Thomas Cohen says:
>
> Graeme Oxley writes:
>
> > I was wondering if anyone could help me with the choice of cam for the mini
> > engine I'm building. The specification is;-
> >
> > 1275 bored to 1312 (+.040)
> > gas flowed and polished head, planed to give 10/1 CR
> > Standard Mk3 Cooper S valves with 140 lb. valve springs
> > Twin 1 1/2 inch S.U's
> > LCB exhaust into 2 inch pipe with straight through silencer
> >
> > I'm builiding the engine to use in hill-climbing/sprinting. I also need to
> > use the car on the road occasionally, so a full-race cam is out. I've heard
> > that the 731 cam is a good compromise, and that it works from 1500 rpm.
> > Haas anyone had experience with this cam? Bearing in mind that the car will
> > only occasionally be used for fast road work, is it possible to get a cam
> > "hotter" than the 731, but still usable on the road?
> What you need with an A-series engine is to have the exhaust duration
> at least the same as the intake, which is where the 731 falls down, as
> it has a longer intake than exhaust. The 643 or possibly the 649, would
> be the choice of the factory cams.
>
> In any case, for sprinting/hillclimbing you will want a hotter cam
> than the 731, especially if it is to be used only occasionally on the
> road. My Clubman GT has a 643 cam in it, which was the original
> Formula Junior cam. It pulls (in a 1293) from about 25-2800, and
> keeps going to about 7200. However, that cam is much older than
> the engine configuration you're using, and to take most advantage
> of the head etc. you'd probably be better off going to a Kent Megadyne
> 286, or Piper Magnum 2 285/2. These give much the same sort of top end, with
> a little more polished bottom end. Not to mention more lift, which
> most (all) factory cams lack.
>
Well I don't have any Mini's right now, but I do have a brace of sprites with
1275's. My Street Sprite has the Kent Megadyne 286, with the lcb header and
a weber 45 DCOE, I'm getting 67 HP at the rear wheels now that Rockwell
Motorsports adjusted the carb correctly. My head is pretty stock, just a bit
of port matching, and since this is notoriusly the weak part of the air flow
system (read engine) I have a lot more cubic dollars I could toss at it.
At idle its pretty rough, but that's partly due to the weber, but above say
2800, it really is smooooooooooooth. Power pulls to about 7500 rpm.
Car Zero has a Paeco 7700 race cam, lots of lift, lots of duration, lots of
power at lots of RPMs. Its sort of laggy below 4500 (well as laggy as
135-140 hp peak can be), but after 4500, it almost has a boost similar to
turbo lag. I wouldn't recommend this cam for street, but it is almost
drivable. I think that Paeco makes similarly designed cams with the power
band moved lower down the rpm range (this one is from 4500-7700).
--
Miq Millman -- miq@sgi.com or {decwrl,pyramid,att}!sgi!miq 415 390 1041
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