Thread: Advice on Lag
View Single Post
JFairman JFairman is offline
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
I've heard the compression ratio on the 3 liter 95mm bore '76 and '77 930 is 6.5:1, is that correct or is that just the '76?

The 97mm bore 3.3 used from '78 through '93 is still low compression but at least it's 7:1 and thats a little better for a street motor. It's also got a little longer stroke crank and that's going to give a little more torque at low rpms where you have the most turbo lag than a motor with lower compression and shorter stroke that's also 300cc's smaller... especially while running stock CIS injection.

The 3.0 has 2mm smaller bore and shorter stroke than the 3.3 and that gives lower mean piston speed and piston distance traveled per crank revoloution. Because of that shorter stroke slinging the weight of the piston back and forth it rev's freer at high rpm's and makes for a better track motor.

A smaller ball bearing Garret turbo (like your GT30) spins up a lot faster than the usual journal bearing 3k 3ldz or K27 turbo's most people run on these cars and that alone will reduce turbo lag better than anything else you do.

Raise compression up around 8:1 to 8.5:1 and run lower boost to compensate for that while using street gas and that will reduce turbo lag and give alot more low speed torque and pep for an all around more drivable street car if thats where you want to go.
Install SC cams with cam timing advanced as far as possible also helps lower range rpm power.

Advancing the ignition timing curve quite a bit from idle up to around 3200 rpms to get away from the stock EPA emission control oriented timing helps too and doesn't cost anything if you do it yourself,,, like you said.
Old 05-30-2013, 08:19 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)