scottdg

I realise this has been asked before, but which downpipe is going to free up the most power and provide the best overall performance gain. Scoobysport or Power Engineering T75. Already have a Scoobysport back and centre and would like to fit one of the above.

Also open to other suggestions.

Thanks in advance. Scottdg (MY00)



Thanks in advance

john banks

Surely this one will be argued until the cows come home?

Conclusions are difficult just like the twin dump vs not debate.

Dyno results will not tell you the answer, although some will disagree with me.

Caronte

I'm curious too. For example having a prodrive mid and back, is it good to install a SS downpipe (referring to diameter, is it the same?). Secondly What about the lambda sensor on the down pipe cat, it will read wrong Oxigen values? Does it requires a new reprogramming then?

Cheers Caronte

dowser

Biggest gain is from replacing the catalyst downpipe with a non-catalyst downpipe.

The differences between the various designs, imho, don't really come into play unless you are significantly increasing the flow (ie; bigger turbo too).

It's then said that a twin pipe design gives more higher up, and the SS more lower down the rev range. Just ensure you get one that doesn't block off the wastegate exit and replacing the oe d/p with any of the others will see you happy.

Oh, it's worth mentioning that mild steel designs are considerably quieter, if that's a requirement.

Richard

Caronte

Hi Dowser,

do you think the less counter-pressure on the exhaust can provoke higher boost pressures with consequent fuel cuts? (i already have the PPP running 1,1 PSI).

Caronte

TonyBurns

iTrader: (3)

Just had a scoobymania D/P fitted its all i can say cos she flys and makes the sound that shes suppose to

Give you the info after the rolling road 2moro

Tony (MY00 PPP, no more hesitation as its been sorted after the solenoid was cleaned and one hell of a nice sound from the PPP exhaust with the DP fitted hmmmmm think im happy with it )
PS, John, go try an STI7, its an amazing car

john banks

STi 7 will try, but I think it will be a bit slow and laggy for my taste 262 BHP and 1470 KG who are they trying to kid!

Evo 7 for me all the way, but I will try an STi 7 just to feel that amazing power to weight ratio

What boost are you getting now Tony? Do you really think the STi 7 was as quick as your car is now?

[Edited by john banks - 2/2/2002 11:21:31 PM]

dowser

Caronte

With a PPP'ed car, decat'ing the d/p will 99% likely give you boost control issues. The OE solenoid set-up is too slow to keep up, and will make some wild overcorrections.

This can be improved by playing with restrictor size, or just junking the OE solenoid and fitting a Dawes (recommend you monitor boost, knock and lambda b4 doing this ).

While it makes it a pain decat'ing a PPP, it's definitely worth it Also remember, you can always refit the original backbox to tame the intial boost problems (OE bbox is restrictive enough to slow spool up again ).

Richard

Caronte

Hi dowser,

I'm a bit scared of dawes devices. I'd prefer not to mount one. As a second option you mentioned modifying the restrictor. Does it means that the hole should be smaller or bigger? Are there any downside of junking the sensor?
What do you think about a proper remap? Is the flash eprom, already modified from Prodrive, re-flasheable?

Thanks for your time

Andrea

john banks

On MY99/00 the hole needs to be larger to lower the boost peaks.

Better still get an adjustable valve - otherwise you will be overboosting in the cold if you run optimal in the warm, and you can be far more precise with a valve. I put an earlier thread in drivetrain about this - see the recent Dawes FAQ thread for the link.

You can also lose the solenoid using a restrictor valve instead which you could recirculate into the intake like the factory system - it is just like using a fixed duty cycle. An added benefit with PPP is you can go up to 18 PSI quite happily with this system. But a Dawes with a bleed hole is a briksker option

What are your objections to the Dawes?

There is no PRESENT commercial arrangement to reprogram directly MY99/00 ECUs.

[Edited by john banks - 2/4/2002 4:02:08 PM]

Caronte

I find dawes devices a good way of "playing" with the engine. If I begin to alterate the values soon or later my engine will blow.
I prefer rather "automatic" settings.
On the same way i would like to increase Hp slightly so i thought of removing the 2nd cat.
What about , instead, if I just take away the up pipe cat. Will it be better regarding the overboost problem, being the second cat left there?

Cheers Andrea

Caronte

BTW , mine is a WRX 01 PPP

dowser

Not sure if my01 suffers from the same boost control issues as my00 cars?

But I do know they have one extra cat, and that you should (I *think* - perhaps check on i-club) remove the up and downpipe ones together. However, this will bring on your check engine light (wrx has second lambda after cat's to measure efficiency...removing cats upsets it!) - buy your decat system from Scoobysport and get a blackbox to fix this free.

IMHO, just remapping the ecu won't solve the problem with crappy boost control, which seems to be more of a design issue - you'll need something like John's circuit to do it electronically, or the Dawes to do it manually.

Just invest in boost/knock/lambda monitoring now - you'll wish you had later anyway - then you'll never have a problem tweaking, unless you really do want to blow up the engine

John - when did you buy your PPP?! At least I got mine at export price

Richard

john banks

I bought my PPP last August.

A remap would solve the boost issues - you just need a different duty cycle map to account for the quicker spool up in a system with less restrictions. The PPP is not designed to go with decat downpipes or uppipes, and that is where the problems come. Also a change in restrictor size will also sort the problem.

You would find it difficult to blow up your engine with a Dawes - you a have a fuel cut which stops you going too silly IMHO.

dowser

Thanks John - you mentioned it before....maybe I believe now (I always assumed response was just too slow and that you couldn't tune it out via duty cycle)

Richard

john banks

You can get stunning boost control with the original 2 port solenoid - it is a software not a hardware issue. You can get the same boost value in every gear except 1st with no peaks at all if you want. A correct static duty cycle will give you hardly any boost spike- you can replace you solenoid with a needle valve with good effects. Even better ramp up the duty cycle during spool up and reduce it towards the correct value for holding it for lightning quick spool up and as much or little peak boost as you want.

TonyBurns

iTrader: (3)

John,
quick go get a test drive of an STi7, it has NO lag and just flies it may be the fact that it feels quicker cos it just handles alot better than my MY00 and as for performance... it feels quicker than the 249bhp my car was pushing out, could just be that big turbo and push back in the seat feel
Also, where can i get a 1.5mm restictor valve from John????

Tony

john banks

No lag from a bigger turbo with a higher torque peak what are you on about m8 ? Subaru are not magicians!

1.5mm from a drill bit stuck in the end of a Dawes. If you are keeping the original solenoid then a restrictor valve as per my earlier post is the way forward if you don't want to drill and solder and drill again to get it right.