CB400SF NC31 - old but not obsolete :)

[pugnator]

The bike is completely assembled and travelled about 8000km around Europe and Russia
I've got about 60hp on the dyno last summer.





At this moment I've bought NC36 engine and working on the turbo build.





But looks like covid-19 somehow suspended the process

[pugnator]

And at last I finished it (sort of).
HKS2530, garage built exhaust and intake manifolds. WBO and EGT sensors for closed loop.
0.5bar of boost. But most of the work on tuning is expected for upcoming spring/summer.
It was really tough work to do. Sometimes I was in total despair due to lack of ideas how to do this or that.
Bypass and boost control valves are from VW. Mounted under the tank.
It works, it drives. I was able even to blow the first one turbocharger, - GT2860 with ceramic exhaust wheel (and it was kind of expected). It was superseded by HKS2530 with inconel exhaust wheel. I was lucky to find one at fair price.
Waiting for the spring.

[Foxy400]

Looks like you've put a lot of work into that. That exhaust system sure looks tricky. What sort of power increase are you getting? More importantly, has it been worth it?

[pugnator]

Looks like you've put a lot of work into that. That exhaust system sure looks tricky. What sort of power increase are you getting? More importantly, has it been worth it?

Yes it was worth it as a fun project. New skills, new friends, new ideas.

It's rather fun to ride it. It's much more quieter than stock and doesn't sound like a rice car with a fart can attached as a plus :D
I wasn't able to get on a dyno last year to tune the EFI correctly. At the time I finished it and made first attempts to ride it started snowing and the temperature dropped below 2-3C. I decided to spend winter time fixing minor issues.
I expect 100-120hp on the wheel using pump gas (100 octane).

[Foxy400]

So that's what, a 100% power gain? Impressive, as long as the bike is still useable on your average (Russian) roads. Well done

[Superjack44]

Nice very nice

[MadMotoUK]

So that's what, a 100% power gain? Impressive, as long as the bike is still useable on your average (Russian) roads. Well done

More like 200%. The NC36 engine (which as I read the thread is the engine that's been modified) would only be 37BHP in standard form.

[MadMotoUK]

Without wishing to offend, but do you know what you are doing with turbos? Have you any idea how to spec them?

I've just had a look at the specs for those turbos you've used as the numbers seemed familiar and rang alarm bells. They are way too large for the 400cc engine. The GT2860RS is designed for engines from 1400cc to 3000cc and 250-360 BHP. The HKS2530 (re-badged Garrett with different shells) was developed for the Skyline and aimed at the 500+ BHP mark.

You'd be much better off using a Garrett GT1241 (good for up to 130BHP) with a 29mm intake, 41mm exhaust and a 35.5mm turbine. Expect a boost from 37BHP (NC36) to around 70-75BHP providing you've got the proper airflow and other engine mods properly done. It's not unknown to obtain around 90BHP but that involves a lot of £££ spent and it's pushing the engine to it's limits.

Bear in mind that in order to fit a turbo to ANY engine, you have to lower compression (this has to be calculated properly) or the pistons will shit themselves and the engine will be destroyed. You also have to adjust the ignition advance and the timing. If you don't, expect very soon to have a rather large paperweight or door stop.

A 400cc bike with an HKS2530 will have MASSIVE lag until you get towards the top of the rev range. No amount of fettling and tuning will make it work properly, it's just way too big. The engine will be a pig on normal roads under normal traffic conditions.

Other than that, your workmanship is brilliant, it looks great :)

[pugnator]

Without wishing to offend, but do you know what you are doing with turbos? Have you any idea how to spec them?
I've just had a look at the specs for those turbos you've used as the numbers seemed familiar and rang alarm bells. They are way too large for the 400cc engine. The GT2860RS is designed for engines from 1400cc to 3000cc and 250-360 BHP. The HKS2530 (re-badged Garrett with different shells) was developed for the Skyline and aimed at the 500+ BHP mark.

Yes, I do know how to spec them and that's the reason I chose 2530 over GT12-17 or IHI VQ50 (which I have on the shelf)

You'd be much better off using a Garrett GT1241 (good for up to 130BHP) with a 29mm intake, 41mm exhaust and a 35.5mm turbine. Expect a boost from 37BHP (NC36) to around 70-75BHP providing you've got the proper airflow and other engine mods properly done. It's not unknown to obtain around 90BHP but that involves a lot of £££ spent and it's pushing the engine to it's limits.

No, it's not like that. You're taking into an account BHP but not engine working RPM ranges, expected spool time/zone etc.
We only have two wheels and not so much grip. You do not want to hit the boost on lower RPM if you're not going to smoke tires only and use it as showbike once a year.
For road bike:
* You want smooth and steady power increase from 7000RPM to the limit.
* The 400cc transmission is glass made, you don't want boost on low RPM. It's much more safer to do it after 7-8k RPM.

Bear in mind that in order to fit a turbo to ANY engine, you have to lower compression (this has to be calculated properly) or the pistons will shit themselves and the engine will be destroyed. You also have to adjust the ignition advance and the timing. If you don't, expect very soon to have a rather large paperweight or door stop.

It's rather a rule of thumb than an actual rule. You want to stay away from pre-ignition, detonation and excessive gas pressure.
Lowering CR is one of the ways to accomplish it. And not the best one. Remember, that engine will run as N/A engine on a pre-spool zone and not too powerful 400cc engine will be even more boring.
You may increase intake opening with new cams, you may play with spark advance. That's why it has to be done on a dyno with precise spark tuning.
Lowering CR with thicker gasket is even worse solution - increasing quench will increase a chance of pre-ignition.
The seconf incarnation of the engine will have custom alum-alloy rods and pistons with slightly less CR, about 10.5:1.

A 400cc bike with an HKS2530 will have MASSIVE lag until you get towards the top of the rev range.

Yes, that's what makes it roadworthy and not a widow maker. You don't want to hit the boost in the middle of the turn when you're tilting and expecting full throttle control and no sudden things.
On the right is GT28 and the other one is IHI VQ50.
There were several tests with different turbos before I came to this setup.

[MadMotoUK]

Obviously you don't have a sound knowledge of turbocharging. Have fun.