Dynamic compression?! Tony and the big dogs needed!

**blackbird1084** · 02-27-2012, 04:37 PM

Ok after running the numbers it's not looking good for pump gas and this cam. Static compression isn't too radical at 11.89:1, but with the cam that's in it the dynamic compression is 10.28:1. Is the too much compression to run pump gas (91-93)? Will I be better off changing cams? I don't want to have a strip only car I plan on driving 4-500 miles a month with it. But I want to be able to run 10's on motor. I need some advice big time!

**RamAir95TA** · 02-27-2012, 09:53 PM

What's the cam specs and full details on the build?

**blackbird1084** · 02-28-2012, 02:32 AM

Ok it's a 383 with splayed 4-bolt mains, scat 3.75" nitride treated crank, scat h-beam 5.7" rods, JE forged flat top 11.89:1 pistons, AFR 210 heads ported by LE 293cfm@.600 intake 226cfm@.600 exhaust 56cc combustion chamber , edelbrock lt1 intake ported by JRB Racing, monoblade tb, comp cams solid roller cam .639/.646 lift 253/270 duration @.050 284/302 duration @.020 intake opens 24 btdc closes 50 abdc exhaust opens 62 bbdc closes 28 atdc 52* overlap 105.5 lsa 103 icl, ud balancer, udp's, 42lb injectors, 255 fp, ewp, 1 3/4 lt's, 3" true duals, 4200 stall, built 4l60e, 3.73's, aluminum ds, and it should weigh 3500 with me in it. If you need anymore info let me know. I need to find out if I need to change cams to even drive it as I don't want to start it up put 91 in it and have it blow up in a block or two because I didn't pay attention.

**96LT1355Z28** · 02-28-2012, 08:49 AM

What engine management are you using (OBDI/II, FAST, etc.) and what rockers are you using. Saw the SR cam and was just wondering if you'll be able to spin it!

**blackbird1084** · 02-28-2012, 09:07 AM

Obd II computer and Jessel shaft mount 1.6 rockers.

**blackbird1084** · 02-28-2012, 01:42 PM

Anybody?

**05hd** · 02-28-2012, 03:57 PM

Originally Posted by blackbird1084

Anybody?

I think you will be fine as long as you:
1. Keep the heads cool
2. Get a professional tune before you romp on it

Having said that, we still need the compressed head gasket thickness and deck height to determine static compression (not just what JE says), then we can plug into a DCR calculator for more accurate numbers. There will still be some fudge factor depending on the valve lash you run and the actual installed ICL.

Also, I hate 91 octane. No 93? How about corn?

**blackbird1084** · 02-28-2012, 04:10 PM

Head gaskets are .039, deck height .026, lash is set at .020. Only one place sells 93 in this area and the same goes for e85. The motor was built at Strokermotor.com which I don't know if they were good or are still good.

**joelster** · 02-28-2012, 04:41 PM

We still need a part number on the piston to see how much valve relief it has.

**05hd** · 02-28-2012, 05:02 PM

Originally Posted by blackbird1084

Head gaskets are .039, deck height .026, lash is set at .020. Only one place sells 93 in this area and the same goes for e85. The motor was built at Strokermotor.com which I don't know if they were good or are still good.

Using those numbers and 5cc valve reliefs in the JEs, I am coming out with 11.5:1 static and 10.13:1 dynamic (ASSuming zero altitude). You could retard cam timing or tighten the lash on the intake rockers (have the intake valve close later) in order to reduce your dynamic compression without changing any parts, aside from an adjustable timing set if you don't have one. For example, if you retard cam timing by 4 degrees, you would be sitting at 9.90:1 DCR.

Your current setup would almost definitely benefit from more octane but I think it is possible to be tuned to run safely on 91. Keep the heads cool and get a good conservative tune.

Never heard of strokermotor.com.