stock cam lift

Ok, I'm in the shop on the laptop (anyone that's been here will tell you that's amazing), and I just disassembled a KZ750 four head and measured the valves.

33mm intake and 30mm exhaust, 81 KZ750H head, haven't got to the GPz750 head yet, but the GPz750 uses the same size valves.

I'm getting ready to work over my head with a mild port and polish. I got a couple questions for Larry C.

Have you ever done a 30 degree backcut on the valves? Was there any noticeable gains in flow doing this? I know small block ford heads respond really good to this, just not sure about a motorcycle head. Also do you think the egr ports in the head will hurt the flow any?

Maybe when I get my head done I could send it in and get some comparison numbers.

I'm wondering how much larger we can go on the valves, both intake and exhaust, with stock and/or larger seats, and if the benefit is worth the cost/effort?
I know the GPz750 Turbo guys go 1mm larger on the exhaust, but with us NA guys not having a pressurized intake, I wonder if 1mm larger intakes would help?

I looked at the valves in the 750 head, and it does look like 1mm (or maybe even 2mm) larger valves will fit, but at around $300 plus the cost of installation, it becomes rather expensive!

But think of the power output with a professionally ported head, bigger valves, and an aggressive cam! Seems to me that 100 rwhp ought to be possible (at least)!

But then there's the cost

Here's a question.. If I have a Kz750 motor all ready equipped with an 810 wiseco kit but it has stock Kz750 cams and the head HAS been ported but not milled. It has been dyno'd at 80RWHP. If I mill the head "GPZ750 guy's say .020-.032" Larger valves and hotter cams can I get around 90-95RWHP? How much can I mill off the head w/out it being a
fuel higher than 93octane? The compression is 10.25:1 with the 810 kit and the head is not milled.

Vach, the word is that you can mill the head down all the way to the 45 degree angle of the valve seat, but I haven't actually done it yet.

I might do it this week sometime (I'm going riding tomorrow, come hell ot high water!), but it will be next year before this thing is running.

Make you a deal, mill the head as far as possible, and if it's to much then I'll send you a 83-85 GPz750 head for the cost of shipping.

Problem is you would have to do the valves and porting again

Racers say they are getting 95-100 hp out of the 810 kitted GPz750 motors with the only other mod being a milled head. I think that has to be hp at the crank as the increase in compression and displacement alone is worth 10-12 hp, and another 2-3 hp for pipe and jetting, and the stock GPz750 has 85 hp at the crank. Larry would know better than I, but I think porting and a different cam ought to add another 20 hp (20%) at the crank due to increased airflow. That would put it at 100 hp (or more) to the ground (rwhp).

Get the weight down to 450lbs (or less) wet (my goal), and a KZ/GPz750 ought to be a fun bike




kxhonda, I am only about 70-75 miles from Warsaw, am I am putting a MegaSquirt EFI system on my KZ750 project, and I have a mill, two lathes, surface grinder, drill press, grinder, etc, along with gas/arc/mig welders.
And I'm willing to help

Steel, what kind of compression are we talking about? Can I run pump gas until what compression ratio? How much will it go up when I mill the head. I just don't want to use racing gas all the time.

According to my calculations, shaving .030" off the head ought to bump the compression to approximately 10.75:1.

Some quotes from the GPz750 FAQ:

I replaced the cylinder with an older 807cc Wiseco kit that I used in another motor and a old 1981 KZ 750 head that I got for free from a friend. I did a valve job to the head and milled .032 off the face, right down to the top of the 45 degree angle of the valve. I then ported the head to allow for more flow. I've never ported a head so I thought I'd start with something that was worth very little. I also made a bracket to hold the sprocket cover tight against the cases where the top mounting bolts were missing. Works perfect. After putting 30 quarter mile runs on this motor, I'm very impressed. The bike will run consistent 10.6's @ 122mph. I run ND w24 es-u plugs firing the 93 octane pump gas that is reformulated with 10% alcohol for emission sensitive areas.

As for piston kits, the Wiseco K 810 kit ( 807 cc, 10.25 to 1) is a less costly way to go compared to the Kaw over size pistons. The kit comes complete with wrist pins, keepers and a Cometic graphite head gasket that is the greatest for sealing tight and having absolutely no leaks. The pistons are forged and machined to exact tolerances so that the set is exactly the same. The valve pockets are cut deeper for higher lift cams. As for horse power with this kit, expect to get 83 to 88 at the rear wheel with the stock deck and head heights.

I suggest you buy the Wiseco kit that has 10.25 to 1 pistons and mill .020" off your head and you won't be disappointed. You'll have to slot the cam sprockets and degree the cams to make them right because of the head milling though.

