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MG ZR ZS ZT Technical - ZS 180 modifications - update

Further to my previous posts on the subject of my testing of a prototype ITG induction system on my ZS 180, well with nearly 1400 miles since fitting I am able to show some interesting results.

The car currently has approaching 6000 miles and the period up to the fit of the ITG has seen an average consumption of 29.2mpg. Since the fit and operating the car over the same main routes has seen the consumption improve to 30.27mpg over 1315 miles.

Today I have also had an opportunity for the car to be run up on the John Wilcox Racing rolling road, both in completely standard form, (an hours refit of the original equipment) and in modified form. (another hour!)

Without listing every single figure, which for the total of six power runs, three for each spec, the overall seat of the pants feelings were confirmed, not quite as good as the similar kit for MGF, but then the induction system on the ZS is quite a bit better in standard form.

As an simplistic average the power was increased by 7% and torque by 6.8%. In more useful detail the 2000 to 4500rpm area, where so much driving is done showed an average increase in power of 9% and torque a smidgen under this. The ITG allowed top end power to hang on much better so instead of seeing a reduction of power from 6000rpm with standard, the power carried on up with a useful extra chunk at 6500rpm. The figures show an increase of 10.15% in power and 9.6% torque at 6500rpm. This could be left as it is and give a less than accurate impression as the peak power comparison between standard and modified, ignoring rpm, shows a gain of 5.77%.

Essentially there are many ways to play with figures, however there was a clear power and torque advantage over the whole tested rev range of 2000rpm to 6500rpm. One specific detailed run was done between 6000rpm and just under the rev limiter at 6750rpm to simply confirm that the power peak point as the tests with the ITG showed power was higher at 6500 than 6000rpm which wasn't the case in standard form. The power was tailing off at 6500, but testing in 500rpm blocks didn't initially show this.

The sound that the system makes is no different to standard unless the throttle is wide open and the revs are past 3000rpm. If so then the added acceleration is accompanied by a deep V6 growl that isn't dissimilar to some Turbo V6 Italian exotica!!

The results are on the whole very pleasing and back to back driving in standard and modified form shows the standard arrangement to feel 'lame' in response. I was actually expecting the power to show greater difference in the 4500 to 6000rpm range than was seen, with less in the lower rev range. Nevertheless it is good to see gains everywhere.

The results of this test have confirmed that ITG will now be developing a production version of the Maxogen induction system for the ZS 180 at a price to be fixed and a date to be arranged. It may help them to gauge demand for this kit it those with an interest were to perhaps send an e-mail to ITG registering their interest. They are currently very committed with several F1 contracts, as well as being the supplier for all BTCC entrants. The latter providing an interesting connection between the three MG EX 259 race cars and the road versions.

For those with ZS 120 models then the new system just coming on line from the 200/25/ZR should be able to provide similar results, with perhaps the exception of the ZR 160 which has a much better induction set up to start with.

Roger Parker

Anything for ZT 190 Rog?


Your modification sounds great.

How does it affect your insurance loading?

George Hunt

Hi Rog

can you let us know what ITG's e mail address is so we can e mail interest to them




I was using the principles that have already been used in the ZT 190. I quote from the launch material on the Z range.

"Begining with the induction system, the air cleaner has an 80mm diameter intake duct in place of a 70mm duct, and a new intake diffuser. This provides a smoother airflow with less than half the usual pressure drop; it has also been tuned for a more sporting induction sound. Internal engine changes include a new inlet cam profile, advancing the inlet valve opening by 4 degrees, and improved porting.

It continues further on with...

A further contribution to the performance boost comes from a new exhaust system with 60mm diameter pipework in place of 57mm, new low restriction metal based styarter and main catalysts and a modified rear silencer unit. This silencer has larger bore internal pipes, twin straignt tail pipes and a mechanical valve, which responds to exhaust pressure at around 4500 rpm to bypass internal baffles."

If you read through this as I did last year, it shows a clear path where all except the the 190 spec can benefit from. I have taken advantage of the improved airfilter route so far, and taking the 5.77% increase seen in peak power places the power within 2 bhp of that of the standard ZT 190. I didn't mention that the torque peak was at 4500 on the standard set up, 500 rpm higher than officially quoted, but with the ITG was at 4000rpm with an 8.8% gain, that would equate to 261Nm.

I mention these details to show why the 190 spec will see far less change than either a ZS 180, a ZT 160 or indeed a Rover 75. It is consequently very difficult to estimate what the differences would be on the 190. However we may well be able to see this in the future, as the benefits now measured on my car with the prototype system may well spur a desire from the Chairman, who runs a Rover 75 (2.5 litre), to develop a system for that. This will then be transferable to ZT.


Insurance issues have to be dealt with on an individual basis. Some companies accept these small changes others don't. I am lucky! (This is a common issue with MGF owners fitting the Maxogen and other 'performance' air filters.


Website is at and e-mail is


Roger Parker

>>I mention these details to show why the 190 spec will see far less change than either a ZS 180, a ZT 160 or indeed a Rover 75.<<

Ah ha! Thanks Rog, you've overlapped a question that was forming in my mind when I read your initial post. As an owner of a 2.0 litre 75, I am very tempted to replace the induction system for the fuel economy and torque benefits.

Whom should I contact about this kit for the Rover?
Rob Bell


In principal, I am very interesting in this kit. In practice, I am concerned by your comments in the other threads about the torque rating of the gearbox. If the kit gives a peak torque of 261Nm against a gearbox rating of 240Nm, that is enough to worry me. This is my only car - reliability has to rate above performance, or even thet better engine note (which is just as much a driver for the mods). Am I blowing this out of proportion?

Steve H


I thought the torque limitation was in the auto box in the 75 which is why the ZT automatic has the same power output as the 75 auto.




All gearboxes have a torque limit which the manufacturer sets to maintain his goals of reliable long terms service.


The PG1 in the uprated form fitted to the ZS 180 has a ceiling of 240Nm with a gross vehicle weight of 1900Kgs. If your operating with the vehicle fully loaded then the gross vehicle weight will be somewhat higher than the 1300Kgs or so kerb weight. Clearly in most circumstances you will never approach the upper weight, so a quite significantly higher torque level can be used with lower weights and no loss of reliability will be seen.

If you were to cross the threshold then the result would be reduced service life and not a sudden failure. This is much the case where high boost turbo conversions are pushing well over 300Nm in cars weighing around 1250kgs. Only after many miles do we see whining diff bearings usually, with perhaps complaining first gear bearings. It is interesting to note that the lower spec gearboxes used with such monster torque and nominally 250bhp also last remarkably well.

Essentially the limit is there, but it is not one that these mild improvements will cause a problem with.

Rob, I have little doubt that the ZT 190 induction system will be a straight swap for your 2 litre V6 items. In the same way I have no doubt that any ITG alternative will also be a simple fit. I do wonder if the lower volume of air the 2 litre draws will be testing the limits of the standard induction run though. This may reduce the gains seen with the 190 kit, but with an ITG kit the airbox is designed to accelerate airflow and so uses the airs own weight to ensure better cylinder filling. For this reason I expect your mid range will still show proportional increases to what I have seen.

Roger Parker

These mods sound great.

I've sent an email to confirm my interest in the induction kit.


Thanks for the info and confirmation Rog. Actually you raise an interesting comparison that probably only has interest to me alone - ie what would be the most economical swap in terms of power/torque/fuel consumption per spent: the ZT induction system or the ITG?

Hmm... I need to think about this a little more.
Rob Bell

This thread was discussed between 23/03/2002 and 02/04/2002

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