454 efficiency - Maximum CR

Propane, Butane, LPG, GPL, C3H8, C4H10
gottago
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Location: British Columbia Canada

Re: 454 efficiency - Maximum CR

Post by gottago » Thu Dec 07, 2017 12:56 pm

Burb that was funny.. I went with the 377 combo partly due to what you describe with your 396.. Huge torque will break things. I also wanted to experiment with the upper rpm capabilities of propane power. I've been around a lot of work vehicles and some big torquers but I haven't had one that could be classified as a screamer. I got into watching the mileage /power tradeoffs some time back and always thought there was more potential than what I ended up with. A long rod 377 was a good starting point.. yes, 400 block, 30 over.. scat crank, 3.5 stroke, Its in a fairly lightweight 89 reg cab chevy shortbox.

The tunnel ram was a big contributor to the increased fuel mileage and the midrange torque. Strange as it may sound.. Highway I'm at about 2200 rpm. Fuel mileage is just average at that, 18 if you drive nice, 16 if a bit on the aggressive side up to 2800 rpm. 700r4 trans.. Where the mileage is exceptional is the lower speed around town sort of thing.. Stop and go and running around like a normal driver I can get up to 25mpg. $50.00 is pretty well 12 hours driving time. That's if you can keep your foot out of it, but I don't mean babying it either. I have a fairly aggressive tune and I'm using vacuum advance. Retarding the cam did something that I can't quite fathom or explain. It seemed that propane liked something about that. It lost some of the low end intensity but broadened it out so nicely it was well worth the tradeoff. In effect the intake / ex close points moved out further but the openings were delayed a bit. That little draw on the intake that overlap provides and when may be why it does what it does. I have a set of 12.5:1 kb domed pistons in it so the dcr stays up with the bigger cam. That was the theory anyway.. It was supposed to take as much advantage of the propane octane as possible. A ft cam is cheaper to experiment with than a roller but a smallish roller may be the way to go.

The afr numbers I get are quite normal. Two mixers did not throw it off at all. I can set them easily for cruise anywhere from 15 - 19 on the gauge. They are responsive and I dip to about 12:5 on the afr at wot. That low end driving around spot where the big mileage numbers show up is at 17 plus on the afr gauge. The power does not lack even this lean, just roll on the throttle and not even all the way and you go up in smoke. Starting did not take much effort at all but I did change technique and added a primer button. Warm starts are immediate on first revolution.

I'm running a set of aftermarket rhs vortec heads. The ones Vizard and Joe Sherman used for their quite impressive cheap sbc builds you find written about in some older magazines. They aren't real big valve or big port heads. They have been smoothed over a bit and run better springs etc.. Size wise, are really small for what they do. I don't know if these results can be replicated in other engines or what parts of this are applicable to any others but I suspect there are some pretty basic underlying fundamentals that could be extrapolated. I know and I should remind people that this combo isn't exactly the traditional way to build a propane engine but its interesting information..

I am going to make one more change on this combo mainly just to see the end results. If you gain more power pretty well all the way through the power band when you heavily retard a cam past its recommended icl that is supposed to tell you something. Like you need a different cam. But by doing so, is that where fuel mileage goes south? I got to where I am by experimenting and I guess I'm obligated to finish the experiment. Might have some more updates for next year.. Meanwhile, some of this sort of thing might make a very nice broad powered fuel efficient big block without having to run out to the extremes on compression etc.. or maybe it won't?


burbfixer
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Re: 454 efficiency - Maximum CR

Post by burbfixer » Tue Dec 12, 2017 2:15 am

The experimenting you and your friends have done has confirmed some of what I've learned from 30+ years of propane experience. AND completely blown some of it out of the water! Good for you! I don't think I've ever heard of that combination of economy/performance in a V8 propane street vehicle, so your efforts are certainly beyond successful already. With few exceptions, the high performance propane engines I've been around have all been in big heavy trucks. When I was ripping around BC & Alberta having a blast with my heavy 396 4x4, I was always just a bit curious how it would have felt if it were lugging around 2000 lbs less truck! If you can pull 25mpg out of a high winding 377, maybe for me 18 or 20 out of a carefully built, fun to drive 454 isn't out of reach!

