360 Cylinder Pressures

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Hi

The cam IS the problem and the Xtreme Energy one I am installing is part number: 20-222-3 as recommended by a Mopar tuner over here.

Thanks for all your inputs guys.

Cheers

Kev
 
Im going out on a limb here, but 279* intake(assuming advertised) is actually a pretty small cam. Maybe what at .050, say 220 to 228. The stock was what, maybe 210*.That would be a sweet street cam with cylinder pressure around 160 to 170.
Now, Im agreeing with everyone that the current cylinder pressure is way low. However, Im not sure that its the whole story.With numbers that low, I would for sure have verified them with a second guage.And if still low, I would follow with a cylinder leakage test. Numbers that low generally point to more serious problems. The leakdown test eliminates the camshaft.
-But thats all moot now that the cam is out.Well, I guess you you could still do the leakage test.If the cam is out, Im again assuming that the lifters are too, which usually means the intake is off too.I just would hate to see you put a different cam in it, bolt it all together, and find very little difference,and all this work was for nothing.
-I guess what Im getting at is; does anyone think you can find 80psi with a cam swap 1 or 2 or even 3 sizes down.Not likely.And until the pressure gets to 140psi+ the bottom is still gonna be soft, especially with 3.23s out back.At 165 the motor comes alive.
-And one more stab at it,timing. Like Crackedback alluded to. Low cylinder pressure,highway gears, and lazy timing, is a sure recipe for a soft bottom end.
-I would have proved the guage first.
-Now, if 279* is not advertised, but .050; well then erase what I said. But who puts a cam that big in a street motor? I mean that would be 40* more than the 292/509 Chrysler Purple. And thats already almost too big in a streeter.
-And most modern small 1 and 2 cylinders start just fine at 40psi and even 30 psi, which is designed that way with the auto-decompressor, so little old ladies can start their lawnmowers.Of course, as soon as it runs and the rpm comes up the a/d dissengages and the engine begins to make power. Just saying
-And I have had engines that run just fine at 120psi. Not a lot of power, but ok for a DD.
-At 80psi and even,that thing should have been leaving a blue trail.Its hard to wear out a top ring(s) and not the oil ring.Im stuck on the compression tester being faulty, and/or lack of follow-up with the leakdown tester,and possibly/likely, some other combination of poor tune. Oh well.
 
So my 2 cents - how tall and wide are the back tires? To the op- you want to burnout the tires? In my opinion trading a cam that comes on at 2000 rpm's for one that seem to come on at 2500 isn't going to get that burnout? I know it's probably to late now, but a stall convertor? A whiplash cam from Hughes that comes on off idle?
Nothing like a v8 mopar 360 that doesn't do a burnout to piss ya off!!
 
AJ/FormS said:
Im going out on a limb here, but 279* intake(assuming advertised) is actually a pretty small cam. Maybe what at .050, say 220 to 228. The stock was what, maybe 210*.That would be a sweet street cam with cylinder pressure around 160 to 170.
Now, Im agreeing with everyone that the current cylinder pressure is way low. However, Im not sure that its the whole story.With numbers that low, I would for sure have verified them with a second guage.And if still low, I would follow with a cylinder leakage test. Numbers that low generally point to more serious problems. The leakdown test eliminates the camshaft.
-But thats all moot now that the cam is out.Well, I guess you you could still do the leakage test.If the cam is out, Im again assuming that the lifters are too, which usually means the intake is off too.I just would hate to see you put a different cam in it, bolt it all together, and find very little difference,and all this work was for nothing.
-I guess what Im getting at is; does anyone think you can find 80psi with a cam swap 1 or 2 or even 3 sizes down.Not likely.And until the pressure gets to 140psi+ the bottom is still gonna be soft, especially with 3.23s out back.At 165 the motor comes alive.
-And one more stab at it,timing. Like Crackedback alluded to. Low cylinder pressure,highway gears, and lazy timing, is a sure recipe for a soft bottom end.
-I would have proved the guage first.
-Now, if 279* is not advertised, but .050; well then erase what I said. But who puts a cam that big in a street motor? I mean that would be 40* more than the 292/509 Chrysler Purple. And thats already almost too big in a streeter.
-And most modern small 1 and 2 cylinders start just fine at 40psi and even 30 psi, which is designed that way with the auto-decompressor, so little old ladies can start their lawnmowers.Of course, as soon as it runs and the rpm comes up the a/d dissengages and the engine begins to make power. Just saying
-And I have had engines that run just fine at 120psi. Not a lot of power, but ok for a DD.
-At 80psi and even,that thing should have been leaving a blue trail.Its hard to wear out a top ring(s) and not the oil ring.Im stuck on the compression tester being faulty, and/or lack of follow-up with the leakdown tester,and possibly/likely, some other combination of poor tune. Oh well.
Click to expand...

