Topic: CB 836cc f1 turbo - spoked kickstart street turbo

[Ilja]

I did quite a lot of driving (600km) on the cbturbo this week since the weather suddenly became really nice and I had the week off!
Front sprocket seems to be fine after all.. i've been pushing it quite a lot but it's still fine. I'll just see how long it will holdup like this, I can always replace the shaft and put in some new HD primary chains at the same time... 

So, last weekend did 2 hours of highway driving on the cb to visit friends who live quite far away.
Everything went fine except that the bike used around 1liter of fuel every 12km... 
Was riding around 130 with some sprints up to 175 (at 6500rpm) on my gps.
When you ride like 130 or 140 with a steady throttle it isn't even boosting.. only as soon as you roll on it directly boosts up if your over 3800rpm so thats perfect.

At my friends place some other friends of mine tried the bike and where also pretty enthausiastic about how it all worked nicely!
When I was driving back late in the evening I had a rendevouz with my guardian angel, didn't see her for a while now.

When I left the highway after 1 hour of continuesly riding 130-150 and was almost home, i suddenly lost the rear brake!!! I looked behind to see if there was an oil-leak but my complete FRIGGING REAR CALIPER was hanging next to the swingarm! It's a cbr900 fireblade caliper which I bought complete with the bracket and mounted it like that on the bike. The bolt, holding the caliper on the bracket was gone and the threads in the bracket showed NO signs at all of any locktite!
So the previous owner must have saved a few bucks not buying loctite 243 when changing brake pads....  It sucked big time, one turn to the left and the caliper would have ended up in my rear wheel spokes.

Next day I fixed it with parts of my other turbo bike (same caliper) and did some more driving and testing the rest of the week.
The bike was running way too rich at WOT (9.5 AF) so I changed the main jets from 135 to 124 and removed the rings underneath the needles so they are at stock position. It's at 10.5 now when you completely floor it... and midrange accelerating from 30-70% throttle is around 11.5-12.5... pretty good.

It's still a tad rich just off-idle, when you cruize the bike with only 1mm of throttle applied.. around 11.5 a/f...
Thats not necessary as your not loading the bike, and should be like 13.5 or something. Probably base fuell pressure...

I can't change the boost at the moment because I got a different WG actuator now..so I ordered a simple ball & spring type of boost controller on ebay.. hopefully it will arrive soon so I can do some testing at higher boost. 

So far so good!

[ivanhoew]

Ilja ,

 i have the same rich mixture on cruise on my bike .

to cure it , i put a t piece on the boost line to the float bowls ,this connects to a  little manual valve to open on the motorway for cruising ,and it leans it out .you could have this operated with a solenoid and a vacuum switch .

the valve must be a sensitive fine adjustment screw valve ,since a little leak makes a big difference.

you can have the valve a little bit open all the time ,and it leans the whole range out .


regards
robert.

[Ilja]

Thanks for that info!
But, do the boost compensation lines also affect  mixture when cruizing off-boost?
I thought they would make no difference in that area since its not boosting... just base fuel pressure would influence that part / lean it out.

[ivanhoew]

it definately does on mine , hey , try it and see ?

[Ilja]

Today I set the base fuel pressure half a turn lower, so the fpr gauge needle is only moving 1-2mm at no boost (base pressure 2psi).. bottom AF is better now.

[Bill/BentON Racing]

Way,to go. Boost on young man!

[Ilja]

By the way... these bikes work so well with the turbo because of the cam timing.

Normally with turbo engines, camshaft overlap (between opening of intake valve and closing of exhaust valve) is the bottom-end killer.
This is because there's a large backpressure (up to twice the boost pressure) between the turbo and the exhaust valves... you get this thing called 'reversion' which contaminates your charge.

On my kawasaki 750 turbo bike a lot of people (including me) experimented with different cams with more duration and lift, but also more overlap... and they all gave the same results.. not much change up top but less bottom end and later spooling. So everyone runs the stock turbo (z650) cams and they make up to 270hp with them.
Kawasaki used the stock z650 cams (with 42degrees overlap) for the turbo.. and the reason was that these out of all cams had the shortest overlap period (out of z650, z750, GPZ750A)

SO, guess what the overlap timing is of the old Honda sohc camshaft? .... its only 10 degrees! Perfect!
This is why my turbo is making boost at 4000rpm and why the bike is still plenty strong off-boost, even with 8:1 compression. 

It would be nice the have the stock cam timing but with a bit more lift though... since there's plenty of space to the piston head. 

[MRieck]

By the way... these bikes work so well with the turbo because of the cam timing.

Normally with turbo engines, camshaft overlap (between opening of intake valve and closing of exhaust valve) is the bottom-end killer.
This is because there's a large backpressure (up to twice the boost pressure) between the turbo and the exhaust valves... you get this thing called 'reversion' which contaminates your charge.

On my kawasaki 750 turbo bike a lot of people (including me) experimented with different cams with more duration and lift, but also more overlap... and they all gave the same results.. not much change up top but less bottom end and later spooling. So everyone runs the stock turbo (z650) cams and they make up to 270hp with them.
Kawasaki used the stock z650 cams (with 42degrees overlap) for the turbo.. and the reason was that these out of all cams had the shortest overlap period (out of z650, z750, GPZ750A)

SO, guess what the overlap timing is of the old Honda sohc camshaft? .... its only 10 degrees! Perfect!
This is why my turbo is making boost at 4000rpm and why the bike is still plenty strong off-boost, even with 8:1 compression. 

It would be nice the have the stock cam timing but with a bit more lift though... since there's plenty of space to the piston head. 

