What Turbo charger to connect to an Audi 4.2L V8?

[AlexTatar]

I've got a 4.2L V8 from a 1995 Audi A8 that i'm putting into my kit car and i want to set up a Bi-turbo system for the engine, (one turbo for each exhaust manifold.) I don't know what size turbo would suit my engine, can anyone give me an idea? - i plan to buy the turbos 2nd hand off ebay or similar.

[AndyS2]

If your doing it on a budget get a couple of K24's from an Audi S2, good for best part of 300bhp each, or if your feeling flush get a couple of GT2871's, they'll do 400+bhp each.

Marc Swanson is the guy to talk to, see here:-

http://www.s2forum.com/forum/showthread.php?t=2349...

http://www.motorgeek.com/viewtopic.php?f=6&t=5...

http://www.efiexpress.com/catalog/

[anonymous-user]

Nice easy one this, as with 4.2 litres spread over 2 banks, thats just over 2 litres per bank, which means there are LOTS of possible turbo's to choose from. Basically, you gota choose between driveability/ boost threshold and ultimate power. So for great driveability without crazy power, a pair of say scooby wrx turbos (220bhp each, so say 440 on your engine), and they will be on boost soon after 2500rpm. Or, for more frights, something bigger like say the turbo off a big boost evo x 2, for more like 600bhp total (assuming your base engine is tough enough etc),

I think for me i'd choose a pair of scooby ones to start, as they are easily availible and cheap.


(if you want real low end performance a pair of audi 1.8t blowers would probably spool up by 1800rpm, but would limit top end performance)

Edited by anonymous-user on Monday 25th October 20:35

[AlexTatar]

I took a look at those GT2871, they're a bit too expensive for me! although i looked at the WRX turbos and they're much better priced, i'd have to create some customised gaskets though to get them to connect up to the Audi's exhaust manifold.
Maybe a turbo like this...?

http://cgi.ebay.co.uk/SUBARU-WRX-STI-TD05-16G-TURB...

Edited by AlexTatar on Monday 25th October 23:47

[thong]

i would like the project sssssooooo much more if you forget them turbo thing's, N/A it,and hope one finds the turbo charger of your dream's lol :-)

[944fan]

AlexTatar said:

I've got a 4.2L V8 from a 1995 Audi A8 that i'm putting into my kit car and i want to set up a Bi-turbo system for the engine, (one turbo for each exhaust manifold.) I don't know what size turbo would suit my engine, can anyone give me an idea? - i plan to buy the turbos 2nd hand off ebay or similar.

A twin turbo V8 in a kit car

I hope you have some big brakes

[AlexTatar]

I measured the car shell and it currently wieghs 800kg... so + the engine.. this baby is gonna be fast!
Unfortunately it hasn't got any brakes on it yet!!!!

[chuntington101]

Have to ask what car it is you are palnning on putting it in.

[AlexTatar]

A toyota mr2 mark 2 of course....!

[dvs_dave]

Supercharging would be A LOT simpler, a lot more compact and with less heat managemrnt issues to deal with. Pretty sure there's a few off the shelf supercharger kits for the 4.2 V8 out there too. ABT do one.

[AlexTatar]

Well the thing is the super charger is chain driven so i'd have to customise the engine to get it to connect up. And not only that; i checked the price of these things.. $5000!? :S

£500 tops i'm afraid! i think the WRX twin turbos will be great.

[chuntington101]

yeah i think a couple of WRX/STI turbos would work a treat. If its going in an MR2 have you considered mounting the turbos in the same place Audi do in RS4/6?

[andygtt]

AlexTatar said:

Well the thing is the super charger is chain driven so i'd have to customise the engine to get it to connect up. And not only that; i checked the price of these things.. $5000!? :S

£500 tops i'm afraid! i think the WRX twin turbos will be great.

the problem will not be the power capability but the amount of revs.... WRX and cossie turbos etc will flow the power you want easily, but maybe not the volume of air that an audi engine will consume at 8000rpm and the WRX and cossie both have much lower rpm redlines, meaning you will get great spool and power to 6500rpm and then it will all be over which may ruin your audi engine and its awsome reving.

of cause you can get a hybrid but thats starting to get expensive.... it may sound a little dawnting, but you really do need to compare compressor maps and pick the one most suitable.

