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BaldiGit

Bike Throttle Bodies. A Fuel Regulator Question?

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Hi, can anyone out there who has modified there engine to fit the Suzuki throttle bodies, answer me a question on the fuel regulator... Like where do you attach the vacuum tube?

 

There are 2 small brass outlets per throttle body, after the butterfly plate (valve side). So I'm thinking either a common link between all 4 throttle bodies, or would just one give a better result?

 

Just to clarify what I'm doing.... I have a set of Suzuki GSXR750 throttle bodies, of which I have made a manifold to fit them on a Ford RS2000 16v (type14) engine. I'm using the RS injectors, fuel rail and fuel regulator and wondering the best place to shove the regulator pipe :sorry: . All this is in a GBS Zero.

 

Any advice would be appreciated.

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I don't have specific experience with the bike bodies/regulators. But, on bodies like Jenveys and typical malpassi-style fuel pressure regulators, I know most people don't bother, just blocking it off with some bent hose. If you do connect to multiple bodies, make sure you put non-return valves in as I believe the pressure will be positive and negative on different bodies at different stages in the engine cycle, causing issues with balance and not accurately operating the regulator diaphragm. But, as said, I believe the effect of air pressure on the fuel regulator is negligible in places like the UK... maybe someone with precise experience of these bodies can comment.

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IMO There seems little logic in using a map for fueling a normally aspirated engine and then allowing variable fuel pressure controlled by the combined vacuums from four intakes. It is more accurate to map load/revs with temperature correction and all the transients at a fixed fuel pressure. Barometric correction, weather and altitude, would have a separate table fed by a baro sensor just as intake air temperature does.

Leave the vacuum tube off and block the stubs. I ran gixer bodies with omex 600 and the regulator worked very accurately. Steady 3bar.

 

Nigel

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Thanks for your replies.

 

Originally the regulator was attached to the inlet plenum of a single throttle body standard Ford setup. I assumed that it not only adjusted for atmospheric pressure but also the load on the engine. I can appreciate that a decent map could tweek the load correctly, but surely it would be better attached for those occasional jaunts up a mountain in a thunder storm..... Also I'm using a Microsquirt ECU and I don't think a barometric sensor is the norm. Or have I missed the point somewhere?

 

I have a question about using non return valves... Surely it will build up a vacuum and it will then stay a vacuum. As it cannot escape...!!! Wouldn't that be the same as blanking the pipe off..??? Or am I misunderstanding you. Maybe you mean between each TB to stop pressure cross contamination?

 

I'm not against blanking it off, but if I was to connect it...... Just one or all 4 linked and why?

Edited by BaldiGit

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Originally the regulator was attached to the inlet plenum of a single throttle body standard Ford setup. I assumed that it not only adjusted for atmospheric pressure but also the load on the engine. I can appreciate that a decent map could tweek the load correctly, but surely it would be better attached for those occasional jaunts up a mountain in a thunder storm..... Also I'm using a Microsquirt ECU and I don't think a barometric sensor is the norm. Or have I missed the point somewhere?

 

I think if you were that fussed you'd be better off setting up the ECU to compensate for baro but, if like you say, your ECU doesn't offer this option then you're a bit stuffed. I've heard of more hassle using the regulator compensation - contamination in the diaphragm/etc.

 

I have a question about using non return valves... Surely it will build up a vacuum and it will then stay a vacuum. As it cannot escape...!!! Wouldn't that be the same as blanking the pipe off..??? Or am I misunderstanding you. Maybe you mean between each TB to stop pressure cross contamination?

Ah no, I see what you mean - no, not in the main run between the regulator and the bodies, but between bodies. Or just don't draw vacuum from multiple bodies - just take it from one, is the simple answer (but then I suspect the vacuum drawn may be less, so if the regulator was calibrated to a single plenum on all 4 cylinders, you could argue this would be equally pointless).

 

I'm not against blanking it off, but if I was to connect it...... Just one or all 4 linked and why?

I don't think it matters. Well, I've never done it, but applying some reasoning...

If connected to just one body, the draw on atmospheric is being created by just two cylinders (presuming the take-off is into both tracts on a single body), drawing through 2 holes (with 2 throttle valves in them).

So in 720 degrees of rotation the engine will 'suck' on that pair of ports twice (each cylinder will do it once).

If connected to both bodies (all 4 inlet ports), in the same rotation you'd have twice as many cylinders drawing against the throttles, but you've got twice as many inlet ports and valves to draw through anyway - so I'm thinking the net vacuum will still be the same (provided one bank can't draw any air from the other, which I suspect would be negligible anyway).

 

So I suspect blank off the one set of bodies and just draw vacuum from t'other. Mind you, whether the vacuum drawn on a pair of ITBs is calibrated the same as the single plenum that your regulator used to run with, I have no idea.

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I can appreciate that a decent map could tweek the load correctly, but surely it would be better attached for those occasional jaunts up a mountain in a thunder storm..... Also I'm using a Microsquirt ECU and I don't think a barometric sensor is the norm. Or have I missed the point somewhere?

