Weird MPG Question

[HOrnbrod]

I asked Lee (Hesco's owner) about the multi-port injectors awhile back and he said they were a waste of money. He claimed there was absolutely no benefit to be gained from them. He's built thousands of performance Jeep engines and prefers the Mopar 53030778 gray tops for the 4.5-4.7 strokers. I do have a new set of the Bosch 703 "Neon" injectors however, and if and when the Mopars go bad I'll throw them in. I know a manual would definitely help out with the powertrain efficiency, but doubt if I'll ever get rid of the AW4.

[Eagle]

Don, you had your stroker dynoed, didn't you? Do you have a torque curve for it? Is it possible that you might do better around town if you put the shifter in "3" to lock out overdrive? If that would put your RPMs closer to the torque peak, it might make a difference.

[HOrnbrod]

Ya, the torque peak is up around 3K RPM. I'll give that a shot, thanks.

[Tex06]

 

 

 

Maybe I'll slap on a stock throttle body that necks down to 56mm and try that. I can also play around with the fuel pressure settings since I have an adjustable regulator and an A/F meter. Ideally I'd like to bring up the in-town MPG w/o affecting the highway MPG. I think I'll start by lowering the fuel pressure a few psi and monitor the A/F. Right now I run at 49/39 psi using the 97 injectors.

 

If you can, track all the mods in excel or something. I'm curious as to what, if any, effect they will have.

 

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[johnj92131]

Don has posted this info before. Think he has run before and after Dyno runs for each/most of his mods. Good, solid info on the same Dyno for years.

[omega_rugal]

running at peak torque doesn not directly translate into better MPGs, quicker acceleration and response but guess what it takes? gasoline...

[HOrnbrod]

17 minutes ago, johnj92131 said:

Don has posted this info before. Think he has run before and after Dyno runs for each/most of his mods. Good, solid info on the same Dyno for years.

 

Thanks John - this is true. I think four runs overall. What's the point of doing a so-called "upgrade" if it doesn't help or even makes things worse? Unfortunately the last dyno run was about ten years ago. The goal after the stroker install was to make up for the ~30% power loss between the stroker engine test stand numbers and the original rear wheel dyno tests. This 30% drivetrain loss was mainly caused by the inefficient AW4. Once that 30% and then some was overcome I didn't do any more runs.

[Tex06]

Don has posted this info before. Think he has run before and after Dyno runs for each/most of his mods. Good, solid info on the same Dyno for years.

I meant for mpg differences. I know he's been pretty good at calculating hp/tq numbers overt the years

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[Eagle]

16 minutes ago, omega_rugal said:

running at peak torque doesn not directly translate into better MPGs, quicker acceleration and response but guess what it takes? gasoline...

 

All things being equal (which they never are), the torque peak is the engine speed at which the engine is operating most efficiently. In a motor vehicle, other factors mess that up, such as mechanical drag and aerodynamic drag, both of which increase exponentially with speed. Nonetheless, it's worth a try. I know that here in Connecticut for many years the maximum speed limit on any highway was 55 MPH. (They've now gone back to 65 for a couple of Interstates.) My '88 Cherokee 4.0L 5-speed (stock tires and gears) only turns about 1540 RPM at 55 MPH. That's far below the torque peak, even for a Renix-era engine. The torque peak for the '88 is at 2400 RPM. I found by actual testing that my highway gas mileage was the same in fourth gear as it was in fifth. In fourth, 55 MPH is 2054 RPM. That's still below the torque peak, but at least it's getting closer.

 

There wasn't enough difference to make me always run in fourth. I used fifth because it was there, and because it might result in less wear on the engine. But fifth was so far under the torque peak that, at 55 and even 60 MPH, most long upgrades required a downshift to fourth.

 

So I think it's worthwhile for Don to at least try it.

[Eagle]

51 minutes ago, johnj92131 said:

Don has posted this info before. Think he has run before and after Dyno runs for each/most of his mods. Good, solid info on the same Dyno for years.

