Ironracer
Gearhead
Wow Kim, that Sucks...
New bb build fuel economy
- Thread starter plymouth1937
- Start date
-
Yupper
You know where the blame for that lies. Do what you can to influence those that can reverse this and are willing to do so.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,858
- Reaction score
- 12,204
When talking about fuel economy, there are several kinds...
1) steady state
2) City
3) hiway
4) average
As to #1;
If it takes 35hp/NET to maintain 65mph in your A-body, then it will take that, no matter what engine you install or how low/ how high, you rev it. All you can do for fuel useage is reduce the internal friction inside the engine, so that more of your Gross hp becomes Net.
The 400 has the biggest bores of all Mopar passenger car engines, so reducing internal friction is gonna be a chore. Making it a 451 is just making matters worse
as for #2
Every time your rpm increases or your speed increases, that costs power, over and above the "steady-state", so fuel economy goes down
as for #3
Hiway is usually thought of as steady state; but if the terrain changes in elevation or the road surface changes, or there are turns involved, those things all cost power, which reduces your economy.
as to #4
the bigger the engine, the more internal friction it will generate. And friction costs power, which reduces fuel economy. Anytime that big engine sees an increase in load, it has to generate enough power to overcome it's internal friction, in addition to that required for the increase in load or rpm or speed. Hence, the average fuel economy of the big 451, will always be less than it would be with a smaller engine
This is irrespective of it's absolute-power.
One of the fastest ways, possibly the single worst way, to lose fuel-economy, is to have lousy cylinder pressure. Not a hope in hell would I build a low-pressure engine for fuel economy.
The Second fastest way, to lose fuel-economy, is to not have adequate Cruise-Timing. With the factory timing controls, it is impossible to supply the engine with enough Cruise-timing below about 2200rpm, no matter how much you modify that timing control, and still be able to floor the pedal. So cruising in double overdrive, geared to 65=1400rpm is not gonna get you the fuel-economy numbers that you crave or imagine. The engine will cruise at 1400 no problem; (even a 318 can make 35hpNet at 1400rpm;) but the engine, any engine, just won't get enough timing at 1400, with the factory-type ignition system, to make it worthwhile, in terms of fuel-economy versus dollars spent.
OK I better unpack that a bit. All engines have a point after TDC to best transfer the Force of the expanding gasses to the crank,where it will NET the best result as to power/torque. All your timing controls are designed to hit that mark under as many circumstances as possible. This works reasonably well in stock configuration, because the cruise-rpm in stock configuration is gonna be in a fairly small window, plus/minus about 10%. So
When fuel economy is the primary goal, then you need;
1) a small bore to stroke ratio; small bore for less friction, and long stroke for effective compression distance after the intake valve closes, but more importantly for Power-extraction before the exhaust valve opens. So,like
a 225 for instance which is 3.40/4.125=0.82! or maybe
a 273 which is 3.63/3.315=1.095, or maybe even
a 360 which is 4.00/3.58=1.117.
Versus ; your contemplated
451 which is 4.34/3.75=1.157, or ouch
a 400 which is 4.34/3.335=1.30 (no wonder they suck gas)
2) as few cylinders as possible, to make the required cruise horsepower, (like a 225 for instance) and have enough hp left over to get up to the Cruising speed, in a reasonable period of time like a 273, to not be an accident waiting to happen. and
3) you will need a stand-alone programmable, Timing Computer. And
4) more than a 2bbl carburator; the very least you will need, is a spreadbore with tiny Primaries. And
5) as much cylinder pressure as the fuel will support without detonating. And
6) long-tube small-pipe headers with a cross-over, to pump up the torque, but these are probably optional if the exhaust manifolds are Not chokes.
7) maybe one of those tail-pipe extractor turbine thingies, lol, ..... kidding!
8) a manual trans is worth about 10%
9) an overdrive is worth about 50% of the percentage in rpm reduction. So if the rpm reduction is 20% the increase in fuel economy to be expected is .20 x .50= .10= 10%; hardly worth the thousands of dollars they cost. Break-even might be a decade or more.
if you wanna talk about performance with economy, that is a separate discussion.
1) steady state
2) City
3) hiway
4) average
As to #1;
If it takes 35hp/NET to maintain 65mph in your A-body, then it will take that, no matter what engine you install or how low/ how high, you rev it. All you can do for fuel useage is reduce the internal friction inside the engine, so that more of your Gross hp becomes Net.
The 400 has the biggest bores of all Mopar passenger car engines, so reducing internal friction is gonna be a chore. Making it a 451 is just making matters worse
as for #2
Every time your rpm increases or your speed increases, that costs power, over and above the "steady-state", so fuel economy goes down
as for #3
Hiway is usually thought of as steady state; but if the terrain changes in elevation or the road surface changes, or there are turns involved, those things all cost power, which reduces your economy.
as to #4
the bigger the engine, the more internal friction it will generate. And friction costs power, which reduces fuel economy. Anytime that big engine sees an increase in load, it has to generate enough power to overcome it's internal friction, in addition to that required for the increase in load or rpm or speed. Hence, the average fuel economy of the big 451, will always be less than it would be with a smaller engine
This is irrespective of it's absolute-power.
One of the fastest ways, possibly the single worst way, to lose fuel-economy, is to have lousy cylinder pressure. Not a hope in hell would I build a low-pressure engine for fuel economy.
The Second fastest way, to lose fuel-economy, is to not have adequate Cruise-Timing. With the factory timing controls, it is impossible to supply the engine with enough Cruise-timing below about 2200rpm, no matter how much you modify that timing control, and still be able to floor the pedal. So cruising in double overdrive, geared to 65=1400rpm is not gonna get you the fuel-economy numbers that you crave or imagine. The engine will cruise at 1400 no problem; (even a 318 can make 35hpNet at 1400rpm;) but the engine, any engine, just won't get enough timing at 1400, with the factory-type ignition system, to make it worthwhile, in terms of fuel-economy versus dollars spent.
OK I better unpack that a bit. All engines have a point after TDC to best transfer the Force of the expanding gasses to the crank,where it will NET the best result as to power/torque. All your timing controls are designed to hit that mark under as many circumstances as possible. This works reasonably well in stock configuration, because the cruise-rpm in stock configuration is gonna be in a fairly small window, plus/minus about 10%. So
When fuel economy is the primary goal, then you need;
1) a small bore to stroke ratio; small bore for less friction, and long stroke for effective compression distance after the intake valve closes, but more importantly for Power-extraction before the exhaust valve opens. So,like
a 225 for instance which is 3.40/4.125=0.82! or maybe
a 273 which is 3.63/3.315=1.095, or maybe even
a 360 which is 4.00/3.58=1.117.
Versus ; your contemplated
451 which is 4.34/3.75=1.157, or ouch
a 400 which is 4.34/3.335=1.30 (no wonder they suck gas)
2) as few cylinders as possible, to make the required cruise horsepower, (like a 225 for instance) and have enough hp left over to get up to the Cruising speed, in a reasonable period of time like a 273, to not be an accident waiting to happen. and
3) you will need a stand-alone programmable, Timing Computer. And
4) more than a 2bbl carburator; the very least you will need, is a spreadbore with tiny Primaries. And
5) as much cylinder pressure as the fuel will support without detonating. And
6) long-tube small-pipe headers with a cross-over, to pump up the torque, but these are probably optional if the exhaust manifolds are Not chokes.
7) maybe one of those tail-pipe extractor turbine thingies, lol, ..... kidding!
8) a manual trans is worth about 10%
9) an overdrive is worth about 50% of the percentage in rpm reduction. So if the rpm reduction is 20% the increase in fuel economy to be expected is .20 x .50= .10= 10%; hardly worth the thousands of dollars they cost. Break-even might be a decade or more.
if you wanna talk about performance with economy, that is a separate discussion.
Last edited:
Steve Bloom
Active Member
Cleaning the spark plugs every week sure helps. Back in the 60's most car owners were expected to do their own maintenance. Plugs, points, (before electronic) condenser, oil changes, timing. Take care of your car with a good tune-up, what you get in MPG is what you get. We don't care how much gas costs, 8lbs of gas can carry a 4,000 lb car 15-20 miles up a hill.
