Vortec torque curves?

[supton]

I've looked, and can't find any. As in, what the supposedly flat curve actually looks like (you know, a plot). I doubt I'll spring for one, but since camping season is here I'm toying with getting a Silverado and a medium sized hard-sided camper. Lately, when toying with a vehicle purchase, I try to look at the gear ratios; and I'm not entirely sure why 3.42 rear gears would be available on a Silverado 1500 with a towing package--with the 4.8L V8. Seems like the rev's would be too low, even while towing in 3rd gear. 2200 rpm at 60mph in 3rd, seems like a good sized hill would drop to 2nd.

I know the Vortec's are the bee's knee's and all; but I haven't seen a curve yet that shows that.

 

[JHZR2]

It would depend upon the mass being towed, right?

 

[hounddog]

By a Dodge hemi and 3.92 gears. The Express package is THOUSANDS under a Chevy. The SLT packages are still thousands below Chevy. Plus they are a towing,running mpg son of a gun. 4.8 with TOW package. LOL. I shopped Chey and Ford for three months and went with the best bang for the buck.

 

[apwillard1986]

Here is the curve for the 4.8:

[img:center]

Shot at 2012-05-22[/img]

 

[46Harry]

I would recommend a 3.73 gear ratio with the 4.8 engine. I had a 2005 Silverado with the 4.8 engine and a 3.73 gear which I thought was a good combination. The 3.73 differential is a 100 buck option though. I have a 2010 Silverado with the 5.3 engine, 6 speed transmission and a 3.42 posi differential which is much better for towing.

 

[apwillard1986]

Here is the Curve for the 5.3. It can be had as part of the All Star package which is a pretty good deal. Lots of upgrades (alloys, auto climate, power drivers seat, towing, 5.3, etc...) for just a bit more than a base LT with the 4.8.

[img:center]

[/img]

 

[Hokiefyd]

I like that GM is programming these engines to be able to take advantage of the higher octane of E85.

We have a short bed, short cab, 4x4 Silverado at work, with the 5.3L. It has power everywhere, but really screams as you get above 3500 rpm or so. It reminds me of the way the V-6 in our MDX pushes you back in the seat more as the engine speed rises. I think the Vortec V-8 engines are the best low-cost V-8s around.

 

[ARCOgraphite]

I'll take a 5.3 in a light, cheap 3rd gen camaro with a 5 speed. + headers and borla exhaust.

Thank You.

 

[A_Harman]

Originally Posted By: apwillard1986
Here is the curve for the 4.8:

[img:center]

Shot at 2012-05-22[/img]


Nice image of the torque curve!
Where did you find that? Can you post a link?

 

[apwillard1986]

Chevrolet previously posted them on the consumer website but they don't any longer... at least, not that I can find. I got them from our GM Dealer Reference site... you have to have a login so a link would be useless. Wish I could help. I also wish this type of info was still available to consumers easily.

It is funny; sometimes the consumer site has more info than the dealer site and sometimes it is reversed.

 

[supton]

Great, got to work, and can't see the pics.

But I'll look later. Thanks!

Yeah, I'm on the fence as to what I want to do; am thinking over a bunch of options. I spoke briefly with my mechanic this morning, and he said the 90's were not a good year for rust on the GM's. I don't think anyone was doing good back then--and I'm not sure going into the 2000's either. Heck, I'm not so sure how they are doing today! So I'm leaning more towards new (the LS motors from what I understand are pretty good), and since Memorial Day is coming up, perhaps new is best. Better deals on the 4.8's, ergo, the question.

Without a doubt the 5.3 is a better motor. And since I'd be wanting to use this for towing, and not commuting, it'd make more sense. BUT money is always a consideration. Plus, I'm not sure why I'd need to pull at speed. But deeper gears would definately be what I'd want, assuming I could get them.

[I think the main allure of the 4.8 is mostly to make the 5.3 look all the better, and to make CAFE requirements. Sell lots of 4.8's to keep CAFE happy; but gear them such that no one would want to tow with them, so you can upsell them on the tow motor. Something like that. Spoke with my father recently, and he towed a 23' camper--with an '87 Astro! Something like 8k total weight, he thinks. It did the job, just not fast. Well, 'till the motor started drinking the oil after 100k... Similar setup, albeit shorter tires--3.42's, 700R4.]

I still have to dig through how to figure out tow ratings, it changes depending upon rear gear and motor as you'd expect. A quick look didn't seem to indicate what I wanted on the corporate site.

 

[Brons2]

I drove a 4.8 once, wasn't really that impressed with the power.

