6.0 with LS3 engine combination

[Dan Shook]

I am considering building a LQ4 and installing LS3/L92 heads, LS3 intake and TBI with a cam, possibly the gm hot cam and springs with headers. I have a few questions, first off what kind of horsepower numbers are realistic with this combination? With this combination of parts is it going to be a major issue to get a wiring harness and pcm to make this combination to work in a very reliable fashion? Does it make sense to go the route of running a carb to simplify the wiring needed to make the fuel injection work? My other concern is am I going to be close enough cost wise to consider going with the gm crate LS3 engine and harness. Any input would be greatly appreciated. Thanks

[csouth]

I would do some research before putting that combo together. The LQ4 is a low compression motor from the start, combining that with the LS3 heads will probably make it a dog. You'll need to mill the heads to raise the compression and would do better a custom grind cam.

I would Google, I'm sure someone has done it before ....

[csouth]

I think you should do some looking on LS1tech if you haven't already. I did a quick look. Probably cost you more money in the end than a good set of cathedral ports for that block.

[SSLOW6.0]

I think you should do some looking on LS1tech if you haven't already. I did a quick look. Probably cost you more money in the end than a good set of cathedral ports for that block.

No, the Cathederal port heads are tinker toys compared to the LS3 heads. Considering that even the best thousand+ dollar each cathedral heads are only comparable to the $756 CNC ported LS3 heads from GMPP, it doesn't make any sense to use cathedral port heads for any build on an engine with a 4 inch or larger bore. That being said at only 4.0 inches you will shroud the intake valve a little, but it's still better flowing than an LS2 or LS6 head.

Second, Carbs on LS motors don't make any sense, if you want a low buck EFI install use a microsquirt. Otherwise you're essentially discarding "free" EFI, its not really free but compared to a multiport system from the aftermarket its 1/10th of the cost to use.

As far as cost is concerned, I swapped an LQ4 with an LS3 cam into my 86 Monte Carlo SS for $3500 all-in. even if you added GMPP CNC ported heads and a fast intake you'd be far below the 5 digit price tag of a GMPP engine.

[rickpaw]

I begged to differ. Stock LQ4/9 heads have chamber volume of around 70cc, whereas the LS3 heads have chamber volume of round 68cc. So on paper an LQ4 with LS3 heads will have higher CR. Plus the LS3 heads flow more, in stock form. If you look on LS1tech.com, you'll see that LQ4/9 with LS3 heads are common.

Cost wise, LQ4/LS3 heads longblock should be cheaper than a crate LS3.

[csouth]

I begged to differ. Stock LQ4/9 heads have chamber volume of around 70cc, whereas the LS3 heads have chamber volume of round 68cc. So on paper an LQ4 with LS3 heads will have higher CR. Plus the LS3 heads flow more, in stock form. If you look on LS1tech.com, you'll see that LQ4/9 with LS3 heads are common.

Cost wise, LQ4/LS3 heads longblock should be cheaper than a crate LS3.

Its not only about the chamber volume, its about the velocity. When i said cathedral I of course was speaking ported not stock. The ported LS2 heads will have higher velocity than a stock LS3 head, that will yield more low end torque.

I will just say the LS3 head have both advantages and disadvantages....

[SSLOW6.0]

Its not only about the chamber volume, its about the velocity. When i said cathedral I of course was speaking ported not stock. The ported LS2 heads will have higher velocity than a stock LS3 head, that will yield more low end torque.

I will just say the LS3 head have both advantages and disadvantages....

For a "budget" street built, the GMPP CNC LS3 head is the only way to go. Less than $1400 for a set of heads that flow more than 350 cfm at 600 lift, a better deal does not exist.

Also GM says you're wrong about low end torque comment.

[csouth]

For a "budget" street built, the GMPP CNC LS3 head is the only way to go. Less than $1400 for a set of heads that flow more than 350 cfm at 600 lift, a better deal does not exist.

Also GM says you're wrong about low end torque comment.

The fact that you tried to make a point by comparing torque on a 6.2L and a 6.0 with different intakes and cam's is a little scary... I'm done....

[jwcarguy]

Dan,

You didn't mention what, if any parts that you have already?
What are your hp goals and driving/ usage for it?

