whatis the stock compression rating in the cylinder heads of an LT1? i recently thought i had burnt a valve and had a compression test done, just wondering if the numbers i got were good or bad.. thanks

 

Should be 10.5:1

 

The numbers you get during a compression test do not really represent the static compression ratio. A lot depends on how the test was performed, how fast was the engine being cranked, condition of engine, etc..
Per the FSM:
Engine should be warmed up
All spark plugs removed (engine will be cold by the time they are all out), but plugs should not be removed when the engine is warm. Figure this one out.
Minimum cranking pressure=100 PSI
Lowest reading should be no less than 70% of highest reading

 

i guess what im getting at is this.... i had one test done at the shop, and got a reading of 0 psi and needed new heads. thats their story. i then took the car to a mechanic i knew and got 190 psi.. is that reading believable?.. and if so, is that about stock compression(psi) for an LT1? thanks

 

if you're looking for a problem, then it doesn't really matterWHAT your reading is so long as the test parameters are the same on every cylinder. the concern here is differential pressure. if you're in tolerance, then who really cares what the pressure readings are? (unless they're considerably low, of course) should be about 160psi (if I recall correctly) in perfect theory, but certainly no less than 100psi.70% between lowest and highest is acceptable;however, MY acceptable limit is 85% - but I'm a tightass. LOL.

 

The 190 reading is possible, again depending on test conditions. I was getting similiar readings on my LT1 when it had a stock cam.The 0 reading is hard to believe, maybe the pressure gauge was not connected properly. If you are really concerned, you may want to try a leakdown test. Is the engine running poorly?

 

the car was running with a very bad miss... it would barely idle, very rarely start when it turned over..there was also a bad sputtering at low rpms under light load... i took it to have diagnostics run on it and after the compression test it somehow came back that i had a burnt or bent valve.. i changed plugs and wires(somehow lol) and changed the fuel filter... i assume the fuel pump is working because i can hear it and when i took the filter off, the line hosed me down.. i did however take the cap back off the distributor and saw that there wasplaces where the spark was jumping cylinders and had literally melted some of the cap... i dont know how this happened.. but it still has a slight miss under a moderate load at low rpms and under heavy throttle at higher speeds... any suggestions will help thanks..

 

did you change the opti?

 

opti, distributor, plugs and wires were all replaced because a bad fuel pump leaked on the distributor.. i just did it all while it was apart.. and its still got a slight miss, and the car still carries on and cuts out under load at high speeds and under acceleration in OD around 1500-2200 rpms

 

timing chain?