Mike Gray

Am I right in saying, the idea of an equal length header is to reduce the back preseure by equalling the exhaust flow into one pipe. Does this mean that if less pressure is produced the turbo will spin up slower and also reduce the max.PSI?

greasemonkey

One of the gains of the equal length setup is a reduction of pressure waves travelling back down one of the headers, but that does not equate to a reduction of exhaust gas pressure at the turbo if that's what you are thinking.

The use of equal length headers improves the efficiency of the Impreza's turbo installation in a number of ways (especially in the 4-2 and twin scroll turbo setup used on the new cars).

The principal gain is in evening out the timing with which the exhaust gas pulses hit the turbine blades.

Imagine a pedal bicycle that, instead of having its cranks set at 180 degrees to each other, they're set at 90 degrees (and so there's a 270 degree gap on the "other" side of the stroke). This would pretty clearly cause a situation where your legs can't drive the bike forward as efficiently as they otherwise would. The same problem applies with the Impreza's unequal length headers.

When the header length is equalised, there's a uniform "pulse-pause-pulse-pause" rhythm to the way the gas pulses arrive at the turbo. With "normal" headers it's more like "pulpulse-pauseee-pause".

In a word, no. The use of equal length headers imparts more energy to the turbo impeller, and so it's possible to obtain better spool and flow characteristics, assuming everything is designed optimally.

Mike Gray

Thanks for your reply. The reason I am asking this question is that I have recently had one fitted to my99 and instead of the torque increasing it reduced by 10 lb/ft and runs out of puff at approx.5700rpm instead of 6500rpm. Is this normal as I was promise an increase of up to 25 lb/ft?

greasemonkey

One of the most important sentences in my previous posts Mike is the one about assuming everything is designed optimally.

What brand of headers did you have fitted, and how does their bore compare with the OE unequal items? Is your MY99 car an otherwise standard UK Turbo 2000 with the regular TD04L turbo, is it a Japanese market car with a VF28/29, or does it have something else? What boost pressures are you running? Have you had the new headers covered in heat wrap or similar insulation to maximise the exhaust gas temperature and velocity?

If you've genuinely and measurably lost torque and power as a result of fitting these headers, I suspect either they haven't been heatwrapped properly, or simply that they are optimised for higher gas flow rates than your current engine/turbo package produces, and thus the bore is a little bigger than ideal for your particular application.

Either way, if you had that 25lb/ft torque promise in writing and have actually lost out on the deal, I'd say you have grounds for a refund.

Pavlo

what headers?

are they leaking and losing boost?

are you just reaching the same limit sooner?

what is the difference at RPM either side of the peak torque?

Paul

[Edited by Pavlo - 1/26/2004 5:33:20 PM]

Mike Gray

The car was bought from new (UK Spec). Had the Prodrive performance kit fitted. This included decat centre exhaust & rear silencer with ECU remap Turbo now 1.1bar (240bhp + 229lb/ft). Then fitted full Decat exhaust & K&N Flat Panel air filter (253bhp + 239lb/ft). Powerstation recommended & fitted header (250bhp + 229lb/ft). They are not heatwrapped & I am not shore about the brand. The plastic under engine shield has been left off. If I replaced it would this help to keep the heat in?

Pavlo

To be honest I would say that there is nothing wrong, provided there are no leaks.

The headers often need remapping to get the most out of them. You may find that the boost has dropped (for whatever reason) and you're making similar power for less boost.

Surely you asked this question at powerstation? Or didn't you get the 'after' RR result from them?

Paul

Mike Gray

It was put on the RR after fitting at Powerstation. Yes I did ask the question. They said "dont take any notice of the results just drive it and feel the difference". Yes its much smoother but less powerful.

Pavlo

Get them wrapped it does help, you may not have been spooling up fully on the rollers, although they *should* have caught that.

They have shown excellent results on other cars though, so I don't think it's money wasted, just not as simple as bolting on and hoping for the best.

paul

MPeart

Mike.

Would you keep SN informed about how you get on. I'm very interested because I have a MY99 with more or less the same spec as yours and this was going to be my next mod done by PS.

Thanks.

Mark.

Mike Gray

Just spoken to Powerstation. They are going to stick it back on the Dino on Friday and make some fine adjustments to the Turbo?
I will keep you in touch.

Andy.F

Get them wrapped Mike. Fitting bare headers is irresponsible of them in my opinion. It is a fire risk as well as losing you power.

Andy

Mike Gray

If I wrap the header will this increase the pressure in the exhaust and spin up the turbo quicker & faster

greasemonkey

Yes, as mentioned above. Insulating them will result in less energy being dissipated as the exhaust gas pulses travel down the pipework, and thus more energy will be imparted to the turbine blades.

Echo Andy's point about the wisdom of the supplier letting you go without (at the very least) advising you to insulate them. :|

WRX_Rich

iTrader: (5)

powerstation fitted my headers - they said that they only wrap the headers on rally cars, as on a road car the wrap gets wet and never lasts more than a year - when I arrived to pick up the car they had wrapped them for me

I still have the undertray on but I will get ride of that as soon as they stop throwing salt on the roads... may be I am wrong to do this

It is hard for me to say what power the headers gave as I also got them to fit a tsl sport cat downpipe and a ecu tek 3 ( mapped to the headers with a fuel pump) the car got 260bhp and 270 lbs.. on thier rollers

I don't like the sound but I wouldn't swap, is there any one else on here with a bugeye with more lbs than bhp?

I watched the lad fit the headers and He had no problems with no leaks

Rich did tell me when I had it done with out a re map they couldn't guarantee results but with a remap I should get 20 \ 25 lbs and I would say thats about what I got

I don't know much about how it all works but I seems that these headers work on smallish turbos ( by looking at my results ) so may be a remap would give you the results you are after. It did with mine and we have simular specs just on different year cars

The only problem I have is it won't hold boost passed 5k, just fitted a HKS hiper and it now holds to 5.5 weird but true. Give powersation a chance they helped me out allot

Mike Gray

Powerstation have now agreed to Heat Wrap the header and replace the undertrays. Will let you no results after Friday

Pavlo

So are you high on torque or low on power?

Paul

WRX_Rich

iTrader: (5)

well I have the mods stated above and got 260bhp and 270lbs (holding 1.24 boost) on powerstation rollers which i have been told is about 20 lbs \ lbs down on power engineering

The car feel so powerfull I asked a question in the general forum about what people have got from their bugeyes on the rollers at powersation but no one replyed

for the money I paid i was well happy with the result overall just a shame I loes boost to early, they said a new turbo would sort that out for me which I can understand

as a novise to all this I will let you decide if this is good or not

Mike Gray

Have now been told that wrapping will eventially destroy the header from over heating. So now I will just replace the undertray to keep off the direct cold air?