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I'm sure there's a great reason for this, but I couldn't find any answers.
Anyway, why has every bike I've seen had the carbs on the back of the cylinder, and the exhaust coming out the front?
It seemed to me like a logical idea for the exhausts to come out of the rear (straighter/easier to make pipes), and the carbs on the front (ram-air effect maybe?)
Educate me:D
Thanks!
 

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On a streetbike you need air filters. And you need room for the front wheel to move up and down, left and right. And you need the engine to be forward on the frame for weight distribution. Makes it hard to put the carbs in front.

I think the 1988-1990 Yamaha TZ250 had the reverse cylinders, with the carbs in front.
 

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I disagree..... have a few with forward facing carbs





quote:Originally posted by UngaWunga

On a streetbike you need air filters. And you need room for the front wheel to move up and down, left and right. And you need the engine to be forward on the frame for weight distribution. Makes it hard to put the carbs in front.

I think the 1988-1990 Yamaha TZ250 had the reverse cylinders, with the carbs in front.
 

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cause that is how Honda does it and that is all that matters.
 

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ive seen quite a few triumphs setup that way. not supposed to be worth the trouble i guess though. imagine tuning a bike to run on the starting grid, at idle, then at 100+ mph setup that way.

jc
 

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tuning them isn't for the faint of tuning ability

very few forward facing applications I see have open stacks

once you pancake filter them

you've made a tough situation much tougher and pretty much negated the only sensible reason for doing it
 

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used to be a semi common conversion to moto-guzzis. Ok maybe not even semi-common but I have seen more than one in my lifetime.

on a four cylinder inline motor, exhaust packaging is problematic because you have electronic components and fleshy rider parts next to very hot pipes.

there is also the issue of the loss of back pressure from getting rid of bends in the exhausts.

BTW there is no "ram air" effect on a forward facing carb unless you have a long and properly calculated intake runner. The front end of a carb is not very aerodynamic and most air will try to flow around it rather than through it.

if you want forced induction, get a turbo or a supercharger (or nitrous). from my limited experience with airplanes, "ram air" is useless under 150 mph, and even then it is worth maybe 2hp on top.
 

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who told you that?


and who told you that last stuff too? same person?


quote:Originally posted by Geeto67

used to be a semi common conversion to moto-guzzis. Ok maybe not even semi-common but I have seen more than one in my lifetime.

on a four cylinder inline motor, exhaust packaging is problematic because you have electronic components and fleshy rider parts next to very hot pipes.

there is also the issue of the loss of back pressure from getting rid of bends in the exhausts.

BTW there is no "ram air" effect on a forward facing carb unless you have a long and properly calculated intake runner. The front end of a carb is not very aerodynamic and most air will try to flow around it rather than through it.

if you want forced induction, get a turbo or a supercharger (or nitrous). from my limited experience with airplanes, "ram air" is useless under 150 mph, and even then it is worth maybe 2hp on top.
 

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the 150mph ram air number came from the Mooney Aircraft Corporation's Operators manual for the 205SE for operating the ram air under 10,000 feet. They give the number in kts, I roughly converted it. I have been in the plane when we have used it, yeah it makes little difference.

additionally I tested the ram air on my pontiac GTO on the dyno. We used a compressed air hose to shoot air into the ram air scoop while dynoing the car. The most we got was 2 hp jump with something like 50 psi. Chevrolet's only literature and testing numbers from car life in 1970 say the chevrolet cowl induction was worth at best 3-5hp and that was only at speeds above 120mph. While cowl induction is technically not ram air the principles are similar and actually CI is more effective.

really what I should have said was, results vary for each application, but ram air is only effective when you have a decent amount of pressure actually flowing into the carb. something you do not get at speeds below 120 mph. the effectiveness is also dependent on atmospehreic pressure. At altitudes above 10,000 feet the Mooney ram air is much much much more effective than below, and at less rpms.

as far as the backpressure issue, that came from a friend who did his own guzzi conversion and had a single piece of straight pipe as his exhaust pipe. he also had to do considerable in head exhaust port work which removed further restrictions.
 

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Oh, from your one very small and grainy picture and the other upside down picture, I can see just what you are talking about.

quote:Originally posted by HackAsaw

I disagree..... have a few with forward facing carbs





quote:Originally posted by UngaWunga

On a streetbike you need air filters. And you need room for the front wheel to move up and down, left and right. And you need the engine to be forward on the frame for weight distribution. Makes it hard to put the carbs in front.

I think the 1988-1990 Yamaha TZ250 had the reverse cylinders, with the carbs in front.
 

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FWIW, Cannondale built a mildly successful motocross bike that had the intake in front, exhaust in rear. I say mildly successful because it actually worked fairly well, was tested by the major mags and deemed close to the big four in performance. The company failed for various reasons, but the bike was pretty cool, a popular Supermoto choice.
 

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I recall reading a recent article, complete with dyno tests, on the very subject

seems it was a 1 liter bike (much closer to sea level than 10,000 feet) and there was a difference in 13, or more, horses if run with 130-ish mph wind stream merely pointed head on to the bike

cycleworld and done within the last year



a tiny-ish jet of compressed air isn't the same

and the thing about back pressure is totally illogical and just plain incorrect


the intake manifold on mine goes positive just over 70 on a decent day

the runner helps but it would do it, at some point, without the runner
 

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I wasn't really aware I was talking about anything ;)

anyhow, the larger pic isn't upside down (it's about 75 degrees counter clockwise and the small one isn't grainy at all.

is this your way of asking to see some other pic?


quote:Originally posted by mut

Oh, from your one very small and grainy picture and the other upside down picture, I can see just what you are talking about.
 

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Isn't there a problem with carbs icing up when out in the cold air? Hack, I'm sure you've said you don't have that problem but I'm sure it's one of the main reasons BMC put the engine in the Mini the way they did.
 

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I cut two loops off the slide spring..... the slide has never frozen and in 2005 it was my only transportation..... all winter long

carb runs quite cold... but not nearly as cold as the runner

very logical when you look at it



I snapped this pix Nov 2005 at about 6 am in the morning

had ridden 55 miles back from Nastyville and the ambient temp was just under 40

it had sat for right about 5 minutes before I could find my camera and snap this

somewhere I have some of it (the runner) frozen solid yet the carb isn't

and this has nothing to do with the carb facing forward..... and BMC hasn't ever done the same thing... backwards or forwards

the same would happen if it were backwards or stuffed between the cylinders

I think I have some frozen pix in a batch of slides Alan Mayes shot of it for IronWorks and his book
 

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Rob,
the problem with the reverse cylinder TZ's is that they sucked up stones from the front tires if you weren't careful about keeping your fairing lowers clean... the front mounted carbs are mounted really low on the engine... and no air filters of course.

Peace
karl
 

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quote:Originally posted by coreyjdl

backpressure is a myth.
LOL...like landing on the moon, or the earth being round, or its okay because she told me she's 18.
 
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