I'd also recommend milling at least .010" to .020" off the head at the same time to get the full advantage of this piston kit. It will make it noticeably better. I'd also remove the cam sprockets and have them slotted so that the cams can be degreed when reinstalled. They won't be close to what the factory recommends because of chain stretch, new head gasket and milling the head. V&H has a video tape on how to perform this procedure.

First you should have .020" (.5mm) milled off the head to ensure the best performance and compression from the kit. This figure is on the safe end as I'm removing much more on my street and race motors. You can safely mill the head right into the intake valve seat and up against the 45 degree angle of the seat. Don't mill into the 45 degree angle. This is somewhere in the area of .032" to .035" of material removed. I'd take a minimum of .020" off and .025" would be even better for the 810 kitted motors. I've have four 810 kitted motors with over .030 milled off the head. Three GPz750 heads and one 81 Kz750 head. If you don't mill at least .020" of the head for the 810 kitted motor you'll be disappointed with the results. Although the valve angle is the same, the 750 has larger valves (33mm intake 29mm exhaust) than the 650 so there might be a problem with clearance. The combustion chamber volume of the 83 GPz750 head is 25.9 mL The 80-82 Kz750 or 83 and later H model heads have a combustion volume of 24.8 mL . The Kz and GPz heads use the exact same valves and springs. The early model 750 heads have the cam tach drive feature also.

From: Allan.Webster@West.Boeing.com (Webster, Allan S)

I emailed you a while ago about my GPZ750 for road racing. Anyhow, I guess the actual horsepower is closer to 100, or maybe 110 This is in the area of .030" to .035" removed from the head surface. Lower than 93 octane fuel can be used, but you'll need a 35 degree total advance ignitor from the 1000R Ninja and a jet kit to make not ping. If you shave the head, you'll also need to degree the cams.

gpzrider.lagemann.org/technical/FAQ2000.htm

Steel thanks, great info.. Looks like .030-.035 is safe for pump gas. 100RWHP? Niiiiiccce.. So will .395 cams work in that set up? Or is that overkill? They do have a .365 lift and 283 degrees that might be better. I'm not exactly sure how to use the formula. I just want to be sure not to over cam but still get the most umph I can.

80-82 Kz750 or 83 and later H model heads have a combustion volume of 24.8 mL

750 valves (33mm intake 29mm exhaust)

Although the valve angle is the same, the 750 has larger valves (33mm intake 29mm exhaust) than the 650 so there might be a problem with clearance.

Does that mean clearance with the 750 head and valves or the 650 head?

May have clearance problems with 750 head milled .035" and stock KZ750 pistons, but I doubt it.
The Wiseco pistons have much deeper valve pockets so you would have to cut it way into the valve seats to have a problem, and by that time it wouldn't run anyway because the valves would not seal.

Until we find someone that's actually run big cams and an 810 kit, it's just wild guessing, but in the end I guess it just depends on how much bottom end you are willing to give up. Big cams make power by shifting the peak torque rpm higher in the rpm band, thus causing a loss of low end grunt. If you are planning on riding in town with stop and go traffic (lights/stop signs/etc), then you would probably want to use the GPz750 cams.

I would like to go with 1mm larger valves (if I can go that large on stock seats), port the head, use the GPz750 cams, and see how it works, if it's not enough (and the funds are available) I'll get a bigger cam. I already have more $$ in the motor than I do in both my 750 twins combined, and that's not counting the tooling I've purchased so I can do most (if not all) of the work myself.

Thanks Steel.. I e-mailed Dynoman and this is what they said. The 118 grind is (.365 283°)

"Kevin, we like the 118 grind for the street, as it has a better overall dynamic fuel curve than the hotter cams.

The 110 (.395) grind is the same price, but is harder on the valve train components, and may cause your piston to valve problems with the milled head."

"Kevin, we like the 118 grind for the street, as it has a better overall dynamic fuel curve than the hotter cams.

I'd say you got a reply from a parrot

"better overall dynamic fuel curve" indeed :laugh:

The answer should have been "It has a broader torque range" or even "it has a broader torque curve", either which would have been more descriptive and accurate. Technobabble, sheesh

It's simple, big cams are peaky, you open the throttle and you have nothing until the rpms get way up there (7k-9k) then it yanks your arms out of their sockets and it's time to shift, takes at least a six speed trans to use it.

Smaller cams (like the 365 discussed) get the front end up at 5k-7k, and give you time to enjoy the rush before you have to shift.

To go fast with a big cam takes concentration, and that's work, smaller cam will not have the top end hp of the big cam, but it's "Fun".

Don't build a bike that you will hate to ride.

Yesterday I found this pic on the 750 turbo forum: