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[JimGnitecki]

I'm not ready to announce just yet how I happened to acquire this profoundly important piece of technical knowledge, but . . .

those of you contemplating engine transplants (not necessarily in an SSR), the LS engine series can be pretty confusing, and it is easy for even a pro to make a significant error. Be careful!!

Quick and highly superficial review of some (not all) of these engines:

LS1 5.7 liter all aluminum (block AND heads), hi-performance heads, 300 to 350 crank hp depending on year & RPO

LS6 5.7 liter all aluminum (block AND heads), higher-performance heads & compression, 385 to 405 crank hp depending on year and RPO

LR4 4.8 liter cast iron block truck engine 270 to 295 crank hp

LM7 5.3 liter cast iron block truck engine, 290 crank hp or so

LM4 5.3 all alloy truck engine (used in 03/04 SSR, Trailblazer, and Envoy). 100 lb lighter than all iron LS engines, and 65 lb lighter than iron block / alloy head LS engines, but still "truck" heads in terms of flow potential (but astonishingly good when used with right cam - up to 6800 rpm!!)

L33 5.3 liter all alloy (similar to LM4) but configured for and used in extended cab pickups only

L59 5.3 liter - flexible fuel vesion of LM7

LQ4 6.0 liter cast iron block, alloy hi performance heads truck & SUV engine, 300 to 325 crank hp

LQ9 6.0 liter cast iron block, alloy hi performance heads, 345 crank hp

LS2 6.0 liter all alloy, high performance heads, 400 crank hp

Confusing, isn't it?

It gets worse.

For example, and ONLY for example, the LQ4, LQ9, and LS2 all look similar, right? Why the difference in power output? Glad you asked. Turns out that tere are subtle and not subtle differences that make a big difference - but can also be eliminated via equivalent hopping-up efforts.

All have the same bore, stroke, and crank.

Rods may or may not be identical - GM is not saying, and no one that I know has the access to, and the knoweldge and equipment, to analyze the rods

Pistons differ. The LQ4 piston is a dished design, cast piston. The purpose of the dish is to reduce compression to 9.4. The LQ9 has a flat top piston, for higher compression (10.08), but it is also higher quality. It's also coated with a heat rejection cotasing top and sides. The LS2 has a lighter weight flat top piston (since it needs to rev much higher).

The cam in the LQ4 and LQ9 is identical, and very conservative (196 In / 207 Ex / 0.467/0.479 lift) - similar to the LM4 and LM7 cams in fact. The cam in the LS2 is the one out of the 2001 (not 2002!) LS6, and is more like 204 In / 211 Ex / 0.525 lift. This results in more rpm at peak power (6250 or so versus 5200) and more power.

The heads in the LQ4 and LQ( started out as different but then standardized on the better of the two. This head is identical to the LS6 = LS2 head, except that it has a larger combustion chamber for lower compression ratio. The combination of larger chamber and dished psirton holds the LQ4 to 9.4. The combination of the same chamber but flat piston gives the LQ9 10.08 to 1 compression. The use of a smaller chamber (64cc versus 71) hikes the LS2 compression ratio to 10.9!

So, the LQ4 makes the least power (300 to 325 hp depending on RPO). The LQ9, with its higher compression and slightly different tune makes 345 hp. The LS2 with its smaller chambers and more aggressive cam makes 400 hp.

Here;s the interesting part on thse 3 engines: The LS2 is costly because the uneducated hotrodders only know that a "Corvette" engine is HOT, and supply and demand takes it from there. (Same way that an LS1 from a Camaro gets $2500 at salvage yards, but an LM7 gets under $1000).

The LQ4 is cheap because no one outside the techies understands that it is incredibly similar to an LS2 except for cam (easily changed) and lower compression (still good, and IDEAL for supercharging), and that the low tech pistons are routinely spun to 6500 to 6800 rpm in magazine buildup projects.

The LQ9 is costlier than the LQ4, because even the technically uneducated know that 345 hp is better than 325, and the cost of ADDING horsepower is statistically about $60 to $75 per crank hp, so that 20 hp is worth $1200 to $1500 if you leave the engine unmodified. If you do modify it via a freer breathing cam, the higher compression and better pistons are still a better starting point. If you take the recipes in the magazine articles, and add better pistons and higher compression, it only gets better.

By the way, the smaller chamber heads from the LS2 are a straight bolt-on to the LQ4 OR LQ9. With the LQ9, you get 10.9 compression that way, same as the LS2. On the LQ4, you get around 10.5.

The same aftermarket, or GM Performance Parts cams, will work on all 3 engines, with the differences in outcome being a result of the different compression ratio (not a huge difference). The pistons on the LS2 being a bit lighter supposedly, will be less stressed at really high rpm, and will put less stress on the vulnerable connecting rod bolts, that when they fail, fail because of inertia loading.

The cast iron blocks of the LQ4 and LQ9 are acknowledged to be both stronger, and also much more easily and cheaply overbored. They can be bored out 0.030" without fanfare, whereas the LS2 with its sleeved bores can only be bored out 0.010, and beyond that requires re-sleeving ($$$). But, the LS2 is lighter by 65 pounds because of that alloy block.

Any of these 3 engines can be pumped to clsoe to 500 crank horsepower while retaining civility and reliability, and to more than that if civility and reliability need not be "perfect".

Here's another neat tidibit: any of the 3 can be stripped off their fuel injection and fed via carburetor, and NOT LOSE POWER, although civility and fuel mileage will lieklysuffer. But the dyno results from multiple independent parties are very clear: the carbs meet, or exceed, the power curves of the EFI.

For you guys with emissions requirements, that is a moot point. But for "Red" on my SLURP project, it is not.

I started by saying "don't confuse these LS variaitons". I meant it. Today, a PRO at one of the country's largest salvage operations was shown to have sent out an LQ4 in place of an LQ9 because he was unaware that there WERE two variations of a 6.0 liter "truck and SUV" engine. He had to correct the error, and did so graciously, but it cost him some money.

Be very careful in analyzing LS engine specs. Theya re NOT obvious, even to the pros. I suspect I may have made some errors even in this quick and dirty summary. If so, those who know better, please feel free to correct me. We want accurate info on this site.

Jim G