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MG MGF Technical - Differences between 120 and 135 engine varients

A nice technical question for you, as in the subject:

what ARE the engine difference between a 120 (as fitted to Stepspeed) and 135's?

Could they be retro-fitted?

I know about the PTP 140/160/... options that Roger looked into.

Neil. (bringing a ZS120 Step demonstrator to Silverstone in addition to NNW49 - the Astra's just gotta go!)

I don't think that the differences between the engines are that significant Neil - perhaps if Rog has time he might be able to identify the specific changes and part numbers.

In summary, from what I know of the differences they consist of:
New 52 mm throttle body
New inlet (and exhaust?) cam
Alloy inlet plenum (as per MGF VVC)
New air box (same pattern as MGF Trophy160)
New exhaust
New version of MEMS

As far as I know, all of the above can be fitted. Of these, the TB and the alloy plenum are easy fits.

The TF exhaust can be fitted if you fit an elbow joint adapter between the catalyst and the exhaust (assuming that you have a pre-2001 model MGF) - plus you'll need some kind of actuator of the "loud pipe" valve. If you decide to fit the new MEMS, then no problem, but the cheapest option here would be to attach a cable to the valve and open it manually from a lever in the cabin! ;o)

The new cams are probably not an economical proposition from the standpoint that they'll cost nearly as much as Piper BP270 cams that'll provide you with up to 30 bhp more power with the appropriate ECU. The combo of BP270 cams plus Emerald ECU is about a grand. No idea how much a new MEMS plus TF135 cams would cost. I'd go for the Piper option preferentially.

If all you want is 135 bhp from your 118 bhp K-series, then this is relatively easy to obtain: K&N air filter (or ITG's maxogen or Mike Satur's Viper kit) plus exhaust (Mike Satur Daytona etc) plus 52 mm Trophy throttle body and 135 bhp is in your grasp.
Rob Bell

But is the gearbox able to take advantage of the extra BHP? presumabley the gearbox is designed to use the revs at maximum torque for the 120bhp engine and the 135bhp variant has a diffrent sweet spot.

Will Munns

The PG1 gearbox is the same one specified for use with the Rover 220 Turbo 'Tomcat' - so power and torque handling simply is not going to be an issue... with respect to gear ratios, doesn't the 135 share the same ratios as the 160 now?

Probably would not be worth retro-fitting to an MGF - as there are more closely stacked ratios available should you so wish ;o)
Rob Bell

arn't we talking about the CVT gearbox here?
Will Munns

Ah! Of course, you are right Will! Thought Neil was thinking about his MGF for some reason! Neil, you are asking about modifying a car you haven't so much as bought yet??? ROFL

I hope that your wife was able to get the car back to the sales bod in time...

As we are talking about the stepspeed, two things to be careful of: engine speed and torque. Not sure about the absolute limits, but exceeding the torque loads could lead to a collection of worn out transmission bands... :o( Is there anything about these figures in the archives or on the net?
Rob Bell

So my question still stands, the CVT transmission keeps the engine at constant rpm whilst accelerating, presumably at the max torque for the 120bhp engine, if you stick in another engine with better breathing(which is the only diffrence on the moderatly higher bhp engines?) then the top end is quicker, is there a significant gain at the rpm the CVT system uses?

Will Munns

Hmm, interesting question Will. Peak power and torque aren't altered all that dramatically with either a filter or an exhaust fitted, so no problem there. I don't know what shape the power curve is with a TTB fitted, but it can't be that much different from standard. If the peak torque and power is developed at the same rpm say, 5%, then the programming of the stepspeed in auto mode need not be altered.

Fitting pipercams however (and perhaps even the 135's cams) is another kettle of fish.

Fortunately there is manual mode to get around this, but I know that that is not the point.

Mild 'standard' MGF tuning mods are unlikely to phase the gearbox, and give you close to the 135's power output. I reckon that this would be the way to go on the Stepspeed.
Rob Bell

I wonder whether the new EDC3 ECU will provide any power improvement. I believe it just may do the opposit.

Though, still courious whether the new OBD ECU can be read out and programmed with other equipment then only 'Testbook'. That would be a great advantage :)

Dieter Koennecke

This thread was discussed between 19/07/2002 and 22/07/2002

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