[anonymous-user]

andygtt said:

AlexTatar said:

Well the thing is the super charger is chain driven so i'd have to customise the engine to get it to connect up. And not only that; i checked the price of these things.. $5000!? :S

£500 tops i'm afraid! i think the WRX twin turbos will be great.

the problem will not be the power capability but the amount of revs.... WRX and cossie turbos etc will flow the power you want easily, but maybe not the volume of air that an audi engine will consume at 8000rpm and the WRX and cossie both have much lower rpm redlines, meaning you will get great spool and power to 6500rpm and then it will all be over which may ruin your audi engine and its awsome reving.

of cause you can get a hybrid but thats starting to get expensive.... it may sound a little dawnting, but you really do need to compare compressor maps and pick the one most suitable.

Not of course completely true regarding power and revs - For a typical "mild boost" turbo engine, the engine's BSAC will be similar for most engines, hence the "power" produced is a direct function of the airflow. So a wrx making say 230bhp, will pretty much use half the airflow of the audi engine making 460bhp. What will change is the compressor pressure ratio that is required to move that volume of air. The larger capacity, higher reving V8 will move more air with less boost, as compared to the scooby which needs a high plenum density to be able to ingest a similar airflow. So, all that means you will not be operating at the same place on the compressor map of the scooby turbo. Now in this case, you will actually be moving down the vertical pressure ratio access and perhaps a small distance along the horizontal mass flow axis. For most compressor maps this will not be an issue, and probably will actually improve compressor efficiency !!


In reality it will probably be the turbines flow capability (and at the low boosts required, the wastegates choke point) that may limit the ultimate rev-ability of this conversion

I suspect that a pair of scibby wrx turbo's will actually be pretty much spot on for this application (assuming as previously mentioned the OP doesnt want a super high power engine (i think 400+ bhp in an MR2 should probably frighten him sufficiently....;-)

[andygtt]

Max, I agree it should be ok, but the audi 4.2 makes around 400bhp as std and peak power is at least 1000rpm higher than the subaru and cossie just thinking its best to check the comp maps before choosing the turbo to go for as it'll be 600bhp plus with turbos.

[GavinPearson]

I think the first step is to decide what power and torque do you want to make, and can you afford to lower CR to avoid a detonation problem, upgrade the rods, deal with exhaust valve issues, and then if you have finished doing all of that, finding a gearbox capable of taking the torque.

It is of course an absolutely massive job and it will inevitably cost a great deal.

I would be tempted to limit torque ambitions to whatever gearbox you have is able to take (I assume you have an Audi V8 FWD manual and are making your car mid engined w/rear transaxle)and keep things as simple as possible.

You might also want to consider a supercharger like an Eaton M112 or maybe a tad bigger, it's sized right, it'll make plenty of power and give near instantaneous response too.

[neal1980]

Subaru Td04l's are my choice for my TVR Chimaera 4.6..

Still in the making but getting there and there so cheap bought 4 now! the last 2 were £18:00!!!

Edited by neal1980 on Tuesday 2nd November 15:50

[chuntington101]

Neal, Have you got any more info on the above build? Looks pretty intresting to say the least! lol

[neal1980]

chuntington101 said:

Neal, Have you got any more info on the above build? Looks pretty intresting to say the least! lol

Just done a full chassis restore and fancied going the turbo route.

Initially was going to be a large single turbo but couldnt make that fit it really was too large! So looking around decided td04's would be the ticket well at least a start as they should flow 260bhp a piece. Everything is pretty custom now but it will be intercooled and I already did megasquirt conversion a few years back, so that should handle the spark and fuel.

Engine is a top hat linered 4.6 low compression.

All done at home in my garage I like the DIY route

[chuntington101]

neal1980 said:

chuntington101 said:

Neal, Have you got any more info on the above build? Looks pretty intresting to say the least! lol

Just done a full chassis restore and fancied going the turbo route.

Initially was going to be a large single turbo but couldnt make that fit it really was too large! So looking around decided td04's would be the ticket well at least a start as they should flow 260bhp a piece. Everything is pretty custom now but it will be intercooled and I already did megasquirt conversion a few years back, so that should handle the spark and fuel.

Engine is a top hat linered 4.6 low compression.

All done at home in my garage I like the DIY route

have you got a build thread or some more build pics?