And I agree, just because a combo is unique, doesn't mean some of the lessons can't be applied to any V8 2valve engine using the same fuel. I personally don't believe engines are fundamentally that different. When you push the limits and think outside the box as you and your friends have done, that is where you really learn some things. As you've expressed several times now, answering one question sucessfully often just raises 2 or 3 more, but It's still good progress. I do have a concern about your statement that you should 'finish your experiment'. After chatting for a while now, I'm doubting someone like yourself will really ever 'finish' :) But at least it's a hobby with a tangible benefit - lower operating costs! As long as parts aren't putting you in hopeless debt, or the time isn't costing you something more important like your family/marriage, carry on & have fun! It does sound to me like you might be flirting with the outer limits of cam optimization with your combo. Actually, is there such a thing as a truly 'optimized' camshaft, especially in a street driven vehicle? It's precision metal stick that has to open and close valves in a complex machine operating in an insanely varying set of circumstances. You've already tweaked and tuned yours to the point that it's doing pretty much everything way, way better than average! I'm not saying stop what your doing, just take a moment now & then to look back at what you've accomplished there!

Everyone, let's re-cap. gottago has just told us that he gets up to 25 mpg in what's likely a 4000 lb pickup truck that smokes the tires at will and revs to 7000 on a fuel that typically costs about 30% less than regular gas where we live. I'm listening, and I hope anyone else interested in affordable propane performance is too!

It also sounds like you're doing all this without the use of feedback control. In the past I worked on the vapor feedback systems every day for years, and briefly even used one myself. They were fine, and seem to do what they were supposed to in a stock application, but in my experience, careful open loop tuning gave better power and mileage results. I also respect the current injection technology, but it seems these systems have also made conversions cost prohibitive for the average user, including me. That's why I stick with the older vehicles and vapor equipment - I can slap on an open loop dry gas system, tune and tweak it as I have time, and the rest of the time it still runs and drives great day to day. Plus I can afford to drive my vehicle.

Any idea what your horsepower is? Since you've been around both the big heavy torquers and the lighter screamer now, how do you think your 377 would be (as is) in a larger, taller geared 4x4? Your trans may not be set up in such a way that you'd know for sure, but do you get the impression the engine would dislike a lower cruise rpm, say 1500 -1700?

gottago
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Location: British Columbia Canada

Re: 454 efficiency - Maximum CR

Post by gottago » Wed Dec 13, 2017 12:56 pm

Thanks for taking note of all that burb.. To answer your question how this would feel in a heavier vehicle and at lower rpm..; I do have to say that the 377 combo is around the weight and rpm range where it works best now. The 377 is known to lighten torque and only make power with rpm. Weight and gearing would lessen the benefits so I would want to go to a big block or at least a longer stroke combo.

I have a half dozen or so other engines and numerous parts still kicking around so you are correct, I will be experimenting with propane power for some time yet. But the 377 is nearing the end for what can be done to improve it. The engine dyno simulation programs are likely biased too high number wise but I use them to see where changes might help. The estimated max hp on this comes in around 427 at 6500 and 437 torque at 4500. Torq stays above 400 right from 2500 rpm to 5500 rpm. That's where it pulls really nice and its not screaming. Above that rpm I suspect some sort of ramming going on but its really a bit much for most usual applications. Was just nice to hear a sbc sound like they used to and to be doing it on propane. .. I've mentioned most of the factors that contributed to the outcome but there are a few points I probably skipped. One being an onboard electronic timing control that hooks up to an msd box. You lock the distributer and then adjust with three tuning dials. I just lengthened the cables to be able to do so while driving. That helped big time to get the amount and rate of curve right. There really was one spot that you had to find that would have taken a lot of time or a dyno to discover. High compression is finicky that way. Theres a narrower band to work with but the benefits are higher too.

