54 replies to this topic

[racingbob]

and whats a vizard sp4 cam?

scatter cam, excellent cam

designed for ultimate street car

powerband in 1275 2000- 7500

used this cam in my race car as well and was 1/2 sec lap

slower than kent 310

[jamiestevenbell]

its a weekend car/track day car every now and then for fun not competition, i dont mind rebuilding after 15-20k miles to be honest but i dont want to be rebuilding every year

Edited by jamiestevenbell, 27 April 2012 - 10:11 PM.

[jaydee]

You're being quite optimistic with the 286..

[jamiestevenbell]

what do you mean by that?

[Cooperman]

With an even hotter engine if you use all that performance, and if you don't there is not much point in having it, you should expect to re-build much more often than 15 to 20,000 miles. Remember you'll be using well over 5000 rpm most of the time with a useable max of around 7000 rpm.

[jaydee]

Wont last that that long before you need to give it a refresh, like new piston rings, cam followers etc..

[jamiestevenbell]

ok so if i said every 9k is that reasonable? how many miles would you expect the engine to do as is before a rebuild?

[jamiestevenbell]

this is what i was thinking about http://www.twinkam.c....&aid=SC216.001 with there fuel injection kit and engine management plus a different cam if needed. Or is there little to be gained from this?

Edited by jamiestevenbell, 27 April 2012 - 10:31 PM.

[jamiestevenbell]

or this http://www.med-engin...6-specification with twin hif38s or twim hif44s

[racingbob]

your engine will not last very long at all if you are using over 7000 revs

i had 2 engines one i reved to 8000 the other 7000

8000 one 4-6 race meeeting and it was out for some reason

7000 one lasted about 10 before needed coming out

in my opinion dont expect 5000 - 10000 miles reving at 7000

if i had a track day car i would be keeping revs to 6500

not unless you got deep pockets

( 4 years racing 1275 cooper s in historic )

[jamiestevenbell]

well if i was to have a 296 cam i wouldnt need to constantly rev at 7k would i? so is what your saying if i dont want to be revving at 7k constant theres no point in a big head/7port?

[Cooperman]

There is no easy option unless you go to forced induction. With the existing spec of your engine you are at the top end of a 'road-useable' car.
So as you demand more power and achieve this with increasingly 'hot' cam and bigger valve head you need more revs in order to generate this power. Going on from there, the power band becomes narrower and a closer ratio gearbox is needed to keep it 'on the cam'. Then, because 1st gear is higher, a lower final drive ratio becomes necessary in order to pull away from rest with the engine 'on the cam'. A lower final drive will give more rpm/mph, so for road cruising more revs will be needed for a given speed.
It's all a trade off really and taking my 1964 'S' as an example, I have a 286 cam and all the other bits to get serious power, but I have a SC CR gearbox and a 3.9:1 final drive. This gives me only 14.5 mph/1000 rpm in 4th. So to cruise at 70 mph I am using just almost 5000 rpm sustained. But if a wide ratio gearbox was used in order to get a low enough first to pull away whilst giving high enough top gear for a decent cruise speed, then the gap when changing gear would drop it out of best power band each time you changed up and you would then need to use even higher revs to prevent it falling back at change up. A 296 cam is even more 'cammy' and 7000 rpm needs to be used to get optimum performance. That wears the engine quickly, in relative terms. How long between re-builds can depend on component and build quality of course. I strip my engine after every 6 or 7 rallies.
That is why race engines with lots of power rev to 8000+ and have very low final drive ratios, and cost a small fortune to build, but if you want to win you need to invest in the best.
The only other answer if a wider power band is to be achieved is to go forced induction with all the pro's and con's of doing that with a turbo-chrger or super-charger.
Always remember, you are dealing with a classic 54 year-old car design and a 60-year old engine design.

[racingbob]

yes dont forget its only a 3 bearing crank

it always seemed to be main bearings that played up

just keep those revs down

if its just a fun day track car concentrate more on suspension

than on your engine with more power leading to more hassle

[Cooperman]

yes dont forget its only a 3 bearing crank

it always seemed to be main bearings that played up

just keep those revs down

if its just a fun day track car concentrate more on suspension

than on your engine with more power leading to more hassle

That's right Bob. The centre main suffers the most as it has to feed two big ends whereas the end mains feed on to just one each. It's almost always the centre main which starts to degrade first. The thrusts are there as well and need oil feed to them. Not the best design of engine ever, is it!
If the car is not going to be used for timed competition as in rallying, hill-climbing or racing it is best not to build too 'hot' an engine. A race/rally/hill-climb car will really not be suitable for regular road driving and if you want a Mini as a competition best build an out-and-out comp car and then have a road car with which to tow it on a trailer. I almost never drive my rally car on the road.

[The Matt]

You can go to a four-bolt centre main bearing, you can spend a lot of money on a really well specced bottom end too.

to be honest, your Mini sounds like a fun little motor as it is. I'd be thinking about forced induction as a next step maybe.