Leakdown results good or bad?

[Machinator]

I bought a compression tester and geuss what all 8 cylinders were inbetween 155-170psi, is that good or bad? If its ok then I am still at a loss as to why my trap speed in the 1/8 mile was so low. I have a dfx clutch so i hope that is not the problem. Guys please chime in!

 

[04SNK390HP]

thats good. I just did mine yesterday. All mine were the same except the #3 cylinder which was 110!!!!!!!!!!!!

 

[IronTerp]

The "compression test" results appear to be fine...all within a normal percentage of each other.

A "leakdown test" is another test entirely and is not to be confused with a "compression test".

 

[Machinator]

The "compression test" results appear to be fine...all within a normal percentage of each other.

A "leakdown test" is another test entirely and is not to be confused with a "compression test".

I did misword it sorry, the car is going back to Texas with me and will be at Murillos soon.

 

[Machinator]

Ttt

 

[93cobra#3326]

also comp test should be done with the engine at full operating temp. to be completely accurate. a cold engine may give false low and erratic readings. you also dont want a large spread between the highest and lowest reading between cylinders.

FYI: i tested mine cold too and had 160-175 because i was lazy

 

[Machinator]

also comp test should be done with the engine at full operating temp. to be completely accurate. a cold engine may give false low and erratic readings. you also dont want a large spread between the highest and lowest reading between cylinders.

FYI: i tested mine cold too and had 160-175 because i was lazy

I warmed the car up and these were the temps. I have a theory about cars that have high compression test results and its not good. We know that some of these engines came with pistons way to tight in the bores and I think these high psi's that some people have when they test the motor isnt good.

 

[IronTerp]

I warmed the car up and these were the temps. I have a theory about cars that have high compression test results and its not good. We know that some of these engines came with pistons way to tight in the bores and I think these high psi's that some people have when they test the motor isnt good.

Another possible explanantion is varying deck heights which shrink the combustion chamber.......

 

[Machinator]

Another possible explanantion is varying deck heights which shrink the combustion chamber.......

I had never thought of this, I would have thought the QA department would catch that but it is a very viable explanation.

 

[WDW MKR]

I had never thought of this, I would have thought the QA department would catch that but it is a very viable explanation.

I'm not so sure these engines had a QC/QA department!

Regardless, variance in deck height is exactly why you don't compare compression test results from both banks. You want the LH cylinders to be within a certain range of each other, and the same for the RH cylinders.

 

[Machinator]

Each bank was all within 15psi of each other so I figure it is good.

 

[WDW MKR]

I think you want less than 5% variance between the cylinders in each bank (1-4 and 5-8). A 15psig difference would be almost 10%. That still isn't terrible, but might be reason for a leakdown test to ensure everything is cool.