Spare engine--high compression build?

[kxpower?]

Hey guys and gals, it looks like dropping the kx500 motor into my ninjette is a little ways off . But I do have a spare 250 motor that needs going through (PO says the guy he got it from reported some mechanical noises). So here's what I'm daydreaming about today: Why not go ahead and get head work while I've got it all pulled apart? I guess it really boils down to availability of performance parts, which I've gathered from years of lurking around these forums that there's not much out there.

Assuming there aren't 13.5:1 pistons out there (I understand the aftermarket ones for the 250R don't fit?), I'd be looking at getting the head milled to bump CR up, getting a 3-angle valve job, and getting a port/polish job. Nothing crazy, just optimizing for premium gas and making it breath a little better. I did the math and it looks like I could get from the stock 12.4:1 to 13.5:1 by milling the head 0.318 mm or 12.5 thousandths. I understand this is an interference engine, but I'd almost bet Kawi left more than 13 thousandths clearance between the valves and pistons. I need to ask my racecar building brother if that's something you can measure to be sure, but I bet there's a way. Nothing like a territorial dispute in your combustion chamber to ruin your day!

Is 13.5:1 a good CR to aim for, or is it too high for premium pump gas? I can usually find 93 octane with no ethanol around here btw. I have access to a few good cylinder head shops around Detroit so I'd imagine just using one of them and assembling the engine at my brother's shop up there. Or is there a good place to send the head for this? Nice thing about this little bitty engine is that shipping a head is cheap! Or am I out of my mind for even wanting to mess with this stuff? Seems like this might make for a good discussion.

[jkv45]

Read through this thread - http://www.ninjette.org/forums/showthread.php?t=126445

You can get more power just by running 87 octane with the stock engine if you can get it without ethanol. 87 with ethanol is probably equal to 93 without - power-wise.

More octane = less power if you aren't detonating.

[alex.s]

octane doesn't effect power. unless you don't detonate or predet. neither of those would be happening in a healthy engine.

do a high comp build and post photos.

[Racer x]

What year engine? The later first gen engine has a funny shape to the combustion chamber. I have not done this but I think you can reshape the combustion chamber to allow for high compression pistons. But I'm not sure. Also I do not recommend cutting the head. The valves are really close to the sides and could cause some clearance problems. The service limit is .019 so I cut .010 off the block top. This raises the compression if pistons can't fit. ALL my personal experience is with the second gen engine so please take this with that in mind.

Also about octane.. low octane will not help power. But high octane will kill power. Over 113 will even be difficult to start with stock compression.

[kxpower?]

Originally Posted by jkv45

Read through this thread - http://www.ninjette.org/forums/showthread.php?t=126445

You can get more power just by running 87 octane with the stock engine if you can get it without ethanol. 87 with ethanol is probably equal to 93 without - power-wise.

More octane = less power if you aren't detonating.

I started paging through it earlier, the whole

Originally Posted by mgentz

ha. lets just say I could have bought a new big bike.

thing kinda turned me off tho lol. And I'm not doing anything on the bottom end. But now that I'm looking more closely at it the head work is gorgeous!

And yeah I only run 87 in my stock motor, premium gas is easy to come by so I'm thinking bumping the CR up to the point that it needs premium would help in the power department.

[jkv45]

Originally Posted by alex.s

octane doesn't effect power. unless you don't detonate or predet. neither of those would be happening in a healthy engine.

Yes it does. Using higher octane than required to just barely keep it from detonating will cost you power in all situations - stock or modified.

The link below is from an engine builder and racer that has a dyno at the shop, and also has the fastest and quickest Ducatis in the U.S.

Read the section about octane and note the words in ALL CAPS.

http://www.motorcycleperf.com/TechTips/BadGasoline.html

[kxpower?]

Originally Posted by Racer x

What year engine? The later first gen engine has a funny shape to the combustion chamber. I have not done this but I think you can reshape the combustion chamber to allow for high compression pistons. But I'm not sure. Also I do not recommend cutting the head. The valves are really close to the sides and could cause some clearance problems. The service limit is .019 so I cut .010 off the block top. This raises the compression if pistons can't fit. ALL my personal experience is with the second gen engine so please take this with that in mind.

Also about octane.. low octane will not help power. But high octane will kill power. Over 113 will even be difficult to start with stock compression.

It's an early one, either 89 or 91. I don't think pistons are even out there for the EX, and even if they were if they're close to what the 250R pistons cost they'd be way out of my budget. Seems like I could get the CR I want with a little machine work and cost a lot less.


I think you're right about cutting the head, so you milled the block where the jug mates up? Seems like a slick way to go, is milling the top of the jug down an option too? Is one any better than the other?

Have you run into any valve/piston clearance problems cutting 0.010? Do you have an idea of a safe limit for cutting? I wonder how close 0.013 would be...

[alex.s]

from that website:

"Octane is an indicator of the speed at which the gasoline burns in the engine."

this is incorrect.

[misfitsailor]

Instead of high compression, have the head ported and polished. The valves are a great idea. You will be surprised at the difference it makes when your engine breathes it's best. In engines that I have built in the past, head work has always made the biggest difference in real-world power output.

[kxpower?]

Originally Posted by misfitsailor

Instead of high compression, have the head ported and polished. The valves are a great idea. You will be surprised at the difference it makes when your engine breathes it's best. In engines that I have built in the past, head work has always made the biggest difference in real-world power output.

