I have a 96 trans am the engine was just redone... Has port and polished heads /intake to match the lt4 hot cam.. I bought the car this way... I have decent top end but no take off... Not even as much as a stock car should have throttle seems slow to respond as well... Just put new plugs and wires on hoping a tune up would do the trick and it didn't... Checked compression today all 8 cylinders tested btween 80 and 110... Has no smog pump no air box as it has a cold air intake on it.
Has a new eagle bottom end the engine was bored .30 .....
Any other suggestions the only thing i haven't gotten taken care of is the new exhaust which goes on monday..
And a computer tune...
The other question is it has an lt1 knock sensor would putting a lt4 knock sensor make that much of a difference? I have read many different things.

Between the specs on the cam are as follows:
The duration at lash point in degrees (intake/exhaust) is 279/287; duration at .050" tappet lift (intake/exhaust) is 218/228; and maximum lift with 1.6 rocker ratio (intake/exhaust) is 525/525. Valve lash is zero/zero and lobe centerline is 112 degrees.


Anyone have any suggestions as i would like to hear some input before i decide to have the engine yanked and redone how i want it...

 

compression seems low, I am all stock except for cam; my compression is 170-180.

 

Whats stock compression we was thinking between 80 and 130 is good compression.

 

80/100 is good compression for a well worn motor-not a new one.

There is no such thing as an LT4 knock sensor. You must mean module. I would not worry about that until the compression issue was investigated. Maybe a leakdown test is in order.

 

Yea this motor was just rebuilt and was bored .30 over... We took it to the guy who built my last motor and he said sounded just from the sounds minus the terrible exhuast leak sounded like a valve issue...
So the compression seems really low is what your saying.

 

and i did mean module lol... Sorry about the mix up...
I;ve got maybe 500 miles on this rebuild. I bought it with 45 when i loaded it up on the trailer...
I didn't know if it was the cam or what never had a lt4 hot cam and not a lot of people talk super high of them.

 

Yes I would do a leak down test, that way you will know what is going on. Could be valves or worn rings, but on a new motor the rings should be good. What did the old spark plugs look like? My car has a lot of low end even when its not running 100%, I have the lt4 hot cam with a a4 and 3.42s.

 

The crappy part is literally the heads were just re done wonder if the shop screwed the guy i bought the car off of and didn't do the head work correctly...
because for the compression supposed to be that much higher... Thats a huge difference...

I've never preformed a leak down test how you do that?
Sorry i have only learned about engines last two years... But i learn fast just want to make sure i preform it correctly.

 

Any any suggestions on why my compression would be so low? Should i test it again to make sure the readings we got was right? and do most people test it by removing all the plugs or whats the common way of doing it?

 

This shows a leak down test on a subaru http://www.youtube.com/watch?v=4HYdaxxas4Y. You should be in the green and not a lot of differences should all be within 15% loss of each other. If your over 40% loss then you would listen for where the air escapes. Exhaust, intake, oil fill cap or radiator. This will tell you if you have a bad exhaust valve, intake valve, worn rings or a blown head gasket.

You could try putting some oil into the cylinder and then do a compression test. If the compression goes way up then this shows your rings are worn. This shows a compression test http://www.youtube.com/watch?v=X_tbk...eature=related.

 

Could the valves all just be too tight? Allowing the low readings?

 

Describe how you did the compression test in detail.

Things people usually miss is do it with the engine warm and the throttle wide open, and give 5 pumps or so on the gauge. Gotta have the battery well charged also and all the spark plugs out

If all of that was done, then i'd reset the valves and try again.

If it still doesn't improve I would be checking cam timing.

 

How we did the compression test was by pulling one plug out at a time... and checking the compression in each cylinder..and just bumped the ignition to til it indicated on the gauge for each cylinder we did. and with the headders trust me not an easy task.

 

Any the engine was relatively warm... We had to let it cool a lil bit as it was too hot at first had been driving it around for half the day and performed the test in afternoon./evening.

 

compression testing should be done at WOT.


I think shoebox's website has the procedure in detail

EDIT: yep...

http://shbox.com/1/4th_gen_tech2.html#compression_test