MPG Motor Magnum vs. Hemi

[mgoblue9798]

Nice going with the Magnum swap, with the EFI you should definitely see some MPG improvements even including a cam and EQ heads (current route I'm going for with a 5.9L in my Duster but it'll be carb'd).

@mgoblue9798 that was the 1st-gen Dak right? Those things are tiny compared to a '94-02 Ram, or an old C-body... would love to get my hands on one with a 5-speed. Or swap a 5.2L into my '93 XJ Cherokee lol.

Major issue with mileage from these motors was they were only used in trucks. There is a guy on Moparts Polara something or another that did a 5.2 swap in a c body and was getting 25mpg. The trucks have the aeordynamics of a brick. I have a 5.9 in a 2002 ram high top van that gets 11mpg. This is after a rebuild with EQ heads, a small Hughes cam, and Magnaflow high flow cat and exhaust. Got the same 11mpg before the build. Point is mileage has a LOT to do with what the engine is in.

 

[AJ/FormS]

If you are really gonna rebuild that 5.2:
Might I suggest aluminum heads,very high compression,a very modest cam to go with that overdrive trans, and fresh-air intake?
I have run 87E10 on 185psi cylinder pressure, and point-to-point, got mileage you might not believe;with a carb, in my 3850pound(loaded), manual-trans,68 Barracuda, and a 1.97 final drive..... with an LA367,even.
No EFI required, when the engine is idling down the hiway at 75mph=1830rpm, mostly on the transfer slots. No; don't try this with a Holley, it's a little tricky. But any spreadbore metering-rod carb will drop you into the zone.
I expect your 3.21x.69=2.21FD and "somewhat heavier" combo won't go 32mpg, but I can see mid 20s easy enough, point-to-point.
But I can also see a rear swap to 2.94s and an A500 (with it's 2.74 low-gear),yielding a similar starter gear, (8.06 vs 7.86) and the new FD (now 2.03) and the smaller displacement 5.2 ....... sneaking up closer to what I was getting. Your tank can't be that much heavier than my barge, can it?
185 psi is a little harder to build in a 318/5.2, than in a 5.9, but with a small enough cam, should be doable. Hyup, should be. In a spread-bore cruiser, I wouldn't be afraid to tickle 195psi with aluminum heads.

Ok some clarification;
IMO
You will get better fuel mileage at 185psi/aluminum heads and a reasonable good tune, including a dial-back timing device,
than you could even dream of getting with 160psi/iron and EFI, perhaps even with computer spark control.
And with no other changes, you will also get more power;the compression increase by itself is worth nearly one cam size.
185psi might sound like a lot, but considering the VE at 2000rpm,with a small cam, it is no strain on the engine or octane whatsoever. And the passing/hill-climbing power will be a welcome relief I know. And in fact your sub-3000rpm performance will approach that of the old stock 413. Whereas your 5.2 at 160psi will not touch it.
Personally, I would leave the 3.21s in there, but I would go with the A518's lower gear ratios. Your 75mph would still be under 2000 with 28s, and the passing power at 60,in second, will be enough to scare you.
Just saying, and trying to get you to think outside the box.

 

[BigBlockMopar]

... Point is mileage has a LOT to do with what the engine is in.

I'm of the same opinion. I've been driving and tuning a 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably.
I've now got my 11.3:1cr 360ci installed in the car which has a significant amount of power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi.

Last year I had installed residual pressure valves in the brake system. 10psi for the rear drums and 2psi for the front discs.
The front disc pressure valve was good for 1 mpg loss in mileage. I removed it recently and promptly got the lost 1 mpg back.

 

[75slant6]

I'm of the same opinion. I've been driving and tuning a 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably.
I've now got my 11.3:1cr 360ci installed in the car which has a significant amount of power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi.

Last year I had installed residual pressure valves in the brake system. 10psi for the rear drums and 2psi for the front discs.
The front disc pressure valve was good for 1 mpg loss in mileage. I removed it recently and promptly got the lost 1 mpg back.

