I have a 2000 LQ4 and I want more low end torque. Having the peak at 4000 just doesn't cut it for towing during low pulls. I tow 7600lbs through the California Sierra Nevada and there are some back roads you just aren't going to drive faster than 25 MPH without dying. My only option right now is to use 1st and wind it up. I have no problem with that but it would be nice to get it into second in that 30-35 range. Don't get me wrong, the LQ4 will wind all day. I am totally impressed. I've pulled some 10 mile 8% stretches and the temps rise to 215 and just hover there. Let's not talk about the MPG though ok? LOL.

I've been reading the dyno results for the L92 head and intake swap and some with cams. From what I can gather, nothing short of boost will improve the low end torque and even then you essentially get the stock 350-ish but you can get that down around 2500-3000 RPM. You do get to enjoy the improvement above that (and some impressive torque to boot.)

Is that a fair assessment? I have just not seen any head/intake/cam swaps that effectively push the peak torque down or even increase the torque below 4000 (to any useful amount). These combos just seem to improve everything above 4000 and some even move the peak RPM up.

Right? Wrong?

 

what tire diameter and gear ratio?

 

More cubes or F/I is about it. You pretty much nailed it. Small gains, yes. Anything more, you need to be blown. Preferably maggie or some other positive displacement blower.

 

Thanks MH, I wanted to make sure I wasn't missing a magical combo.

As for the tires/gears - Stock 245s and 4.10's.

 

From looking at the results of various combos on the internet and realizing what you want to do with the combo, I'll throw in my two sense. I am not an engine builder by any-means, but I do quite a bit of research on things before I act. So here's what I would try in your situation: 5.3 Iron block tested to ensure bore size will be good at 3.905". Pick up a good quality 4" stroke crank rotating assembly with rods and pistons (forged if you intend to do crazy power adders in the future) everything balanced!

You'll end up with a roughly 383 cubic inch engine that will be more efficient than building a 402, via the smaller diameter bore (read up on flame propagation, bore to efficiency relationships). The 4" stroke crank will help with your torque figures throughout the rev range. Most important, talk to a PROFESSIONAL to get your camshaft figures specd. out. Lay all of your cards on the table with this person so that they can determine the ideal lobe profile, ICL, ECL, LSA, and Overlap which ultimately determines your dynamic compression ratio. I'd be looking at decent set of cylinder heads worked over in the right places, say a set of 243's with very good valve job, throat transistion, bowls blended, and combustion chamber work. Or pick up a set of quality aftermarket heads from a sponsor with their optimizations applied. Good set of valve springs also required, as you said you have times where you run in the upper RPM ranges for extended periods, check installed height. A set of hardened pushrods of the correct length for your application that apply the optimum pre-load on the lifters you choose will keep Sewing Machine sound effects to a minimum. Top it off with a TBSS intake and 90MM throttle body cable/dbw depending on your application. Don't forget to pick up injectors that will supply enough fuel for your combo, as stockers won't cut it.

After all this if you feel it is not enough, you will have the option to go and toss on some forced induction. Eaton TVS would be the first choice, weather its the 1900 or 2300 you'd be best served contacting Magnacharger or a sponsor that sells them for their experience.

But, after my novel that I wrote above, if you want to go directly to FI then a supercharger would serve you best. 6.0L plus Eaton TVS, and you'll be pretty happy more than likely. If not, then apply the engine package I just listed and enjoy!

 

Here's from personal experience towing with a boosted truck;
I'm running a 6.0 with a Radix s/c, towing my 24' boat after installing the s/c made a HUGE improvement. Moving from a stop and pulling the boat out of the water on a pretty steep grade doesn't take any effort. Gas mileage while towing is better than when I was running n/a.
I couldn't be any happier with the tq gain and towing improvements from the s/c.

 

When my motor was still 6.0 liters with the blower (and intercooler), it felt like it had more torque in that range than it did at peak without the blower. That was at 11 psi.

 

IMO, skip the cam, different heads, larger engine, etc and slap on a used M112 Magnacharger. Unless your motor is already worn out, the small Maggie is the most cost effective solution and will give you the most results in the RPM range you're seeking. Even adding headers would probably take away a little low RPM torque although it would definetely healp above 3k. Any cam bigger than stock will just move the power band and peak torque away from your goal. Same with any larger heads let alone aftermarket heads. Stroker would and very small cam would have some more low end torque but the stroker combo's all have long term (ie:100k+ reliablilty due to the pin location) in what sounds like your DD and tow vehicle. A small, tight turbo would also work but I think the Maggie would do a better job.

Rick

 

It's funny when I talk to the old guys about towing with their 6.0L's and they mention the same thing. The torque peak is too high when the real problem is they are driving a heavy *** truck and towing a heavy *** trailer with a 364 cubic inch motor. A job that used to be reserved for a 454 or bigger. An MP112 Radix style blower is great for towing if tuned in right. Milage can be very rough though as once you get into power enrichment (about 40% throttle) which can be very often when towing your milage will go right down the crapper. My recomendation would be a set of PRC stage 2.5 5.3L heads, small cam, headers, thermostat, cat back, cold air intake, and some good tuning. A 6.0L with some compression will have quite a bit more torque than your LQ4 and will require the same fuel as you would have with a blower. My wife's Tahoe with LQ4 with 5.3L heads and a cam pulled off just over 15mpg while towing 4500lbs or so with the Tahoe also fully loaded down with only a 3.42 gear. If you want to run the small cubes you need to help them out.

 

boost is never the wrong answer