barkingspud

iTrader: (3)

Like the title...What would be the highest SCR I could run for 93 Octane pump gas? I tried searching came up with a bunch of hits that were useless. Thanks in advance....

BS

KCFormula

iTrader: (4)

I would like more info on this as well. Although I believe it would have a lot to do with the DCR as well. And maybe combustion chamber shape. Is there a known limit? At what point does using a methanol kit become a good idea?

barkingspud

iTrader: (3)

Well....I am referring to an NA motor.....DCR is still a factor though. I understand that a DCR of 8.5 or less is preferred.....

Ferocity02

iTrader: (60)

DCR is what you should be concerned about, much more so than SCR. I'd go with an DCR of 8.75 or less with 93 octane.

yak

iTrader: (15)

DCR is what matters most. I would say that 8.7 drc and no more than 12.0 scr with a good tune. btw, where in the western burbs are you?

Manic Mechanic

iTrader: (3)

Barking Spud, This is what they are talking about.
SCR = static compression ratio. The physical difference between combustion space volumes at bottom dead center and top dead center.

DCR = dynamic compression ratio. The compression ratio actually produced during operation. It is a fine tuning of sorts on the SCR. It varies with cam timing, intake manifold tuning, RPM, and load.

You could have a high SCR that convention says won't work on pump gas but with a long duration cam that bleeds off compression at low engine speeds your DCR is lower so it works great. Find a knowledgeable engine builder and or cam grinder. Comparing cam specs for others compression ratios will give you a guideline. If you're just wanting the highest safe number that will work with street cams then the answer is stock.

Vernon

barkingspud

iTrader: (3)

Thanks Vernon...I will have a chat with my engine builder....I'm not looking for something too well behaved on the street......But, I do want to run readily available pump gas though.

NoGamesLS1

iTrader: (16)

I am running 12.5:1 SRC with a trex on CA 91 so you could run a bit more on 93

Ari G

iTrader: (25)

CR is nothing you can calculate accuratly to go with octane number,has to do with so many variables

barkingspud

iTrader: (3)

hmmmm....I hope my engine builder has a better answer than that.....

Quick96ss

iTrader: (7)

iam running 12:1 on pump gas 93 octane.. Tuned by Speed Inc...

8ty8 LS1

iTrader: (3)

is there a formula to calculate DCR? and or SCR? thanks.

Ferocity02

iTrader: (60)

Whats your DCR and timing? You can run as much compression as you want, but without high octane fuel you will have to cut down a lot on timing, it's just a trade-off.

383Z4ME

This is a pretty good write-up with a link to a calculator at the bottom.

http://members.uia.net/pkelley2/DynamicCR.html

Ferocity02

iTrader: (60)

SCR is pretty easy to calculate by hand, it's just volume at BDC over volume at TDC. DCR is much more difficult to calculate though as it takes into consideration valve timing, rod length, as well as the volumes from the SCR calcs. Definitely tedious to do by hand. If you search for DCR calculator on google you will find plenty.

2fast97Z

iTrader: (20)

my old lt1 383 was 12.5:1 and i ran 93 and it was a daily driver and tuned by madz28..never a problem

KCFormula

iTrader: (4)

How big of a cam did you have? I wonder if the guys with the Trex are getting away with it because by nature it bleeds off a lot of compression?
A local guy is in the high 13s:1 compression and he runs a mix of 104 and pump gas depending on the weather but he also has a Trex.

MadBill

Or, just read the sticky at the top of this Advanced Tech Page: https://ls1tech.com/forums/advanced-engineering-tech/394937-updated-valve-event-dcr-scr-header-length-spreadsheet.html

kars10_4

Does the rule of DCR being below 8.5 only apply to higher performance engines? Because I found the LS1 in stock form to have a DCR of 9.52 using the link provided by 383Z4ME.

2fast97Z

iTrader: (20)

I had the LE4 Cam