Someday I too am likely to go the bbc route. My younger brother is trying to talk me into building one. It has potential to amplify that sweet midrange pull that I favour, (2000- 5000 rpm)
For you..
maybe for me 18 or 20 out of a carefully built, fun to drive 454 isn't out of reach!
exactly... I believe it is possible, just how to get there? What worked for a long rod short stroke motor isn't totally apples to apples here. Some of the theory behind what it did and why may be able to be bent a little though.. One point you made about how propane mixers work and how two may not be detrimental to mileage is a good point to keep in mind and maybe incorporate even for a low rpm application. I used the 377 / cam combo to lighten the pull, drop vacuum etc at low rpm to see how mileage responded. Two mixers were better than one. There are a couple of schools of thought on that alone.. In effect I worsened performance from where it could be at low rpm in a way that decreasedflow and thus decreased cylinder filling. Less fuel going in. Compression becomes vital, you have to maximise every bit of what you have left. I don't have many supporters on this point but I don't have a lot of other explanations for the good low speed mileage either. My gearing worked with that too, yours won't.. Where do the extra cubes come into play to compensate for dropping some early max torque in exchange for mileage and a broader power band ? ? Somewhere in here the extra power of a big block will compensate for what has to be done to raise fuel mileage as long as compression stays in the right range. Will even allow for the higher gearing and increase mileage even further if you get it right.. I have mentioned about how just adding cam lift dropped fuel mileage for me and I have avoided the all out rv grinds since. Duration isn't supposed to help mileage much either but within reason it is the lesser of the fuel killing evils imo.. There is a balancing act to it.. Flow through head matching duration and lift resultant compression, vacuum draw etc.. .. Have fun!

storm
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Re: 454 efficiency - Maximum CR

Post by storm » Wed Dec 13, 2017 2:30 pm

gottago wrote:
Wed Dec 13, 2017 12:56 pm
There is a balancing act to it.. Flow through head matching duration and lift resultant compression, vacuum draw etc.. .. Have fun!
This is what its all about.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
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Re: 454 efficiency - Maximum CR

Post by gottago » Thu Dec 14, 2017 4:38 pm

In regard fuel mileage I'd like to relate some experiences I had many years back. Two of my first old school performance cars got 25 mpg. Both were high compression and one even had a bigger cam heads and intake than stock. Both were high geared. One big block , one sbc. Medium heavy cars. That was gasoline but it still made me realize power and mileage can be had in the same combo.

Iit was an amc 360 cu in that taught me a few other things though.. It was a relatively new vehicle to me and I took it on a fairly long highway drive to a big city. It ran well and seemed to be performing better than ever when we got to the city. On the way back it seemed to gradually be loosing power but it was in the middle of nowhere halfway back when things got so bad it could hardly climb a hill. There was no noise or back firing or anything. I had no choice but to continue. It would still do a hundred mph down hill and could maintain highway speed on the straights but it rapidly lost power going up hill so bad that at the end I was down in first gear floored and dropping under 10mph.. I eventually made it to the next town a couple hundred miles along the way and took it into a tuneup shop in the morning. The engine had rocker arm shafts that had apparently loosened off and the shims had slid out. So in effect I had dropped a ton of lift and some duration but lsa stayed the same. Lesson was that what had taken a full tank of fuel one way only took a half tank on the return trip back. Which then led to running rhoads variable lifters in several other combinations over the years. A fellow that used to have the cam motion website published figures on how much lift any cubic in engine really need. It was surprisingly small. Find a half a dozen little things that gain 1-2 mpg each and the benefits begin to add up.

BigBlockMopar
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Re: 454 efficiency - Maximum CR

Post by BigBlockMopar » Thu Dec 14, 2017 4:55 pm

I've been thinking for quite a while about what cam to run in my recently built Mopar 360ci engine.
'Common sense' made me go with a CompCams XE256H, but this was mostly based on its advertised operating range, because I would be shooting for best 'MPG' (and power).
I did however go with a 1.6 rocker ratio.
To say I'm fed up with the tremendous lousy mileage of my current mid '80s 318ci engine is an understatement (11.5mpg year average).
The hotrodder in me was very much leaning to a cam with some more duration like 268, and there's some wondering now how such a cam will 'MPG'.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

storm
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Re: 454 efficiency - Maximum CR

