anybody know what compression my compression tester gauge should read on low comp accralite pistons on a frst, im getting 60psi on number 1 and around 100psi on the others,i know they should be the same so im ganna change the rings,but it would help if i knew how much they should be at! ive been told standard pistons should read around 150psi,would it be lower as they are low comp,or shouldnt that effect the reading??

thanks alot

 

About the 100-120psi would be about right. Have you performed a wet and dry test to verify the rings?

 

i put some oil in and retested,reading went up about 10psi on each,so low comp pistons will give a lesser reading on a compression test then?

 

Wet test would indicate fubar rings then. Yes mate low comp pistons will have a reduced reading on the compression test. (As the name suggests low compression pistons)

 

so youd say rings need doing?

i thought low comps would give a lesser reading but the old man was saying different

 

You're absolutely right the whole point in low comp pistons is that they drop the compression. As such will give a leeser reading than standard pistons. Turbo cars will give a lesser reading than an N/A car anyway. As the wet test raised the readings I would say it's fairly safe to say you could do with some new rings. Do check with others first though

 

i changed the cam over today and checked again and got the following readings...

piper t2 cam: cylinder no.1: 60psi,the rest made around 100psi

standard cam: cylinder no.1: 100psi,the rest made around 140psi

now cylinder 1 is still down 40psi but why have they gone up using a standard cam? im ganna change the rings this wednesday anyway but is 40psi down on one piston ganna make much difference in power??

cheers lads

 

anyone???

 

Not sure why changing the cam would alter the compression test results.

 

thats what confusing me.....

 

is it not something to do with the vavles being open more on a higher lift cam? or is that not how it works

either way, you have a problem with cylinder number 1

 

I spose if the valves are opened earlier/later in the cycle that may cause the difference in compression

 

maybe the piper cam lobes are worn check both cams for wear. you probably wont notice any difference in power the turbo will raise the compression .. is the engine missing at idle

 

ive taken the head off and there are some little marks on the pistons where the valves have hit (the piper vernier pulley had no tdc mark on it so i presumed it was the same as my kent one,so must of happened when i turned it over) ,have taken the valves out of number one and put them in the pillar drill to test but they seem ok. any suggestions?