Sure..... that makes perfect sense. You have a mechanism shoving charge into the cylinder at 2 to 6 atmospheres...you don't need overlap. Look at all the turbo grinds. Problem is the small, sharp nose on aftermarket turbo cams if you want to use it for practical applications. In the 1st generation busa's the hot set up was...and still is...Yoshimura Stage 1 cams which just increased the exhaust. Man that was top secret sh!t back in the day

[Mitchell]

Dude that thing is awesome!!!! How is your transmission seem to be holding up? I run 8psi on my turbo 750 ive replace 2nd gear twice already in the 5 years ive had it going and it seems like its going to need whole new trans soon, it likes to jump out of gear under full boost in any gear 1st through 5th

[MRieck]

Dude that thing is awesome!!!! How is your transmission seem to be holding up? I run 8psi on my turbo 750 ive replace 2nd gear twice already in the 5 years ive had it going and it seems like its going to need whole new trans soon, it likes to jump out of gear under full boost in any gear 1st through 5th

Is it undercut? Try cyro....it might help too.

[Ilja]

Up to now its fine.... it jumped out of 4th a few times but that was due to my tarozzi rearset locking up (chromed pivot axle chrome coming off)
And I hear some loud 'clunking' when engaging throttle driving away.

I think otherwise its holding up great..
If you lose a gear due to dogs and dont replace the fork... it will happen again. I had a lot of gearbox trouble with older dirtbikes.....

And getting it undercut would be good... my kawi turbo has that from factory.

Any pics or info on that 750 turbo??

[Mitchell]

Yep replaced forks and drum both times, i just got off the phone with the guys that cryo freeze it seems kinda pricey $8 dollars per pound, but the guy said he does alot of bike transmissions with really good results he said it most likley would'nt cure it but would make it last for alot longer. I've never had the trans undercut the motor is a bone stock k3. Sorry no pics i just had to get a new phone and all the pics i had were on my old one. I used a td04 13c turbo from a volvo and made a header out of an old kerker i picked up out the junk yard, just cut it up and reshaped it, blowthrough with cb 650 cv carbs

[Mitchell]

Oh i just rememberd i think i got a youtube video of it let me see

[Mitchell]

[MRieck]

Yep replaced forks and drum both times, i just got off the phone with the guys that cryo freeze it seems kinda pricey $8 dollars per pound, but the guy said he does alot of bike transmissions with really good results he said it most likley would'nt cure it but would make it last for alot longer. I've never had the trans undercut the motor is a bone stock k3. Sorry no pics i just had to get a new phone and all the pics i had were on my old one. I used a td04 13c turbo from a volvo and made a header out of an old kerker i picked up out the junk yard, just cut it up and reshaped it, blowthrough with cb 650 cv carbs

I think guys would be surprised at a real undercut vs a factory job....it's quite different. Gast does a good job but doesn't give it away.

[Retro Rocket]

Yep replaced forks and drum both times, i just got off the phone with the guys that cryo freeze it seems kinda pricey $8 dollars per pound, but the guy said he does alot of bike transmissions with really good results he said it most likley would'nt cure it but would make it last for alot longer. I've never had the trans undercut the motor is a bone stock k3. Sorry no pics i just had to get a new phone and all the pics i had were on my old one. I used a td04 13c turbo from a volvo and made a header out of an old kerker i picked up out the junk yard, just cut it up and reshaped it, blowthrough with cb 650 cv carbs

I think guys would be surprised at a real undercut vs a factory job....it's quite different. Gast does a good job but doesn't give it away.

Yes, there's a reason most high powered bikes either have, or work better with back/undercut gears...

[Mitchell]

Whats the deal on having them under cut? Do you just have 2nd done? Or 2nd through 5th? I've always heard 2nd is the worst.

[Mitchell]

Llja have you thought about water meth injection for your turbo ride? I played around with it some on my turbo and let me tell ya running no intercooler it makes a huge diffarence in power. I ran a 1gph nozzle pre turbo, had it spraying right in front of the nut that holds the compressor wheel on with an smc enterprize controller (i think that company went out of buisness now) with a small 100 psi 12v pump i got off ebay, i used a small 2 quart windsheild washer tank i picked up from the local parts store and fit it all inside one side of my saddle baggs. With blue windsheild washer fluid it did really well, then one day i decided to run strait meth through it, Holy cow it made it so much faster on topend it scared me. I ended up takeing the whole setup off ofter  i ran the 100% meth through it, i didnt feel my frame brakes and 40 year old spoke wheels were designed to go that fast, but with your suspension and aluminum wheels and nice brakes you should be able to handle it.

[Ilja]

Lol

[Ilja]

See if i can find a better pic...

[Ilja]

Yess found some.
So this bike is scary fast... at 1 bar and higher its really like entering warp speed if you roll on throttle on the highway. It does 250-265 kmh (on german autobahn  ) but it needs a lockup clutch badly as even with HD springs and new plates it doesnt hold.
Between 5000 and 6500 rpm it get 100 extra ponys or something.
But!!! The cb750 outperforms the kawi up to 5000rpm. Much better bottom end with the CV carbs, the extra cc's , the short 10degree cam overlap and the small turbo.
As i said I dont know the difference and pros/cons with or without IC as I installed it directly when building the bike.

[Ilja]

And some more... 

[MRieck]

Nice work.....now go vacuum that lathe

[ivanhoew]

Ilja

i think i figured out that the intercooler on the 500 takes it from 110 bhp to 135bhp @9500rpm  on 15 psi . it can get too hot to touch on one side ,and barely luke  warm on the other .

regards
robert

[Ilja]

Are you making 135hp with a 500? Well done!!
Did you happen to do some dyno runs with and without ic?

About feeling the heath... I reached down and felt how hot the transfer pipe was a few times, but it was barely warming up!
I might do a dyno run as it is right now and then another one with the IC..