entropy
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posted July 06, 2002 02:33 PM
paging Y2KZX12R: valve timing???
Y2KZX12R,
I am going into the motor again and replacing the 1361 crank with a billet 1375. At the same time the stock cams are being replaced with Lee's cams & springs.
The builder did some clean up on the ports, and is reseating the valves. Interestingly, he radiused the lip on the cut around the intake valves much like you showed on a recent post (thanks for the pics  ).
My question is whether or not you might have some advice on valve timing for this set up. Lee said 105/107-109, then when I called him a few weeks later he said 106-108/108-112. This is quite a range and I am a bit perplexed....
Any hints????
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Y2KZX12R
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posted July 06, 2002 03:27 PM
Well, cam timing is a funny thing..... :)
Some things that work on one setup may not on another. Its trial and error. I have cam timing that no one else is running that I know of. Thats because of the way I chose to make the engine run.
So what I'm getting at is... what are you going to do with the engine? Do you want corner carving midrange and want to make your 12r feal like (dare I say it?) a Busa? Or is your goal having absolute peak power?
With a stock engine I gan give better advice. But your engine is a completely different animal. And you all ready have compression issues. So retarding the intake cam on that engine will drop the dynamic compression nicely.
The exhaust? Well, from the different cam timings I've tried to date on 1200 cc's I found that the zx12r, with the factory cams, likes to be 1 or 2 degrees apart on lobe sepeeration when you are running the intake cam at 104 (stock)or less. I've graphed the results using software and then compared to the realworld results. One of the programs I use can be skewed to be really friggin close. And the pedictions followed the real world amaizingy accurate once some peramiters are changed. Anyway, I've played with the numbers for the 1270 and 1361 many times but have never had a realworld test bike to skew numbers to make accurate predictions for those combos.
But 106/104 for the 1270 will give a very similar powerband to a stock zx12r. The curve will obviously be higher but very similar.
The 1361 having a different stroke is a bit trickeyier to predict. When you change the stroke of an engine several important things change along with the stroke. Like rod stroke ratio, mean piston speed, rod angle, swept volume relative to crank angle, piston acceleration, etc.
When you change cams it gets even worse. It creates huge numbers of variables like ramp speeds, mean port velocity, max valve window area, overlap, seat to seat timings, and of corse, cam centerline etc.
And that was your basic question.
What cam timing to run with that combo?
So, even with PC's and software, the best way to find the optimum cam timing for any combo is still trial and error. Sorry to say.
But if you do some dyno pulls with a known "blueprinted" engine. And then make some changes to the cam timing, and do another set of pulls, you can skew the software to MUCH more accurately predict any other cam timing for THAT particular engine combo. And thats where it starts getting fun.
But my short opinion is just an educated guess of 107/105 for a similar to stock torque peak rpm 1361 and factory cams.
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entropy
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posted July 06, 2002 05:27 PM
Y2KZX12R,
thanks for the lengthy reply; it is really appreciated.
What I am looking for is power at 9500-11400 for dragging. I really don't care if I lose hp below 9000 or so, in fact that might help me fight wheelies in 1st gear. I pretty much use the bike only for 1/4 mile and a few top end runs now and then .
Its such a pain to access the 12's motor, I'd like to get something close the with the set up the builder is putting together now.
I am OK with wrenches but haven't done any valve timing...
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posted July 06, 2002 06:32 PM
 Edited By: Y2KZX12R on 6 Jul 2002 19:35
Well if your builder has done zx12's of this combo before then he may know what works good.
Schnitz racing likes 105/105 with 1200cc and factory cams. At least I think is was Schnitz. Muzzy likes 105/100.
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entropy
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posted July 06, 2002 07:47 PM
Mine is the first 12 he has built, and I told him that Lee said 105/107-109, and he also said 106-108/108-112.
so I guess I should try 105/107 or 107/109???????
what would you guess would be the difference between these 2 options??? (or is there just no way to even guess directionally how it would go)
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ra12r
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posted July 06, 2002 08:02 PM
With those options you are lowering your compression because you are closing the exhaust valve later. You are retarding both your numbers and the exhaust even more than the intake. What are the numbers on your cams?! duration and lift?! compare those to the factory cams and then you will have a better gage. When you get your cams from Lee, measure them yourself to know what you are really getting. I have heard some stories about "special" cams and then they found out they were still the factory kawasaki zx12 cams.........just measure, then you will know for sure.
