vortec head 89 tbi engine

[2424]

hello all, I have been reading this forum and have enjoyed it. I am a veteran engine builder, sprint cars and drag, for years. I am currently embarking on a engine for my sons 89 chevy pickup. Frame off restoration, nice piece. I have been concerned with the efi. Plan to use stock system. Vortec heads, vortec pistons, block decked to zero, Scat 4340 crank (no cast cranks here) and Crower sportsman rods. The aim is a everyday driver that runs good, torque and mileage and not over 5500 rpm. Plan to use GMPP manifold, new exhaust with improved y pipe, converter, muffler ect. My concern is the compression ratio. Quick calc says 9.4, although I have not cc the parts yet, and I will soon. I have the ability to machine the pistons to change that if needed, cnc is my business. Programmer for 35+ years. I have d cupped pistons for many custom builds for street friends in the past. As far as cam is concerned my understanding is a very wide LSA is required with this system, and am planning on that. So that leaves me with a relatively high dynamic CR. I want this thing to run on 87 and will do what is needed to make that happen. Have several stock roller cores for regrind (Crower) and will go that route. So my Question is, where do I need to be on the CR without a big tuning rodeo that I don't have time for. Thank You 2424

[dave w]

I use the decimal point rule for compression ratio vs. octane, which goes like this:
8.7:1 = 87 Octane
8.9:1 = 89 Octane
9.2:1 = 92 Octane

Quench is key! http://www.superchevy.com/how-to/engines-drivetrain/94138-piston-head-clearance-guide/

dave w

[lionelhutz]

What kind of LSA do you consider very wide?

[2424]

What kind of LSA do you consider very wide?
I consider 114-117 wide. Thanks for the reply

[2424]

I use the decimal point rule for compression ratio vs. octane, which goes like this:
8.7:1 = 87 Octane
8.9:1 = 89 Octane
9.2:1 = 92 Octane

Quench is key! http://www.superchevy.com/how-to/engines-drivetrain/94138-piston-head-clearance-guide/

dave w
I figured about 8.8 to 9.0 but maybe you guys know something about the vortec head I don't. More tolerant because of combustion chamber? Thanks for the reply

[lionelhutz]

I've run very well with 110* to 112* LSA. You don't need over 114* for it to work.

[2424]

I use the decimal point rule for compression ratio vs. octane, which goes like this:
8.7:1 = 87 Octane
8.9:1 = 89 Octane
9.2:1 = 92 Octane

Quench is key! http://www.superchevy.com/how-to/engines-drivetrain/94138-piston-head-clearance-guide/

dave w
Zero piston to deck with .039 gasket

[dave w]

A quench of 0.039 is a touch to tight for me, I favor a quench in the .042 to .045 range.

The Vortec head is a fast burn design, allowing for more spark advance compared the pre-Vortec factory heads.

dave w