Not sure if this will help anybody else, but....

I have just recently had a MONGOOSE full system fitted to MY94 WRX. All seemed well (the bhp was up by over 20bhp http://bbs.scoobynet.co.uk/smile.gif), but the torque remained the same @ 246 ft/lb http://bbs.scoobynet.co.uk/mad.gif. On inpsection of the rolling road figures, the boost only peaked (1.1/1.2 bar) @ 5.5k, instead of the expected 3.7k.

The car has been fitted with a UNICHIP, so don't have a heartattack over the boost figures! http://bbs.scoobynet.co.uk/wink.gif

To try and relieve the problem, the car was played around with yesterday (using jets). This had no bearing on the situation. Everything was checked out, the turbo, the wastegate, the actuator and the boost solenoid, but to no avail. A quick phone call was made to Turbo Techniques, and the problem was explained. The outcome of the conversation, came down to a problem with the MONGOOSE downpipe.

Basically when the system was fitted, it caused major overboost (upto nearly 1.4 bar in 3rd!!!) - because it is so free flowing. There seems to be a major problem with the way that several downpipes are designed. The Mongoose system like many, has a massive exhaust flange that covers the wastegate exit. Thus meaning the wastegate is offloading against a solid piece of metal, instead of venting straight into the downpipe. This causes the wastegate not to be able to dump the gas quick enough to do it's job and spin up the turbo to MAX boost when it should!

After looking at another WRX, fitted with a PE downpipe, they have actually grafted on another pipe that exists on the flange (behind wastegate exit), and then mates that back into the downpipe - meaning the wastegate can dump properly.

Where as the above problem would not cause issues, if the car was standard, if higher boost was needed (when chipped), it will.

I am not sure if this is contained to early WRX's (as I know the turbo is of a different kind).

I spoke to COLLINS today, with the response of "Take upto BLUE FLAME (Manufact.), they may be able to help you!!!!!" - Not the kind of response I hoped for, after spending nearly £500.00 on the system. http://bbs.scoobynet.co.uk/mad.gif

I am now having another pipe grafted on myself, the week after next. And I have been assured this will fix the problem.

With so many threads on the BBS, concerning the purchase of exhausts and others with boost problems, I hope this will be of some help!.

Shaun.

P.S. has anybody else had similar problems?

[This message has been edited by Shaun (edited 26-04-2000).]

The Scoobysport and a couple of others also deal with the wastegate blockage, using different methods, some use the 2 pipes like the PE one (BPM's is one) whereas SS use a larger opening that has been gas flowed. The main reason yours was probably done like it was, is thats the way the standard downpipe is made and they probably just copied the flange ???

This is all a bit of a puzzle as ... the standard downpipe also blanks/restricts the wastegate outlet.

The mod you suggest brings the Mongoose in line with several other manufacturers ... and could make it worse, the reason you get overboost is that more airflow equals a more "excited" engine and so the boost builds better due to higher exhaust gas velocities, as you have a Unichip a simple map adjustment should fix it. The early turbo's are floating sleeve bearing types and don't spin up like the later ones,the factory down pipe/exhaust is restrictive and the Mongoose as changed all that, hence the need for some map adjustment. Its all understandable and normal.

Bob

Bob,

But how can a re-map of the UNICHIP change the way the boost is delivered?

The only parameters available to the mapper, are ignition & fueling. As mine does not have an EBC connected, boost cannot be mapped.

Before the Mongoose was put on, the boost was reaching it's 1.1/1.2 bar, at the correct rate, but because of the restriction the bhp/torque figures were rubbish.

Obviously with the less restriction the boost did over shoot, but that was sorted by adjusting the bleed valve - this is not the problem. The problem here, is because the exhaust is free flowing (which is causing the boost to rise very quickly), the wastgate cannot dump quick enough to keep up with the rest of the throughput. Hence the reason why MAX boost is not being met untill 5.5k - that's the problem!!

Am I, or my tuners, missing something here?

Shaun.

P.S. I have also been reliably informed that WRC cars have the same problems, hence the reason why there downpipes are ovaled, to cover the wastgate exit - as IC described another manufacturer does.


[This message has been edited by Shaun (edited 27-04-2000).]

[This message has been edited by Shaun (edited 27-04-2000).]

It may be that the diameter of the rest of the system is affecting the efficiency at lower rev's and preventing full boost being achieved until further up the range.

Pete,

The Mongoose has a 3" bore!!!!??????

Shaun.

Shaun has missed a quite inportant fact from his tale.

We pumped the wastegate fuly open (Until it hit the exhaust flange) and the engine still made 1 bar of boost at 6000rpm. I am certain that this will be fixed when the exhaust is modified. I am sure Shaun will keep you posted.

Rich