Post by storm » Thu Dec 14, 2017 10:09 pm

My old Pontiac 400 taught me alot, I could get 22-24 mpg (4.5 litres = 1 gallon in Australia) in the 1977 Trans Am Bandit (genuine car not a faker). The basic spec of the car were 400 ci (6.6 L) engine, 4 speed Saginaw, GM 10 bolt diff with 3.08 ratio, 8" rims with 265/60-15 tyres. Cruising at 100-110 km/h was about 2400-2500 rpm. My Brock on the other hand is a 308 (5 L), T350, 3.55 Borg Warner diff, 7" rims with 225/60-15 tyres and cruising at 100km/h is about 3000rpm. The Brock uses about the same amount of fuel as TA did with an engine that is 1.6 litres smaller in a marginally lighter car.

I purchased all the Pontiac performance material I could and all of it said basically the same thing. Note these things work for any engine not just Pontiacs.
1. Use a spread bore carb (Rochestor Quadrajet preferably) and stay as much as humanly possibly on the primaries.
2. Use stock style cams on stock style heads. Standard performance Pontiac heads generally flowed well to .4-.45 lift so Pontiac used 1.5 rockers on standard performance engines and 1.65 rockers on true high performance engines (e.g. late Ram Air) to achieve .4-.45 valve lift. Any more lift and performance, as well as fuel economy, suffered.
3. Tread lightly on the accelerator pedal. It is all to easy to mash the pedal and feel the raw power push from behind and get you from 0 to naughty naughty really quickly but doing that absolutely murders fuel consumption. Each and every time the accelerator pump is used you are injecting up to 10 times (depending on the size of the accelerator pump) the amount of fuel you would normally use into the intake.
4. Tyre pressures are extremely important, I try to keep mine at 30 + psi at all times. 30 for around town driving, 32-34 for highway driving. Rolling resistance on large (wide) tyres has a huge impact on economy.The TA had 265/60-15 tyres on 8" rims, the Brock (one of my current cars) has 225/60-15, my wagon has 205/60-15 and you can feel the difference between them.
5. Use an engine oil of the correct viscosity for the climate you are in and/or the condition of the engine. If you go to heavy you'll use more fuel if you go to light you'll use more fuel. It's all about having to pump the oil (if it's to heavy) or to much friction (if the oil is to light) and what the engine has to do to combat it.

Other things that hurt economy are
1. Wrong diff ratios for what the car gets used for. If the engine is most, fuel, efficient at 2000 rpm that is where you'll get best fuel economy.
2. Diffs that are just to big for the purpose. Example, a Ford 9" is huge and requires more power to use it compared to a smaller diff. Sure they are strong but very few cars really need such a big diff.
3. Brakes that aren't adjusted properly.
4. Weight, take the junk out the boot and help the car loose some weight.

Back to cam choices,
1. figure out what rpm you want to run at
2. at what lift heads have peak flow
3. what type of idle you want
and go from there as a starting point.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
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Re: 454 efficiency - Maximum CR

Post by gottago » Thu Dec 14, 2017 10:46 pm

To say I'm fed up with the tremendous lousy mileage of my current mid '80s 318ci engine is an understatement (11.5mpg year average).
I have been there too. I'm also old enough to recall those old 318 mopars that got 22 plus mpg. I had one in a coronet. Not a real light car but that little v8 pushed it well. It helps to have an idea what sort of power it takes to make a certain vehicle weight drive as you would like it. Too small a motor for the vehicle will cost you as much in fuel as too large. Compression and head sizes can be adjusted to some degree and create an individual rpm power band for each engine choice. What you might put in a 318 to operate a certain weight vehicle will be entirely different than you would put in a 360 + cu. in..

It can be a frustrating process to get all those little pieces working right and working together. For fuel mileage without exception, all my best were high compression. Propane suits that line of modifications.

One more short story, a v6 minivan that went from 17 mpg to 26 mpg. It was running on propane since new. I got it well used, 120,000 km. It went extremely well, faster than most stock v8s. Just a little 3 litre mitsubushi . I took it in once for a professional tune up at a well respected propane shop. It gained a full 8-9 mpg. Downside, it ran like a v6 afterwards.. Just saying, the propane system is quite basic but it does need to be adjusted properly for its intended purpose. Both tunes on this engine ran adequately for regular driving.