 

[440Magnum]

Originally Posted By: Hokiefyd
I like that GM is programming these engines to be able to take advantage of the higher octane of E85.


All the Flex Fuel engine manufacturers do, whether they publish it or not. My 08 Ram (4.7) flex-fuel pulls significantly harder on E85 than gasoline. The low end of the RPM range especially benefits since the 4.7 has such a small displacement to work with. The fuel cost is a break-even. E-85 is consistently $.20/gal cheaper, but its almost exactly offset by higher consumption. I'd use it much more, but I also have to go out of my way to buy it.

All that said, and despite the fact that the 4.7 is a superb engine, my truck is ONLY a 4.7 instead of a Hemi because the dealer couldn't move it off the lot without knocking almost $15k off the price back the fall of 08. In the same way, I'd strongly reccomend the GM 5.3 over their 4.8, and for all the same reasons- anything less than ~5-5.25L in a truck is just asking a bit much of it. Yes, I've towed ~4k pounds with mine, but it had to work a lot more than I would want it to on a day-in day-out basis. Plus, the smaller engines rarely get better mpg than the next size larger, although with conservative highway cruising they CAN do better. I usually get 19-21 highway MPG (gasoline/E10, not E85) in the Ram 4.7 running on flat I-10 at 70. Best of 22.5 average from Austin TX to Gulfport MS, worst average of 18.8 into a headwind, New Orleans to Katy.

 

[supton]

I thought on the E85 stuff they could just use some really low octane gas, and mix it with the high octane ethanol, and make it, well, 87 octane. Perhaps by not having to mix in anything to make the base gasoline stock they gain some BTU's (I looked at this briefly a week or so ago, and it seemed all octane boosters--MTBE, TAME, ethanol--had less BUT's per gallon than straight gasoline). Beats me. Oh wait: IIRC they do play with timing/injected amount when they detect high levels of ethanol. I don't want to say they are allowed to emit emissions at a different rate--but perhaps they can "get away with something".

 

[OVERKILL]

Originally Posted By: supton
I thought on the E85 stuff they could just use some really low octane gas, and mix it with the high octane ethanol, and make it, well, 87 octane. Perhaps by not having to mix in anything to make the base gasoline stock they gain some BTU's (I looked at this briefly a week or so ago, and it seemed all octane boosters--MTBE, TAME, ethanol--had less BUT's per gallon than straight gasoline). Beats me. Oh wait: IIRC they do play with timing/injected amount when they detect high levels of ethanol. I don't want to say they are allowed to emit emissions at a different rate--but perhaps they can "get away with something".


E85 is in the mid 90's for octane.

 

[Hokiefyd]

Originally Posted By: ARCOgraphite
I'll take a 5.3 in a light, cheap 3rd gen camaro with a 5 speed. + headers and borla exhaust.


That would be right fun. That engine would get real lively in a light car like that.

 

[supton]

Oh really? I thought (assumed) it'd be 87 octane. I don't think I've ever seen a pump for E85.

If that's the case, well, since variable valve timing is all the rage (as it ought to be) then it's easy to play with compression ratio on the fly. By playing with when the intake valve closes you can bleed off some compression (Atkinson cycle) and tolerate lower octane gasoline. Or close it earlier, and reap the benefits of higher octane.

 

[ARCOgraphite]

4.8 is about as big as you want an engine (cyl bore) to be. In fact its too big. Thats two 2.4L 4 cyls under the hood. If thats not big enough for general purpose use, then the engine is tuned wrong. This aint the 60's. This 4.8 would walk all over an old 70s 350 v8 I would imagine.

 

[dave1251]

How much does the camper weight? If people could tow safely with a pickup 30 years ago with 165HP, 235LB of torque, with a 3 speed transmission, and 3.42 and 3.08 gears. Your 4.8 Silverado with 302 HP and 305LB of torque with 3.42 gears and 4 speed transmission you are looking for will tow a reasonably sized trailer fine, it will just lag behind performance wise behind other modern pickups. My advice is just to drive a couple of different pickups regardless of brand in your price range and just pick the one you like best and which one will best suit your needs.

 

[ARCOgraphite]

Originally Posted By: supton
Oh really? I thought (assumed) it'd be 87 octane. I don't think I've ever seen a pump for E85.

If that's the case, well, since variable valve timing is all the rage (as it ought to be) then it's easy to play with compression ratio on the fly. By playing with when the intake valve closes you can bleed off some compression (Atkinson cycle) and tolerate lower octane gasoline. Or close it earlier, and reap the benefits of higher octane.
i dont think the vvt is "smart" other than at idle or wot - i would guess its phasing with op and rpm.