Just bolting on a set of OEM 243/799 heads on a stock LQ4 will effectively raise torque 18-20lb-ft/18-20hp everywhere. Not just from 4000+ as a camshaft will, but from idle to red line. You can thank the bump in compression for most of that gain.

Once you swap in even a small cam such as the TR220, torque and horsepower will be down where a heavy truck needs it most, to favor the top end around 4300-5800+/-. Sure you might see a peak gain of 30-33hp and 5-10lb-ft of torque, but chances are you've also lost over 20lb-ft of torque and 10hp from idle ALL THE WAY to ~4000. When I say enthusiasts should always shoot for the most power under the curve, I'm talking about this exact type of scenario: having more average torque and horsepower over the course of the RPM band will win races all day long compared to a motor that is very peaky.

Bolting on a set of 243/799 heads will bump compression up past 10:1. Mill them down .030-.040" for a 10.5-10.6:1 compression ratio and you'll notice a big improvement in throttle response, power and fuel efficiency.

 

450/450 isn't going to be achievable without some miracle unless you add in boost or nitrous. If you want more torque though you need alot more comression as you have chosen. If torque is your main goal go for a set of PRC 5.3L heads or buy some 5.3L heads and try to copy their results. 243/799's will also get you there, but not with as much compression. Do you have a performance goal also or just a dyno goal?

 

my goal is just to have a badass hotrod, wether a dyno or the 1/4. im just looking to get the best performance out of my truck that i can, and learn everything i can along the way. cuz when i started with this truck i didnt know a damn thing bout it. but i sat back and read the forums and asked a question now and then and when it came time to start the build i was able to do it. but in the course of the build i started to go the wrong way. the was headed to being a dyno queen, which doesnt do much good on the street, unless your trying to achive top speed. after talkin with a couple of people i realized i need to ask a couple of questions and set the build in the right direction.

you guys have helped me alot, and this is the direction i will go in. im gonna get the 243s and install them with the lq9 pistons for the time being. later on this year or next ill have a cam custom ground for my setup and at that time have the heads worked to compliment the cam and the rest of my setup. i should have this done and some sheets to show you within a couple of months.

thanks again for all your help and input.

 

Why are you so insistant on flat tops? You can get eleven to one compression with out adding the cost of lq9 pistons. My lq4 with .020" off my 243's and .040 cometics is gonna be very close to 11 to 1. You don't need to spend the money on pistons just close the gap a little.

 

Here's what made 459hp/442tq. Start with an LS3. Compared to your motor, it has a few more cubes and way better heads along with 11:1 comp. Add all the usual bolt ons and an XER281 cam. Specs are 232/234, .600 lift, 112 LSA. You won't hit these #'s because of your heavy *** tranny and rear end. You won't much like anything about the setup except the mean idle. It had drivability issues in a 6sp manual tranny vette that weighs about half of what your truck weighs. It would be really ugly in a heavy truck with a slush box.

To get to your goals, you need to build you a 408. If that's not in the cards and forced induction/nitrous won't be considered, I think you're SOL. A maggie would get you there for not much more money than a heads/cam bolt ons setup. It would have stock drivability and more power down low than you would know what to do with.

 

cuz i have a set in hand and dont have to pay for the machining cost.

down the road a bigger cube motor is in the plan but thats is farther off than i can plan right now. right now it is just to get the most out of my setup i can. which will put me between 400 and 450 rwhp and rwtq. i can be happy with that for now. but like they say once you get the mod bug it never ends. lol

 

With a 6 speed you'll be fast even without alot of torque, but torque will make it more fun to drive. I'd go with your flat tops and a set of ported 862's with 2" intake valves in them and an XER273HR cam. The 114LSA will keep the low speed and low rpm driveability within a nice range as well as being able to pull to 6600rpm without a problem. You could also go with the XR275HR and get great torque out of it, but the XER273HR would get you similar torque with more power past 5200rpm making that 6 speed a blast. The compression you'd get with the flat tops and 862 heads would well over 11:1 giving you fairly big torque numbers and excellent power even below 3000rpm. If you check around the 862's with bigger valves and ported make very good power. Search PRC 5.3L 2.5's and you'll see numbers similar to what you're looking for. If you buy your own set and have it done it will be alot cheaper unless you can find a set used and already done. There will be no need to mill them either making them just a bolt on. I'm looking for a similar thing with a power band just like my dyno sheet, but 100hp and 100ftlbs of torque more down the road.

 

wouldnt i run into timing issues with that much compression? even if i am running 91/93?

 

unless you want to run race gas all the time, 11-1 is about as high you want to go.
right now a set of LS6 heads, 243. have the same size valves, same size ports just like your 317's. but a smaller combustion chamber.
just bolting on a set will up you HP.
with just a little porting and some polishing you can make them flow so much better
then what you have now.
shave them down 0.40 will give an even bigger bump in power.

next is fuel, if you cant feed the pig right your gona have issues.
when you get up around the 400 hp range stock injectors wont cut it any more.
an after market regulator may be needed to up fuel pressure.

then it all down to the tuning and you could be looking at 450 or damn close to it.

 

What octane you will need depends on DCR not SCR. People go well over 11:1 and run just fine on 93. 9:1 DCR is regarded as the point when you'll need to switch over to race gas. So you'll need to the valve timing specs on your cam and then you can calculate your DCR based on what combustion chamber size you choose.