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Choosing a Camshaft


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#1 XTT

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Posted 08 April 2005 - 10:13 PM

Hello all,

I have a 1989 1275 Metro engine fitted in my Mini, the head will be comprehensively tuned/flowed/opened/skimmed @ an engineering company and the biggest possible valves will be fitted. The chambers will be changed from heart shaped to oval shapped. Piston Rings will be changed as a precaution. The only two things remaining are the rockers and the camshaft...

Here are my questions then...

1) What's the difference between slot drive and spider drive and how can i tell which one's for my engine?

2) is a 296' cam too much for my spec?

3) Someone told me about high compression pistons that are completely flat at the top, is that true and is it worth buying and fitting them?

4)shall i go for 1.3 , 1.5 or 1.7 rockers??

5) will my 45mm SU carb be enough after all these or do I need a twin-carb set-up?

6)Will I need an uprated oil pump?

I know that these things were probably asked 10000000 times before :lol:

#2 Purple Tom

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Posted 08 April 2005 - 11:56 PM

1 - Slot drive was the oil pump drive type fitted to most A+ engine camshafts, and all 1275 A+'s. Spider drive IIRC was the one used in early Cooper 1275 A's (as in 60's cars). So your Metro 1275 will be a slot drive.

2 - not sure

3 - again, not sure :erm:

4 - ah, I think you'd be best off with 1.5:1 ratio rockers, thats what everyone else seems to fit!

5 - its actually 44mm, and yes your HIF44/HS6 carb will handle most engines up to about 110 bhp, so it will be fine with your spec. Twins are reputedly better as they deliver a more even fuel flow to all cylinders, but can be a pain to set up. However if you can get a decent set they may offer slightly more power, but i'd stick with the single to be honest.

6 - Its always a good idea when you're doing this kind of work, as the engine will undoubtedly be working harder. But too much oil pressure is sometimes not a good thing. I think a standard new oil pump will be fine, and providing the engine is maintained and not driven hard when cold for example, then it should be ok.

Please someone correct me if i'm wrong on any points there!

#3 Bungle

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Posted 09 April 2005 - 07:36 AM

3) high compression pistons

it depends what compression raito your after and the head chambers cc

#4 998dave

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Posted 09 April 2005 - 07:44 AM

1. agreed

2. I think 296' may be too much, a 286 may be better and hold the bottome end better. Vizard suggests that some of the peakier cams will provide better results with a 3-1 manifold rather then an lcb.

3. As you're machining the head out using flat top pistons may result in requiring less skimming of the head to get the CR back, which will make you less likely to break into the oilways I guess...

4. I'd go 1.5 but remember these place more stress on your valve guides by putting more sideways force on the valve. Roller tips may be the way to go if you have the funds.

5. Agreed, although some fancy set ups are available and can be good fun. Refer to Vizard if you want to read more.

6. New oil filter and water pump, plus making sure the oil ways, oil filter and radiator are all in good condition would all be a good idea to ensure longevity of the engine and adequate cooling.

Dave




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