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1275 Cooper - What Would You Do To Increase Power/performance

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#1 GermanMoreno


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Posted 21 May 2020 - 05:30 PM

I want to increase the power in my 1275 cooper carb (eventually). I want to know what would be the ideal process to upgrade slowly but surely.

What should I start with and what should I end with. Let me know what you would do. I am looking into the John Cooper conversions, but it seems like there are cheaper and more powerful options out there. Open to suggestions!

#2 luismx123


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Posted 21 May 2020 - 05:59 PM

You need the engine to breath better. A stage 1 kit is usually good for about 10-15% more power. Maybe more. Really simple to add.

Next you can look into getting a new head or yours reworked. This works best when adding a new cam, but its not needed - unless you want more. 

I think you need to give us more information on what you have installed. Manifolds, carb/carbs, Final drive ration, etc. 

I know im not an expert, nor do i have as much experience as many on here, but for me,  "tuning" a mini is always looking for the next weakest link and then replacing it. Its usually wheels/suspension/geometry set up, then improving the engines breathing capabilities, then cylinder head/cam shaft combination and then start again from the front ;)


p.s those kits can be put together for far less. Its been discussed a bit here quite a bit ;)

Edited by luismx123, 21 May 2020 - 06:00 PM.

#3 MrBounce


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Posted 21 May 2020 - 07:43 PM

A Stage One kit would certainly be my first port of call. I fitted one to my Mayfair about 20 years ago and it utterly transformed the car. 


My questions to you would be a) What do you want out of the car? b) what's your budget? c) Is it an everyday driver? d) How fast do you want it to go? e) Are your suspension and brake components up to tuning?


I'd always suggest making sure that your brakes and suspension are in tip top condition before tuning. I did everything except balljoints. Then this happened:




(Don't worry, she was nicely rebuilt, but it showed me to NEVER skimp on anything important).

#4 GermanMoreno


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Posted 21 May 2020 - 07:47 PM

Thanks guys, my car is completely stock in terms of engine 1275, HIFF44 carb. Suspension has only hi-los, nothing fancy. regular shocks.

Its a summer car,

Where I live in Canada, I do mostly highway. I want a bit more response from the car. basically a fast road is what I am looking for

#5 Cooperman


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Posted 21 May 2020 - 07:54 PM

To increase the performance the first thing to do is to make it go around corners more quickly. This means better brake pads, better damping and accurate suspension settings.

Then the overall weight should be reduced if possible.

After that consider improving the engine specification to increase the torque.

A better cylinder head is the key to improved performance. When I first got it my 1990 Cooper had 33.5 mm inlet valves. I just fitted a slightly gas-flowed MG Metro head and put the CR up to 10.2:1. The flywheel was lightened and it now has a pre-Verto unit. The HIF44 carb was improved and a twin-box RC 40 exhaust system was fitted. I put in a 266 cam (well, MG Metro one, but they are irtually identical). The distributor I changed for an Aldon Yellow.

Once set up on the rollers it gave peak power of 84 bhp at 5700 rpm and peak torque at around 4300 rpm.

I also fitted a 3.44:1 FDR to improve acceleration.

For the road that is quite enough and anything further will reduce the driveability of the car and tend to make it 'fussy'.

#6 minidizzy


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Posted 21 May 2020 - 11:44 PM

Cooperman, I am interested that you replaced the cam with a MG Metro one. The 1990 Cooper was supposed to have MG cam when it left the factory. I remember your story of Rover's cash flow issues and the need to substitute lesser cams on some cars. It looks as if your Cooper suffered that indignity.

#7 panky


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Posted 22 May 2020 - 09:36 AM

My '91 Cooper does have an MG cam in it and I've had the car from when it was four years old so I suspect it came out of the factory with it.

Not long after I got it I did the stage 1 thing but didn't really notice much difference - except the noise of the K&N. When the RC40 the kit came with fell to bits a couple of years later I fitted a stage 3(?) head, millenium RC40 and a Piper 285 cam, it was a bit wild.

I've since gon back to the MG cam and put the original air box back on with a K&N element, the car is so much nicer to drive now - nice and torquey and a lot quieter.

#8 Cooperman


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Posted 22 May 2020 - 03:29 PM

When I first got my 1990 Cooper I was building an 'Endurance Spec' rally car.
However, I struggled to find a firm original spec for the cam. It had never been rebuilt so I rebored it to them max allowed under the regs, +60 thou, and fitted a brand new MG Metro cam.
Interestingly, the originsl standard head had 33.5 mm inlets, but the Haynes book stated 35.6 mm, so I fitted an MG Metro head with the right amount skimmed.
The regs required a 'standard' engine and gearbox, but I did some small improvements to the head by grinding away a bit of the valve guide bosses and cleaning up the short-side radius into the valve seat. I di lightly de-shroud the valves a bit.
For the 'standard' gearbox a set of the original ratio 'S' gears were fitted with a 3.44 fdr and a criss-pin diff.
The inlet manifold had the 'casting flash' removed and the carb was gas flowed a bit.
I also lightened the flywheel a bit, but it has since been fitted with a lightened steel flywheel.
My longert term plan is a fully flowed head and twin HS4's as it is now just a road rally car and no longer governed by the endurance regs. It is also now on 10" wheels to improve it a bit more.

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