So what fuel mileage do you get?

 

[AJ/FormS]

I'm of the same opinion. I've been driving and tuning a 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably.
I've now got my 11.3:1cr 360ci installed in the car which has a significant amount of power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi.

Last year I had installed residual pressure valves in the brake system. 10psi for the rear drums and 2psi for the front discs.
The front disc pressure valve was good for 1 mpg loss in mileage. I removed it recently and promptly got the lost 1 mpg back.

A few years ago,I also had an 11.3- 367, but my pressure never got quite that high. Even with the small [email protected], (270/276/110) Hughes cam, my gauge only hit 190 IIRC. It's good to know there is plenty of headroom. Mine ran on 87E10. That was an awesome street cam, and got awesome fuel-mileage with a manual trans and a FinalDrive ratio of just a tic under 2.0.
I can't thank you enough for posting that pressure.

What was your thinking behind dragging the front brakes?

 

[BigBlockMopar]

After I had installed the res.valves I noticed the front wheels where always hard to rotate by hand when jacked up.
Too hard to be 'right'. Now that I removed the front res.valves again I notice just a slight drag just a like any other car has.

My mileage ranged between 10 and 11mpg. Around 9.5 with the front residual valves installed.
Mileage is always worse in wintertime, better when the weather warms up. But this spring I didn't notice the mileage improving again when temps went up, which let me to suspect the brakes.

Mind you, I'm running LPG / Propane.
CompCams XE256H
Always drive fairly short 15-30 minute trips. 60/40 highway/city.
A518 transmission - 8-3/4" rearaxle w/3.55 gears.

 

[AJ/FormS]

After I had installed the res.valves I noticed the front wheels where always hard to rotate by hand when jacked up.
Too hard to be 'right'. Now that I removed the front res.valves again I notice just a slight drag just a like any other car has.

My mileage ranged between 10 and 11mpg. Around 9.5 with the front residual valves installed.
Mileage is always worse in wintertime, better when the weather warms up. But this spring I didn't notice the mileage improving again when temps went up, which let me to suspect the brakes.

Mind you, I'm running LPG / Propane.
CompCams XE256H
Always drive fairly short 15-30 minute trips. 60/40 highway/city.
A518 transmission - 8-3/4" rearaxle w/3.55 gears.

No fair!
208/210 on propane is excellent but I thought since you didn't mention it earlier that you were on pumpgas.
I bet that combo was/is a torque monster.

I set my front wheel bearings to the loose side of the spec, so the discs can knock-back the pistons, helping seal-retraction, and, bottom-line, to help reduce mechanical drag to increase mpgs.
At my elevation,If I ran a 256 in at 106,my pressure could be up around 200 as well.
How do you convert propane useage to mpgs?

 

[BigBlockMopar]

MPG is calculated the same as with gasoline... Liquid propane tanked versus miles driven.
I've got a phone-app which I use to keep track of the mileage for over a number of years now.
Great (or not) to see mileage rise or (usually) drop based on outside temp differences or (sometimes) changes on the car.

I'm kinda blaming the transmission (A518) and the perhaps in-efficient / old design(?) '60s stall convertor (non-lockup) I've used in it for the crappy mileage the car is getting.

 

[AJ/FormS]

MPG is calculated the same as with gasoline... Liquid propane tanked versus miles driven.
I've got a phone-app which I use to keep track of the mileage for over a number of years now.
Great (or not) to see mileage rise or (usually) drop based on outside temp differences or (sometimes) changes on the car.

I'm kinda blaming the transmission (A518) and the perhaps in-efficient / old design(?) '60s stall convertor (non-lockup) I've used in it for the crappy mileage the car is getting.