BigBlockMopar
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Re: 454 efficiency - Maximum CR

Post by BigBlockMopar » Fri Dec 15, 2017 7:19 pm

Without trying to hijack burb's topic, I'll post some of the things I did to my car in an attempt to improve it's economy, yet to no/hardly any avail;

I think I have touched/changed just about everything on my car that I tought it would improve mileage, but it all turned out it did not improve mileage considerably.
The car however did become more pleasant to drive overall, but still at the 'costs' of a mostly unchanged economy unfortunatly.
Only thing left untouched are the engine internals.

Here are some of the Mileage Improvement “upgrades” I did over time;

- Thin oil (0w20) / Occassionally mixed with 10w40. • Went from 10w40 to 5w30/5w20 to 0w20. Noticed some increased torque with cold morning starts. Engine runs cooler as well.
- Digital ignition tuning • Big improvement in low rpm torque and drivability. Increased engine vacuum along the range.
- 2-bbl to IMPCO 4-bbl with Edelbrock Performer intake • Improved throttle reponse and torque.
- Recurved IMPCO mixer • Good AFR numbers.
- AFR gauge installed and used for tuning • Increased torque.
- Cold air intake ducting • Less noticable heatsoak-effects.
- New timing chain set • Improved torque at first when installed few years ago. Not noticable anymore.
- Lighter 17” wheels w/ good brand tires. • Better handling.
- Tire pressures between 37-40 psi. • Less rolling resistance / improved grip.
- A518 Overdrive transmission • Less RPM on highway, added gear improved driving fun.
- 3.55:1 rear axle gears. • Better acceleration and highway RPM-range.
- Aluminium dragrace frontrunner as spare wheel. • Weightsavings.
- Front airdam to minimize undercar turbulence • Effect undetectable. Looks nice enough.
- New exhaust headers, full length into mandrell bent dual 2.5" exhaust system with low restriction Borla ProST mufflers. • No improvement on chassis dyno!

'Possible Downgrades’:
- 1” larger ‘60s stall convertor. • Was as a result of the A518 transmission (NON-lockup).
- 'Light' 904 transmission to heavier internals A518 overdrive transmission + longer/worse first gear ratio.
- 7-1/4” to 8-3/4” rear axle.

Most likely (left over) reasons for bad mileage;
- Lame 80’s cam specs.
- Low 8.6:1 engine Compression Ratio.
- Large stall convertor from fullsize car. • More mass. Build in the ’60s, perhaps non-efficient. • I noticed difference between stall convertor size when revving the engine.
- Longer 1st gear in A518 transmission. • Doesn't help at accelerating.

Below are the camspecs of a mid '80s 318ci (8.6:1) engine;

Code: Select all

						VALVE LIFT	——INTAKE VALVE TIMING——|——EXHAUST VALVE TIMING——
 ENGINE             	ROCKER   LOBE LIFT  	ZERO LASH   	OPENS CLOSES DURATION  |OPENS  CLOSES DURATION 
 DISP./HP.          	RATIO   (Int./Exh.)	(Int./Exh.) 	(°BTDC) (°ABC)  (Deg.) |(°BBC) (°ATC)  (Deg.)
===================+===================================================================================

 318/ALL		1.50	.248/.266	.373/.400  	  10	 50     240	  52   	16	248

----------
 360/
 CompCams XE256H	1.50	.298/.303	.447/.455	  22	 54	256	  68	20	268
			1.60	.298/.303	.476/.485
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

storm
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Location: NSW, Australia

Re: 454 efficiency - Maximum CR

Post by storm » Fri Dec 15, 2017 7:45 pm

Frank could you split this topic please?

