Low compression versus hight compression engine ?

[carlosramalho]

Hi All,

Sorry, May be I will do a silly question! But we are in silly season, so my question is:

What are the diferences between low and hight compression engine?
Cheers
Carlos

[chrisryder]

What do you want to know?

How to identify one from the other?

What makes one low compression and one high compression?

What the difference in performance is?

[carlosramalho]

What do you want to know?

How to identify one from the other?

What makes one low compression and one high compression?

What the difference in performance is?

Hi chrisryder,
I would Like to know All!
I' m complet New about this matter! For that reason I did this question!
Cheers
Carlos

[JOWETTJAVELIN]

Low comp. will give a very low output and thus less performance (probably better on fuel), and will run on almost anything. Paraffin, 2 star, white spirit, moonshine - you name it.

The higher the comp. ratio the better the grade of fuel needed to give better performance and prevent 'knocking'.

P.S. what is this silly season you speak of? I'm intrigued...

[bmcecosse]

One has low compression = lower power and HEAVIER fuel consumption if asked to run the car at the same speed as an engine with high compression - which has more power and better fuel economy. The Low CR engines were designed to run on cheaper low octane fuel - (POOL Petrol) - this no longer available - so a higher CR takes advantage of today's higher Octane fuels and gives better efficiency and is therefore the way to go. However - the CR we talk of is the 'Volumetric Compression Ratio' - and what actually matters is the 'Barometric Compression Ratio' which is the ratio of the pressure in the cylinder at TDC over the pressure at BDC ! This depends on both the VCR and the efficiency with which the engine can 'breathe' in air..... So my mates 911T has a VCR of only 8:1 - but thanks to good head/valve/inlet manifold design and triple downdraft IDA Webers - it goes like sh!t off a shovel!

[lambrettalad]

bmc
hope you didn't cook your eggs and bacon on that shovel

[bmcecosse]

Not me - vegetarian! But i believe in the old days - the footplate crew cooked their breakfast first - and then used the shovel for other essential duties later........

[mike.perry]

A high comp A Series engine would have almost flat top pistons, a low comp engine would have dished pistons. The engines can be identified by H or L in the engine number. L.C. engines were used for LCVs, military vehicles and marine engines.
The side valve engine was built to run on low octane fuel with flat top pistons and a 6.7 : 1 CR. It is necessary to skim the head to raise the CR

[carlosramalho]

My question, was because my Morris Oxforf series. IV -1958 is a LC engine!
What you think about this? The engine is a 1500cc.
Cheers
Carlos

[JOWETTJAVELIN]

It simply means that your Oxford will run on cheaper grades of fuel but will be quite slow. BMC generally fitted LC engines to export cars.

[liammonty]

One of my Minors (1968 2 door) has the original 1098 low comp engine (never rebuilt), and to be honest, it has as much power as most HC 1098 cars I've driven (and before anyone tells me otherwise, the engine is the correct one- some cars did have LC engines ). On paper it should be 5 bhp less, but I think the torque output is much the same. I suspect that there were bad ones and good ones of each engine type- tolerances back then weren't what they are now. I think to say that a car with a LC engine will be really slow is not necessarily true though.

[JOWETTJAVELIN]

What I would really like to see is a car with an original factory optional diesel engine, like a diesel Morris Oxford or Standard Vanguard. Those were the days when lorries and buses ran on petrol, so diesel engined cars are rare survivors.

I wonder what economy figures are and performance, bear in mind pre-turbo.

Was diesel an option on a Minor/A series?

[chesney]

I think some diesel tractor engines were made, I remember a minor van had one, but he added a turbo to make it go up hills. Not sure how close it is to a conventional A series though..

[MarkyB]

Was diesel an option on a Minor/A series?

I'm pretty sure they weren't an option, diesel engines then were very basic, heavy, noisy and smelly.
Not an attractive option.

[bmcecosse]

The diesel A series is a hopeless thing - 18 bhp IIRC and at v low revs.........

[IaininTenbury]

Here's the tractor (BMC Mini) engine:[frame][/frame]
And no not really suitable for a Minor, though that van with one fitted (was it in New Zealand or Australia?) appeals just down to the 'barking mad ness' off it

[youngcamper]

I guess If you were going to fit a diesel 948 to anything a A40 farina or a35 would be a better and lighter starting point