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MG MGF Technical - Alterrnative throttle body, update of the week

unfortunately the related thread has gone already to the archive.

Anyway, me lucky presents the re-worked Opel C20NE part:

Nearly ready ;). The bracket and adaption plate was done from 1.5mm and 2.5mm aluminum sheet metal. Ball joint and throttle cable adapter got shortened and screwed together. Drawings to follow, as promised.
Works will go on next weekend.
I only still need to re-wire the throttle sensor (swap the connection) and drill/screw it to the new made adaption plate in the applicable angle.

I'm without the car for the next week, cause it is at the workshop for 20.000km service. Whole week, cause I'm employed 300km apart.

Complain related to a sticking throttle and this should be fixed. I hope they will install the MY2001 throttle. Though, I'll remove it later and can sell it ;). Fuel tank change got advised also.

PS. have collected some more throttle bodies for later sales ;)
Dieter Koennecke

What on earth is this. I want some. Dave.

Dave, you've gotta midget, do you ?
Suppose it will be to huge for a Midget and a throttle position sensor is also to hard stuff for it ;)
Dieter Koennecke

This throttle has a diameter that is a full 6mm greater than the standard 49mm...

Up shoot will be the potential for more air into the engine (Le Mans and WRC cars run with throttle restrictors designed specifically to reduce power) and potentially more power.

Very interesting idea Dieter (as usual!!!)

A couple of questions:

1. Will the fueling be adequate for the additional air flow the throttle will provide?
2. Will the rest of the air intake system be adequate to make the most of the extra air entering through the throttle (ie are there other restrictions in the 1.8i/ VVC inlet track/ plenums)?
3. Will the MEMS be able to cope with and provide fuelling for the additional air flow?



PS I gather that the Trophy 160 has a larger-than-standard throttle body- anyone know the throttle diameter for this?
Rob Bell

I find it hard to believe that a 49mm orifice provides a significant restriction for a 160bhp engine (let alone a 118bhp one). For example the Porker 911 GT3 car produces 410bhp with a 43.1mm restrictor. In 1976 Formula 3 cars used a 23mm restrictor which limited them to around 165bhp. Current F3 cars use a 26mm restrictor and produce around 210bhp.

Mike Bees

Fair point. Afterall, do not WRC 280+ bhp cars run with 49 mm restrictors?
Rob Bell

Interesting Dieter, I may well got for this as I have a permantly sticky throttle anyway.
Will email you.


no answers due any of the questions. I only can assume that the speed of air to the manifold will decrease.

>1. Will the fueling be adequate for the additional air flow the throttle will provide?
Dunno, but assume what Rog mentioned due additional mods to the manifold (VVC intake manifold to add to the MPI). Remapped ECU should follow at any time if works got ready.

>2. Will the rest of the air intake system be adequate to make the most of the extra air entering through the throttle (ie are there other restrictions in the 1.8i/ VVC inlet track/ plenums)?
Guess not, thats the reason why I try to follow Rogs works :)

>3. Will the MEMS be able to cope with and provide fuelling for the additional air flow?
As mentioned, only a few air more if applicable, so no problem and not much advantage. Later I'l add also the power boost valve and the VVC inlet track.

I miss a fourth point of unknown terms.
That flap has a non linear opening curve related to the accelerator pedal movement. Means that the last 45 degrees open very quick on accelerating. Wander what diffrence this will make. I hope it will not only result in more fuel consumption, though.

Suppose there will no remarkable power increase as discussed already the other week.

But who cares, I'll only copy things which where done already at the Elise. :) .. and sold as new by a German Elise Tuner for lots of $$$$. (300 GBP)

I'm sure that the needle bearings at the flap axle will never again result in a sticking flap. That parts runs smooth like a cat in the dark.

So wait with patience. I'll report what I can find out and let the ride behavior cross check by more experienced drivers. September Treffen is near.

Gareth, one reserved 4you.

