I'm in the middle of restoring/building a 3rd gen and I bought an lm7 to stick in it. The engine is supposed to have around 10k on its refresh (honed, new pistons/rings, main bearings, cam bearings, lifter and seals). It's supposed to have flat top pistons 10.6:1 with 862 heads and an LS3 cam in it. Previous owner claims about 405hp @6100 and 398lb ft @4900 at the crank. With 15% reduction at the wheels, should put it at around 345/335. This setup is in a car right now and that "feels" about right.
I'm about to pull it from the car its in and would like to see a bit better numbers, around 425 at the wheels + or - a few. I bought an LS6 intake (it currently still has the truck intake on it) and was wondering if there's any way to see those numbers on this setup for around $1500?

 

The truck intake it going to make more than the LS6 intake in most situations.
The LS3 cam is also way too small to make 425 at the wheels, and it'll be a major major stretch to do it on stock 862 heads.

 

The truck intake won't fit under the hood so it's gotta go. Would a set of LS1 heads and cam get me there? (I have a buddy that'll give them to me) What cam would be best for this setup?

 

IF you use the LS1 heads get them ported. Then they will do you some good.

 

LS1 heads aren't much of an improvement over the truck heads, and they will lower compression. LS1 cam is smaller than LS3 cam.

If you want stock style heads, you'll need 243 or 799 heads that have been milled to keep compression up, and a fairly larger aftermarket cam.

 

425 at the wheels will take work but not impossible.

HP is just torque x rpm \ 5252

You'll only get X amount of torque out of an NA street engine. On a 5.3 Around 400-430 at the flywheel. So the only way to get the hp up where you want it is to add rpm until you get the hp you want.

 

Ok, so let me rephrase my question.

I am looking for laughs per $. I'm not building a race car, just something I can hoon around in and maybe even commute in if it turns out well. This engine already almost doubles the HP this IROC came with but I keep hearing how easy it is to make HP with an LS setup so...what would be the best bang for the buck (approx $1500 of them)? I don't want to do NOS, just motor.

 

A turbo or 2

 

For $1500?

Speed Engineering 1 7/8" long tubes, 243/799 heads milled .035", Howard's cam and springs (I like 190325-12 cam and 98113 springs for a street driven 5.3), and try to find a used FAST 92 for a good price.

Should make ~ 475HP at the crank.

 

DAMN...now that's the kinda info I'm looking for! Thanks!

 

I did the SE long tubes, Howards cam/springs (115 LSA version of the cam for better idle) and stock truck intake on a 5.3 Chevelle a couple of years ago.

The 112 LSA cam will sound better, the FAST will make more power up top.

 

243 heads and our high lift ASA cam will idle pretty wicked and make some pretty impressive power. Id recommend an ls6 intake for your budget. That would get you well within your power range and fun factor.
Our high lift asa cam and spring kit is $479 shipped.

 

http://www.trucktrend.com/how-to/engine/1208tr-5-3l-bow-tie-builds-mild-to-wild/

Hope this helps as well.

 

Got to love the ASA cam. It is recommended highly in the community.