thunder550

iTrader: (70)

Trying to find out what CR I want to run the new 408 at. I was originally thinking 9.5:1 and about 15 psi. I am thinking now that I might be better off going closer to 10:1 and dropping the boost level a little bit. What do you guys think is the best combination of boost and CR for a DD that needs plenty of torque for towing during the summer but still wants to haul ***** at the track?

1slow01Z71

iTrader: (36)

While I have no personal experience yet(mine will be 9.4CR) from all the readin gon tech and talking to some of the engine builders and Richard from WCCH it seems a low to mid 9:1CR is your best bet in our heavy trucks for good response out of boost but still be able to push decent boost. Also you would be amazed in the difference that 4" stroke crank makes for low rpm tq. You just cant kill it, thus I went even bigger to the 246* cam from the 237/242. Just my .02. My truck will be together and running second week of Dec baring anymore hicupps.

F8L Z71

I'm not overly happy with my high compression low boost setup. I'm going to try and drop it back down to 9.0-9.5:1 or so.

cablebandit

iTrader: (37)

8.5 to 9.0

vanillagorilla

iTrader: (1)

I say 8.7:1. Out of boost, a 408 will have no problem moving that truck. Besides if you really are driving this everyday you're going to be running the pee-water 91 octane we have here. I get bad batches from time to time and I know it. If you have a 10:1 SCR with boost, you stand a chance being screwed.

kbracing96

iTrader: (26)

I'm with the rest of these guys, I think low 9's would be a good DD for your truck.

Bill Reid

iTrader: (14)

Yep, nothing really higher than 9.1 if you want to give your tuner a good amount of space to tune well with our best pump gas. You can always cam the motor to be a little more responsive down low if that is a concern. If you stick with a positive displacement blower like a Magnuson I wouldn't be worried at all by going with vanilla's suggestion of 8.7:1. I have built many FI motors with that exact CR target.

Good luck with whatever you decide

Bill

thunder550

iTrader: (70)

Hmmmm ok....I'll have to see what I can do to drop the CR a little bit. Maybe go with some pistons with a little bigger dish. I'm already at a .06 head gasket, don't think I can go a whole lot bigger than that.

vanillagorilla

iTrader: (1)

JE makes them!

thunder550

iTrader: (70)

I asked once before and was told that Diamond pistons were kind of heavy....are they good quality though? What's wrong with going with a little heavier piston if I am not spinning the motor up very high?

Reason I ask is that if I get the pistons through TSP (they only have Mahle and Diamond) he's going to throw the rod and main bearings in for free.