1. HKS Blow off valve, is this the same thing as a Dump valve. I thought the impreza had a blow off valve that was not venting to atmosphere. Does this make a nice Tiss sound? what is it's purpose, has it any benifit.

2. I plan to fit a Scorpian exhuast,to be different. what are the likely effects of removing the second cat and fitting this 3' system.

Thanks to anyone who can help http://bbs.sidc.co.uk/smile.gif

MR LEIGH AS YOU SAID THE HKS BLOW OFF VALVE IS A (DUMP VALVE)WHICH WILL OUTLET INTO THE ATMOSPHERE AND SOUNDS GREAT.YOU WILL FIND YOUR CAR WILL PERFORM BETTER WITH THE NEW EXHAUST. THE DOWNSIDE IS THE CAR MAY NOT PASS THE MOT EMISSION TEST.GOOD LUCK PETER.

MR LEIGH AS YOU SAID THE HKS BLOW OFF VALVE IS A (DUMP VALVE)WHICH WILL OUTLET INTO THE ATMOSPHERE AND SOUNDS GREAT.YOU WILL FIND YOUR CAR WILL PERFORM BETTER WITH THE NEW EXHAUST. THE DOWNSIDE IS THE CAR MAY NOT PASS THE MOT EMISSION TEST.GOOD LUCK PETER.

Dear,Mr.Leigh(very formal)!

I've just had the middle cat' taken out of my 98'STi4,and replaced with a Magnex De-cat'pipe.The front pipe,and box had already been replaced with Scoobysport parts.

I put the car on PE's dyno first,then changed the middle pipe,and back on the dyno.There were only minor gains on the peaks,but the turbo span up earlier,and gained about 5/10 bhp/ftlbs through the mid' range.
A friend with a 98 WRX,SS front pipe,did the same test but with a SS Back box.
He also had minor peak gains,but was up. 25ftlbs@ 3000rpm
20ftlbs@ 3500rpm
5 ftlbs@ 4000rpm
simular for bhp.
The biggest gains are had by changing the front pipe.20 bhp/ftlbs peak is acommon gain,with bigger gains in some areas.Expect a lot more noise(worth it)even more fun.
HKS valve(all mouth no trousers)LOT of money,NO gains.If you want,change the filter to an induction kit.Small gain,5 'ish bhp/ftlbs,helps mid range,and you hear the air dump through the system + induction roar!!
£100 approx'.

Hope this helps
Mark.A.

[This message has been edited by R19KET (edited 18-04-99).]

To R19KET.
Did changing the middle pipe require a lot of time and effort? Can someone do it on his own? Does it require any special tools and do they put any adhesive at the joints?
In Greece you have to pass an emmissions test once a year and if I decide to decat I will have to do the pipe changing it by myself (in my back-garden). If it there is no danger destroying the engine I think I will do it as it will offer 20bhp and a lot of sound effects as you say.

Hi,dmel
Apart from raising the car up to access the bolts(4)it's quite easy,to change the middle pipe.Have some exhaust paste handy just incase.
The front pipe is a S.O.B to change.It takes about 2.5/3 hours(worth it).
None of the changes will hurt the engine.The BHP/FTLB gains are due to better gas flow,but if you have access to a rolling road you could check the CO2(7/8 % is ideal)
just to be on the safe side.
Your emitions should be ok if you remove the middle cat',but will FAIL if you change the front.
A lot depends on how old your car is,and when it will need to be tested ?.

Hope this helps, Mark.A.

Will removing the second cat cause a loss of back pressure that might have some negative effect. would the HKS blow off valve be more effective that the OE part, or do you fit it as well as. I will go for a HKS induction kit and a blow off valve if its not likely to cause any mechanical problems. I live for excess. its damm hard to make your subaru indivdual. thanks for the advice its much appreciated. http://bbs.sidc.co.uk/smile.gif

Dear,Mr.Leigh,

1)You only use 1 valve.Dump valves don't give any extra power.I advise you to listen to one before you spend circa £250 on a HKS.

2)I don't know of anyone who has had adverse effects from changing any part of the exhaust.ONLY GAINS !!!!
DOWNSIDE: Emissions if you remove front pipe,noise(subjective)

3)Paint your car PINK,havn't seen one of those yet!

Hope this helps Mark.A.

Does a front downpipe replacement (to remove the front cat) need to be gas flowed?

If so how is this done and why?

Thanks for your help Mark. Pink, I like the sound of that, I just sold a Citrus Yellow Mondeo.

Hi Mike,
The front pipe go's straight on(2.5 hrs 'ish)
I tried a HKS pipe first.Gave 22 bhp/ftlbs approx' increase.+ very good mid' range.Very noisey though.
Scoobysports pipe is better gas flowed,so I switched.Better pick up,stronger mid'range,5 ftlb increase,same bhp,BUT:10/15 bhp/ftlb increase between 3500>6500(Piper x induction fitted).Now much quieter exhaust,but some induction noise,and you can hear the air dumping through the system.
Hope this helps. Mark.A.

where can i get HKS bits? MARK A, I take it you dont like the sound of the blow off valve! is it not loud enough to warrent£250?
Are induction kits much lowder than the Ramair panel filter. are they likely to provide more power?

Mr.Leigh,
I can see that there's no stopping you.HKS products can be got from Torque Developments on Tel.07000-867783 or try Technical Tuning Tel.0181-881-9966.Also check some of the Grey importers (adverts in the mag's).
Induction kits are noisier,they vary depending on make.The 10 bhp claims seem to be optimistic,better mid' range though.

I have used TD before,comments via my email?
Mark@Racket.uk.co

HTH'S Mark.A.