I think I'd blame that camshaft.Specs are 256/268/110.
It's only got 42* of overlap, but in your application, at up to 1800 or maybe as high as 2000 rpm, a lot of that propane could be scooting straight across the top of the piston and out the back door.And with your gears, 65~1980 rpm at zero slip; right at the top of the crap-zone. You might want to think in terms of less overlap.
A little smaller cam on a 114LSA would have about the same compression /power durations, but the overlap could be reduced to say 25 from 42 . Yes you would lose a bit of absolute power at higher rpms,but you would gain a fatter powerband to pull those wide automatic ratios, and so I doubt your average power would change much.
Here's a theoretical cam worth perusing:
int....comp....pwr...exh....o/lap...in at
256....126.....118....268...42......106........... your current cam
250....122.....117....256...25..... 113........... replacement cam
There are others
I'm just trying to be helpful, and
Just something to think about.

 

[MopaR&D]

MPG is calculated the same as with gasoline... Liquid propane tanked versus miles driven.
I've got a phone-app which I use to keep track of the mileage for over a number of years now.
Great (or not) to see mileage rise or (usually) drop based on outside temp differences or (sometimes) changes on the car.

I'm kinda blaming the transmission (A518) and the perhaps in-efficient / old design(?) '60s stall convertor (non-lockup) I've used in it for the crappy mileage the car is getting.

I think you're on the right track with the transmission losing efficiency, there are people running much bigger cams than yours who are also getting better MPG but they're usually running taller gears with a 904 auto or some type of manual trans. I personally was able to get 17 MPG on a long road trip in my Duster, it had a 10.5:1 360 with a small 256/262/114 Voodoo cam, I also found later upon installing a wideband O2 sensor that the carb could be tuned leaner at cruise and I picked up another 2 MPG. Also was running a fairly loose (cheap) 2600-stall converter with an A-904 and 2.94 gears in the rear. But at the end of the day doesn't propane have less energy density than gasoline anyway so your mileage will always be less?

 

[BigBlockMopar]

AJ, help is much appreciated.
I've only driven with this 360 engine (and cam) for about 3 weeks. And had 3 tank fill ups.
But till now the mileage has been the same with the bone stockish 318 ('88 block w/ stock rollercam) and early '80s "302"-heads.

I have no issues with swapping cams, but if I do I want to step up to a (solid) roller.

Propane make less power in the same built engine, but if the build is optimized for propane it can come very close or sometimes surpass gasoline power.

When I got my Dart it had the 318 in it with a 904 transmission and a 7-1/4" 3.23 rear axle.
It could (once) manage 17mpg on a long highway trip, keeping it below 65mph.
(Fact was the engine started running hot if went faster so had to drive just over 60 all the time).
Found out later the engine was running very lean too.

 

[AJ/FormS]

AJ, help is much appreciated.
I've only driven with this 360 engine (and cam) for about 3 weeks. And had 3 tank fill ups.
But till now the mileage has the same with the bone stockish 318 ('88 block w/ stock rollercam) and early '80s "302"-heads.

I have no issues with swapping cams, but if I do I want to step up to a (solid) roller.

Propane make less power in the same built engine, but if the build is optimized for propane it can come very close or sometimes surpass gasoline power.

When I got my Dart it had the 318 in it with a 904 transmission and a 7-1/4" 3.23 rear axle.
It could (once) manage 17mpg on a long highway trip, keeping it below 65mph.
(Fact was the engine started running hot if went faster so had to drive just over 60 all the time).
Found out later the engine was running very lean too.

18 years ago, I was thinking of going LPG/CNG with my 11.3- 360 as well, but as you probably know, 11.3 is on the low side for propane....... they say. I threw out all my propane/CNG literature, but memory says those gasses liked 13/14 to one with iron heads. I can't say if that is true or not, that's a long time ago. I also seem to remember the companies pedaling the equipment were also recommending a very wide LSA; 115 IIRC.
In your case; if in fact the 11.3 is on the low side, then a solid lifter cam would be part of the answer. This is because you can run a smaller advertised cam that will trap more charge and increase your cylinder pressure,yet maintain the same .050 specs.
Stated another way; with same advertised specs, a solid will yield more .050 duration , and so ... more absolute power.
However, when going from a flat tappet to a roller you have to bare in mind that the rollers usually have quite a bit slower opening/closing ramps, and this doesn't usually cause a problem........ until you start trying to increase cylinder pressure on an already built engine, while trying to maintain the same absolute power.

