Drive pressure and exhaust sizing/wastegate queries

B

Bbw22

New member
Good evening all.

I have a 3 litre idi that was previously running 39psi boost pressure for 65psi drive pressure with a 48mm inducer on the comp and a 48mm exducer on the turbine. The turbo couldnt make any more boost. I have replaced the turbo for a slightly larger turbo with 52.5mm inducer on the comp and 52.5mm exducer on the turbine. Exhaust housings arent directly comparible but are of a very similar size. The results are not what I was hoping for...The turbo can indeed make more boost but at the cost of very high drive pressure and no performance gain. 45psi boost results in 80psi drive pressure and slower acceleration times than the original smaller turbo at 39psi. To make 45psi on the new turbo the wastegate must be held closed completely, hence the high drive pressures.

My dilema is as follows, as the rear housing at the moment is essentially ungated as held closed it is taking 80psi drive to create 45psi boost. How do I rectify this? I cant overcome the thinking that I should downsize the turbine housing to allow the turbine housing to make better use of the exhaust gas and open the wastegate to bleed off any excess exhaust, lowering drive pressure whilst maintaining shaft speed to maintain boost pressure. Surely a larger turbine housing would require even more exhaust energy to maintain the shaft speed required for 45psi boost?

Any input much appreciated

Thanks in advance
 
Maybe a larger turbine housing and more fuel would help. Or more timing with the current configuration. Late fuel is always hotter.
 
You need smaller compressor wheel. I have never seen same size or bigger compressor inducer than turbine exducer work very well, their boost to backpressure ratio is always bad.
 
Leiffi said:
You need smaller compressor wheel. I have never seen same size or bigger compressor inducer than turbine exducer work very well, their boost to backpressure ratio is always bad.
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I was suspicious about that. Gassers do this regularly but rarely have I seen it in diesel application.

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Get away from the square turbo measurements. Square turbos in diesel applications tend to bark and snap shafts quite frequently.
 
I've always been curious where the sweet spot is. I assume you would need target flow rate and real world testing to figure it out, but it looks like a ratio of .8 to .9 of comp size to turbo exducer seems to be what is marketed the most.
Savage Fabrications in California toys with tighter turbines geared toward more specific torque bands for mild engines. He's to only one I've seen do field follow style testing.

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biggy238 said:
I've always been curious where the sweet spot is. I assume you would need target flow rate and real world testing to figure it out, but it looks like a ratio of .8 to .9 of comp size to turbo exducer seems to be what is marketed the most.
Savage Fabrications in California toys with tighter turbines geared toward more specific torque bands for mild engines. He's to only one I've seen do field follow style testing.

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Just buy turbos from real turbo manufacturers, they dont build any BS turbos. At least I have never seen those "square" turbos from Holset, Garrett or BW.
 
Most of the higher pressure ratio compressor trims use a larger turbine wheel exducer in relation to the compressor inducer. Compressor inducer is not the only thing worth looking at. For example a bigger compressor exducer will perform better at higher pressures with less likely hood of surge.So if your 52mm inducer wheel has a smallish 56mm exducer then it will not be as ideal as a 52mm inducer with a 60mm exducer.

In my experience I've found that a slightly tighter A/R turbine seems to work best when the compressor and turbine are properly matched. For example I've never had any good results when up sizing the hx35 turbine housing from 12cm. Years ago I tried 14,16,18.5 and 21cm housings back to back and 56 and 58mm inducer compressors. 58mm inducer worked best with 12cm and used to be the hot ticket for my old 5.9.

I'm kinda sold on the he351cw turbine housing with a bigger wheel. My 2.0L VW TDI uses a Savage Fabrication Villain turbine housing with a 68mm exducer for the high pressure stage. I run a small 58mm compressor inducer on it (s300gx). Previously on this engine I ran the twin volute 14cm/.80 A/R turbine housing with a 65mm turbine wheel. The villain out performs it in every way. No need for a divided turbine housing. The open volute works and the wastegate flow is far better compared to the divided borg warner housing. Drive vs boost pressure is similar to the borg however spool is much better.Whats not to love?
 
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andy2 said:
Most of the higher pressure ratio compressor trims use a larger turbine wheel exducer in relation to the compressor inducer. Compressor inducer is not the only thing worth looking at. For example a bigger compressor exducer will perform better at higher pressures with less likely hood of surge.So if your 52mm inducer wheel has a smallish 56mm exducer then it will not be as ideal as a 52mm inducer with a 60mm exducer.

In my experience I've found that a slightly tighter A/R turbine seems to work best when the compressor and turbine are properly matched. For example I've never had any good results when up sizing the hx35 turbine housing from 12cm. Years ago I tried 14,16,18.5 and 21cm housings back to back and 56 and 58mm inducer compressors. 58mm inducer worked best with 12cm and used to be the hot ticket for my old 5.9.

I'm kinda sold on the he351cw turbine housing with a bigger wheel. My 2.0L VW TDI uses a Savage Fabrication Villain turbine housing with a 68mm exducer for the high pressure stage. I run a small 58mm compressor inducer on it (s300gx). Previously on this engine I ran the twin volute 14cm/.80 A/R turbine housing with a 65mm turbine wheel. The villain out performs it in every way. No need for a divided turbine housing. The open volute works and the wastegate flow is far better compared to the divided borg warner housing. Drive vs boost pressure is similar to the borg however spool is much better.Whats not to love?
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I was being vague, but you are exactly right, you have to be able to generate enough shaft torque to hit your target flow rate.


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biggy238 said:
Savage Fabrications in California toys with tighter turbines geared toward more specific torque bands for mild engines. He's to only one I've seen do field follow style testing.
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There are mule engines wore out testing turbos on the engine dyno every year, main difference is it's not on YouTube.
 
Smokem said:
There are mule engines wore out testing turbos on the engine dyno every year, main difference is it's not on YouTube.
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Lots of those Turbonetics chargers measure out "square" , yeah? Remember those mentioned in some of our conversations years ago!
 
Here is a comparison of the same turbocharger with a few alterations to the compressor design, but the blade count/configuration was not changed.

CWCBD.jpg
 
Yes, that particular data is from a Limited Pro Stock setup. What I was trying to show is it is not uncommon to see 2:1 boost vs drive in this situation, and that altering the compressor can reduce drive pressure while simultaneously increase boost pressure.
 
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