Yeah well it is just a simulation and not really designed for the LS engines. But man that thing would FLY at highway speeds when you kicked it back to 2nd gear (have my program set to allow a WOT kickdown to 2nd at 83MPH). I'd like to find a dyno that can handle 4WDs to see what it's really putting down. I'll have to go dig one up once I get the oil leakage problems resolved.

Speeder wrote:

Dyno2000 Advanced Engine Simulation
Version 3.10
April 25, 2001

hehe got the same. But your 4.8 is embarrassing my 5.7 so I'll start fresh with a new file...

It'll do that in real life too. I've run a couple of Vortec trucks, and one of them was running Flowmaster 40s so there was no confusion as to whether that one was running or not.

Can you post a "prnt scrn" of the options you chose for your 4.8 in DD2000. Even vith the same cam, I'm shy 40tq from yours

Not surprising. I didn't notice that the base I was running off at work was using the 5.3 stroke. The one I was running at home was a 4.8 though. Those numbers I posted were done at work, so my fault. Now when I had the engine done I had the guy up the compression a bit too. He couldn't give me a definite number but said it would be at least 10.2:1 so that's what I'm running. I'm hoping when it comes back that it'll be a bit higher than that as I wanted 10.5:1. Engine was bored .040 over too.

0 degrees cam advance


4 degrees cam advance

Did you change the valves? Cause the info I got for the 5.3 is: 1.89" INT 1.55" EXH

DANG IT!!! No, they are stock valves. Reran though, and the difference is minimal. Not seeing more than a difference of 1HP or 1TQ with the valve size changed. On some RPMs it's +1, on others it's -1, and on still others it's 0, so it doesn't make much difference. Thanks though, I've corrected it on mine.

Speeder wrote:

Instead I'm going to address the low end by getting with the torque converter maker to see if they can redo my converter for a bit more stall speed. The truck also needs new tires, so I'm going to go with a slightly shorter tire to effectively increase the differential ratio. I'm hoping that this will give me a boost in mileage by getting me a little higher in the powerband. At cruise it feels like I'm too far down the band. These small changes should get me out of the hole a lot faster plus set my cruise RPM high enough to get me out of the bog range and improve mileage. If I knew when I was doing my diff gears what I know now I'd have either stayed with 3.73s or switched to 4.10s.

Can't wait to get all this together so I can use the wideband on it.

What's your current stall speed?

What's your lower average cruise speed?


I'll post my custom cam numbers tonight.
With my modified XR259 and my 4.8 configuration, I get a torque boost around 30tq-lbs @ 2000 rpm. and not much lossed @ 5500rpm

Current stall speed is factory, thinking of changing it. Stall won't matter for cruise on a locking converter.

Right now I'm cruising somewhere around 2000RPM at 75-80MPH, and something like 1700@65. Not really sure. It's one of those things you only pay attention to when there's a problem.

So, this is what I started with:



This is what it looks like with a short duration intake lobe:
-Increased +32tq @ 2000rpm -20tq@5500
-Max torque same but @ 3500 instead of 4500rpm.
-9* less overlap
It be nice to have a turbo to pick up the torque above 3500rpm for acceleration without sacrificing fuel economy during normal driving.





Last edited by CrazyHoe on Thu Mar 15, 2012 10:28 pm; edited 3 times in total

Hmm, second photo's missing.

Doing a head to head comparison, there is no cam equal to the 259 that I've been able to find if DD2000 is any judge. Wouldn't mind seeing the cam you came up with.

Keep in mind I'm just having fun with numbers here. I just found it interesting how the torque shifts with the intake duration...

10% more torque @ 2k that's like going from a 350 to a 383...

It would feel more responsive when cruising with the converter locked up.



Last edited by CrazyHoe on Fri Mar 16, 2012 1:49 pm; edited 1 time in total

Interesting read on fuel efficiency

http://www.rs25.com/forums/f4/t156942-mpgs-efficiency-torque-curves-shifting.html

Speeder wrote:

My new thinking now is to get to 100+MPH as quickly as possible, then coast in neutral. If I can get to speed faster it'll use less fuel, right?

Turns out that pulsing the gas peddle, full throttle then coasting (without unlocking the verter and engaging the "accelerator pump") while keeping the desired speed is the most fuel efficient way to drive.

The ideal gas engine would not have a throttle (which causes vacuum and pumping losses) but would have it's power output solely control by valve timing.

I am shocked to see such good numbers on the 4.8L. Makes my L31 look sick. What kind of mileage are you trying to acheive? Are you trying to see which is more efficent to acheiving your gas milage goals, a high compression ratio verses a lower compression. Once you have your engine running the way you want it, what kind of transmission are you using? Tire size and gear ratio. Are you using electric fans. I will sit back and see what you come up with. This is interesting.