Going back to the former examples; see #1 and #2 below; Firstly I couldn't find a roller XE256, so Ima guessing your 360 is an LA block with a flat tappet hydro in it. So when swapping to a Solid roller,you will want to maintain that 212/218 .050 spec if at all possible. I have seen some solid roller with ramps of 38*, so 212/218 plus 38, yields 250/256, and adding a couple for lashing, I get 252/258, and we want to spread the Lsa to 114. Lets see what that looks like; see #3 below. Ok, so, we see that the pressure dropped 9psi/14VP , not the best . Lets advance the cam to, in at 110 and that would be example 3b). And that is sneaking back up to your current specs.Ok great, but I see that the power duration is down to 116, and I see an opportunity to extract a bit more energy here for economy, and that gets us to 4), which looks like a fair trade.
So as you can see, the rollers cannot maintain the same pressure/VP, as your current combo, with the same .050s
What about a solid Flat Tappet? Glad you asked, but you won't gain anything over a solid roller, and the solid roller will make more power than a same-sized solid FT, size for size...... so that's kindof a bust.
On the off chance that you currently have a preponderance of unusable low-rpm power, you could up-size intake duration one size, with the solid roller,and gain some high-rpm power. And that takes us to #5.
But I'll bet your 11.3Scr was achieved with a zero deck and the Fell-Pro .039 gasket for a Q of .039. And....... I ran a Q of .028 for over a year on 87E10 in mine; so that's 2.48cc right there. Recalculating your Scr for the difference, I get a new Scr of 11.67....... and you see where I'm going right... #6
Of course with the new higher Scr, that leads to #7,lol. OOps, we gave up some fuel economy on that one, but we got a ton of absolute power over the baseline.
Ok so #7 is a bust. How about #8?
So #8... is a full size .050 bigger Solid roller than your current FTH. That should be good for around plus 18hp. The powerband is also widened for the automatic, and so will generate more average hp from the torque peak to the power peak and a bit beyond. The 8* less overlap will help prevent LPG from escaping across the piston. The pressure/VP is down some, but Ima thinking that will be a non-issue. Ima thinking; winner!

Ok so, this is just an exercise in what ifs. I did not go looking for any of these cams, and so far as I know, yours is the only one that actually exists.
You can slam the door on escaping LPG just by running it at a higher rpm.You don't necessarily need a different cam. If you slowly rev it up in Park, while watching the vacuum build on a gauge, you will see the vacuum climb to plateau somewhere around 2000. When it does, this is the lowest rpm you want to cruise at for best fuel efficiency. At/above this plateau is when the overlap period is no longer allowing monkey-business in the intake, and the theory is that time is no longer great enough for significant LPG loss across the top of the piston. So you want to spend as little time as possible, below that rpm.Especially at hiway cruising.Sometimes increasing your hiway cruise speed nets an INCREASE in mpgs, just because of that steenking overlap period.
>Also IIRC LPG wants early ignition timing.... and lots of it.
Try this: get the rpm up to about 2200, on the fast-idle step. Then advance the timing until the rpm no longer rises. Make sure the Vcan is on the sparkport and is being activated. At 2200 rpm it should be; but just pull it off and see if the rpm changes.If it drops, that's good. Ok check the timing now at 2200. That is the advance, that the engine wants, at that rpm with no load on it. It may not want quite that much when cruising. Ok kick her off the fast idle and return the timing to your baseline.
Now think about it.
I bet you didn't have nearly enough,lol. My engine accepts up to 63 degrees at 2150 (on gas) for cruising at 65. I don't run it quite that high. The more I advanced it, the faster the car drove... with the gas pedal locked. So I reduced the foot-feeder, to drop the mph back to 65; so now I was cruising at the same speed with less throttle opening..... and the fuel economy increased. But even better, at the new timing and throttle opening, I was able to lean her out some more. I won't tell you that I got her up to 32MpgUS, point to point, over a 10 hour cruise ; nobody believes that. But I can say over 20USg, and somehow that sounds more believable. Ok I cheated; I had a double overdrive manual trans with a final-drive of a tic under 2.0,lol, and a [email protected] cam. Your results may vary.......
>So, no matter what cam is in it;
Perhaps run a little more rpm at hiway speed. This will slam the door on the LPG escaping across the piston, as will keeping the Rs above say 2200/2400 rpm around town.
Put a low-pressure gauge on the crankcase (leave PCV installed), and run it up to where you can see it from the cab. Leave it there for a few days, and make sure you never see pressure on it below about 3500 rpm.

