Smallblock efficiency or How to have your cake and eat it too

[SLOPAR72]

A lot of stock 340's got 20 mpg back in '68 and '69.They really are the best all around engine in an A body!
I know a lot of guys with big blocks, big and small strokers or nasty small blocks that won't go to cruz night get togethers if they are more than 6 or 7 miles away just because of poor mpg.

In the mid 90's my brother had an all original and basically untouched 69 Cuda (340 4spd) and with 3.55's he could average about 17mpg on the highway. He never tuned on it but I am sure had he worked with it there was another 2mpg somewhere. Not bad for a 14" tire IMO....

JW

 

[ir3333]

Just to clarify...i'm talking 20 mpg imperial gallon.

 

[rumblefish360]

Lose enough!

 

[RAMM]

In the mid 90's my brother had an all original and basically untouched 69 Cuda (340 4spd) and with 3.55's he could average about 17mpg on the highway. He never tuned on it but I am sure had he worked with it there was another 2mpg somewhere. Not bad for a 14" tire IMO....

JW

Again, nowhere near 500 HP. Wow is this convoluted. J.Rob

 

[MOPAROFFICIAL]

I haven't read past the first page , I intend to ,don't get me wrong, but I stopped and thought right away after reading the the first post back too and I would always tell people how important running in in or near the middle of the cam Power Band. People would laugh and say "oh yeah ? okay well my power bands 3000-7000... so I'll go down the freeway at 4500..huh... yeah right" ...but thing is...you get worse milage under the cam range. You want to get as much of your low speed driving into the cam range as possible. It runs dirty if you dont and the gas is going out the tail pipe.
I still have the five pages to read and in fact earlier I was wondering where this thread went cuz I only saw the first post when he first put it up.... but basically when we spend all our time on the site talk and a heck of a lot about making power and doing it expensive or cheaper ,his way, my way, or their way ...we don't really dive into the other end of the pool, where we started from. I think about all the the 70-71 dusters that were ordered up with 4 wheel drum .. on purpose. They drag less and you went faster that way.. that works for milage too...anyways, i gotta read all this to see IF there is anything new i havent already known about. Cracking beer now...

 

[MOPAROFFICIAL]

But what if we do all city driving, no highway? For me highway mileage never happens in LA lol.

I agree that LA highway mileage never happens, it's always stop n go.

Tiny cam in that case, some lift, mostly by rocker ratio of course.

 

[MOPAROFFICIAL]

Let's talk about the camshaft. Here we don't necessarily need to pull WAY back on cam timing and run a little weenie cam. After all we are talking about a musclecar and in this case a 340. I know a solid FT cam up to 250 @ .050" with .560" lift on a 112 LSA can pull down a solid 19MPG if the carb and ignition are spot on. I would use EDM lifters here as well. You cannot beat a solid flat tappet for stone axe reliability /cost/performance. A word about solid rollers here as I know some of you would choose them. I would not as I do not trust them in MY engine that I am going to drive hundreds of KM's in single 3-4hr trips. I will gladly give up the 20-25 hp a roller might give me in exchange for not trashing my engine and leaving me on the side of the road at some point. So. what about hydraulic rollers you say? Well they aren't going to give me the RPM capability of a solid and this 340 will easily make power past their limits of about 6700. Besides I hate hydraulics in a muscle car. J.Rob

On lifters..The thing is, you argue a little ways outside of what we are talking about. Hyd rollers will go the distance. 6700, that is high for them..though they do it...its just that I dont believe that in this 'quest for mileage' one would need to turn that much rpm. Low psi solid roller can hang in there. I put 3hr road trips on mine many times occasional 5-hour trip to Fresno. Quality parts count for sonething. however I'm not going to argue your choice of lifter, that's your right.You're entitled to it and I'm not necessarily against it ,solid flat, i just don't believe theyd be any issue if app'd / spec'd correctly.
Longevity accounts for something too, 6.2 rod helps, ...but not if the rpm eats that up...the wear/friction comes back.
I gotta keep reading the rest, didnt wanna lose my thought. I like where you're going though, but that cam...hmm ...think that will last long? I had a nice [email protected] .573 110...
Fast.

