318 compression test results

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Flyinbrian72duster

Flyinbrian72duster

Dart and duster
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Just did a compression test on my 318 with 90k results are 1-125psi dry 132 wet 2-123dry 134wet 3-114dry 118wet 4- 138dry 153wet 5-134dry 140wet 6-125dry 135wet 7-137dry 138wet 8-136dry 148wet test was performed engine at operating temp all plugs out throttle at wot
I checked cylinder 3 twice each way. My question is my teener to tired for a cam
 
Results in PSI, test was performed engine at operating temp all plugs out throttle at wot.
1-125dry 132wet
2-123dry 134wet
3-114dry 118wet
4-138dry 153wet
5-134dry 140wet
6-125dry 135wet
7-137dry 138wet
8-136dry 148wet

I rearranged this so it was easier to follow.

What year is your 318? Low compression on one cylinder could be a few things.
 
dano said:
Results in PSI, test was performed engine at operating temp all plugs out throttle at wot.
1-125dry 132wet
2-123dry 134wet
3-114dry 118wet
4-138dry 153wet
5-134dry 140wet
6-125dry 135wet
7-137dry 138wet
8-136dry 148wet

I rearranged this so it was easier to follow.

What year is your 318? Low compression on one cylinder could be a few things.
Click to expand...
Thank you for the rearrangement. It's a 71 90k I do know valve seals are gone only get a puff of smoke few times a year after start up
 
If you can, do a leak down test, it tells a better story of condition of your short block
 
Flyinbrian72duster said:
Just did a compression test on my 318 with 90k results are 1-125psi dry 132 wet 2-123dry 134wet 3-114dry 118wet 4- 138dry 153wet 5-134dry 140wet 6-125dry 135wet 7-137dry 138wet 8-136dry 148wet test was performed engine at operating temp all plugs out throttle at wot
I checked cylinder 3 twice each way. My question is my teener to tired for a cam
Click to expand...
Probably a bad exhaust valve/seat.
 
16433138704471665447784217198245.jpg
that's cylinder 3 both sides of plug
16433139314745929353364471739208.jpg
 
If it doesn't burn oil, and the oil pressure is good, I wouldn't have a problem with pulling the heads, doing a good 3 angle valve job, and installing a relatively mild cam (like the old purple 340 cam or a bit less) if you're keeping everything else stock. If you up grade the intake and exhaust and maybe rear axle ratio, you might consider something a bit more high performance. You don't want to get carried away with the cam unless you're going to pull the engine down further and checking piston to valve clearance and getting some new valve springs.
 
With the head work, install the correct valve springs for you cam and be sure the guides are topped or your lift works with their height. As stated, don't get carried away with the cam, it becomes a slippery slope.

What cam are you considering?
 
dano said:
With the head work, install the correct valve springs for you cam and be sure the guides are topped or your lift works with their height. As stated, don't get carried away with the cam, it becomes a slippery slope.

What cam are you considering?
Click to expand...
Something like the 340 cam. I do have a Eddie performer intake ,650 avs carb,electronic ignition, 3:55 sure grip, 2.5 inch dual exhaust currently on it
 
Flyinbrian72duster said:
Something like the 340 cam. I do have a Eddie performer intake ,650 avs carb,electronic ignition, 3:55 sure grip, 2.5 inch dual exhaust currently on it
Click to expand...
That should work fine together. A bit more compression ratio, and some headers would help a bit more, but, as Dano mentioned, it's a slippery slope when you start doing upgrades. Where do you stop? Doing one thing effects a lot of other things the faster you want to go.
 
They're just ok. After a valve job, a slight head shave, and a thinner head gasket, that will help a lot.
 
The cam I was thinking is .429/
444 lift duration 268/276 overlap 44 centerline 114 if I'm correct that's the 340 cam. Or theres this cam .410/.425lift 248/256duration 32overlap 110 degree
There both purple hyd cams which one would be best
 
Without porting the heads, putting in bigger valves won't help. I'd go with the first cam.
 
Gonna do the leak down test 2morrow been snow plowing all damm day. So far I got 3 of you saying to do it and one of course saying not to. I do have a 79 360 sitting but gonna need a rebuild. If I did the 360 dont you need a different torque converter.
 
What you need is;
a TC balanced for a 360, or
a flexplate for a 360 and a zero balanced TC.
Pre 1967 TCs have a different spline count inside, and a different diameter crank pilot.
This means you can use any NON loc-up, post 1967, 318 convertor which I think are all zero-balanced, , on any other post 1967 engine, with the correct flexplate.
You can knock the balance weights off any TC to make it a zero-balance TC.
 
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If you do a LD test it might tell you two things;
1) the condition of the very top of the cylinder, and
2) which valves are leaking and how badly.

Well wait a sec, the compression test already told us about the valves, and
when the heads come off for a valve job, you can physically inspect the tops of the cylinders......... So I mean, you can do an LD test but in my thinking it its like arriving at your destination with a flat tire and saying "I wonder when that happened"?
 
Last edited:
AJ/FormS said:
If you do a LD test it might tell you two things;
1) the condition of the very top of the cylinder, and
2) which valves are leaking and how badly.

Well wait a sec, the compression test already told us about the valves, and
when the heads come off for a valve job, you can physically inspect the tops of the cylinders......... So I mean, you can do an LD test but in my thinking it its like arriving at your destination with a flat tire and saying "I wonder when that happened>?
Click to expand...
So is it worth it to do heads and a cam
 
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