Compression test numbers?
 

As per an argument with Snwy:D, here's what I got:

#1: 156
#2: 151
#3: 153
#4: 155
#5: 151
#6: 152

I did this test with the engine completely Cold, and the ambient temperature outside was only about 5 degrees Celsius(41 degrees Fahrenheit).

Opinions? Good? Bad?

The engine only has 175000km on it (108 739 miles) and its a 1979 if that makes any difference.

Thanks,

Derek

they're pretty even across the board, i think they look good

agreed. plenty high, and pretty much even across all cylinders.

they arent low low, but they are taking some performance, like i said, originaly numbers are more like 180.... its not bad your okey dokey, but its development. i was just saying that in teh previous thread because it might be a source of the white smoke from the exhaust.

i dunno, some ppl report 120 from there really worn motors, those look to be okay. if you had it emmisions tested it would really show ya how its doing. my motor has 220 across the board, but that kinda has a super high cr :D

what octane are you runnin with that CR?

87 and a little amount of 14 year old fuel.:(

^^^ I think he was askin Shady. :D

uh, yeah, that was a shot to shady, but you might wanna just splurge and get you some 97 octane, and go buy you some octane booster to go with it, and just blow some funk out that motor. Its what i would do. Even if it doesn't blow the funk out completely, it'll at least help it a little. Makes my Z run noticably better if i just run a tank of the good stuff through it now and again. Just a thought.

the way its seat tuned right now (no pre ignition) i can run 92 octane. here we have 94 octane at every pump, but its an xtra 5 cents per liter. 92 is 8 cents more than the sign price. all i can say is ouch. im gonna need 110 for the racecar!!

Gear it to run ethanol and i'll see if i can't ship you some shine up there.:wasted:

If only the stuff didn't eat up anything rubber.

lol 87 thats bad
here we have 91, 95 and 98

Those are all fine. The '79 with N47 head w/stock 44.6cc combustion chamber and dished pistons (-10.9cc) should be around 165 psi brand new for a factory rated 8.3:1 compression ratio. I'll bet money, if you run that compression test again and put a few drops of oil in the spark plug hole before you run the test, you'll pick up about 5 to 10psi on each cylinder with a "wet" test. Pretty much what you did was a "dry" test. That oil will help seal the compression rings a little more and give you some missing psi like it would have when the motor is running normally.

Not really. The rest of the world calculates octane slightly different than the US. Your 98 octane is roughly equal to US 94 octane, your 95 is about the same as our 91 and your 91 is about the same as our 87... so, it's not as bad as you would think just by looking at the answer, you really need to know the equation. ;)

ahhh i see now i have some knowledge to go and throw at my mates tomorrow. cheers

A18DXD fuel from ERC. So what if it causes cancer and mutates babies? It only costs like 30 bucks a gallon. running any higher octane than you need to prevent pinging is wasted money. higher octane fuels are harder to ignite, thus the combustion event takes place a little too late when you run high octane in a low compression engine and you could possibly lose a little power. Tried 110 on the dyno in a 9:1 chevy and then went to 91 with a little polypropylene dioxide and picked up like 10 horse across the sheet. I have no idea where to get these good additives except ERC and don't think they will like our Cats, but they make power. make the fire at hot and as fast at possible without pre-ignition.

I've also read somewhere that octane ratings vary for the same exact fuel based on what altitude the fuel is being sold at. Fuel rated for X ammount sold at sea level will have a different rating than the exact same load of fuel if it's trucked to a city at 5000' elevation. Most brand name gas stations around where I live (4000'+ elevation) only have an octane rating on Premium of 91, yet the same companies premium over the hill at around 1000' elevation is rated as 92, some are rated 93 at sea level, yet it's all the same gas.

Bringin it back - I decided to do compression test numbers as well
I haven't done the wet test yet so here's the dry
#1 165
#2 160
#3 165
#4 165
#5 165
#6 165

They're all give or take 1-2psi since it was analog and I was too lazy to guestimate the small differences but they were real close to 165 each time (except #2).
202Kmiles '83
I guess they aren't bad but I think i need some new spark plugs though.

mine are 180 across the board!!!! lol

I hope you're talking about the 280Z and not the 260ZT

ok mine are about 280psi across the board for me..






(12.75:1 C/R)

I actually just did a compression test a few weeks ago because of this thread, and mine were all still right about 140 across.

What's that in?! the bike?

R1's are 12.7:1 sooo prolly. whered you get the 5 from though?

its 12.75:1 most of those specs you see online usually are a little funky, like the whole R1's weigh 800 pounds BS.