Stef

There's been a lot of talk on other threads about how fitting a downpipe transforms the way the car drives, yet the rolling road hasn't shown this on the figures anywhere.
I know there have been a couple of comparisons that have shown good increases, but these are all imports bar Jonathan's RB5, and are not the norm' based on the amount of people that have changed their d/p.
I'd have thought any increase in bhp and especially torque would be plain to see on a dyno, like it was when Jonathan put the PE one on his car.
Can anyone please explain this?
Is the increase psychological or something?

Stef.

bob

I had the PE T75 downpipe and center section fitted and gained 22 bhp. See Dyno page.
MY98, The car does have more get up and go now but I think the improved sound also has something to do with it.

Bob Iles

[This message has been edited by bob (edited 14-12-1999).]

Craig H

I think the bottom line power gains are negligible. But it's like anything that increase breathing - the car reacts faster, in our case, the turbo spools up faster.
When my STi was std, I couldn't keep up with a friends Cerbera (spped six) - wasn't a massive difference, but he pulled away. After SS downpipe and Blitz induction, he now struggles to stay with me. My cars only 20bhp up on std, but the way it pulls now is in a different league.

Bajie

Does it sound as good as the Speed Six.

Craig H

No

Ian Cook

Ooh Insomnia a wonderful thing

It could also be the fact the power isnt increasing much, but the rolling road graphs could be moving left or down the rev range quite a lot, meaning faster spool up and on the road performance feels a lot more than is shown on the rolling roads. Has anyone done a comparison between 2 graphs for a 99 MY car with and without a downpipe for the graph position not its peak powers. Maybe Paul Strong can do this as he has access to most of the graphs, doesnt have to be same car etc, just a comparitive thing.

Just a suggestion.

pat

Hi all!

First of all, does it sound as good as a Speed Six? Pass. Having not heard one (Speed Six, that is!) I have no basis for a comparison. Having heard a Group A Rally Scooby up close, it does sound rather similar (bar the backfiring caused by the antilag on the GpA car).

A possible reason that it doesn't show up on the rollers is that power runs are done in 4th. Speed builds up slowly... the flow into the turbo is determined by the volumetric efficiency of the engine and the engine speed (assuming a lambda value close to one). The flow out of the turbo is determined by the restrictions in the exhaust system. It is therefore possible that the engine isn't accelerating rapidly enough to give the flow required to spin up the turbo regardless of the fact that the pressure differential across (and hence effectiveness of) the turbine has been raised for the same flow rate.

On the road you will definitely notice a downpipe! As a bonus the sound (without cats) is absolutely awesome :-)

Cheers,

Pat.

Stef

OK guys.
Until now I have never driven a car with no cat in the d/p so have been left to guess why the gains rarely seem to show on a rolling-road.
After the fitting of mine at the weekend however, I can see what people mean!
In-gear acceleration is transformed, it picks up sooooooooooo much quicker.
I cannot believe the torque figure has not increased dramatically.
The fact that it sounds like a WRC, spits flame like a WRC, and enables the soft whistle of the turbo to be heard are simply big blobs of tasty icing on a delicious cake!
I'm looking forward to taking my car to PE just to see if my gains are also invisible.
I know there's a RR day elsewhere soon, but as all my rund have been at PE, I need a level playing field.
I'll let you know how I get on.

Stef.


[This message has been edited by Stef (edited 21-01-2000).]

JamesS

As I understand it the UK car has two CATS one in the downpipe and one in the centre section.

What happens to the middle CAT when a de-CAT downpipe is fitted?

I assume there are two CATS due to the very high exhaust gas temperature and high flow rate, compared to an NA car, due to turbo.

If the first (probably high temp resistant) CAT is removed the second CAT will see higher temps and flow rates.

Is this not likely to roast/break down the honeycomb structure of the second CAT?

Iknow you could rip both out but some posts seem to suggest that the noise is fairly unpleasant (in terms of `loudness`) when cruising etc. Now I LIKE good noise (have an SS back box) but not to the apparant extent that a full de-cat can bring. Any comments?

Ian Cook

The reason the UK cars have 2 cats is because without they will not pass a startup emissions test to get through the whole vehicle approval. with one cat removed the other can still pass an mot, but should not suffer unduly.

Gethin

If anything my car is now quieter after fitting the scoobysport downpipe and de-cat centre section. I have a magnex back box, and the noise was quite "boomy" under load low in the rev range before. It's quieter on the motorway too now. But when the car is pushed....the devil himself is woken !!! Big Grins

Power is also up from 289 to 313 and 234 to 268lbs from before (although the cold weather would push this figure up). My dyno is on Paul's site if you want a butchers.