Dieter Koennecke

Keep us posted Dieter. Remember to port and gass flow the cylinder head and fit a nice free-flowing exhaust manifold! ;o))

Remember- always something else to do!
Rob Bell

Rob, Psst.... !! not so loud, please ;)
If 'she' reads it I'll get problems.
Had to dismantle the airfilter already cause of 2much noise. That was my contribution due to the Milltek installation agreement with the wife.

2expensive 4me

Dieter Koennecke

I can see possible problems with part throttle fuelling rather than full throttle. This because the engine managment operates on principles of manifold depression and throttle angle. At a given throttle opening the airflow allowed past the throttle will be greater than previous. So to still cruise at a given speed would need the throttle to be closed slightly.

MEMS will be looking at the throttle opening and fuelling accordingly. The manifold depression will have some compensating effect but overall as part throttle is always the worst part of any mapping cycle I see the greatest potential for upset being here.

Full throttle and full power needs to see very significant engine and power changes before remapping becomes a requirment.

Roger Parker

I thought the MEMS only used throttle angle for transients, i.e. accel/decel. fuelling?

Mike Bees

there is also a pressure sensor (MAP)inside of MEMS.

I assume that the 'Bosch Motronic' works in the same way or nearly the same. There should be related documents anywhere in the web. Carl mentioneed already some points to look for in an email.

Rog, I'm with you in the partial throttle open case. Anyway, I'll write down all measures and experiences and report them later. :)
No question, the Exchange of the existing to the GM body will be done without damaging or cutting anything.

CU tomorrow afternoon ;)
Dieter Koennecke

Hmm, is everybody sleeping or on vacancies ??

Anyway, here is the best I found (in Russia) ;)

Check No. 1317 and No. 13, the Throttle Potentiometer :)
The inlet manifold pressure sensor (No. 2) is included in the MEMS box as at our MEMS1.9.
Dieter Koennecke

JZX3491 has 3 Connections
1 YP (C159-9) yellow-purple / VE+
2 YG (C159-8) yellow-green / WIPE
3 KB (159-30) pink-black / Sensor ground

resistances in idle position
1 to 3 is 4.48 kOhm

1 or 3 to WIPE resistance in idle is
1-2 4,48 kOhm
3-2 is 0.76 kOhm

WIPE resistance, same in full throttle is
1-2 is 0.68 KOhm
3-2 is 4.05 KOhm

Voltage if ignition on. Between WIPE and Ground is

2-3 is 0.7 Volt in throttle close position
2-3 is 4.31 Volt in throttle full open position

Now the mechanicals.
If I attach the sensor in the same resistance position to the larger diameter body than the sensor is located nearly inline with the fixture holes.
BUT !!!
The sample I saw at the Elise is NOT inline attached. This means that the Voltage in idle is higher at that sample than at the MGF standard (O.7V)
Also the full throttle voltage will be higher than the above mentioned 4.05 Volt

And now the question of a more or less stupid guy ;)

We know about two sensors which have main influence on the fuel-air mixture.
-The inlet manifold underpressure
-The throttle position
- (crank position also but can be left out here)

Underpressure raises if the engine revs higher, is it ?
Underpressure gets also influenced by the throttle position, is it ?

The underpressure will be lower in case of using the GM throttle body cause the throttle body has a much larger diameter. I think the pressure difference to the inlet manifold will be lowere at last at full throttle.

How in heaven does this work together ?
Should I just follow the Elise installation and increase the input voltage to MEMS ?

Any suggestions on how I should carry out tests are welcome.

Dieter Koennecke


I see this is 'my thread' ;)

Problem solved, cause it wasn't a problem. Just my own madness.

The 0.71 Volt is a must, cause it controls the idle revs of the engine to 800 revs.

After having installed the GM body and all brackets and hoses and joints I started the engine and realised 1300 revs in idle mode.
Made the sensor screws loose ... and suddenly the revs dropped down by 100 revs. Slight movement of the loose sensor moves idle revs up and down.

Now I adjusted the throttle sensor to a position were the idle revs are 800 (app.)

Going out for a car wash and nice ride now.

