mark245

I have an my94 UK car that has had the PE phase 1 carried out. Loads more torque, but the turbo is not kicking in fully until about 3900 rpm. I am not concerned with outright power, but would like more useable power lower down. What is the feasibility of fitting one of the later , smaller turbos to acheive this?I know a downpipe would help,. and would consider this as well. Any thoughts on this?

Thanks, mark

stv555

The problem with fitting a smaller unit is the pay-off versus top-end power. The smaller unit will spin up faster and provide good torque low-down, but the overall throughput of the unit will be restricted at large throttle openings and high rpm.

The ideal setup would be a twin turbo setup with one compressor feeding a pair of cylinders, then you could downsize the turbo with no danger of compromising the throughput.

R19KET

Mark,

The first thing I would do, is speak to David Power, tell him the problem, and ask him if he can re-map the Phase 1. 3900rpm for max boost/torque, sounds VERY high for a UK car, and I'm sure the map can be improved.

Even the STi's come in earlier than that, particually with the Possum, .

Mark.

mark245

Thanks for the replies so far fella's. I did'nt explain things too well after reading my initial post. Yes, the turbo is boosting well before 3900 rpm, but peak torque is at that figure. Back in 1988 I bought a Lancia delta HF 4wd. This had a small turbo, and in many ways this was a better drive than the Integrale I bought a year later to replace it. Motorsport aspirations on the part on Lancia dictacted that the Integrale needed a big turbo, so engine response suffered. Basically I want a bit more engine response from my car, and I know the later Impreza's have that. I'm willing to suffer a loss of top end power for more torque lower down the rev range. Is a turbo swap feasible to a later , smaller type?

again, many thanks, Mark

R19KET

Mark,

I'm not too up on the UK cars, but would expect the IHI turbos to be interchangeable.

BUT: The point is, that other UK turbos spin up, and PEAK much earlier than your car. A down pipe/exhaust, would make a very big difference, but the Phase 1 map will make the biggest. It's much cheaper, and easier to ask PE to re-map for bottom end torque, than buy a new turbo, and still need the PH1 re-mapped to suit it. The standard down pipe is VERY restrictive, and slows the turbo spining up. Change that, and get a re-map after, you will be amazed. If not, you can still get a smaller turbo.

You may be able to swap with someone who wants your bigger turbo.

Mark.

strong

Judging by the graphs of your car ('Mark Sleap' on the dyno site), I doubt a re-map alone will help - the re-maps don't bring the turbo in earlier just give you a bigger kick when the turbo does come in.

What Mark says about a downpipe and then a re-map is right though. It's probably a better first attempt at improved driveability than trying to swap turbos.

[A note to Mark (R19KET): as you'll see from the graphs, his 94MY has much more lag than the newer UK cars (looks like an old WRX graph) - nothing the re-map can drastically change.]

Paul.

Nico van Steen

Mark,

Not all units are interchangeable. I have an Aussie magazine (Zoom issue no.21) where they replace the IHI TD05 of a MY96 to a MY99 (OEM with IHI TD04) Due to outlet/inlet differences the turbo housing has to be adjusted. This is for the UK versions turbo's. Can't comment for the VF turbo's on the Sti's.

Nico van Steen

AlanW

Totally agree with Mr Strong. I've been reading about tuning and setting up Turbo cars. This basically states that to reduce lag you can resize your turbo ie. make it smaller (fairly expensive) get a turbo with variable vanes (ultra expensive) or go for a lower back pressure after the turbo or finally you change the exhaust manifold for one of them power ones as that should increase exhaust gas flow.

I am not an expert by any means, so I could be wrong.

Alan

AlanW

Oops,
Forgot to mention that when looking at downpipes apparently it is better to have seperate pipes for the turbine outlet and the wastegate outlet. This is due to uneven mixing of the exhaust gas causing back pressure after the Turbo. Although I'm not sure how much torque you would lose/gain at a defined RPM.

