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 Advantages Of Smaller Exhaust Housings On Turbos?  

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Terrible One
  • Terrible One
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Post #1 post 17th August 2004 - 03:28 AM
Is there any downside of running a smaller A/R ratio on the exhaust housing on a turbo like a 0.6 for example instead of a 1.0? I know it'll give more boost lower in the rev range but will it increase exhaust pressure and lose power that way?
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17SLO
Post #2

pfft
whatever ur running a A/R 1 on will be huge anyway


no 4 banger is spoolin that up till 5,500 anyway


but a drop that small will not have much affect apart from quicker spoolup, and the standard big bore exaust will get rid of the gas quick enuff anyway
180bfj20det
Post #3

a/r is a ratio. so even tho an a/r of 1 on the exhaust is generally very big for a 4, this is not always the case. For example, if you were to keep the standard turbine on a cappacino turbo, but replace the exhuast housing with a bigger one so the a/r became 1, you would still have a turbo that would boost early in the rev range for a 4 cylinder 1.5L+.

Sometimes there is no downside to running a smaller ex housing. For example, back to back testing by rpm horsepowerinabox.com has shown that the smallest GT30 turbo is best for 2L street engines and that going bigger in the GT30 series range only increases lag, no power advantage (all about 300 rwkw on street fuel, this figure can alter significantly depending on your engine combo).

But for any turbo, the smaller exhuast a/r, the less laggy, but the less power potential it has. However, all depends on what engine you put the turbo on.

`nigno
Post #4

Basically a general rule is:
Smaller A/R = Less lag which means on boost earlier.

Although it does have a lot to do with other things such as impeller size etc etc. that is just a general rule that applies in almost 100% of cases.

Terrible One
Post #5

I thought that would be the case.

I'm building a turbo 202 (3.3L six) that I'm going to get around 350rwhp from (260kw) on around 1 bar of boost and I can't work out what size turbo I'm going to use. I want something that will spool up fairly quickly and just fry the tyres with ease. I was looking at a GT3037 ball bearing turbo that has a compressor that will flow 52lb/min which is right what I want (around 520hp) and it has a choice of two exhaust housing A/R's, 0.63 and 0.82 and I thought that the 0.63 would be good for street use to make boost quick but I thought there might be a setback to a smaller A/R.

Do you guys think this would be suitable for what I want?

SupraCrazy
Post #6

If you have a small exhaust wheel & a small A/R you'll get compressor surge, and you don't want that.

Too people worry about A/R with lag, it's mostly the wheel diameter they gotta concern themselves with.

psi999
Post #7

for that setup i would be looking at a 0.82 housing or larger.... otherwise you will choke the engine.
TurbostyleR
Post #8

with a larger A/R you will have more lag, however you will have more top end torque...

I notice when i race cars with similar hp as me but with smaller turbos i generally pull out ahead big time in 4th gear due to the torque you get with a larger rear housing/wheel...

Fixxxer
Post #9

Yes, go the larger housing and heed the advice of the people above this post, too small an exhaust wheel will choke the turbo. If you are seeking 52lb/min flow, make sure that the compressor map is at its most efficient at the boost u want to run it at, i.e., that its peak efficiency matches the 52lb/min flow @ 16psi.
Fixxxer smile.gif

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