 

[T56MaxTorq]

If the RPMs are kept high enough that *shouldn't* be a problem. With a high-overlap cam what happens during part-throttle low-load situations (below the effective RPM the cam is meant to work at) is exhaust gases get pulled back into the intake manifold because the pressure in the intake is always at least slightly lower than in the exhaust; unburned fuel gets spewed out the exhaust because of misfiring and incomplete cylinder filling which is caused by the exhaust gases diluting the intake charge, like uncontrolled EGR basically. At WOT or heavy load things change completely, as the RPMs get into the "tuned" range of the intake, cam and exhaust headers there is the vacuum on the exhaust side which pulls extra intake charge into the cylinders (we know it as scavenging).

So in short if there is any vacuum in the intake from the throttle plates being anything but wide open the concern is for exhaust going into the intake, not intake charge flowing into the exhaust. Of course I'm sure there are exceptions and this is a big generalization, and I'm not trying to be a know-it-all just adding to the discussion.

Yeah exactly, fuel is more-or-less bypassed during the whole process of having larger overlap until you can reach that pressure threshold. That was a great explanation, thank you.

I think the real issue here is getting a 450hp engine to pump out an efficient 50 hp at low, highway rpm. To take higher advantage of any scavenging effects and to allow for a smaller cam - Maybe Rhodes lifters would help. Any cam will have to be matched with the highest quality headers, intake, port match, chain tensioner, and a really really good tune

 

[MOPAROFFICIAL]

Wouldn't it be nice to get our old 60's classics up to 30 mpg like the modern muscle cars?

This is an interesting question. Given your car is current state, how about a lot of our cars current state of tune or performance ... would you even want to daily drive them?
I eventually get sick of rowing gears in stoo in go...no ac...lol and every mfr wants to test you, no matter what they drive...fkn people...
..yeah how about these people? The ones in the priuses? Lane sweeps,cut you off out of nowhere...the ones you toss large coke into their open window and begin threatening their life, huh?
The more i drive my 1967 Plymouth...the more frequent almost getting run into or in an accident occurs. I got hit coming home from a car show that was 3 miles away.

So say it got 30 miles per gallon, would you drive it that much more and put it out there to be susceptible to some jerk off running into it? Its a tough question, i know weve all been there....hair raising...top blowing pissed.
Also who builds a muscle car and then complains about gas mileage in the 1st place. Im at a loss.

 

[moper]

The weight and mph came out to 470-ish. And it idles like a kitten. Why 2k? How the hell do I know. It’s not my car. In fact it’s probably been sitting for 2-3 years if Facebook is a solid indicator. Point is, this is nothing new. And certainly not anything special. Just good matching of parts and good tuning. Plus I’d prefer a 422 at 470+ and big torque off idle than a 480+ 340. Btw, I did one of those with iron beads and a hydraulic cam 5-6 years before the 422. Nothing new or special my friend. High quality machining and matched parts. Oh, and my power numbers are all from weight and mph. Not dyno. So like full exhaust, air cleaner, actual corner station gasoline... etc etc.

 

[rumblefish360]

The biggest thing to creating power is a nice easy path for air in & air out. A small cam will carry well.

Engine masters did a test with a 372 cube Chevy and a Hyd. roller, ported heads AG etc.... the result with the small cam was 477 HP. OK, your gonna day they had open headers. Correct! However your own exhaust system should flow as close to possible if not dead exact. And that goes for everything else they do on the show. Ignition, good fuel, free flowing intake and exhaust. Etc.

Below is the same cam EM used on there Chevy mill but only for my wife’s .030/360. It has more lift. And it works really well with the ported heads. The 3.55 gears? Not so mileage friendly at 70mph.

Someone mentioned Rhoads Lifters. I have used these before and there “ticking” being to loud is over rated IMO or to many pansies have overly sensitive ears. I have used these with very good results on single pattern cams, intake side use only, regular lifter on the exhaust. Like a split pattern cam until 3K. On Cams a little to large for the application on hand.
(Think spare parts build, as little money involved as possible.)

