#6

[F5 Dave]

So you need to destroke it to 100 yeah?

Then is BoB still running at Ruapuna? Even if you have turbo lag it will blitz everything else.

[speedpro]

BOB is being advertised. Looks like it is happening at a meeting with races on the big track, but the BOB on the B track. Last I looked there was no permit listed.

Correct, it will be a 100 for entry to BOB. I'm not that interested in winning. This bike has been all about the build. I really need to sort out the BOB thing. Cricket and I are both keen to go. He'll ride the FZR/MB bike.

One thing I have been considering is donating the Wigram GP trophy back to the bucket community in the Chch area. It's a real bit of the local bucket history of Chch and might make a nice trophy if repackaged and renamed.

I've also been "chatting" with ChatGPT about the turbo. My main goal with this motor was to make 40hp which has been achieved. The stretch goal is 50hp which looks achievable running 20psi boost. Sketchy has run 20psi. He ended up with a 2-piece conrod but he thought that was down to a trigger error earlier on causing ignition mayhem which did a bit of damage. My engine is still relatively mildly tuned. There's heaps of fuel being tipped in and the timing is still on the cautious side. What might be a problem is injector duty cycle. Currently it's peaking at 70% which is an ideal maximum. I have run 100% with smaller injectors but supposedly that's not desirable. I could up the fuel pressure, there's still headroom with the pump. What would be cool is adding secondary, overhead, shower-type injectors but I'm too lazy to bother with the fabrication, plus I'm spending time getting my other bike going again.

[Sketchy_Racer]

BOB is being advertised. Looks like it is happening at a meeting with races on the big track, but the BOB on the B track. Last I looked there was no permit listed.

Correct, it will be a 100 for entry to BOB. I'm not that interested in winning. This bike has been all about the build. I really need to sort out the BOB thing. Cricket and I are both keen to go. He'll ride the FZR/MB bike.

One thing I have been considering is donating the Wigram GP trophy back to the bucket community in the Chch area. It's a real bit of the local bucket history of Chch and might make a nice trophy if repackaged and renamed.

I've also been "chatting" with ChatGPT about the turbo. My main goal with this motor was to make 40hp which has been achieved. The stretch goal is 50hp which looks achievable running 20psi boost. Sketchy has run 20psi. He ended up with a 2-piece conrod but he thought that was down to a trigger error earlier on causing ignition mayhem which did a bit of damage. My engine is still relatively mildly tuned. There's heaps of fuel being tipped in and the timing is still on the cautious side. What might be a problem is injector duty cycle. Currently it's peaking at 70% which is an ideal maximum. I have run 100% with smaller injectors but supposedly that's not desirable. I could up the fuel pressure, there's still headroom with the pump. What would be cool is adding secondary, overhead, shower-type injectors but I'm too lazy to bother with the fabrication, plus I'm spending time getting my other bike going again.

An update to my 2 piece conrod haha

I rebuilt it the same with 3LN rods and pistons and still at 20psi, but then torched 2 pistons between the ring land. The 3LN piston have very small ring lands, so I decided to swap to the 2KR pistons and rods as they have pretty much twice the amount of material between the crown and first ring and also twice the thickness between rings.

This worked great and I had the bike back on track at 20psi for about 5 test days so probably 200 laps or so. So naturally I decided to turn up the boost more to 24psi.

After one afternoon of testing, ejected another rod. Same as last time it turned the rod into an S bend then fatigue fracture is my best guess.

At this point i've run out of injector size at 95% duty, but one idea I had was to point one into the turbo inlet like the old indy car turbos did. Helps with reducing IAT and for me much easier than trying to fit shower injectors

It's now about to get sleeved down to a 100cc trying out some 3D printed pistons. With the smaller capacity, I think my injectors will now be okay, but I really want to push the boost to 28psi to recover the lost power from the reduction in capacity. With the reduction of flow im also considering trying to rev it a bit harder. I'm thinking of some titanium retainers and some custom valve springs maybe.

Too many cool bucket projects on the go, not enough time (and motivation)

[jato]

this is a cool thread! workshops all over the country building super buckets...
a thought is that with an engine getting in the vicinity of "bursting" adding boost will increase (mostly compressive) load on the workings at a roughly proportional rate to psi but adding rpm increases compressive and tensile loads at an exponential rate. it could be the more "reliable" engine has sky high boost rather than rpm.

[speedpro]

Sketchy are you running the under-piston oil jets? Supposedly they help keep piston temps down and therefore strength up. Good to hear that you are getting laps in on the bike. I'm real keen to hear how your printed pistons handle it.
Regarding revving it, with the valve springs at the correct installed height or maybe a smidge tighter, they seem to be reliable to the redline for whichever model. I don't have anything like the time on mine as you do on yours but so far on this motor I've had no problems with running it to 18,000 where I have the rev limiter set. Using the later 3LN model thin stem valves will help as they are lighter than the earlier 2KR model. The longer rods also help by reducing peak piston acceleration.
Valve springs are an issue with FZR250s. I've measured more than a few and every single one has been installed over length. The FZRs have a bit of a reputation for dropping valves and I suspect the springs are the cause.
My old turbo race bike used to damage the ring lands. It used to end up with a stack you could remove - top ring, ring land, 2nd ring, ring land, oil ring. I always put it down to detonation. Fitting premium JE forged pistons and running methanol fixed it. My suspicion would be heat weakening the pistons followed by detonation. I have a det sensor I'll be fitting once I start pushing it. Kris, dyno guy, fitted a det sensor during tuning but never detected detonation in mine.

[Sketchy_Racer]

Sketchy are you running the under-piston oil jets? Supposedly they help keep piston temps down and therefore strength up. Good to hear that you are getting laps in on the bike. I'm real keen to hear how your printed pistons handle it.
Regarding revving it, with the valve springs at the correct installed height or maybe a smidge tighter, they seem to be reliable to the redline for whichever model. I don't have anything like the time on mine as you do on yours but so far on this motor I've had no problems with running it to 18,000 where I have the rev limiter set. Using the later 3LN model thin stem valves will help as they are lighter than the earlier 2KR model. The longer rods also help by reducing peak piston acceleration.
Valve springs are an issue with FZR250s. I've measured more than a few and every single one has been installed over length. The FZRs have a bit of a reputation for dropping valves and I suspect the springs are the cause.
My old turbo race bike used to damage the ring lands. It used to end up with a stack you could remove - top ring, ring land, 2nd ring, ring land, oil ring. I always put it down to detonation. Fitting premium JE forged pistons and running methanol fixed it. My suspicion would be heat weakening the pistons followed by detonation. I have a det sensor I'll be fitting once I start pushing it. Kris, dyno guy, fitted a det sensor during tuning but never detected detonation in mine.

Yes, I have the 3LN engine with the oil squirters and small valve stems, but with the 2KR rods and pistons for reasons mentioned.

I have high hopes for the 3d printed piston, because of the reduction in diameter from 48mm to 43mm, I've been able to add a lot of crown thickness and wall thickness while still keeping the mass equal to the stock pistons so I dont have to rebalance the crank.

The biggest issue with sleeving it down is that I will have to put cuts in the top of the sleeves to allow clearance for the valves to open, which causes three problems, one is that it severely shrouds the valve when open. Second is that it creates a pocket at TDC that may be susceptible to trapped gasses and detonation. Finally, trying to keep the compression ratio at a reasonable level gets really hard as the cylinders get smaller.

Only one way to find out though, hoping to have both the FZR and the TST ready to go for the BOB