Why do L92/LS3 heads tend to disappoint so often?
 

From the very begining ive never understood the 'hype' about the new GM ls3 engine, ten years after the gen III ls6 making 400hp, GM came out with the 6.2liter brother making 426hp. 26 more horsepower with 30 m ore cubes just doesnt strike me as that impressive to begin with, that being said, the biggest change to this version of the ls3 engines https://mechanicfaq.com/ls3-intake-manifold/ is the 'l92' head that they come with. With 260cc intake ports, big valves, offset rockers and excellent flow numbers even from the factory, you'd think these would be the head to have. The more time i spend online and at the track, the more i find guys going no faster, or even going slower when swapping these heads onto various LS2 and 6.0 variants from the old cathedral port style. I know this is a very broad and vague question, but what comes to my mind is back in the 70's when the 4v cleveland heads were supposed to be the 'hot ticket' but many of the guys that switched to them saw no improvements. Anybody have any thoughts as to why this seems to be so common?

It's a velocity issue. The L92 heads have large rectangle intake ports and larger intake runners. The problem with this is slower air speed velocity and atomization into the combustion chamber at lower rpms. This creates an issue of less torque at low rpm where you need it to get off the line.
Another factor is some guys have their engine/cam/converter/gear combos setup to make great power with cathedral port heads, then decide to swap on "better flowing" heads, then comes in the issue of mismatched parts. The heads flow more than the entire setup is designed for and throws everything out of balance. In which case, they have to start changing cams, converters, and gears to start matching the potential of the heads. Proof that bigger isn't always better.

That said, however, if the engine combo is built particularly for the higher flowing heads, then the setup can have great potential.

As for the disappointment of the larger heads and more cubic inches only making 30 hp more over the LS6, keep in mind it may not necessarily be how much power it makes, but the way it makes it. Also, the LS6 cam has more exhaust lift and duration than the stock LS3 cam, which can make significant differences. I say that because the LS engines seem to drastically respond to even small cam changes. I've never personally driven a vehicle with the LS3 or L92 engines, so I really don't know how to compare them to the LS1 setup in my 68 C10. But, I do know that many in the autocross world run the LS3/525 crate engine which is basically a hot cammed stock LS3 making 525hp/489tq. My LS1 has AFR heads and a custom ground cam to make 531hp/475tq.

The other thing to consider is the size difference- 1/2 liter, or about 30cubic inches. Proportionately, just on displacement, if the LS6 does 400HP, then the 6.2 should do 436, which is close to what it does, with a SMALLER cam than the LS6! As said, the LS3 is about potential. You want 500HP? Put in a bigger cam. THAT'S IT. The intake is good for that and the heads good for 600HP, UNPORTED. See what we mean?

Its all math, velocity, shape, turbulence and reversion in port design and parts matching for your set-up. Too many people worry about flow numbers instead of velocity and port shape, theres way more involved in heads then just a flow number. Also why does everyone think a ls1 or a ls2 that is spinning 5800-6800 on average required a 260 cfm port, it doesnt. This is why you let a pro decide what cylinder heads to run on a particular set-up. Just saying ls3 heads are better because of a flow number is just stupid.

1. SAE tested the 405HP LS6 and the 436HP (not 426) LS3 with different standards.
2. The LS3 has a smaller cam.
3. You need ported stock castings or aftermarket castings along with a good aftermarket intake to even compare to the stock LS3 head and intake manifold.
4. Cathedral heads are less sensitive to cam timing, whereas the rectangle ports need careful cam selection on <400" engines.
5. Welcome to 2007!

this made laugh!!

[QUOTE=biketopia;20021991]Me Too!!

If they were "so bad"....why did GM put them on 6.0L truck motors ? (LY6)

And....in theory... at 315 +/- CFM they're good for over 625 HP using 2 - 2.2 HP per CFM

l92 are good bang for the buck... especially if they come on your junk yard engine. Its all about matching parts to your combination (car weight, RPM, transmission, stall, gear ration etc).

There are better options with aftermarket but the cost goes up. But matching the perfect aftermarket head for your project and combination should always make more hp, but at a higher cost!

For me for my 68 Nova (If I can ever get it on the road) about 400 RWHP is basically a carb, cam kit and intake with decent exhaust.. and from a 1800 CAD junk yard ly6 motor with 3X,000 Km on it that is pretty good value for a classic car. To get that from a SBC you going to put big bucks in it and have worst drive-ability, larger cam etc etc.... Not trashing the old SBC platform.. I love it.. just on a budget.. a ls just makes sense for my project (There are a ton of really fast sbc cars at the drag strip every year).

Its about perspective and expectations. There has been a lot of hype with the heads.. They are not the end all and be all.. but good value and power with the right combination.

B

Not sure what is so funny or are you agreeing with the post ?
He spoke the truth. What I laugh about is people that say they lose low end torque, Tell GM they were wrong for putting them on 6.0 truck engine then, Funny thing is the LY6 6.0 will out pull the older 6.0's
If we're talking stock heads not ported cathedrals against stock LS3 heads a properly cammed LS3 head will out perform cathedral ports heads with ease.

Absolutely agreeing with the post.

If I could go faster with 243/799s, I'm gonna get a set.....LOL

Parts combination is what wins races and mismatched parts are far too common place to single out something like this.

L92 heads need more attention to cam choice and really wake up as the cubes go up. for 6.0L or smaller I prefer cathedrals. 6.2L or bigger? Square ports for me