I see no reason why they could t help but at the same time I don’t think there the “Magic” lifter and the right cam should be selected first. I guess someone could try to add them in later for a comparison?

Use of these lifters on both sides of the cam can help make for a broader power band stretching the flexibility of the vehicle. That’s what I found out with my first use of them.

 

[famous bob]

That's impressive but doubt it makes 500 HP. Why less than 2k in miles a year? One of the main reasons I started this was because many people are deterred from driving their pride an joy because of the abysmal mileage. J.Rob

I haven`t checked it exactly. but my 440/505 w/ fuel inj. gets better that 8 mpg !,

 

[evil66]

This might sound like a stupid question but can someone clarify for me which gallon measurement we are talking about,i believe there is one that is bigger than the other. Imperial vs US liquid gallon.
I come from the other side of the world where we use litres and kilometres.

 

[4spdragtop]

Our side does too lol

This might sound like a stupid question but can someone clarify for me which gallon measurement we are talking about,i believe there is one that is bigger than the other. Imperial vs us liquid gallon.
I come from the other side of the world where we use litres and kilometres.

 

[stixx]

This might sound like a stupid question but can someone clarify for me which gallon measurement we are talking about

Sure this is no stupid question... it can get a bit confusing with all the different units worldwide. I am calculating liters per kilometer myself

The US gallon is 3.875 liters while the imperial gallon (UK) is a bit bigger at 4.546 liters (or litres to make it even more complicated).
And around this thread all numbers were given as miles to the US gallon... famous bob who posted last is happy to burn 30L per 100 km. No pun intended!

 

[evil66]

Thanks for clarifying that. I think i had better keep watching this thread because it looks like i am only getting about 11mpg (US) from my 408 W2 combo. I suppose the 3.9 gears and converter probably dont help too much but im sure it could be improved.
I have bought an afr gauge to try and get it more economical when cruising and am interested in what RAMM has to say about timing and if i should be using vacuum advance when cruising as i currently run an msd dizzy with no vacuum advance.

Sure this is no stupid question... it can get a bit confusing with all the different units worldwide. I am calculating liters per kilometer myself

The US gallon is 3.875 liters while the imperial gallon (UK) is a bit bigger at 4.546 liters (or litres to make it even more complicated).
And around this thread all numbers were given as miles to the US gallon... famous bob who posted last is happy to burn 30L per 100 km. No pun intended!

 

[mderoy340]

Thanks for clarifying that. I think i had better keep watching this thread because it looks like i am only getting about 11mpg (US) from my 408 W2 combo. I suppose the 3.9 gears and converter probably dont help too much but im sure it could be improved.
I have bought an afr gauge to try and get it more economical when cruising and am interested in what RAMM has to say about timing and if i should be using vacuum advance when cruising as i currently run an msd dizzy with no vacuum advance.

Vacuum advance will improve the cruise mpg with a properly jetted carb. There are several threads about ignition curve setups.

 

[rumblefish360]

This might sound like a stupid question but can someone clarify for me which gallon measurement we are talking about,i believe there is one that is bigger than the other. Imperial vs US liquid gallon.
I come from the other side of the world where we use litres and kilometres.

When I read these threads on mileage, I try to remember to take note of where the poster is located. It is frustrating when there location under there screen name isn’t properly listed. Some fellas I know are in the U.S., some I know ware in Canada or NZ or ....

Thanks for clarifying that. I think i had better keep watching this thread because it looks like i am only getting about 11mpg (US) from my 408 W2 combo. I suppose the 3.9 gears and converter probably dont help too much but im sure it could be improved.
I have bought an afr gauge to try and get it more economical when cruising and am interested in what RAMM has to say about timing and if i should be using vacuum advance when cruising as i currently run an msd dizzy with no vacuum advance.

Well! Your headed in the right direction with that air fuel gauge. A good & wise move on many fronts. The addition of the vacuum advance will add a few miles to the gallon. The engine will be happier.

What are the sizes of the;

Tires
Cam
Carb
Engine
Stall of the converter?

As these are key/contributing factors.

