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Highest boost on stock turbo?


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if you have a series one in resonable condition it should cope with 1 bar (14.5psi) Remember if you not flooring it everywhere, its not running 1bar everywhere, but it will be there when you need it. And if its stuffs up, theres a good excuse to highflow it. Seriously tho, i have mates that give em heaps running 1bar and no probs yet.

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good point, i was assuming fmic! 10psi would be more sensible with stock cooler, as there is a huge pressure drop over those things, so much that the turbo can be producing as much as 20psi before the cooler!

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SLY33, the pressure drop isnt that much. I did a measurment at and the drop was 1psi during the midrange to 1.5psi at the top end. I dont think a 600x270x70 tube and fin core will do alot better... Bar & plate will tho.

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think 1 bar is 14.7 psi anyhow. But regardless its not the BOOST that kills the turbo its the heat generated. Soo.... It can be said to be safer to run higher boost when at the drags coz of the short period of time that full boost is actually used. However the fact that more boost in theory should = more hp depending on other mods. More hp = more heat generated.

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Busky2k, an article in zoom showed tim at RPM testing the std cooler showing there to be a substantial pressure difference. 1 to 1.5psi pressure drop may be present when running stock boost, but up the boost, and watch the pressure difference. Pump a bar through the std cooler and there will heaps more than 1.5psi drop over the cooler. I remember the article stating they saw 20 maybe 22psi before the cooler to get 12psi at the manifold.

sweetr33, i know heat kills turbos, but in the case of std r33 turbo's i believe its actually shaft 'speed' (hence boost) that we have to watch out for. As with these turbos, failure is commonly due to the delaminating of the exhaust wheel.

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There are two problems with the standard turbo, both centred around the ceramic exhaust turbine.

Firstly, being ceramic the turbine is sweated/bonded onto the common shaft and therefore it does not like too much resistance ie; the exhaust is pushing the turbine while the compressor is trying to move air into the engine. Too much resistance (boost) and the turbine and the shaft part company.

The second problem is one of heat, the ceramic turbine will only handle a certain amount of heat coupled with this resistance. The heat builds up over several minutes of very hard driving (say on a circuit) and the turbine shatters or parts company with the shaft. Leaning out the engine to achieve more horsepower also increases the temperature of the exhaust.

So to answer your question, our experience has been that 0.7 bar (10 lbs) is OK for a road car as long as it is only in short bursts so that the heat does not build up. If you do any circuit work or long distance high speed stuff, then 0.6 bar (9 lbs) may well be the safe max.

The boost readings above are at the engine inlet. The boost at the turbo will of course be higher than that depending on the airflow of the intercooler and the pipework. By reducing this restriction (better intercooler) you can have more than 0.7 bar at the engine but still have the same resistance (boost) at the turbo.

With a really good intercooler and pipes we have achieved 0.8 bar (12 lbs) on a 225 RWKW road car reliably. But 5 hard laps on the circuit and the smoke escaped.

Sorry that this is a complex answer to your questions but it is a complex scenario.

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I personally wouldn't go above 0.7 or 0.8 bar on the stock turbo / stock intercooler combo for the street. I run 1.0 bar now with a FMIC but that is only for short burts. No problems whatsoever.

Basically, take Sydneykid's advice :D

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SLY33, this is from my own measurments, plumbing the boost gauge before the intercooler and then after, at 14psi, not stock boost (enough air to flow 170rwkw). Its one thing to read a mag, and another to actually measure it yourself! Thats why i did it..

The article in zoom magazine was talking about a HKS GT-RS or something similar from memory, which would flow heaps more than stock, and yes the pressure drop will be alot more. However with a stock turbo, it wouldnt nearly be as much, but I have to take into account I have an SR20 where as you boys have an RB25.

Im just sayin the stock cooler isnt as restrictive as everyone makes out to be for light mods, but thermodynamically, even for stock its a piece of shit....

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  • 4 weeks later...
So to answer your question, our experience has been that 0.7 bar (10 lbs) is OK for a road car as long as it is only in short bursts so that the heat does not build up. If you do any circuit work or long distance high speed stuff, then 0.6 bar (9 lbs) may well be the safe max.

The boost readings above are at the engine inlet. The boost at the turbo will of course be higher than that depending on the airflow of the intercooler and the pipework. By reducing this restriction (better intercooler) you can have more than 0.7 bar at the engine but still have the same resistance (boost) at the turbo.

With a really good intercooler and pipes we have achieved 0.8 bar (12 lbs) on a 225 RWKW road car reliably. But 5 hard laps on the circuit and the smoke escaped.

Sorry that this is a complex answer to your questions but it is a complex scenario.

So sydneykid...is the below correct ??

If you were running stock turbo and intercooler, then using a boost controller you would be wise to go no more than a 9psi setting for reliability..

However..

If you were running the stock turbo with...say...a GTR intercooler, an 11-12psi setting (electronic boost controller) would be reliable ??

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Hi Gizmo, 9 to 10 psi on the standard turbo and intercooler and 11 to 12 psi on the standard turbo with a GTR intercooler. On the road, should be no problems as the heat build up isn't extreme. But on the circuit, 4 or 5 hard laps will still be a problem.

Hope that helps some more.

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Hi Enrico, "So u achieved 225rwkws on a stock turbo at 12psi?" It was actually 0.85 bar (12.4 PSI) on an R34 GTT, but it had a lot of mods....

Standard R34 GTR Intercooler

Alloy pipework 63 mm from the turbo to the intercooler and 75 mm from the intercooler to the throttle body

HKS BOV (non plumb back)

Alloy pipework from AFM to turbo (it kept sucking the standard one closed)

Power FC with boost controller

POD with CAI and heat shielding

Tomei 256/260 Poncams

Sard Injectors

Bosch 044 in tank fuel pump

Split dump pipe with 3.5" hi flow cat and exhaust

Electric fan

OS Giken twin plate clutch

When the turbine died after 4 laps at Eastern Creek, we sent it off to GCG for a ball bearing hi flow and it made 268 rwkw at 1.3 bar (19 PSI). I also ported the head and polished the combustion chambers and ceramic coated the exhaust manifold, while we were waiting for the turbo to come back.

Best all round RB25DET I have driven, daily in city traffic, on the freeway, drags and circuit. I have driven higher powered ones, but this was a great all rounder.

Hope that answered your question.

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