I agree. the thumpr cam is not that big! its 227 at .050 and set on a 102 IC! even if the engine had a mechanical compression of 7.5 to 1 and a 63 deg IVC it should still produce 110psi cranking compression with the thumpr. the 262 you mentioned has an IVC of 57 its only going to add a few psi to the cranking compression.

I think you need to do a leak down test on the engine, either the gauge is way off, the test was done wrong, or something else is not right in the engine.
I do agree that the thumpr cam is too big for a stock 360, and the 262 will be way more streetable and fun, but I dont think that is why the compression reads that low, if you were using an accurate gauge that is.
 
The Thumpr cam comes in at 2000rpm, the Xtreme Energy one comes in at 1300rpm.

We didn't try a second gauge, but 2 Mopar guys over here say the Thump range are useless for anything other than an unstable idle, and the cam is the problem coupled with the 360's relatively low compression.
Anyway, really appreciate all your experience and input but I guess I will just bite the bullet and install the new cam and see what the result is.
I'll keep you posted.
Cheers
Kev
 
Subscribed, I hope you continue with the updates!
For what it's worth, my first small block was a 1972 360. The only real difference between it and 73-up was that it had factory flat tops, no valve reliefs, rated at 8.8:1. Never any machine work, std bore, bearing size, oem valve job, etc. J heads. Guy I got it from did a re-ring in 87', along with a Crane 224/[email protected] cam. When I did a compression test, I got 140-145 straight across. After 10 years of abuse by him, and 3 by me. It was a pig with a stock converter. Dead stop, barely a squeal. It had 2.76 gears. However, a 10-15 mph roll, I'd be sideways! It really woke up with a 2700 stall, even more with a 3100 and 3.23 gears. Ran 13.6@100 with tire spin, 2.1 second 60'
I know big cams can kill cylinder pressure. But, in MY opinion, never by that much, especially with that cam. I would still expect 125 or so if it was not worn out. Just my opinion, and I learn best when I'm proven wrong! Lol
On the other hand, I hope your cam swap solves the problem and you are back on the road soon.
 
KevC said:
The Thumpr cam comes in at 2000rpm, the Xtreme Energy one comes in at 1300rpm.

We didn't try a second gauge, but 2 Mopar guys over here say the Thump range are useless for anything other than an unstable idle, and the cam is the problem coupled with the 360's relatively low compression.
Anyway, really appreciate all your experience and input but I guess I will just bite the bullet and install the new cam and see what the result is.
I'll keep you posted.
Cheers
Kev
Click to expand...

If it's installed wrong, it won't matter what the book says about where the cam comes on.

Did you check the installed centerline before tearing it down?
What were the readings from the wet compression test?

The camshaft likely wasn't the issue in your case. I've run 284/484 mopar cams, bigger than the thmpr by 14* at .050, in 8:1 360's that would KILL the tires. According to the books, it shouldn't run well.

I'll bet the thmpr cam installed centerline was way off the mark and the timing was a not up to snuff.

Care to answer the ignition timing question or is that not important? :)

I'm not a rocket appliance, but, I stayed in a holiday inn last night! :)
 
This ^^. Bet the cam was not degreed correctly and your Ignition timing/components and carb tuning need to be addressed as well.
 
Centreline was bang on when we checked.
Did not check ignition timing.
Car came with Vac advance disconnected and when I did connect it ran like a dog!
Did check ignition timing and it was correct to specs.

New cam is installed and motor should be ready to fire in 2 weeks (I only get to work on it on Sundays and then only for a short while)

Cheers

Kev
 
Thanks for all the info guys, any updates on how the new cam worked out?
 
Hi Guys

Sorry it has been so long replying. With the new cam installed the car is a completely different beast, it drives better and lights the tyres much more easily.
I have been enjoying using the car hence the lack of posts, and the weather over here has been reasonably good for a change!!
I have also replaced the Eddy with a Holley 600cfm and it start better and performs better.
I still think compression is pretty low and I will run another test as soon as I get chance, just to see.
I can't thank you all enough for your inputs.

Cheers

Kev
 
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