Compression Test Readings

[richardm6994]

hi all,

 

can anyone tell me what psi to expect on a compression test (engine hot) for my 2.1 pinto.

 

I've done the test today and getting around 210psi on each cylinder (220 max), but I dont know if this is good, bad or problimatic (too high)

 

cheers

[Shaft]

Stop titsing about with it Rich and get out with us instead.... you missed a brilliant drive out today mate, even the average speed cameras have gone from Snakes Pass, which is nice! (just incase we crept over slightly)

 

I'd say they're pretty good values mate to be honest.

 

Pressure in PSi = Force (in lb's) / (Area, in Sq In).

 

HTH,

 

Nick.

[richardm6994]

lol!!! I can't wait.......thinking of painting the car orange so I fit in!!!

 

When i got up this morning and saw the weather I thought of you guys being out!! so out of pure envy I simply sat in the car making brum-brum noises!!! not as much fun tho!

 

Then I thought I'd better do a comp test before paying for the rolling road session on the 2nd April...just to double check all was okay

[Snapperpaul]

220 is high

Usualy look at 190 to 200 for a modified high compression engine.

What cam are you running?

The more mild a cam the higher the compression

[richardm6994]

Kent FR32,

 

I've done the compression test again (engine temp at 85 degrees) and got;

 

cyl 1 = 200psi

cyl 2 = 205psi

cyl 3 = 210psi

cyl 4 = 205psi

 

each cylinder is up to 90% of its pressure after 2 strokes...the last bit of pressure comes after another 2 or 3 more strokes.

 

 

I'm not sure why I got the 220 psi (cyl 3) reading.

 

I suppose we'll for certain if I've got a problem after the rolling road in a few weeks.....

[Snapperpaul]

High compression is NOT a problem, it's a benefit.

Means the rings are good.

2.1 will give more compression than a 2.0 as the bore is bigger and the combustion chamber is not, result = more mixture compressed in a standard chamber

Don't worry but do make sure you use good fuel and get the ignition timing right, you don't want detonation (pinking)

[Longboarder]

Isn't it more about the figures being close/well matched from cylinder to cylinder rather than the actual PSI. I suspect most compression testers give a fairly innacurate PSI reading but it is repeatable.

 

Nigel

[Shaft]

Plus 1

 

Fully agree with Nigel, very wise words.

[Guest Gibbynolds]

Hi peeps 

I have a 2.1 pinto fast road cam. Big valve head. I’ve fitted a facet push pump and king filter/regulator set at 3.5 psi burton racing say that 3.5 is right. It’s got brand new Webber 45’s. On turnover I’ve had it flooding and fuel pooring out the trumpets. Ive adjusted it down to 2psi now. But My compression is down to 80psi on all cylinders.  So I put some oil down the plug hole and it’s gone sky high nearly 300psi I’m thinking the fuel washed the oil out of the rings so they wasn’t making a seal ? Now the I’ll I’ve used is very thick so put the compression up. 
 

thoughts please ?? 

[Snapperpaul]

300psi is not achievable on a Pinto so suggest you gauge is not working properly

[Mrbarry]

My thoughts are change the oil as fast as possible. If it was over fuelling as much as you say then fuel will have run past the rings and the oil is scrap now. Running the engine like that will wash the bores in seconds. 
Low compression is a sign of a problem, gas escaping somewhere. Oil down the bores will cause a massive seal on the rings for a compression test and if the results rise like yours that’s proof it’s rings or bores at fault. If the compression is still low with oil poured in the bores it’s head at fault, valves not seating, stems bent, head gasket not sealing.... 

 

Id swap the oil ASAP and get the engine hot then retest. Use Mineral oil it will help the rings cut to seal to the bores, synth or cemi is too slippery for that. 

[kevin the chicken]

You are right with the fuel pressure, I had leaks everywhere on the carbs until I put a regulator on and adjusted the pressure down. I think I used 2 or 2.5 psi like you. They do need low pressure but plenty of flow when they get working properly.