 

[T56MaxTorq]

The biggest thing anyone can do to improve mileage and efficiency is a tune up and changing your driving habits - going the speed limit most importantly.

I’d only trust GPS for distance. Not an imperfect speedometer and tire size.

And what do we do about all the different fuel blends and grades? E-free, E-10, E-15, winter blend, summer blend. Not to mention all the different fuels internationally. I run E-85 and my fuel mileage sucks! It’s pretty obvious as to why - less BTU. So many more variables to list. I think a big takeaway on discussions about fuel mileage is that when someone mentions their fuel mileage - how do you believe them? X miles per gallon is useless info unless you’ve used GPS for mileage and measured the fuel going out accurately.

 

[YY1]

I'm not sure how, but I could not register for the site without a location.

Not sure how others have that as blank.

 

[rumblefish360]

I'm not sure how, but I could not register for the site without a location.

Not sure how others have that as blank.

You can have a choice for it to been seen under your name or not. There is a way to change your “Fl” to nothing or something personal or funny.

I was poking around yesterday and couldn’t find it.

The biggest thing anyone can do to improve mileage and efficiency is a tune up and changing your driving habits - going the speed limit most importantly.

I’d only trust GPS for distance. Not an imperfect speedometer and tire size.

And what do we do about all the different fuel blends and grades? E-free, E-10, E-15, winter blend, summer blend. Not to mention all the different fuels internationally. I run E-85 and my fuel mileage sucks! It’s pretty obvious as to why - less BTU. So many more variables to list. I think a big takeaway on discussions about fuel mileage is that when someone mentions their fuel mileage - how do you believe them? X miles per gallon is useless info unless you’ve used GPS for mileage and measured the fuel going out accurately.

I think fuel blend (gas only) has an effect but is largely over rated but yet noticeable though not on a huge scale. Like a 3/4/5 MPG drop.

RAMM & others have outlined the basics. The true trick is actually nailing it.

 

[YY1]

I've played around with gas from different stations/brands a fair amount in the past, and somewhat recently after noticing my daily driver- 2015 Renegade 1.4T/6 speed manual got 1-3 MPG average better using (gasp) circle K 87 oct gas over three tanks on the same work-home circuit compared to racetrac. Both are generic.

In the past I noted that my 5.9 didn't care at all which 87 octane gas was used.

My 2.4L 5 speed manual 2003 P/T cruiser got 1-2 MPG better using Racetrac 87 vs Walmart/Murphy or about the difference of the 3c per gallon price difference.

I also noted that the 5.9 ran no different and got no better MPG on 89 vs 87 octane from the same station over at least three tanks.

I try to average all my testing over three full tanks.

That same 5.9 showed only marginal improvement with pinging under WOT (which is what I was actually testing for but recorded MPG as well) and no improvement in MPG on 93 octane vs 89 or 87.

 

[MOPAROFFICIAL]

Toss some fuel system cleaner, carb/injector cleaner if you want to squeeze 1-2 more mpg out your car.

 

[AJ/FormS]

Cruise advance is very important. But more is not always better.
At steady-state cruise rpm, the engine wants a ton of advance, until it wants not one degree more. With an unmodded Vcan in a factory D I'm pretty sure it would be almost impossible to give a high-compression engine, too much; even up to a cruise-rpm of 2800/3000.......... unless you are one of those guys who insists on running all-in-timing at 2800 or less.... lol..... even then, I suspect it could use more.
However, chasing the perfect cruise-timing is kindof a diminishing return. Your engine could plateau at some mpg with say 48/52* timing, and not show any better mpg with any more timing.
On the flip-side; if you are cruising at 2200 rpm with 25* advance and no Vcan , well, .............. you are leaving a lot under the table. My Eddie headed 10.9Scr 367 running at 205*F,likes mid to hi 50s there, being just on the plateau, with up to 63* showing very little change.I don't know that an iron-headed 360 would need/want/ or accept, that much; I suspect not.
At 2200rpm, the factory V-can D would be hard pressed to deliver more than 40/42 with 14* initial.

 

[ir3333]

I would think the airgap style intake would hurt mileage.