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Re: [oletrucks] selecting a turbo (help me)

To: CLLLSLS@aol.com
Subject: Re: [oletrucks] selecting a turbo (help me)
From: miq@teleport.com
Date: Wed, 15 Mar 2000 18:35:48 -0800 (PST)
CLLLSLS@aol.com says:
> 
> Hey everyone,
> 
> Finally got Corky Bells "Maximum Boost" in the mail yesterday. Very good 
> book! Really covers the everything, but I'm having a not so easy time 
> understanding exactly how to select the turbo I need.

Great book.  I've read it cover to cover twice now.

> The basic formula for flow rate (cfm):     cid X rpm X .5 X VE
>                                                                   1728
> 
> 279 X 3500 X .5 X .75 / 1728= 212 CFM 
> 
> I want to run a pretty serious 7-10 pounds boost through my 270, so figuring 
> for 10 PSI, the pressure ratio ((14.7+boost)/14.7) is 1.68. Yes, I will be 
> doing some serious intercooling.
> 
> 1.68 X 212 = 356 CFM 
> 
> So I need a turbo with a compressor that will operate most efficiently @ 10 
> PSI @ 356 CFM. It seems as if using the redline RPM in the formula would mean 
> my turbo's gonna be working most efficiently, creating the least heat, when 
> the engine's at it's redline. Is this the way it should be?
> 
> If these specs are right, selecting the right compressor shouldn't be hard, 
> but what about the turbine? Corky focusses entirely on street and racing 

You need something like a Garrett T3, with a 60 Compressor, running a HSG
A/R Turbine of around 1 - 1.1 you should see about 320 bhp.

This is assuming you are going to spin as high a 5000 rpm,  if you go for
lower top rpm, the compressor will have to be smaller and the turbine as
well.


> Do I want to lean one way or the other towards more top end torque and later 
> boost with a larger turbine or more low end torque and less top end with a 
> smaller turbine or is right in the middle the perfect solution for my truck? 
> What's gonna make this truck the funnest to drive?

That's up to you.  Do you want to spin the engine up or have low end grunt?

And now here's the reason I responded to the list instead of privately:

this link  http://www.turbofast.com.au/TFmatch.html

has a java applet to help you size turbos for just about any application.

-- 
__
Miq Millman   miq@teleport.com  
Tualatin, OR
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959

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