What causes the 03 cobras to get low compression on the driver side? Should motor get rebuilt or heads be swapped to fix the problem?
Thanks for info
Thanks for info
low compression on driver side question?
- Thread starter LETHL 03
- Start date
your motor is about to blow up lol jk..i had same issue then spun barring
Pistons, rings and cylinders with detonation damage.
First find out why it detonated and fix that, then evaluate the extent of the damage and go from there.
thanks guys. car is running strong, still trapping 122-124 on the 1/4 mile, but i want to get it fix so maybe some CP pistons and cams can be my next upgrade :banana:
Its your head. I had the same problem. How many miles are you at? You may get away with just rebuilding the head.
im at 32k miles.
What were the compression numbers? Did you try putting a little bit of oil in the cylinder to see if the compression came up? Are you having any other symptoms, misfire, rough idle, knocking / ticking noises? Any responses your getting here are just guesses. Unless you do a little more diagnostics you wont know. There are ways to narrow down the source of the compression loss without tearing the motor apart or guessing.
What compression readings are you getting on the drivers side. Do you hear a miss? My #8 cylinder was at 90psi the other three were between 100 and 130psi on the drivers side and missing bad on the drivers side. I could really hear it from the tail pipe. My motor was at around 110k miles and like yours still running strong. My trap speeds were at 122 and last dyno it made 500rwhp. When I tore down the motor the cylinders looked fine pistons were in great shape. As for the heads, It was hard to see anything wrong with them. Im still waiting on the machine shop to tell me about the heads. If I was only at 32k miles I would of just pulled the head, rebuilt, and do the head cooling mod.
Like what what said above, what were the pressures. My experience is if one side is lower then the other it's probably cam timing. I have seen the pressures off as much as 30psi from the drivers side to the passengers side.
I had the same problem. Melted all 4 on the drivers side.
For whatever reason(s) the left side seems to be the first side to have problems.
We all assumed it was heat related and I have yet to see that debunked.
Over heated guides will eventually degrade your exhaust valve seal to the seat.
So it could be valves.
Over heated or detonation damaged pistons(which will also rapidly become over heated) will grow out into the walls, ring end gaps disappear, ring ends butt, rings push out contact the walls, begin to drag on the walls or seize and bend or rip out the top ring and land.
Or it could be pistons.
It could also be cam timing but that does not appear out of no where like this other stuff does.
This post:
If the compression come up after adding a little oil it is most likely hurt pistons.
If it does NOT, then it is most likely guide/head/valve related.
We all assumed it was heat related and I have yet to see that debunked.
Over heated guides will eventually degrade your exhaust valve seal to the seat.
So it could be valves.
Over heated or detonation damaged pistons(which will also rapidly become over heated) will grow out into the walls, ring end gaps disappear, ring ends butt, rings push out contact the walls, begin to drag on the walls or seize and bend or rip out the top ring and land.
Or it could be pistons.
It could also be cam timing but that does not appear out of no where like this other stuff does.
This post:
If the compression come up after adding a little oil it is most likely hurt pistons.
If it does NOT, then it is most likely guide/head/valve related.
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In my case, when I added oil compression went up but like I said before my pistons were fine as were the cylinder walls. What I forgot to mention was the discoloration on water ports around the exhaust ports . They were much darker on the drivers side compared to the passenger side. Adding oil woukd also constrict air leafing through the valves and give a higher compression reading.
What is the lowest number you would say is good compression. I had 6 cylinders read 160psi and then 7+8 read 140. Still good right?
^^^^ Those are still pretty good. But they may be on their way out, not trying to scare you, just saying. Those two always seem to be ones that go first, even on the B headed Cobra's. Head cooling mod may help prolong it. It definitely won't hurt it.
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^ Thanks for the insight. I already am planning a build that will start when this one dies or in DEC '13.
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