BigLee
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| posted on 2/4/13 at 07:20 PM |
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Supercharged MX5 throttle issue
Evening all,
I need some help diagnosing an issue I have on my MX5 with the throttle. It is a mk 1 1600cc with an Eaton M45 supercharger from a mini. I
didn't set it up so my knowledge isn't what it should be. There is a second throttle body that works in tandem with the primary one (the
same as what you would normally find on the inlet plenum of an MX5) that opens before the supercharger. This is operated from the same throttle cable.
There is also a bypass valve from a BMW being used (presumedly through witchcraft or something) to control the air going through or not through the
supercharger. From the charger it runs through a front mounted intercooler. It has the standard ecu with a greddy emanage blue as a piggyback to
control the ignition.
Anyway, I am no way complaining at what this car can do as it goes like stick on full throttle, and is docile enough when gentle. It's the
middle ground that's the problem. If driven 'normally' there is a massive stutter when is goes from boost to no boost, making me
look a little like a spaz who doesn't know how to drive. If I fully lift off when I reach my desired speed, it doesn't do it, only when I
gently lift off. Why is this? Fuelling? Cut off of air?
Secondly, and you may not get this, I'd like to turn the supercharger off every now and again. Obviously it's always spinning, but if the
bypass valve exists, surely it could be active all the time so no air is being forced in. Maintaining a constant speed is hard on the motorway when
the supercharger keeps kicking in. When this thing is whining, then it's accelerating. Also for roads with speed bumps it would be easier to
navigate without boosting between stops. Any thoughts on this greatly appreciated.
The only advice I've had so far generally revolves around spending lots of money on a standalone ecu which all in is £1000+ to do it
properly.
Let me know if you need anymore info.
Cheers
Lee
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mark chandler
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| posted on 2/4/13 at 07:36 PM |
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Not sure why you need 2 x TB's unless they did not remove the original to make it more responsive, may be easier to get rid as not really
required (it may however be running the TPS)
All you need is a TB infront of the supercharger, the exhaust from this goes straight through the intercooler to cool the air then straight into the
inlet.
The pressure bypass works on vacumn so when cruising and slowing down the S/C is spinning but not really doing much, when you floor it the vacumn
drops away and all air is compressed, high vacumn keeps it open, it should be plumbed between the TB and the S/C inlet.
No point turning it off, when it is not producing pressure it is also not using a huge amount of power, as it is unstable when cruising this implies
that the vacumn bypass is not operating correctly, maybe its sticking then lurching between closed and open or the mixtures and timing are way off.
[Edited on 2/4/13 by mark chandler]
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johnH20
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| posted on 2/4/13 at 08:28 PM |
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'The Knowledge' on all this can be found on the MX5Nutz forum. Look under the engine tuning section. I am not an expert on all this but I
think one of the advantages of the so called dual throttle is inlet noise control.
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rdodger
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| posted on 2/4/13 at 08:55 PM |
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I have run dual throttle bodies on my supercharged 5. The reason to use one is normally when an intercooler is fitted. The intercooler adds a lot of
unthrottled air as the throttle body is on the back of the charger. This leads to idle droop and stalling.
Moving it to the inlet manifold makes it so loud your ears bleed!
If you have no intercooler a dummy throttle body can be used on the inlet manifold.
You can tie the bypass open and the charger won't boost. That bit is easy!
The emanage should be ok with a MP45 and smallish injectors.
The stutter you describe may be due to an imbalance in the 2 throttle bodies.
To set them up you need to have the charger TB cracked open on the stop. Then adjust the cables so they move together and both open fully. As said
already said there is loads of info on this on NUTZ.
The dual TB was designed to run with a 70mm TB on the charger and the aluminium disc on the inlet TB was fitted offset to open the charger TB slower
but hit WOT at the same time.
I think if you can balance the TB's then it will help a lot. The emanage can be tuned too and that should help.
