no cigar

Hey guys I'm spec'ing a cam for my LQ9 combo. It's a .020 over LQ4 with flat tops and unported 243 heads. I'm prioritizing Low/Mid end over any top end. This is for a 2 door Blazer/Tahoe that will almost never see over 5500rpm. I'm about 90% decided on the EPS 222/226-113. My main question is around the exhaust duration and the benefits over the trusty 222/224, and the effect of possibly going with a 114-116 LSA.

* Is the +4 deg split between intake and exhaust duration going to have a real adverse impact on a heavy truck with larger tires?
* Would there be any improvement in driveability by going custom and expanding the LSA to 114-116? I'm not wanting a thumping cam at all. In fact I am deciding on this cam over the 222/224-112 from COMP for that reason.
*Would L92/LS3 heads run any better (or worse) with only a .020 over 6.0? I just don't want to kill port velocity on the bottom end.

Other pertinent info: .051 head gasket, tune for 89-93, 3200 stall, 4L60E

Thanks for the help guys! I'm 90% there!

G Atsma

LS engines like some duration split, with rectangular heads liking even more than cathedrals. Longer exhaust duration allows better evacuation at higher RPMs

bbond105

Give Geoff a call at EPS. You can't go wrong with one of his cams. I had him grind a cam for me with his lobes and you will not believe how much quieter the valve train is.

no cigar

Thanks! I definitely will today.

Do either of you think that rectangle heads will be of use with a 6.0 when focusing on low-mid range?

Thanks!

wannafbody

iTrader: (2)

Nope. I find the square heads on my dad's 6.0 to be doggish below 2500 rpm. I'd do ported 243 heads.

ragtopz28

iTrader: (57)

Have you considered some 706/862 heads? They are cheap and will get you some more compression.

no cigar

I thought about those but figured the intake was a little choked down for a 6.0. I do have the original 317 heads that came off the engine as well. How much could I shave off those to bump compression? Is the port geometry about the same in the 317 as the 243?

Bspeck82

Call Jeff and ask him, he is very knowledgeable and will call back if he doesn't answer right away. Tell him you want a cam that makes great torque for towing but with a healthy power bump across the enritre power band. Asking for tighter centerline's isn't so cut and dry as you might think. It changes the entire dynamic of the cam. Typically if you think LSA will make or break your combo then chances are you have the wrong durations (valve events) in the first place.

gagliano7

Advance induction can port your 317 heads and weld the chambers for more compression. They are one of the best LS head porters. The 317 and 243 heads are very similar. The 317 heads are 71.06 cc chamber while the 243 have a 64.45 cc chamber.

http://lsx4u.com/lsxinfo/heads.html

Ls7colorado

iTrader: (3)

I would personally run the unported 243's with flat tops that will get you right about 11:1 and will make more low end torque that then rectangle port heads.
You will need 91/93 octane
You wont need them ported unless you want max high RPM HP witch you don't.

What size tires and what gears are you running?

ragtopz28

iTrader: (57)

This is why I asked OP about considering the 706/862. They are proven the best of all stock configurations in the low/med rpm range.

Ls7colorado

iTrader: (3)

Those would also work well for low end, BUT will raise compression over 11.6:1 if I calculated it right, could still work but in the heat would be pushing it depending on the tune.

no cigar

Ragtop, I did think about those but I'm trying to keep compression around 10.5-11.0. These Texas summers can be brutal, and especially in stop-go traffic.

The goal is to run 35x12x50 tires. IIRC this truck has a 3.08 highway rear end. I still want it to have some highway manners and driveability. Thats most the reason behind wanting to open up the LSA a little bit more to alleviate a super choppy cam that surges a lot.

ragtopz28

iTrader: (57)

Agree, a good tune is always imperative! Compression is a good thing, detonation is not!

Ls7colorado

iTrader: (3)

no cigar

Sorry. I looked at the RPO code and I have 3.73 axle ratio. This truck will mainly be a cruiser and maybe some light towing (jet ski, bbq pit). For the most part it needs highway manners as the family ranch is a 4 hour drive from where I live.

Ls7colorado

iTrader: (3)

even 3.73s with 35's will constantly be shifting out of overdrive on the highway unless your on completely flat ground.

Bspeck82

Ya not trying to sound like a jerk but if you wanted a nice cruiser you should leave it stock. Once you add some taller tires and more gear it will drive worse and have terrible mpg. Nature of the beast. If it is for towing and causing i wouldn't touch the motor internals either unless it breaks down. Just my 2¢. But if you insist, a nice exhaust, 243s and a small towing truck cam will do wonders and should have a touch of lope to it. You don't want too much compression with a small cam because you can run into detonation issues with such a high DCR

tech@WS6store

iTrader: (2)

Cut the lsa narrower and use a smaller cam.
The tsp stage 3 high lift would work the best in that situation on a 110 lsa. The wider lsa will push the powerband up and do exactly what you dont want. the larger duration will also.
Use 243 heads. any smaller you may have octane/fuel quality issues.
I run 3 trucks and have used multiple cams in them and tested out lots of options.