did a compression test and number seem to be low . range around 155psi on all 4 cyc.

 

I have that type of compression on a 8.4:1cr motor.

i would say you probably should be around 180psi go do a leakdown test and see what condition the motors in

 

mine is at 185 across..

84.5mm cp 9 to 1's
89mm crank
gsr head
.040 head gasket

 

depends on alot of factors which include, what head, what gasket, how much material has been machined off, and what cams you have. etc etc

I'd do a leakdown if your worried.


Modified by sewell94 at 1:14 PM 7/22/2008

 

i saw 195-200 across the board on my 84mm 9:1. this is with reshaped chambers which reduce compression a little bit. 155 does seem a bit low.

 

I got 180 across with 84mm 9 to 1 pistons and .056 headgasket which calculated to 8 to 1 compression

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hotrod99 &raquo;</TD></TR><TR><TD CLASS="quote">I got 180 across with 84mm 9 to 1 pistons and .056 headgasket which calculated to 8 to 1 compression</TD></TR></TABLE>

your a tad bit high for a 8:1 compression motor.

 

sorry to thread jack, I have 81.5 9 to 1 and my compression is about 220 across

 

motor is a gsr bore 84mm w/ itr cams. motor has about 1,000 miles on it. stock factory head gasket w/ no head shave.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hbyrd8701 &raquo;</TD></TR><TR><TD CLASS="quote">sorry to thread jack, I have 81.5 9 to 1 and my compression is about 220 across</TD></TR></TABLE>

i have the same thing only pumping 155 !

maybe your guage is off (to the OP)

have you tried a differant tester ?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DaveF &raquo;</TD></TR><TR><TD CLASS="quote">

i have the same thing only pumping 155 !

maybe your guage is off (to the OP)

have you tried a differant tester ?</TD></TR></TABLE>

im not sure if the guage is off but i will try another one and see. maybe do a leakdown test while im at it.

 

Honestly, if all cylinders are equal, and leakdown is minimal, you're probably just fine.

 

180-190 with the throttle open.

 

did you shut the fuel off when you did it?

 

also do you have it wide open when cranking?

i run 9:1. b16 head itr cams, gsr block 84mm with ls crank. i see between 190 and 195 compression, 6 cranks hot motor when its wide open

 

84mm, 9:1 cp, 89mm crank, milled b16 head, oem hg - 183-185 across.

 

ok i did another compression check and leak down on my motor. 7 cranks with fuel shut off and wide open throttle for compression check. NO oil was added to cyl. TDC for every cyl. test on leak down. motor was warm up before all testing.

compression test cyl. / leak down
#4- 157psi leak down- 50%
#3- 145psi leak down- 65%
#2- 160psi leak down- 40%
#1- 157pis leak down- 40%

 

83mm cp 9.1, oem headgasket i got 200 even across.

 

where was the air leaking down from? was it coming through the valves or the crank breathers? if it was the valves...are you dead sure your timing is on?

 

81mm 9:1 gsr oem hg 180psi across the board here

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">where was the air leaking down from? was it coming through the valves or the crank breathers? if it was the valves...are you dead sure your timing is on?</TD></TR></TABLE>

i didnt check where the air was leaking from. the timing was on tdc on every cyl. before leakdown. are the leak down test results normal? when the engine is on idle i can see some white smoke coming out from crank breather of valve cover.

 

150 across with my 8.3:1 motor! your a bit low... but if its consistant i would not really worry...

 

Im 84mm at 9:1 and I have 195+ psi on a COLD motor across all cylinders. Im very happy with the ring gaps I did on this motor. I was 180+psi on the last build, same bore and CR.

 

u do it when the motor was warm?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by A.E Motoring &raquo;</TD></TR><TR><TD CLASS="quote">u do it when the motor was warm?</TD></TR></TABLE>

yes the engine was warm and ring gaps were gap to spec from the box.