Dateline, February, 2007

Engine builder for Seldom Seen Slim Landspeed Racing
By Bill Hoddinott

  • Bill: Mike, thanks for taking the time to tell us about the turbo 250 Ninja you built for Jon and Nancy. I have an '88 model myself I've done over 100K miles on and I'm very fond of it!

  • Mike: Sure, Bill, glad to! And you're absolutely right, the 250 Ninja has been a tremendous success for Kawasaki. When you have one model that stays in the shops unchanged for so many years, that can only mean it sells in large numbers and continues to make money for the manufacturer and the dealers.

  • Bill: How did you approach the turbo conversion for this engine?

  • Mike: Nobody has ever applied a turbo to one of these before, as far as I know. There are many, many turbo racing engines in existence, and a large body of knowledge exists about it; so I just had to start with the fundamentals and work from there.

  • Bill: I know that turbocharging for aircraft engines goes clear back to around 1920, so there's nothing new about it.

  • Mike: Right, and it can certainly make tremendous horsepower for you in any engine if it's built right and can stand the pressure structurally.

    When Jon brought this project to me, he already had some pieces from work other shops had started, and I used them. They included a set of Carrillo rods and a pair of JE pistons to lower the compression. The stock Ninja has 12.4 compression, and these knocked that down to 9.66.

  • But I wanted the ratio down even a little more, and the end result was some work on the pistons, and even a shim under the cylinder barrel. I ended up with 9.44 to 1, and on a comic note, the visible shim under the barrel made the Bonneville tech inspector suspect we had a stroker crank in it! But no, it was and is a dead stock Kawasaki crankshaft and bearings; as they found out when the bore and stroke were measured.

  • Bill: What was done to the head?

  • Mike: I ported it out a little and installed 1mm larger intake and exhaust valves on the stock seat inserts. Stainless steel intakes and Inconel 1700 degree material for the exhausts. The exhaust restriction of the turbo creates extra heat on your exhaust valves and you want the best material available.

  • The larger valves meant adding small notches to the cylinders to clear, and these also helped gas flow.

    I was able to cajole Megacycle Cams into grinding me some turbo racing cams with a little higher lift and reduced overlap. This being a four-valve design with DOHC you can adjust the overlap a little if you want. These points are important with a turbo. I speced the valve stems a tad longer than stock to make up for the small cam base circles and keep the finger-type cam followers in the right relationship with the valve tips. And used some special valve springs since the valves are a little heavier than stock and I knew the engine would spend a lot of time near the red-line. All this equipment has worked fine for us.

  • Bill: What did you do about lubrication?

  • Mike: The crank and oil pump are stock. Kawasaki puts a good high-volume pump in these. But I replaced the stock oil pressure relief valve with a ZX 12 type, which gives slightly higher oil pressure, and better characteristics in my opinion. I use Maxima Synthetic Blend 20w-50 racing oil in all the engines I build. In this one it gives 83 psi cold and 66 psi hot, which is plenty.

  • Bill: Did you find that the stock head gasket was reliable?

  • Mike: Yes, we've had no trouble with it. I did replace the original cylinder head bolts with ARP studs of the same form - not oversize - and used ARP washers and nuts. I might mention that we also replaced the stock 8mm bolts on the bottom of the crankcase, at the three main bearing positions, with ARP studs. Studs give a bit more strength and stability for an extreme-duty engine and help keep it tied and clamped together.

  • I think the stock cylinder head on this engine is a good strong solid piece, large for its size in relation to the two small bores of the cylinders. The stock head gasket is one-piece steel, with an embossment around the cylinders apparently formed by pressing the steel. The whole thing is coated with Viton high-temp rubber, and we haven't had any trouble with combustion or water leaks.

  • Bill: What performance did you see on the dyno, compared with the stock Ninja?

  • Mike: Using a chassis dyno, about 47 horsepower at the rear wheel, compared with about 30 for the stocker. At 47, the Motec sensor, which is very accurate, said we had 10.5 psi manifold pressure. The bike gauge said 12.5 at the same time. While at Speed Week we ran the bike gauge at 15 psi, so we had a little more power at the Flats. We have a good intercooler for the intake air, supplied with ice water from the original fuel tank.

  • Bill: Yes, Jon told me you converted the gas tank for ice water, and built a small fuel tank which is mounted under the rider's right leg. Jon told us in the present form, the engine is dead at the bottom end and the rider has to scream it and slip the clutch to start the bike from rest.

  • Mike: That's right. You understand the smallest turbo available is just barely small enough for this 250cc capacity. This means you are a bit short of exhaust volume to spool it up and make some pressure at the bottom of the rev range. This is one issue that we need some more time to work on. We were a bit rushed this summer to get the bike finished enough to run it at Speed Week, and I think it did pretty well, considering.

  • As it is now, you start to get some boost at 6000, and it comes to life gradually up to 9000, when suddenly it REALLY comes alive, and maximum torque appears at about 10,000; the same place in the rev band as the stock Ninja. So yeah, right now it's like one of the old-fashioned two-stroke Yamaha racers that ran the same way, except those had even less rev range.

  • Bill: How did you set up the EFI to replace the stock Ninja carburetors?

  • Mike: I located some 32mm throttle bodies for fuel injection, made by Gen B in England, and these work with EFI controlled by the Motec 'brain'. The turbo compressor blows through them.

  • Bill: How much spark lead does the turbo engine want?

  • Mike: The Motec provides 38 degrees max, which works best. This is a few degrees less than the stock NA engine uses. Full data acquisition is part of the Motec deal, the EFI is controlled by an O2 sensor and a pressure sensor. So we know what happened by downloading the data after every run.

  • Bill: How does the electrical system differ from stock?

  • Mike: The stock alternator is retained but due to the extra electrical equipment an oversized battery is fitted. The only real electrical problem we had at Speed Week was salt corrosion of some of our connectors.

  • Bill: Bonneville is notorious for that. I must say the stock electrical system on my old '88 Ninja has been totally trouble-free all down through the 15 years I've owned it.

  • Mike: Don't take it to Bonneville, then! (Chuckling) Despite the finest anti-corrosion coatings on the fittings, we still had some headaches.

  • Bill: Okay, Mike, I guess we've covered about everything. Congratulations once again on your success building this record-setting one-off 250! Maybe we'll touch base again later as development continues, and thank you.

  • Mike: As Jon told you, he wants to see if we can develop this engine to a full 80 reliable horsepower. If so, he's thinking a small mc streamliner to go for 200 mph.

  • Bill: Sounds terrific, Mike; we'll be watching with interest!

  • End
    Reprinted with permission from Bonneville Racing News. Copyrightę, 2007 William Richard Hoddinott.
    Reproduction without permission of the author is prohibited.


    Copyrightę, 2003-2007 by SpinMasters Web Designs. All rights reserved.