ESE's works engine tuner

[richban]

Interesting to watch your progress with the intake and how such a small change in length makes such a real difference

I think we are chasing the same thing Peak torque at 12000rpm.

[bucketracer]

The compromise in plenum volume is as follows:

A larger volume leaves more available air to the engine within its reach, and so long as this air can be replenished in time through the intake system, then the engine never has to work hard to get intake air because there’s always enough of it sitting there in the larger plenum.

As the plenum volume gets smaller, it becomes easier for the engine to rapidly consume all of the air in the plenum and thus it would have to spend a lot of effort (after the initial draw of air) trying to suck air in all the way through the entire intake system to stay alive.

The problem with a larger plenum is that it hurts throttle response. Throttle response is very much affected by throttle pressure (or in other words how fast the engine can consume all the air in the plenum and create a significant amount of vacuum in the manifold to draw in fresh air). The smaller the plenum (or smaller the runners), the higher the gas velocity, the faster the pressure drop, the sooner the new air rushes in, the faster the throttle response.

This usually leads to an oddball design by most OEM’s of an oversized plenum wit h a smaller throttle body and runners to try to boost gas velocity, or an undersized plenum (that will be consumed faster for better response) but with a larger throttle body that will not bottle neck the engine as it tries to pull in more air from the outside to stay alive at higher flow demands at higher rpms.

http://www.superchargerperformance.c...anifold-design

[Henk]

OK going out on a limb here and proposing something that is probably idiotic and definitely stretches the rules as far as they can go.
Would it be possible to feed the plenum with a CV carb as big as you like with the butterfly locked at wide open or removed so that the metering is controlled entirely by the slide and vacuum in the plenum, then put a legal sized choke in the plenum feeding into the cases controlled by the throttle cable.
Not sure how you would control the valve in the plenum in such a way that there is no massive air leak causing a possibly fatal lean condition. As I said, probably idiotic.

[richban]

OK going out on a limb here and proposing something that is probably idiotic and definitely stretches the rules as far as they can go.
Would it be possible to feed the plenum with a CV carb as big as you like with the butterfly locked at wide open or removed so that the metering is controlled entirely by the slide and vacuum in the plenum, then put a legal sized choke in the plenum feeding into the cases controlled by the throttle cable.
Not sure how you would control the valve in the plenum in such a way that there is no massive air leak causing a possibly fatal lean condition. As I said, probably idiotic.

Just change the rules.

[TZ350]

Would it be possible to feed the plenum with a CV carb as big as you like........ so that the metering is controlled entirely by the slide and vacuum in the plenum, then put a legal sized choke in the plenum feeding into the cases

CV carb opens in proportion to the vacuum in the plenum, self adjusting, yes that is interesting, thanks Henk....

I will hold onto that idea, it could become usefull, a plan "B".

[TZ350]

This gives me hope, I estimate, my plenum is five times the engine capacity.

"30 years ago not much was known about the relevance of plenum volume although it was generally considered that it should not be too large or responsiveness would suffer, which is still true. It is now known that in a tuned, single intake, plenum induction system, top end power increases with the volume of the plenum. Ten times engine capacity would not be too big - indeed bigger still would be better, though rather impractical."

From http://www.jagweb.com/aj6eng/technics.php

This article also points out that for a forward facing intake, at 150mph the air pressure is 0.35 psi, so not much supercharging effect to be had from pointing the carbs intake into the wind.

[TZ350]

The plenum chamber past another test today, we had our first major backfire without any engine damage, the blow off plate did its job.

With some jetting changes I was able to improve the carburation. With some more work I think I will be able to dial the carb in and get it all running properly.

Everything has had to be richend up compared to the conventional setup. Interestingly it does not spit much fuel out unless you give it more throttle than it needs then it gets the Blllarrrs and spits fuel 450mm, yes, we measured it.

I also think that for a motor that peaks at 9500 that using a std GP125 disk valve for an inlet timing of 145/60 205 duration with a 34mm port diameter is too wild. I may have to make some milder rotary valve disks.

I have found you can’t give this engine a big fist full of throttle, you have to dial it on carefully, just like a 70's TZ. But it takes off on a ¼-1/3 throttle with the same enthusiasm it used too before on full throttle. So by the time I can get it onto ½-3/4 throttle the end of the drive is coming up faster than I like.

There are still a few flat spots in the carburation but I expect to get them dialled out ok. The bike is still on Taupo gearing and even holding it in 1st gear, and using 1/3 throttle it’s just to fast for the drive. To finish setting up the carb I will have to change the gearing or find a quiet road some where I can get it onto full throttle and revved out.

It might just be the “excitement” talking, but I recon it’s faster than before.

I am sure looking forward to "Dyno Time".

[TZ350]

Just change the rules.

NOoo...no no no ...we are so enjoying the challange of the 24mm carb restriction, and now think we have cracked it. Water cooling would be nice, although we think we have a good handle on the cooling issues too.

No rule changes, unless its that FXR's are only allowed one front fork leg.

[Buckets4Me]

I will hold onto that idea, it could become usefull, a plan "B".

dont you mean plan "R" ????
you tried plan B some time ago
I think the copper was plan"K"

[Henk]

No rule changes, unless its that FXR's are only allowed one front fork leg.

Right I'm off to design a single sided, carbon fibre, hub center steering setup as a contingency plan. might as well make it 2wd while I'm at it.
Actually that would be cool, shame I don't have the talent.

[Pumba]

Now there was a photo on the FXR site that would be apropriate about now but buggered if I can find it. Bust just imagine how easy the changes to wets would be.

[jasonu]

Just change the rules.

Or run a water cooled 100cc...

[TZ350]

It's a slide show, downlodable PDF, about the theory of 4-stroke inlet tuning, check the "rule of thumb" second to last slide.

For 2-strokes just half the runner length. www.not2fast.com/gasflow/Lecture08.ppt

Maybe more for 4-strokes but lots of interesting stuff here:- http://www.not2fast.com/

[bucketracer]

Or run a water cooled 100cc...

I suspect Dad thinks it's too easy. and is married to the idea of a 125 air cooled

[bucketracer]

Abstract

Naturally aspirated racing engines have tuned intake systems and can now achieve volumetric efficiencies in excess of 125% and peak engine speeds in excess of 18,000 rev/min.

Engines designed for single seater racing commonly dispense with the intake manifold and its convoluted and restricting flow path preferring single lengths of pipe feeding each cylinder separately.

An investigation into the intake process on a single cylinder racing engine has shown that inertial ram effects make a strong contribution to the intake process at high engine speeds whereas acoustic resonance effects are more important to the rather weak wave action that occurs at low engine speeds.

http://www.sciencedirect.com/science...8eeba5bf0b4fe2