Lockhart88Iroc

I've got a pretty much complete l31 (except for intake manifold) and am looking to rebuild it. So I'll start with what I know, and then add all the ?'s at the end. I know it's stock compression is 9.4:1. If I go with flat tops, and deck the block and have the heads milled much, my compression will be over 11:1 even with a .036 gasket. With the stock style dished pistons, having the heads milled a little and having the block decked, I'll be around 10-10.5:1, which seems ideal. My goal is only 325rwhp. I plan to port and polish the heads and intake, along with siameseing the intake channels, and adding an intake spacer, with the lt4 hot cam, threaded rocker studs and springs. Adding the headers and other bolt on goodies also. And lastly a dyno tune. All I really have is the block, crank, rods and pistons, oil pan, heads (valves and springs only, I will need new springs). I do have an LB9 with 120k miles to cannibalize. Assuming I can recycle some of the small innards of the lb9 (the roller lifters and push rods and such). Would anyone recommend a rebuild kit and give me some advice as to what I should cannibalize? I don't wanna spend over a grand on the kit. But would y'all recommend the dished or flat tops? Basically I just wanna hear everyone's 2 cents on my project, your opinions. Chastise or whatever, just explain please. Y'all are awesome, thanks guys.

Lockhart88Iroc

Btw my dad is the brains, I've never done this before (it's my first car with more than 6 cylinders). So far I've been learning, but am still just a strong back and a weak mind compared to him. Mostly I've just been parts hunting.

1gary

This part isn't going to cost anything.Verify the block casting number over the flywheel/flexplate in the rear of the engine.Look at the casting number on both heads under the valve covers. Post that and we can go on from there.

jokerZ71

An L31 will be a #880 block w/ either 062/906 heads.A stock L31 will make close to 300 fwhp with a good 4 bbl,headers & free flow exhaust.It's advertised 255 HP rating is net HP as installed in a production vehicle w/ factory tuning.The Comp XR264 will get you up to 330/340.The L31 should already have roller lifters.The Vortec heads will need some work for lifts over .470 & definetly need to be ck for cracks.The flat tops are gonna have you on the ragged edge of detonation.A better choice would be a D cup piston like a KB-193 12cc dishThis will give you the benefits of a flat top while retaining some volume to keep CR in ck.Deck the block to approx .010 to .015 & use a GM .028 headgasket.The LT4 Hot cam will work as well & prolly give you more HP,but,it is an outdated design.Beware of rebuild kits.Make sure pistons have a 1.56" compression hgt.A lot of kits come with a 1.54" or 1.548" hgt.They will put your piston too low in the bore,killing power & reducing detonation resistance.

1gary

He wants 325 at the rear wheels.But before all this,my suggestion is for him to know what he actually has.

jokerZ71

Sorry didn't catch that.The LT4 Hot cam in a well built Vortec headed 350 will give you that easily.An L31 w/ 750 carb,headers,& the LT4 Hot cam will be knocking on the door of 400 HP.It's a pretty common recipe proven to work.There are other cams out there that will work as well,or,better.The Hot cam is easy on the valvetrain tho.It doesn't have the aggressive lobe profiles of the Xtreme or VooDoo cams.

Lockhart88Iroc

It's an 880 block with 906 heads. Straight out of a 97 silverado, one of my main concerns is i won't be able to use hardly anything from my lb9, which would make this much more expensive

Lockhart88Iroc

Thanks man, that's some good stuff to know. To the others, yes I do what I have for the most part but I should have included numbers, which are the 880 block and 906 heads, with that being known now, do y'all think I'll be able to use much from the lb9? Idk what the stock l31 rockers look like exactly, but I assume they are similiar to the lt1 rockers which I have seen. Are these decent rockers? Obviously I need screw in rocker studs for a heavier cam, and the valve guides (remember I'm new to this, I think that what they're called) need to be milled down to allow the lift. But do y'all think I'll be able to use much of that lb9? Like lifters and pushrods and such?

Lockhart88Iroc

Sorry for the redundancy in my questions, I just got done with a cal based physics test and my brain is fried...

jokerZ71

If your LB9 is a roller,the lifters should work.Your 906 heads use a 1.5 self aligning rocker arm,or'you can use screw in studs w/ guide plates.There are drop in spring kits that will let you run up to .530 lift with no machine work to the heads.The heads hit max flow @ a lil over .500 anyway,so,more lift won't really help.A new set of Delphi OEM roller lifters is only $100.You definitely wanna keep this thing roller.Don't cheap out for a flat tappet.

Lockhart88Iroc

Understood, definitely want generate a minimum of friction wherever possible. I heard in a previous post that the lt4 hot cam was out dated, any recommendations to replace that with? Do you have a link for the springs? Alex makes a spring set I think. Also my lb9 computer will run all the l31 with the mods if I get it tuned right? I will try and get a set of 24lb ls style injectors, assuming they fit. Last thing (until I find another question to ask) will my stock rods handle all this? My dad likes to smooth and polish them up a but to make it hard for a crack to find a place to start. Is this a viable solution? Or old motor voodoo? I definitely don't want to throw a rod, but if the stock are good then ok.

1gary

Stock rods with ARP bolts.Keep the rpm's down.But as Joker and I have said.Check out exactly what you have first.Mag the heads,check the bores,check the deck,check the alinement of the mains,mag and check the crank.Don't side step these steps.

Alot of the rebuild kits use the wrong pin height for pistons turning a engine into a real turd.Don't cut a block or heads for a increase in SCR.Joker pointed you to the correct pistons to use. Take that advise to heart. Then set the quench correctly. This is going to help you in so many ways.

jokerZ71

What intake & fuel delivery are you planning on?The LT4 Hot cam was originally designed for showroom road racing,but,it is a decent cam & does really well with Vortec heads.With the proper fuel & exhaust to support it,a Vortec 5.7 w/ Hot cam is an almost guaranteed 400 fwhp.Maybe outdated was a bad term.It's a GM cam so it does have kinda long lazy ramps,but,that's not necessarily a bad thing.The Comp Extreme series & Lunati VooDoo cams can be kinda Tuff on the valvetrain with their aggressive ramps.The PM rods that come in the Vortec are good rods & will work fine for the power level you're looking at.The only concern I would have is if this a really high milage engine would be the fatigue factor on them.I would @ the very least ck sizing & install new studs.Either with GM or ARP.