Gethin
MY97 WRX

sunilp

My UK PPP is slightly quieter on full throttle after fitting Downpipe.

Stef

Quieter?
You're kidding right?
My system is much louder since fitting my d/p, at every level, but thankfully still not annoyingly loud on the motorway.
People tend to look over their shoulder before I get to them now, rather than glancing across as I go past!
I can't see how fitting a d/p can make a car quieter. Weird.

James.
My car is completely de-catted now, as I had already fitted a Scorpion mid and back section.
As to whether the noise is displeasant or not, well that's a matter of opinion.
I reckon it's utterly awesome.

Stef.

sunilp

Stef, i repeat,

MY CAR IS QUIETER AFTER FITTING THE SS DOWNPIPE.

What can i say, "thats just the way it is, somethings will never change"....lol

Have fun...you terror!

Andy Banks

Agree with you Stef, mine was slightly louder. I think the cat muffles the sound somewhat. Turbo lag definitely seems to be reduced, much more explosive.

So is there any way of measuring the turbo lag accurately, if the rolling road doesn't show much difference?

Annoyingly though, after 6 months this mod has caused the heat shield to rattle at certain rev range. Removing it and adding heat insulation to the downpipe helped, but I can still hear the heat shield underneeath the car rattling, but only occassionaly.

Anyone else had this prob. since changing d/p?

Andy

ChrisPaulson

Does anyone know of a downpipe friendly MOT centre in the Derby area?

Mines just failed the emmision test

Gethin

My car failed the first test but then passed the long run one.

Give your car a caning before you visit the MOT place and you might get away with it.

Gethin.
MY97 WRX

pwebb

Andy - heatshield mounting is a problem after fitting a 3rd party downpipe - SSport for example don't even bother to place mounting points for the shield where the OEM downpipe has two...perceived wisdom is to lag the pipe instead but I did manage to get my heatshield re-fitted by C+K,Manchester using the remaining points - it waggles a bit now under heavy acceleration - worse when its cold - but I can live with this - causes some vibration right through the steering wheel.
Better to have plenty of insulation around the turbo area though as any excess heat around the cylinders can lead to an increased chance of piston damage - already a risk with wrx/sti engines.

As stef and others have said though the increase in pick-up is awesome. I also get a lot of turbo whoosh audible from inside the car and all hell breaks out when I floor the throttle - especially good for ridding oneself of tailgating reps. - some of them actually look frightened by the noise!

In terms of Rolling Road gains - I will be measuring this shortly but can confirm that boost is now up to 18 psi peak and 15.5 psi held (1.3 kg/cm2 and 1.1 kg/cm2)- about an 8% increase - not due to cold weather either - I will be amazed if this does not correspond to a hike in bhp and torque aswell.

Most fun is driving through tunnels - 7500 rpm under the runway tunnels at Manchester Airport is absolutely blood curdling - hoping to post some sound clips soon -
how infantile eh?

cheers,

Paul W

RaymondH

When I fitted my SS downpipe I replaced the heat shield on the turbo only - the pipe has no heat shield or lagging. Is this the wrong thing to do and should I fit the heat shield off the original catted pipe? So far I have had no problems.

Raymond.

Pete Croney

Paul

Glad your pleased with the downpipe

I did expect Pete to call, about fitting.

We trim the heat shield across and down the corner, so the bit that is vibrating on yours is removed. I would get Pete to do this for you.

Also get him to check why you now get vibration through the steering, as this is not related to the downpipe. The downpipe is no where near the steering column or rack and the cause must be from something else that has been done.

sunilp

Yawn

I'm tired .....feckin budgets!

pat

Pete,

you are correct in stating that the downpipe doesn't go anywhere near the steering. But my car experienced exactly the same thing after having the downpipe fitted.... odd but true. Not a problem at all, but interesting nontheless.

Paul,

The good news is that it doesn't last long... [the vibration, that is :-)] After a week or so the vibration will disappear again. In my case, it was due to a tight-ish fit; once the pipe gets hot it finds its own shape. Mine is now a very happy downpipe and I have no more vibration than with the Subaru one [but the car does go a lot better :-)]

Cheers,

Pat.

pwebb

Pete + Pat

can confirm that the vibration is not as bad as it was - now it only does it when the engine is cold - the vibration shakes the whole bulkhead - that's why it can feel like its coming through the steering column - I don't notice this so much now - but driving an unmodified wrx the other day (loan car) it made me notice it again when I switched back to my car and the engine was still warming up.

some insulation material either side of the bulkhead would probably eliminate this - but what the heck - this is an impreza not a porsche - there are plenty of other spurious noises inside the car anyway ;-)

cheers,

Paul W