I ran my compression test on a warmed up motor, carb open, all plugs out. Motor is the original 74 400 in my 74 Laguna with 80's 305 heads and a mystery cam. As expected most of the numbers were very high I had first run the test on a 5 degree motor and the numbers were lower

(1) cold 195 hot 205 psi (2) cold 180 hot 215 psi

(3) 180 / 215 (4) 157 / 195

(5) 160 / 180 (6) 180 / 200

(7) 132 / 158 (8) 150 / 170


The proper 400 flexplate is missing and the motor has been run with a 305 blue flexplate for god knows how long. The idle oil pressure drops down to 10 or so when hot.

One of my concerns is that the rear bearing is worn, and this may be effecting the compression in cyls 7 and 8 due to piston wobbling etc...

As another weird thing, #3 shot out coolant when the motor was hot, but not after it cooled down. I could not really notice any steam coming out of the drivers side pipe, not anymore than normal as it is 5 degreees now.

The heads are coming off when I get the car home anyways to get rid of those 305 heads, I can't imagine the coolant came anywhere but from the intake or head esp with the compression so high on that cyl. I will check out the valves to see if any are burned.

Any comments or suggestions??

Well keep your fingers crossed ,and hope its just a headgasket!!

GOODLUCK
jason

dam you got alot of compression with those 305 heads on a 400 ..prob got a too small of cam too ..by looking at your compression...i wonder if they drill the steam holes in the heads..???

Yup I was quite suprised to see those 215 psi reading for sure!! The static CR figures out to 10:1 assuming 58cc chambers, -20cc dish pistons (stock 400) and 0.040 deck clearence.

I had put some regular unleaded in there just after picking the car up, I never would have guessed so much compression. The timing is set at 18 deg initial, blown vac pot 32 total with a very long delay before rising, looks like stock weights in the dist no binding etc.

I will be shocked to find any steam holes on there, having used crappy 601 heads and a standard flexplate (probably from the same LG-4 the heads came from it's blue typical 78 up factory overspray) I would not be shocked to find the stock cam, though there is a chrome timing cover, so maybe they did slip in a cam. It may have the lobes worn, hence the higher cranking compression. The Idle vac is 24" too, another sign of a mild cam.

Btw there is a Holley single plane intake (looks like a Torquer II) of unknown part# and a 4160 Vac sec single feed 600 cfm carb. Quite a bit of 80's random hotrodding. Oh yeah all this is feeding into stock exhaust manifolds piped into 3" side pipes

You are going to go thru the whole motor right? Well over 10% difference in cranking compression even between the better cylinders.

Ha!! I ran 87/89 octane with 225psi cranking compression on hyper pistons for a little while, until I found out that I had that much compression and that the octane level was that low. Spiked it with 114 octane for a little while until I ran out, then ran it with 89 octane again. Pistons are all still in one piece and look great. 80's #416 305 heads.

Trever