Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) ARP4 "Handbook", and other useful information

My car has done around 500+ miles now, and I have also driven the factory car quite extensively i.e 300 miles or so in it.

The factory car pulls much more strongly at low revs in higher gears than my car. That may be down to the mileage. If I try to accelerate in 4th or 5th at below 3K revs my car simply gets much noisier with very little change in forward momentum! However above 4K revs mine really starts to come alive, and things get progressively more interesting beyond that! It's definately a screamer, and as mentioned previously I think would benefit from a lower final drive for road use to keep engine in power at typical sensible road speeds. It's not a quiet cruiser.

Conversely the Roadster always has power on tap even at low revs in top, and based on comparing the two back to back is a better touring car (at least would be with the better chassis/brakes etc).

Just my views of course, others will differ ...

It is not easy to translate but when he took delivery of his new arp4 he has tought that he will keep the roadster.At the end of
the trip he was very happy with the arp4 and will not keep the
roadster.The cosworth engine needs maybee a longer run in.He has
analysed the power curve of the cosworth again the 2 litres
duratech.Till 4000 rpm the power is almost the same .He find
also that the rear ratio has to be changed to reach the maximum
speed at the maximum poxer of 224 cv in 5th.

Thanks for that Thierry, all very interesting. I can't help wonder if the engine can't given longer trumpets and a 4-1 exhaust system, with a rolling road re-map to maximise the bottom end a bit to make it more drivable in real world conditions?

Or buy a Roadster


I too like Dave W would love to see a back to back comparison of the ARP4 & a Roadster.

perhaps the Cosworth engine needs at least 1000 miles before it comes alive.

I find it responsive enough beyond 3500rpm, but I haven't driven mine for 2 weeks.

Could the weak torque (if so?) of the Cosworth engine at low revs be caused by using the roller barrel TBs instead of butterflies? I'm no technical expert but I think the airflow is best at full throttle using roller barrels but the flow is more complicated in comparison with the butterfly system at part throttle.

I made estimates on the French forum in order to compare different configurations and motors on a PLUS 4 basis including the ARP4. I didn't have the ARP4 handbook and the estimates are made on a basis of 39 km/h at 1000 rpm instead of 42 km:h at 1000 rpm.

Have a look on the different charts, in French, sorry.

a small lexical:

courbe de puissance : power curve
puissance necessaire: power used for air and rolling resistance
rapports de pont: rear axle ratios
réserve de puissance: power reserve= motor power - power used (air resistance)

http://mog.vosforums.com/viewtopic.php?f=9&t=6817&start=500

post on february the 17th 2016 6:53pm

The concern is the final drive ratio. Maximun speed could be reached with the 4th gear.

A similar but different engine. The Plus 4 SS has a Mazda MZR engine with a variable inlet cam. I believe the inlet cam was changed to a fast road cam for the SS. The MZR VVC gives better torque at low to mid range. Also the Plus 4 SS exhaust is optimised for torque and the engine is not so highly tuned.

I certainly wouldn't mind having one in my car but I could not talk Morgan into fitting that engine into a bespoke car when we ordered ours.

Translated from the link above:

At first glance, the Cosworth power difference compared to the standard Duratec 2L (142 hp)

between 2000 and 2700 rpm -3 hp average for the COSWORTH (2700 rpm vs 61 hp 64 hp)

almost equal between 2700 and 3000 rpm

between 3000 and 3900 rpm +3 hp on average for the COSWORTH (3800 rpm vs 93 hp 96 hp)

between 4300 and 4800 -7 hp average for the COSWORTH (at 4600 rpm 113 hp vs 121 hp) the flattest part of the curve

The power shoots up from 5000 rpm:

+10hp at 5100
+23hp at 5500
+40hp at 6000

Any errors in translation are mine.

This means, that the Cosworth engine should be good for cruising purpose after running in, because the low rev figures are quite good when compared with the standard Duratec. And the standard Duratec is always good for cruising. I'm not sure if the gap in the 4K rev band is so essential but it could be noticeable...perhaps only when directly compared. Otherwise you have a good benefit of the Cosworth when revving high out. It would be interesting what the users will tell after 6000 miles or so running in. My 4/4 was really very tired when renting her for the weekend with 1.600 km on the clock. When I bought her as a demo car with 6000 km on the clock the engine was not to compare.