Port/polish is the main goal here, my thinking is I could raise compression too without a lot of effort, seeing as these things are happy with 87 stock I figure there's plenty of room to safely raise the CR if I'm willing to run premium.

[jkv45]

Originally Posted by alex.s

from that website:

"Octane is an indicator of the speed at which the gasoline burns in the engine."

this is incorrect.

It's not a Technical Paper on octane, but his results and statements concerning the effect of excess octane are correct based on his tests and dyno numbers.

[Racer x]

Just to splash cold water on this. We are pulling all the stops. Unlimited budget. And forty HP is the goal. I have sixty with nitrous and turbos get that also.but I could buy a new house for what that cost. So if money I is an issue and you just want a faster bike. Get a used 600. They make ninety HP and cost less than my nitrous system alone. But if you want a fast 250 ninja than have at it. We are having a very good time with this bike.

[quarterliter]

Originally Posted by alex.s

octane doesn't effect power. unless you don't detonate or predet. neither of those would be happening in a healthy engine.

do a high comp build and post photos.

"Extra" octane does reduce performance

[alex.s]

https://en.wikipedia.org/wiki/Octane_rating#Effects

[Racer x]

One thing about high octane is even with relatively low compression you can run mor timing advance. This will make more power. I ran timing as far as forty four degrees on a stock engine with 110 octane fuel.
If you want power from the fuel. Oxygenated fuel will definitely make more power. But you need to jet for it.

[jkv45]

Originally Posted by alex.s

https://en.wikipedia.org/wiki/Octane_rating#Effects

The link below has some specific information about the effect of higher than required octane on HP. The tests even used a higher performance engine (Honda RC-51) that recommended high octane fuel - and it still made more power on 87. I do not recommend running a lower octane level than recommended, but it shows you that a moderately high performance engine like the Ninja, that recommends 87, will perform worse with anything higher.

http://www.rc51.org/fuel.htm - section 3 (below) - but read it all

"3. In testing various grades of pump gas I consistently found that 87 octane fuel makes 1-2 more horsepower than those exact same bikes ran on Premium 93 octane. We tested five liter class motorcycles (97 CBR900RR, 02 Honda 919, 2000 RC51, 2000 GSXR750 & an 02 R1) & only the R1 seemed unaffected by the octane of the fuel. Now I am certainly not going to tell you to run less than the recommended octane (92) in your RC51 as the specific needs of the motor dictate that a higher octane fuel is needed, but the results are blatant in that more octane does not mean more power.

It is only fair that I note that when testing the pump gas on some of the 600's (Yamaha R6 & the GSXR600) the inverse was true in that they did lose a little horsepower on the 87 octane vs the 93 octane. Most likely because of the higher compression ratios of the smaller motors, however the CBR600F4i gained a little horsepower."


The cycles that lost power recommended Premium, and most likely were detonating on 87. Any amount of detonation will kill power, and running just enough octane to get right up to the point of detonating yields the maximum power. Most likely that point is below 87 octane for a stock Ninja.

In addition, running gas without ethanol will also improve performance.

87 octane without ethanol will give you the best performance you can get from a stock Ninja.

[kxpower?]

Wow you gotta love where internet discussions wind up! @Racer x thanks for splashing the cold water, I've read a lot of your threads and I just want to apply some of what you've done to a low budget build. There are plenty of stops like 3 kids and one on the way and very limited space and a crazy career and even crazier marriage going on! Not to mention trying to maintain a competitive level of training in Jiu Jitsu. I'm with everyone else, there's plenty of other places to debate what octane does to power.


I'm just thinking out loud wondering if what sounds like some easy (cheap) machine work would be a good thing to consider when looking at my situation.

much love guys and gals I'm about 6 beers in here!

[jkv45]

Originally Posted by kxpower?

I'm with everyone else, there's plenty of other places to debate what octane does to power.

I guess I should apologize for giving you the info then.

Because you are running Premium when you don't need to you are giving away power and money. If you start looking for more power it's something you should know about, but whatever...

[kxpower?]

Originally Posted by jkv45

I guess I should apologize for giving you the info then.
Because you are running Premium when you don't need to you are giving away power and money. If you start looking for more power it's something you should know about, but whatever...

I didn't mean any disrespect with that post. But I really don't see where anyone said anything about running premium in a stock motor.

[jkv45]

Originally Posted by kxpower?

I didn't mean any disrespect with that post. But I really don't see where anyone said anything about running premium in a stock motor.

That is true - my mistake. I took your comment about being able to fine 93 with no ethanol to mean that's what you're currently running - which doesn't sound like the case.

The octane discussion doesn't directly apply here then, but there are plenty of people with misconceptions about it's benefits for a stock engine, so it may have done some good along the way.

Sorry about that...


Jay

[kxpower?]

Originally Posted by jkv45

That is true - my mistake. I took your comment about being able to fine 93 with no ethanol to mean that's what you're currently running - which doesn't sound like the case.

The octane discussion doesn't directly apply here then, but there are plenty of people with misconceptions about it's benefits for a stock engine, so it may have done some good along the way.

Sorry about that...


Jay

Haha yeah I felt like that was important to point out, my dad had a 77 bmw rs that was so high strung it'd ping all over the place if you rode by a 91 octane pump. My brother discovered this on a ride to montana, he had to carry bottles of octane booster for when he couldn't get 93.

God knows what that old beast would have done on today's gasahol...