Cam selection

[ftpiercecracker1]

I have read several papers about SCR and DCR including the one here in the FAQ section and i still dont fully understand.
basically keep the the SCR under 12.50:1?
and the DCR under 9.3:1?

Since this truck will be used strictly as a toy, I dont really care about having to run high octane. I just want to make sure there will be NO pinging/knocking or detonation what so ever.

A cam with an evenly distributed torque/HP curve is what I am after. This truck will be used in trails and mud.

Thanks for the help.

[Muad'Dib]

In speaking about the pinging issue, ~8 DCR is "safe".
I run premium and i have almost 8.5 DCR. I get a very slight ping at sea level which required some octane booster. I live at 3500+ above sea level so for DD its a non issue. A tight quench and polished Combustion Chamber helps me here.

So here are the main factors:

DCR
Quench
Combustion Chamber surface
Altitude

My "recommendation" would be to make sure that you have a tight quench and polish your combustion chambers. Then you can make the choice on what DCR to go with based in your normal altitude.

[ftpiercecracker1]

just for clarification, the "quench" is the distance from the top of the piston to the bottom of the head right?

Which would mean you would want a 0.00 quench height, right?
Altitude will be AT sealevel, south florida.

[Antifreeze2]

You kinda need something between the block and the head (Head Gasket). Although perfect quench would be near 0, you need to account for metal expanding when heated and stressed. I'm no expert, but I believe that's why we shoot for .045" ish of quench.

[SilverXJ]

Perfect quench would not be 0. It isn't effective that small, and you have to take into account bearing clearances, rod stretch, metal growth, and piston rock. I wouldn't go less than .030"

[Dezertxj88]

Perfect quench would not be 0. It isn't effective that small, and you have to take into account bearing clearances, rod stretch, metal growth, and piston rock. I wouldn't go less than .030"

Witha higher lift cam than stock, you may not even want it that tight!
And the only way to get it that tight would be to have the pistons above the deck...my setup was .005 above deck, with 0 decking needed. And I would of had a .038 quench and I didn't want to go any tighter for fear of PVC.

[ftpiercecracker1]

Ok so the quench is something has to be delt with real time while building the engine. There is no "set" number to aim for, each build will require a different quench height. gotcha.

[Muad'Dib]

You can easily set a target quench. Most shoot for thier head gasket thickness. I used a Mopar Performance MLS @.044. so .044 is my Quench. Now, how much to shave off the block to get your desired quench will be based off the components you use and what length it all is together. A mock up of the crank \ bearings \ rods and pistons will be required for this. Your machine shop will do this for you since they have the precision equipment to do so. For example i told them i wanted 0 deck height (which makes my HG my quench) and they did the rest.

[IH 392]

It's hard to recommend a desired quench clearance that will be correct for all engines, but I think 0.038" of clearance between the quench surfaces is an absolute minimum in an engine with a 4" bore and about 0.007" of piston wall clearance.
A safe figure for all around performance is 0.040", anything up to about 0,045 is probably ok, if you let quench clearance open up too much-to 0.060" or more you're going to lose power.

That's with old school forged pistons, in our smaller bore engines with cast or hyperutectic pistons it could be closed up some, I would (and am going to) shoot for 0 deck with the thin head gasket.

[ftpiercecracker1]

I feel that I am getting way ahead of myself, but either way it sounds good fellas, now i just have to wait for my engine to come back from the shop. Not very good at waiting.