I am hoping to get a BPM Downpipe, so I'll post the difference when I know.

GavinP

Mark,

Funny you should talk about 94 cars and lag...

I have a 94 WRX Automatic which is worse - I am in the process of replacing the downpipe and fitting a Link.

Incidentally, MRT sell a kit which allows you to fit an STi turbo to an earlier car with a 90 degree inlet (SUWE037c).

I have a Pipercross induction kit which seems to make the turbo spin up quicker but the noise is an acquired taste...

MRT also sell a replacement feed pipe from the air filter box to the turbo so this may be an option if you don't want an induction kit. See

mark245

I asked PE to remap for torque, but as paul says, they cannot make the turbo come in any quicker. Sounds like a downpipe swap may be worth a try. Anyone who has done this on an early car, who found the turbo kicked in lower down the rev range?
I asked Merv at PE about fitting a downpipe and he said everyone who has had it done says it makes a big difference, and basically I would need a short dyno session to optimise for the new part, but not a full remap.I know some dyno plots have'nt shown what a big improvement to driveability the downpipe makes, and my thinking was that with a turbo change I would definately acheive my aim.
Gavin, thanks for the info. Interesting about the exhaust wrap, I was thinking about that to cut down on noise [ must be getting old!!]. I'll have a look at MRT's site

Mark

[This message has been edited by mark245 (edited 24-01-2000).]

firefox

guys...guys...guys... lol

J.

mark245

Thanks Jay, can you expand on that!!

Mark

Dr Hu

Sorry guy's big post following.......

It's not as easy as you think just swapping turbo's, the inlet trunking is completely different for the early to late cars.

On early cars the air duct inlet goes to the top of the turbo, then through a alumininum 90 degree cast pipe bolted to the turbo flange, so the air enters the turbo sideways.

On later cars the turbo inlet was changed dramatically to get rid of the 90 bend in the inlet, the inlet now comes from the air box then UNDER the arched inlet manifolds and straight into the turbo with no sharp bends.

So you would have to buy new inlet trunk parts, new airbox and also possibly the later manifold which has much more room under it for the turbo ducting. Also if you look at the block on your car you notice coolant, fuel and PCV piping on the block where the ducting lies on later cars, all this was moved to allow the ducting to go under the manifold.

HOWEVER, you can cheat, the turbo IS a bolt for bolt straight swap, you can buy a Blue Silicon hose that fits the turbo throat pefectly with a 90 sharp bend, cut the silicon hose AS TIGHT AS POSSIBLE to the 90 bend to allow you to get a large hose clamp on, then acquire an inch or so of metal or strong plastic pipe the same internal diamater as the silicon and your old inlet boot, this acts as a sleeve to join the two hoses together, two large hose clamps and your away.

Basically you have swapped the cast aluminium pipe which will NOT bolt to the new turbo, for a silicon hose which you can use hose clamps on, so that you leave all your existing inlet trunking in place.

I have done this on a Legacy Turbo, which used an identical engine/turbo to the early Impreza, with perfect results. And YES it made a huge difference to spool up time.

I even still have the turbo/hose combo in my garage, as when I sold my Legacy I converted it back to standard.

If you like I can take some digital photos of it so you can see the bush mechanics it needs to make it fit!!

PS Turbos are tres expensive, why don't you search for a later car - as it was'nt just a turbo swap, the whole engine was redesigned with new cams, heads (higher CR), valves etc to improve breathing.

mark245

Dr Hu, thanks for all the info. Yes, changing to a later car would be logical, and the money I have spent on mine, I could have done so[ but I dont think I'm alone there!!]. It has '98 spec STI4 suspension, ALK, steel drop links, uprated bushes , 16" wheels etc etc, so this side of the car i am happy with. By the sounds of it the turbo swap is feasible, but I am swaying towards a downpipe change first, and see how it goes from there [ more money!!]. It would be good to hear from anyone with an early car who has done this, to gauge results. Also, which type would give best results in terms of low down torque?

Many thanks all,
Mark