DIY Turbo Discussion greddy on a 1.8? homebrew kit?
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turbo confusion

 
Old 08-27-2010, 06:11 AM
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right iam after 280whp on 1.8 1996 trying to decide what turbo is best.basically want to thrash it on track.

i asked the uk garret dealer about the disco potato gt 2860rs he doesnt recommend 0.86 ar on turbine side for anything under 2.5 litre engine capacity.
and says the 0.64 is better do you agree with that?

from what i read on here larger turbine a/r is better for sustained high rpm use so does that mean the .64 is no use for me?
i also read that the gt2860rs and gt2871r and gt2876r all have the same hotside turbine trim and wheel dia so they should all take the same time to spool up.so does that mean i should go with the gt2876r as it has a bigger compressor would it make more power accross all the rev range?
or is a combination of bigger turbo gt2876r and smaller ar0.64 the way to go?so many things to think about ive got a headache please put me out my misery
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Old 08-27-2010, 10:53 AM
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Originally Posted by delcbr View Post
i asked the uk garret dealer about the disco potato gt 2860rs he doesnt recommend 0.86 ar on turbine side for anything under 2.5 litre engine capacity.
Oh noes!!!1! I'll be running a .86 A/R 2860RS on my puny 1.8L with Absurdflow, I guess it will suck! I'll just have to abandon my build plans and sell the car. LOL

from what i read on here larger turbine a/r is better for sustained high rpm use so does that mean the .64 is no use for me?
The .64 will spool sooner but not flow as much up top. On track where you'll never be below 3500-4000 rpm, you want the .86.

i also read that the gt2860rs and gt2871r and gt2876r all have the same hotside turbine trim and wheel dia so they should all take the same time to spool up.
Not really. They all have the same 53.8mm 76 trim turbine wheel, however a bigger compressor has a bigger wheel with more mass, and it takes more exhaust energy (basically rpm) to spin up that mass. You need to search the forum for dyno plots and see for yourself what kind of spool & power people are getting with different turbos.

blah blah blah
A 2860 should get you to your power goal. If you want to go much higher you'll want a 2871 because it will be more efficient in the 300+ range. Either way I'd go with a .86 turbine for a track car.
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Old 08-27-2010, 10:55 AM
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Your garret dealer is full of crap.
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Old 08-27-2010, 11:00 AM
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Originally Posted by delcbr View Post
i asked the uk garret dealer about the disco potato gt 2860rs he doesnt recommend 0.86 ar on turbine side for anything under 2.5 litre engine capacity.
and says the 0.64 is better do you agree with that?
No, and I bet his boss in the US disagrees too.

This is my car with a turbine housing that's obviously too big on a BEGi log manifold at 16psi.

The gang of FMII cars that day made between 210-230whp at the most, and I'd estimate that your car would do the same on this dyno. I like my 2860rs/.86 because 16psi is right in the fat of the efficiency (I presume judging from output "delta") and any more power than that is going to drastically shorten the life of the trans. I have a grossly superior set of hot-parts now and have the boost turned down to 11psi and making slightly less power and happier for it.
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Old 08-27-2010, 11:01 AM
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Originally Posted by ScottFW View Post
The .64 will spool sooner but not flow as much up top. On track where you'll never be below 3500-4000 rpm, you want the .86.
I must admit that I like the 3200rpm spool at 4krpm peak torque. At Eagle's Canyon I'm short shifting into 4th 3300rpm or so and still throttle steering the car through a series of corners while other cry about shifting.
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