 

I know he has the numbers, but I don't have them. I don't really care what the actual numbers are. The point is that his around-town gas mileage sucks. If it turns out that he's operating well below whatever his torque peak RPM is, it's very possible that his fuel economy might increase if he stays in a lower gear, to keep the engine running closer to the torque peak RPM. The AW4 likes to shift into 4th gear (overdrive) at a much lower speed than where I would choose to shift a manual transmission into overdrive, so it's worth a try.

 

Don said he's running 31" tires and 4.10 gears. By my chart, at 40 MPH in overdrive the engine would only be turning 1394 RPM. And I think the AW4 will go into 4th at 40 MPH. At 45 MPH, it would be turning 1568 RPM. Still WAAAY below the torque peak, and probably not even sneaking into the "fat" part of the torque curve.

 

Keep it in third gear (direct, 1:1 ratio) and the RPMs become 1859 at 40 MPH and 2091 at 45 MPH. I would think that's getting into a more useful region of the torque curve.

[HOrnbrod]

22 minutes ago, Eagle said:

Keep it in third gear (direct, 1:1 ratio) and the RPMs become 1859 at 40 MPH and 2091 at 45 MPH. I would think that's getting into a more useful region of the torque curve.

 

Will do, starting today for at least until the next fill-up.

[gogmorgo]

The thing about your peak torque is that your dyno runs are at wide-open throttle and 100% engine load. What happens at low load and part throttle isn't necessarily going to be reflected in your power runs.

The other thing is you need a specific amount of power to keep you moving at a certain speed, no matter which gear you're in, and you need to burn a specific amount of fuel to maintain that power level which will consume a specific volume of air, even if the air is moving more quickly through the engine. Yes there may be more efficient extraction of power from the fuel at certain speeds, but it's not going to be a huge difference, and the extra power needed to keep everything spinning faster is likely just going to negate that.

 

So pretty much colour me pessimistic that it'll have any effect at all, but it's worth a shot and I am curious, and I trust Hornbrod will be as scientific as possible about recording the effects. 

 

I'll add that in the brief amount of time spent driving my Lada with fifth gear (until it quit staying in gear) it did tend to get slightly better mpg than it did in fourth, although the difference was negligeable compared to the difference between two different drivers with different driving styles after fifth became useless again. But this doesn't really have much bearing either, because the Niva is an entirely different animal.

[HOrnbrod]

Well, just got back from spending about 1-1/2 hr. running around town: beer, dog food, lawn mower gas, paid a couple of bills, etc. in that priority. Kept it in 3rd, 50MPH @ ~2500RPM max. Felt strange driving that slow w/o O/D. We'll continue and see what happens. One-half tank approx. to go, then we'll do it again on a full tank.

[Eagle]

I was thinking of "around town" as being generally 45 and under -- mostly under.

 

Going back to the root of these engines, my family was a Hudson ==> AMC family. Between my parents, my brother, and myself we've owned a number of the old AMC versions of this engine, ranging from 199 c.i.d. to 232 c.i.d. to 258 c.i.d. Also owned any number of Javelins and AMXs with V8s. All were standard transmissions, from before the days of overdrive (except as an expensive option, which we never opted for). Regardless of gearing and tire size combination, the end result was always 24 MPH per 1,000 RPM in top gear -- so 60 MPH was exactly 2500 RPM, and 3,000 RPM gave a nice, slightly extra-legal 72 MPH cruise.

 

I know for those accustomed to newer vehicles with 5- and 6-speed transmissions the idea of running around at 2500 RPM seems like "burning up the engine," but it isn't.

 

Don, with your tire and gear combination 50 MPH in 3rd gear should be 2323 RPM. Overdrive at 50 should be 1743. I'd probably let it go into overdrive at 50, but I'd certainly try keeping to 3rd below 50 just to see what happens.