Comparative Chart
.....int.....comp.....pwr....exh...o/lap...in at/ICA....Lsa......050s ............................psi/VP
1) 256...126.....118...268...42.....106/54... 110... 212/218 current FTH.. 202/190
2) 250....122......117....256...25..... 113/58.....114... 208/214 theoretical FTH 195/178
______________________solid rollers below_________________
3) 252....121.....116....258...27......113/59.....114... 212/218 solid roller........ 193/176
3b)252...124.....113....258...27......110/56.....114....212/218......................... 198/184
4) 252....123.....119....256...30......111/57.....112....212/216....................... 197/181
5) 258....118.....112....266...34......113/62.....114....218/226....................... 188/167
_________________________ below at 11.67Scr _______________
6) ............... same as #5 .............................................................................. 196/174
7) 262....118.....108....270....38......111/62.....114....222/230....................... 196/174
8) 260...118.....112..264....34......112/62...114....220/224..................... 196/174
1 to 5 are at 11.3Scr and 6 to 8 are at 11.67Scr and; All are at 500ft, for comparison.

10) 250..129...115...262....36......106/51....114....206/212 your current
cam, converted to "solids" with lash allowance of 3* at each end
11) 252...127.....116....260....32.....110/53......112....206/214 the factory 360 2bbl cam

 

[mgoblue9798]

I think you're on the right track with the transmission losing efficiency, there are people running much bigger cams than yours who are also getting better MPG but they're usually running taller gears with a 904 auto or some type of manual trans. I personally was able to get 17 MPG on a long road trip in my Duster, it had a 10.5:1 360 with a small 256/262/114 Voodoo cam, I also found later upon installing a wideband O2 sensor that the carb could be tuned leaner at cruise and I picked up another 2 MPG. Also was running a fairly loose (cheap) 2600-stall converter with an A-904 and 2.94 gears in the rear. But at the end of the day doesn't propane have less energy density than gasoline anyway so your mileage will always be less?

I installed a new from Chrysler non lockup 518 in my Challenger convertible in 1994. With a rebuilt 340 10.5 -1 pistons, hookers, 1406 carb, edlebrock performer intake, a mopar purpleshaft 272 455 cam, and 3.55 gear it would get 20mpg.

 

[BigBlockMopar]

AJ,
Lots of fun facts to digest.

The 360 is a LA indeed.
Used it with 1.6 rockers at first but went to 1.5 Cranes later.
Quench height is around .028-.030".
I ran the cam with hydraulic lifters converted to solids as the hydraulic lifters kept collapsing. A cam change might be in the works in the future, maybe even aluminium heads, but I want to get the mileage to an 'acceptable' level first. This probably means "fixing" the transmission.

