Hope you can stand another "compression test results" thread

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jcolman

jcolman

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The engine hasn't been putting out the power that I think it should. Also I got some "pull back" into the exhaust pipe at idle so this leads me to think I've got some sticky or burned valves. Before I put the plugs back in and run some seafoam through the engine, what are your thoughts on these numbers? Flat top pistons, 10:5-1 cr, .30 over. cam is supposed to be 490/490 262 duration.

I may have to take the car to a shop and have a complete valve job done.

Compression test was done with cold engine and no oil added in plug holes. I know my car idles rich as most of the plugs had soot on them.

Cylinder # 1 186
Cylinder # 2 183
Cylinder # 3 155
Cylinder # 4 195
Cylinder # 5 170
Cylinder # 6 180
Cylinder # 7 150
Cylinder # 8 180
 
3 is the worst. Clean up the tune up and go run the snot out of it and the numbers should get closer together. I doubt you need a valve job. If you have soot on the plugs your tune up is killing power like a ****. I’d deal with that first.
 
In my opinion- I have seen engines like yours before where they have a large variance in readings. You do not have burned valves - the pressure in a burned valve cylinder would be much lower. The lower cylinder pressure cylinders are on one bank, #3 and #7. The only reasonable explanation is uneven cylinder sealing requiring honing, piston fit, rings, etc. You should look elsewhere for a loss of power.
 
Buy or build a leakdown tester. .040 orifice and an air pressure regulator. If you have a compression gauge that quick connects, you can usually use it. Remove the Schrader valve. Google it. Lots of info on the 'net about them

The Horrid Freight one does not use "convention" and in my opinion is a waste of time. I modified one to use the "standard" .040" orifice and 80-100psi
 
gambled..........and lost.........on a Horrid Freight. Turns out they do NOT use the standard .040 orifice. Bought a .040 some sort of carb jet off egag and made my own. It would have been cheaper, in the end, to start from scratch, damn near. Although the HF unit yielded "the basics" including plug hose/ adapters etc

Wiki page on these testers, they were born in aviation

en.wikipedia.org

Leak-down tester - Wikipedia

en.wikipedia.org en.wikipedia.org

leak_down_tester-gif.gif

The HF after modification. Changed the one gauge with an old AC manifold one for the higher pressure
img_0914cs-jpg.jpg

I found a .040 some sort of carb jet on Egag and lucked out--was able to reach into the HF body and tap it to screw the jet/ orifice right in
img_0913cs-jpg.jpg
 
Looking at the inconsistency of the compression #'s on all cylinders, I'm thinking a valve sealing problem.
 
Rat Bastid said:
3 is the worst. Clean up the tune up and go run the snot out of it and the numbers should get closer together. I doubt you need a valve job. If you have soot on the plugs your tune up is killing power like a ****. I’d deal with that first.
Click to expand...

jcolman said:
The engine hasn't been putting out the power that I think it should. Also I got some "pull back" into the exhaust pipe at idle so this leads me to think I've got some sticky or burned valves. Before I put the plugs back in and run some seafoam through the engine, what are your thoughts on these numbers? Flat top pistons, 10:5-1 cr, .30 over. cam is supposed to be 490/490 262 duration.

I may have to take the car to a shop and have a complete valve job done.

Compression test was done with cold engine and no oil added in plug holes. I know my car idles rich as most of the plugs had soot on them.

Cylinder # 1 186
Cylinder # 2 183
Cylinder # 3 155
Cylinder # 4 195
Cylinder # 5 170
Cylinder # 6 180
Cylinder # 7 150
Cylinder # 8 180
Click to expand...


What about #7...
 
fishmens67 said:
Looking at the inconsistency of the compression #'s on all cylinders, I'm thinking a valve sealing problem.
Click to expand...
This is my thinking as well. After I put all the plugs back in (after much swearing on #'s 5 & 7 due to the Hooker headers) I warmed up the motor and added some sea foam. After letting it run for about 3 minutes, I shut it off, let it set for 5 minutes, then went for an aggressive drive. The engine "seemed" to perform a tad better and smoother but that could be my imagination. I may end up taking the car to a machine shop in town that does valve jobs and have them take a look at my heads, especially the drivers side head since the three lowest numbers on on that side.
 
jcolman said:
You didn't miss this....I should have mentioned it in my first post. Small block 340. LA
Click to expand...
One thing for sure if that's 262 at 50 duration it's not going to idle very well regardless.., unless the idols turned up a good tick...
Being as were within 60 days of Black Friday I would be thinking about a set of speedmaster heads fully loaded for $700 to my door... You take it to a shop for head work and let them pull them off and put them back on and work on them I can guarantee you'll pay more than that...
 
j par said:
One thing for sure if that's 262 at 50 duration it's not going to idle very well regardless.., unless the idols turned up a good tick...
Being as were within 60 days of Black Friday I would be thinking about a set of speedmaster heads fully loaded for $700 to my door... You take it to a shop for head work and let them pull them off and put them back on and work on them I can guarantee you'll pay more than that...
Click to expand...

Thats seat timing.
 
j par said:
One thing for sure if that's 262 at 50 duration it's not going to idle very well regardless.., unless the idols turned up a good tick...
Being as were within 60 days of Black Friday I would be thinking about a set of speedmaster heads fully loaded for $700 to my door... You take it to a shop for head work and let them pull them off and put them back on and work on them I can guarantee you'll pay more than that...
Click to expand...
I have the idle set at 1000 rpm now. A bit high I know. If I was going to keep the car, I would be interested in new heads but the car is for sale. I'm just trying to get it running as best as it can.
 
jcolman said:
Unknown. The car was raced (drag strip) before it was retired.
Click to expand...
Get a cell phone or tablet plug in bore scope. Look for gouges and ridge in the cylinder walls. It's not uncommon to start with intentions of pulling the heads to have valve work done or install new heads to find the cylinders need re done.
 
jcolman said:
I have the idle set at 1000 rpm now. A bit high I know. If I was going to keep the car, I would be interested in new heads but the car is for sale. I'm just trying to get it running as best as it can.
Click to expand...
Well if it's a profit thing the last thing I would do is take it to a shop....
 
Garrett Ellison said:
Get a cell phone or tablet plug in bore scope. Look for gouges and ridge in the cylinder walls. It's not uncommon to start with intentions of pulling the heads to have valve work done or install new heads to find the cylinders need re done.
Click to expand...
Yep. This happened to me. Looked in the bores with a camera. Saw some coolant in one. Turns out the 8553 gaskets weren’t sealing well (compression test was good) and coolant was seeping into the bores…pitted.
 
Hmmm all on the drivers side. Has the car been sitting or often used? Ever rebuilt and what head gasket if it was rebuilt? If rebuilt were the heads and deck checked for flatness? If it was me my next step would be a leak down test before I did anything
 
Leak it down. I suspect you will see something you don't like. I hope not but it's a hotrod and you don't know the build history specifically. Nice car and you'll figure it out...

JW
 
I hope you did the compression test with the throttle at WOT??

Less than WOT, results are unreliable.
 
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