Turbo bobber build thread.

[hamburgler]

79 Suzuki GS750 converted to a hard tail bobber chopper. Just pickup up the first piece for the project - the turbo. I believe it's off a 2.0L Saab. #452068. Anyone know the trim? It's pretty small but might still be a little big for the bike. Plan to run 5-7 psi (whatever the WG is set at). Does anyone know if I can run the oil return to the plate cartridge for the oil filter? Its the first pic below. I think this would be better than running it to the oil cap. I just dont know if that cartridge is under pressure or not. I don't think so but who knows...

This is probably going to take a while with work and all but I am going to try and get it done as fast as I can. I'll keep this thread updated.

[Steve]

If the turbo came off a 2.0 liter engine, don't expect to get much pressure out of it by blowing only 750 cc through it.

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[Erki]

I'm interested in this build. Not that I want a turbo bike I Just love watching custom stuff come together.

[hamburgler]

If the turbo came off a 2.0 liter engine, don't expect to get much pressure out of it by blowing only 750 cc through it.

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I thought so too but it was undersized for the Saab 2.0L engine. Here are the numbers:



Looks like I should see 6psi by 3000rpm, however the turbo will be most efficient around 8-9000rpm (I don't plan to hit that very much).

I am thinking about running a small intercooler at the front of the bike but I don't want to restrict air flow to the motor. I'll see what I can find.

[ArttuH]

You can't route oil return from turbo to oil filter. The return path must go to the sump without any restriction and the line must be continuously downhill. And naturally centre of the turbo must be above oil level. There is full oil pressure on the filter so routing return there will result massive oil leak from the turbo.

Does your engine have plain or roller bearings on the crank? (I guess roller bearings) In case of roller bearings you probably need to invent something to increase oil pressure for the turbo.

So the turbo is Garrett TO25? I guess it suits pretty well for your engine though I don't believe you will reach 6 psi at 3000 rpm. I had a GT1749V turbo on my 1100 which is roughly similar size turbo than TO25 but has variable geometry turbine that makes it spool up sooner than conventional turbos. It started to boost around 3000 rpm but needed about 4000 rpm to reach 6 psi.

[Curly]

Compressor maps are ideal scenarios, it'll all depend on the flow characteristics of the manifold, intake and exhaust.

I for one believe it's a great size, nearly the same one I have on my 1.6, which is a td04. Seems like a budget build? They're readily available, so that's good too.

Engine management? megasquirt? I'd still run the intercooler, use the same car the turbo came from

[ArttuH]

I am thinking about running a small intercooler at the front of the bike but I don't want to restrict air flow to the motor. I'll see what I can find.

Oh, I forgot to comment this. I wouldn't bother with intercooler if you are going to use just 6-7 psi boost. Compared to added complexity benefits would be minimal. When going above 15 psi it's different story. And even then water injection might be more feasible solution.

[John Kat]

Oh, I forgot to comment this. I wouldn't bother with intercooler if you are going to use just 6-7 psi boost. Compared to added complexity benefits would be minimal. When going above 15 psi it's different story. And even then water injection might be more feasible solution.

+1 on the need for an intercooler.

[hamburgler]

You can't route oil return from turbo to oil filter. The return path must go to the sump without any restriction and the line must be continuously downhill. And naturally centre of the turbo must be above oil level. There is full oil pressure on the filter so routing return there will result massive oil leak from the turbo.

Does your engine have plain or roller bearings on the crank? (I guess roller bearings) In case of roller bearings you probably need to invent something to increase oil pressure for the turbo.

So the turbo is Garrett TO25? I guess it suits pretty well for your engine though I don't believe you will reach 6 psi at 3000 rpm. I had a GT1749V turbo on my 1100 which is roughly similar size turbo than TO25 but has variable geometry turbine that makes it spool up sooner than conventional turbos. It started to boost around 3000 rpm but needed about 4000 rpm to reach 6 psi.

For oil pressure There is a banjo fitting with a very small hole - this should increase the pressure to the turbo. Ill try to keep the turbo high when I make the manifold so the drain can go to the oil cap.

The GT17 was a lot bigger from what I remember. I was originally looking at that one but this one popped from a buddy so I took it.

[hamburgler]

Compressor maps are ideal scenarios, it'll all depend on the flow characteristics of the manifold, intake and exhaust.

I for one believe it's a great size, nearly the same one I have on my 1.6, which is a td04. Seems like a budget build? They're readily available, so that's good too.

