Topic: Old Skool Turbo CB750

[voxonda]

Hey there, maybe you like this. One of my cb750's is treaded with a Airtech (Garrett)T2 turbo. Since I have no experience with Turbo's and I am doing everything by myself, and something will(!) go wrong, I thought why not let everybody here know.
some of the used pieces:




And some of them mounted:



More to follow.

Cheers.

[andy750]

Looking forward to seeing how this turns out - if nothing else it looks VERY cool!!

Good luck
Andy

[rbmgf7]

I don't know much about Turbocharger models myself but I think T2's are pretty common. I've only heard those things used on import tuner cars and those are typically in the 2.0L range. This thing seems like it'll SCREAM!!

[walkingchaos]

I started out working on imports and still do. The T2 is a pretty common smaller turbo for the 1.6 - 2.0 L cars. Im really interested to see how this bike build goes.

[Shenanigans]

Would like to see how this build goes and I am watching.

Good luck

[texaninseattle]

are you running the stock static compression ratio on that engine?
how much pressure are you intending to run?

[voxonda]

This is a 'fake' engine, just to make everything fit. I've got a couple of choices, F1 or K7 engine. The F1 has a 850 kit and a prepped head. The K7 is standard. Have no intention to wring the neck to get as many horses as possible, want to keep in in one piece. The K7 is most likely to be used, has a CR of 9,2:1, so cannot run,too, high pressures. Engine is good no need to take it apart. Have a set of DOHC750 rods which are 1.0 m/m shorter.But for now can live with a fairly low pressure. We will see, though befor final assembly have to make up my mind about the CR/pressure isue.

[dp2275]

nice!  i got my start dicking with turbo cars (ive got an old turbocharged bmw with 420+hp) and would love to do something similar with my k4 750.  few questions..

-howd you go about sizing a carb for that turbo?
-what size exhaust housing are you using?

if it helps ya any..my bmw uses the 'm20' engine.  its a sohc inline 6 with a similar piston/valvetrain design as the sohc750.  they run around 8.8:1 compression stock.  by using a larger exhaust housing on the turbo and a normally aspirated cam that flows decently, we keep egt's down and reduce detonation allowing higher boost levels to be run (18+psi).  especially when considering these honda motors are air/oil cooled, id be careful about staying away from a small turbine housing if you are keeping the 9.2:1 compression!

[Soos]

If you are looking for a set of DOHC 750 rods I got a set i'd part with.


l8r

[voxonda]

nice!  i got my start dicking with turbo cars (ive got an old turbocharged bmw with 420+hp) and would love to do something similar with my k4 750.  few questions..

-howd you go about sizing a carb for that turbo?
-what size exhaust housing are you using?

if it helps ya any..my bmw uses the 'm20' engine.  its a sohc inline 6 with a similar piston/valvetrain design as the sohc750.  they run around 8.8:1 compression stock.  by using a larger exhaust housing on the turbo and a normally aspirated cam that flows decently, we keep egt's down and reduce detonation allowing higher boost levels to be run (18+psi).  especially when considering these honda motors are air/oil cooled, id be careful about staying away from a small turbine housing if you are keeping the 9.2:1 compression!

Hey dp,

I use a Mikuni HSR42, a common carb for this. Because I haven't got a clue I looked around. It was this or a S&S, but that's more suitable for dragracing. What the exhaust housing is, will look what I have got tomorrow. Thinking of starting with a minor 8psi. Don't think detonation will be a problem(??)
Looking for something like 90 - 100 hp.
What is egt? My english is not that good, considering I am from Holland.

Cheers, Rob

[texaninseattle]

egt= exhaust gas temperature

[voxonda]

egt= exhaust gas tempurature

Of course, thanks for explaining.

[dp2275]

Hey dp,

I use a Mikuni HSR42, a common carb for this. Because I haven't got a clue I looked around. It was this or a S&S, but that's more suitable for dragracing. What the exhaust housing is, will look what I have got tomorrow. Thinking of starting with a minor 8psi. Don't think detonation will be a problem(??)
Looking for something like 90 - 100 hp.
What is egt? My english is not that good, considering I am from Holland.

