LQ4 into '83 K2500, looking for suggestions.

Hello everyone, I've been reading and researching LS engines for several months now. I have a 2000 LQ4 with ~200k miles on it that was a running take out. I want a modern, powerful, efficient engine that I can put some miles on before it needs a rebuild (again).

Currently my truck has a 400 sbc, SM465, NP208, and 4.10 gears f/r. I also have an NV4500 & NP241 for it, to go in with the LQ4. I want to build this as a DD, so I'm trying to figure out how to squeeze some fuel economy out of an LQ4. With the gearing of the NV4500 I am also tempted to put 3.73s in my diffs, I have the early NV4500 with deep low gear. The truck doesn't tow or haul regularly, but if I need it to I don't want it to...well frankly, I don't want it to suck at it.

Also, my '83 is a one-family truck, my dad bought it the same month I was born...to say I am attached to it is an understatement. I grew up in this truck with my dad. It has close to 500,000 miles on it, the 400 sbc is the 6th or 7th engine (went through about 5 "Hecho en Mexico" rebuilds in the early 90s (my dad wasn't buying them)). The most major departure from stock modification I have done to it is remove the smog pump. It still has an egr, still has the heat riser after the passenger manifold, still has a quadrajet ('85/'86 model, elec choke, no b-s, no elec feedback garbage)...the plastic intake tube was cracked out really badly where it slips over the air cleaner pan intake so I went to the dealership about 8 years ago and was able to buy a new one. That all being said, with the LS swap and NV4500 upgrade I still want it to appear stock. Part of my inspiration comes from Holley's '67 Shop Truck. To maintain the stock appearance I would like to use a 4-bbl manifold, like the GMPP ones, a fuel injection throttle body (Holley & FAST are the first two that come to mind...), and either relocate the coils or cover them. Don't know about aftermarket EFI controllers so was thinking GM ECM. I won't have a MAF, which if I understand correctly is called speed density (correct me if wrong), can a GM ECM be tuned/setup for speed density or MAF-less system? Fuel delivery I was thinking having the manifold bosses drilled and an injector at the end of each runner (like the Holley build). I want my factory (tall) air cleaner to sit atop the LQ4.

My plans are (were) to tear my LQ4 down, have the major components checked out at a competent shop, new bearings, seals, etc everywhere. I need advice and/or recommendations for a fuel efficient build. I am leaning towards keeping my iron heads and port/gasket matching them to the manifold. Is there a more efficient cam over the stock truck cam, or an equally efficient one the offers more power/torque? Should I bump it up to LQ9ish compression, 10.0:1 from 9.4:1. I want it to be 87 octane friendly if possible, my 400 sbc pings on < 89/90 now and it's friggen expensive.

I am tired of turning almost 3,000rpm with an old carb'd sbc to go down the highway at 70mph. Am I off my rocker on what I'm trying to do? I know there is a lot of potential in tuning, just don't know where to start. Cam? Pistons? Rods? Heads & hardware? Injectors? A great big thank you to anyone who can help me out.

Books I have and have read cover to cover (multiple times): Motorbooks Workshop - How to Build and Modify GM LS-Series Engines by Joseph Potak and How to Rebuild GM LS-Series Engines by Chris Werner.

First off, welcome to the site. Lots of guys here with info that should help you with your build.

Secondly, sounds like you're going to have a nice truck when you're done.

I would think you're heading in the right direction by changing gear ratios if you want to keep the old trans with the "Granny Gear". If I recall, that trans doesn't have an overdrive, right? If that is the case, 3.73s will help with the fuel mileage. And since it has the Granny, you can get your towing loads going alot easier. If the other trans you have has an overdrive, but no low Granny, a 3.73 will still get the load going without alot of clutching and be decent with highway fuel mileage.

I understand how you would want to keep it stock looking, but from a driveability standpoint, I think the fuel injection system is hard to beat. That, coupled with the right gears and trans would make a great daily driver that would run well on 87 octane gas. Just my 2 cents.

As for cam selections, I don't really know which one would help you out. Bumping compression up would help, but that may not be a wise route with iron heads. Aluminum heads are more friendly for higher compression ratios from a detonation standpoint.


If your 6.0 was not an oil burner and had good oil pressure with no noises, I wouldn't hesitate to drop it in and drive it for a while 'til your funds let you build it the way you want. My 6.0 had 140,000 on it and all I did was change the rear main seal and cover gasket. The engine runs like a charm, doesn't burn a drop of oil and gets my truck going pretty well with it's 3.73 gears and auto trans. I had some 3500-4000 lb. loads in my truck and it gets it going in a heartbeat. I couldn't be happier.

I'm sure some guys wll chime in soon and give you some more insight that will give you some ideas on which way to proceed. Good luck!

John, my current 4 speed is non OD with a Low first: 6:55, 3.58, 1.57, 1.0. The NV4500 I intend to put in does have OD and a Low first: 6.34, 3.44, 1.71, 1.00, 0.73.

Thank you for the encouraging words.

Bump. I thought there would be more advice/input here.

As far as the engine goes, I would lose the iron heads. They're heavy and inefficient. Swap them for a set of 243 or 799 casting aluminum heads. This will give you a very notable bump in compression, compression is efficient power. Meaning no noticeable loss in fuel mileage. With a very very mild tune you could run 87 octane too. But I suggest you sit down, do some math and look at how much you actually save running 87 over 91 or 93. I know for me, in a 98 liter tank the savings is $7 per tank. Running higher octane means more timing. More timing is more power, and more efficiency which is more mileage.

As far as a cam choice, considering what you want, I'd pick a stock LS6 cam. Or the venerable 212/218 which has been the standard mild truck cam for years.

As far as the engine goes, I would lose the iron heads. They're heavy and inefficient. Swap them for a set of 243 or 799 casting aluminum heads. This will give you a very notable bump in compression, compression is efficient power. Meaning no noticeable loss in fuel mileage. With a very very mild tune you could run 87 octane too. But I suggest you sit down, do some math and look at how much you actually save running 87 over 91 or 93. I know for me, in a 98 liter tank the savings is $7 per tank. Running higher octane means more timing. More timing is more power, and more efficiency which is more mileage.

As far as a cam choice, considering what you want, I'd pick a stock LS6 cam. Or the venerable 212/218 which has been the standard mild truck cam for years.

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Originally Posted by Frenchy

As far as the engine goes, I would lose the iron heads. They're heavy and inefficient. Swap them for a set of 243 or 799 casting aluminum heads. This will give you a very notable bump in compression, compression is efficient power. Meaning no noticeable loss in fuel mileage. With a very very mild tune you could run 87 octane too. But I suggest you sit down, do some math and look at how much you actually save running 87 over 91 or 93. I know for me, in a 98 liter tank the savings is $7 per tank. Running higher octane means more timing. More timing is more power, and more efficiency which is more mileage.

As far as a cam choice, considering what you want, I'd pick a stock LS6 cam. Or the venerable 212/218 which has been the standard mild truck cam for years.

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At 5 $ or so a tank... its worth it regardless.

In Paris, premium is 35 cents higher than 87. So a 25 gallon tank, that's an extra 8.75 a tank. If you can afford to drive a 3/4 ton truck, you can afford the extra 8-9 bucks to run good fuel. As stated above, more octane means more timing, which leads to more efficient power that's relatively cheap. But if 8-9 bucks is too much, go buy you a Honda, I hear they're really cheap to drive.