Thought I would post this here. The plan is to build a CB750 turbo bike and put the turbo kit together myself, the original turbo kits from back in the day are getting thin on the ground and more expensive (1500-2000USD) as people are building period correct restomods.
The plan will be to not over capitalize on this project and do all work myself, I have experience building bike engines but have never turbo'd one.
Specs -
Pull through system
Mikuni HSR42
Garrett gt12
Make my own manifolds - copies of ATP/Rajay kits
Dyna 2000 ignition
836cc or 970cc - undecided as I already have the 970 Arias but want reliability
8~8.5:1CR

Some help will be needed from more experienced members on what fueling will be required, such as pumps etc and will be sourcing what parts I can second hand and rebuilding where needed.
Currently waiting for Joe Hallies book to arrive to get a solid plan together.

So if anyone has a second hand gt12 they want to offload - let me know as I can't post in the classifieds - must not have a high enough post count yet..?.
I have copied my post on the SOHC/4 forum below.

Thanks.

Hi forum, I am considering builing my own turbo kit for one of my project cb750's, this would be a project and may take some time as I have 2 other motors to finish first, possibly then move house and as finances allow.

Current specs -
1. Pull through system
2. HSR42 Mikuni
3. Oil feed from oil pressure switch (with a t-peice fitted),return to the clutch cover and cooler
4. Garret GT12/IHI or similar, have not ruled out a Rajay B25, depending on cost, but a rebuild and age may rule it out.
5. Manifolds I can make as I have a Tig. I would like to make them close to what has been proven before such as the ATP intake and its split plenum. And some ideas on the exhaust dimensions used on other kits from the day
6. Majority of parts will be sourced second hand through places like ebay
7. Capacity would be 836cc @ 8:1CR and 10psi - this will be a street bike

I do need some help and forum members ideas and thoughts on fueling requirements under boost and will probably PM some of the below owners of these bikes for their thoughts if they dont post here.

There are some really great turbo bikes already featured on the sohc/4 forum such as -

Jim F's - http://forums.sohc4.net/index.php/topic,101267.msg1131201.html#msg1131201
Bamboozler's - http://forums.sohc4.net/index.php/topic,59262.0.html
Voxondas - http://forums.sohc4.net/index.php/topic,41157.msg424250.html#msg424250
Blue71turbo's - http://forums.sohc4.net/index.php?topic=56783.msg612975#msg612975
76kcafe's - http://forums.sohc4.net/index.php/topic,140453.msg1591644.html#msg1591644
Boosted applications thread - http://forums.sohc4.net/index.php/topic,58771.25.html
More good info here - http://forums.sohc4.net/index.php/topic,134478.msg1513446.html#msg1513446
And more - http://forums.sohc4.net/index.php/topic,131098.msg1461795.html#msg1461795

Firstly I'm asking the forum members who have a turbo system that I'll be chasing some dimensions of inlet manifolds and exhaust headers from manufacturers like ATP, Rajay & MrTurbo as well as mounting brackets and photos as to what people have done previously.

Looking forward to any and all input on this.

 

I'll be watching this one, single stick 750's are Kewl.

 

I noticed that you want to use a draw-through carburetor and a Garrett GT12. That turbo won't have much oil control on the compressor side when exposed to the vacuum created by having a throttle blade upstream. Worse, I don't think there are any drop-in carbon seals available for it.

 

You are correct drop in carbon seals are not available - however carbon seal from the Hitachi HT10/12 can be retro fitted, or alternately run a carbon sealed HT10 from a Mazda RX7. I have been looking a bit further into turbo sizing and think the GT12 is a bit too small for what I'm after.
Currently trying to research carbon sealed alternatives - such as the HT10/12, but cannot find any Hitachi compressor maps or specs online, need to do the math before I pull the trigger on anything.
Failing this start to look at going to a push through design similar to this http://forums.sohc4.net/index.php/topic,59262.0.html which uses a Garrett GT2052.

 

Used to have a 78 CB750K, great bike

I wouldnt go big on the displacement, you need the bore thickness. Since its aircooled, thermal management is more important than anything.

My question is wouldnt a blow through system be easier to set up and tune? Nothing in the turbo to go bang.

Could put a Microsquirt on her and convert the carbs to efi.

Just thinking out loud

 

Yeah still a toss up for displacement, probably go 836 as turbo pistons are readily available in this c.c.
The 970 Arias that I already have would need to be modded to bring C.R. down to acceptable levels and as you said at that c.c cooling can be an issue. EFI/Microsquirt is out as I just want to keep it simple and wont be running crazy boost ~6/8psi - Dyna 2000 ignition is retardable under boost so should manage detonation issues easily.

 

Just thought about this, barrier coat the pistons. Microblue Racing has a killer low friction coating, Swaintech for the crowns.