Happy (currently)
Dieter Koennecke

Whow !!!

left the car wash out but tried the car for a 45 miles motorway ride.
It's amazing !! Can't explain what that thing really does, but I have the feeling that the car got more torque in any way. Acceleration seams much quicker. The engine revs like hanging at my foot. I wonder whether this relates to the non-linear distance change from the accerator cable to the gear segment at the throttle flap axle. So it may result in more fuel consumption ;)

Tried to prove this 'more torque' feeling by reaching top speed in 5th gear. Unfortunately there was to much traffic today and I always got stopped by slow riding Golf and other crap on the motorway. Anyway, top speed seams not changed. My car did the 5800 revs before on a plane Motorway with 'wind from rear' and I assume it will not have increased. Downhill is another case ;)
Next test will be on monday when I go again 100 miles eastwards to the workplace.

BTW, looks cool, does it ?

Dieter Koennecke

Hi Dieter.. (Long time no see!)

it sounds amazing!

I just wish you were here in NZ. so you can do it for me!


When it's fully done please post the 'installation / modification of throttle body with part no.' on your site!

I would get those parts, and pay someone to do it for me. (of course with your instructions)

Grin. Thanks


Hi Dieter,
congrats to the throttle-swap ! Sounds as this will be the next comming conversion for the "Green Frog" then.. I assume that if fuelling is not altered too much by fiddling with the pot. angle the benefit will be torque (faster acc.) and not so much horsepower (higher top speed ). E-mail will follow when I have scanned thru "Test-Book" for angle / voltage reading for the standard pot. Back to work tomorrow -so parcel will soon be on its way... Well done !

Best regards , Carl.

Dieter - if you're getting the same speed relative to revs, then top speed will not be altered, provided the engine will still rev through the full range with the new body: all the drive ratios are the same, aren't they?

Ed Clarke

Ed, no question.
May be a misunderstanding, though. I don't measure top speed by looking at the speedo, cause its not exact enough. Measuring top speed in 5th by rev meter reading is much more precise. I think if top speed increases than there must be more power. But we assume and also Rog mentiones the other week that there will be not more horsepower with a larger intake diameter.

Dieter Koennecke

Nice one Dieter- the installation looks very professional and tidy. Your feedback regarding the improvement of the engine's 'responsiveness' is very interesting. Well done!

Obviously your experience with fuel consumption will be equally important, but what *I* really want to see now are some rolling road power curves. From what you describe, this simple 'bolt-on' modification (no dumming down of your installation- all the very best ideas are the simplest ones!) I would guess is probably giving you at least an extra 5 bhp/ 5 lb.ft to be so palpable. The shape of the torque curve would be very very interesting to me (at least! ;o))
Rob Bell

Ah. Top speed isn't a result of the rev limiter then - I thought it was :-)

E (never got to top speed yet)
Ed Clarke

> The shape of the torque curve would be very very interesting to me (at least! ;o))

For me also. :) May be I find a cheap solution to let it measure at any time together with some other chaps for comparisons ...
But at first I wanna add a cotton fabric airfilter to the standard airfilter box. K&N or Green or BMC or thing like that. I removed already the connection hose between the airfilter box and the IMO useless resonator box and replaced it with a cold air pipe which leads downwards to the left air intake. Not direct into, but to the direction only.

The set-up would than be:
- panel replacement filter with short way to cold air
- GM throttle body
- Milltek Exhaust

I suppose the limiter can be applicable in 5th gear at a tuned VVC only (on revs, not on speedo reading). The 1,8i would be very heavy tuned if such car reaches 7300? revs or what in 5th... *grin*.
I assume topspeed at the 1.8i with 6400 rtevs and downhill or slightly more would be a great target without chang
Dieter Koennecke

There should be some interesting top-speed figures (or close to top speed anyway) gathered by Roger Parker who used a radar speed gun at the recent Bruntingthorpe Social Motorsport day organised by the MGCC F register. Roger stood almost at the end of a two mile straight and took accurate speed readings of us blasting by with foot to the floor. My own (VVC + ITG air filter + Phoenix exhaust) F registered 115mph on his gun when my speedo was showing around 124-5ish. Continuing past him and still accelerating my speedo topped out at 132mph before I had to brake. With the error of the speedo then this would equate to around 120-122mph true speed.


