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IANMM
17-08-2010, 13:52
Just done my compression test on my engine (warm) and these are the results.....

Cylinder 1 129

Cylinder 2 128

Cylinder 3 125

Cylinder 4 129


now they all look sound to me...........i have blocked off my extra breather off the mechanical pump section so the only breather going onto my catch tank is now off the rocker cover but im still concerned why my car chucks out oil into the catch tank on high revs/hitting rev limiter......

any ideas?
James5
17-08-2010, 14:00
They all look ok as all around the same, but I would have expected them to all be about 150psi are you standard or low comp engine?

Did you do the test with the engine warm and the throttle open?
IANMM
17-08-2010, 14:01
yeah throttle open....standard comp
James5
17-08-2010, 14:04
im still concerned why my car chucks out oil into the catch tank on high revs/hitting rev limiter......

any ideas?

I also done the extra breather to the block made very little difference at the time.

Sounds like you are pressurising the sump and forcing the engine oil up into the sump. Mine did the same I ended up replacing the rings with total seals, replacing the valve stem seals and getting new valve guides to be put on just to be on the safe side then done a few miles all good and then sold engine on in favour of f4r lump:crap:. My comp tests were good aswell back then.
Andrew Cooke
17-08-2010, 14:28
they look low for a standard compression engine, you might want to consider a leakdown test.
IANMM
19-08-2010, 13:44
bloody hell another bit of kit i need to buy :(
IANMM
19-08-2010, 13:49
anyone worked out the maximum pressure from the compression ratio ?
IANMM
19-08-2010, 13:59
is it standard compression ratio is 7.8-1

you need to calculate what the maximum pressure within the combustion chamber should be, to do this multiply the compression ratio by 1.38 to work in Bar, alternatively multiply the compression ratio by 20 if you want to work in psi. You will also need to calculate the figures for 66% and 80% maximum pressure to do a comprehensive test.


7.8 x 20 = 156 (100%)

156 x .8 = 124.8 (80%)

156 x .66 = 102.96 (66%)
olidaviesuk
19-08-2010, 14:00
Stick a couple of squirts of oil into the cylinders then repeat the compression test, if the compressions increase then it's the rings, otherwise time to buy a leakdown tester :sad2:


bloody hell another bit of kit i need to buy :(
Andrew Cooke
19-08-2010, 14:28
is it standard compression ratio is 7.8-1

you need to calculate what the maximum pressure within the combustion chamber should be, to do this multiply the compression ratio by 1.38 to work in Bar, alternatively multiply the compression ratio by 20 if you want to work in psi. You will also need to calculate the figures for 66% and 80% maximum pressure to do a comprehensive test.


7.8 x 20 = 156 (100%)

156 x .8 = 124.8 (80%)

156 x .66 = 102.96 (66%)

that looks a bit rule of thumb, try this.

http://www.wallaceracing.com/dynamic-cr.php
IANMM
19-08-2010, 14:34
that looks a bit rule of thumb, try this.

http://www.wallaceracing.com/dynamic-cr.php



errrrrr where the hell do i get all them measurements from lol
IANMM
19-08-2010, 14:42
Number of Cylinders :4 Bore in Inches : 2.99 Stroke in Inches : 3.03 Rod Length in Inches : ?? Static Compression Ratio : 7.9(:1) Inlet Valve Closes ABDC : ?? º Boost Pressure in PSI : 17 Target Altitude??
IANMM
19-08-2010, 14:42
anyone help filling in them gaps?
Andrew Cooke
19-08-2010, 15:20
rod length 5.039"

altitude, 100ft will do, it's not like you're in the rockies.

Which cam?
Mart
19-08-2010, 15:39
Just done my compression test on my engine (warm) and these are the results.....

Cylinder 1 129

Cylinder 2 128

Cylinder 3 125

Cylinder 4 129


Which cam are you running? If standard, those figures aren't so good. If a hot stick, the figures are what I'd expect to see, assuming everything else is equal.
Andrew Cooke
19-08-2010, 15:41
try something like 39 deg for a 285 and 28 deg for a standard cam
Mart
19-08-2010, 15:45
I said hot stick ;)
IANMM
20-08-2010, 07:30
yeah a 285 cam

Static compression ratio of 7.9:1.
Effective stroke is 2.78 inches.
Your dynamic compression ratio is 7.31:1 .
Your dynamic cranking pressure is 141.33 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 17 PSI is 15.76 :1.
V/P (Volume to Pressure Index) is 33