Chevy 97 wrote:

I am shocked to see such good numbers on the 4.8L. ....

Those are just a reference, in a perfect puter world...

I suspect Jim has chosen higher flowing head numbers...

Heh heh, actually I chose the only heads I knew were LS-based that was listed in DD2000. They should be close enough to what I have anyway, and the difference in cams vs heads won't be enough to matter.

Chevy97, higher compression, all else being equal, makes more HP, more torque and when driven conservatively will get better mileage. So far as the rest of the truck, I'm running a 2000 Silverado reg cab Autotrac 4x4 with a 4L80E transmission with a TCI low gear set making 1st 2.75 and 2nd 1.57. A 4L60E would get a little better output since it has lighter parts and takes less driveline power, but I don't like installing new transmissions every 6 months. I also have 3.42 rear gears and 31.7 inch tires. The exhaust is Pacesetter longtubes through a Magnafow performance cat, and Dynomax Super Turbo. Tubing is dual 3 inch into a combiner, single 3 inch to the muffler, then dual 2.5 over the axle and out the back.

So far I was getting 15MPG out of the truck, with the mechanical fan. I never was able to tune properly since the engine was blowing so much oil out that I didn't want to risk the wideband O2 being damaged. When I get the engine back, hopefully it won't be leaking and I can tune. I will be installing a smaller diameter tire to improve the ratio. When my rear gears popped a couple of years ago I went from 3.73 to 3.42 for mileage, but between the gears and the tire diameter I put the engine too far down the powerband. Knowing what I do now, I'd have either stayed with 3.73s or gone to 4.10s for mileage to keep the engine in its ideal powerband for mileage. Having the RPMs too far down is just as bad as having the RPMs too high. So far as my mileage goal I was shooting for 25MPG. I have a set of electric fans and a radiator for a 2006 Silverado GMT800, and the test fit was perfect. I probably won't hit 25MPG, but between the fans, an actual tune and the shorter tires I'm hoping to at least break 20MPG. My mother's truck is my inspiration, she has a 2007 2WD ext cab with a 4.8L.

Just talked to my dad, he said the engine is ready. Apparently two problems were found. One was a long bolt installed in the side of the block that didn't belong. Nobody will own up to it. No idea, but the bolt has been corrected. Second problem, there was a piece of metal jammed in one of the valves between the valve and the seat, so the guy did a full valve job on both heads. No idea how this might have happened either. He is also supposed to have done a pressure check, so now everything is good. I'll be picking the engine up next week sometime. All the pistons and rings were good, no ring lineups or anything. I really hope this gets it. Anyhoo, won't know anything for a while as I'm sending the trans back to FLT to find out why it never has shifted correctly on the 2-3.

I have the stock size tires, 245-75R16. 3.73 gears, 4L60E, L31 with a power tower and a K&N filter, Factory exhaust. I get 15 to 16 empty. I haven't checked mileage with the camper. I never use overdrive with the 4L60E with the camper on. I am around 3000 rpm. This is one reason I want a 4L80E, I want a FF rearend but drop the gearing to 4.10. That will raise the RPM's when in overdrive. The engine should be in a better range for driving down the Highway. I still want a big block, but I want to shoot for the milage I am getting now. Last night I was looking through the GM parts catolog, I found the crank I want. This way instead of a 454, I will have a 427. That is big enough for me. If I had a newer truck that is a 3/4 T, I would want either the LSX454 or the 427 anyway. My truck isn't my DD, But I still want it to perform the best and keep the mileage up. I will have electric fans on. I have them here. I have a few things to do before getting them on. My dad with his duramax gets 20mpg. My brother in laws is about the same. I want to stay with gas. Speeder, I hope they find the shifting problem with your transmission. It is interesting to hear what is wrong.

Something to keep in mind on the 4L80E is that the OD is not as deep as on the 4L60E so just switching transmissions will up your highway RPMs. And, as stock the 4L80E will feel more like a 4L60E taking off in second. Factory first on a 4L80E is 2.48 where the 4L60E is 3.01, so the 4L60E pulls harder in first. This was why I went with the low gear set with mine, wanted to try and keep some takeoff power.

On the big block, it's going to be just about as hard to convert from a small block to a big block as it would be to convert from a small block to a large cube LSx. Physically it's just a matter of getting some engine mount adapters and sticking it in, the hard part is the wiring but even that shouldn't be that big a deal. And, a big block will add a couple hundred extra pounds to the nose over an LSx conversion that you'll have to pay to carry around. Something to think about.