Congrats Dieter,

This work proves on which level you're playing.... way above mine.
Two questions for you:
1) Does the revs drop quicker than on a standard engine?
2) For when is the production planned ;-)


Dieter, you could try getting hold of an AP22 timing device. Okay, it is not as accurate as a dynometer or other professional test equipment, but it is capable of recording reproducible data that could be very interesting (acceleration times, estimated power and torque etc). As it is a removeable box, it can be transfered from one car to another relatively easily for comparisons.
Rob Bell

Dieter - you misunderstood, I wasn't saying that the MEMS only use throttle angle. When I said "I think the MEMS only uses the throttle angle for transients" that's exactly what I meant, the throttle angle is only used for transients it's not used to index the main fuel/ignition maps. The MAP sensor is used to index the map.

By 'transients' I mean the extra globs of fuel that the engine needs when the throttle is snapped open (and extra -ve globs when it's snapped shut :-)

Mike Bees


many thanks for your kind additional explanation. Of course I didn't get what you said.
Now it comes clear. Guess thats it.
Fits also to my experience while I tried to adjust the idle revs.

Anyway, I wonder what will happens if I join a MOT test at any time with that flap related to Exhaust gases etc. (Dunno the test name)

I just got a link to a german language installation guide for the throttle body from R.E.D.

Rob, where in heaven should I get that device ;) It's more expensive with 180 quid than any other more important stuff for the dark side :) Have you got one ?

Erik, you should try it yourself. IMO revs can't drop quicker, cause the drop is more related to the stepper motor. But that's only a guess. I assume Mike and other speciallists will know better.
I only can say it drops better at my car, cause it doesn't stick like the old one. No production from my side :) Stuff gets to the webside.
Do you wanna raw second hand body for own works ? Have some at home from purchasing more than I need and also options to get more :)

Dieter Koennecke

No, but I know someone who has Dieter... ;o)
Rob Bell


Seeing Dieter pull of this great throttle body trick, might give us the extra kick in the but we need to give it a try ourselves. On the other hand,... he is a mechanical eng, we are not (at least I ain´t). I wonder how easy it is to mess things up when playing around in the engine bay at this mechanical level? Looking forward to Dieter´s installation guidelines to judge if I can or can´t.



compared to what you already fiddled at your car, this is a 'game'. Only four screws.... *g*, OK and the hard to get individual additional parts ;)

>No, but I know someone who has Dieter... ;o)

Err, ;)
.. but I just got the message that the German ADAC (like AA) makes power tests for members for 13 quid only ... *g*... and my son is a member :c)

FAO Mike,
discussion wents on also at our small German Forum. We've got a mechanics student who looked up the files from old Bosch ECUs. Nikolaj mention about the growing developments over the years. I still assume that it can't be much different to the MEMS ECU. Physics is the same, is it.

Stage 1 (Bosch Jetronic) had a switch only at the flap to indicating whether there is idle mode or full load. Required acceleration data came from the air intake 'vacuum' sensor.

The only early stage with a throttle sensor he found was the (Mono-Jetronic). This one had a Potentiometer that on one hand indicated the current position of the flap but also the gradient of opening or closing speed. That sytem hadn't any 'vacuum' sensor.

Now the MGF has both like any of the later but early Motronic ECUs.

We wonder whether to less fuel gets to the engine under full load cause may be the vacuum sensor indicates more pressure (less vacuum) than with the standard small diameter.
Anyway, Nikolaj has got one of the second hand parts and will hopefully soon test it together with his already installed power boost valve at his VVC.

Dieter Koennecke

Fantastic- look forward to seeing those result Dieter. Out of curiousity, what effect, if any, is there on the exhaust emissions? CO/HCs still within limits?

