Vortec350ss

iTrader: (20)

Hey Guys,

I have some pretty basic questions here, and I'm really just looking for opinions from a few people who have been around the block.

I am comparing the LY6 to the LQ4. Stock they both have basically the same compression at 9.6:1. I know the LY6 has VVT, and the L92 square port heads. Does the LY6 have the same rotating assembly as the LQ4 it replaced with the stronger rods etc of the 2005+ models, or does it use weaker parts? I know the LY6 uses the 87mm intake, but for this comparison lets say they both do. The one last question is the limitations of the LY6 block. Is 4.030 the max, or being a GEN IV can it be taken out to the 4.060 of its 6.2 brothers? I know the rule of thumb is that 4.030 is the max on a GEN III 6.0.

Now I'm gonna throw a twist in it. Lets say the LQ4 had the benefit of a 243/799 head, the 87mm intake, and both engines were running the 2002+ LS6 cam. Looking at the specs of that cam it seems that it is better tailored to the square port head design. I'm surprised that GM didn't use it in the LS3 and instead chose to stick with the LS2 cam... but that's a whole different discussion... Only thing I can think is for fuel efficiency and emissions. SO, to recap, a 2005+ LQ4 with 243 heads (I think a 10.4:1 compression or so), the 87mm intake, and the 2002+ LS6 cam, or a LY6 with VVT delete and the 2002+ LS6 cam as well. Which is your choice and why? Lets not turn this into a "why would you use that cam" thread... yes I know it leaves power on the table. I have my reasons for this question specifically, so lets keep it on track.

I do love the square port heads, but I don't know that they are a better choice than the 243's on a 4" bore without decent work. If ported heads were an option it would be a no brainer in my eyes... but I'm comparing as cast factory parts.

batboy

iTrader: (6)

They both basically have similar rotating assemblies. The safe max bore is 4.030" which means they all can handle that size. Most 6.0 iron blocks (at least 75% of them) can be bored to 4.065", but you should sonic test the block first. Note: 6.2 blocks have a stock bore of 4.065", not 4.060" like you posted. Not sure why you are obsessed with a LS6 cam, there are way better cams available nowadays.

Vortec350ss

iTrader: (20)

Thanks for the info... and I realized it was .065" after i published the thread, but I was too lazy to go back.

Funny how in the first response you dig on the LS6 cam which I specifically asked people not to do, but you didn't answer the more important question: with a mild cam which heads do you prefer on a 4" bore, and why. I want to take everything into consideration too... compression(advantage 243), air flow(advantage L92)... all of it. Remember, 4" bore with a stock bottom end.

I'm not obsessed with the LS6 cam, but for this specific example I think its the best choice. It needs to maintain all stock drivability, it needs to be able to handle a TON of miles with no maintenance (valve springs, and other valvetrain wear), and it has to be as cheap as possible. I'm not sure what that criteria there is a better answer. If you think there is one I'd be happy to hear about it, but its not why I started the thread.

53bowtie

iTrader: (6)

IMHO I would run the 243 heads. They obviously give you a bump in compression as you already stated which is essentially free power (from a parts point of view). Plus, from the research I have done on here and the builds I have reviewed (skeet's for one) the L92 heads need to have some work done in order to work properly on a 4" bore. They will work no doubt but with the valve shrouding that can occure the difference in actual flow between the 243 heads and the L92 heads on a 4" bore may not be as much as you think.

Since you didn't mention FI or NA I would look at it like this.......

NA = 243
FI = L92

TXSZ66AVLANCHE

iTrader: (7)

I have a LY6 machined to 4.065" with LS3 heads and 24x crank, have about 20k of daily abuse on it now. Broke the engine in with a LS9 cam and it pulled dam good even though its a "boost only" cam some say. Current cam is 216/224 .533/.533 117lsa

1FastBrick

iTrader: (17)

For a daily driver I would Would go with the 243 heads. IMO the Cathedral ports have better street manners in the Lower RPM range were your going to spend most of your time.

If it were a Max effort build, I would do the Square port heads.

TXSZ66AVLANCHE

iTrader: (7)

Ive read the same thing about LS3 heads, but I have not noticed any torque or power loss on the low end compared to my old 243 head engine.

1994Vmax

iTrader: (4)

That's because 99% of square port head supporters also drive regular cab short box 2wd's.... or extended cab 1/2 tons that have nothing in the way of weight. Add a few thousand lbs to the equation and the noticeable torque loss of the L92 at lower speeds becomes very apparent. Not to mention the valve shrouding on the 4" bore. I mean it's not a coincidence GM added granny low first in the transmission and VVT to advance the cam on the L92 headed 6 liter HD's right out the gate in 2007... and it wasn't all for "fuel economy".

Cathedrals are better on the street for most people...... And yes the rectangulars can do well for all out power at higher rpm. The port size, shape and valve size determine those characteristics.

But if you are really dead set on a rectangular port setup I have a brand new in the crate L96 6 liter GM replacement longblock for sale lol. The L96 was just the flex fuel version of the LY6. J/K, you are way too far away.

Vortec350ss

iTrader: (20)

No such thing as too far for the right part... But this is a budget fix, and budget it will stay.

It's going into a Saab 9-7x, and I'll use a 3000 converter too, so I guess real bottom end power isn't a huge concern. Besides, no matter what it will out gun a 5.3 with bottom end power.

So I guess my next question becomes what would it take for this LY6 to outgun an LS2? I'd imagine the LS6 cam is worth a lot of power since this is a 2500 engine and most likely has a tiny cam. Also, it's rated at more than 10 hp less than the L76. Anyone know why? Think the LS6 cam would put it in LS2 territory?

I bring this up because it could either keep the square port top end, or pull the 799's from the 5.3 and run that top end. I'm just curious which you guys think would run harder.

1994Vmax

iTrader: (4)

Although I really can't back this as I can't find specs on the marine engine...... my L96 I have is a boat engine technically by part number. For what it's worth everything specs the same as the truck engine so unless the cam is actually different.... which I doubt..... it's all in the calibration. The boat version like mine is rated 385 hp/ 400 lb ft...... so not far off of an LS2 really.

You will get support for both..... but since you already have the cathedrals I would go that route myself.

Like mentioned stock to stock all out top end power the L92 head will win...... it's all in the numbers.