compression

[gp13069]

what should the compression psi in each cylinder be?
the last time I did a compression check on my 3.1 1991 block with 1989 2.8 heads it was around 225 psi per cylinder. is that to high & if so what should it be?
that's with the block zero decked
.040 taken off the bottom of each head.
.060 head gasket.

[robertisaar]

whats wrong with more compression? i think 150-175 is normal. but what kind of static compression are you running?

[IsaacHayes]

What quench does that work out to?

[gp13069]

I have to Guess on the static compression im running never measured. i would guess in the range of 12:0 - 13.5:1 I know if i run 87 pump gas it barely runs at all but if i run 91 it runs like a champ no knock
quench ? i not sure what that means ?

[robertisaar]

quench is the area left in the combustion chamber once the piston is at top dead center. i wouldn't even think of running 87 in that, thats asking for detonation. i don't know if 91 is even enough at that level. i'm guessing you meant rear wheel drive 2.8 pistons in a fwd 3.1 block right?

[gp13069]

Well, the block has a letter T on both sides of it and the number in the middle of the t are 23 and 22. on the knock sensor side there is a letter R. if i get the casting # off the block it will that tell us?
what i had to work with was 2.8 heads shaved .040 + intake , 3.1 block zero decked, with 2.8 crank & rod's, the fwd. pistons are small dished Teflon coated & .030 over bore,
as for the cam it wasn't my choice the guy who built this engine told me that it would open the valves quit a bit more than stock. he was right it does open the valve a lot more. that pretty much it.

[mtownfiero]

how do you test compression?

[bszopi]

With a compression tester.

Seriously though, that is how you do it. It is a tool with a gauge that screws into the spark plug hole.

[robertisaar]

don't forget to remove all of the spark plugs or else you could get bad readings.

[gp13069]

ok this is what ill do i will get a compression tester and test it again. i'm on vacation now and i ll check the compression in the engine once i get in the car. and well see what i get then. un less i can do it on the stand but that is not a good idea. i don't think?

[IsaacHayes]

You can test it on the stand. Hook the starter up and turn it over with no plugs. But you won't get a true reading as you should do it with a warm engine so that the rings/cyl walls are expanded.

[gp13069]

how warm? 15 mile trip or 7 mile trip? The threads expand and contract with the plugs in or out. I do not want to mess up the threads!

Got it in and running I'm running 89 octane right now. It seams to be OK until warm then on start up it's like the timing is to far advanced. but cold it's fine.
Since I raised the comp ratio I should use a cooler plug right? When I get an answer I will Do compression test when I change the plugs.
I was pressed for time and had to get it running or i would have tested it earlier. thanks

[Lilchief]

How much cr are you running? Mine has 9.8-1 and had to have the timing set to 2 degrees BTC by the chip during the start up and then changes to 10 after it's running. Had the same simptom. Started good when cold but not when warmed up.

[Lilchief]

Sorry didn't see the earlier post on the cr .

[gp13069]

Ok I got, for this week on 89 octane fuel, my results were 328 miles on 14.49 gallons. that's about 22 mpg & hard starts when hot. So i will see what i get on 93 this week. so far the hot starts are better. im going to fix my exhaust so its quiet and then see what's next.