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Cam And Head Suggestions


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#1 scottv1025

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Posted 06 November 2020 - 04:59 AM

I'm having a 1275 austin america block done with 10:1 ratio pistons . I have not decided on a dual H2 carb or dual H4 carb . Im looking for a fun fast mini. That I can mess around a 1 to 2 times a week . What cam , head and carbs should I go with? I have a good source that gave me suggestions. But what everyone think? Thank you in advance

Edited by scottv1025, 06 November 2020 - 05:00 AM.


#2 ACDodd

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Posted 06 November 2020 - 08:35 AM

What rev range do you drive in?

Ac

#3 Cooperman

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Posted 06 November 2020 - 05:47 PM

You will get a lot of very different opinions.

In the end it comes down to personal preferences, but one thing to do is not to 'over cam' the engine and thus end up with good power, but at very high rpm's.

My personal preference is for a nicely gas-flowed head with 35.6 mm inlet valves and 29.5 mm exhausts. A compression ratio of just below 10:1 should be ok for most quality petrol in the USA so long as the distributor has the correct advance curve.

For the cam, a Kent 266 or equivalent always works well and gives good mid-range power & torque. There are other good options, but look at the cam graphs as a comparison. Ideally you need peak power around the 5500 to 5700 rpm and peak torque at c.4000 rpm with useable torque from about 2200 rpm. Torque is more important than outright power.

With regard to the carbs, my personal preference is for twin hS4's, but that's because I grew up with 1275 Cooper 'S;' cars in competition and we always used twin 1.5 carbs. A single HIF44 would give as good a result so long as a good inlet manifold is fitted, but the twin HS4's do look and sound great.

The exhaust system needs to be efficient and an LCB with a 1.75" diameter twin silencer box RC40 or Maniflow is always a good choice.

However, the really important thing is to have a top quality and accurate engine build. Time the camshaft in to the right figure using either a vernier adjustable sprocket or offset woodruff key (lots of stuff on here about how to do this).

A slightly lightened flywheel helps with acceleration and a final drive ratio of 3.44:1 works well (that is the original Cooper 'S' ratio).

As I said, this is just me personal preference which I know works well on the road.



#4 Luke Denver

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Posted 17 September 2021 - 01:16 PM

You will get a lot of very different opinions.
In the end it comes down to personal preferences, but one thing to do is not to 'over cam' the engine and thus end up with good power, but at very high rpm's.
My personal preference is for a nicely gas-flowed head with 35.6 mm inlet valves and 29.5 mm exhausts. A compression ratio of just below 10:1 should be ok for most quality petrol in the USA so long as the distributor has the correct advance curve.
For the cam, a Kent 266 or equivalent always works well and gives good mid-range power & torque. There are other good options, but look at the cam graphs as a comparison. Ideally you need peak power around the 5500 to 5700 rpm and peak torque at c.4000 rpm with useable torque from about 2200 rpm. Torque is more important than outright power.
With regard to the carbs, my personal preference is for twin hS4's, but that's because I grew up with 1275 Cooper 'S;' cars in competition and we always used twin 1.5 carbs. A single HIF44 would give as good a result so long as a good inlet manifold is fitted, but the twin HS4's do look and sound great.
The exhaust system needs to be efficient and an LCB with a 1.75" diameter twin silencer box RC40 or Maniflow is always a good choice.
However, the really important thing is to have a top quality and accurate engine build. Time the camshaft in to the right figure using either a vernier adjustable sprocket or offset woodruff key (lots of stuff on here about how to do this).
A slightly lightened flywheel helps with acceleration and a final drive ratio of 3.44:1 works well (that is the original Cooper 'S' ratio).
As I said, this is just me personal preference which I know works well on the road.



#5 Luke Denver

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Posted 17 September 2021 - 01:22 PM

Hi, sorry to revive an old thread I’m quite new to this (never posted on here before) but have been reading up on a few of the posts to help me with my build. From what I have seen you seem very clued up on all this and I really like the sound of what you describe in this post, it’s pretty much what I’m looking to go for. So I have stripped down a 1275 Austin metro engine initially to check if all is in good order but after finding that the cam in the engine is not an mg metro one I have decided to fit a Kent 266 as after reading up it seems exactly what I need everyday road use and that little bit of oomph when I put my food down (which is quite often) so basically what I want to know is all of the bits I will need in order to get my engine running nicely with this cam I have the 35mm larger head pretty sure it’s 12g940 and at the moment I don’t really want to change much on this as I don’t have the money or resources so I would like to keep that as it is and then down the line get it all fancied up. So for now what cam followers, valve springs ( as they look tired) distributo, exhaust, carb, timing chain (thinking duplex) will I need to get this engine running well ready for a nice done up head in the future. Literally any information is appreciated as I’m just stuck on what parts to buy at the moment thank you so much for your time~ Luke




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