Author Topic: 78 CB750F Turbo, post build review  (Read 68493 times)

0 Members and 1 Guest are viewing this topic.

Offline Ilja

  • Hot Shot
  • ***
  • Posts: 338
Re: 78 CB750F Turbo, post build review
« Reply #125 on: August 14, 2015, 02:04:41 AM »
How's this bike doing at the moment? I've read the tread with great interest as it's very detailed, basically a how-to-turbo your bike. Very good writeup!

I'm also working on a cb750 turbo at the moment, which is coming along nicely...

Next to the cb750 turbo I already have a z650 turbo with 750 factory turbo engine... but completely modified.
This one has DFI and a garrett T25. Boost comes in around 4.5k rpm and I can set it anywhere from 5 to 22psi on 98 octane fuel.
The bike is slow off-boost, but when it comes in it becomes literally scary fast, almost impossible to wack the trottle except in fifth gear.


So then I figured I would like to have a bike with a small, fast spoolin turbo and stock gearing which you can still use on the road without losing your license instantly. Also the other bike constantly has electrical issues with the ECU rebooting and stuff..  And I like the kickstarter...  :P


I lowered compression by adding a 1.5mm base gasket instead of the oem gasket, used an MLS head gasket and bored it out to 836cc with the cruzimage piston kit. Next to that I ported the head, welded on 34mm intake channels and installed CV34 carbs.
The only thing im worried about so fat is the camchain.... I replaced it with a new one, but it became so tight by adding an additional 1mm to the base gasket that I almost couldn't get the sprocket on. I hope it stretches a little on first usage and doesn't instantly break...  :o

So, I was wondering.. why didn't you try to gravity drain the oil to the sump as it's a dry-sump engine? My turbo sits way above oil level so it should be possible. Yours might be a little bit lower but still above oil level..
If you make the drain port in the sump pan it will possibly be below oil level which could cause pressure issues, but I want to add a t-piece to vent to a breather port..
Did you consider doing something like that?

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 19,905
  • Saver of unloved motorcycles.
Re: 78 CB750F Turbo, post build review
« Reply #126 on: November 24, 2021, 10:44:05 PM »
 Bump just because it will be easier for me to find.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.