Building an LQ4 junkyard motor for my 02 Silverado. I started a thread on the performance truck forum but I figured there are probably more guys on here who can advise me since frankly I have no idea what I'm doing. I've built Harley motors but never an LS platform. Constructive criticism is appreciated.
This will be a daily driver, wanting mid-range power for towing and for fun of course. Will be having block machined when i get the rotating assembly in, I ordered an L8T rotating assy from Mast. 4.020" bore, 3.858" stroke, flat top pistons with valve reliefs. LS3 823 heads are coming from ebay, I know (I believe) cathedral ports make better mid range power but I am setting this up so I can put an LSA blower on when budget allows. Though I will probably run it NA for awhile.

I'm not sure what cam to run. I was originally looking at the BTR truck norris cam but was advised that while great for something like a 5.3, the BTR cam will not be big enough for the 392CI that this motor will be. The sales rep at Mast told me I should go with their Franks Red Hot cam which is spec'ed at
0.604/0.604 Lift 222/234 Duration- Lobe Sep 112+2 (I'm not sure what "+2" means)
Or one of their supercharger cams. I'm not smart on cams at all, I don't know how much duration is ok for a daily driver and I don't want to have to spin the motor up to 6 grand to make power.

My math comes out to 10.62:1 if I run a .060 head gasket which is high for running boost but I believe there are quite a few guys running blowers on stock LS3's which are 10.7:1. I'd like to run flex fuel also which will help, so I'll have to get enough pump and injector to support. And I think a new ECM, looking through HP tuners I don't believe mine has the parameters to run ethanol.

 

L8T crank on order. 823 heads are in. LSA blower is on order from boost district.

Talked to local machine shop about my build. The guy has been building race motors for years and has a snazzy 5 axis CNC machine. He said he has a program to open up the comb chamb size (he built a program for it because he's done it before), or alternatively we could machine more dish into the pistons, to lower compression. Does anyone know if either of those practices are common or preferred?

 

In a boosted build, I’d definitely cut the chamber before I cut the piston dome. Having said that, I’ve seen plenty of guys run 10.6 with boost. It lowers your tuning window some, but very doable with todays efficient heads and intercoolers. Meth injection will also help cool things. You want a great tuner here. Not a good tuner, a GREAT tuner.

 

Thanks for the reply. The plan is to run E85 most of the time. I ordered the blower with the Griptec hub and a 2.95 pulley as well as a 2.55. I'm thinking it would be cool to run 2.55 around town where I know I've got E85 and then have the 2.95 and a second tune for road trips.
I need to order a throttle body (drive by cable). According to "on all cylinders" the LSA blower has a throttle body diameter of 87mm but if you search for "LSA throttle body", everything is 92mm or bigger. I could be remembering wrong but I thought you wanted to match the diameter of the throttle body to the inlet size. I thought a bigger throttle body just made it hard to tune.

 

You typically won’t see much of an increase in going with a larger TB on a blower application unless you port the snout. And then you’ll end up getting the blower itself ported because this obsession never ends. I honestly don’t know if an LSA has an 87 or a 90 bolted to it, from the factory. I’m gonna move this over to the Forced Induction section. Those guys are smarter than me on this blower stuff.

 

I’m putting together an ls3 for boost and wanted lower compression so I softened the chambers on my cnc Bridgeport. I haven’t measured the chambers yet but it should put me in a better spot and I’m more comfortable using a thicker head gasket now that the head side of the chamber isn’t flat.
I cut it about 005 deeper than I meant to but I think it will be fine. If not, these castings are cheap.
This mod should open up the tuning window as well. It’s becoming more common and lots of head shops will do it for a very reasonable cost. Something to look consider.

 

My Z28 is 93 plus windshield washer fluid. 16 PSI, LS6 Compression ratio (10.6). No issues. Timing was neutered because it would pickup knock until I added the WMI. Huge advantage.

 

I appreciate this answer, I had totally forgotten that "softening" the comb chamber was a thing, I actually have a friend with a ZR1 who had that procedure done to his fancy-pants Frankenstein heads. He's overdriving his 2650 and making stupid amounts of power. That's actually the car that made me want to get into tinkering with blowers. I believe I'll go that route.
You also got me back down the rabbit hole researching squish and flame front. Looking at what goes on at the micro scale during intake, compression, combustion, is really complex but the more I read about it the more it's starting to make sense. 20 years ago it seems like no one was talking about dynamic compression or squish but now it's like I'm behind the curve on what is considered common knowledge.

 

So did you settle on a camshaft yet or still doing some research? Are you going to run the stock size lower pulley?
I've only tuned on a few blower cars, so I am no expert. I do tune on a LSA car that is on a 5.3 with adapter plates. It's a 10.5:1 compression setup and mostly run on E. We have almost 16# of boost in it now, and so far it hasn't been bad to tune at all.
Your definitely going to want to talk to a good converter company and let them know what you're after.

 

I talked to BTR and they advised I just order a custom grind since the motor is a nonstandard bore and stroke and of course running forced induction. I need to get basically everything else figured out as the custom order sheet wants specs for everything about the build. So I need to get the heads worked and CC'ed before I order the cam.