340 Compression Readings

[7212Mopar]

I have a 70 340 with 904, 3.23 SG in my 73 Challenger. The valves tap loudly since the beginning of the year so I did not drive her much at all. I had been researching to see what is going on. Based on that, most likely I will need to do something with the valvetrain repairs. So I am thinking might as well do some upgrades for more power. I am hoping the pistons, rings and engine block is good. The engine does not burn oil at all, just some minor leaks at the gasket so I assume these are good signs. I took some dry compression readings on a hot engine awhile back. Let me know what you guys think if the readings are reasonable for upgrading with RHS heads, mild camshaft with full hydraulic roller valvetrain setup. I have no idea what the previous owner had done to the engine if any. I will be in between jobs for the next few weeks and will start the engine tear down today. I should find out more in the next few days I hope. Here are the readings.  #5 and #8 difference is 12 %. I read highest and lowest should not be more than 10%.

#1 160 pisg
#2 153 psig
#3 153 psig
#4 157 pisg
#5 148 psig
#6 158 pisg
#7 148 psig
#8 168 psig

[cudabob496]

look good to me, and this product will probably
make them even better.

http://www.restoreusa.com/

[7212Mopar]

Thanks. Too late to try Restore now. Radiator, fan, water pump already out. Working on removing the fuel system and the intake manifold.

[cudabob496]

Thanks. Too late to try Restore now. Radiator, fan, water pump already out. Working on removing the fuel system and the intake manifold.

cool, but I'm not a small block guy, so better get other opinions

[Chryco Psycho]

AT 12 % I would not be too worried , the problem could be in the valve sealing anyway so new heads could improve the #s .
 you will get a better idea once the heads are off just looking things over .
Are you looking at Lunati VooDoo for cams ?

[7212Mopar]

At this point I am thinking going with Hughes hydraulic roller lifters, 1.5 roller rockers and then order their custom pushrods. All the Hughes camshaft selections require 165 psig compression minimum, not sure why. Camshaft I had been looking at is Howards Cams retrofit hydraulic roller 711915-12, 221 intake at 0.05, 0.474 lift; 225 exhaust at 0.05, 0.500 lift, 112 LSA, 1800-5700 RPM and 1800+ stall. The Lunati roller cam selection has more lift and duration. I already have the Edelbrock RPM air gap intake and an AVS 650 carb to go with it. I have no idea what stall speed I have on the existing torque converter that is bolted to a 904 AT. Also thinking of getting TTI headers. Car will be mainly for crusing around town and open up once awhile on the freeway when it is clear. I think this cam will have good idle and vacuum. I am open to suggestion and it will be awhile before I start ordering parts. I need to measure and get all the steps in my head clearly before starting.

[cudabob496]

its important to make sure the cam duration you select is compatible with your compression ratio,
or too much duration will bleed cylinder pressure, and make you lose power.

[7212Mopar]

Almost done with disassembly, still need to pull the camshaft and timing chain. Everything looks good, no bend pushrods, no broken springs, valves seating fine, rockers look fine, so have no clue what is causing the tapping. The sound kind of like tong, tong instead of tick. May be bad lifters collapsing? They all slide out the bores easily and I did not feel any ridges. Bottom of the lifters all look fine too. The only thing left to check is the camshaft and the eccentric.

Lots of cleaning to do before I can measure how far up the pistons are sticking out, suppose to be 0.018. I like to go with close chamber RHS iron heads and may be 0.056 gasket like one other member had done.

Also will get a better catch can to avoid all the carbon deposit in the combustion chamber.

[cudabob496]

most likely a lifter causing the noise

[jimynick]

It's too bad you got in a rush and pulled it down before you could find the problem. I'd've taken a .010 or .020" feeler gauge and tried it between each rocker and the valve to see if they were the problem while it was running. If you Google that piston # you should be able to find the CH or compression height and using that and a wee bit of math, you can determine the height of the piston in the bore, as long as it hasn't been decked too much. Hughes likely wants that many psi to make up for what it bleeds off during overlap, although a 112' LDA shouldn't be that bad. I'd call the cam manufacturer and speak to them; they spend large money on help for people and they know their stuff better than anyone else. If you've got an old ring, break it in half and use it for a scraper to clean your pistons of carbon. Remember, knocks/rattles, etc. need clearance to generate their noise, so make sure everything is kosher before you bolt 'er back up. Good luck 

[mrbill426]

Those are SpeedPro forged pistons; 10 to 1 compression, +.030"; definitely not stock.  Those can be noisy on their own.

 

Almost done with disassembly, still need to pull the camshaft and timing chain. Everything looks good, no bend pushrods, no broken springs, valves seating fine, rockers look fine, so have no clue what is causing the tapping. The sound kind of like tong, tong instead of tick. May be bad lifters collapsing? They all slide out the bores easily and I did not feel any ridges. Bottom of the lifters all look fine too. The only thing left to check is the camshaft and the eccentric.

Lots of cleaning to do before I can measure how far up the pistons are sticking out, suppose to be 0.018. I like to go with close chamber RHS iron heads and may be 0.056 gasket like one other member had done.

Also will get a better catch can to avoid all the carbon deposit in the combustion chamber.

[Moparal]

your head gasket could be leaking between 5 and 7

[7212Mopar]

your head gasket could be leaking between 5 and 7

I see that could be a possibility. I should have done a wet compression test also. I will running a thick head gasket for the RHS heads and for sure will need to get a high quality one from Cometic MLS.

[cudabob496]

can use a metal ruler, and some feeler gauges, to check surface flatness on block and heads

[cudabob496]

not gonna put it on an engine stand?