Cheers, Rob

with good gas, i dont see 8psi causing any problems on these motors.  if you havent already, id look into stronger headstuds.  another factor to consider is timing advance.  ideally, youd want to pull timing around torque peak...but since you have a mechanical timing advance, you might want to modify the unit to limit total advance. 

ultimately, itd be nice to have fuel injection and direct timing control via a standalone ecu for myself as thats what im used to tuning...  i might try this next spring with a spare VEMS unit i have lying around (kinda like megasquirt).  but, you have to work with what you have 

are you making your own turbo manifold?

[voxonda]

I know from a firm called Becker, back in th 70's they used a ATP turbo kit on a standard K2 engine with no problems at all, even with the old gasoline. Rolled out something like 85-90 bhp.
Have some APE studs lying around but want to put them in the 850 engine. And do not want to split the engine just yet. Although have to to make it more suitable for a bit more pressure.
For the ignition was thinking of, maybe a DYNA2000.
I have made the intake manifold, with splitter and will make complete, stainless, engine to turbo system.


Cheers, Rob

[dp2275]

dyna 2000 would be a good idea!  they allow you to create your own timing maps via laptop, correct?

cant wait to see this thing come together! 

[walkingchaos]

forget seeing, i want to hear it >=)   please tell me you plan to vent to atmosphere and not recirc.  . . . give it a nice HSSS.

[voxonda]

forget seeing, i want to hear it >=)   please tell me you plan to vent to atmosphere and not recirc.  . . . give it a nice HSSS.

Straight into the atmosphere...................................

[voxonda]

dyna 2000 would be a good idea!  they allow you to create your own timing maps via laptop, correct?

cant wait to see this thing come together! 

Yes, feel Dyna2000 is the way to go. Also have my replica JAPAUTO racer with DYNA "S" and my MARTIN framed F2 with a micro-digital from Boyer Bransden. Think with the 2000 can cope with the advance 'problem'.

cheers.

[rachet]

Ok, I'm curious. . .

I look forward to your results.  Would you be willing to explain your choice on a single carb and how that might affect the overall performance?  Is that normal for turbos?  I can see the higher volume of air pushing the gas faster causing a need for more gas, is that single carb a really high flow model or something? 

I know little and less about turbos so I appreciate your patience! 

Rachet~

[dp2275]

in short, a turbo is an air compressor.  by forcing more air into the engine, there is potential for more horsepower.  of course, with more air, you need more fuel.  blowing compressed air through carbs can cause a host of problems...a simple fix is by using 1 large carb on the intake side of the turbo instead of four smaller units on the compressed side so that air is sucked through and not blown through.

[voxonda]

Nowadays you see a lot of Turbo's placed in front of EFI systems and even in front of carb's, from a air fuel mixing point of view a better solution. In my 'old skool' solution the mixture tend to fall apart because it has to go tru the comressor and into a somewhat inefficient intake manifold. This is not such a problem other than in low revs.
A very good book about "Turbocharging, Supercharging & Nitrous Oxide" is from Joe Haile.

[Soos]

I will agree on the DYNA2000.
If you opt for it, i'd splurge on the Cruvemaker software for it as well.
I have both and am VERY pleased with them.

Not only can you program your advance(or retard) curves, you can see things like time at XX,XXX rpm, # of times started, and a few other techie info related to your ignition unit.

Awesome to see someone doing a turbo setup, and doing a build post about it!!

l8r

[voxonda]

Well first have to put the exhaust together, so the whole thing starts to look like something. Dyna comes later. Ordered some stainless tube and welding bends so can get started. Will keep you posted!

[rachet]

Thank you for explanations!  I'm looking forward to seeing this come together. 

[Superbiker_uk]

Looking forward to seeing more on this project

Also have my replica JAPAUTO racer with DYNA "S" and my MARTIN framed F2 with a micro-digital from Boyer Bransden

In the interim do you have pictures of your other machines to post or elsewhere on the web? Sorry to go off topic but I would love to see more of the JAPAUTO racer - loved the video
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