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Old 12-13-2012, 09:03 PM   #16 (permalink)
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how is the stock exhaust port in stock form in your opinion?
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Old 12-13-2012, 09:13 PM   #17 (permalink)
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Originally Posted by CFM-Z440 View Post
I haven't got any yet, but I will soon. I'm working on The LTR head today. Basically, it looks like the bare epoxy, but with black over it. I get in too big of a hurry to remember to snap some pictures some times. I forgot to get pics of the stock exhaust port, but I've got some of the finished port. I may have to borrow someone else's stock exhaust port photo.


More info coming soon
Thanks CFM i've always wondered what one of your works of art look like ready to bolt on looking forward to what's next!
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Old 12-13-2012, 10:11 PM   #18 (permalink)
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I'm thinkin about goin bigger bore than the 474 kit. Now do you think just going bigger bore is better or do I go stroker? I know I've got to get bigger cams. One of the builders over on ltr450hq goes bigger on the valves. If I go to 100mm do you think I should get the bigger valves or stay with what I got?
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Old 12-13-2012, 11:10 PM   #19 (permalink)
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how is the stock exhaust port in stock form in your opinion?
The exhaust port took a lot of work actually for a 474. It might not be quite as bad with a 450. The port layout isn't bad, it's just smallish all the way through the port. Overall, the exhaust port got noticeably bigger. The Z head probably got just as much cut out of it. Yours especially for a 490 with +1's.

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Originally Posted by betterton_49 View Post
I'm thinkin about goin bigger bore than the 474 kit. Now do you think just going bigger bore is better or do I go stroker? I know I've got to get bigger cams. One of the builders over on ltr450hq goes bigger on the valves. If I go to 100mm do you think I should get the bigger valves or stay with what I got?
I'm not familiar with the LTR or it's quirks, but bore vs stroke when you're only talking 20ish cc's, I don't think you'd really tell the difference in either route. However 100mm is a a lot of piston, and makes a pretty wide combustion chamber, which is a little more prone to detonation, and might take a little more timing to make it really run. A high compression, dome piston can make matters worse and hurt combustion efficiency. You can't get by with quite as much compression per octane number either. You tighten your tuneability range that way.

The stroker is a little less headache (as strange as that sounds), but stroke limits rpm potential. If it's just a couple mm, then it won't make much difference, and if you already were staying within the 10,500 rev limit, the stoker won't hurt you a bit. The down side to the stroker, is they usually use a shorter rod ratio which wears pistons and cylinders faster, (but helps fight detonation) or you end up needing an expensive stroker piston.

Technically, you could (if it's all setup right, and doesn't bring on some combustion problem) get a little more horsepower from an all bore build, because you COULD turn it 12,000 rpm and still have a decent life span from it, if the valvetrain can handle it.

I would prefer +1 valves all the way around even for a 474. I would definitely go with +1 valves for anything bigger! To be honest, I think this head that I'm working on would benefit from +1 valves. Peak flow still isn't getting as high as the Z head. I know that a different valve seat profile can get it there, but it may have to give up some low lift flow to get it, and this is doing better than the Z heads at low to mid lift. With +1's you can gain across the board.

To run 490+ cc's with stock valves would shorten your rpm range. It creates a catch 22. It limits high rpm power unless you add bigger cams, which limit low end power. You can pick up better overall power with bigger valves.

I wouldn't waste your time doing any of it without porting though, especially on the exhaust side. A 490 would be really stuffed up trying to breathe through the stock exhaust port. The exhaust side especially has to completely change to make it worth the bigger valves.
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Old 12-14-2012, 12:19 AM   #20 (permalink)
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I was actually thinking about bigger valves but I just don't have the cash. Stage2 will be bigger cams and valves if it ever happens!
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Old 12-19-2012, 07:59 PM   #21 (permalink)
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Originally Posted by CFM-Z440 View Post
I'm not familiar with the LTR or it's quirks, but bore vs stroke when you're only talking 20ish cc's, I don't think you'd really tell the difference in either route.

