class never materialized. So instead of just freshening up my 468, here I am with no class to race in, and a bunch of money in a tweener.
I now also realize that I'm not going to achieve my goal of low 10's with this combo. Hopefully mid tens though.
Pretty frustrating.
And Harold, please define slow.
Ron