Ninja 300 Engine in a Pre-gen

[tfkrocks]

http://www.bayarearidersforum.com/fo...d.php?t=494205

Someone did it, if anyone here was interested.

[RacinNinja]

SOunds like he needs to undercut the gears in the tranny.....having shifting issues.

32 MM carbs and a bolt in 300 engine, eh? Interestingly enough, it's only a 4 HP bump over a new-gen 250 though....his dyno'd out at 35 HP, my 250 is 31 HP.

Should have gone with larger carbs. They are not the same as throttle bodies.....carbs have a venturi that slims down the air stream and a slide too.

I'd go at least 34MM carbs on that one. Maybe 36.

I'd also look at the advance curves between the 300 ECU and the pre-gen CDI. I'll bet they're different.........but a cheap ignition box for a pre-gen would fix that.

[crazymadbastard]

sweet!

[jkv45]

Originally Posted by RacinNinja

SOunds like he needs to undercut the gears in the tranny.....having shifting issues.

32 MM carbs and a bolt in 300 engine, eh? Interestingly enough, it's only a 4 HP bump over a new-gen 250 though....his dyno'd out at 35 HP, my 250 is 31 HP.

Should have gone with larger carbs. They are not the same as throttle bodies.....carbs have a venturi that slims down the air stream and a slide too.

I'd go at least 34MM carbs on that one. Maybe 36.

I'd also look at the advance curves between the 300 ECU and the pre-gen CDI. I'll bet they're different.........but a cheap ignition box for a pre-gen would fix that.

It does seem like the 300 needs some trans work if you plan to push it pretty hard.

His dyno numbers are right on with most of the runs I've seen - which is to say not overwhelming. Even though your 250 engine is pretty close, I would expect the 300 to make its power lower and have a bit more torque. Judging from the port differences I agree that it could most likely use more than 32mm carbs. That may be holding it back at this point.

I'd like to see what kind of numbers a fully-built 300 would produce.

[RacinNinja]

Originally Posted by jkv45

It does seem like the 300 needs some trans work if you plan to push it pretty hard.

His dyno numbers are right on with most of the runs I've seen - which is to say not overwhelming. Even though your 250 engine is pretty close, I would expect the 300 to make its power lower and have a bit more torque. Judging from the port differences I agree that it could most likely use more than 32mm carbs. That may be holding it back at this point.

I'd like to see what kind of numbers a fully-built 300 would produce.

I definitely agree that peak HP is not the whole story. The 250 puts out a measly 16 ft lbs of torque with the 300 only an extra 2 ft lbs more, according to a Cycle World dyno. Compare that to my 40 year old 350 single putting out almost 23 ft lbs.....

It is good to note, however, that his dyno numbers at the rear fit perfectly with the FI model.

Dood did a good job on this swap for sure!

It's just that, while I was in there, I'd be doing a bit more hop up for all the work. Then again, I don't know the class he's running in and the rules for it either.

[InvisiBill]

FYI, the EX500 uses CVK34 carbs. I assume it would be plenty for the 300 too.

The Gen1 and Gen2 500s use different ignition pickups as well. The Gen1 flywheel has exploding magnets, but you can swap in the Gen2 flywheel if you just modify the triggers a bit. You might be able to do something similar with the 300 flywheel to make it work with the PreGen ignition.

Personally, a lot of the reason I'd want the 300 engine is for the EFI. Pairing the engine with mostly PreGen parts seems less than ideal to me, though obviously much cheaper and simpler.

[Ghostt]

[RacinNinja]

Originally Posted by InvisiBill

FYI, the EX500 uses CVK34 carbs. I assume it would be plenty for the 300 too.

The Gen1 and Gen2 500s use different ignition pickups as well. The Gen1 flywheel has exploding magnets, but you can swap in the Gen2 flywheel if you just modify the triggers a bit. You might be able to do something similar with the 300 flywheel to make it work with the PreGen ignition.

Personally, a lot of the reason I'd want the 300 engine is for the EFI. Pairing the engine with mostly PreGen parts seems less than ideal to me, though obviously much cheaper and simpler.

This is true but if you consider the HP increase to cost ratio, it's pretty affordable. Squeezing out another 5-6 HP out of a 250 costs a lot of money compared to bolting in a 300 and a bit of carb tuning.

You can pick up a 300 motor for 5-600 bucks off FleaBay and re-use a lot of things you have on hand.

Bore, pistons, cam, etc would cost you well north of that to mod a 250.

[Ghostt]

Something to keep in mind when the 250 engine wears out.

[HoneyBadgerRy]

About the cvk34, you would likely need different carb boots.

[sharky nrk]

So the curious thought then is - are the pregen and newgen ignition, flywheel, and covers also exchangeable? Would the same process work as is with the new gen? I do think the 300 swap if it can be done for a reasonably cheap sum would allow the 250s to continue as a competitive option vs the newer 300+ class bikes. To me is seems like it would cost less to swap the 300 mill than to do a 250 sbk build to 300cc range.

[bruce71198]

Originally Posted by InvisiBill

FYI, the EX500 uses CVK34 carbs. I assume it would be plenty for the 300 too.


