Safe Boost Level (with an Intercooler, FCD, water-injection)

BoostAddict · Post by **BoostAddict** » Mon Jul 19, 2004 5:08 pm

I have a question about the safe amount of boost that I can run with my setup.

1991 Legacy Sport Sedan (manual)
EJ22T
2002 WRX Intercooler
TurboXS manual boost controller
HKS SSQ blow-off valve
3" stainless steel DP-back exhaust

... I will be soldering up a VRG3-design Fuel Cut Defender and installing it shortly. I would like to know how many PSI's of boost I could run every day without overworking the engine. How many pounds of boost can the stock Legacy Turbo fuel pump handle? What is the upper-limit of effeciency on the IHI RHB5 that comes in the Legacy Turbo?

From what I've heard, the stock Liberty Turbo in Australia and New Zealand came from the factory with an EJ22T pre-set at 15 PSI. Would that be a safe everyday boost level?

What is the maxium amount of boost that I could run once in a while at the drag-strip?

Would water-injection raise my safe boost limit (what level would that be?) or would it just make the engine more efficient and add a few Hp? I've researched water-injection quite a bit, but I still can't find decent information about how it works and what performance gains (in terms of HP) I can expect from my setup if I was to use water-injection.

Thanks in advance for the answers.
P.

eastbaysubaru · Post by **eastbaysubaru** » Mon Jul 19, 2004 7:21 pm

The Australian Legacys only had the 2.0t, not the 2.2t that we got. They also had an AWIC and a different turbo which allowed them to run higher boost levels.

-Brian

BoostAddict · Post by **BoostAddict** » Mon Jul 19, 2004 7:41 pm

Thanks for the info. I've 'gotta read up on those old-school Liberty's from down under. I've always thought that they came with the same IHI RHB5 as we have in North America.

Anyways, back to the topic. Can anyone answer any of my questions from above?

Thanks,
P.

rsstiboy · Post by **rsstiboy** » Tue Jul 20, 2004 12:50 am

our Australian liberties run 11psi stock with a 14.7psi boost cut, the internals of our 2ltr motor can take 23-24psi howver we are limiting boost to 19-20psi due to the head gasket wanting to go after that amount of boost level, obviously we need fuel, exhaust, intake, and ecu upgrades as well to run that sort of setup.

kelley · Post by **kelley** » Tue Jul 20, 2004 1:16 am

you ought to be safe running up to 13 psi. that is what I ran with the stock turbo, but had a stand alone ecu. so not 100% sure.
now 11 psi on an ej20g is differant than 11 psi on an ej22g. these motors will not be making the same power at the same boost level.
the 22g will take 20psi with the appropriate changes. that is what I will run when I get my car back to gether very soon. ran 15 psi for a couple years. my limiting factor was fuel. got that solved so will run 20 w/ the vf23.

BoostAddict · Post by **BoostAddict** » Tue Jul 20, 2004 2:49 am

I figured that 13psi would be definitely safe. The question still is: with a stock ECU, all the mods mentioned above in my setup-listing and an FCD... what is the absolute highest level of boost that the EJ22T and the IHI RHB5 can handle at the track (not for everyday use) using 94 octane fuel and an octane booster?

Would 15-18psi be getting close to blowing up the engine or approaching the outer limits of the turbo's efficiency and compression map? Approximately what kind of WHP would I be making at that level and in what range should my 1/4mile times be?

georryan · Post by **georryan** » Tue Jul 20, 2004 3:37 am

Well you won't be blowing up the engine, but you won't be making any gains, either. You'll just be pushing more hot air into the engine. At 15 it is debated whether the turbo is making any added power, at 18 it definately is not. The turbo caps out in its efficiency somewhere around 13-14 psi.

georryan · Post by **georryan** » Tue Jul 20, 2004 3:39 am

Now, I haven't actually run those levels of boost, so your welcome to try it out and contradict me, but everthing I've learned so far pretty much goes into my post.

BoostAddict · Post by **BoostAddict** » Tue Jul 20, 2004 3:28 pm

So does everyone agree that the stock IHI RHB5 should be run at a maximum of 15psi? (or is there anyone that tried boosting it higher and got some additional HP's?)

Would water-injection enable me to boost at higher levels and thus unleash a bit more power, or would it just make boosting at 15psi more efficient (because of the colder intake temperatures)?

georryan · Post by **georryan** » Tue Jul 20, 2004 5:27 pm

Well it has more to do with the amount of work the turbo is doing to push the amount of air you want from what I understand. For intance, the vf-23 will push more air at a lower psi than our turbos and be more effecient. The amount of work our turbos has to put out in order to push that much psi and with the cfm rating it has, well, it is counterproductive at that point at about 15 and greater. That's how I understand it. Someone with more knowledge in the area is welcome to contradict me.

legacy92ej22t · Post by **legacy92ej22t** » Tue Jul 20, 2004 7:52 pm

Man it's crazy but I left a nice sized post on this thread last night and now it's gone!

Anyways what I had said was that you can run about 14 psi which is at the extreme limit of the turbos efficiency range. With those mods you could probably get away with 15 psi but it won't bve much of a difference.

The Liberty RS came with the VF12. I'm not sure but it may have the RHB5 designation. RHB5 is the exhaust turbine housing size designation.

georryan · Post by **georryan** » Tue Jul 20, 2004 10:14 pm

Now that is the turbine HOUSEING designation, not the fan. The fan pushes the air. So if the two have hte same housing designation then you can take take the vf-12 fan and put it in a vf-11 and voila, you have a vf-12. If you get my drift, and with any larger fan, you'll change the stats of the turbo.

legacy92ej22t · Post by **legacy92ej22t** » Tue Jul 20, 2004 10:46 pm

Ya, if the VF11 and VF12's both are RHB5's then you could swap over the compressor but you'll have to swap over the compressor housing as well as the VF12 is much larger. I'm not even sure if the VF12 is a RHB5 on the exhaust side though so it's just talk.

Rsstiboy- Do you know what the designation is on the VF12's exhaust turbine housing?

georryan · Post by **georryan** » Wed Jul 21, 2004 12:38 am

I'd take a vf-12 if it was given to me

BoostAddict · Post by **BoostAddict** » Wed Jul 21, 2004 3:00 pm

What exactly would water injection change at 15psi of boost? Would it enable the engine to run more efficient? I can't seem to get an answer to that simple question and it's bugging me. I've searched for posts on this topic, but with no luck.

Has anyone tried water-injection at 15psi and could they share their findings with us. What exactly do you gain with that method?

mTk · Post by **mTk** » Wed Jul 21, 2004 4:15 pm

It would cool the air and create less chance of engine knock. However it's better to actually get the car running properly and just use water injection as a safety measure. there are many turbos that can out do the airflow of the rhb5@15psi and still be efficient.

MK

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Safe Boost Level (with an Intercooler, FCD, water-injection)

Safe Boost Level (with an Intercooler, FCD, water-injection)