6.0l needs rebuild suggestions for mpg

[tnrussell50]

Hello all, first actual post on here!

The ride : '02 Yukon XL Denali AWD with Nelson Tune

6.0l has piston slap and now knock sensor is out.

So, I figure if I gotta yank the intake, I might at well keep going. I need some advice on any changes I should make while I am there, other than decking, balance etc.

I want as much mpg as I can get without losing power. Currently just fresh air, no other adds.

This is an LQ4. Should I go with the LQ9 piston?
Should I change cams, or will added duration bring down the mpg?
Prices are about 825 to 1000, less cam and probably bolts. Anybody got a lead on a cheaper kit?

Thanks in advance
Russell

[2500Ak]

Hello all, first actual post on here!

The ride : '02 Yukon XL Denali AWD with Nelson Tune

6.0l has piston slap and now knock sensor is out.

So, I figure if I gotta yank the intake, I might at well keep going. I need some advice on any changes I should make while I am there, other than decking, balance etc.

I want as much mpg as I can get without losing power. Currently just fresh air, no other adds.

This is an LQ4. Should I go with the LQ9 piston?
Should I change cams, or will added duration bring down the mpg?
Prices are about 825 to 1000, less cam and probably bolts. Anybody got a lead on a cheaper kit?

Thanks in advance
Russell

It's not really durrations so much as it is overlap, you get it by adding the intake and exhaust (advertised not @.50) durations, divide that by 4, subtract the LSA, multiply the results by 2. Or use this calculator:

http://www.wallaceracing.com/overlap-calc.php

If you have a lot of overlap the engine will need to sit at higher rpms to be happy, and at higher rpms may pass fuel out the exahust valve before it closes.

In your cased I'd get a small cam if you're after mileage and power, not a useless cam like the stock one. Thunder racing makes a 214/220+2 on 115 that should maintain the stock band but give you a little more preformance. The zo6 cam is cheap 207/218 on 117.5 I think, and a little better than stock. The GT2-3 or something like it might increase mileage but I'm not sure, I heard that it did a while back.

Remember the stock cams are made to LEV standards, meaning the LSA is a little too wide, or the durrations are a little to small, or both.

LQ9 pistons are flat tops aren't they? Yeah, that may give you a little more compression. If you can find them cheap go for it.

That is my take on the matter anyways.

[TimeLimitHit]

i would have a nice valve job done on your stock heads, have them clean up and change the angles in the bowl to flow better. I mean if you are trying to keep good economy there isnt much you can do. free flow exhaust, cold air intake, maybe a performance maf. I picked a few brains at local speed shops around here and ALL of them advised against changing the cam. I have an lq4 in my truck and all i wanted was more towing power and better economy. All the builders i talked to said just do a valve job and have a nice free flow intake and exhaust. If you start doing porting and such it will only benefit you on the upper end, thus defeating the point of trying to achieve better fuel economy. The stock lq4 cam is fine the way it is. i spent 400 on my head work and i can honestly say i notice a difference before and after, not much, but a difference. Are you going to feel a new cam at 20% throttle? probably not. remember you are going for economy. 99% of the mods out there are intended to net you more power, not better economy. get the head work, decarbon your intake and clean the tb, clean the fuel injectors, tune it up and call it a day.

There is a free way to get better economy, ditch any extra weight you can afford to lose. if you have a third row seat that you dont use, take it out. things like that

[2500Ak]

i would have a nice valve job done on your stock heads, have them clean up and change the angles in the bowl to flow better. I mean if you are trying to keep good economy there isnt much you can do. free flow exhaust, cold air intake, maybe a performance maf. I picked a few brains at local speed shops around here and ALL of them advised against changing the cam. I have an lq4 in my truck and all i wanted was more towing power and better economy. All the builders i talked to said just do a valve job and have a nice free flow intake and exhaust. If you start doing porting and such it will only benefit you on the upper end, thus defeating the point of trying to achieve better fuel economy. The stock lq4 cam is fine the way it is. i spent 400 on my head work and i can honestly say i notice a difference before and after, not much, but a difference. Are you going to feel a new cam at 20% throttle? probably not. remember you are going for economy. 99% of the mods out there are intended to net you more power, not better economy. get the head work, decarbon your intake and clean the tb, clean the fuel injectors, tune it up and call it a day.

There is a free way to get better economy, ditch any extra weight you can afford to lose. if you have a third row seat that you dont use, take it out. things like that

I disagree with some of this, the stock cam was made to meet LEV standards for vehical emissions not fuel, or power efficency. A preformance MAF is a complete waste of money, they only throw off the stock tuning. The importance of headwork is in camming, stock heads almost utterly stop gaining power after about .550 lift; heads that have been worked over keep gaining power well into the .600 range, and more lift for horsepower is a free gain unless you count more expensive springs and titanium retainers. I'd bet even the Zo6 cam you'd see a very large improvement, as opposed to stock heads with Zo6 cam because of the extra .08 or so of lift.

Many preformance shops I've talked too know very little about GenIII engines, are terrified of EFI, and make most of their money rebuilding old GenI and GenII blocks and carbeurated engines or selling snake-oil products. They aren't all trustworthy and many have limited areas of expertise.

If you're taking the engine apart you might as well get a very small cam, probably something in the 20x/21x range that has low lift (.551 or below) and stockish LSA (114-117.5), so you can use a cheap 50$ set of zo6 spring, if nothing else the Zo6 cam can be had for very little money off ebay usually (corvette and other LS6 car owners sell them when they swap their cams out); unless you can get the LQ9 pistons cheap its probably not worth it.

Some other things ouy may consider, LS2 timing chains can be had for 30$ and are much beefier, I think melling makes a higher volume oil pump, the lifters in the pre-04 engines were an inferior deisgn and prone to ratteling, hardend pushrods are usually about 100$ and are much stronger than stock. There's a lot of little things like that make the engine stronger that don't cost a whole lot. If you're going to the trouble of tearing it down you might as well do it right.

One last thing on those knock sensors, when you replace them entomb them in RTV sealant. They go out because eventually water gets in there and ruins them, pretty sure there was a tsb on that.

[tnrussell50]

Thanks for the info guys! Yeah, I saw the TSB, shortly after I cleaned the engine.... doh! I haven't had any experience with these new gen engines so, I definitely appreciate the insight on lifters and whatnot. Got a local machine shop, Kim Barr Racing. They have done some nice work on the new stuff.

[RedHeartbeat]

Ah, so you're in the DFW area.