ToGGoT

Hi guys, posted this question on another forum, but noone replied, so i thought i'd try here!

Am trying to figure out which turbo would be "best" for use on my bike.

Its an 80's BMW brick with a water cooled 1ltr horizontal 4cyl. So well over engineered, but very sluggish and heavy.

Have been digging through the compressor maps, but its proving difficult to find something that suits. I intend to set it up as a blow though with the existing air flow meter at about 5psi to start, and eventually go to a Megasquirt ECU with proper MAP sensor, and hop up to 7-8 psi. So not a high boost application by any means.

At 5psi, i calculate the pressure ratio to be 1.34. I guess i'm looking at a pretty small turbo to do that no?

Ideally i'd like boost to come in earlyish at about 2000 - 2500rpm, and run through to about 7000rpm. Though the peak torque NA is about 6000rpm, peak power NA is 8000rpm, and redline is 8500rpm.

I'd been looking at a TE04H-13C11, but looking at the compressor maps, i think thats going to be too small. There is a project thread online somewhere where the guy has used a GT-12 on his 750 version, again at low boost, but there isnt any detailed info on there.

Looking around a bit more, i came across the GT-1548, with the bigger A/R than the standard GT-1544 versions. This looks more appropriate for my needs as far as i can see, but i am concerned it might be a bit big. I think im only going to be looking at 120bhp when its done and set up.


I've mapped the CFM values for my bike onto the turbo map, at 500rpm intervals here:



The first arrow is 2500rpm, where i'd like the boost to start ideally, the second is peak torque at 6000rpm, the second is peak power at 8000rpm.

Does this look right, or is it too big/too small/etc etc?


Either way - the numbers give me a headache! If i know what/where im looking for, i can plot my numbers onto a compressor map, but im not 100% certain exactly what im looking for, so any help would be great! As far as i know i might be looking at completely the wrong thing!

Cheers!

ToGGoT

[EDIT] Mods, could you move this to Forced Induction please? I could have sworn that was where i tried to post it...[/EDIT]

coxy

Turbo should be OK we have used bigger on Yamaha 700 raptor singles and Polaris RZR 800 twins.
You will need at least a good piggyback system,we use Moristech at work,others may wark but not a powercommander.
Upgrade the clutch and convert the gearbox from Tapered races to deep angular contact type ball bearings as BMW did to R1100 gearboxes for more strength and lasting ability.
The driveshaft is two tubes bonded together with rubber,some have issues with stock bikes so beware.
Plenty of Turbo bike experience starting when I worked for Kawasaki Motors in the days of GPZ 750 E1 amd E2 turbos,Also spent 10 years as a BMW technician in the main BMW dealer and previous distributorship in Australia Tom Byrne Motorcycles so should be able to help you regarding any info.
Hope you are starting with either a K1100 or late K100RS 4 valve so at least you will have all the best stock bits. Cheers Steve
PS the BMW so called clean bearing mod was only applied by them to R1100 gearboxes but should be possible and a big reliability improvement to a K series box.