4age 16v - low compression

[number_33]

Hi guys,

I have a 4age 16v bigport. Rebuild with high lift cams in and ex. I got the shim kit, HC piston, valve springs, and practically everything for the head.
*Added = Using a ITB BT*


As for the bottom end, using a rebalanced stock crank.
Engine has just done first initial stage of run in with rev limit on 3.5k

Problem:
The compression is evenly low on all 4 cyclinder. Sent to the engine builder, for check-ups and the head and bottom is fine. Can't figure out what is the problem and at the moment the mechanic and engine builder reckons its the crank pressure. They are telling me that it is not cranking enough of pressure to get the compression up with the high lift cams. Any ideas?

Basically, has anyone used before a high lift cams and have similiar problems? OR is there something i am missing that might be causing the problem?

[number_33]

Also forgot to add, if its the crank pressure, what needs to be done to rectify the problem?

[ke70dave]

how low are we talking here?

those 288 cams are pretty chunky, that will lower your dynamic (right word?) compression considerably.

also what is "crank pressure"???

[number_33]

I forgot the numbers already, i find out from the mech first thing monday. I only can recall that its going almost like a 8:1 CR or like a stock 4age CR
But a high compression engine should run with this high lift cams correct? Why would it go down?

[number_33]

Update - Forgot to add also i am running a ITB BT as well

[slide86]

way to much valve overlap?

are you sure the cams have been setup properly. one cam might be out a tooth, this combined with the large duration might be affecting your compression.

NOTE= compression RATIO and compression in the cylinder are two different things.

you say teh comp is low on all cylinders, i gather this means you have used a compression tested???? what were the results in psi?

[number_33]

They are new cams, but i will get the cams check for setup and tooth.
Yes, i did a compression test check, i forgot the numbers, but on monday i will get it again.

Would the compression ratio go down if the compression in the cyclinder are down or vice versa?

[ke70dave]

nope

compression ratio is the ratio between the volume in the cyclinder at top dead centre, and the volume at bottom dead centre.

if its driving crap then i would say that your cam timing is out.

iver never dealt with aftermarket cams, but you may need adjustable cam gears in order to "Dial them in". maybe someone with experience with this type of thing can jump in.

if your engine is now an interference engine (high lift cams + high comp pistons) becareful playing with cam timing.

[number_33]

Good days guys,
Went today to the workshop, the compression is at 130 on all 4 cyclinder. Suppose to be at 200 to 220.
I have an aftermarket cam gears as well, and we did check if the camshafts are overlaping, seems to be fine.
The engine builder is coming to have a look again to see it.

[number_33]

Also, can anyone please give me contacts of engine builders that are specialise on 4age?

Getting some 2nd opinions might help out.