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Discussion Starter · #1 · (Edited)
I was wondering if anyone can tell me what RPM range for peak HP for a 730 (with the other mods in my sig for my green V). I probably will be installing a tach this Friday and have a couple of clutch springs to try out but there isn't a dyno anywhere near me that I know of to tune it on.

I thought I had read somewhere that stock motors peaked right around 6700-6800rpms and that someone else had dynoed their 730 that had slightly ported heads and bigger carbs (I think) and it make peak HP at around 7400-7500rpms.

Any guess what RPM range mine would peak out at?

Would I want the spring to over-rev past that range buy a few hundred RPMs (or more)? I am really only concerned about what will make me the quickest in up to 500'. I don't really care about top speed because I won't ever ride as fast as it can go anyway. I want to be quick but don't care so much about being fast. :D
 

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Discussion Starter · #3 ·
That's it what I was guessing based on what I had read here in other threads. Do you normally want to over-rev a few hundred RPMs past that or try to keep it at your peak RPM?
 

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WEll I edited my last post because I wasn't sure if you had stock valves.

That's a question for John, he's the clutch wiz, it would make most sense to me to try and clutch for that RPM
 

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When I was building mine I talked to John about clutching and he told me for 300' drags I should be shifting out around 7500-7800. When I got it dialed in at around 7600 I could feel the difference from when I started in the low 7000's.
 

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I run a comet black and shiftout is at 7650.I ran a 5.2 in 300ft sand drags and that was my best time.
 

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Mine revs out to a little over 7850. This is with a JH Roller Clutch, Dalton Orange/Blue spring, in the sand with paddles.

On the NOS, it shoots up to around 9000. :D
 

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Discussion Starter · #8 ·
WEll I edited my last post because I wasn't sure if you had stock valves.

That's a question for John, he's the clutch wiz, it would make most sense to me to try and clutch for that RPM
Yes, I have stock valves (all new ones with the build). I may PM VFJ but I like to try to get answers from others as well. I am sure John is flooded with all sorts of questions all the time.


I run a comet black and shiftout is at 7650.I ran a 5.2 in 300ft sand drags and that was my best time.
I am not sure what it takes as far as HP increase to gain .455 seconds in 300' but I am hoping this 730 with the right clutching will do a 5.2 also. My best with my stock, bolt-on motor was a 5.655 with an EPI Almond spring and 24" 8-paddle Extremes.
 

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Discussion Starter · #9 ·
Mine revs out to a little over 7850. This is with a JH Roller Clutch, Dalton Orange/Blue spring, in the sand with paddles.

On the NOS, it shoots up to around 9000. :D
I guess I am curious if there is any point to having it rev more than a few hundred RPMs past the peak HP range. It seems like most 730's have their peak HP under 7500rpms.

I forget, where is the stock rev limiter? Is it 8000rpms or 8500rpms or something else?
 

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It would depend more on your cams than anything else.
 

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It's hard to compare my setup to yours. I run 36mm carbs. Have 1mm larger valves and my clutch is nothing like what most are running.

It loves the RPM range it runs in. As far as the 9000 with NOS, trust me you wouldn't complain.:D
 

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Discussion Starter · #13 ·
I was only referring to "over-rev" as revving past where a dyno graph would should as being your peak HP range. I would think you would want to keep it near that.
 

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I believe that John's other tidbit of advice was to have shift out about 200 rpm's below peak HP.
 

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get it to shift out 7500-7700 range and you will be very happy. 730's like that with stock heads or even a mild port running stage 2, 3, xx, or fundy race cams the same range or about 7700-7900 will work fine.

on +1.5 valve ported heads 8300 rpm is what I set them up for. on Bwoody's 70 rwhp 730 his shifted out at 83-8400 to get that power down. and that was all with stock carbs.

If your's is at 9000 you don't know the NOS performance you are missing by adding weight to the flyweights to bring down that RPM and convert that to forward power. but N/A performance would be hampered so it's a one sided factor on what you mainly do.

on NOS. get that weight up. just the power addition will make the motor rev 1000-1500 more just by pushin ghte button. so adding weight will shift faster adn go forward faster as well. nos is an absolute gain when you push the button.

JOhn
 

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Discussion Starter · #16 ·
Thanks John.

I'll work on getting mine in the 7500-7700 range with either spring changes or with heavier weights if I am revving too high.

Does your Stage 3 clutch mod make it rev higher because of the extra belt travel? I am just wondering if I will have to re-clutch it all over again if I get it dialed in before I do the clutch mod.
 

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Heavier weights it will rev LOWER. bad idea. especially for sand. you won't overrev it unless you run the 360 weights 47gram and a heavy azz apring.

use the stock weights 54 gram and a spring like the Polaris Yellow or Brown.

the stage 3 clutch will add approx 150 RPM over the stock clutch with the same weight and clutch setup.

it's a simple setup.

John
 

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Discussion Starter · #18 ·
OK. If I get my tach wired up tomorrow like I am hoping, I should be able to find out where I am at right now with my stock clutch, stock weights, and EPI Almond spring (w/2 shims) on Saturday on the ice. I have no idea where I am at right now.

When I am checking for shiftout RPMs, from a start I will notice the RPMs increase rapidly and then pretty much hold at a particular RPM, correct?
 

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Where does the stock CDI redline at on the KFX?
 

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Discussion Starter · #20 ·
Where does the stock CDI redline at on the KFX?
I just found an old post by VFJ that says the stock rev limiter is 8600rpms.

Looks like if anyone with a mildly built 730 is hitting the stock rev limiter, they would be WAY over-revving since I am being told the peak HP range is usually between 7300-7700rpms.
 
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