Paul57

I could use some help on determining if my numbers are too high. Most of the (Google) information out there is about "traditional" old school chevy's. I have done some searching on here and got conflicting information. The calculator puts me at 9:1 DCR and 185 psi cranking pressure. Is this too much for 91 or 93 octane??

S10xGN

iTrader: (11)

I wouldn't think so, Paul. The 9:1 seems borderline, but the 185 psi is well within limits. Hell, my old stock '81 280ZX cranked at 220 psi...

Paul57

Would cranking pressure be a more accurate (real world) number to follow than DCR??? Can cranking pressure and DCR vary...in other words, could a 8.8 DCR equal more than 185 pressure with a different set-up??? These are the calculators I used... http://www.csgnetwork.com/compcalc.html http://www.wallaceracing.com/dynamic-cr.php

Samer

What inputs are you using to calculate your DCR?
What is your SCR? ABDC?

Paul57

Bore 4, Stroke 3.622, Rod 6.098, SCR 11.31, ABDC 64.5, Gasket .051 4.020
63 cc chambers with -.006 Piston (deck)
Am I on the right track???

s346k

iTrader: (4)

how did you get the piston measurement? i know i've measured stock ls1s 8-10 thou out of the hole.

Paul57

An EXTREMELY knowledgeable shop said .005-.007. I figured they had more sophisticated tooling than me.

outkast6991

iTrader: (34)

my lq9 measured .008 out of the hole

Paul57

I wonder if the .005-.007 comes from figuring a loss of .003 due to cylinder pressures?? We are measuring with zero load. Maybe .001 for wrist pin, .001 for rod bearing and .001 for crank bearing load???

Paul57

I am beginning to think the calculator needs to be recalculated. Has anyone found these calculators to be inaccurate on the pressure?? I have seen a couple posts that stated factory LS1's are 190-200.

S10xGN

iTrader: (11)

I just checked my Maverick's engine ('03 Corvette 350 HP) two days ago and got from 175 - 205 with a torquer v.2 cam...

Paul57

That seems to fit right in the range that I have read about.
What does the calculator say you should be at??

S10xGN

iTrader: (11)

Took me awhile to find my cam card. Using stock bore/stroke/rod dimensions, 17' altitude and 10.25:1 static:

Static compression ratio of 10.25:1.
Effective stroke is 3.21 inches.
Your dynamic compression ratio is 9.20:1 .
Your dynamic cranking pressure is 190.33 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 9.20 :1.
V/P (Volume to Pressure Index) is 175

Paul57

The cranking pressure on the calculator is right in the middle of your actual/real world check. Obviously, the calculator doesn't need recalculating then. Thanks for taking the time to check...that was appreciated. I feel a lot better about my numbers now especially when I have heard that many LSx's are 190-200 (like yours) on pump gas. I take it you are running 93 pump gas??? Are you using the .051 head gasket???

S10xGN

iTrader: (11)

Pump gas, we still have 93 here. The HG's are whatever was stock on an '03, the heads have never been off...

Grr

iTrader: (2)

just checking my math here, but using the 98-00 stock cam and the factory 10.1CR I get intake closing at 37* and a dynamic compression of 9.44 and 196psi.

I am doing a heads only build and am using E85, compression will be close to 12.4 or so. With the same 37* IVC and 12.4 I get DCR of 11.5 and 255psi, which is about what I wanted and will make a pile of tq.

jimbob

iTrader: (4)

Sorry, your using the wrong numbers. To get 37abdc you would need a cam with an advertised base duration of 200-210 degrees depending on advance. Not going to happen... Your abdc at base duration is more like mid 60's with a healthy cam. Use base duration ....not .050 abdc....

Also, with the stock cams i've seen. Stock compression LS1's are way below 8 to 1 DCR. Very slow closing intake abdc.

Paul57 is correct. Most fresh LS1's crank around 190-200psi stock. With an actuall DCR of 9 to 1, look for around 230 psi. So, that calc your using must have a wide window. As an example 8.77 DCR was 230psi on my old combo. I have heard of up to 240 psi at 9 to 1 DCR. But cams are not ground to exact spects. Plus there rated at .006 base duration vice .001 so there's more fudge room. When it comes to stock ls1's there not exactly the same SCR, cam used and timing gears, ect. These would all make small differences in PSI for that 190-200 psi window.

This info for DCR is just for crank psi. In the real world how much actual DCR you can run depends on, cylinder fill (think heads and intake), rh, altitude, cooling, SCR, fuel used and some others that it's too late at night to remember.

Pump E85 your running does have it's limits. Mainly, the crap 87 octane added. Only gets worse in the winter. If you make your own fuel or add Torco you can run some crazy SCR/DCR's. If using pump actual E85 summer blend, I would not go more than 13.5 SCR due to variances in fuel, and the resulting tuning changes caused by this.

Grr

iTrader: (2)

I am using the GM stock 98-00 cam specs which were found on a cam doctor to be:

Intake
198.9@.050
0.498"
ICL 119

Exhaust
209.3@.050
ECL 119.8
LSA 119.45

This gives:
IVO .050
-19.6
IVC
38.4

Using this calculator that specifically lists to use the .050" numbers
http://www.rbracing-rsr.com/comprAdvHD.htm
and the specs
Bore-3.9
Stroke-3.622
Rod-6.098
Static Compression-10.1:1
IVC @.050-38.4*ATDC
0 boost
0 Altitude

Results:
Effective stroke-3.33"
Dynamic compression- 9.37:1
Cranking Pressure-194.84 psi

So I cant see what numbers Im using that are wrong to get this value.

Paul57

I think it would be more accurate to use a calculator that is "at" closing or .006 from closing, at the most.

jimbob

iTrader: (4)

Your intake valve has to be closed to build compression, at .050 duration it is still open. The .004-.006 base duration figures are what you need to use. Even these are a little off for actual closed duration but close enough with all the variances found in the cam and valve train. I can't remember the base duration off hand for an LS1 cam but if you search around this site, or the net you'll find it. Plug that number in and the DCR will plummet....