 

Oh, by the way, the regulator compensation is not really for barometric pressure - it reduces the fuel pressure when you're idling, because the manifold vacuum is at it's highest and the vacuum within the throttle bodie can 'draw' more fuel out of the injector than at higher RPMs where the manifold pressure is less. By disconnecting, the pressure regulator will deliver a constant fuel pressure - higher at idle engine speeds than with the vacuum connected... but, as Nigel says, a decent map will compensate for this anyway. This is probably why everyone I've ever seen moving to throttle bodies has just left it blanked off - they've always had to go to a specific custom map anyway by way of the throttle body swap, so any differences due to fuel pressure have been catered for in the mapping session.

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That was what I thought the regulator was for and I was a little thrown by the mention of barometric pressure....!!!!

 

The TB's are individual not paired, and expanding on the fact that the regulator only needs to sense idle (max vacuum). In hindsight I can't see it mattering if it's one or all 4. And come to that why it would be necessary at all..?? Was it maybe the fact that the original ECU was a one size fits all with a basic map, and the regulator compensated a bit?

 

But I still don't understand why you would need non return valves. I can only see that making the matter worse as once the vacuum has been established it can't go anywhere. And the regulator would be constantly in a low pressure state.

 

Also I'm told that a MAP sensor is a waist of time with TB's and the ECU just uses the throttle position sensor. The rest is down to the ECU map. Although I am going to use a wide band lambda which should help.

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Hmmm, maybe you're right. Maybe I've got my wires crossed somewhere along the way :) it was a comment I vaguely remember during a chat with someone. <heads off to google, but can't find anything backing up the premise>... oh well...

 

You don't need to use a MAP sensor, no. My competition car just runs a TPS but then that's been driven balls-to-the-wall everywhere so refinement at partial throttle openings isn't really top of my list ;). MAP's are bit awkward on ITBs, but I believe can deliver a more refined performance for 'road' cars. Never used that myself; always used just TPS.

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Another idea on the RS2000 forums is to use a small chamber (hence the fuel filter) and a restrictor ( a MIG welding tip) to smooth out the pulses. But I think they have somehow got the standard ECU to work with MAP and fuel regulator attached to they're chamber. Sounds a little dubious....

 

I think what I will do is make up a chamber and attach the MAP. But have tube blankers in my pocket on the day. And ask the guy who's going to set it up for me how he wants it.... Can't loose that way (last famous words).

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Indeed. Trust the mapper, do it how he recommends, then anything that doesn't work out is his fault ;)

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Sorry if I have sown seeds of confusion. As I understand it and on a quick read of the microsquirt pages the ecu can use MAP/MAF or TPS to sense engine load. MAP has the advantage of being sensitive for load change at small throttle openings where TPS is less sensitive for small openings but more sensitive for large ones where MAP's sensitivity is poorer. Depending on your application you may want to use either (or both if your ecu can handle using both).

MAP is commonly installed in induction systems where there is a single throttle body and a plenum feeding four intakes and reads the pressure in the plenum. It can be installed where there are four throttle-bodies by piping a take-off from each of the manifold runners on the engine side of the butterfly's individually into a sealed plenum chamber and reading the vacuum in that plenum with the MAP sensor. No valves and the plenum will have five air pipe connections in a 4 cylinder engine and will give a good usable MAP signal. I would not use MAP from a single runner of four throttle-bodies. Pressure pulsations will be more pronounced at low revs and the MAP in each runner is individual and may not give an accurate figure for the other three runners.

When running the ecu will look up a map of fuelling written using load and rpm. It then makes corrections to this depending on sensor input and correction tables written for each sensor. Common corrections are for engine coolant temperature and intake air temperature. Additional correction can be made by a barometric sensor and this would be useful in a country like Switzerland or in a blown application. Not very useful in England although in mountainous areas of Wales or Scotland you might fit it. Further the ecu will also have special/correction tables for altering fuel in special situations such as start routine, idle and transients such as acceleration/deceleration.

With all that under accurate control of the ecu a vacuum device altering fuel pressure seems like a crude addition.

Interestingly your microsquirt ecu can take a baro sensor input on pin 29 of the plug. Also the MAP sensor itself takes a baro reading at start-up and uses that as it's reference barometric pressure throughout a run.

 

The purpose of a vacuum operated variable fuel pressure regulator is to maintain a fixed pressure differential between the fuel pressure and the manifold pressure. Manifold pressure can be read as load. A map can be written for the engine using a fixed fuel pressure regulator. A different map can be written for the engine using a vacuum operated variable regulator. Either will work fine. Most tuners prefer to use a mechanically adjustable fuel regulator, set the fuel pressure using a fuel pressure gauge and map with that.

 

Nigel

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Nigel you put me to shame..... I have put off reading the Microsquirt manual in detail, but should knuckle down and give it a good read.

 

Thank you for the info, that seems to cover all the bases. I think I'll make up a small plenum and attach the MAP sensor as I feel it might be more driveable around town etc.

 

I'm more after smooth driveability than raw power. The only reason I went down the TB's route is because the standard injection system just doesn't physically fit under the bonnet...!!! The Car when finished weighs a little over half a tonne. So the power to weight ratio is getting near supercar anyhow. Any more power would be like putting LSD in a rottweilers dish suprised.jpg

 

Maybe I should look into a manual fuel pressure regulator. I would hate to have to get it setup on a rolling road twice because the original wasn't stable enough...

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