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  #1  
Old 04-02-2013, 06:55 PM
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Compression testing round 2

I had the day off and was bored so I compression tested the hemi after 18k on the new cam and heads. I was surprised by the results.

After my head and cam install at 83k I did a compression check twice, at 1k and 5k. Each time I had choppy cylinder compression ranging from 155-165 psi. Not anything that is bad, and just figured that was due to almost being at 100k miles.

Well, today was a totally different story at 100,725 miles. I did the passenger side first and booyah.... 177 to 180 psi all cylinders. Drivers side... Same thing 177-180 steady. I was in disbelief and ran every cylinder multiple times.

Anyway, the only thing I have done since that point was tighten up my underdrive pulley... Which completely stopped my random misfires codes. Also, cleaned my intake manifold with degreaser and a bath. And finally... I'm over half way through a autorx oil treatment and seeing a lot of small black particles in my catch can.

What do you guys think? I am dumbfounded by the results. You think the autorx has freed up the rings? Or was it the under drive pulley and intake manifold cleaning?
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Old 04-02-2013, 10:24 PM
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Re: Compression testing round 2

Were the other checks done when you were in Vermont? What is the altitudes at the places where you did the CC's? Could be as simple as different density altitudes, maybe all the parts have gotten used to each other, or some of you cleaning has helped. I just did mine before and after the cam swaps on both my Hemi rides and the afters all went up about 15 PSI from the befores, and they're all lower than yours because I am at ~3000 ft. elevation with DA's around 4500 ft.. I've been wanting to redo mine too, just to see now that everything has settled in. I only have about 4000 miles on the LX and about 15K plus on the WK. I just put the UD pulley on the WK this past Saturday and will do the LX this weekend. I did my first short trip with it (in windy conditions) and couldn't tell for sure if it's making a difference. Did you do yours when you did the cam? That's when I should have done mine.
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Old 04-02-2013, 11:46 PM
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Re: Compression testing round 2

Oh sorry, I meant harmonic balancer.... I don't think I'm ready to invest in an underdrive pulley. I have the original alternator, power steering pump, and ac compressor and don't want to mess with them considering my black jeep is going to fry this summer in the 100+ degree days. I know my power steering pump is slowly on its way out also, after having my hose come off in wyoming and having to drive for 30 miles with no fluid to the nearest town. As for elevation... I am at 25 ft here and back in vermont I was as 250 ft. On the lx forum one guy was saying that brand new hemi's have 175 psi brand new... And 155 to 165psi after 100k. So I'm guessing it is the valve seals that start to degrade after 100k miles and not the rings?--- justifying my readings.
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Old 04-03-2013, 12:06 AM
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Re: Compression testing round 2

A interesting read for anyone considering the product

Auto-RX Oil Treatment. Don't Do It. - i-Club
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Old 04-03-2013, 10:12 AM
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Re: Compression testing round 2

That guy who posted that autorx on that forum is a troll. He goes to all the forums and posts the same bull. I'm thinking he had a bad seal that had some carbon build up on it and the treatment cleaned it up. I read all the forums out there and he was the only dude with anything bad to say about autorx. Autorx doesn't claim to fix broken seals. I think it's funny how one claimed that autorx caused his oil pan to pop off... I'm thinking a lot of people with really old crappy cars use the stuff looking for a miracle, but they get their old cracked seals cleaned off and don't like the consequences. I haven't noticed anything but black soot accumulating in my catch can, and obviously a mysterious increase in compression. I don't advocate anyone do the product, kind of expensive, but I was a sucker and bought it last year so thought it was time to get rid of it.
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Old 04-03-2013, 05:50 PM
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Re: Compression testing round 2

Dan, didn't you put new heads on? If so, they should have had new valve seals. When I changed the valve springs on mine (heads on) I also changed the valve seals. Cost wasn't bad at all. The WK had around 60K on it and the LX had just over 50K and the seals from both looked about the same......fine. I still have the old ones sitting in a box in the garage.

Ya, I don't know how this UD pulley thing is going to work, but thought I'd give it a try. I read a bunch of reviews/dyno tests (independent I hope) that all showed a slight increase in hp and torque. I've been monitoring the voltage and it doesn't appear to be any different than before but, then again, I haven't had to run the air yet. Time will tell. Oh, I put the SLP 25% pulley (847-100235) on. My son and I did it all from the top, without removing anything but the intake tube. Took about 3 hours to do, and would have been less if we had had the pulley installer tool......I have it now for the LX though.
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Old 04-03-2013, 10:18 PM
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Re: Compression testing round 2

I have the special tool to push the harmonic damper on.... And I can't get it to fit between the fan and the damper bolt. How did you get the underdrive pulley started? Not enough room to whack it on with a hammer and wooden block. I do have new heads.... I was just saying that if a jeep with 100k on it usually has compression of 150-160 psi as the guy on the lx forum says.... then it must be the valves and seals that start degrading causing psi loss... Because I have 100k and I'm right back up to 175 psi with the new heads. Makes me pretty confident in the piston and ring design.
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Old 04-05-2013, 04:31 PM
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Re: Compression testing round 2

Compression psi is affected by the cam and also the cam timing as well. a cam with more overlap will bleed off the pressure a little bit before they get closed. The cam timing changes where the piston is in the cylinder when the valves seat ,also altering your numbers.
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Old 04-05-2013, 06:05 PM
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Re: Compression testing round 2

Dan, what we did is kinda Mickey Mouse, but it worked. I didn't want to have to move or remove that damn radiator and fan again. Here's what we did. We hooked a long curved metal pry bar around the sway bar with it facing up. We put a large socket in the pulley cavity and kept it square with the pulley and in place with the pry bar. Then we hammered on the pry bar until the pulley was on far enough to grab some threads. We were kind of sweating it...whether it would work or not.

When I do the Maggie this weekend, it has to have the fan/radiator moved (just loosen and drop down), but I got a longer bolt (14mm X 1.5 thread pitch X 120 MM long), so it should go on easier. I also took the washer off the old crank bolt and put it on the new longer one. The new bolt is about 3/4 in. longer than the stock crank bolt, so should grab the threads in the crank easily.....I hope.

4.whoa, your last post reminds me of my younger days when I knew less than I do now (which isn't very much). I had a 350 Chevy that I was going to make into an economy ride. I thought I'd be smart and put the Duntov 350 hydraulic cam (a moderate grind with a fair amount of overlap), and lower the compression of the engine to ~9:1. Boy, was it a dog.....really sounded nice though. It was doing just like you said, blowing a bunch of the compression out the exhaust. I should have been running ~11:1 to make it work half way decent.
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Old 04-05-2013, 07:18 PM
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Re: Compression testing round 2

^ before I got the hemi I spent a lot of time on 4.0 stroker research, WOW they go on and on about every little point DCR,SCR and how far you can push it ....not alot of tuning options with those unless you get a stand-alone system.
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Old 04-05-2013, 08:00 PM
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Re: Compression testing round 2

I dont think my cam has much overlap, since it is the mildest cam that inertia offers. I just have a hard time explaining the 15-25 psi increase since I last tested.... a few months ago. Maybe all the black soot in my catch can is from the rings being cleaned out.... im going to take a picture of it when I get enough in there, I just dumped it last week.
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