It'll also be interesting to hear about Nikolaj's experiences :o)

Rob Bell

I'm quite surprised that the rather simple idea of fitting a bigger diameter throttle body for more power and torque seems to be new to most of you! At last some kind of usefull K-Series tuning that comes from the other side of the channel ;-) !
As Dieter already mentioned bigger throttle bodies are offered by at least 2 companies here in Germany one of which just sells those worked-on Opel/Vauxhall/GM parts, and they don't come cheap! So thanks to Dieter for paving the way to a great DIY solution! I will try it on my VVC as soon as I have the time and I will then tell you about the results. Rolling Road tests of several Elise VVC owners have shown that typically around 165 bhp can be achieved on a VVC with a larger throttle body, free flow Kat and Exhaust and a decent cotton air filter, the throttle body being said to make the biggest difference subjectively. Now I still have the standard Kat and exhaust but I do have a power boost Valve fitted which at least one of those german tuners says gives you the possibility to extract the full potential of such a bigger throttle body because it enables you to adjust the amount of fuel going into the engine accordingly, so that the engine allways has the best mixture (slightly rich at around Lambda=0.9). We'll see!!!

Mate you need to translate your documents for desperate english language chaps !! ;)öhung.htm

Translators like reply sh*t only.

BTW, I had a call with Matthias P. this morning. He wants to keep the GM body I forwarded. So good hope on professional made assembly brackets and Poti-flange. OK, he's busy, so it wiil last some time :(

I do another set of home made brackets, but they are for Gareth. Now I miss aluminum sheet metal 1.5mm or 2mm thickness (150x140mm) and 3mm thickness (30x70mm) ;)
Dieter Koennecke


Better get yourself a VTA-n°, to get "legal" in the throttlebody business.



BTW. Doesn´t the (P)FBV only work at full throttle. So completely open valve. The extra air coming in(cause of the larger diameter) at anytime (except full throttle) won´t result in an extra amount of fuel injected by the FBV. Does the mems correct at this point??


David, anything that is not full throttle will be corrected by MEMS through the Lambda sensor, so you'll always have the "correct" mixture of Lambda=1. On full throttle the lambda correction is disabled and you can adjust the mixture to a power boosting lambda=0.9 via the Power-Boost-Valve. Also when opening the throttle quickly the lambda correction should be disabled for around 2 seconds in order to have a richer mixture for enhanced engine response, so in that case too, the PBV is allowed to work its magic ;-)
Dieter, I should have written everything in english right from the start, now it would be quite a lot to translate, which is a bit demotivating... but one day I promise....

>I should have written everything in english right from the start

Haarrr, Haa... you are on the way to getting a 'true engineer'.
Thinking, why should I put hands to anything twice which I've already done or found.

can't get VTA-n° ?? ... wanna LOL 2.
Please gimme a hint.

>opening the throttle quickly the lambda correction should be disabled for around 2 seconds in order to have a richer mixture for enhanced engine response

I assume this is what I found ?
Dunno, but I like these 2 seconds pressure to my back. :))))
Dieter Koennecke

Hi all,
totally agree with Nikolaj - FSE-boost-valve DOES make an improvement! The slight hesitation on lower revs dissappear and also some more grunt at upper revs starting at around 5500. But remember : No improvements on a pure stock engine ! A good airfilter and probably also sport exthaust system needed. With or without cat seems to be less of a problem as at least on my VVC no real gain noted. Made some tests before and after MoT (MoT needs the cat - at least here in Sweden!)but honestly couldn´t find any diff. I think Rob wrote something similare some time ago...
Anyway - will closely monitor what happends when my VVC gets equiped with big bore throttle-body.
My first tests with enrichment was some time ago - before fitting the FSE. I then just blocked the return-hose during acc with an electric one-way valve. Was a bit cruel but did work fine. After that decided to fit a FSE-valve. Unfortunatly one has to measure any changes in exthaust gases with a separate lambda-sonde because during acc. the "on-board" one is of no use. MEMS does in one way or another "insert" a pre-choosen voltage instead of the "true" measured one under those moments of MEMS out of loop work.

Regards , Carl.

This thread was discussed between 05/08/2001 and 18/08/2001

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