In a message dated 22/03/02 11:19:02 AM Pacific Standard Time,
owner-mgs-digest@autox.team.net writes:
>
>
> The engine is bored with the bores offset, so core penetration is
> not such a problem. The crank is also offset ground to give the longer
> stroke. Any "good" machine shop can duplicate this job, as it is a common
> hot rod trick. Problem is, you end up with a throwaway block and crank.
> Great if all you are going to do is drive on weekends.
>
Dodgy cast iron that weeps coolant into the cylinders is a problem with too
large a bore, as is insufficient head gasket material unless the bores are
offset.
I have done larger, but advise people to stick to about 1950 cc to be safe.
The use of the longer stroke to increase capacity is not a bad one given that
most engines will see only street use and spend very little time at high RPM.
> Mike's monster 8,000 rpm engine is also a short lived beastie. It
> might be able to blow off stock Miatas, but I don't think drivability is
> going to be great at that level of development.
>
An 8000 rpm MGB engine with a stock siamesed head is a whizz-bang. The only
way you can get power to increase after the high 6000 rpm range (that is, a
power peak above 6500 or so) is to use brutally high compression, wild cam
timing, and ports that are enlarged past the point of sensible low end torque
production. Oh yeah - and the bottom end has to be a megabuck item to stand
up even temporarily.
If you want an engine that will function at high RPM, and by that I mean
continue to increae power output, AND have reasonable low end performance,
you need to start with something that produces a bunch more BMEP than the MGB
head will ever show.
Examples -
1. Stock MGB - nice flexible cooking motor, peak of around 5800 rpm
(shifting above 6000 a total waste of time)
2. Stock MGA Twincam - flexible in mid range, power peak at 6800 rpm (no
point shifting much above 7000)
3. Racing MGB - power peak can be raised to 6800 range, and the thing will
run to 7500 or even 8000, but isn't making any more power up there
4. Racing Twincam - power peak can be around 7250 or so (using my own as
an example), with up to 7700 or so usable, and engine retains excellent
bottom end behaviour, although it doesn't really dig in until 4500 or so.
5. Street/racing engine design (using my Lamborghini as an example, better
even than the Twincam - a short stroke motor) - peak power 7800 rpm, yet
pulls away quietly at 1000 rpm in 5th gear
Building a honking great high revving MGB has been done any number of times
(I've done it myself), but asking them to also be drivable as a grocery
getter is like asking a 3 toed sloth to dance Swan Lake - the fact that they
try normally elicits polite applause, but no one takes it too seriously if
they aren't budding Nureyevs.
Bill
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