The Gen1 and Gen2 500s use different ignition pickups as well. The Gen1 flywheel has exploding magnets, but you can swap in the Gen2 flywheel if you just modify the triggers a bit. You might be able to do something similar with the 300 flywheel to make it work with the PreGen ignition.

Personally, a lot of the reason I'd want the 300 engine is for the EFI. Pairing the engine with mostly PreGen parts seems less than ideal to me, though obviously much cheaper and simpler.

The carbs are spread farther apart on the 500. IIRC I couldn't get them close enough together to fit the 250.
The 250 flywheel bolts to the 300 crank. I'm pretty sure the side covers are interchangeable.

Originally Posted by RacinNinja

This is true but if you consider the HP increase to cost ratio, it's pretty affordable. Squeezing out another 5-6 HP out of a 250 costs a lot of money compared to bolting in a 300 and a bit of carb tuning.


Bore, pistons, cam, etc would cost you well north of that to mod a 250.

I made 41.2 HP for around $1000 in parts just for comparison

[InvisiBill]

Originally Posted by bruce71198

The carbs are spread farther apart on the 500. IIRC I couldn't get them close enough together to fit the 250.
The 250 flywheel bolts to the 300 crank. I'm pretty sure the side covers are interchangeable.

Yeah, the post mentioned that the flywheel and cover both bolted on. I wasn't sure if there was any reason to prefer the new flywheel or if modifying it might be easier (like if you had an engineless bike, so no flywheel/cover to swap on).

The 500 switched from a single trigger and multiple pickups to multiple triggers and a single pickup, so the side covers and harnesses are different. What should be a fairly simple swap turns into a bunch of parts needing to be changed for everything to match up. Chopping down the trigger ends up being the simplest way to make everything work together. Just thought I'd point out another option, but it doesn't really seem like this would be all that useful on the 250/300 stuff.

Originally Posted by bruce71198

I made 41.2 HP for around $1000 in parts just for comparison

I wasn't sure how much your stuff cost, but I knew I had seen numbers higher than his. His method seems sort of like a drop-in big bore upgrade.

Originally Posted by Grease_Monkey

Now if you have the money to spend, then just get an engine with complete harness, ECU and Rectifier. Then, all it is wiring up powers and grounds. But, that leads into more money for the engine, more time wiring, more money to buy an ECU tuning upgrade, learning how to use it and/or paying some one, even more money, who already does, to dyno tune it for me.

With my budget, all the pieces I already have, and Kawi's ability to try and not break the mold with their modern engine designs, it was fitting for me to use as much from the 250 as possible.

He mentioned seeing a whole 300 engine with electronics for $900. I (not really having the skills to do something like this anyway) would probably go that route myself. Like I said, the EFI is a big reason I'd want the 300 over the 250. But I also like the suspension and cosmetic upgrades of the 300, so everything would probably lean toward me just getting a 300 anyway.


If I was going to the trouble of swapping in an engine from a different bike, but still keeping the carbs, I'd be tempted to go this route. If you're racing, there are classes and such to consider. But if you're not limited like that, this should give you even more power, and you don't need to figure out the proper fueling/ignition stuff to go along with the swapped engine.

[RacinNinja]

Converting a 250 to EFI though would require the 300 gas tank.....unless the fuel pump and all the other goodies bolt in to the 250 tank.

[HoneyBadgerRy]

Originally Posted by RacinNinja

Converting a 250 to EFI though would require the 300 gas tank.....unless the fuel pump and all the other goodies bolt in to the 250 tank.

They make a kit to convert the ninja 250 to efi with the stock gastank.

[bruce71198]

Originally Posted by RacinNinja

Converting a 250 to EFI though would require the 300 gas tank.....unless the fuel pump and all the other goodies bolt in to the 250 tank.

An external pump of the correct rating for pressure and GPM could be used and are readily available.

[RacinNinja]

Originally Posted by bruce71198

An external pump of the correct rating for pressure and GPM could be used and are readily available.

I was wondering about that and the thought had crossed my mind.

I was just curious what other ideas were since people seemed to want to keep the EFI for the 300 in a 250 frame but hadn't mentioned the fuel side of things.

Personally, I think the pre-gen chassis is a terrible idea for the 300 conversion but that's me. I'd have popped into a 2008+.

I like the idea of re-using the pre-ignition and carbs though. Keeps things a bit more simple with no apparent decrease in performance.

[bruce71198]

Originally Posted by RacinNinja

I was wondering about that and the thought had crossed my mind.

I was just curious what other ideas were since people seemed to want to keep the EFI for the 300 in a 250 frame but hadn't mentioned the fuel side of things.

Personally, I think the pre-gen chassis is a terrible idea for the 300 conversion but that's me. I'd have popped into a 2008+.

I like the idea of re-using the pre-ignition and carbs though. Keeps things a bit more simple with no apparent decrease in performance.

I'm a carburetor fan, you can keep your EFI

[RacinNinja]

Originally Posted by bruce71198

I'm a carburetor fan, you can keep your EFI

I'd slap a set of Mikuni VM34's on there and see what happens.

[chugs]

I've been following on grease_monkey on barf, I might do an FI application into my pregen this summer.