Ignition timing on the engine is fully digital, so I can enter any ignition advance at any RPM and load/vacuum range.
The ignition table has 16x16 cells.
Currently I'm running max. 32° at 2800rpm at high load/WOT, and max 42° at no load/high vacuum.
Part throttle driving is generally around 30°.
The current cam 'really' starts to work from around 2250 rpm when floored and pulls nice and strong. Especially compared to the bone stockish 318ci I had before.

 

[AJ/FormS]

Unless there is something truly wrong with the A518, I don't think you will gain any meaningful mpgs from a rebuild. In steady state operation, the powerloss thru it is not much different than the A500, and only a little more than a GM .
The TC however could be a more likely culprit.
At your Quench, it would be hard to increase the Scr without major cash outlay.pressure however, can be jacked around pretty good with changes in ICA.
IDK anything about LPG, but I think your engine combo is well thought out. I imagine you're a pretty sharp tuner, so you keep after it and i think you will make it the best that it can be.

Your cam tho still has the hydraulic acceleration ramps on it, even tho you're running "solids". That thus makes your cam appear to the engine to be one size smaller @.050. Further more, the lash you are running is stealing another 3*or so of ICA, and a total of 6 degrees less intake and exhaust duration, and so about 6 degrees of overlap.
Go back to post 62 and I'll I add your net numbers as #10, as a best guess as to what your engine is seeing. Compare #10 to #11 the factory 2bbl cam. they are practically dead ringers.

 

[BigBlockMopar]

I tried to build this engine with LPG in mind, so a healthy compression ratio, polished chambers and ports, full length headers, cold air intake and Edelbrock AirGap to keep the charge cool.

The stall convertor is a big 12"(?) unit made in the '60s (non-lockup, for stock 727s out of a C-body).
I have driven the car shortly with a different A518 with Lock-up in between, which had a 11" convertor. I could notice by how the engine revved in Neutral at the time, that the convertor was lighter, compared to the 12" convertor I had before and after this again (The Lock-up 518 ate its OD-unit so I had to swap it out again for the non-lockup unit I still had).
I hope the A500 I have (to be rebuild) will add some mileage.
The cam I'm currently using has very little lash (hydr.cam w/ solid lifters) at just around .008", which tightens up a few thou when the engine warms up. This is ofcourse to take up the lash while the lifter is still on the 'ramp' of the lobe and prevent clatter and shorten valve train life.

 

[AJ/FormS]

With .008, you may be walking a thin line between the engine barely surviving and self destructing. The exhaust valve needs seat time to shed heat. And if the valves don't fully close, there goes your cylinder pressure and MPGs along with it.
You might be able to get a grip on this with a vacuum reading at say 100*F and compare it to when fully warmed up. I have never had to do this so I'm just tossing out ideas. I know my slanty told me it wanted more clearance when I did this, and the idle improved remarkably.

 

[slicknapier]

Holy hell! you guys make me realize how little I know. I've been researching camshafts and still have a hard time understanding exactly what I'm looking for in a cam as far as duration, lift, cylinder pressure etc...

 

[mgoblue9798]

Holy hell! you guys make me realize how little I know. I've been researching camshafts and still have a hard time understanding exactly what I'm looking for in a cam as far as duration, lift, cylinder pressure etc...

You and me both. The more you know, the more you realize how little you know sometimes. I know enough to pick a good cam grind for the street engines I build, but not a clue when it comes to actually designing a custom one like these guys are talking about.

 

[BigBlockMopar]

AJ, I have checked/confirmed some valves start to hang open (hot) with .005" (cold) lash.

From digesting information from various sources I've gathered that hydraulic cam 'ramps' are actually quicker, because they are made with the presumption that the lifter is already in contact (preloaded) with the cam.
Solid cams have a slightly softer ramp to first take up the lash and then start with the actual lobe.
This is why putting solid lifters on a hydraulic cam can give a slight improvement (more rpms) over a hydr/hydr setup.
These days cam companies advertise with 'tight lash'-cams as if they've invented something new, but in effect they are just putting hydraulic lobes on a solid cam.