Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) ARP4 - First impressions.

I certainly appreciate the candid report PaulJ. It is interesting, My 3.5 +8 is not what a Morgan Sports Car is all about. A light weight Sports Car with no more than 2.0 ltr that performs is. One of My friends managed to buy one of the few 3.0ltr Roadsters available in the U.S. I drove this Roadster with the Owner aboard. He was aghast at the RPM's I was using to get a bit of performance. I tried to explain the "Sweet Spot" engines perform at. Poor Roadster, it is and will be lugged to death by the Owner. No explanation I could give helped the situation.

My DHC with ZETEC/Webber DCOE's rev willingly to 6,500 - 7,000 RPM for power. Believe Me this is not "State of the Art" stuff. We Americans are so used to large (lazy) engines, that We don't know how to drive a light Sports Car.

Button

Ooh! You naughty, naughty boy, look forward to seeing you in it.

You make some interesting points Button

Interested to hear more about your DHC !

With the different,wider, tyres fitted to the ARP4 22psi may be ok but on my car with the standard Plus 4 tyres 22psi it too soft and the car feels very squirmy on the road. 24psi is the minimum I use and I am much more likely to use 25psi and even 26psi when I have a heavy load.

There are a lot of debates on this subject but it comes down to what feels right for you.

OK! But I will start a New Thread.

Button
Seattle

I've tried lots of tyre pressure combinations on my 4/4 1.8 4 seater and when I'm on my own in the car I tend to prefer even lower than 22 psi which is the recommended

I was down to 18 on all four the other day and I quite liked it

Wasn't going fast though

Great

The Cosworth is tuned for speed with an increased power in high rpm. Generaly these motors have less power at low rpm and must be used at high rpm to get the benefit of the tuning.
In the case of the Cosworth the losses at low rpm are well limited, but the torque graph has a hole between 4200 and 4800 rpm. Increasing of torque and power rocket after 5000 rpm.

Compared to the standard Duratec 145 Bhp :

from 2000 to 2700 -4 Bhp -10%
from 2700 to 3000 +0,8 Bhp +1%
from 3000 to 3900 +3,8 Bhp +5%
from 4200 to 4800 -7 Bhp -6%
at 5500 +23 Bhp +16%
at 6000 +43 Bhp +30%
et 6500 +97 Bhp the standard Duratec has only 103 Bhp at this rpm, power decreasing dramaticaly after 6000 rpm.

The AR P4 seems to have the same Mazda gearbox than the PLUS 4 (to be confirmed) with a 3,9:1 rear axle but larger wheel 16 " vs 15 ". They have quite the same speed at 1000 rpm :

in 5th gear :

AR P4 : 38,7 km/h (24,2 mph)
PLUS 4 Mazda gearbox 38,2 km/h (23,9 mph)
PLUS 4 2005 40,5 km/h (25,1 mph) Ford gearbox

Real benefits come above 5000 rpm.

Thanks for the detailed infos, CBY, Re the tyre size and their influence on the final ratio, the use of 16 inch rims with the ARP4 is not so very dramatical because the corresponding tyres are lower profile ones...225/55/16.
If you compare this tyre diameter with others you get exactly the same all in all tyre diameter as a 4/4 165/80/15 or a Roadster Sport/Plus4Supersort 205/65/15.
Only the regular Plus4 tyre is a bit smaller in diameter when I recall correctly a 195/60/15.

The standard Plus 4 with 195/60/15 tyres is quite a bit lower than the 4/4 with 165/80/15 tyres. A radius of 307mm as against 322mm; a difference of 15mm. This explains why the Plus 4 is very prone to touch down on speed bumps. I understand they have had homologation problems in Australia because many have a clearance of less than the required 100mm under the centre of the car.

There is a useful tool to compare tyre sizes at http://www.1010tires.com/Tools/Tire-Size-Calculator but they have recently deleted some sizes not commonly available in the US of A.

There is another at http://www.tyresizecalculator.com/