Starting off the truck is a 04 2500hd that tows a car trailer 8-10 times a year. Current mods are long tubes, exhaust, 216/220 .550 112lsa with supporting valvetrain, stock converter, ls3 injectors.
Question is, I have a set of ported/milled .030 243’s with a complete tbss intake. I also have a complete set of 823’s also with a complete l92 intake.
Being that the 243’s are milled I’ve seen on other posts compression numbers in the high 10’s to low 11’s, seems awful high for a pump gas truck that’s heavy. I don’t know my piston/deck height currently so it’s hard to get a accurate static/dynamic ratio using calculators.
Stock 823’s obviously make power, but up high where the truck doesn’t live very much, and possibly need a cam with a larger split to take full advantage of the square port heads.
When I get home from work, I’ll have the heads cc’d to get a better idea of a number to plug into a calculator
Anyone have success with .030 243’s in a heavy truck? Or was it a constant battle fighting knock/detonation? What are your opinions on which route I should go with.

 

Cathedrals

 

I'm not saying you should use the 823's but you have to keep in mind that they did come on 6.0 truck engines so it's not like they are terrible down low, They are pretty good if matched with the correct cam.

 

I'd go with ported 243. The 823 are soggy down low on a 6.0, at least according to my butt dyno.

 

This seems to be the general consensus from most members, unless I was going to go with a Lsa charged later on, which isn’t in the books the I should stick with my 243/tbss set up

 

Sub'd because i have a 03 2500hd 6.0

Mines nearly stock tho. Did 15.9 on the dragy

 

Same here, in a light car there great. But a 6.0 with 317's seems to pull MUCH better than a 6.0 with 823's below 3000rpm or so

 

My dad has a 08 2500 HD with 6.0 and 823. It's a sluggish down low and it has 3.73 rear gears.

 

I think one reason the LQ4 is sluggish is the lower compression it has compared to most other LS engines, except maybe the LM7.

 

Mine has 4.10s but i put 285/70 17 h2 wheels on it. Even with 4.10s it's geared to long tho. It runs 55mph in 1st and 90 in second. Which is likely reasons they feel a little sluggish especially today where 10 speed autos are becoming the norm.

I have a udp on it, ported tb and ss silverado timing tables. I did a 93 octane tune for it a while back and that pepped it up pretty good but with the mpg's it gets it just wasn't worth it. The 15.9 dragy was on 87 octane.

I bought some oe efans for it a couple weeks ago. It still has the stock exhaust on it but it's starting to fall apart. Had to weld up cracks in the muffler last year so i may do some se headers and their exhaust. I don't want it loud tho because i pull with/load it a fair amount.

A tb ss intake and 90mm tb probably be a good upgrade too. Some 1.8 or 1.9 roller rockers seem to put low and mid range tq in ls stuff which is what a heavy vehicle needs.

yea it's meant to run on 87 octane.

 

Don’t L92 headed 6.0’s make more HP AND TQ than the cathedral ones?

 

They do but they have vvt too.

 

it’s at higher rpm also
my lm7 suburban with 3.73 has more torque below 2500rpm than my 2012 6.0 work truck. And the work truck has 4.10s only about 1000 lbs difference in the 2

 

Most folks that put the square ports on a 6liter over cam them, and then they seem soggy down low. Last 6liter I built I used the CNC GM LS3’s with light valves. I used offset dowels to move the intake valve away from the cylinder wall, and worked with Tony Mamo on a cam for torque. Had a 219/231 cut for it. This is in a 99 4x4 ext cab that pulls a trailer a lot, and it’s very, very torquey. Used a LY6 intake and a 92mm NW Tb. Align honed the mains with ARP main studs, balanced the assembly using steel H-beams. Didn’t cut corners and paid attention to the details. .045” quench and 10.75 compression. 1.875 headers. Tuned on 93 because that’s all he runs. It works well. Not overcammed and a great working combination, which is most important.

 

my 2500 hd goes up the road at about 2k at 60mph and almost 2500 at slightly over 70mph with the equivalent of 33x12.50 17. So that6the typical range it does most of its pulling in.

You can probably +500-700rpm for when it downshifts to 3rd from od.

Then on hard pulls in 2nd gear 60mph is about 4k rpm.

Very seldom do i run it harder than that. Usually in 2nd I'm not at full throttle. It just needs the gear.

But that's a typical rpm range it works in.

 

Even with the stock cam the 08, 6.0 L76 or needs to get to 3000 rpm to start pulling. Even my 5.3 with 243 heads still needs rpm to get into the power band.

 

It almost feels like tm gets involved if you get into the throttle to fast. Which i think could just be a drop in port velocity.

 

It could be a torque management issue or it could be the converter. What's weird is I drove someone's GMC and it felt different. He had a single cab and I have a crew cab so there might be a weight difference.

 

I’ve been wondering kind of the same, I drive a stock 6.0 crew cab and wondered if or what would be worth doing without having to run 93. From reading this the 706 heads with their bump in compression is worth more the flow numbers.

http://www.superchevy.com/how-to/eng...nder-head-test

 

It is at times. Especially when you probably ain't using all of the flow in the heads anyway.

But with compression typically comes the need for better fuel.