budget throttle bodies management

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apologies - only just had time to read through all this:

a log pot could be used as Wayne says, but I don't think there'd be a problem in tracing quickly across the sites as he says - at least not in running - but trying to map the thing would be awkward i suppose that's one advantage of certain aftermarket systems where the resolution for different parts of the map can be adjusted to suit the application.

the bodies are not the only reason for the throttle sensitivity though - you've probably effectively decreased the volume of air between valves and throttle(s) to 1/3, 1/4 or maybe less than what it was. Because of the elastic nature of air having to accelerate when a throttle is opened, this will naturally make a throttle closer to the valves more sensitive. This is one of their biggest benefits for those looking to engine upgrades - the rapid response. However, as we all know - nothing comes for free and there will always be some sort of trade-off.

cheers,
tt

 

Just to make sure Ive got it straight in my head is the problem with bike carbs the initial throttle plate angle and how much they flow for relatively little spindle movement or is it the rate of change of pot signal because of the fast opening?

 

A more elegant engineering solution than using a logarithmic pot would be to use a linear one and amplify its voltage output. Therefore you'd get the full voltage output swing over a smaller resistance change and hence throttle angle. You could even build a variable gain amp. This would allow you to adjust the gain to choose the throttle angles you wanted the map to respond to. The amplifiers output would need to be clamped @ 5V .

The one disadvantage is that there would be a bigger step (throttle wise) between the end of the map and WOT. However, the flow characteristics of a butterfly valve almost negate this.

 

Right than, what seems to be the problem here, steep angle butterflies or the pot it self? If its butterflies than the problem might be solved by use of secondary butterflies opening after the main ones, making airflow smoother, either by stepper motor or mechanicly. Gsxr1000 bodies have this second butterflies built in. Few mods to spindles would see them opening as required.

 

and don't forget - the throttle is only part of the problem. Even with a throttle fix it will never be as smooth as a standard set-up due to the reduced valve to throttle volume.

t

 

Could some of this be made up in the design of the inlet manifold ?

 

you could use longer runners but the design of the intake manifold will only affect smoothness in terms of equally distributing air to all cylinders

tt

 

Anyone? tt?

 

the large change in flow for minimal change in throttle angle is what Wayne is talking about

anyhow mate, what are you still doing up - you should be in be early for a full day job hunting tomorrow

tt

 

some interesting posts wayne,while weve still got your attention,whats your veiws on this topic on rolling roads,flywheel figures,atw`s&coastdown figures
http://www.clubgti.com/forum/forum_posts.asp?TID=23701&KW=G% 5FV%5FK

ps,there goes your early night

 

Here's one I prepared earlier....

Camber, toe, tyre width, compound, pressure, diameter, tread pattern, construction, roller separation, roller diameter and the weight placed on top of it all has an affect upon wheel power/flywheel power figures. So soes gearbox temp, oil, design, driveshaft angles..... the variables are endless.
Yes, it is the wheel power that moves the car along the road, but you are on a rolling road, not a real road, and on a rolling road your tyre is between two rollers (usually) and the contact patches are not at the bottom of the tyre and therefor camber causes scrub across the roller etc. etc.

What I am getting at is that the 'numbers' are for comparison only rather than an ipso-facto measurement and it will vary, sometimes by a lot, from car to car and dyno to dyno depending upon many factors. There is absolutely no percentage that you can add to wheel power to get flywheel power. A before and after comparison should be all that matters on YOUR OWN car.
Peak figures are also mis-represented often. It is the area under the curve through the rpm band that your gearbox forces your engine to use that matters in terms of outright speed. If I lift a rev limiter to a level higher than you might think the peak is at, it is usually because it will yield more area under the curve and will therefor net more outright performance.
Comparison is only sensible with total consistancy.

 

I remember ernie saying his was a bit jumpy on the throttle(2ltr 16v vauxhall kit car on bike bodies)proberly due to the above,then when he drove mine commented on how smooth it it was,I dont think Nick posts on here,not seen him or heard him for a while

 

The way that's going I shall have to get the spanners back out soon...........might be problems though I hear they've done away with points and SU's, what ever next!

 

lol - I adjusted a carburettor today, first time in aaaaaaaaaaaaages

 

Every new buiness needs a show car so i'm fitting a pair of these, that'll impress the boys!

 

if we need some electrickery to sort this out we can do some here, i'll set it as a project for the students

 

If the bike throttle shuts at a highish angle that must mean the butterfly plate is an oval shape? So what if you were to grind it down a bit to make it more circular, surely you could get it to sit at less of an angle at idle then?

 

FAR too many big words in this but sounds great all the same !

Great reading guys keep it going !

 

I don't understand much of this either but think I get the gist. GSXR750/1000 bodies from 2000 on (IIRC) have 2 butterflies, can't these be used to good effect as alluded to earlier?