BigBlockMopar here's what I'd do for a start with your car:
1. get a lockup converter for the A518 and make sure it functions when driving.
2. 5w20 oil at the thinnest, any oil that starts with a 0 is for modern tight clearance engines like the Ford modular V8.
3. cold air intake is a great addition if you want more power not if you want more economy. The colder the air the denser it is the more fuel is required.
4. more info on the heads is needed to comment on the cam. the CompCams is a big change from the 318/ALL and I'd suggest you are loosing to much cylinder pressure on a low comp engine.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

gottago
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Re: 454 efficiency - Maximum CR

Post by gottago » Fri Dec 15, 2017 10:58 pm

Ditto on cylinder pressure. That is the #1 biggest factor contributing to the lack of fuel mileage. Compression adds fuel mileage, not just performance. All the little things will help but not like adding compression will.

storm
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Re: 454 efficiency - Maximum CR

Post by storm » Sat Dec 16, 2017 2:48 am

Here's a screenshot taken from http://users.erols.com/srweiss/tablehdc.htm#Chrysler that gives a basic idea of the flow of bog stock standard 318 heads on an LA engine.
Chrysler_flow_numbers.png
Take note of the slow down of flow after .4 lift which makes a cam that lifts anything over .4-.45 at the valves a waste of time and effort. So called "High Performance" or "Street Performance" cams on basically bog stock engines really don't achieve much simply because the heads don't flow much more, and sometimes even flow less, past .4-.45 valve lift.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

BigBlockMopar
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Re: 454 efficiency - Maximum CR

Post by BigBlockMopar » Sat Dec 16, 2017 4:19 am

Splitting the topic might be useful if I were to proceed with the 318, but my lengthy post was more to show the things I had done already which didn't do much for economy in my case, so that would leave the engine as the single source of the 'problem'.

Hence why I decided to build a fresh high CR engine, which goal is just about inline with this topic.
The 360ci has the CompCams XE256h cam installed which specs are listed above in the code-window in my previous reply.
I used 318ci '302'-swirl heads as the small chambers helped upping the CR, along with the 0-deck pistons and a smooth/polish job on the ports and chamber.

I agree that too much lift doesn't add anything if the rest doens't need it.

I've driven with a A518 OD-transmission WITH lockup convertor for some time until the OD-unit broke.
The lockup improved drivability and the lockup felt like a small extra gear.
On these transmissions the lockup function only works in 3rd and 4th (OD) gear. As the OD and Lockup were manually operated by a switch, I only got to use Lockup in 4th gear.

I used 5w20 for a while too but went to 0w20 synthetic oil when I could buy them at $2.15 per bottle.
This change has had no noticable effect on oil pressure, which is still around 50-60 while driving and 25-35 when hot idling @ 500-600rpm.
Mostly in summertime I occassionaly mix in a bottle of 10w40 oil.

The cold air intake has greatly reduced the laziness I felt in the car/engine when it has been driven for a long while at stop-and-go traffic speeds.
Which is why I believe incoming air should be as cold as possible.
Cold dense air, means more mixture into the engine, would relate to more power delivered with same throttle opening. In effect less throttle is needed for similar engine/car speed.

I've never seen a setup where preheated intake air had better ecomony.
Hot intake air was more a kneejerk reaction in the '70/80s to comply with (gasoline) emission rules. Economy was not even considered at the time I feel as the factories had a tough time getting the exhaust clean enough.

I hope that with the compression increase the 360ci has, the car's 'mileage problems' will be gone and all the other mods I have done to the car will be beneficial and noticable... :)
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

Frank
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Re: 454 efficiency - Maximum CR

Post by Frank » Sat Dec 16, 2017 11:44 am

I could split this topic but I think BigBlockMopar added information about his own car for references to the points he was making rather than wanting to start another discussion.

My understanding about improving fuel efficiency comes down to a two things:
  • minimizing power losses
  • maximizing combustion pressure
A major power loss is pumping loss and this is reduced by keeping manifold vacuum as low as possible. This is the reason that overdrive gears help so much. Heated air with its lower density should also theoretically reduce manifold vacuum but the snorkels definitely reduce WOT power. Besides helping NOx, EGR should also help to reduce manifold vacuum. Low viscosity oil should help too but lubrication frictional loss is much smaller and harder to measure. Lower oil temperature indicates lower frictional loss.

Maximizing combustion pressure with optimized fuel mixtures and ignition timing tends to increase manifold vacuum. Raising the compression ratio also raises combustion pressure (as well as improving thermal efficiency).

