Call me a n00b if you want, but can somebody explain to me the difference between running two different sized turbos at the same boost, other than spool time? The reason I ask is because I recently blew my T25 and am looking into an upgraded replacement. I'm looking at the Gt2871r and have read that the two different Air Ratio options will support different horsepower levels at similar boost levels and with similar engine work. I thought 16 psi was 16 psi, regardless of turbo size. Can somebody help me out?
I'm set on the .64, by the way.
Difference between different sized turbos, same boost?
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doridori23
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Re: Difference between different sized turbos, same boost? (steeda763)
There are quite a few things that will make the diff turbos give you diff power numbers.
Assuming 7psi (stock) boost levels T28 running right at the start of its efficiency island for a 2L motor. GT2871R (.64) is actually below its efficiency level and the wastegate is dumping a ton of exhaust gasses. You'll have odd surging and poor overall performance/response.
The T28 is the winner in overall performance here
Assuming 12psi T28 running at the end of its efficiency island for a 2L motor. GT28 running at the start of its efficiency island.
The winner here will be largely decided by cams, intake, and exhaust efficiency
Assuming 20 psi T28 Running well beyond the choke line for the turbo. This will create excessive amounts of heat (latent heat of compression) and carries a high risk of detonation. Boost at higher RPMs will tail off as it simply can not flow that much air. GT28 Running in the upper reaches of the turbos range. Turbo running happy with excellent midrange response.
GT28 will provide more power due to lower intake temps and the T28 is serisously in the red.
Assuming 24PSI T28 If the impeller doesn't explode in the midrange spool-up then the 425+ deg intake temps will surely melt pistons and cause catastrauphic detonation. GT28 At the peak of its efficiency Island. Midrange power will be the same as at 20psi however from 5000RPM up it will be a screaming banshee capable of 450whp with supporting mods (500whp on a .86ar due to exhaust gasses haveing less backpressure and a free'r path)
Gee...T28 blewup on Interstate80 and GT28 drove home happily
Its all an efficiency game. Garret has an excellent calculator based on engine displacement, hp goals, and driving preferenced (midrange drift/daily scream machine or highend track terror)
Assuming 7psi (stock) boost levels T28 running right at the start of its efficiency island for a 2L motor. GT2871R (.64) is actually below its efficiency level and the wastegate is dumping a ton of exhaust gasses. You'll have odd surging and poor overall performance/response.
The T28 is the winner in overall performance here
Assuming 12psi T28 running at the end of its efficiency island for a 2L motor. GT28 running at the start of its efficiency island.
The winner here will be largely decided by cams, intake, and exhaust efficiency
Assuming 20 psi T28 Running well beyond the choke line for the turbo. This will create excessive amounts of heat (latent heat of compression) and carries a high risk of detonation. Boost at higher RPMs will tail off as it simply can not flow that much air. GT28 Running in the upper reaches of the turbos range. Turbo running happy with excellent midrange response.
GT28 will provide more power due to lower intake temps and the T28 is serisously in the red.
Assuming 24PSI T28 If the impeller doesn't explode in the midrange spool-up then the 425+ deg intake temps will surely melt pistons and cause catastrauphic detonation. GT28 At the peak of its efficiency Island. Midrange power will be the same as at 20psi however from 5000RPM up it will be a screaming banshee capable of 450whp with supporting mods (500whp on a .86ar due to exhaust gasses haveing less backpressure and a free'r path)
Gee...T28 blewup on Interstate80 and GT28 drove home happily
Its all an efficiency game. Garret has an excellent calculator based on engine displacement, hp goals, and driving preferenced (midrange drift/daily scream machine or highend track terror)
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doridori23
- Posts: 271
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Re: Difference between different sized turbos, same boost? (steeda763)
BTW Why are you set on the .64?
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slowasss13
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Re: Difference between different sized turbos, same boost? (steeda763)
your right 16 psi is 16 psi but........ the afishancy (spl!) of the turbo changes produsing less heat = more power ... if a turbo flows air ezer it wont have to work as hard to get to the 16 psi ...pls a/r will change spool time / peak air flow ... hope this helped
sean
sean
Re: Difference between different sized turbos, same boost? (slowasss13)
Thanks for the response DoriDori...that really cleared it up for me. I wasn't even thinking about the air temp leaving the compressor!
As for why I'm set on the .64, it's because I don't have exorbitant horsepower goals, and I like the quicker spool.
My blown T25 spools fully under load around 3800 - 4200 rpm, depending on how it feels that day. I plan on getting cams, which will obviously open up the exhaust and spool the turbo quicker. If the .86 can spool up around that, or quicker, I'll get that (invitation for more information!).
As for why I'm set on the .64, it's because I don't have exorbitant horsepower goals, and I like the quicker spool.
My blown T25 spools fully under load around 3800 - 4200 rpm, depending on how it feels that day. I plan on getting cams, which will obviously open up the exhaust and spool the turbo quicker. If the .86 can spool up around that, or quicker, I'll get that (invitation for more information!).