Turbo Bypass (fwd)

[Rausch, Bernd]

Hi Greg,

I saw your post on the DIY_EFI List an found you quite knowledgefull. I
need a little bit help with a project.
I am actually building an engine for my Renault Alpine Europacup race
car.

6cyl
2,5L
7,8:1 cr
276 deg 10mm lift cams
6 injectors 266ml/min

I am using a free programmable ECU from a German manufacturer (Lenz).
My goal is to get about 350hp out of it.
My big problem is the turbocharger. The engine has a modified Garrett T3
on it and had stock about 250-270 hp. (with cr8,7:1 and stock cams)
Nobody can tell me what the limits of this turbocharger are. I have
looked at the turbo and found the following:

label:
No Client 104052
No. S. QC 1469
Model DEV

On the compressor/turbine:
20E87 / DH5
M4
A/R 48
115-54

Do you have an idea where to get specs for this turbo ?

Any help would be greatly appreciated.

mfg

Bernd 

-----Original Message-----
From: bearbvd at sni.net [mailto:bearbvd at sni.net]
Sent: Dienstag, 11. August 1998 23:25
To: diy_efi at efi332.eng.ohio-state.edu
Subject: Re: Turbo Bypass (fwd)


 -- Forwarded message follows ---

>Does anyone have any thoughts or references to info on the type and
>positioning of Turbocharger bypass valves?
>
>Things I'm wondering about...
>
>- bypass to compressor inlet vs. dump to atmosphere
>- pre-intercooler vs, post-I/C dump point
>- effects on A/F Ratio
        My first and best thought is AVOID USING BLOW OFF VALVEs IF YOU
POSSIBLY CAN! How? Draw through a throttle body(s) into the
compressor(s),
and run the compressor(s) in vacuum at part throttle. No restriction
points
between compressor(s) and intake ports. Yep, you need to have the best
compressor seal to do it this way, but it's well worth it. It becomes
virtually impossible to put a properly selected compressor into surge,
You
will have much shorter spool up time (because the compressor will be
spinning far faster as part throttle). You will have much lower exhaust
back-pressure on the engine at part throttle, and consequently longer
life
and lower cruising BSFC (better mileage).
        As far as I'm concerned a throttle between compressor and intake
only happened because factories wanted to add turbos with a minimum
number
of part revisions and cheap seals. Yes, some of the early porsche race
turbo cars did it to get better throttle response with relatively
primitive
design turbos. This is just not that much of a factor any more, and
those p
cars were pretty much an efficiency be damned design. If you really want
to
chat about efficiency and turbos, get hold of me off list (this is a bit
off mission) and we'll talk about using long tube headers with turbos.
                                        Regards :), Greg