lowest reasonable highway rpm for a 440?
#1058351
08/21/11 11:01 AM
08/21/11 11:01 AM
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Joined: Jan 2003
Posts: 28,096 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
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Irving, TX
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I was just running the numbers for the OD swap in the Imperial. I will be using Edelbrock heads on a stock-ish cam 440 and shoving around a 5300 lb Imperial. It wears 3.23 gears out back. Without OD I'm looking at 2500 rpm for 65 mph and 2900 rpm for 75 mph. With OD I'm looking at 1700 rpm for 65 mph and 2000 rpm for 75 mph. 1700 rpm seems pretty low for a 440 to lug around that much weight. Is that too low for an efficient cruise? Stepping up to 3.55 gears would increase rpm by 250 or so. Please stay away from the "engine should run at peak torque rpm blah blah blah" uneducated BS. We all know that's not true in the real world. If it were true, our cars would get amazing mileage at 4000 rpm. On the up side of things, with the 3.23 and 518 if I could hit 6000 rpm the car would be cruising at 228 mph. Do you think John Force has a spare engine I could borrow?
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058352
08/21/11 11:28 AM
08/21/11 11:28 AM
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Joined: Jul 2008
Posts: 30,632 Florida STAYcation
IcorkSOAK
Financed his waterbed
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Financed his waterbed
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Posts: 30,632
Florida STAYcation
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Eddy heads on a pIMP-mobile ? ... ...are you looking at competeing with that Cleveland IMP ...or is this going to be a cruiser that gets super MPG ? In a non-towing combo ...I would look at a 516 head. And KEEP the 1.60 valve. And toss-in a 2.76 gear.
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058356
08/21/11 01:48 PM
08/21/11 01:48 PM
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Joined: Jan 2003
Posts: 21,122 Niles , Ohio
therocks
oh wait.but hey.lets see.oh yeah.
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oh wait.but hey.lets see.oh yeah.
Joined: Jan 2003
Posts: 21,122
Niles , Ohio
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My Imps had 2.70 gears.They all cruised allday.Never did get the RPMs but it was low.Rocky
Chrysler Firepower
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058357
08/21/11 02:27 PM
08/21/11 02:27 PM
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Joined: Jan 2006
Posts: 8,162 USA
360view
Moparts resident spammer
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Moparts resident spammer
Joined: Jan 2006
Posts: 8,162
USA
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Prior to adding the OD you could try a few 'real world' experiments by adding a vacuum gauge connected to the intake manifold then driving in top gear at 1700 rpm at whatever mph the current ratios give, up a progression of ever steeper hills, to increase load on the engine. When the vacuum drops below the 6 to 8 inches of Mercury level, you are getting out of the operating region of good fuel economy. You can estimate your horsepower load at different speeds and grades of hills using the stuff found in this article; http://web.archive.org/web/20061123075351/http://www.etrucker.com/content/downloads/ccj0302.pdfnotice it is in pdf format Although the article is focusing on big trucks, the same applies to cars climbing hills This admittedly old (1960s) but 'universal' BSFC graph from the Taylors at MIT for engines shows the 'island' of good fuel economy: Notice the bottom line of the graph is not rpm but 'average piston speed' in feet per minute which you get by converting your stroke from inches to feet, doubling it since it goes up and then down once per each revolution of the engine shaft, then multiplying by rpm
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Re: lowest reasonable highway rpm for a 440?
[Re: 360view]
#1058358
08/21/11 03:35 PM
08/21/11 03:35 PM
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Joined: Aug 2006
Posts: 247 DuPont, Washington
DZJim
enthusiast
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enthusiast
Joined: Aug 2006
Posts: 247
DuPont, Washington
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Quote:
Prior to adding the OD you could try a few 'real world' experiments by adding a vacuum gauge connected to the intake manifold then driving in top gear at 1700 rpm at whatever mph the current ratios give, up a progression of ever steeper hills, to increase load on the engine.
When the vacuum drops below the 6 to 8 inches of Mercury level, you are getting out of the operating region of good fuel economy.
You can estimate your horsepower load at different speeds and grades of hills using the stuff found in this article;
http://web.archive.org/web/20061123075351/http://www.etrucker.com/content/downloads/ccj0302.pdf
notice it is in pdf format
Although the article is focusing on big trucks, the same applies to cars climbing hills
This admittedly old (1960s) but 'universal' BSFC graph from the Taylors at MIT for engines shows the 'island' of good fuel economy:
Notice the bottom line of the graph is not rpm but 'average piston speed' in feet per minute which you get by converting your stroke from inches to feet, doubling it since it goes up and then down once per each revolution of the engine shaft, then multiplying by rpm
I didn't crunch through the above, but looks like good info.
Depends...
