jgreenwald

Alright, everyone. After bashing my head against the wall for months I figured I would do the logical thing and post here, so here it goes:

2003 Silverado 1500HD with a 6.0 LQ4

About 3 months ago I sucked in a piston-full of water and bent a rod. Long story short, the rod bent, piston hit the crank (no damage to crank), and boyyyy was it knocking. So I did the logical thing and while it was out, I figured I would give it some Ba**s. After all, this is a work truck and I really just need it to be reliable and tow fine.

So here is the build list:

Comp Cams 266/270 (part number CCA-54-452-11)
New Rods
LQ9 Pistons to bump compression
New bearings throughout
7.4 Pushrods
New lifters
Tune from PCM in Mooresville, NC.

So here is my question: why is this truck SLOWWWWW. I mean I feel like I'm driving a 80's Chevette. It won't turn over the tires in gravel.

Overall it 'runs' fine, no noises will run at 90mph down the road, etc etc. but I cannot get over how slow this thing is and how there is NO POWER. To the point that it struggles to pull itself up a mountain when going to the Mtns for the weekend. You get the picture.

I chose that Cam based on the recommendation of the guys at Summit, am I missing something? Is the tune trash? Anything else I need to check?

Thanks in advance!

RB04Av

I'd check the simple stoooopid things like cam timing. dot-to-dot etc) Sounds kinda like the cam is a tooth (or more) retarded.

dannyz

Did you measure to check pushrod length with the new cam?

68Formula

Start with a compression check.

tblentrprz

What ICL was the cam installed at?

cino

iTrader: (28)

It sounds like the cam is off a tooth. I’d check dot marks on sprockets and while at it, degree camshaft to confirm install as per cam card.

Summitracing

Sorry to hear the cam isn't what you hoped for. If the cam was installed with zero advance, intake closing point is 41 abdc. Our SUM-8718 tow cam has an intake closing of 33 and our SUM-8712 stage 1 truck cam has a closing of 36 to put that in perspective. If you wanted to put another 4 degrees of advance in to match SUM-8712, we offer an upper gear with degree bushings so you wouldn't even need to pull the pump. 58x gear is SUM-G6644-4X 24X gear is SUM-G6643-1X If you don't think that's going to do what you're looking for, the SUM-8719 cam is the LS6 spring .550 lift version of drop-in SUM-8712. Both have that 36 intake closing point. PM us if one of these solutions is right for you and we'll do our best to help out.

jgreenwald

Would 4 degrees of cam timing make THAT big of a difference?

RB04Av

No.

It would make MORE THAN THAT.

Check your sprocket alignment. I'd be willing to bet, if I was the betting kind at all, that your cam is one tooth BEHIND where it ought to be.

Summitracing

We'd recommend you put a few cams through our cam timing calculator found here. We'd also recommend you watch this video It will seem pretty basic, but it really does hit on the interactions happening between overlap etc. Exhaust blowdown and intake closing point (which is the most important of the four events). You can't start building compression until the intake valve is closed and it's THE tradeoff in low rpm grunt vs. high rpm power. When you spend 30 minutes running through a few cams, it's going to give you a good understanding of what's going on and what can be done to fix the problem. If you advance the cam, the other big change you will notice is a lumpier idle...that's a function of intake opening sooner into tdc which is also noticed as a lower idle vacuum.

As RB said, it could be a tooth off and that would explain why the problem is Soo Bad because, while the cam can be improved upon, it's shouldn't be that terrible. What's hurting on that particular cam is the wide LSA. We came out with that stand-alone adjustable top gear for exactly this reason...an inexpensive way for people to tweak their timing to perfection, so that remains an option. We'll continue to monitor this and pm us if you need help.

Ls7colorado

iTrader: (3)

Is the truck slower than before? A 3/4 ton truck is not very fast with a 6.0 in it.
Maybe the ignition timing is really conservative??