Fuel mixtures and ignition timing work together and in opposite ways to improve fuel economy. This summer, I was working on jetting the Quadrajet that now replaces the Carter 9625 AFB carburetor on the 225 slant six in my 65 Barracuda. The best fuel economy I got with the AFB was around 29 mpg (imperial) with 2.5° initial timing. The Quadrjajet came off of my 77 Pontiac and has primary metering rod APT. For those of you not familiar with this carburetor, the metering rods are tapered and the APT adjusts how far down the metering rods sit in the jets at high vacuum.

To correct my lean cruise condition, I set my neutral idle speed to 2000 RPM so that the primary circuit was in operation. At 0 turns out (ie meter rods fully inserted in the jets), the engine had a noticeable miss. By about 2 turns out, the miss mostly disappeared. As I turned the APT out, I had to keep closing the throttle to maintain 2000 RPM. After 5.5 turns out, there was no further increase in RPM so this was my fuel economy starting point.

I have a Direct Connection PN 2444648 distributor (12° @ 2200 RPM centrifugal & 7° @ 13" Hg vacuum) in this engine, so I adjusted the timing with the Quadrajet to:
  • 10° initial
  • 34° mechanical @ 2200 RPM
  • 48° total @ 13" Hg vacuum
I mostly drive my car during summer at highway speeds and I found that my highway fuel economy with the APT at 5.5 turns was about 25 mpg. As I kept leaning my part throttle fuel mixture (turning the APT IN), my fuel economy kept improving. By 4.0 turns OUT (from zero), my highway fuel economy improved to over 31 mpg. Further leaning to 3.5 turns saw my highway fuel economy drop to 29 mpg. I've got the APT at 3.75 turns now and I'm waiting for spring to continue.

I think I can make further highway fuel economy gains with a bit more vacuum advance.

The point I am trying to make is that getting the best economy requires a lean fuel mixture (which reduces manifold vacuum) as well as optimized ignition timing to get the combustion pressure peak to occur at the point that produces the maximum torque on the crankshaft.

Having more advance is not necessarily better. One of our members (65CrewCabPW) found that the slant six in his truck needed very little advance for power and economy. See Propane truck update.

storm
Posts: 565
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: 454 efficiency - Maximum CR

Post by storm » Sat Dec 16, 2017 2:34 pm

BigBlockMopar wrote:
Sat Dec 16, 2017 4:19 am
Cold dense air, means more mixture into the engine, would relate to more power delivered with same throttle opening. In effect less throttle is needed for similar engine/car speed.
Your assumption of more power is correct but more power does not equal better fuel economy in every instance. The more air you put in the more fuel you need, the denser the air you put in the more fuel you need, both point to higher fuel consumption when all else is equal.
BigBlockMopar wrote:
Sat Dec 16, 2017 4:19 am
I've never seen a setup where preheated intake air had better ecomony.
Don't confuse non cold air with deliberately pre-heated air. Manufacturers fitted pipes to draw air off the exhaust manifolds to help engines come of chokes quicker thus limiting emissions, this is pre-heated intake air and it is detrimental to performance when the engine is at operating temperature. In every instance I personally know the owner and vehicle where the owner has fitted some sort of CAI they have complained about increased fuel consumption. The only change they made was a CAI and their fuel consumption increased everytime. Each and every change made to a vehicle is a compromise.
Frank wrote:
Sat Dec 16, 2017 11:44 am
The point I am trying to make is that getting the best economy requires a lean fuel mixture (which reduces manifold vacuum) as well as optimized ignition timing to get the combustion pressure peak to occur at the point that produces the maximum torque on the crankshaft.

Having more advance is not necessarily better. One of our members (65CrewCabPW) found that the slant six in his truck needed very little advance for power and economy. See Propane truck update.
Timing requirements are different for different engine and different fuels but the one thing that remains the same is the point where the combustion process puts the most pressure on the piston is about 16-18 degrees ATDC. Timing needs to be adjusted so that maximum effort on the piston occurs at this time. Any earlier and the leverage effect is to small any later and the flame front is chasing the piston, rather than pushing it, down the bore.
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Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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