I have a similar combo in my personal 68', but started as a 6.0L iron block (LQ4), but installed a new rotating assembly out of a LS2 6.0L crate engine (flat top pistons, floating pins and stronger rods), GM LS3 cylinder heads, custom grind cam from Geoff @ EPS with all supporting valvetrain mods/ upgrades and LS3 intake manifold w/ 92mm TB

[Dan Shook]

My goal would be around 500 hp. I have a high mileage LQ4 that will need rebuilt is what I have now. The usage for the car at this point is a driver / cruiser but I want it to be super reliable to be able to take on longer trip so reliability is very important. I am concerned with the wiring to make it work. I don't want a highly customized wiring harness that has the potential to be troublesome.

[SSLOW6.0]

My goal would be around 500 hp. I have a high mileage LQ4 that will need rebuilt is what I have now. The usage for the car at this point is a driver / cruiser but I want it to be super reliable to be able to take on longer trip so reliability is very important. I am concerned with the wiring to make it work. I don't want a highly customized wiring harness that has the potential to be troublesome.

What year LQ4? is it a Gen III or Gen IV Motor? If its a Gen IV you should be able to a DBW GM crate motor harness and just get it re-tuned for your application. If not you're looking at a custom harness from one of many reliable vendors (painless, PSI, EFIsource etc) To get 500 hp (im assuming crank hp) you're going to need some good cathedral style heads and close to 11-1 compression. You can reuse the factory LS crank, they are plenty strong, but you may want to look at upgraded rods and a flat top piston. I'd recommend the GMPP CNC LS3 heads and an LS3 or L92 intake (depending on vehicle weight and where you want your torque) If you're going to go with a rectangle port head, I'd also recommend going .030 or .040 over to help un-shroud the intake valve. As far as cam grinds go, Talk to Texas Speed and Performance, they can set you up with lifters, cam and valve springs that will work with the combo you have. The wiring is pretty simple in my opinion, but I'm a techie. Remember since LS motors don't have a distributor (unless you get one of the funky aftermarket covers) you're always reliant on some form of computer for spark, whether you do a carb or EFI. Personally I trust the robustness of GM's or even DIYautotune's computers before I trust aftermarket MSD junk, but that's just my experience with MSD.

[T/A Addict]

Exactly the same build that I am looking at doing... I've researched a ton of builds to gather as much info as possible before starting. 500 hp is a good number with heads, cam and exhaust as these guys have mentioned.

[mert.celet]

You may want to look at CamMotion for their LLSR setups. I know it's more $$$ and a little more maintenance but You get great results. As per Your HP goal, You may like it.
LS3 heads perform exceptionally well with LLSR cams.

I will disagree with a carb setup instantly. EFI stuff is addicting.

[andrewb70]

I agree with much that has been said here. I will also add that using a single plane intake with a carb will kill about 40lb/ft of torque down low as compared to a LS3 intake (which are very good and barely get beaten by the FAST intake...)

Andrew

[mert.celet]

And if You decide to go with the fast intake, make sure You take Your time with the runners and do a little port matching with Your cylinder heads. The results are always outstanding. And You will have fun doing it.

[andrewb70]

LS2 = 6.0L
LS3 = 6.2L

Not exactly apples to apples...but I certainly don't think rectangular port heads negatively impact torque.

Andrew

[SSLOW6.0]

LS2 = 6.0L
LS3 = 6.2L

Not exactly apples to apples...but I certainly don't think rectangular port heads negatively impact torque.

Andrew

If 10 cubic inches makes a 25 ft/lb difference, Everyone needs to .065 overbore their motor STAT lol.

[andrewb70]

If 10 cubic inches makes a 25 ft/lb difference, Everyone needs to .065 overbore their motor STAT lol.

10 cubic inches can easily be 10-15 lb/ft....

Andrew

[SSLOW6.0]

10 cubic inches can easily be 10-15 lb/ft....

Andrew

1.5 ft/lbs per inch is almost unheard of an old gas NA pushrod motor. If we were talking Honda K series motors I'd be more inclined to believe it. 2.5 is impossible.

[andrewb70]

1.5 ft/lbs per inch is almost unheard of an old gas NA pushrod motor. If we were talking Honda K series motors I'd be more inclined to believe it. 2.5 is impossible.

I said 1-1.5...which is not unheard of for a LS engine...

Andrew