A friend of mine has a 408 in his 03 silverado. He had a performance shop do the engine set up. This is the set up. 408 (eagle rotating assembly with dished pistons) 9.2 compression, scoggin dickey 243s, HT1 cam, and a Edelbrock pro flow xt, headers, aftermarket exhaust, 2800 stall and a mail order tune. Ever since they done the engine hes not been satisfied with it. He was planning on a dyno tune but I just don't think its going to make enough difference for him. Since its a low compression engine even with the 243s I don't really see alot to be had swapping heads/cam. How would the 243s and HT1 do with boost? I would assume the 408 could handle a low boost setting and thats imo his best bet? What do you guys think? see any other options for n/a or would boost be the best solution?

 

Boost would be the best solution, of course. The engine sounds like it's set up nicely for it. The 243 heads are great for boost but that cam with a 111LSA would need to be changed. I'd go a little bigger, too.

 

That's a tiny cam for a 408, the one in my 5.3 is bigger than that. I'd start with a cam swap, something in the 230@.050 range on the intake side even with the low compression.

 

What the hell was that engine builder thinking? That's a good cam for a 4.8. either better cam and higher comp pistons or better cam and boost. Either way the HT1's gotta go

 

Holy crap that HT1 cam is choking that motor. A think swapping to a TU2 Speedinc cam with a smallish turbo build would make it a lot more fun. Trick has several different kits that would work great. I think a BW s475 on a stage 3 trick kit at about 8lbs of boost would make that motor come alive. Hello 600rwhp. If he insists on stay NA which the low compression will not like then I would go with a 229/234 .603/.607 LSA 110or at least a 226/230 cam on the maximum most mild side.

 

Engine is set up for boost. OBLIGE IT!

 

Yea I would never set an engine up for 9:1 compression if I wan't putting boost through it. You could run 20+ lbs of boost through it if it is set up properly.

 

why the hell would an engine builder set up a n/a setup with such low compression and a tiny cam for a 408??? too late now. boost the **** out of it and make it happy.

 

IMO this is what happened. The guy took the motor to somewhere not familiar with LS engines. He all ready had the heads/cam in a stock 6.0 and hes the kind of guy that tries to cut corners on critical parts. I'm guessing the Eagle kit was the cheapest available he could find and it offered 1 of 2 piston choices. Either a 4.5 dish or 29. They probably thought to themselves either over 11 to 1 or 9 to 1 and since hes dd'ing this thing 9 to 1 is safer. After talking to the guy he wants to stay N/A, hes going to try milling the **** out of the 243s (come to find out they aren't even ported). Now after doing the math, If he goes from 65cc to 57 that still only puts him at 9.9 to 1. Going from a .048 compressed gasket to a .021 gasket will put him at 10.5 but I'm not even sure that would even work or if they make a 0.021 gasket. I mainly see in the .040-.050 range. With the 29cc dish I'm assuming ptv problems won't be an issue with a 230s, 600ish lift cam.

 

PTV clearance might be an issue...it really depends how aggressive the lobe is, regardless of max lift. Contact usually occurs around 10-15 degrees ATDC when the valve is outrunning the piston. Clearly this is also well below the max lift of the lobe.