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Discussion Starter #1
I'm wondering what would be the best compressor to turbine A/R values to get the best low RPM spool? Does anyone have some guidelines on what the effects of higher or lower A/R compressor or turbine have?

I've read through the FAQ many times, but it does elaborate on this very much.

For example, a turbo I am looking at is described as having a rapid spool with the specs:
T04E "O" trim T3/T4
Divided Tang T3/T4 flange
.57T COMPRESSOR WHEEL STAGE III
.84 A/R TURBINE HOUSING
.50 A/R COMPRESSOR HOUSING

I've never seen a turbo with such different A/R values. Usually I hear of .42/.48 or something like that as having a quick spool. I would have thought that a larger turbine A/R would increase lag, but wouldn't that also mean it would spool up at a higher RPM?
 

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94 civic si
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good question, id like to know the same.
 

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'89 CRX HF
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For example, a turbo I am looking at is described as having a rapid spool with the specs:
T04E "O" trim T3/T4
Divided Tang T3/T4 flange
.57T COMPRESSOR WHEEL STAGE III
.84 A/R TURBINE HOUSING
.50 A/R COMPRESSOR HOUSING
rofl! t4 .84 exhaust housing, good luck spooling that before 6500 with a d-series...

for "quick" spool with any t3 or t3/t4 hybrid, go with a .48 a/r turbine side
 

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basically= the smaller the a/r or the turbine housing, the quicker the spool... On a 57 trim the exhaust a/r is a .63; this usually starts to spool at ~4500 rpm, and pulls pretty much as far as you dare to rev it... Check out drunkinmaster1 's set-up, and do searches...
 

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95 CX Hatch
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42/48 hella fast spool, pisses out up top in the revs at higher boost levels
48/50 excellent spool up can keep up better in the upper range for a stock engine running moderate boost levels
48/60 great spool for a daily driver making hp in the 270-300 range
48/63 fair and tolerable spool to daily but has no problem making the hp

anything bigger....keep it on the track
 

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Discussion Starter #8
Thanks, that's what I thought, from all the reading of the FAQ and posts in this section. There just seems to be so much misinformation out there... Like I said, the turbo spec'd above was described as having a 'rapid spool'. I suppose that could mean just about anything when not in the context of a particular engine...

So what about when the turbine A/R is a low value, but the compressor A/R is very large? I understand that choosing the turbine A/R is a compromise between slow RPM spool and top-end horsepower, but what affect does the compressor A/R have?

I've done a lot of reading here on this site, and elsewhere, but this relationship has never really between clearly described. It is simply overwhleming how many A/R, trim, housing, inducer, etc. combinations there are, it's really hard to make a clear informed decision, other than just copying what someone has found to work...

Thanks guys for you patience, and knowledge!!

Hmm, another post in parallel to mine above from Bizzar may have already helped answer this...
 

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no love for the 60/63?

i used one on my stock y7, and i loved it. late spool, but it pulled hard as hell up top.

matt
 

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so what would the a/r rating(spool rpm) be on a dsm td05h-14b?
Here's a chart that has A/R to CM^3:

6 cm2 = 0.41 A/R
7 cm2 = 0.49 A/R
8 cm2 = 0.57 A/R
9 cm2 = 0.65 A/R
10 cm2 = 0.73 A/R
11 cm2 = 0.81 A/R
12 cm2 = 0.89 A/R
 
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