Martin Koiryohann
Well-Known Member
low compression DOSE NOT MEAN GOOD MPGS the key os turning less rpms over drives & gears . that how the new cars run soongood . u cantake a doggymotor &S makit run good out of the hole with a good set of gears if u want the most mpgs out of a motir good comptression & the right cam A GOOD RV CAM WOULD BE A GOOD PIK
famous bob
mopar misfit
^^^^^^^^^^^^^^^^^^^^^^^^^this !!
MopaR&D
Nerd Member
It's all relative, there's "fuel economy" and then there's "what's the best I can get out of a big block?"
No good reason not to try to get the best gas mileage out of any street-driven engine regardless of its size. Most of it comes down to the tune anyway which if the tune is good then not only will gas mileage be better but the engine will last longer and have better driveability.
James Clews
Well-Known Member
In australia in the early seventies a mate of ours was retiring and about to tow his caravan around Australia and had an almost new Ford Falcon panelvan with 250 cu ins six in it and it got about 12mpg towing and was slow. He wanted to build up his 1952 dodge truck up to tow with. We convinced him to buy all the parts out of a dodge car that was wrecking at the time and we had a low compression 440 engine to install. He put the 440 and torqueflite in it with 2.92 dodge diff , power steering etc. It was a weapon with power to spare and got 21mpg towing the caravan. He went all over Australia and it never missed a beat.
mygasser
Well-Known Member
for sure when pulling a lot of weight bigger power just loafing along will be more economical than low power working it's nuts off. that's a given.
Jim,
I remember him. Small grandson used to sit in the middle of the front seat. Dodge would blow past new V8 XB/XC Falcons going up Mount White towing the van. Must have been a WTF moment for the Ferd drivers.....
I remember him. Small grandson used to sit in the middle of the front seat. Dodge would blow past new V8 XB/XC Falcons going up Mount White towing the van. Must have been a WTF moment for the Ferd drivers.....
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,858
- Reaction score
- 12,204
I built my 367, for street performance with fuel economy in mind.
But Economy extends to the cost of fuel, so I wanted to try and run 87 gas.
To whit, I thought compression would be the #1 thing. But with iron heads the pressure tops out at around 155 psi. Well I thought about that for a bit. This was in 1998. I had heard that alloy heads could support at least 1 point more compression. I found out later, after more research, why this was said, and also how conservative this was.
So I built my engine for a target of 185psi using alloy heads and a tight Squish, and put the thought of water-injection in the back of my mind, just in case. I put a 292/.509 Mopar cam into it. the pressure was 177psi, close enough.
Well, the beast burned 87E10 right from the get-go, with full-timing no less!
I didn't like that cam, pulled it out, and swapped in a cam three sizes smaller with no other changes.
The pressure jumped to about 195.
This combo made tons of torque, good power, and great fuel-mileage. In fact so good that nobody believes it when I speak the number, so I rarely do. Yes it still runs full-timing on 87E10. It now has over 100,000 miles on it.
The point of this story is that the entire purchase-price of the closed-chamber alloy-heads was recouped in fuel savings within three years as a DD. Since then it has been saving me gas money every time I start it up.
Lest you think that 195psi is a fabrication, I did a survey here on FABO several years ago, and found out that a few members here are running the same and more, to even a tic over 200psi.
There is IMO, NO DOWNSIDE to running these high pressures, for several reasons;
1) your engine is rarely at WOT, so rarely creating these high pressures
2) Your engine is only capable of inhaling a full load of air , for a very narrow rpm window. and only if you cammed it up to do that, and matched all the components to that cam.
3) When cruising in a steady state, your throttle is only open as far as it needs to be to create the motive power for that circumstance..... so the EFFECTIVE compression ratio is NOT nearly what the math says it should be. My Scr to achieve that 190+psi was 11.3. But if my car only requires 35/40 hp to cruise 65mph, maybe the Effective Compression ratio, might be 5/1; IDK just guessing.
If I gear that beast to go 65mph @1600rpm, the throttle will have to be quite far open to get the required air. If I install a small-primary carb, it may get up on the mainjets, where I can control the actual fuel going into the engine, very accurately. That thinking is what got me the very high fuel-economy.
And it can do the same for you. Camming it for that very high pressure is the key.
But if you want to run big-number rear gears, well then this is not gonna work for you. Unless you have an overdrive.
