Boost thresholds for R33 - is it before or after the intercooler?

[slayer]

Hi, everyone seems to universally agree that 12PSI is about the max safe limit for a Series 1 R33 GTS-T stock turbo.

Thats cool, fitted a boost gauge and ready to tweak up a gated bleed valve (as a short term boost gain before I fit the new ECU).

One question - I have tapped into the stock in-dash boost gauge pickup on the manifold, and as I had heard I see about 5.5 PSI, then 7PSI above 5500 RPM - thats cool.

But I am aware that there is a large pressure drop between the turbo and the manifold across the piping, intercooler etc.... its the 12PSI everyone talks about as the safe limit at the manifold, or before the intercooler at the turbo outlet (I dont think pressure is normally read there but it makes a big difference!).

I am concerned if I set it up for 12PSI at the manifold then the turbo must be boosting harder than that, and some pressure is being lost across the intercooler.

Anyone know for sure which it is??

Ta

Conrad

[SLY33]

thats actually interestsing. But i do believe the 12psi is after the presure drop from the intercooler. So yes, the turbo is boosting harder than that, but everyone does it, and it seems fine. RPM did a test (in a Zoom Mag, dont know what issue) and found over 20psi before the intercooler to get 12psi after it! (std heatsoaked intercooler.)

So it seems the 12psi is the safe limit in regards to detonation and means safe for the engine, not so much worrying about the turbo itself. The ceramic turbine wheels of the series 1's must be ok seeing that so many ppl boost up with the std cooler, and i dont hear of many of those turbos failing.

[Steve]

If you are using a stock coola, perhaps 10psi would be safer. The stock coola has (I believe) a 7psi drop between 6 and 7000rpm.

Have you done the exhaust yet? From the sounds of things you havent, because with an exhaust your boost will rise to about 9psi. Just remeber that the exhaust will change your boost, so if you fit one with a bleed, dont remeber to readjust it

Steve

[Guest nismogtsx]

Interesting question....

Why not tap a line into the pipe off the turbo and run a tempory gadge from there just to see ya self... I dont believe that the turbo would be doing 20 psi if its 12 at the manifold... I mean at 20 it would be falling apart....

I know the stock coolers are pretty average (better than nothing) but i dont see that higher boost drop...

Try it and see... Ill try my car tommorrow and tell ya what i get...

[slayer]

yep, its an interesting question (12PSI at turbo or manifold) - mine is completely stock at the moment so I am keeping boost conservative as I am also concerned with exhaust impeller temps with all that backpressure.

Hopefully I will be able to put together the funds soon to put a 3" system on, then I will go for 10PSI.

Hmm, might try patching the boost gauge in prior to the intercooler and see what it reads... 7PSI drop sounds pretty serious, I would be stuned if the stock turbo could sustain 20PSI..

One thing I have noticed, even with the bleeder completely open it is now boosting to 7PSI then bleeding back to 5ish, as opposed to 5.5PSI then switching up to 7. Plus it is coming on boost quicker now which is fun

I think higher boost low in the rev range then bleeding off makes it feel less impressive but would be safer in terms of leaning out etc.. I will look for a second hand EBC, as I know how dramatic a difference they can make.

[Freebaggin]

Slayer/Sly33, you're on the right track re pressure drop across factory intercooler. It was my car that did that test on my request (you might notice a Black R33 with DTMs in many issues of Zoom and HPI as Tim and I use my car as a bit of a test bed, for example 1st with LT-12 Plug-in).

I wanted to know the performance of the factory one compared to the RPM/Horsepowerinabox 75mm thick Bar & Plate I was buying at the time.

So the test included pressure drop across the coolers as well as temperature checks, and yes the factory cooler has a 6psi pressure drop across it at anything over 5000rpm at WOT.

However alot of guys run 12psi with standard turbo and they have hung on for ages no worries so they are very tough.

I now run a max of 15psi with large FMIC as the pressure drop is less than 1psi now, so the turbo does not overspeed as much as it did at 12psi with factory IC.

[Merli]

When people say "12 psi is max safe boost" for the stock turbo, they mean 12psi which the engine sees.

To measure this, you measure boost in the intake plenum. Tap into the fuel presure regulator line, which is where most people take boost readings from, as this is a vacuum line straight from the plenum chamber.

Yes, your turbo is actually making more than 12psi, but that's taken into account.

[Guest INASNT]

Originally posted by Merli

When people say "12 psi is max safe boost" for the stock turbo, they mean 12psi which the engine sees.

To measure this, you measure boost in the intake plenum. Tap into the fuel presure regulator line, which is where most people take boost readings from, as this is a vacuum line straight from the plenum chamber.

Yes, your turbo is actually making more than 12psi, but that's taken into account.

wtf? how can that be? coz the stock cooler drops about 5-7psi high up in the rev range, then u get a fmic and u saying since the there is about 1 psi pressure drop with a good fmic u can run the turbo at 18psi coz its running the same as before with the stock cooler??

u cant say oh yeah stock cooler is expected to drop X amount of psi no matter what condition it is in then, so as long as the intake boost is 12psi the turbo will be ok! :confused: