help me decide on engine build: big cams, compression and NOS vs low compression TURBO????

My Sportster came with Keihn.
How about one of the 50mm injector
bodies from a RC-51?

My advice, as I think I have suggested before, is to start with a GPz750 turbo engine. Kawasaki put a lot of effort into that engine, starting with the (K)Z650 engine in 1980 and modifying it until 1984 when they deemed it suitable for turbo use. I would not second guess their efforts and attempt to turbo the 650, almost nothing is shared between the two engines. The turbo engine is superior in every detail.

I would also not attempt to get 180hp on pump gas. It's do-able, but only with very good control and an intercooler in my opinion. If you want 180hp and pump fuel you need a ZX12R (which I think you already have). One of the guys on my site got 176hp at 15psi, but he had two rows of injectors, a programmable DFI unit and an intercooler. Most "normal" 750s will take 20psi to reach this power level, which is outside the scope of pump fuel.

Steell the turbo engine as standard does not have high impedance injectors. It does however have larger injectors than the GPz1100, but smaller throttle bodies. Powercommanders will only run with high impedance injectors though, so a swap to high-impedance is necessary for this mod. My "street" 750 cost about £3000 ($6000) to modify but I had access to certain parts from my earlier project. I could build a duplicate for about £5000 ($10000), but that would not include my labour cost. As usual, speed costs, it all depends how fast you want to go :laugh:

Lorcan, thx for the info. I started a thread on your site as well to make sure you got involved:P
if i cant get 180hp thats fine, but i would like to max it out :evil: . you think 160 would be do-able without the cooler or water injection on the kz? (im going to try for about 240 hp with nitrous on the zx12r this summer, dual stages :evil: )
I know i should start with the actual turbo motor, but so far i have seen 1 turbo in person, and that was in another province! just seeing another kz (no matter the size) is rare here
about the injectors, does it matter what type i use with megasquirt, or is one type easier than the other? low impedance vs high?
so im looking for 270cc/min injectors correct? or a fuel pump with enough of a psi jump to bump the gpz1100 injectors (180-200) up to the right amount...
going from 36 psi fuel pressure to 46psi fuel pressure puts them at 203-226
(going by the charts and converters here www.megamanual.com/v22manual/minj.htm#size )

Post edited by: 77KZ650, at: 2007/05/11 17:02

another reply on the ms board

There's a guy in KS that used the laptop in the driveway to get his BMW flat-4 drivable, then put it in a backpack to log and rode with occasional roadside stops to use VE Analyzer in MLV. After a couple hours of tweaking, it was ready for daily driving. Now he uses a Palm just to monitor and do minor tweaks and logs.

I use a similar system when tuning cars alone as I like to keep my attention on the road and just glance at the screen from time to time. Can't beat the Palm in race cars, velcroed to your thigh, dash or whatever.

steell wrote:

I measure them at 35mm though.
are you sure you dont have the later ones? they were listed as 35. or maybe its kinda the same deal as the 28mm carbs measuring 28.7mm. maybe the 34s are 34.9?

I don't understand the 3.3 bar regulator thing, the regulator should be referenced to manifold pressure.
can you explain what you mean here? i thout it was just saying what the fuel pressure was

Don't forget that you can also run two sets of four injectors, one at the thottlebodies and one upstream, some new bikes are doing this. The second set kicks when when the boost builds.
that sounds a bit complex. maybe on a second project when i know what im doing (it actually would be a great way to design a turbo setup for my 12 so i could keep all the functions of the ecu that dont deal with the motor....) is it possible to run 8 injectors that act like 4? by that i mean the pairs squirt at the same time to act like a bigger injector. (easy way to avoid buying bigger injectors and figuring out if they fit?)

I sure am glad Lorcan chimed in here, he has probably forgotten more about the 750 Turbo's than I will ever know

The MS1 MegaSquirt has two injector drivers, and can drive four injectors off each one with no problem. The best thing is to have the second set kick in only when you get to the point you actually need the extra fuel. And you mount them upstream to allow for more time for the fuel to mix with the air at higher rpm. I believe the code that is needed is MSnS, the same code that Dave Sloan is running that allows him to control ignition.

Do a search on msefi for "dual table".

The fuel pressure regulator is referenced to manifold pressure, that's so the fuel pressure is always 36 psi (or whatever) above manifold pressure, otherwise it would be real difficult to control the fuel, because different amounts of fuel would be injected depending on the difference in pressure. And it's the EFI controllers job to determine how much fuel to inject, no sense making it more difficult than it is already.

I am reasonably certain that I have two sets of GPz1100 throttlebodies, and they measure 35mm ID at the engine side. I believe the 750 Turbo has 34mm throttlebodies, but Lorcan will know for sure.

oh now theres something i didnt know. I thought that the pressure regulator kept it at a constant pressure, not a constant pressure above the manifold pressure.
so the code that runs either extra injectors or ignition, is it just that? one or the other? or will it run 2 sets of 4 injectors and the ignition aswell? (ill search, but if you know right off the top of your head that would be great too:P )

Following up on what Lorcan said. Another good reason on using a GPz turbo motor is the fact that the conrods are different. The wrist pin size is 16mm instead of 15 as fitted to std 650's and 750's. This means that you wouldn't be able to fit Wiseco's 810cc turbo piston set onto your rods.

You could still use a 650 or 750 block and put a spacer underneath to get the compression down a bit, but you aren't going to hit 160hp with that setup on the street.

Try and look for a genuine turbo engine. The cost of one will save you loads of hassle in the long run. Believe me I know.

well F*** that throws the whole project out the window:pinch: I was sure that they all shared the same con rods (and therefor piston pins). hmmm. how much of a base spacer would it take to get back down to 8:1?:blink: or is it even possible? (enough slack in the cam chain???) I dont even want to think about customs pistons (because if i did, i might as well get resleeved and go 880cc... maybe in a few yrs just for the hell of it, but its not even close to being in the budget now) haha i need a sponcer:P
hmmm, do the cranks share the same pins? would i be able to use 750 turbo conrods and then the 810 turbo pistons???
maybe ill just build a NA motor if it prooves to be too expensive. Im convinced to give megasquirt a try, and that would cut the cost of hooking up nitrous WAY down because i could go with a $300 dry kit VS a wet kit for at least 3X that

Hey Scott - Let me chime in here referring back to your original question about what combo to go with.

It seems you are leaning towards the turbo set up but I would caution going down this road. Putting a turbo on a bike isn't an easy job and getting it dialed in might leave you parked for a long time trying to figure it out unless you have experience with this type of set-up.

Here is a simpler package I would consider....

Pick up a Gpz1100 motor for your Kz650 and shoehorn it into the frame. Strip off the black engine paint to give it a Kz engine finish.

These bulletproof motors came in around 120 h.p. Stuff in a big bore kit from APE and get the head done by a shop that specialises in Kz drag bikes. APE can also handle this work. Add a pipe and you should be around 150 hp or so. If this doesn't give you a chubby then look at a shot of nitrous, but I suspect this will satisfy your need for speed. This could probably be done for under $5K.

It has been said here before...you can't beat the factory platform set-up for reliability and with this type of displacement in a 650's middleweight frame (gusseted of course to handle the extra oomph) this bike would be more than a handful.

Cheers-Colin Firth-Ontario Canada

I don't get in here often enough to keep up with the questions, but...

The turbo has bigger stronger rods with bigger wrist pins as Zephyr says, and a whole host of other upgrades. It has an excellent scavenging system. The gearbox is overdriven (runs faster) to take more torque. The clutch is beefed up. It already has a well mapped fuel injection system that can fuel it to 140hp with no mods at all. It has ready made headers. It has an oil system designed for turbo use. It has a CDI unit that only allows 30 degrees of timing so it needs no additional retard. It has a ready made plenum. I could go on, but it's quicker to say that turboing a bike is a wallet-emptying experience at the best of times, so why make it harder work than it needs to be?

To get to some of the other questions, the turbo has injector bodies that are 34mm at the inlet, but only 29mm at the outlet. The 1100 bodies are 34-35mm all the way through. For 180hp I would go with 300-310cc/min injectors. I got 196hp out of 310cc injectors but they were pretty much maxed out with safe fuelling (11:1) and it's better not to run them at extended duty cycles.

I don't know much about MS as I've never used it. You would have to check with them which injectors it works with (or works best with).

Regarding fuel pressure it is usual to run a 1:1 pressure regulator. As has already been explained, this raises the fuel pressure by 1psi for every 1psi of boost, otherwise the boost pressure would eventually try to force the fuel back through the injector resulting in a poor spray pattern. It is possible though to use a rising rate FPR. I have used one which had a 3:1 ratio, so bumped the fuel pressure by 3psi for every 1psi of boost. This works well for small (stock) injectors. On my old bike I had it running stock pressure at idle (36psi) but 70psi under 15psi boost. Note that a normal 1:1 FPR is NOT rising rate, despite what many turbo sites claim, so you have to be a little careful when shopping for these. You can still map the bike as normal when using rising rate, just be aware that if you change the rate you will have to remap. You also need to make sure that your fuel pump has sufficient flow at the new pressure, as with electric pumps the flow goes DOWN as the pressure goes up.

Nothing like having tons of experience with the GPz750 Turbo's!

By the way Lorcan, when are you going to break the 211 mph in your sig? Any meets coming up that I should be watching for results from?

I am sure you aren't giving up