Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Morgan need to give the new Plus 4 more power

Remapping can make a big difference. I had the chip changed on my Alfa 75 Twin Spark years ago. There was no noticeable improvement in outright performance but the torque characteristics were much better - many bends that had previously required second gear could be taken in third.

Absolutely right ! Masses can be done to the fantasic duratec 2 litre engine , that's why I bought a plus 4 duratec !

Had words with Nick Potter - the caterham specialist I use- about improving torque and power and his comments were to put in R400 cams (and then get Northants to do set up to keep torque at around 4k revs which I haven't done yet .) Supercharging is a very good next upgrade , possibly next year , power is then at mid range rather than 7k revs - 30% increase in power allowing for 20 bhp take up by charger ?

CBY / Meabh
To give you an idea - I use custom ratios of:
2.2:1 - 1st
1.54:1 - 2nd
1.21:1 - 3rd
1:1 - 4th
0.87:1 5th

4.1:1 rear diff

205/50/15 rear tyres

This gives use of the full box (just) on longer circuits and a useful 1st at the back hairpin at Curborough. This gives a theoretical top speed of something like 130mph maxing out on top (from what I can remember).

It also means that between shifts the rpm drop brings the next gear in just as the engine comes "on cam". Makes the gearbox fully usable at sensible speeds whilst making the most of the engine dynamics. Many Morgan's could benefit from this rather than the obvious more power.

For road use I would even drop 1st to 2.39:1 to make pulling away slightly easier... With some analysis you'll be able to see how the saloon based gearboxes often used are not ideal for a lightweight "sports car"..... With Morgan often using the final drive in the diff to tune the gearbox to he car - this does not help with ratio suitability within the box though - meaning it often ends up under geared at one end and over geared at the other.

Often described as making 2nd and 3rd usable and 6th for cruising. Turning and 6 speed into effectively a 3 speed - jag anyone?

Don't forget that the Plus 4 SS uses a Mazda engine with Ti-VCT. This means twin variable cams that allow the cams to be phased to give better torque at low revs. Even before Omex laid their hands on it it was a more powerful engine than the standard Duratec which is in the same family of engines.

CBY/Cerealsurfer/Peter.

This is such an interesting thread. Today here was dry with a light breeze so I popped out to look at the 4500 rpm/mph relationship. I was able to effect two runs on straight roads (it was lunch time with no one about much).Anyway 4500 rpm achieved an indicated 110 mph ( and it was still accelerating hard) so given a speedometer error of 8% lets say that still means approx 102 mph. There was not enough road room to reach the rev limit of 6500 but I know that it will reach that in fourth though I have no track experience to see if it will reach that in fifth. I am the second owner of the car, taking over from the previous engineer owner at 8000 milesso I cannot know whether the gearing is standard 3:1:75. and as I have said before the re-map from Omex did not include any changes to the internals. I would love to hear further of peoples experiences.

I fully agree with cerealsurfer on the choice which confirm my feeling.

Overall ratio (gear* rear axle)

......custom ratio......PLUS 4 2005 std... %

1st......9.80(road)........13.46..............+27%
2nd......6.31...............7.76..............+18%
3rd......4.96...............5.07..............+2%
4th......4.10...............3.73..............-10%
5th......3.57...............2.85..............-25%

1st and 2nd are to short, 4th and 5th are too long.
With a tuned motor they use a 5th gear which correspond to the standard 4th. minus 25% on 5th!
I guess that the maximun speed with my mog could be reached only with the 4th. I never try.

The first modification to do is not to increase the power but to change the ratios... which is surely more expensive.

What overall ratios are used on the present PLUS 4?

According to the manual the ratios for the current Plus 4 and 4/4 are:

Gear Ratios. Plus 4. 4/4
1st. 3.87. 3.136
2nd. 2.08. 1.888
3rd. 1.36. 1.330
4th. 1.00. 1.00
5th. 0.76. 0.814
Final Drive Ratio. 3.73:1. 3.73:1

Both use the Mazda MX5 gearbox. We are now getting way beyond my technical comfort zone so please note that these figures have been directly copied from the latest user manual and any comments or inference of the validity of these figures need to come from someone who actually knows what they are talking about, in other words not me!

If anyone is interested the formatting didn't copy through but the first set of figures are the plus 4 and the second set of figures are the 4/4

Here are a couple of interesting Dyno charts.

The first was given to me by Mogsport and shows a standard Plus 4 against one fitted with throttle bodies and a Librands exhaust. Note that there are some reasonable torque gains at about 3,000 rpm.



The second is a similar chart that was published by Aero Racing for the Plus 4 SS to which I have added the Omex curves.