Reverant on NUTZ builds megasquirt specifically for the 5. I have one and they are very good. Price wise around £500. Dale tuned mine and it runs like
stock. Well stock with 220bhp 
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BigLee
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| posted on 2/4/13 at 08:58 PM |
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quote:
Originally posted by johnH20
'The Knowledge' on all this can be found on the MX5Nutz forum. Look under the engine tuning section. I am not an expert on all this but I
think one of the advantages of the so called dual throttle is inlet noise control.
It seems most on MX5Nutz run the twin throttle body setup. I just don't want to join a new forum to ask one question. I know a few on here are
familiar with supercharger setups. So long as I can smooth out the transition between 'on' and 'off' supercharged power
I'll be happy. 
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rdodger
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| posted on 2/4/13 at 09:05 PM |
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quote:
Originally posted by johnH20
'The Knowledge' on all this can be found on the MX5Nutz forum. Look under the engine tuning section. I am not an expert on all this but I
think one of the advantages of the so called dual throttle is inlet noise control.
The DTB are always noisier than single TB. Half the battle with set up is getting rid of the electric sounding whine.
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BigLee
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| posted on 2/4/13 at 09:05 PM |
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quote:
Originally posted by rdodger
I have run dual throttle bodies on my supercharged 5. The reason to use one is normally when an intercooler is fitted. The intercooler adds a lot of
unthrottled air as the throttle body is on the back of the charger. This leads to idle droop and stalling.
Moving it to the inlet manifold makes it so loud your ears bleed!
If you have no intercooler a dummy throttle body can be used on the inlet manifold.
You can tie the bypass open and the charger won't boost. That bit is easy!
The emanage should be ok with a MP45 and smallish injectors.
The stutter you describe may be due to an imbalance in the 2 throttle bodies.
To set them up you need to have the charger TB cracked open on the stop. Then adjust the cables so they move together and both open fully. As said
already said there is loads of info on this on NUTZ.
The dual TB was designed to run with a 70mm TB on the charger and the aluminium disc on the inlet TB was fitted offset to open the charger TB slower
but hit WOT at the same time.
I think if you can balance the TB's then it will help a lot. The emanage can be tuned too and that should help.
Reverant on NUTZ builds megasquirt specifically for the 5. I have one and they are very good. Price wise around £500. Dale tuned mine and it runs like
stock. Well stock with 220bhp
That's great ta. I am running injectors from the 1800cc so not huge by any means. I did plan on putting some adjustment in the cable to the
second TB, using something like cable adjusters from bicycle brakes, then small adjustments are easy. I was hoping it would be something as simple as
that.
Funny you should mention the Megasquirt, it's something I've been looking at. I'm only running about 180bhp at the min so would be
happy to take it to 200bhp+ with stock drivability. Did you get yours mapped pre install?
How do I keep the bypass open?
Lee
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rdodger
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| posted on 3/4/13 at 08:05 AM |
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You can just tie the bypass open with a bit of wire.
My Megasquirt is a MX5 specific plug and play. It is enhanced to idle up when A/C, P/S activate etc
Spec
* Digital alternator control, tuned to output 14.4V
* Battery voltage light (steady on when engine not running and voltage > 11V, blinking slowly when engine off and voltage <11V OR engine
running and voltage < 13.5V, blinking rapidly when engine is running and voltage > 15.5V.
* Proper idle valve frequency through hardware multiplication: 488Hz
* A/C idle up function: the car will never stall again when you switch the A/C on
* Going WOT or over 5000rpm switches the A/C off
* Both fans turn on with the A/C
* First fan turns on at 96C, second fan turns on at 101C (configurable through the MS)
* CEL flashes slowly when coolant > 101C, flashes rapidly when coolant > 105C, is steady on when coolant > 110C
* Power steering idle up (when parked and turning the steering wheel)
* Fans turn off when VSS>120Km/h, unless seriously overheating (coolant > 110C)
* Idle valve completely off unless speed < 15km/h OR transmission is in neutral OR you are pressing the clutch pedal (helps engine braking, avoids
early overrun fuel cut ending)
The new ones have dual map, launch/boost control Knock control etc.
It came with a base map that was good enough to drive the car to Dale to get it mapped.
[Edited on 3/4/13 by rdodger]
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