s480 vs gt4508r

PACougar said:
I don't know that I would go with that assumption. I know several people who have ran the GTX4508R as a single on Duramax's and they blew up quite quickly. The journal bearings are cheap and easy to rebuild.

I went back and forth on this for a long time between the GTX4508R and a S480. I ended up with FI's Billet S480 with a race cover. THe compressor wheel isn't just a billet copy of BW's, it's got a freaking 120mm exducer on it. So far I couldn't be happier, it spools a lot faster then I had thought it would.
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BB takes maybe 20x higher thrustloads than any journal bearing. If those Duramax guys blew their turbos, they were just wrong size for their engine. Also spoolup is more about right turbo match than bearings or brand of charger.
 
Leiffi said:
BB takes maybe 20x higher thrustloads than any journal bearing. If those Duramax guys blew their turbos, they were just wrong size for their engine. Also spoolup is more about right turbo match than bearings or brand of charger.
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They were specifically GTX4508R's ran as singles. I just know they seem to have problems in that application. I completely agree with you about spool up, the right turbo makes all the difference.
 
Smokem said:
This needs repeated.
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Durability is also about right match. And power. Reading this board I see mostly badly matched turbos, for example higher boost than backpressure is very rare. But that is also about other engine tuning, mostly injection timing.
 
Leiffi said:
Durability is also about right match. And power. Reading this board I see mostly badly matched turbos, for example higher boost than backpressure is very rare. But that is also about other engine tuning, mostly injection timing.
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On a single application you're not going to see higher boost than backpressure, well not unless you don't want to spool the charger.
 
Let me rephrase what I was saying, I don't mean it's not possible on any single. I'm talking about big singles and I realize it's possible, it's just going to limit you in a big way if that's your goal.
 
I ended off tossing a billet s475 on the truck this weekend to try that out and I think that'll be the all around winner. I don't think I have the ability to take full advantage of the air flow difference between the 75 and 80. When I do get to that point I'll probably stick with the bw. The truck never really gets street driven and I think swapping the cam and converter will make a big enough spool up difference in the bw 80 to be happy with that. Thank for all the input.
 
Love my GTX4508R! Drive is also lower than boost; even under WOT. Slowest climbing drive pressure setup I've ever had and it runs the best. Few Videos in my youtube link if interested.
 
PACougar said:
On a single application you're not going to see higher boost than backpressure, well not unless you don't want to spool the charger.
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seen it many times, only way to get power from any engine. If boost is lower than backpressure, you have wrong turbo. For best driveability on the street you can use one step smaller exhaust housing and let backpressure climb at max power rpm but at lower rpm it should stay equal or lower than boost.
 
PACougar said:
Let me rephrase what I was saying, I don't mean it's not possible on any single. I'm talking about big singles and I realize it's possible, it's just going to limit you in a big way if that's your goal.
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how it's going to limit you ?
 
Leiffi said:
seen it many times, only way to get power from any engine. If boost is lower than backpressure, you have wrong turbo. For best driveability on the street you can use one step smaller exhaust housing and let backpressure climb at max power rpm but at lower rpm it should stay equal or lower than boost.
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I completely agree at lower rpm it should be below boost. I'm speaking strictly about max power in a drivable street application.
 
PACougar said:
I completely agree at lower rpm it should be below boost. I'm speaking strictly about max power in a drivable street application.
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OK, I agree. Even then, only about 7 psi higher than boost at peak power. Trying to push higher than that usually gains nothing in power, only higher EGT and more smoke.
 
If your turbo is matched for peak efficiency of the turbo drive to boost should be around no more than 20 percent difference. Make sure to pick a turbo for your engine goals not the turbos peak power ability.
 
PACougar said:
On a single application you're not going to see higher boost than backpressure, well not unless you don't want to spool the charger.
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I have to disagree with you there. I switched from a 475/83/.90 where max boost was 55# and drive was at 70# at WOT (and drive was always at least 10# above boost at any point) to a 475/87/.90 where max boost was 60# and drive was the same at WOT. Yes, the 87 TW spooled about 150 rpm slower on the street but once it got started it would outperform the 83 TW in literally every way. And the 475/87 consistently kept drive 15# under boost on the street.
 
PACougar said:
Let me rephrase what I was saying, I don't mean it's not possible on any single. I'm talking about big singles and I realize it's possible, it's just going to limit you in a big way if that's your goal.
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So let's talk about a big single.

We run a Precision Gen2 Promod88, it spools fine on fuel. Backpressure is less than boost all the way to 80psi+. And if 1250whp uncorrected on fuel is being limitied in a big way, than I am fine with being limited in a big way.
 
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Well I just saw 70psi drive and ~40 psi boost yesterday at WOT below 3000rpm so either i ha e a huge boost leak somewhere or this turbo is grossly mismatched.


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Blacksdieselhp said:
The reason i mentioned Holset, if your looking into a big unit(bigger than 80mm), and money isnt a problem, there is no doubt Holset is the way to go. There is a reason the pullers use hx82's and hc5a's.
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The CDS Prostock turbocharger is built on an HX82 frame, but if you think it uses a Holset turbine wheel, you would be mistaken.
 
dvst8r said:
So let's talk about a big single.

We run a Precision Gen2 Promod88, it spools fine on fuel. Backpressure is less than boost all the way to 80psi+. And if 1250whp uncorrected on fuel is being limitied in a big way, than I am fine with being limited in a big way.
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So it spools pretty decent on the street then? I assume it has nice drivability for a big single. I only say that because we're talking about a street truck with a big single.
 
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