Well, I appreciate your input. But I am finding it hard to find specifics wrt spool time, and actual hot side and cold side turbo sizing for a 4.5L.

I emailed the people that actually do the rear mount turbos on the S4, but I received no response. Not that I thought I would.

The entire dynasty of rear mount turbos is based on keeping the trial and error of sizing at the rear secret.

I also appreciate Mark telling me his thoughts.

Spooling by 3000 is fine by me. Not running out of steam until 6500 is also important. But honestly, I won't do this unless I can keep the price down VERY low. Because if it gets expensive, I will just do a SC. Its just too easy.

But the rear mount turbo idea sounds interesting, and for what it may cost, a good deal.

No Cat should make the turbo spool quicker, and leave more heat in the air. I don't know if I would want to put it infront of the trans, or further back where the muffler goes.

I think I need to learn how to weld like this:
http://www.iwsti.com/forums/off-topic/137191-rear-mount-turbo-porn-56k-you-will-here-month.html

So a single turbo on a 4.5L should be quite big. Like 96 or so, right?

Mark,
I have a turbo and intercooler.... I need your exhaust plumbing.... PM a cost. Also, I sent Jeff, then you an offer for some drivetrain components at his request. Never heard a peep....:confused:

There is no magic here....you just have to size one and try it. I would go one size down on the turbine compared to front mount and then try a couple of a/r ratios on that. I would stay far, far away from any turbo that is an off brand name....they are bad news. I only use Garrett. I have 17,000 miles on my system now and have not heard a peep from either turbo...they are reliable pieces. You put a Chinese turbo on the car and you'll be having issues with it...it's not worth the risk.

I know you are right about the chinese thing. The power master seems like a quality unit.

I was hoping to find a BB one that was used.

Get a used K27 for the rear. Maybe not the optimum, but for a couple hundreded dollars, your in business and making doo power. A K27 should support up to 550HP. If it ws good enough for Porsche, it's good enough for me. Blow the turbo, just buy another K27..

Of course this advice is only for those of us on the DIY budget..

What size is a K27?

You can get the K27 with T3 flanges to make hook up easier. K27 is the big brother to the k26 that came on the 944turbo. Someday when I get all the parts to go turbo, I'm going with a pair of these. $500 for a pair, even if they only last a year... A bit more oldschool design, but still effective. No ball bearings etc..

http://www.sakuraindustry.com/osc/im...tang_K27_1.JPG
http://www.sakuraindustry.com/osc/im...tang_K27_2.JPG
INLET 2.75"
OUTLET 2.75"
BEARING TYPE WET FLOAT BEARINGS/oil cool
OIL INLET 1/8 NPT
MAX PSI CAPACITY 35PSI
COMPRESSOR 63 AR
INDUCER 49.15mm
Exducer 80.84
Trim 36.9
Turbine .87 AR
Inducer 67.16mm
Exducer 75.85mm
Trim 78.4
FLANGE TYPE T3 FLANGE
DOWN PIPE FLANGE TYPE 6 BOLT STANDARD
MAX HP 550hp

You'll have to go twin to not choke the exhaust on a 928: All K26's and probably all K27's are sized for 3.6 (rare) & smaller engines. The backpressure would cause major detonation issues I'd bet.

Agreed: skip the cheaper Chinese turbo's: go with a used Garrett or Precision before you go with a new Chinese turbo.

EMission testing results
 

Ok, here's my emission-testing numbers:

For 2400 running test:
HC 36 out of 220 (which is the max. allowed)
CO .38 out of 1.20

For idle, 705rpm:
HC 140 out of 220
CO .66 out of 1.20

30# injectors, stock fuel pressure yet an SMT-6 to pull back during cruise & idle.

My maps are set for about 15.0-15.3 Air-fuel, though my O2 pulls back to below 14.7 attempting to correct to 14.7. I get a slight hunt at idle like this, it likes to be at or just below 15.0 to remove any idle hunting.

Boostlogic routinely sets their cars in the mid 13's for idle, but many of these are mostly off-road Supras.

Why are the boost levels kept so low? 5-7psi? Ricers are hitting 25psi on stock bottom ends. I'd think we could hit 15psi safely.

compression amigo, compression

Engine management, complete fuel systems, expense, etc.

Not buying it. Many Hondas have higer compression yet boost like crazy. Meth injection would allow for more boost with out detonation or retarding timing as much.

I would be one of those people! SmileWavy

The higher the boost the fewer good parts are left when the air fuel mix etc goes boom. Some racers are happy with 30 1/4 miles passes between booms.

Ethanol removes all those BOOM problems. Nearly completely.

Most of those high boost Hondas have firering head gasket, aftermarket head studs and cast iron blocks. For longevity, I would stick with 7 psi or less. I am running 1 bar boost on my otherwise stock 931 and have realized a rebuild every 3 years.

Dennis

Agreed. A simple water injection or meth injection cures the detonation issues. Only issue is when the meth tank is empty you have to dial the boost back. I have run up to 250RWHP of N2O with meth injection and 6* retard on timing with no isses. Of course not with the frequency I would be using boost on a turbo..

He said ethanol not methanol.