30 replies to this topic

[Cooperman]

I built a fairly mild 998 which put out 66 bhp at 6000 rpm. Just changed the cam (a 510), head (12G295), 1.5" SU, everything accurately machined and assembled with an original 998 Cooper exhaust system and a Howley alloy inlet manifold.

Lovely engine the 998.

[mini danny]

Ya mines very strange very low on power :/ im also running a single box maniflow 1 3/4 centre exit exhaust

Dan

[Cooperman]

Ya mines very strange very low on power :/ im also running a single box maniflow 1 3/4 centre exit exhaust

Dan

 

I wouldn't be able to resist pulling it apart to find out why.

Your exhaust is about perfect for the car.

[mini danny]

The only problem with pulling her apart is shes my daily driver again and as I work 10 mile from my house shes needed will have to try sort transport for a week or so


Dan

[mini danny]

Ok I done compression test today got 150-160 on 2, 3, 4 but cylinder one was 125-130 but when I put a little bit of oil down the bore and done the test again it also came upto 150-160 so cylinder one rings are blowing past slightly but not that bad.



Dan

[Cooperman]

Compressions seem a bit low, but not excessively so. You need to accurately measure the cam timing.

[MIGLIACARS]

Compressions seem a bit low, but not excessively so. You need to accurately measure the cam timing.

Just out of curiosity, does low compression make Hugh differences in power.

 

lets say  10-1 compressions engine gave 100bhp

what would the same engine with a 9-1 compression make

[Cooperman]

You lose a bit of power and torque with lower CR.

It's hard to give specific figures as so much depends on the build and specification.

The A-series does like high compression to get best power.

Going down from, say, 10:1 to 9:1 will cause a loss of several bhp.

[Gremlin]

You lose a bit of power and torque with lower CR.
It's hard to give specific figures as so much depends on the build and specification.
The A-series does like high compression to get best power.
Going down from, say, 10:1 to 9:1 will cause a loss of several bhp.

Would you notice a massive difference if it was 11:1 instead of 10:1?

[Cooperman]

 

You lose a bit of power and torque with lower CR.
It's hard to give specific figures as so much depends on the build and specification.
The A-series does like high compression to get best power.
Going down from, say, 10:1 to 9:1 will cause a loss of several bhp.

Would you notice a massive difference if it was 11:1 instead of 10:1?

 

You would if you didn't use 97+ oct petrol plus octane booster and the correct ignition advance curve!

Seriously the increase from 10 to 11 would certainly give a bit more power & torque, especially with a good cam & well-flowed head.

[coopdog]

I've been told its like 1%

[Earwax]

to migliacars

 

there are calculators that show typical gains    for different horsepower :   example ( not sure if 100% correct )   http://www.wallacera...m/hp-cr-chg.php

 

generally  less than 4 hp on a mini   probably 1-2    but i don't know if that takes into account changing other variables ( such as advancing the timing )

 

my interpretation, for a road car RON 97 98 somewhere above 9 but not over 11       

[Cooperman]

To return to the OP's problem, I am wondering not just about the cam timing, but about the cam itself.

I don't know the year of manufacture of the OP's engine, but during the Austin-Rover & later the Rover years, the company were very slow to pay their suppliers, with the result that some parts were what happened to be 'in stock' at Longbridge. The cam manufacturers would sometimes decline to supply as they had not been paid for up to 6 months, so Rover used whatever they had that would go into an A-series block. Thus whilst one 1275 Cooper might get an MG Metro cam, another might get a basic Maestro cam, or whatever they had. The same could apply to other parts.

Edited by Cooperman, 19 September 2013 - 05:48 PM.

[ACDodd]

It's about 3%. Up or down.

Ac

[Tamworthbay]

To return to the OP's problem, I am wondering not just about the cam timing, but about the cam itself.
I don't know the year of manufacture of the OP's engine, but during the Austin-Rover & later the Rover years, the company were very slow to pay their suppliers, with the result that some parts were what happened to be 'in stock' at Longbridge. The cam manufacturers would sometimes decline to supply as they had not been paid for up to 6 months, so Rover used whatever they had that would go into an A-series block. Thus whilst one 1275 Cooper might get an MG Metro cam, another might get a basic Maestro cam, or whatever they had. The same could apply to other parts.

No surprise there, we have an ex BL toolmaker at our place and the stories of management cluelessness are painful to hear.