Need help with LS3 Build
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Need help with LS3 Build 
I've been lurking on this forum for a few years now and finally have a reason to post. After reading a GMHTP article on their budget 408 build I couldn't resist any longer and bought a bare LS3 block to build up and eventually drop in my '05 GTO next Spring. I'm hoping that some of you that are part of this community can help guide me in the right direction and offer some constructive advice and encouragement.I am not a mechanic by any stretch of the imagination but I've wrangled a local performance shop to help me in the build. On top of that, I've read every Cartech book out there on the LS Engine as well as a few engine blueprinting books to help with the basics.
So here is the plan:
Stroke to 427ci and keep N/A.
CNC ported L92 heads
Forged internals
600hp target
I've put together a rough build sheet that covers most of the essentials but the intake manifold (ported ls3/FAST/sheetmetal?) and cam specs are two of the areas I'm still debating. Cams are an area that I'm completely clueless in.
Josh
Last edited by billygoatmass; Aug 17, 2009 at 01:37 PM.
you dont need a big cam to make big pwoer especially with the ls3.
600hp should be no problem period even with the base ci ls3 but a 427 will make it that much easier. i cam heads supporting mods hello 550+hp
600hp should be no problem period even with the base ci ls3 but a 427 will make it that much easier. i cam heads supporting mods hello 550+hp
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I thought the same. I didn't want to have to use a huge cam to get there (car is a DD) so I figured I'd start with the stroker kit and see where it progressed.
I dont think you need to stoke it either cause i kno a guy who races a t/a with a 427 ls3 with out of the box et heads and ls7 manifold with a hydrolic cam and his car made 630rwhp thourgh a turbo 400 on a mustang dyno. So if i were you i would do a forged stock cubic inch or even a 418 and not bore the block and you could still hit your goal with the right top end and hit it with n20 or boast if you ever change your mind
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I decided on N/A just to try and keep things simple. I don't drag the car the much so N20 was not something I wanted to get into. I have a turbo car already (Solstice GXP) and a TT kit for the Goat would end up being another $6K+ on top of the engine cost. Granted I could wait until I got used to the power level before adding the turbos.
If I changed my mind, I would have to keep the bores a bit smaller with this block, correct? Would boring out for the 427ci leave the cylinder walls too thin to support big boost?
You don't bore the block on an Ls3 to get 427. To get 427ci out of an ls3 block you run a 4.1" stroke. If you want to hit your hp goal without a problem, Id run the 427 ls3 with Ls3 heads and an Ls3 intake. You can run a small cam and daily drive the crap out of the car. Sure you could do it with a stock displacement Ls3, but the driveabilty wont be ideal. Talk to Lg motorsports or thunderracing for a cam. Lg has stock ci ls3's putting down near 500 to the tire with their ls3 specific cams.
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I thought you needed a 4.07 bore and 4.1 stroke to get the 427ci. At least that's the way that I've seen it on some short blocks out there. Scoggins sells theirs that way I believe. I bought a bare block that has to be honed anyway so I should end up 4.07.
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The cylinders are honed to size. I have a 427 ls3 and I Put the pistons that came in the kit into one cylinder and it fits, but the cylinders have to honed for the correct tolerance. But boring would take off a considerable amount of material.
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I don't know why I was using boring and honing interchangeably...I know exactly what you mean. I haven't selected the rotating assembly yet so we'll see where I end up clearance-wise. I do know that I would prefer 4340 forged pistons over the 2618 but there seem to be limited choices that work with the L92 heads. What did you end up choosing?
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I 'm using a Scat crank and Mahle pistons on my build. It's only a 414 the block is 4.065 with a 4.00 stroke. Like posted above just hone the bore to the pistons. I wouldn't run TSP on my car get the heads hand ported or from WCCH. Have some one who knows these heads grind a cam. I used FTI (Ed Curtis). You don't need a big cam for these heads, and with the LS3 intake you will have a great DD. I've bought a bunch of stuff from SDPC. They are good to work with.
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I'm not an expert either but I can share my experience. I have the SD Ls3 427 build too only with different heads... AFR 225's. Callies, Compstar Manley, Clevite, Akerly, Comp, PAC, Harland Sharpe, Melling, FAST90 - Ls2 TB, Ed Curtis CAM, Ozz700, RPM 5, DTE 3 and I put down 483 rwhp 478 lb ft tq. (107 degrees and humid that day) I went with a NA setup - 11.1 CR and asked Ed for a "street and cruiser" cam, and while it's mid range and drives almost like stock, look at the torque numbers. It pulls like a freight train.
Last edited by billygoatmass; Aug 1, 2009 at 05:23 PM.
Huh??? Guys are putting down 500rwhp all day with Ls3's, some are stock displacement, Where are you getting your *** backwards info? 
OP is doing a nice build, would hate to see it make lackluster results with a set of budget PRC heads.
Thought you meant Ls3 heads in general, my bad. I have no experience with texas speed, But I have read a few posts with people who have bought there heads. Only bad things i've heard was more with the finish work of the heads and some quality complaints, But the flow numbers are up there and people seem to still make good power with them. Did you run those heads and have a bad experience??
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I'm confused as well. Which head combo is he referring to? I'm open to any and all suggestions at this point. It seems like ported L92 heads were a no brainer based on results folks have had so far. As to who I buy them from, that's a horse of another color. It appears that I have some research to do to make sure I get a good port job from a company that will stand behind their product. Someone above mentioned AFR heads which I know plenty of LS1/2 guys run with a lot of success.