Rear Mounted Turbo Blow Through

[ColinH]

My first post here so hello all. I am planning to turbo my Mk2 Bandit 1200 over winter. Still deciding on a few things such as EFI or carbs etc. I was going draw through purely because I like the location and look of setup. Then I looked at disadvantages and decided against. 
 

My plan is to blow through but with similar turbo position mount, where airbox would be. Other option is between swingarm and frame if I go for extended arm.

First build so will be 7-8psi boost on stock engine which I am rebuilding head at moment. I’m thinking of something like TD04-13 as it’s easy to source, good value and proven. Maybe not perfect with remote turbo though, maybe slower to spool? 

I was planning to use 4 to one down pipes on bike now then reduce diameter of single pipe to keep velocity higher to turbine.

My thoughts were that the longer it stays in single 1.5” pipe, before converging, the better for velocity of gases. But knowing that testing beats any thoughts of a green forged induction fiddler, what are people’s experience of this? 
 

My main motivation for build is a turbo bike, just because, and it will be a fun fabrication and machining project. I wanted to make something a bit different from front mount turbo systems which can be bought in kit form. Not knocking them as they were built by people with much greater knowledge than me. 

Edited October 24 by ColinH
Very bad gramma

[Gixer1460]

You say a 'suck through' has disadvantages but your proposal seems to have just as many just different! Packaging for one and laggy response for another. I think i've only seen one or two 'remote' turbo's fitted in bikes - neither were very good, they worked but not very well! Experience shows that either front mount turbo and blow through or rear mount and draw / suck through work well - i've done both but may try a suck through but with EFI to improve the fueling aspect - old skool looks but with better set up possibilities.

[TLRS]

If it’s more about the challenge of the build it’s no problem. Bruteforce has a turbo hidden behind the engine. Though the build thread might have gotten lost.

[ColinH]

6 hours ago, Gixer1460 said:

You say a 'suck through' has disadvantages but your proposal seems to have just as many just different! Packaging for one and laggy response for another. I think i've only seen one or two 'remote' turbo's fitted in bikes - neither were very good, they worked but not very well! Experience shows that either front mount turbo and blow through or rear mount and draw / suck through work well - i've done both but may try a suck through but with EFI to improve the fueling aspect - old skool looks but with better set up possibilities.

Thanks for your input. I’m assuming that draw through you get the delay to turbine spool but very short delay to build pressures. Remote blow through would be very similar wouldn’t it? I’m not questioning you as I hate those that ask for advice then supposedly know better, it’s more for my understanding

packaging is no problem and the challenge of that is something that appeals. I will be doing my own fab, machining, welding etc so cost there isn’t an issue.

[ColinH]

4 hours ago, TLRS said:

If it’s more about the challenge of the build it’s no problem. Bruteforce has a turbo hidden behind the engine. Though the build thread might have gotten lost.

Thanks for that I will have a look and see if I can find it.

There was an MT10 done recently and that was one that triggered the idea. 
 

https://purposebuiltmoto.com/blogs/news/yamaha-mt10-turbo-kit

[ColinH]

6 hours ago, Gixer1460 said:

You say a 'suck through' has disadvantages but your proposal seems to have just as many just different! Packaging for one and laggy response for another. I think i've only seen one or two 'remote' turbo's fitted in bikes - neither were very good, they worked but not very well! Experience shows that either front mount turbo and blow through or rear mount and draw / suck through work well - i've done both but may try a suck through but with EFI to improve the fueling aspect - old skool looks but with better set up possibilities.

I missed the point about EFI on draw through. Would that be single injector post turbo and butterfly pre turbo? Or maybe 4 injectors but I guess that’s blow through if after turbo 

[Gixer1460]

What I was planning was 4 injectors close to head with single throttle body made from S&S shorty carb - would fool casual observer! Response never was an issue, just accurate fueling. Short primary exhaust 28mm tube to 32/35mm pipe to turbine worked well enough

[peter1127]

Welcome! 

Only valid reason for draw trough setup or "draw trough positioning" of the turbo would be looks. It has no benefits other then easier access of the single carb and easier oil return.  I dont get the point of the turbo further back. Response would be worse, and the turbo isnt visible anymore.  But if stealth is the objective I guess it does that.

Yes, spoolup will be slower. Possibly a fancy ball bearing modern high tech turbo would be better, but not sure if its worth it.  Small diameter piping towards the turbinehousing and cerakote or heatwrap to keep the heat in might help a bit. 

One injector could work, but causes uneven AFR if your manifold is not perfectly designed. Personally I would  have 4 injectors at the inlet manifold. If you bother to convert to EFI, you might as well do it with 4 injectors. If you batch fire them there is no added complexity, and its good enough. I'm using microsquirt and happy with it.

In case of injectors at the manifold you dont need a turbo that is fuel resistant, but it still needs to be able to deal with vacuum or it will smoke like a mf

You could also just use the classic one large carb setup, and have the retro on/off behavior and backfires. Gotta love that! 

[ColinH]

2 hours ago, peter1127 said:

Welcome! 

Only valid reason for draw trough setup or "draw trough positioning" of the turbo would be looks. It has no benefits other then easier access of the single carb and easier oil return.  I dont get the point of the turbo further back. Response would be worse, and the turbo isnt visible anymore.  But if stealth is the objective I guess it does that.

Yes, spoolup will be slower. Possibly a fancy ball bearing modern high tech turbo would be better, but not sure if its worth it.  Small diameter piping towards the turbinehousing and cerakote or heatwrap to keep the heat in might help a bit. 

One injector could work, but causes uneven AFR if your manifold is not perfectly designed. Personally I would  have 4 injectors at the inlet manifold. If you bother to convert to EFI, you might as well do it with 4 injectors. If you batch fire them there is no added complexity, and its good enough. I'm using microsquirt and happy with it.

In case of injectors at the manifold you dont need a turbo that is fuel resistant, but it still needs to be able to deal with vacuum or it will smoke like a mf

You could also just use the classic one large carb setup, and have the retro on/off behavior and backfires. Gotta love that! 

That’s a great point I hadn’t considered. I want this thing to look fast as well as be fast so hiding the turbo doesn’t make much sense.

I love making things different but maybe that’s better to do with my tubular swingarm build, new rear end etc than change things that affect performance 

[Gixer1460]

4 hours ago, peter1127 said:

 it still needs to be able to deal with vacuum or it will smoke like a mf

I considered that but as fuel flow via intake is independent of vacuum with efi, I was considering using a BOV as a priority valve or open with vacuum, close with boost. Who knows if it'll work but costs nowt to try or add a carbon seal!

[ColinH]

Thanks to all for the input. I have now decided on blow through setup with turbo at front of engine and probably EFI along with now going hyabusa pistons to drop CR and allow more boost. This was a case of "while you're down there" 

I will start a build thread now I have some direction.

[peter1127]

I made most of the turbo stuff myself, except the header/turbo which I bought from proboost. They make complete kits, but also can deliver parts only for reasonable prices. Good bang for the buck imo.

Edited October 25 by peter1127