One would think you wouldnt notice a difference with only 20cc's but my old LTR when i first got it was a 470 big bore with a 13.5:1 compression piston.

At the end of the MX season when i was doing my winter rebuild i Bought a ATP 14:1 piston and a new cylinder that was stock bore and you could definitely tell the loss in power even though i had jumped up the compression.

It could be because of the extremely high bump on the top of the piston that was contributing to the loss of power but im not really sure.

The motor with the 14:1 piston was also a ticking time bomb though
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Old 12-20-2012, 10:46 AM   #22 (permalink)
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One would think you wouldnt notice a difference with only 20cc's but my old LTR when i first got it was a 470 big bore with a 13.5:1 compression piston.

At the end of the MX season when i was doing my winter rebuild i Bought a ATP 14:1 piston and a new cylinder that was stock bore and you could definitely tell the loss in power even though i had jumped up the compression.

It could be because of the extremely high bump on the top of the piston that was contributing to the loss of power but im not really sure.

The motor with the 14:1 piston was also a ticking time bomb though

I wasn't trying to say that you couldn't tell a difference in 20cc's of displacement. What I was trying to say, is that weather you gain 20cc's with bore, or stroke, that they are close enough to the same thing that you wouldn't be able to tell which one was a stroker, and which one was all bore. The characteristic of a "high revving big bore", or a "torque monster stroker" would hardly be noticeable.


Also, high compression doesn't really add much stress to an engine if everything is done right. The hardest stress on the power train is during the power stroke, and a 55hp engine puts the same amount of force to the power train weather it's 12:1 or 14:1 Although, with the LTR I can totally see where there would be no gain from a dome piston. It's already got a pretty flat, wide combustion chamber. Sticking a dome in it would hurt combustion.
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Old 12-24-2012, 04:33 AM   #23 (permalink)
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Have you done any throttle body porting? I was looking at no loss throttle bodys but theyre so expensive itd be ridiculous not to port.
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Old 12-24-2012, 09:32 AM   #24 (permalink)
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Have you done any throttle body porting? I was looking at no loss throttle bodys but theyre so expensive itd be ridiculous not to port.
No, I havent looked at an LTR throttle body. Honestly, I think it's a bit too small on these big bores, so anything that can be done would probably help. Speaking from past experience with race car carbs, there is usually something to gain by thinning the shaft and butterfly, if that's what you mean.
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Old 12-24-2012, 11:11 AM   #25 (permalink)
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get rid of those screw heads on the butterfly shaft, those kill more than you would think.
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Old 12-24-2012, 11:51 PM   #26 (permalink)
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Still think im gonna have to send my head your way cfm when i redo my trans this winter trying to squeeze one more dunes trip in before i do. Ever think about doin TB work?
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Twist throttle
Cylinder works 474 kit
Stage 2 hotcams
Rpm ported head
Dasa exhaust
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Old 12-25-2012, 01:52 AM   #27 (permalink)
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Still think im gonna have to send my head your way cfm when i redo my trans this winter trying to squeeze one more dunes trip in before i do. Ever think about doin TB work?
It'd be fun to experiment with if nothing else. I could flow test it with and without the tb and see how necessary it is, and record before and after to get an idea of what can be gained.
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Custom Web Cams, with adjustable sprockets,
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DRZ Manual Decomp. CFM Motorsports porting,
HSR45 carb, Custom intake,
Barker's Performance Full Exhaust
Trailtech flywheel, Dyna Programable


Need a Barker exhaust system? Web Cams? Valves? Porting? Shocks rebuilt?
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Old 12-25-2012, 03:30 AM   #28 (permalink)
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Tempting.... Ill be getting with you in the near future on this!
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Noleen j6 rear
Atv fourplay mgc aarms
Streamline stabilizer
Koq +2 stem
Flexx barrs
Odi locking grips
Twist throttle
Cylinder works 474 kit
Stage 2 hotcams
Rpm ported head
Dasa exhaust
Bling star rotor and sprocket guards
Streamline rear disc
Ac nerfs
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Kms intake next
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