Do carbon deposits on the piston increase the compression ratio and compression test?

Just curious.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Increase in ratio?, maybe on a very small scale. No effect on cranking compression unless it's so bad it causing the rings to bind in their grooves somehow.

Devon

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

I was just thinking, if it is taking up space in the combustion chamber, it is making that space smaller so the same volume is being squashed into a smaller space. as if a dished piston became flat or domed. right ?

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Yes, but on a very small scale. Why do you ask?

Devon

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

I ask because I am planning to do a compression test but if there is carbon buildup in the chambers then it may give me a falsely high reading. Ive been googling the water trick to steam clean the deposits out.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Don't worry about it. Cranking compression (pounds per square inch) does not necessarily correlate with compression ratio.

Are you familiar with performing the test?

Devon

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

yea ive done it about 10 times before over the years. I do peak comp and leakdown. im no expert but. I have a gage, it threads in to the hole. I take out all the plugs and squirt oil on the far wall if i have a low reading.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Squirting the oil in doesn't fix the low compression, it only makes the guage read higher..

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

I usually leave the plugs in, except for the cyl being tested of course. The engine cools down too much if you spend time pulling all the plugs before you start. Don't forget to have the throttle open a bit before cranking too. I think you'll be pleased with the numbers being it's a pretty low milage engine.

Devon

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

The oil isnt meant to fix anything, its just part of the test... if after squirting the oil the compression comes up it means the rings are worn. If it doesnt come up it means a leaky valve.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

I hope so. The number 7 plug was quite oily when I pulled them to replace. All the others were normal looking. I havent checked them since I tuned up the ignition system though. I guess ill find out when i do the test.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Carbon will make the engine detonate and ping and should be removed... I take the engine appart to clean it, i have not had very good luck with any misting techniques... get in there and clean it right.... if you do mist it, besure to clean the spark plugs after as they will foul up...

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

Seafoam seems to work in removing built up carbon deposits. Smokes like a bitch, though. I use a fuel stabilizer called PRI-G that prevents gasoline degradation from creating carbon deposits in the first place. But with 40K miles, I cant see how carbon could have built up enough to be noticeable if the car runs well.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

maybe there is no carbon buildup.

I was told that 87 octane was the correct gas for this engine, but maybe it isnt after all.
Here it is ........ http://v8buick.com/showpost.php?p=1557232&postcount=13

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

:idea2: 93 is cheaper than a re-build...

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

It only takes a few hours to remove the intake, heads and clean everything, no need for a rebuild. It will run way better with clean piston tops and head chambers.. While you are at it pollish these surfaces.... I run 87 octane on low comp 350s all the time with no detonation. You will never clean out all the carbon deposits with seafoam or water unless it is very new thin build up. I do not like fouling my plugs and exhaust with the carbon anyways.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

which car are you running low CR and 87? what kind of ETs do you have and hp/torque? Ineresting.

 

Re: Do carbon deposits on the piston increase the compression ratio and compression t

I have run 6 different low comp 350s in my 76, 75, and a 83 Regal and all ran fine on 87 octane...I prefer premium as I could get better tune up and run larger gap on the plugs. I ran high 12s with some nitrous and a low comp 350 in the 83 regal. I made 398 hp and 425 ft of tq with a built up forged piston engine at 8.3:1 compression using home ported heads.... I plan to make over 440 hp with my next engine then add twin turbos on top of that.