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entropy
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posted July 07, 2002 03:24 AM
ra12r,
thanks for the suggestion, I'll have the builder measure them.
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krexken
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posted July 07, 2002 04:30 PM
Don't know if it's any help but I went with the middle of the road settings he suggested, 105/107. Mine was peaking right near the limiter. The small cam of Lee's that I used had .015 more lift than the stock intake cam.
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posted July 07, 2002 06:12 PM
I agree with ra12r that 107 on the intake lowers the dynamic compression more than 105 does.
The exhaust valve timing is whats puzzling me.
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entropy
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posted July 08, 2002 03:32 AM
puzzling in what way (the 107 for exhaust)?????
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posted July 08, 2002 04:09 AM
I'm just wondering about overlap and scavenging. I never tried the exhaust that late on the 12r.
With such a big bore and short stroke on the stock engine, it seems late to me.??? Maybe it works well on that combo.?
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ra12r
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posted July 08, 2002 08:53 AM
Entropy, those are the settings that they use on the busa's with web cams......I have no idea why they have the exhaust set at a later degree than the intake, but it seems to work for the busa's.
I personally would love to see the research dyno's that muzzy has with the cams at all the different settings. That info is as valuable as the statement to put them at 105/100.
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entropy
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posted July 08, 2002 10:58 AM
Lee had his cams for the 12 ground at Web's; hmmmmmm.... At least they came to me in a Web's box, but it didn't say what the lift and duration was. I will call Lee's tomorrow and try again have him give me those numbers, then perhaps you experts (i sure ain't one) can point me towards a good direction.
thanks for your attention to this
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entropy
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posted July 09, 2002 08:51 AM
Edited By: entropy on 10 Jul 2002 04:55
OK Guys,
The specs on my "Lee's cams" are:
int: lift: .415, duration: 252@.050
exh: lift: .378, duration: 244@.050
Stock lift was measured at: int=.350, exh=.335
Lee said go with 106/108 for torqier response, 108/110-113 for peakier.
any comments would be appreciated. The builder is bolting the bottom end together right now, so time to decide on cam timing is today went with 106/108
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posted July 10, 2002 04:59 AM
Sounds like a plan.
Once you dyno it and get a repeatable power curve then you will have somthing to compare other cam timings to.
In any case you wont be short on power. 
Good luck
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entropy
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posted July 10, 2002 06:20 AM
Boing! Duh!
It just occured to me that you, the tech expert, are the probably same Jim which I talked to last summer about getting together in Conn for a beer and heat blanket. I got wound up with family stuff last year and couldn't make it. Too damn bad.  I would learn a lot talking to you I am sure.
The builder is talking just like you, that OK, put it together at 106/108, but run it in, do a dyno, then change it, dyno, reset, dyno... is the only way to get it "right"
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Y2KZX12R
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posted July 10, 2002 06:53 AM
Yea, I remember now. I didnt remember who it was.
Well. I'm up early on sunday AMs riding in the NW corner of CT,MA,NY corners. Usually RT-7 area. Sometimes RT-22 NY.
I have to avoid western Mass for a while.
Maybe I'll see ya up that way. I'm usually in a black Vanson suit, black RF-8, Sidi vert2, green 2000. Most likely riding with a blue 99 zx-9r.
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entropy
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posted July 10, 2002 07:50 AM
well, since I live in Houston... But, my parents and bro live in Charlton Mass, so I get up there now and again.
good choice on bike & leathers! (I also have a green 2000 and black Vanson suit)
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Y2KZX12R
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posted July 10, 2002 02:04 PM
Ok, I thought you were from NY.
Well next time you are in Mass drop me an email.
Yea I like vanson leathers. They are a bit heavy but well made.
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