But Economy extends to the cost of fuel, so I wanted to try and run 87 gas.
To whit, I thought compression would be the #1 thing. But with iron heads the pressure tops out at around 155 psi. Well I thought about that for a bit. This was in 1998. I had heard that alloy heads could support at least 1 point more compression. I found out later, after more research, why this was said, and also how conservative this was.
So I built my engine for a target of 185psi using alloy heads and a tight Squish, and put the thought of water-injection in the back of my mind, just in case. I put a 292/.509 Mopar cam into it. the pressure was 177psi, close enough.
Well, the beast burned 87E10 right from the get-go, with full-timing no less!
I didn't like that cam, pulled it out, and swapped in a cam three sizes smaller with no other changes.
The pressure jumped to about 195.
This combo made tons of torque, good power, and great fuel-mileage. In fact so good that nobody believes it when I speak the number, so I rarely do. Yes it still runs full-timing on 87E10. It now has over 100,000 miles on it.
The point of this story is that the entire purchase-price of the closed-chamber alloy-heads was recouped in fuel savings within three years as a DD. Since then it has been saving me gas money every time I start it up.
Lest you think that 195psi is a fabrication, I did a survey here on FABO several years ago, and found out that a few members here are running the same and more, to even a tic over 200psi.
There is IMO, NO DOWNSIDE to running these high pressures, for several reasons;
1) your engine is rarely at WOT, so rarely creating these high pressures
2) Your engine is only capable of inhaling a full load of air , for a very narrow rpm window. and only if you cammed it up to do that, and matched all the components to that cam.
3) When cruising in a steady state, your throttle is only open as far as it needs to be to create the motive power for that circumstance..... so the EFFECTIVE compression ratio is NOT nearly what the math says it should be. My Scr to achieve that 190+psi was 11.3. But if my car only requires 35/40 hp to cruise 65mph, maybe the Effective Compression ratio, might be 5/1; IDK just guessing.
If I gear that beast to go 65mph @1600rpm, the throttle will have to be quite far open to get the required air. If I install a small-primary carb, it may get up on the mainjets, where I can control the actual fuel going into the engine, very accurately. That thinking is what got me the very high fuel-economy.
And it can do the same for you. Camming it for that very high pressure is the key.
But if you want to run big-number rear gears, well then this is not gonna work for you. Unless you have an overdrive.
plymouth1937
Well-Known Member
Hi like your way of thinking,what cam did you put in,specs ? This build is still on the drawing board and im gona start saving up parts soon,just want to get it sort of right from the start,im going whid the stock 400 cui and close chamber iron heads,got a buddy whid a full service head shop and he makes 5 angle valve Jobs for nothing so im covered in that part of the build,I always belived in high comp and low friction so im going thath route
mygasser
Well-Known Member
hi, i no you already said your english isn't that great but after someone pointing out it's 'with' not 'whid' i would've thought you could've got that right by now. just saying.... 
jos51700
Green Bearing thread connoisseur
I had the same thought as the other guy, but I generally give non native English speakers a pass, versus dumbass American youths that don't have an excuse other than poor parents.
So far as the build, rule number one build the car as light as possible. That motor needs to be small block light.
I would focus more on drivetrain than motor. Tall gears and overdrive, and figure out your cruise rpm, and build your motor for peak torque at that rpm.
So then your motor ends up being a low rpm high torque cam, heads optimized for your cruise rpm, and 9.0 compression and that should yield decent fuel economy. The trick with economy is to build your combo around your given cruise speed, instead of building it around a certain elapsed time, horsepower, or sound.
When I worked on Harley's, there was a guy in the shop turning out some REALLY hot big twins that usually had a significant increase in economy because they were just idling down the highway.
How much driving do you plan on doing, what mileage does it get now, what does that cost ??
plymouth1937
Well-Known Member
Don’t Let the negative comments get to u. We are here to help. Kim
Last edited:
Don't know what others been saying but I'm not trying to be a dick I'd appreciate if you don't talk to me like that, I was only trying help which I assume your on here for.
mygasser
Well-Known Member
If we're being picky.... you should never start a sentence with the word 'and' whether you use a capitol 'A' or not
-
