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Old 07-29-2012, 06:46 PM   #16
Strong Bad
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Quote:
Originally Posted by Twin-shocker View Post
Its really very silly for those who dont know how to waste time trying to "port" a 2T cylinder, when in most cases the squish clearance is going to be way out, and exhaust and intake systems are likely to be a very long way from ideal.
Squish clearance can only be way out in one way...too much, too little and you will be banging the piston on the head. Too little and your compression will be lacking. A stock bike's squish clearance is usually "in the hunt" and total compression is more of a concern than simple squish clearance. IMO that is.
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Old 07-29-2012, 07:28 PM   #17
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In my experience Yamaha squish tends to be around 1.7MM from the factory. They really benefit from correction.
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Old 07-29-2012, 08:46 PM   #18
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My friend Mean Dean Travis had both a fully tricked out FMF RM80 and a fully tricked out DG RM80. I thought they were both too pipey for their own good but it's damn hard to soup up a 80 and not make them too pipey. I agree that most people should leave their ports alone for just F'ing them up but then there are some of us that can actually port. Cleaning up ports does make a difference IMO but it really depends on what you start with. Back in the seventies, a lot of them came out of the crate looking like crap! Without changing the timing at all you could often get things flowing a lot better. The trick with the tranfers is to keep their "aim" right. I think a mirror polish on the exhaust does more than keep carbon from building up. It helps them FLOW. I use to get mine like a mirror and then every couple of tanks put the piston on TDC and clean them back up real quick for big payoffs! A friend of mine's dad use to polish the inside of his pipes with a frayed auto emergency brake cable. He said it made a noticeable difference and from my experience with exhaust ports, I don't doubt it although I have never tried it.

I know exactly what willis is saying about velocity over volume. I could look up the tried and true formula that proves this. More tuners should keep velocity in mind over volume but they don't. I grew up around short track races and I have seen SO many strokers tuned to a stand still for trumping volume over velocity. Most often by hogging out exhaust port height but . . . . High RPM power? First you have to GET to high RPM!!

supershaft screwed with this post 07-29-2012 at 08:54 PM
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Old 07-29-2012, 09:52 PM   #19
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In most cases correcting factory squish clearance (which is generally way off!) and paying careful attention to intake and exhaust systems, will make far more difference than any porting job, most of which will make bikes run worse, unless riding WOT at all times is intended.
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Old 07-30-2012, 05:17 AM   #20
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A good pipe will increase flow far more than "port matching" ever will.

After spending a decade (uhm.....two) with a (sometimes wet) Superflow 600 screaming in my ears I found finish does nothing to foster increased flow. As long as it has a smooth clean profile there's nothing more you can do. The boundary layer is up to 1 mm thick and cancels anything more than a smooth finish. You should see what a pitot tube does to flow.And that my friends is empirical not anecdotal evidence.
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Old 07-30-2012, 10:13 AM   #21
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Polished ports seem to work effectively in parting customers from quite large amounts of money, but do serve as a very good indicator to help avoid anyone suggesting this improves a motor in any way!
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Old 07-30-2012, 03:53 PM   #22
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When I was a kid we didn't have a flow bench but we did have a dyno. Maybe there isn't much difference between a mirror finished exhaust port and a mirror finished export that has been ruffed up by a bead blaster. I have never done that test. But I do know that a mirror finished export over most stock finishes makes a big diff and keeping it spotless makes all the difference. The exhaust port sees most everything twice and therein is the difference IMO. That and flowing exhaust very well might not show the advantage for everything going on in them velocity wise. The other ports don't deal with sonic and supersonic. You can't reproduce that with a flow bench.

Of course a good pipe over a crappy one will make a huge difference but that is beside the point.
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Old 07-30-2012, 04:34 PM   #23
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Originally Posted by supershaft View Post
When I was a kid we didn't have a flow bench but we did have a dyno. Maybe there isn't much difference between a mirror finished exhaust port and a mirror finished export that has been ruffed up by a bead blaster. I have never done that test. But I do know that a mirror finished export over most stock finishes makes a big diff and keeping it spotless makes all the difference. The exhaust port sees most everything twice and therein is the difference IMO. That and flowing exhaust very well might not show the advantage for everything going on in them velocity wise. The other ports don't deal with sonic and supersonic. You can't reproduce that with a flow bench.

Of course a good pipe over a crappy one will make a huge difference but that is beside the point.

