Compression at cilynders

[AngelV8efi]

Hello all!!!!!

Sorry about my english, but this is not my mother language.
Any case, this is a web reference in other countries, as Spain!!!!

I am an user of a fantastic Range Rover Classic.
Obvioulsy petrol engine, but in Spain this kind of four wheels are diesel......

We have a discussion about what pression in cilinders are correct.
The only reference we have is ratio Air:fuel, but I would like to confirm bar or psi pressure in cilynders, in an official reference.

Motor               Alimentación                    Compresión      Caja de Cambios
3.5                    
22D00001      Fuel Injection                      8,13:1 C/R      Manual Gearbox
23D00001      Fuel Injection                      8,13:1 C/R      Automatic Gearbox
24D00001      Fuel Injection                      9,35:1 C/R      Manual Gearbox
25D00001      Fuel Injection                      9,35:1 C/R      Automatic Gearbox
26D00001      Carbureted   Detoxed          9,35:1 C/R      Manual Gearbox
27D00001      Carbureted   Detoxed          9,35:1 C/R      Automatic Gearbox
28D00001      Carbureted   Non Detoxed   8,13:1 C/R      Manual Gearbox
29D00001      Carbureted   Non Detoxed   8,13:1 C/R      Automatic Gearbox
30D00001      Carbureted   Detoxed           8,13:1 C/R      Manual Gearbox
   
3.9                    
35D00001      Fuel Injection                      9,35:1 C/R      Manual Gearbox
36D00001      Fuel Injection                      9,35:1 C/R      Automatic Gearbox
37D00001      Fuel Injection                      8,13:1 C/R      Manual Gearbox
38D00001      Fuel Injection                      8,13:1 C/R      Automatic Gearbox

Also it generates doubs about compression 8,13:1. I supouse that this is air:fuel. But.
We have doubt about what compression in Bar or PSI should shown for each cylinder.


Thanks in advance for your kind cooperation.
Regards,
Angel.

[BlownMGB-V8]

The main concern is that there not be much variation between cylinders. Actual compression test results can vary anywhere from 120psi to about 180psi and still run acceptably well with the usual range centered around 140-160psi for gasoline engines. A 5% variation is acceptable. 10% is cause for concern but the engine will still run and provide usable service. Much more than that will begin to cause various problems and indicates a rebuild may be in your future.

Jim

[AngelV8efi]

Great!!!

Do you have any official refference.
Sorry to ask about this (I have looked your number of post and image of your beautiful car), but in addiction to your comment I would like to contrast with a LR catalog.

In fact, in Spain for this motor, the answer is EXACT as you comment but for RRC V8.

what you comment is 140-160 psi (9,5 Bar to 11 Bar), for ALL gasoline engines?

Is a coincidence the number of the compression 9,35:1 (or 8,13:1) with the compression in Bar 9,5 Bar in the cilynders.

I apreciatte your grammar in your text, so I can read it easily.!!!!!

[BlownMGB-V8]

Angel, the simple rule of thumb is atmospheric times compression ratio, so at sea level and about (using round numbers for ease of calculations) 15psi at 8:1 gives  120 psi, 10:1 gives 150 psi, etc. If you know your exact atmospheric pressure and compression test results you can calculate your static compression ratio.

That is far from the end of it though, as when running the engine's Dynamic C/R is much more important. But if interested you should search that and make a study of it because it can get rather involved and is greatly influenced by the cam profiles and timing.

Jim

[minorv8]

A couple of links to explain the static compression ratio ( e.g. the value 8.13:1 or 9.35:1 stamped on the block).

http://en.wikipedia.org/wiki/Compression_ratio

http://constructionmanuals.tpub.com/14264/css/14264_57.htm

[AngelV8efi]

Thanks for your answers.!!!!!

I read before CR in Wikipedia.
And I understand the rule eg: 9,35:1

But, for example, when I put the manometer in the engine, the number could go from 0 psi (broken) to 180 psi.

I understand that is correct when:
"with the usual range centered around 140-160psi for gasoline engines",

And you later say:
"If you know your exact atmospheric pressure and compression test results"

That´s the question, I know the compression test results, eg:150 psi, and I would like to know what figures are correct for a Range Rover Classic.

My conclussion, once you have posted, is that should be between 140-160 psi, and ALL cilynders with similar values.

Thanks again!!!!!
I really apreciate it.

[AngelV8efi]

Hi!

I have found this on the net:

http://forums.roversnorth.com/showthread.php?2094-Cylinder-compression-test-specs-for-4-2-engines

I spent a few days looking for the values for the cylinder compression test figures for my 1995 Classic Range Rover 4.2 with 8.94:1 compression ratio but there was no info. Even the factory repair manual levels out the info for the 4.2 engine. A few years ago I spent the day at the Rover factory in Birmingham UK on tour and drive event, I remember the gentleman who ran this department was a retired engineer for Range Rover. I was able to get hold of him by email and he responded with the following info:

Hello Scot,
Nicky tells me you are having problems finding the cylinder pressures for your V8 4.2 L. Well guess what, so am I. I can find the pressures for a 3.9L ( Both comp ratios) but not the 4.2L.

So what I have done is to extrapolate the info from the 3.9L into the 4.2L and it looks like this:-

3.9L (8.13:1 ratio) Cyl Pressures should be 150/160 psi.

3.9L (9.35:1 ratio) Cyl Pressures should be 170/180 psi

Extrapolating from the above 4.2L (8.94:1 ratio) Cyl Pressures should be 165/175 psi



It seems that it is difficult to confirm with official datas.

Thanks to all.