cgEvan

iTrader: (1)

The current setup is a stock '02 LM7, running 799s milled .025", .650" lift dual valve springs (keepers, retainers, seats, obviously), Comp Cams hardened pushrods, TSP MS3, TBSS intake manifold, with an Edelbrock 90mm.

I probably only have 500 miles on this new setup, if that, but the opportunity presents itself to trade my complete 799 heads for PRC 5.3 stage 2.5s (the specs are equivelant, not sure if they are PRC). The ports next to known PRC stage 2.5s are definitely bigger. The valves are upgraded and the heads are milled .030" from stock. This friend of mine doesn't want any cash on top, so I feel as this is a good deal.

The MS3 feels a bit too big for the 5.3 (imagine that!), so I was thinking about trading these heads and going for a bigger bore. I've read a few different answers as far as boring out an LM7 block, but mainly ultra sonic test it to see if it can withstand the bore. I would like to keep the stock crank, so a stroker isn't the route for me. However, I would like to upgrade the rods. Not looking to ever turbo or ever really do more than weekend rides around town, with an occasional trip to the strip for a few runs, the eagle H beam 6.125" rods are calling.

With the only thought in mind being, "bigger is always better", I keep finding myself on the Wiseco 3.905" forged -3cc piston page. Now, I MAY end up installing a small 100 shot on the motor, but again nothing major. As far as bore size and dish/dome size, I'm lost. I would like to think 425-450whp through a 4L60e with around a 3k stall is plausible with this build but how to get there is the question.

What bottom end would you build, if you were going with aftermarket rods, aftermarket pistons, and stock crank, in an LM7 block, with my new top end if you were shooting for 425-450whp through a 4L60e?

batboy

iTrader: (6)

I'd bore it out to LS1 specs and use forged LS1 rods with ARP bolts and flattop forged pistons, assuming you are staying with the stock crank. But, if I was doing it, I'd probably go one step further and swap in a 383 forged stroker rotating assembly.

As for the heads, I dunno, 5.3 heads milled .030" with a MS3 cam might result in valve to piston clearance issues.

bww3588

iTrader: (49)

The ms3 should clear the 3 cc pistons your looking at. My ms4 cleared with plenty of space with the same heads and similar pistons.

bww3588

iTrader: (49)

Once you do the heads and bore it to ls1 specs, the intake will be your weak link. The ms4 likes to rev and makes the majority of its power above 5500, where the Ls2 truck intake dies. I would look into a fast intake.

RezinTexas

just a thought - if you are going to bore to 3.905" that is going to cost in the neighborhood of $300. For that money you can buy a LQ4 bare block, maybe a small amount extra for a clean up hone. All your parts and accessories (minus pistons of course) will swap over.

Here's an example of one for sale
http://houston.craigslist.org/pts/3235396026.html

cgEvan

iTrader: (1)

I've thought about that, but I know my stuff is good, rather than trusting someone else. Especially if I end up travelling to buy something. It's always an option and I stay pretty open minded to ideas, though.

Thank you all for the replies, and more are still welcomed!