Hey Dustin,
I have a turbocharged inline6 in my car, and used Corky's book as a
guide also. The difference between out trucks and cars is most likely in the
way the exhaust gasses pulse through the manifold into the turbine and the
torque curve, of course. I like the smaller T3/T4 style turbine, about what
you would find in the GMC Typhoon. In fact, the Typhoon is probably a good
reference point to start with. Call or surf Turbonetics; that's who built my
turbo and it matches your specs pretty close. If possible, have a dyno run
done on your truck to determine the torque and HP curves. I'll bet your
truck motor has a pretty low redline and that will dictate a smaller turbo.
Keep you intercooler in the 6" by 18" dimension, maybe 3" thick. This will
keep your lag down and still let you boost up around 15psi efficiently. My
turbo starts building boost at 1900rpm and is at full boost in the blink of
an eye. This is what Corky means by FUN!!
Hope this helps! Any questions, let me know.
Tim
'50 Chev 1/2t dlx
> -----Original Message-----
> From: CLLLSLS@aol.com [SMTP:CLLLSLS@aol.com]
> Sent: Wednesday, March 15, 2000 7:19 PM
> To: oletrucks@autox.team.net
> Subject: [oletrucks] selecting a turbo (help me)
>
> 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.
>
> 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
> applications and doesn't say much about truck applications other than
> "they
> might be different."
>
> I'm gonna have a 3.19:1 final drive ratio with the 30% overdrive and 4.56
> gears running stock 17" split rims and big truck radials. The RPM's will
> be
> right in spec for cruising at 75.
>
> 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?
>
> I guess one of the reasons I'm not so confident making decisions is
> because
> my application's only gonna see 3500 RPM. I'm thinking that means I will
> need
> a smaller turbine than most engines because I will need the boost to come
> on
> at a lower RPM, at about 1000.
>
> FYI, the engine's a 1948 270 GMC six it has/will have:
>
> 279 cid
> 4" stroke
> stock head
> stock 7.5:1 compression forged pistons
> TPI
> water intercooling
> dry sump lube
> water cooled bearing, remote wastegate turbo
>
> Please, please let me know if I'm on the right track here or just
> constructively criticise.
>
> Dustin
> 50 & 53 GMC 1/2 tons
> 48 GMC 3/4 ton
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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