The V8 Owners Forum -

My engine is very rough and I have just carried out a compression test with these astonishing results:
Dry cylinders 1 to 8
92,97,80,70,20,139,70,90
Wet
102, 100,90,60,20,155,95,100

This is supposed to be a high compression Tuscan Challenge engine (albeit fitted with Real Steel composite gaskets. Clearly something is amiss with the heads, but are readings of 90 a bit low?

What should I be thinking about in terms of potential faults to give this diversity of readings before I strip the heads off?

Any thoughts would be appreciated

Did you have the throttle fully open when you were cranking the engine over?
If the answer is yes then you do have a problem, it might not be the heads though, it could be the bores, pistons and rings.


Edit, just spotted that one cylinder is at 155 which is not bad yet another is at 60 which is terrible!

Edit.. Another at 20, is there even a piston in the bore?

I think its time to pull the heads - 20 - bent valve or burnt out seat or blown head into the valley - whats the crankcase pressure like?

155 is low for a high compression engine 175 is more what you would be looking for minimum.

Are these with the engine warm throttle open and taken on about the 8th push?

Worst case it could be that the piston has broken up in the 20 and then all the shrapnel has been blown around the rest of the engine .

I await the pictures.

I don't know of any common reason why you'd get a much higher than normal reading. If you ignore the 155, I'd have said your gauge was reading wrong.

However, before ripping things apart, I'd have a leak-down test done.