Cam, carb, manifold, heads? Grade; uphill even a tiny bit makes big difference. Wind, a little headwind makes a difference. Aerodynamic drag is proportional to the speed squared. 55 mph with 15 mph headwind is 70 mph for drag purposes. Big difference in drag. Tire type and pressure. Steel on steel is good e.g. railways. Obviously can't do that with your car, but you get the idea. Wheel alignment. Fluid viscosities in trans and axle, synthetics?.
I got a 250cc on/off road bike w/6spd trans. Torque below 4,000 rpm is negligible. It'll cruise along just fine at 55 mph in 6th until I hit a little uphill; have to downshift right away.
Almost same with my Corolla 5spd. BB MOPAR torque is a different story.
My $0.02
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Re: lowest reasonable highway rpm for a 440?
[Re: MoparMarq]
#1058360
08/21/11 04:34 PM
08/21/11 04:34 PM
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Joined: Jul 2008
Posts: 30,632 Florida STAYcation
IcorkSOAK
Financed his waterbed
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Financed his waterbed
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Florida STAYcation
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Quote:
Didn't some of the later '70s and '80s B/F/M/J bodies have 2.45 gears and 318s? I may be out in left field here, but seems like with a big block it would be a non-issue.
You beeez in the RIGHT FIELD ...IMO. A 440 with a torque cam and a MPG intake and carb ....1700 should not be a problem. 'Specially on the Texas highways.
I have got a torque-monster in-the-works for my motorhome. I am shooting for 2600 rpm or so running 60 mph ... but I will NOT have the aero of the IMP ...and will have a GVW weight of nearly 16,000 at times.
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058362
08/21/11 04:59 PM
08/21/11 04:59 PM
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Joined: Jan 2003
Posts: 3,719 Space Station #5
471Magnum
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master
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Space Station #5
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Depends on your carburetor somewhat. You'll run rich and your gas mileage will suck if you don't get out of the idle circuit. Really need to be above 2000 rpm for best mileage.
Had a .64 OD and 3.55 gears on my Charger way back when. I was lugging along below 65 mph getting 12 mph. Wind it out to 75 and I'd get 16 mpg. Eventually I put in a set of 4.10's.
-Jim
I can fix it... my old man is a television repairman. He's got the ultimate set of tools... I can fix it.
Currently Mopar-less
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Re: lowest reasonable highway rpm for a 440?
[Re: 471Magnum]
#1058363
08/21/11 05:59 PM
08/21/11 05:59 PM
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Joined: Jan 2005
Posts: 12,478 Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
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Kalispell Mt.
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Bigger valves installed properly (deshrouded and good valve job)improves flow even through the same size port, in order for more air to flow through the same port it HAS to have MORE velocity, therefore a bigger valve will have more velocity in the port not less. Any one who beleives otherwise is it is very elementary physics not rocket science. Velocity at the valve will probably decrease but total flow will go up and that means you can make the same power with a smaller cam and a smaller cam will help MPG. As for gearing, lug the snot out of it. My 5.9 in my 3/4 ton ram turns 1500 at 60 and gets much better MPG in OD than 3rd. You car is slightly more aero dynamic and probably lighter than a jacked up extended cab 4x4 3/4 ton and your engine is definately more powerfull even at those low RPM. You definately do NOT need to be above 2000 for best MPG, mabey best passing power but it is bad for MPG.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: lowest reasonable highway rpm for a 440?
[Re: HotRodDave]
#1058364
08/21/11 06:50 PM
08/21/11 06:50 PM
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Joined: Oct 2007
Posts: 3,933 Oregon
hooziewhatsit
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360View, I crunched some numbers real quick... Assuming a 4" stroker ( ), at 1700 rpms the piston speed is 1133 ft/sec, right in the sweet spot of that graph. Assuming a BMEP of 100 psi, we can figure the needed torque to be roughly 275 ft-lbs, at that 1700 RPMs. bmep link So, does it make sense that if we build an engine with that amount of torque at that rpm, adjust the rest of the gearing as needed to get a good highway speed at that rpm, that we should get the optimal mileage out of it? Of course, depending on the air & rolling resistance, I guess we may still need more power to move along though... Or am I way off
If you ever find yourself in a fair fight, your tactics suck.
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058366
08/21/11 07:58 PM
08/21/11 07:58 PM
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Joined: Dec 2005
Posts: 1,168 Cruising!
QuickDodge
super stock
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super stock
Joined: Dec 2005
Posts: 1,168
Cruising!
