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Discussion Starter #1
What should my next step be for more power? I don't like nitrous and I'm not really prepared to turbocharge my bike. Any ideas? Also, I'm no longer running Ram Air, the ducts were gone when I got the bike. Is this going to cost me any serious power at speed?
 

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it's gonna cost ya a little bit.. but how often do you go over 120mph? thats sorta where they start picking up.. you're eclipsing port velocity at that point.

cam timing, ignition timing and head/piston work are the only things that make power other than power adders..
 

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you could always make some gearing changes too. not gonna give you more power per say. but youll get some quicker acceleration. of course your top end will suffer.
 

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from where you are, the "easiest" horsepower is in the cylinder head...

- a good porting/reshaping by some one who knows wtf they are doing (ie not a harley guy). I know two guys on the forum that did epoxy port work with very favorable results...I've always stuck to smoothing the casting/machining irregularities.

- a 5 angle valve job (or oversize valves..i wouldn't bother)
- degree the cams
- aftermarket cams (which will require new springs).
- zx9r (94-97 vintage) pistons to make it an 794cc.
- 2mm over zx9r pistons and resleeve (840cc)
- zx9r motor swap
- newer bike
 

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Discussion Starter #6
I don't know if I'll ever take the bike to the track or the strip. I never really planned on it. The head work and zx9 pistons sound like a good deal though and I'm definitely going to get an adjustable timing rotor soon. I think +4 degrees will really wake up the low end. As for the ram air working at over 120mph, I make it over 120 every so often so I may spring for the missing ram air duct work if I can find on ebay. My question is, how will head work and the larger bore affect the zx9 carbs and cams I'm currently running? Will they be enough or will I end up buying aftermarket cams? And what about jetting on the carbs? The kit in it is a dynojet and the only place where they really fail is below 3000rpms. If you're not really careful the bike stalls pretty easy on a standard launch. Launching hard it does great. This also makes the bike a little sluggish cruising in a parking lot. I have to clutch it and rev it a little to keep it moving below 3k. Gearing is something I already did just to help the low speed driveability and I didn't lose so much top end that I'll care. Anyway, thanks for the suggestions and any more info about head and cylinder changes is welcome! Approximate prices for head work would be great. I love this bike but I can't justify dumping half the cost of a new bike into the engine on this one.
 

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I think the ram air will effect the bike below 120 mph, it's worth the $50 it would cost to replace. Larger bore and portwork will enhance the carbs and cams, you'll be able to use all the air you can get into the motor. I'm assuming you have 40mm cvk's those are kind of big for a 750, that's why you have the low speed bogging. You should expect yo pay $500 for port work (street port) and about $250 for a valve job if you don't need any parts other than seal.
 

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I think the ram air will effect the bike below 120 mph, it's worth the $50 it would cost to replace. Larger bore and portwork will enhance the carbs and cams, you'll be able to use all the air you can get into the motor. I'm assuming you have 40mm cvk's those are kind of big for a 750, that's why you have the low speed bogging. You should expect yo pay $500 for port work (street port) and about $250 for a valve job if you don't need any parts other than seal.
Ram air has absolutely NO effect on the bike below 120mph & only adds 8-10 hp at speed...do some research.
 
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Ram air has absolutely NO effect on the bike below 120mph & only adds 8-10 hp at speed...do some research.
So at 120mph you get 8 horsepower like flicking a switch, it just comes on, huh silly me. Maybe it's relative and you get more the faster you go with The horsepower gain starting at the point the box pressure exceeds the vacuum at the top of the carbs, I might be wrong & I don't know what speed you would need to be traveling to pressurize the box but I do know it's better to have the air box together with the ram air intakes then it is to not have it.
 

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Hey smart guy, I did about ten minutes of research and found that ram air on a 7R starts to pressurize the airbox at about 40mph, it exceeds ambient at 60mph and peaks about 170mph now if only they had completed the test we would know what that's worth.
 

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so...your research consists of one example of one model of bike ?
very complete indeed...
 

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Actually Sport Rider tested about eight models from Suzuki, Honda, Kawasaki & Yamaha. Their research showed that Kawasaki was way ahead of the rest when it came to ram air induction and the 7R had an extremely efficent system. Unfortunitly they never dyno tested the 7R. Read it if you are interested.
Sport Rider-ram air induction test for sport bike motorcycles
I just posted what was relevant to the OP.
 

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The benefits of ram air are 2
1- fresh cool air...not hot air from under the rider seat, or under the tank
2- ambient air pressure or more...the old bike drawing air under the tank or seat - that area would be below ambient as soon as a bike is in motion.

I wouldn't count on a superbike air box kit to add much power...maybe a couple ponies way at top speed. You'll also have to relocate the ignition coils to install it.

Pistons and bore work will set you back ... unless you have a machinist friend to do it for cheap. When I had my zx8 (based on a 91 motor with 93 cams) it had a monster mid range. Make sure the machinist puts a new bevel on the bottom of the sleeves, or it will suck to install the block.

Head work...for drag use, just some nice blending work where the machine work for the valve seats meet the ports will net benefits....along with cleaning up any ratty spots in the casting.

Anything you do to suck in more air will take jet kit work. Jet kit...I wouldn't use on for drag strip use.

Rotating weight of the zx7r can be addressed... the rear wheel/rotor is a boat anchor (21#)....you could look at a zx9r (2000+ -16#), zx10 (15#) zx12/14r rear wheel. This will take custom spacers....or look at a 5 spoke marchesini from a ducati or aprilia.
 

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ram air does have an effect. .yes.. but theres so many variables it's almost a moot point.

"typically" all ram air starts "working" at 120, since you're eclipsing port velocity at WOT and starting the foce-feed. using bernoulli's principle, you'll find that most bikes never exceed 1psi of pressure at even 200mph.

but the air density and coolness is whats magic. at 40mph, it depends oin what gear you're in.. gear dictates engine speed. engine speed dictates lbs/hr or cfm needed. if you're getting more cfm than the motor needs, naturally you'll introduce "boost" and create power.
 
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