16 replies to this topic

[Joe555]

Is 10.6:1 too high for a 1293?

[Swift_General]

Depends. You will need to supply more info on engine spec.

[racingbob]

in my opinion probably not ideal but i wouldnt be to worried about it

 

if it was me i would take touch off the head if not fitted

 

 is it a fast road engine not used daily like mine

 

my engine is running over 11.1 again not ideal

 

mg metro engine stage 3 head etc

 

been on there for 12000 miles use v power 99 octane plus 

 

millers octane been no problems and uses very little oil

 

been on there 3 years now

 

if i used it daily would have changed the head long ago

 

i have another head to go on to bring it back to about 10.1

 

which will fit when weather warms up

 

someone with more experience can give you more info

 

need your engine spec

 

but hasnt been a problem on my car so far with over 11.1

[Dusky]

All depends. The race engien runs like 14:1..

[ACDodd]

What cam and rocker combination?

Ac

[Joe555]

Metro A+ engine, just been bored to 1293cc, SW5-7 cam, 1.5 rockers. HIF44, light flywheel, 35.6mm inlet-29mm exhaust valves, P21253 pistons. If the compression is too high what is the best way to reduce it. And if it's ok what petrol will I have to use or will I need additives.  

[carbon]

With your spec you should be OK at CR 10.6:1, but to get the best performance:

- only use a reliable 99 octane fuel such as Shell V-Power

- needs very careful set-up of timing and distributor advance curve

- make absolutely sure you don't run under load with lean mixture

 

Out of interest, how do you know it is 10.6:1?

[ACDodd]

I would be at 9.75:1 personally.

Ac

[Dusky]

Reduce it by either increasing piston dish ( costly) or by getting a dremel and increase the combustion chamber cc. 
its not too hard to do this if you go slow.

[MIGLIACARS]

It will last longer with lower compression, but depends on how you drive it for how long and how may miles you do, more compession will give better power, but will put more stress on the engine, 

a metro turbo ran 9.1 with boost and the factory offered a warrenty with them>> so i dont think you will be blowing head gaskets left right and center.

as above said race engine run upto 14.1 they race flat out for 20 mins and last but dont do 1000s of miles

[carbon]

I would be at 9.75:1 personally.

Ac

Agree that 9.75:1 is a safer option than 10.6:1

[MRA]

It will last longer with lower compression, but depends on how you drive it for how long and how may miles you do, more compession will give better power, but will put more stress on the engine, 

a metro turbo ran 9.1 with boost and the factory offered a warrenty with them>> so i dont think you will be blowing head gaskets left right and center.

as above said race engine run upto 14.1 they race flat out for 20 mins and last but dont do 1000s of miles

 

A race engine typically has a large overlap that allows only clean mixture into the cylinder so doesn't get any ram effects due to the exhaust valve being closed, your road cam will close the exhaust earlier thus getting a bit of "ram air" effect in to the chamber thus the effective compression can be higher on the non race engine due to this effect, or at the very least it will be higher volumetric efficiency per CR.

[Cooperman]

It will be fine so long as the distributor advance curve is correct and you always use a 98 RON fuel, or add an octane booster like Castrol Valvemaster Plus.

[gazza82]

And if it's ok what petrol will I have to use or will I need additives.  

If you have hardened valve seats you can just use unleaded, otherwise you will need an additive like ValveMaster.

[skoughi]

I followed AC's advice and reduced mine from 10.3-1 down to 9.8-1. Re-cut valve seats so they are slightly deeper and ground out the chambers slightly (rough as a dogs dinner!) also put my dizzy to Aldon to get the curve matched to the 266 camshaft. I can only get 95 unleaded so wasn't wanting to chance it and hopefully will get a little bit more life out of my poorly built engine! I did it bytheway!