[omega_rugal]

for an inline 6 or a crossplane V8, running at 2500-3000 is not stressful, in a way is a good rpm range to be in, with air, oil and coolant flowing at a good rate...

 

in a inline 4 or a V6 running at those revs or more means the internal components literally fight to stay together due the imbalanced designs, OD helps in this case

[gogmorgo]

Meh. The Niva runs 4500rpm at 60mph and doesn't seem any the worse for it. If the manufacturer didn't want it revving the high they would've out the redline lower. The Lada lump hits fuel

cutoff at 6500rpm but will rev far beyond that if you surprise it. 

[HOrnbrod]

What's the Lada engine, about 1.5L 4-banger or so? A little short-stroke engine like that should rev to 9-10K before it blows up. By design. Comparing that engine to a Jeep I6 is apples and oranges.

 

One of the reasons I quit having dynos done for every upgrade is because I couldn't stand it when the revs were high. You ever heard a Jeep stroker screaming at 5-6K RPM? It's not pleasant when it's your's and you're not used to it.      The AMC 6-bangers were never built for high RPM, they were built originally for low RPM torque, like a tractor engine.  Lee at Hesco used to get a laugh when I was cringing at these RPMs. He told me that every stroker coming out of their shop was dyno tested up to 7K RPM. That's one of the reasons why their engines have the best rep in the business.

[Eagle]

7,000 RPM? I thought in-line sixes had a destructive harmonic at 6,000 or 6,500 RPM.

 

There was never any reason to push an AMC (or Jeep) I-6 even to 5,000 RPM. They're long stroke engines, designed and built for torque, not high-RPM horsepower. Long stroke engines don't particularly like to rev. Among all the Cherokees and Comanches I've owned through the years, completely ignoring the AMC cars, I've easily put over a half million miles on the 4.0L engine -- probably closer to a million. I don't think I've ever taken one above 3,500 RPM, and I rarely go over 2,500. My usual shift point with the 5-speeds is between 2,000 and 2,200 RPM.

[HOrnbrod]

30 minutes ago, Eagle said:

7,000 RPM? I thought in-line sixes had a destructive harmonic at 6,000 or 6,500 RPM.

 

All your comments pertain to stock engines. Of course they are long stroke tractor torque engines. Didn't I say that? 6200-rpm redline is the high standard for production line stock crank engines.  That spec doesn't pertain to most built strokers. A 12 counterweight balanced crank can easily do 7K or more, and that's what reputable Jeep I6 engine builders test them at. Even Hesco's 6 counterweight balanced cranks like mine are tested briefly up to 7K. That's why they cost so damn much.

[gogmorgo]

The Lada 1.7 is a slightly oversquare (short-stroke) engine, and was developed by boring out the slightly undersquare 1.6L which is pretty much a 60's era OHC 4-banger, from 3.11 to 3.23" (3.15" stroke). So yeah, completely different animal. 9k is probably asking a bit much from it but it will hit 8000rpm before the computer figures things out if you stomp on it in low-range 1st gear.

 

That said, I have no qualms hitting 4500+ rpm with a 4.0. Would I do it all day every day? Nah, what's the point? But with bigger, better quality bearings in it and a timing chain that doesn't require manual re-tensioning every oil change, I see no reason it won't survive. They're pretty popular in LeMons racing because of their power and reliability (and ease of finding cheap replacements), which says a fair bit about the engine. Racing reliable is not the same as street reliable. 

Now I have actually killed a 4.0, but that was a 300,000 mile engine with a history of low oil pressure that spent a good half-hour at WOT on the highway. It still ran and drove (and did another forty miles at 80mph to make it to where I was going), just sounded like someone trying to break into a submarine with a jackhammer. Arguably that's a case for just-because-you-can-doesn't-mean-you-should, but I pretty frequently hit 4000+ rpm merging onto the highway because when you're turning left from a stop sign across the two-lane highway that is the second-busiest pass through the Canadian Rockies, you don't just poke along when you find an opening. Doesn't bother me none.