KZ750 twin exhaust cam for intake for more power?

I just have trouble believing that Kawi would "waste" horsepower if simply changing the grind on the cams would magically make more power. It would cost them nothing to change the cam grind, and using the same cam for both would actually save money. If it does make more HP somewhere, I suspect you lose somewhere else.

I think that is what they did on the 550's... use same grind on both cams to save a few bucks. Even on the later ZX550, they use the same grind for both cams, but they altered the sprocket to change the timing on the intake cam.

So yeah, seems like they would have done the same on the 750 twin if they thought it was a good idea.

Maybe a drivability issue shows up, or maybe it gets harder to start/kick (if both cams use the same grind on the 750 twin)?

All stock motors are designed for maximum power at the drawing board but by the time they get to the production stage they are compromised and restricted by noise reg's, reliability,fuel consumption and emmissions etc.
Fitting the inlet cam should increase power at higher revs but maybe at the expense of bottom end power and an eratic idle.
The exhaust staying open longer will allow some compression and fuel charge to escape making the engine less efficient at lower revs but at higher revs will give more time for burnt gasses to escape and allow a fuller charge of fuel mixture to enter the cylinder , Hence more power.
This is the basic concept of performance cams.
Kawasaki could have done this at the factory but the 750 twin was not built as a sports/performance machine and would have probably exploded before the warranty ran out.

some guys in germany did the trick and got more power up the RPMs. Twinnbikes.de or .com. I was told that some one is racing a twin with 90HP at the rear wheel wit only one time a crank seizure..
I'm putting an turbo on a twin with 860cc. The engines can handel it....

martijn wrote:

some guys in germany did the trick and got more power up the RPMs. Twinnbikes.de or .com. I was told that some one is racing a twin with 90HP at the rear wheel wit only one time a crank seizure..
I'm putting an turbo on a twin with 860cc. The engines can handel it....

Fellows name is Fernando, races in the VRRA heavyweight class against 1000cc fours. I do believe he held a track record in his class at one point too. His cylinder head is heavily modded with larger valves/porting/custom ground cams/shim under bucket....39mm CR's and a whole host of other exotica like custom pistons. Apparently it spit a shim out through the cam cover at HIGH rpm before the SUB mod LOL. I have a pic kickin around of him changing rod bearings while the bike was laid on its side...yes the oil pan comes off without having to remove engine from the frame :ohmy:

Wow! Sure is a lot of misinformation in this thread.

First off, the idea is to replace the intake cam with an extra exhaust cam as the exhaust has more lift and duration.

Cut off the tach drive end of the cam with a sawzall and it will drop right in, valve spacing is the same for intake and exhaust.

According to the guy I talked to that races WERA (with 90+ hp at the rear wheel, and I have a bunch of pics) using a spare exhaust cam on the intake is a step up in power (first step).

By the way, that 90+ rear wheel hp did not come cheap, he has broken pretty much all the parts in the motor at one time or another. He intially contacted me after breaking a cam chain due to .650 lift cams, and he runs shim under bucket with 36mm buckets.

This is the answer I was looking for. I'm only looking to get an extra 15hp and call it good. Thanks.

dnz wrote:

This is the answer I was looking for. I'm only looking to get an extra 15hp and call it good. Thanks.

15hp? That's a near 30% increase, and not something that's going to be obtained by swapping in a exhaust cam for the intake cam. You are only going to pick up maybe a couple hp on the cam swap, another 13-14 hp is going to take head porting, more compression, and probably more displacement.

Good luck on your mission

steell wrote:

Wow! Sure is a lot of misinformation in this thread.

First off, the idea is to replace the intake cam with an extra exhaust cam as the exhaust has more lift and duration.

Cut off the tach drive end of the cam with a sawzall and it will drop right in, valve spacing is the same for intake and exhaust.

According to the guy I talked to that races WERA (with 90+ hp at the rear wheel, and I have a bunch of pics) using a spare exhaust cam on the intake is a step up in power (first step).

By the way, that 90+ rear wheel hp did not come cheap, he has broken pretty much all the parts in the motor at one time or another. He intially contacted me after breaking a cam chain due to .650 lift cams, and he runs shim under bucket with 36mm buckets.

Ooooh....I'd love to see some pics of that bike! :woohoo:

steell wrote:

dnz wrote:

This is the answer I was looking for. I'm only looking to get an extra 15hp and call it good. Thanks.

15hp? That's a near 30% increase, and not something that's going to be obtained by swapping in a exhaust cam for the intake cam. You are only going to pick up maybe a couple hp on the cam swap, another 13-14 hp is going to take head porting, more compression, and probably more displacement.

Good luck on your mission

I was thinking the exhaust cam, porting,custom pipes, carb tweeaking and a really light chassis. I only have the engine so everything is going to built up around it. Maybe 15hp wont even be needed. When you put it at a 30% increase it seems a bit much, but I think at least 10hp can affordably be done. I am wanting to build a commuter/canyon carver. I'm on the fence on the frame type I want. I want suspension in the rear for sure. I'm thinking of getting a more modern donor roller chassis and fabbing the motor to fit. I know it will be a challenge and different but thats what makes it fun. Thanks for the help and insight.

Here is what I'm using on the 1980 KZ750G 750 twin that I'm building for a woman that divorced me 38 years ago

2000 Suzuki 750 Katana forks with Race Tech cartridge emulators and springs, matching 17" wheels, 1983 GPz750 swing arm modified for dual shocks, 2001-2003 Yamaha R6 CV throttle bodies (they look like CV carbs) and a MegaSquirt EFI controller. I haven't decided whether to use Mac 2 into 1 or dual exhaust with replica Dunstall mufflers.

I have everything but the Dunstall replica mufflers, just got to get off my butt and do it :laugh:

I have everything but the triple tree, wheels, and brakes, to convert my own bike also

dnz wrote:

This is the answer I was looking for. I'm only looking to get an extra 15hp and call it good. Thanks.

I'd be genuinely amazed if you got 15 Hp but maybe. One thing to remember: the guys that make aftermarket headers dyno tune them to the engines as built by the factory. Screwing with the cams might move it off the tune point. The "hot" set of headers I used to run definitely made a little more HP with the stock cams and a slight increase in jetting. I seriously doubt they make 15 more HP, maybe 10% - 15% more which would be about 5 - 8 HP. I am currently running the MAC 2-1 headers with stock baffle and they do not give a power increase compared to stock. They also are not tuned because the left downpipe is about a foot longer than the right so they can't be matched for scavenging. They work OK, but not a performance pipe. I don't know where to get a good tuned exhaust for the 750 twin these days, MAC is the only company making anything for them.