I used the KB Pistons DCR calculator for my setup. I`m still using the stock short block, so for a baseline, I entered some known data to calculate the STOCK Static Compression Ratio of 10.4-10.5.Please, if anyone has any input to dispute/help with any of this data it is greatly appreciated!
Here`s how a stock long block LT1 may end up(not my current setup!)
- Stock LT1 heads 54cc
Piston head volume 8cc (I found this on a search)
Gasket thickness .049 (from SAE paper on the LT1)
Gasket bore 4.125 (this was a guess)
Bore 4.00
Deck .015 (guess here also)
Stroke 3.48
I did this part just to help give an accurate answer for the following calculations. I sorta reverse engineered the deck and gasket bore to equal the known stock LT1 CR of 10.4-10.5.
The Static CR came out to 10.455 for a STOCK LT1. I didn`t figure DCR.

Now, here`s my CURRENT combo( With a Comp Xtreme Solid Roller
Gross: 268/274;
.050":230/236 112LSA ground straight up)
- AFR heads 53cc
Piston 8cc
FelPro gasket .039
Gasket bore 4.125
Bore 4.00
Deck .015
Stroke 3.48
Rod 5.70
Intake Closing 66* (I got this from ADV. Dur minus .050" Dur. divide by 2 and add that # to the IN. CL. @ .050") I saw this on one of SStrokerAce`s past posts. Don`t know if should be done differently because it`s a solid roller?
Here`s the cam card info (@.050")
OPEN CLOSE
In 3* 47*

Ex 50* 6*

All this data puts the DCR @ 8.586, Static @ 10.872:1

The reason I didn`t get the Comp ground with 4* advance is I had thought I would move it around with a cam degree bushing. After I got the cam I was told you CAN`T do that with an LT1 because the OPTI references of the cam gear/cam. That would put the OPTI out of time.
So, now the top/front of the engine is apart, and I thought maybe going with a smaller cam (Not doing any more draggin, more street use/road race track days).I was thinking either getting another 230/236 cam with the 4* advance (8.852 DCR) or maybe a 224/230 112LSA either straight up (DCR would be 8.787) or with 4* advance(9.042 DCR - too much!?)
Any insight from the cam gurus?
Thanks!
Chad

 

Anyone have anything to say about this?

 

If your 9-1DCR figures are correct that will fly. Ya better know what your input dimensions are to KNOW that it is correct.(NO guessing)
Put any of your cam choices on a 108+4 and see where that leaves ya. Get the ACTUAL IVC figures also not figured ones.

If ya still run power brakes the vacuum is in the 11-12in range and shoud be OK.

 

You also have to account for the valve lash.

How much are you running?

Bret

 

Vacuum with my current 230/236 is 16.5 in., so I don`t think vacuum is a prob.
From my first post, did I figure the IVC correctly?
(I got this from ADV. Dur minus .050" Dur. divide by 2 and add that # to the IN. CL. @ .050") I saw this on one of SStrokerAce`s past posts. Don`t know if should be done differently because it`s a solid roller?I tightened the lash a bit from Comp`s recommended. It`s at .014/.016".
If I did the 224/230/112 +4*ADV, is this how the timing would be?:
(@.015")

Open Close
In: 23* 59*

Ex: 70* 18*

Thanks!

 

FWIW the cranking compression is 190psi with the current 230/236/112. Is it true that 200psi is about max for pump gas? I run min. 92.

And, am I nuts to be thinking of a SR this small? I realize I may be pushing the limit here. Most guys probably think I`m crazy! Most people are always looking for more.
Yeah, I could just step into a small HR, but my current valvetrain is in great shape (especially my 888 lifters), I just want to bring the powerband down some and gain some bottom end. It still will haul a**.

 

I can tell ya your DCR if you give me the lash.

 

Lash: .014"/.016"

 

Your static is 10.880.Your DCR is 8.591.
This is using your GUESS figures for piston height / to deck of .015 and your GUESS of 8CC's on valve reliefs.
If the block wasn't decked it is MORE than.015. If it has been decked there is no telling.
If the pistons have 4 eyebrows 8CC's may be close. If they have 2 eyebrows it ain't even close(4-5)
That's with the 112ICL+0.

The 112+4 would be 10.880 static and 8.858 DCR.

 

1racerdude, just to clarify which two cams did you figure? 230/236 or 224/230.


This is a stock, unmolested short block. Yes, the pistons have 4 eyebrows, I found the 8cc info from a search (if it was a reliable search?).OK, so lets take worst case scenario and the pistons are only .005 in the hole, doubtful for a bone stock short block , but hey, what the heck. That will add about .250 to those DCR figures. Goin` the other way say to .025 in the hole, it probably doesn`t matter, only that it lowers the DCR. So I`m thinking this all is pretty safe as far as those few data points are concerned. I completely understand what your saying about guessing.
Hey, thanks.

 

That was the 230/236@50 on a 112+0 and the same cam on a 112+4.
A stock piston height is more like .025 in the hole and the 4 eyebrow is a bit less than 8CC's. I used the Fel Pro 1074 gasket.
The thing with .020/.025 in the hole and .039 gasket ya are not doing yourself any favors toward detionation.

 

You know I just remembered something, yeah if it is more in the hole the DCR drops, but how it impacts quench would be bad=more chance of DETON;is this right?
I got the FelPro 1074

 

My calculations are about spot on to what you got.

 

Yea the more the distance the more chance of detionation. 0.035 would be the tightest to run on the street and ya are running.060 I don't like it but ya might consider the .026 Impy gasket and a tad larger cam to keep the DCR in line.

 

You make a good point. Quench= turbulence=better combustion! Maybe, and that`s a big maybe, I`ll pull one head and measure that bank. Or I`ll just keep what`s in there. At least it never detonated with the 230/236/112/112
Thank You