Somewhat bummed at 450RWHP, 500+rw torque

[Scottie-GNZ]

I am sure a lot of thought went into your nice repsonse but I have a couple of comments.

 

I know there's hordes of people telling you to just "turn up the boost" ... but I'll be the first to disagree. The more you tun up the boost' date=' the less responsive your package is going to be.[/quote']

First I ever heard of that one and the opposite of what I and every turbo driver I know has experienced. Turning the boost up should not change the responsiveness of the engine, just add more HP at the new peak boost level.

 

 

The Gran National turbos are decently sized, but probably quite undersized for your application, and somewhat outdated.

Cannot disagree with the "outdated" statement. However, this V8 engine is 3.14L per bank/turbo and the GN engine is 3.8L. Unless he is looking to make well over 700hp, I am not sure this is a valid statement.

 

 

You may be under the surge line (each turbo is pushing a theoretic 4 psi, way outside of where it was balanced for)

I hope I am not misinterpreting what you are saying but he is running 8psi and I interpret this statement as saying 8psi = 4psi per turbo.

[cyrus]

I'm told the cam is fairly mild and I can get about 150 hp more with a different bumpstick.

 

Unless the cam is a broomstick that sounds optimistic.

[dr_hunt]

Well, then how much does bumpstick change the total HP output in a turbo engine. Say for example a sbc as is the case here. What cam you running silicone boy?

 

What would be the difference, say with a .480 lift 230 dur at .050 and 114LSA hydraulic turbo grind and say what I'm running solid roller .618/.630 244/250 @.050 and 114LSA, just curious??

[silicone boy]

It's been so long since I started the project that I can't remember off the top of my head what the cam is, but it's purpose was for a streetable, smooth idling normally aspirated stroker motor and not optimized for a turbo application. Lift was about .480 at .050. I agree that an extra 150 hp with a more aggressive cam is optimistic.

 

Well' date=' then how much does bumpstick change the total HP output in a turbo engine. Say for example a sbc as is the case here. What cam you running silicone boy?

 

What would be the difference, say with a .480 lift 230 dur at .050 and 114LSA hydraulic turbo grind and say what I'm running solid roller .618/.630 244/250 @.050 and 114LSA, just curious??[/quote']

[silicone boy]

I found the cam specs. It's a Comp Cams Extreme Energy 270 hydraulic roller. Complete specs can be found here:

 

http://www.compcams.com/Technical/Search/CamDetails.asp?PartNumber=08-422-8

 

Again, more for streetability at lower RPM than all out turbo performance.

 

As for the choice of the Buick GN turbos, they can be found everywhere and I wanted to keep this a budget install. It didn't turn out that way and I ended up rebuilding the turbos anyway. I would have done better to purchase turbos that are more optimized to the application, but as our resident GN expert Scottie has indicated, they aren't bad either.

[Z-Gad]

Doesn't look too bad to use as a turbo cam... maybe could use a little wider lobe seperation ~114 or so, but it should work fine. Doesn't look like much overlap either...

Camshaft Specification Table

Part Number 08-422-8

Engine -9999 Chevrolet

305ci-350ci

8cyl.

Grind Number CS XR270HR-10

Description

Intake Exhaust

Valve Adjustment 0 0

Gross Valve Lift 0.495 0.502

Duration At 0.006 Tappet Lift 270 276

Valve Timing At 0.006

Open Close

Intake 29 61

Exhaust 72 24

These Specs Are For The Cam Installed At 106 Intake CL

Intake Exhaust

Duration At 0.05 218 224

Lobe Lift 0.33 0.335

Lobe Separation 110

Recommended Valve Springs 986-16

[silicone boy]

Thanks for the reassurance on the cam. I was not quite sure how it would do with the turbos. My goal was to be able to reliably drive the thing to the track, so idle quality was important, and the reason for the boost was to be able to chase down the pesky Vettes down the straights..