MurrayZA

I've heard about hybridding a TD04 by machining it to fit a TD05 compressor wheel. Can anyone give me any further information about this - expected gains, spool up, what boost to run, where to get one, etc - I have an 01 WRX, full decat, PPP, Unichip, MRT TMIC,
running 245bhp-ish at 0.95 bar boost.

john banks

The exhaust side will still be too small.

MurrayZA

Why do you say that - I have heard it works well? What would the "too small" exhaust side cause ?

ChristianR

iTrader: (1)

Speak to Mark @ Lateral Performance (http://www.lateralperformance.com/)

[Edited by ChristianR - 4/22/2003 2:06:49 PM]

john banks

The exhaust wheel and the housing of a TD04 are simply too small for good top end boost and therefore ultimate airflow and power. Too much exhaust gas back pressure is present which blows the wastegate open or kills the timing if you try and hold the wastegate shut. I say this because I have mapped two cars with them on (well I don't think they were TD05 wheels but they had a bigger compressor and clipped turbine), they were about 290-300 BHP. Whilst they are an improvement, I feel there are better replacement turbo options now available which have a more worthwhile improvement (eg up to 80 BHP more with other supporting components vs approx 20 BHP for a TD04 hybrid) without significant losses low down. Would also agree to speak to Mark, he can supply you TD04 hybrid, TD05 conversions, various hybrids.

IMHO after playing with a lot of the common Subaru bolt on turbos on mine and other's cars I think the TD05 16G small is very well balanced. The exhaust side is not so big that it won't easily make 1 bar in the 2700-2800 RPM range, about 3000 RPM in 4th gear, 3200 RPM in 3rd. Yet it is happy to hold 1.4 bar perhaps more at 6000 RPM which is plenty enough for most people with standard engines. However, it is noteworthy that this exhaust setup can still get 430+ BHP out of a 20G wheel.

I like the VF28/29/35 for their quick spool up, but only the VF35 spools quicker/earlier than the TD05 from what I've seen, but does run out of puff earlier.

The TD04 is great for a 215-225 BHP standard car or up to 20% improvement with decat, map etc.

[Edited by john banks - 4/22/2003 2:39:19 PM]

MurrayZA

Thanks for your input John, since I live in very hot high 30
degrees C+, high altitude area, keeping things cool is a major
concern, hence my quest for a bigger turbo that will have almost
no lag difference (say 250 rpm over the std TD04) but provider
cooler charge and a larger range (boost held till higer RPM). (we
also have really **** 93 Ron fuel that I boost to 96 with NF)
Few cars (scoobs) here spool over 1.2 bar for engine safety sake.
I'm trying to find a good solution to this rather localised
problem. Had a VF23 that worked the dogs danglies, but waiting
for 4K rpm till the boost had reached 1.0 bar was just crazy in
traffic - drove me nutz.

john banks

It will always be a trade off which is altogether more unpleasant at altitude with high temps. Like hell for a turbocharged car

MurrayZA

Rather tricky to say the least. I drool every time I read of a car with more than 1.3 bar boost, here you'd be picking up little pieces of motor within 5000km... Bigger turbos work well here
as they keep the charge temps down but then you have to tap
your fingers on the dash till 4K rpm comes around. Was running
1.1 bar on my VF giving about 290hp - very nice (between 4000 and
7000). Looking for a compromise - 270 hp with 500 rpm less lag - any suggestions to the turbo of choice for such an application ? TD04 runs very hot (red hot to be precise) and kinda runs out of puff. I'm one of the believers in "area under the graph" rather than one huge peak at 6000rpm...

john banks

IMHO TD05 is the best choice for you. Dig out some of my area under the curve graphs.

Also consider the TD05 16G large which you would have to get custom built. This has a slightly more favourable surge line which would help, plus it runs cooler at higher pressure ratios. From the compressor map it looks good but I don't have personal experience of it.

MurrayZA

Thanks John, will do just that - your help is much appreciated.

john banks

Although I sound like a boring TD05 evangelist, why not plot out some load lines for an EJ20 and work out the PR at altitude and then compare to the other available turbos and you'll see why I suggest the 16G small or large over anything else.

MurrayZA

I couldn't plot a bar graph of chocolates sold in a candy shop even if I tried 8-(. I have driven a '96 GT with the TD05, stock standard and found it to be somewhat laggy but strong to red line. I have also driven a 97 GT with a TD05 which seemed strong as an ox from low down but ran out of vroom at 5500k rpm. Any ideas on that one ?

john banks

Depends on how you taper the top end boost, also the non-STi heads limit things.

MurrayZA

My theory was with the better breathing on my car (decat, TMIC, down pipe, up pipe) the car spools up quicker than a std car - thus a slightly bigger turbo will spool to match the std spool up - and the std mapping will be very suited to the situation. Then use the unichip to add a bit more fuel and boost taper up the rev range to allow for the better boost retention of the bigger turbo. Not being a Harvard Grad. on this, but to me it seems like a feasable plan. Due to our conditions, a 20bhp increase is very significant and would suit me just fine, especially if that 20bhp can be held across the range from 3250rpm up.

john banks

You've outlined the reasons yourself why you both need to undersize and oversize a turbo for your conditions. Hence you need a very efficient compromise. It is because the TD05 seems to match the best TD04 setups to 3000 RPM and after that take off that I suggest it.

MurrayZA

Perfect - going to look into the costing on a TD05 vs a TD04
hybrid (have a spare TD04 already - so that helps the hybrid
cause). Will see if I can source a 2nd hand TD05 locally -
could be a bit of a mission in itself. Do you get a bolt on
replacement TD05 - or will I need to mod it () the TD05?

john banks

You need a front entry compressor cover and consider a turbo overhaul. Speak to Mark at Lateral Performance.

MurrayZA

Will do just that, thanks. And thanks again for all the input!