731 cam Vs Standard

[rolesyboy]

I have been offered a 731 cam which I could fit to my 1275 S. Anybody have any experience of them? I seem to recall they were a good Road Rally cam in their day but that is my lot. What difference will it make to a 1275 S? What are they worth nowadays? Good condition and looks pretty well unused. Cheers. Mark

[pad4]

just thinking out loud here but isnt the 731 the lesser used of cams, i seem to recall no one having anything good to say about it

what you using the car for - road, rally or ???

i think if youre going to spend cash on a cam , it needs to be a wise choice you make

pad

[mk1]

It's not a case of not having anything good to say about it.

The thing is that the 731 was designed specifically for the 997 Cooper engine. In that long stroke / small bore application it works pretty well, but as I am sure you appreciate there aren't many people tuning 997's nowadays. When this cam is shoehorned into other more high revving applications it can be disappointing, giving a pretty lumpy tick over & no appreciable increase in top end either!

The good old SW5 is a much better option in a 1275 or even a 998 engine for that matter.

M

[Simon776]

I seem to recall it worked OK in a 1275 but lots of people put them in 998s where it didn't really.

Modern cams are undoubtedly better though.

[mk1]

From the main MK1 site.

Hard to read, but interesting.

[LMM76C]

I seem to recall it worked OK in a 1275 but lots of people put them in 998s where it didn't really.

Despite being officially called a "rally" cam by BMC, the 731 never seemed to be used by the works S rally cars, which tended to use the later standard S cam, the 510, whenever the 544 or 648 wasn't used.
I co-drove a 998 Cooper with a 731 and all appropriate other mods on the Scottish in period and it was gutless on the road sections where I was in the driving seat.

[graham in aus]

In about 1979 (!) I did what was probably one of my first 'mods' to a mini, I put a 731 into my Damask Red 10" 1275GT. I kept the single 1 1/2 and 'de-coked' the head ( ) THe other essential mods were the yellow fibreglass 'whip Arial' and 10 X 6 KN Star Mag Alloys with W+P arches!

Result, no discernable performance difference what-so ever! But Man it looked the Bizzo!

[Lord Croker]

I used a 731 in a 1293 'S' that I drove on road / occasional stage rallies, I was not disappointed with it, but on the other hand it was not outstanding, bearing in mind I wasn't looking for power at 8000 rpm, it was geared more for torque, which it possessed in bucket loads! I was initially concerned that the 731 had 3/8" wide lobes instead of the 1/2" which most other camshafts seemed to have, however it turned out not to a problem, showing no serious signs of cam or follower wear after many miles of a mix of competition & road use. I don't know what all you guys will think of this, but I had an Austin Healey Sprite 1275cc, so the first thing to do was to remove the engine strip it, balance & lighten, port & chamber the head, & someone (an experienced builder & driver of rally Minis) suggested a 948 (88G229 for a spline drive) camshaft as fitted to the 997 Cooper. It went like a scalded cat & I've been a great advocate of that cam ever since, I wish I had tried one in the 'S'. It also works very well in 998's. To be honest, I have no idea what a slightly used 731 would be worth, but what I would say, examine it carefully, an original is identified by 3 rings, 3/8" lobes & pin drive.

[mk1]

The reason that most of the BMC rally cars used the standard cam is that most of them ran in Group 2 & they HAD to use the standard production cam.

[carbon]

Interesting thread, is the 731 profile really that mediocre?

For example if you look at the timings for the AC Dodds RS+ cam then it looks awfully close to the 731 timing with 5 degrees of cam advance and a lot more lift. Granted the acceleration rates are also likely to be faster on the RS+.

Could the 731 actually work well in a 1275 with 1.5 lift rockers? I've not tried this yet, has anyone else got practical experience?

PS. There are factory 731's with 1/2 inch lobes as well

[Mini4Ever]

Interesting discussion on here as I was considering to put one into my 998, but now I think that the 88G229/2A948 (the std 997 cam).

[LMM76C]

The reason that most of the BMC rally cars used the standard cam is that most of them ran in Group 2 & they HAD to use the standard production cam.

Most did run in Group 2 - where the camshaft was free. Group 1 required the standard cam - but there were very few works entries in total in Gp1 in comparison with Gp2 (or even Gp6).
Lets not have capitals (ie. shouting) when you are factually incorrect?

[Simon776]

I was considering to put one into my 998, but now I think that the 88G229/2A948 (the std 997 cam).

I tried that permutation as well and it seemed to make very little difference.

[cheleker]

I have a similar letter around here someplace from Downton dated in the early 1970s that says much the same thing; i.e., they could find no reason to use a 731 in a Cooper S.