Sadly even if the polished exhaust ports do make a big difference on the dyno, I wonder if this is really worth the effort as carbon will build up pretty quickly on anything other than a race motor which gets stripped very regularly, and the polished finish will then be gone?
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Old 07-30-2012, 05:28 PM   #24
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Originally Posted by supershaft View Post
When I was a kid we didn't have a flow bench but we did have a dyno. Maybe there isn't much difference between a mirror finished exhaust port and a mirror finished export that has been ruffed up by a bead blaster. I have never done that test. But I do know that a mirror finished export over most stock finishes makes a big diff and keeping it spotless makes all the difference. The exhaust port sees most everything twice and therein is the difference IMO. That and flowing exhaust very well might not show the advantage for everything going on in them velocity wise. The other ports don't deal with sonic and supersonic. You can't reproduce that with a flow bench.
Ever heard of a pitot tube? W/O using Google?

When does an exhaust port go trans sonic? Please show your work.
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Old 07-31-2012, 12:17 AM   #25
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Maybe the mirror finish port guy is someone ripping off gullible customers with this type of work? After all shine is much much easier than doing a job that might actually work.
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Old 07-31-2012, 09:37 PM   #26
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Putting you engine at TDC and taking off a pipe to clean up you exhaust port is easy.

No gullible customers involved with my findings. Just a couple of guys racing for our shop back the seventies.

Trans sonic? Explosions have trans sonic pressure waves. What do you think pushes a bullet to trans sonic speeds? But let's just stay with sonic for now. A flow bench can't duplicate that either. Surely you must understand that flowing exhaust is much further from what actually goes on in there in a running engine than flowing intake.

I don't know about new bikes but back in the seventies a good port job made all the difference in the world. Granted, most of them weren't good but that is beside the point.
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Old 07-31-2012, 09:55 PM   #27
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I don't know about new bikes but back in the seventies a good port job made all the difference in the world. Granted, most of them weren't good but that is beside the point.
Yes, I was talking about the old stuff, before it was possible to translate design to production easily.
I didn't find it necessary to alter port timing to get large gains of low-to-mid power.
It is also unwise to attempt to make race bike power from an enduro-style engine. But these can have fabulous, usable powerbands when set up properly.
Did anyone else mess with case reed intakes? I worked over a slug of an RM250's intake tract, it seemed like the case passage was an afterthought, advertising hype, or maybe it was difficult to cast. I made the case passage much larger, man, that bike made everyone jump back the first time it was started. It had a new bark from before, never did rev high, but the torque made it a real competitor.
I think it's about making the best of what you have.
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Old 08-01-2012, 12:16 AM   #28
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In regard to making the type of alterations to porting that seem popular in the world of those who charge top dollar for a polished finish, I wonder as it seems these guys know better than those who manufactured the bikes, why they arent working for the factories rather than offering 25-50% power increases to customers through crude hack jobs and polishing?
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Old 08-01-2012, 05:35 AM   #29
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Putting you engine at TDC and taking off a pipe to clean up you exhaust port is easy.

No gullible customers involved with my findings. Just a couple of guys racing for our shop back the seventies.

Trans sonic? Explosions have trans sonic pressure waves. What do you think pushes a bullet to trans sonic speeds? But let's just stay with sonic for now. A flow bench can't duplicate that either. Surely you must understand that flowing exhaust is much further from what actually goes on in there in a running engine than flowing intake.

I don't know about new bikes but back in the seventies a good port job made all the difference in the world. Granted, most of them weren't good but that is beside the point.
First of all you failed to answer my query. Try that first. When does the burning (hint hint) charge go trans sonic? Please show the math.

Now please tell me when the fuel/air charge explodes. Your failure to comprehend the events inside an engine is staggering for someone who claims so much.

Do yourself a favor and read and understand some Vannick,Mike Chapman or maybe Heywood before you enter into a discussion about combustion. At this point you're so absolutely clueless it's a waste of bandwidth. Nothing like a battle of wits with a buffoon.
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Old 08-01-2012, 08:13 AM   #30
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Hubristic theory is one thing, horsepower to the ground and being able to manipulate the power band where you want it is a completely different matter. NONE of the greatest 2 stroke motocross tuners of the 70's had anything more than a high school diploma. Back in the day, we not only gave riders more horsepower, we gave them horse power their riding ability could use. Donnie Emler's FMF had a great advantage in his first shop with the dirt road and lot next to the shop. He learned how to develop real world horsepower that would win on the track, not set speed records on Bonneville Salt Flats. Back in the 70's the speed shops who did well were the ones that realized that not all of their customers could used mega HP with a very narrow powerband the pros could ride. Their services matched both the pipe and the porting to the rider's ability.

Hard to lower the exhaust port bringing the powerband down into a lower rpm. The Power Valve that came in the 80's did exactly that, it allowed for a variable exhaust port timing. Increasing bottom end is easier done with a longer headpipe and/or center section with the pipe. Increasing the volume in your intake is what killed your torque.
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