Compression, how much is too much for 93

[B4C]

So I finally got a good deal on a ls1 383 stroker. The only thing I don't like is that the static compression is 11.9:1. It has 63cc chber trickflow 215 heads. I have a set of afr 205 heads with 66cc Chambers which would bring me to 11.5:1 which is where I originally wanted to be at. Think I will run into issues with the current setup? Should I swap the afr heads on? The cam is huge so I'm sure that is helping the dynamic compression ratio.

[Blackbirdws6]

I think you will be fine if running 93 with the right tune.

[B4C]

I'm confident in the tuner, and really all we have up here for gas is top tier and they all have 93. No Wawa junk gas since there are none around.

[Joey D]

My 383 ls1 in my old 99z was 11.8 i believe and it ran great on 93. Drove it daily for a while till I bent a pushrod

[KirkEvil]

You should calculate DCR based on the cam to determine how close to the limits of pump gas you are. Both those heads have good combustion chambers so you can push it a little further.

Post the cam card, head gasket thickness, and piston to deck height at TDC if you know it.

[B4C]

383 Ls1 block 11:9:1 CR
4" Callies Compstar crank
6.125 Callies Compstar rods
3.905 -3cc Diamond pistons
63cc Trickflow 220 heads w/PRC .650 dual springs
BTR pushrods
ARP bolts throughout
BTR custom grind cam 243/250 .623/.615 112+4
FAST 102mm intake (port matched)
FAST 92mm throttle body
FAST 46lb injectors (factory ls2/3 rail)
Powerbond UD pulley
Double roller billet timing set
SLP ported oil pump


That's all I know about the engine. Guy was parting his car on tech and I bought it off him.

[KirkEvil]

Originally Posted by B4C

383 Ls1 block 11:9:1 CR
4" Callies Compstar crank
6.125 Callies Compstar rods
3.905 -3cc Diamond pistons
63cc Trickflow 220 heads w/PRC .650 dual springs
BTR pushrods
ARP bolts throughout
BTR custom grind cam 243/250 .623/.615 112+4
FAST 102mm intake (port matched)
FAST 92mm throttle body
FAST 46lb injectors (factory ls2/3 rail)
Powerbond UD pulley
Double roller billet timing set
SLP ported oil pump


That's all I know about the engine. Guy was parting his car on tech and I bought it off him.

You need to find out head gasket thickness.

You need to know cam duration @ .006 lift to calc/estimate DCR. I dont see a shelf-available grind come up in googling those specs so Im guessing its a custom cam that may have proprietary lobes. My best guess based on comps lobe charts I am coming up with the following:

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.030" gasket (concerning piston clearance):
12.07:1 SCR
8.87:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.040" gasket (My preference):
11.77:1 SCR
8.66:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.045" gasket:
11.63:1 SCR
8.56:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.051" gasket (stock gasket thk):
11.46:1 SCR
8.44:1 DCR

Where did you get the 11.9:1 SCR from?

My general research:
91 octane: 8.5:1 DCR
92 octane: 8.5-8.6:1 DCR
93 octane: 8.7-8.8:1 DCR

Personally Ive run 8.88:1 DCR on an LS1, and 8.72:1 on an LS2 without issues running 93 pump.

[sweetbmxrider]

Originally Posted by KirkEvil

Personally Ive run 8.88:1 DCR on an LS1, and 8.72:1 on an LS2 without issues running 93 pump.

Here's the thing about advice on the internet......



























.......anyone can put a hole in your theory

[B4C]

Originally Posted by KirkEvil

You need to find out head gasket thickness.

You need to know cam duration @ .006 lift to calc/estimate DCR. I dont see a shelf-available grind come up in googling those specs so Im guessing its a custom cam that may have proprietary lobes. My best guess based on comps lobe charts I am coming up with the following:

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.030" gasket (concerning piston clearance):
12.07:1 SCR
8.87:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.040" gasket (My preference):
11.77:1 SCR
8.66:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.045" gasket:
11.63:1 SCR
8.56:1 DCR

Assume 63cc, .005" OOTH, 74.5 IVC @.006, 0.051" gasket (stock gasket thk):
11.46:1 SCR
8.44:1 DCR

Where did you get the 11.9:1 SCR from?

My general research:
91 octane: 8.5:1 DCR
92 octane: 8.5-8.6:1 DCR
93 octane: 8.7-8.8:1 DCR

Personally Ive run 8.88:1 DCR on an LS1, and 8.72:1 on an LS2 without issues running 93 pump.

I did not calculate the 11.9:1. Is there a way to measure the head gasket with it installed. I'll pull the rear cover and see if the cam has a serial number or something. He said it was a custom grind.