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Some of the Buick Roadmaster's had 2.56 rear axles with an overdrive transmission. (There transmission's overdrive ratio is nearly identical to the 518's ratio) These cars had 350 engines and weighed about 4200 lbs. I think this gearing put them at around 1300 rpm at 60 mph. I know a guy who is a Roadmaster fanatic. He thinks the 2.56 was a little to much gear. He likes the 2.72(?) or 2.94(?)axle ratio's better. It is very true that gearing the car so it will obtain best fuel economy WILL make the transmission shift in and out of overdrive more frequently. (particularly in the 40-60 mph range) When I'm driving a vehicle with real stiff gears, I manually shift the transmission into third gear until I'm on the highway, then shift into overdrive. If an automatic transmission is making the engine lug, the shift points on the transmission should probably be adjusted. (or manually downshift it) If you want to run real stiff gears a lock up torque converter will be necessary. Otherwise, the torque converter will slip more at low rpms. I believe some higher stall, lock up converters are available. These should help with both performace and economy. Getting the idle mixture set lean will be critcal to achieving good fuel economy at real low rpms. The following article on how to tune a carb for economy is worth a read, even though the carb is on a chevy the same priciples would apply on a Mopar. http://www.chevyhiperformance.com/tech/e...eage/index.htmlPersonally, I'd try a 2.76 to 3.23 ratio depending what I had on hand at the time. I'd guess a 2.92 with a higher stall, lock up converter would be best, but that's a guess, since I've never built anything like an Imperial. A 3.23 would certainly help performance, but would probably hurt highway fuel economy just a bit. It might help around town mileage though? I'm quite interested in building a C-body as a cruiser / summertime driver. When you get this done, I'd be very interested in the results you achieve.
Last edited by QuickDodge; 08/21/11 08:05 PM.
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Re: lowest reasonable highway rpm for a 440?
[Re: 471Magnum]
#1058367
08/21/11 08:25 PM
08/21/11 08:25 PM
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Joined: Jul 2008
Posts: 30,632 Florida STAYcation
IcorkSOAK
Financed his waterbed
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Financed his waterbed
Joined: Jul 2008
Posts: 30,632
Florida STAYcation
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Quote:
Depends on your carburetor somewhat. You'll run rich and your gas mileage will suck if you don't get out of the idle circuit. Really need to be above 2000 rpm for best mileage.
DEPENDS on what carb you are running ... a small primary venturi with Xcellent fuel mixing is the ticket. And GUESS WHAT carb that is ?
I read some really detailed cyl-head-chat about power and MPG. I think it was a related hi-tech article when I was searching for a lab in the Chicago area that did work on the topic of Tribology ... (the study of friction in a internal combustion engine!)
It said that in the IDEAL WORLD ... you would want to reduce and expand intake valve and port size based on the rpm range of the engine.
Since this is not possible on any of our-junk ... I am going to reduce intake port size by at least 30% ... in combination with directing the air-fuel mixture to one-side of the port to hopefully enhance the swirl-effect.
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Re: lowest reasonable highway rpm for a 440?
[Re: IcorkSOAK]
#1058368
08/21/11 11:14 PM
08/21/11 11:14 PM
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Joined: Jan 2003
Posts: 28,096 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
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Thanks for the input so far. I forgot about the Diplomats and their 2.45 rear gears. I had one and it was a pig around town. It did cruise nicely on the highway. I will most likely make the Power Tour with a carburetor. However, I will be reverting back to my old ways and stuffing this in the Imperial. When I do that, I'll probably switch back to the smaller 900 cfm throttle body. No doubt throttle response would be much better than with the 1700 cfm unit I've currently got on it. There is a slim chance it will be EFI'd for the Tour but that will depend on how the rest of the build is going. Within a year carb tuning should not be an issue.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: lowest reasonable highway rpm for a 440?
[Re: feets]
#1058369
08/22/11 12:01 AM
08/22/11 12:01 AM
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Joined: Jan 2003
Posts: 21,455 A collage of whims
topside
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 21,455
A collage of whims
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Had a Diplomat coupe years ago: 318 4bbl, lockup converter & OD, most likely a 2.45 gear, 235/70R15s. It was laaaazzy around town, but IIRC 75MPH was something like 17-1800RPM, and it was fine, even on small hills & headwinds. Something like California's Grapevine would have me either giving it some boot or pulling it down a gear. For a carb I'd want a T-Quad for its small primaries, but why bother if your plans are to run the EFI/Turbo setup? With carbs, I get the best MPG driving with as little throttle as possible; 2 of my EFI cars pull better MPG at the lowest RPM they'll turn & still pull the car, which with a carb would man frequent large throttle openings & low vacuum to maintain speed. The 3rd (it's the least aerodynamic) gets better MPG @ 3000RPM than at 2700. Mystifying? Nope, aero. My GMC 454 dually (5500 lbs, 4.10, TH400, Gear Vendors = 3.23ish gear) makes its max TQ @ 1700, but that doesn't equate to hwy speeds; 65-70 = 2700RPM. Needs more gear towing uphill, but unladen it's a freakin' locomotive. Hopefully your turbo setup is sized right so it won't require much RPM. Seems like a really good application for a stroker motor.
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