Topic: looking to build a high 9 or low 10 second cb750 turbo dragbike

[76kcafe]

I have a 74 cb750k that I am building into a dragbike that I would to run high 9 or low 10 seconds in the 1/4 mile. As of now I have a stock head that is ported and has lager valves and a norris turbo cam. I also have a complete atp turbo kit with a mr. turbo mikuni carb. Has anyone on here built a higher horsepower turbo cb750? I am just wondering what are going to be the best internals to use? Also will I be able to use a 811cc or 836cc kit or will I need to go bigger? I am not sure on the boost level yet but I am thinking if I want it to run that fast it is going to be pretty high.  I am on some what of a budget so I would like to get the best parts I can for the money I have. Thanks in advance.

[jweeks]

76kcafe,
     I'm not into turbo's. There is no category to drag race one that a turbo is an advantage. All CB750's in drag racing are bracket racers. Tuning a turbo for consistency is very challenging.
     The obvious stuff is needed:
Balanced crank
steel aftermarket rods
good aftermarket valve springs/retainers
aftermarket pistons - the bigger the size the easier it will be to achieve your goals. Compression ratio should be moderate (9:1?)
aftermarket ignition system - I like MSD
lockup/slider clutch
undercut transmission gears with an air shifter
high octane racing gas
dyno tuning to prevent over lean conditions
A chassis that is set up to handle the power of the motor

     Some time looking at APE and Cycle X stuff if you want new parts. Ebay and Dragbike.com classifieds if you want used stuff.
Just a rough guess: 100 horses at the rear wheel for mid/low tens; about 125 horses for mid/higher nines. Good luck spending time and money to achieve your goal.

     Read the Hondamatic drag bike buildup that Sam's doing for useful tidbits. I've got two gears, 100 horses at the rear wheel, and 10 second time slips with carbs. That's why I sign this -

                                                                       Mr.  Hondamatic

[76kcafe]

Im not looking for it to be consistant. It is going to be ridden on the street mostly and I wanted something different so that is why I am going with the turbo setup. Thanks for the info.

[turboguzzi]

Im not looking for it to be consistant. It is going to be ridden on the street mostly and I wanted something different so that is why I am going with the turbo setup. Thanks for the info.

this one is defientely going to be different.

dont know if a 9-10 sec bike will be streetable but member "blue71turbo" runs one, look him up.

good luck, should be a "fun build" as we say here.

TG

[754]

Nitrohunter on here ran almost 10 flat on a turbo 750 with stock pistons!!
 Make sure you good rods and pistons (with correct compression ratio) into this motor. Good luck, and have fun..

[dhb53]

With a turbo 811 mid 10 sec times will be no problem on the street .In 1977 I put 50,000 miles on my turbo 823 running 20 lbs of boost.at the strip.I used 8 to 1 compression with yoshi aluminum rods.The hard part is getting the engine to boost in lower gears because the turbo kits in those days was to big for the 811 honda. you will need very strong valve springs  to run high boost.you can turn your engine to 15 and 16 thousand rpm. I did bend a lot of valves till I got the right combination

[76kcafe]

Did you actually ride 50,000 miles with the yoshimura aluminum rods and a turbo? I actually have a set of them but I was told not to use them on the street.

[BLUE71TURBO]

 76Kcafe,  JWEEKS pretty much summed it up on the internals for a turbo engine.  The crank,rods, and pistons are the most important.  Have the crank checked for straitness and balance. Use the best steel rods you can afford to buy, and go as big as you can on forged pistons ( 8.5 to 1 or lower )  And titanium retainers with better valve springs.  With a turbo you don't have to rev the crap out of it like a normally aspirated engine. The boost pressure takes care of that.  Bottom line it all depends on how fast and dependable you want to be.  To have both it's expensive. Also using water/ alcohol injection really helps when using pump gas.
     When i know i'm going to be runing alot of boost i run VP C-16 Racing fuel.  the most boost i have run is
  20 LBS  Late one night on the freeway and it scared the sh1t out of me !  I had to hold on so tight that i put a dent in my gas tank from slamming my knees together.  Oh yea, you should install heavy duty case and cylinder studs.  A longer swing arm will help alot also.

[NitroHunter]

Low 10 second CB 750 runs (usually) require good rods, good fuel, and an air shifter. 
The B-25 Rajay spools up faster than the E models,it has slightly less air flow but it's quicker boost = lower ETs. Your ATP kit most likely has this.
I bent several sets of modified steel rods but had no problems with golden rods on the street or track.
Make sure you have GOOD fuel flow before you twist up the wastegate screw, lean is mean. An electric pump will prove to be a good investment if you get serious about making horsepower. Just don't rattle the motor from too little fuel or too low octane rating for the cylinder pressure (boost) you choose to run. Be conservative with your ignition timing.
A copper head gasket with good studs will outlive the bike.
And yes that 736cc (mostly stock) time bomb ran 10.000 at a Dragbike USA race. 30 lbs boost, ERC 118 fuel, and stock pistons, rods and pins. Oh yeah 5 base gaskets to lower the compression...
Good luck with your project.

[76kcafe]

Thanks everyone for the info. I think I'm going to go with a 836 with 8.5:1 and I am not sure which rods yet. The head already has better springs and titanium retainers so the head should be good to go. The bike is extended 4 inches already so that will help out a little to. As far as an air shifter, I do have one but I put newer sportbike rear set on the bike and it doesnt look like it will fit very well with that set up.

[Big Jay]

I would say a 890 turbo pistons. Carrillos, tool steel pins, balanced and polished crank, our springs and retainers, o'ring block copper gasket.

We can help you with all of it.  http://cbrzone.com/sohc.html

[NitroHunter]

I tucked the air cylinder under the stock shift lever so I could foot shift while street riding, there is plenty of room even with only 2" of ground clearance. I would try to keep the air cylinder's leverage as close to the shifter shaft as possible.
If you are serious about a low 10 second ET then I would strongly advise figuring out how to make this work for your set up, as even Pee Wee Gleason couldn't outshift that little thumb button... 
Just my .02