When I ordered the Plus 4 the Plus 4 SS was in production. Morgan, I believe for reasons of homologation, refused to make me a left hand drive version of the Plus 4 SS and also refused to put the Mazda engine in a bespoke Plus 4. They did however agree to supply, via Aero Racing, the SS exhaust system.

Before I comment I would say that the sports manifold with the standard cat etc. That you describe as being a no-cost option would be quite different to the system fitted to my car. My manifold is quite long and the cat is under the right hand running board just in front of the silencer. This is said to be good for torque but has issues with getting the cat up to working temperature.

My experience is as follows.
Within 50km of picking the car up we had our first MIL (Malfunction Indicator Light). We were still at Malvern so we returned to the factory and they reset the error in the ECU. I must say that while we were running the car in I quite liked the sound and appreciated the bark when under acceleration. Around town it was quite acceptably muted but to too much smile

We continued to have MILs which I then reset myself using an app and a Bluetooth OBD2 dongle. We also had quite a bit of exhaust smell coming into the cockpit (a problem well known to Plus 4 SS owners before they received the ECU map upgrade). Various efforts were made by Morgan to resolve this problem including sending what was supposed to be a 400 cell cat which later turned out to be another 200 cell cat! They also supplied and paid to have fitted manifold wrap. Nothing really worked but I started to realise that the exhaust sytem, whilst providing a noticeable increase in power, was just too far outside the parameters that the ECU could cope with. The only answer would have been a re-map.

In the end I fitted individual throttle bodies and with careful tuning of the Omex ECU (that replaced the engine management of the original ECU) I was able to get the emissions to where the car would pass an MOT.

At this point jump forward 50,000 km and the exhaust smells returned. At this point I turned to an Italian cat maker that had been recommended by Heinz who uses one of his 300 cell cats on his 4/4, https://brainkat.it/en/

I was originally expecting to upgrade the existing cat with a new core however the owner of Brain advised me the the size of the Morgan supplied cat would, according to their standards, only be suitable for a maximum engine size of 1600cc. I then started doing a lot of calculations to work out the diameter of 300 cell core that would provide a similar gas flow to the existing 200 cell core. In the end I also opted for a higher quality coating on the core that would start to function at lower temperatures.

Amazingly I seem to have got it right and after the new cat was fitted I noticed a slight increase in mid range torque plus the exhaust note under acceleration and at touring speeds was slightly lower in both volume and tone. Definitely a bonus for touring where a load exhaust can be tiring. The fuel map was still within the correct parameters as with the smaller 200 cell cat.

After all that my opinion on the fitting the AR Racing Exhaust system with the standard cat is that because they are using the standard cat, and I must assume either the standard or a similar to standard manifold, you will avoid the problems with exhaust emissions, MILs and excessive noise. You probably only get slight or no noticeable performance increase but you will probably get a very enjoyable roar when you decide to put your foot down. Since it is a no-cost option I would go for it and at some point get one of the re-maps of the ECU that is offered.

Peter

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