I have an LS7 crate motor that I pulled out of my car this summer. It had a "slap" of "knock" between 2 pistons. My mechanic thinks cracked piston. I am going to rebuild it this winter for a project 71 car I am putting together. I am looking for suggestions on how I should build it to be streetable. It wasn't very street friendly with the 12:25:1 and messing with HO fuel was a pain. It has 990 heads and an LS6 intake. I will need a new carb. It will have to fit under a functional cowl hood. I want it to run on pump gas. I would like to have a "big lumpy cam" lope to it. Tell me how to build it!

I turned down a real deal on one of those engines when I bouth my LS6 from a dealer. Somebody ordered the LS7 and failed to pick it up. I assume any deposit was forfeit.

Anyway the issue with that motor as far as street-abiltiy is as you have identified the compression and the cam. I know there are lots of potential cam selections out there and I won't even consider makin a suggestion on what to use. Everyone is a cam EXPERT it seems.

What I will say is this..if your block is std bore and you think 10.2 with open chambers is liveable drop me a line via E-mail hpexpatriot@yahoo.com. I have a set of NEW NEVER RUN STD BORE LS6 Pistons that came outta my LS6. I went all the way down to 9.1 to 1 and sometimes I wished I stayed at 10.2

Easy as pie my friend, SRP medium dome pistons ( 10.25:1) and a solid cam similar to the LUnati/UD 406A3 or A6 ( A6 should be good to 6500+, A3 to 6200 rpm + ) solid cam ground on a 108 LSa if you can take it. smile.gif It'll have the L88/Ls7 idle and a much more useable powerband.

Jim that's bascially what I did to the old L88 to make it streetable.

Keep everything else stock except the rockers, you'll need long slots or rollers. And I am a fan of the 'oil bleed' solid lifters for extended street use. Keep everything else the HD LS7 parts ( oil pump, rods, etc etc etc). That should be an easy 11 sec motor with some gear,. Even the springs should work out fine as they should check in at 115 seat /330 open. ( you'll need to remove inners for break-in for a silid cam with the intensity I mentioned.

Thanks Gene,
what if I wanted to go with a hyd cam to avoid adjusting? what am I sacraficing other than upper RPM range?

Oh, maybe 5% of the torque output, maybe. If you like rough idles, the hyds idle rougher for a comparable grind, imho.

Solid lifter cams are not all the hassle that some people think. I checked our L78 after 20K miles and the clearances were still within a couple of thousandths of what they should have been. Might have been set that way in the first place. If they need setting all the time, something is backing off or wearing out. I've probably gone 250K miles on L72 and L78 engines and the cam has never been an issue. Going to high pressure springs could change the picture though. Then again, these cars don't get all that many miles put on them today.

how about a carb recommendation.

I don't want to hijack the thread, but I am another Buffalo guy here with an L88 short but with 990 iron heads and Gene I'd like to get your email for some advice on, builders,local machine shop etc..

So far, I am in agreement with what everyone has said. Im just here to add a little. As far as the solid lifter issue, it really isnt an issue like it used to be. All the valvetrain hardware you can buy nowadays is just better and things keep in check pretty good, so it isnt that frequent. Another thing, depending on what you mean by comparable, valve lash itself is the reason why a seemingly identical hydro camshaft will idle rougher than its solid counterpart. The valve in the solid camshaft doesn not open when the lifter first comes in contact with the cam lobe, it has to make up for the lash setting and it will take a few degrees of rotation before the lift at the lobe is high enough to make the rocker contact the lifter. A comparable solid camshaft would be 6-8 degrees larger than the hydro cam in order for everything to match up right. And finally, carb cfm requirement is a product of engine rpm, engine displacement and volumetric efficiency, so use this formula.
Engine rpm X Engine displacement X volumetric efficiency / .3456

Volumetric efficiency on your motor will probably fall around 90-95%. Could be a little higher, but it all depends on how well you camshaft is actually matched to your heads, so Id say use .90 to be safe at probably 6500rpm(VE is highest at horsepower peak and will drop off slightly and from what the users say of this camshaft it sounds like its horsepower should peak at around 6200 with rougly 6500 being the overall peak rpm). Select a carb that is slightly higher than what your answer is. Probably an 800-850 double pumper is gonna be close.

L71, the guy who put mine together is in the process of moving his shop. The only two guys around here that I know well enough to recommend are Carl McQuillen out in Leroy ( top notch) and Bob Pfeiffer in Collins. Think Bob is under the name SS Machine on Shirley Rd. He probably doensn't know me, but Carl does. Both are excellent, Bob actually will do the work. He's VERY busy. Carl has good machinists in his shop. I've heard good about JanCen, but never any personal experience.

AS you know, about now is a good time to approach them.

Again, there may be more good shops around, but I've seen these guys' work. There are plenty of horror stories too, so do ask around. Places I would NEVER bring my stuff.

Jim, I needed an 850 to feed the 427 at 7000 rpms, so you'll need all that at 6700. You could go large QJ or 800-850 cfm Holley. Trouble with big Holley's in that they suck gas bad. You arent going to drive this thing much are ya? smile.gif

Ideal carb would be a 830 cfm annular Holley. I never did get around to getting one on top the 427 since I went trips. Used to go up on Ebay and hunt them, around $200-250 on the best deals. Heard nothing but good on the HP950 as well.

In a hyd cam I'd look at the Lunati 302A8, or the Isky 292Mega, something along those lines.

Gene,

Thanks for the input on machine shops etc.. I'd like to get some feed back on my current set up and modifications that you would suggest.

I took a 240 mile trip last weekend with the chevelle,288/296F10 cam 255/263@50 .612/.630 lift.comp 10.7,850 double pumper,3.73 gears.I got 15mpg which I didn't think was bad.You just have to resist the temptation to put your foot in it,I did ok most of the time! smile.gif

Man, I couldn't get an 850 to squeeze anything near that! That's awesome!

Loose the cam. There is probabily no worse cam ever made by anyone. Cut the compression with a better set of pistons (the stockers are a poor design)and get a good solid in the 250 at .050 range and it will run just fine.