Engine management? megasquirt? I'd still run the intercooler, use the same car the turbo came from

I will look into fitting an intercooler in there after I get it running. My only concern is that I won't get the motor running at 6psi. Has anyone ever successfully done a turbo carburetor before?

At the moment I pan to run boost to the fuel tank, as well as to the top caps of the carbs and the bottom vents (to keep everything in equilibrium).

[Curly]

Yes it's been done, blow through as you're doing. Not sure how many builds are on this site, but again, check oldskoolsuzuki.com(.net?).

I wouldn't boost the fuel tank, it's vented. I don't know enough about carb theory to know if they'll work under boost. I know with cars, normally aspirated fuel systems don't know how to respond to boost, there's just no device to "read" a boost signal. Fuel pressure regulators are used, which have a boost signal, and raises fuel pressure as turbo pressure increases. Again, that's with a fuel pump and fuel injection.

Not only that, but my limited carb knowledge is with cv, not your older models. Do you have a wideband you can put in the exhaust? AEM Uegos can be had on ebay for under $200 these days. Very useful tuning device.

[Steve]

Has anyone ever successfully done a turbo carburetor before?

At the moment I pan to run boost to the fuel tank, as well as to the top caps of the carbs and the bottom vents (to keep everything in equilibrium).

To do a successful "blow-through" setup, you will have to totally enclose the carbs so that the turbo pressurizes the entire carb assembly, as well as feeding the air through the throats. Not particularly easy, considering that you still need access for your throttle and "choke" cables/linkages.

It would be much easier to use a single carb in a "draw-through" setup that is bolted to the intake of the carb. With this setup, you would have a log- or spider-type exhaust manifold that would direct the exhaust to the turbo, which is mounted where your airbox and carbs are right now. The output of the turbo goes to a simple manifold that feeds the intake ports on the engine. The turbo's exhaust is usually on the left side, the carb would be on the right. Click HERE to see a typical system installed on a Bandit, or click HERE to see another system on a KZ1300.

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[hamburgler]

To do a successful "blow-through" setup, you will have to totally enclose the carbs so that the turbo pressurizes the entire carb assembly, as well as feeding the air through the throats. Not particularly easy, considering that you still need access for your throttle and "choke" cables/linkages.

It would be much easier to use a single carb in a "draw-through" setup that is bolted to the intake of the carb. With this setup, you would have a log- or spider-type exhaust manifold that would direct the exhaust to the turbo, which is mounted where your airbox and carbs are right now. The output of the turbo goes to a simple manifold that feeds the intake ports on the engine. The turbo's exhaust is usually on the left side, the carb would be on the right. Click HERE to see a typical system installed on a Bandit, or click HERE to see another system on a KZ1300.

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This is what I plan to do and I think it will work. Opinions are welcome! Everything should be under the same pressure. Fuel pressure will be boost pressure plus pressure head. I just don't know how those bottom fittings will work when not in boost. I've read that if they are restricted at all the bike will stall. From what I understand those bottom vents help the fuel drain from the tank. So when not in boost I am going to need enough vacuum to help that fuel drain. I just don't know if Ill get that suction I need to serve as a vent.

[ArttuH]

You will need a proper fuel pump with boost referenced fuel regulator. In theory pressurized tank may work but I wouldn't bother even trying it since the fuel pump solution is tested widely and proven to work.

You will also need dynamic boost pressure (pitot tube) for float bowls. Pressure in the float bowls must be slightly higher than boost pressure in the carb inlets to ensure correct enrichment under boost.

There are couple of useful links about this:

http://forum.oldskoolsuzuki.info/cgi-bin/Yabb/YaBB.pl?num=1107708284

http://www.turbo-bike.net/Pressurize%20carbs.htm

[hamburgler]

You will need a proper fuel pump with boost referenced fuel regulator. In theory pressurized tank may work but I wouldn't bother even trying it since the fuel pump solution is tested widely and proven to work.

You will also need dynamic boost pressure (pitot tube) for float bowls. Pressure in the float bowls must be slightly higher than boost pressure in the carb inlets to ensure correct enrichment under boost.

There are couple of useful links about this:

http://forum.oldskoolsuzuki.info/cgi-bin/Yabb/YaBB.pl?num=1107708284

http://www.turbo-bike.net/Pressurize%20carbs.htm

Good links! I might have to re think the original design. I really dont want to have to run a fuel pump but I guess we'll see what happens. Have you ever heard of anyone running boost to the tank? I am only going to run 5-6 psi. I could see it being a problem at high boost levels but I am already super rich at idle.

I do have a plx wideband that Ill hook up for the first test ride.