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

[RAMM]

I have a 410 stroker in my aussie charger. it weighs around 3100lbs . On a recent trip to our annual chryslers on the murray meeting 550 kls (350miles) I got 21 mpg going down and 22mpg comming back sitting on a comfortable 120 kph (about 75 mph) My car has a 410 with 236 @ 50 thou roller hyd cam with edelbrock heads 800 avs carb five speed manual box and 3.91 diff ratio. The best thing I ever bought for the car was the air fuel ratio guage that has enabiled me to tune this car so good. It has run a best of 11.4 down the qtr but yes I do lighten it by taking bumpers,sway bars and passenger seat out to run these times. With the five speed and 28 inch tyres it cruises at 110kph(70mph) @ 2400rpm. Just in a niece torque curve and very pleasant drive! I know our imperial gallon is slightly larger than your US gallon but I think that is really impressive considering my 351 clevelands in the early eighties could do no better than 15mpg even with there 2.76 diff ratios in standard form. Hell even back in the seventies my 340 charger with sic pack and 3.91 diff would get 21mpg it is just hard to not use that right pedal too much but with all the HWY Patrol Cars on our road networks and the large fines and pionts systems it is a big deterrent to keep the speeds down compared to the early seventies.

Now this is what I'm talking about for the most part. I highlighted in bold the most important part of your message which is what I'm going to talk about soon.

Overall though you have a well sorted combo to run 11.4 and achieve very good mileage thankyou for the contribution. The wideband and a really good timing light and understanding both of them will get us even further. J.Rob

 

[RAMM]

My 340 gets about 80 miles out of a 10 gallon tank...and uses a 1/2 litre of oil at the same time, I would aim for something better than that with your build and I’m sure you’ll be successful...

View attachment 1715327205

At 8mpg I hope you have more smiles/gallon because of all the power or you just can't keep your foot out of it. Oh BTW ditch those Total Seal Gapless tops and let us know if the mileage change. J.Rob

 

[67autocross]

The rings are coming out of the 340 in a few weeks... it might even get put back on the Dyno the same day as my my magnum RAMM replica build... just waiting on the oil pan for the last month and it’s done.

 

[RAMM]

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.

And this is exactly why I felt the timing was right to start this thread. Considering you are Canadian and the price per litre of fuel is expected to keep rising for the summer in part due to the carbon tax--I'd like to see as many carbon spewing Mopars on the road which essentially flips off the Trudeau gvnmt with every gas station they pass. J.Rob

 

[krazykuda]

A lot of you keep missing the 500HP AND 19-20 mpg part. I don't care about stock 318's/340's,360's,383's etc.... that did or could have gotten 20 mpg-ev.en still they would be the exception rather than the rule

Your Dad's bone stock Charger with a 360 had no where near 500 hp.

Oddly enough my father had that exact car when I was a baby, was yours blue with a white vinyl top and interior? lol. J.Rob

I was just pointing out that 18 - 20 MPG in a small block is not impossible....

Sorry we had daily drivers and didn't need 500 HP....


I threw my engine together with spare parts and only had $300 into the engine....

 

[67autocross]

My wife’s 5.0 Mustang coyote pulls down 30 mpg ... I wonder if she would notice if I borrowed the drive train for my Dart...

 

[ir3333]

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

 

[stixx]

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

Could well be RAMM's next iteration on the subject. Same theories apply, just scale them down a bit to arrive at less than 450 - 500 HP.

 

[67autocross]

Okay... so measuring the 500 horsepower part is easy ... but do you have a car you are putting it in to demonstrate the mpg results?

 

[T56MaxTorq]

RAMM, I think if your cam is too large like the 250 you mentioned, you’ll bypass to much fuel during overlap on the highway, and fuel mileage will always suffer.

I think you’d want a mild, high torque cam with the most flat torque curve possible with a higher ring gear.

 

[MopaR&D]

RAMM, I think if your cam is too large like the 250 you mentioned, you’ll bypass to much fuel during overlap on the highway, and fuel mileage will always suffer.

I think you’d want a mild, high torque cam with the most flat torque curve possible with a higher ring gear.

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.

 

[toolmanmike]

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

They can with double overdrives,cylinder cancelling, fuel injection, variable valve timing and the like. Hemi Demon Challengers don't get 30 mpg in drag mode either. More like 3 mpg.

 

[krazykuda]

They run better when they're loose.

Are we talkin' cars or women here???? ^^^^^^

 

[str12-340]

RAMM ; great thread! I'll be following for my Road trip Dart. Thanks for tipping me off...

 

[Krooser]

I vote for a well set-up Quadrajet....

 

[YY1]

Could the OP explain the benefits of his short block selection versus starting with a 5.9 Magnum (or a bored to similar size 5.2)?

I used a "G-Tech" accelerometer to analyze a country road 1/8 mile pass in my 2000 Dakota R/T (stock with 3.92 gear, except cat back duals and a K&N filter system, 4200 pounds with me in it).

The HP used for that balls to the wall run according to the device was "78"
based on that I'm not sure 80HP is required to keep a 3200# A body up with traffic.

With the factory 46RE O/D, that truck gets 17-18 on the highway, and about 13 average in mixed driving, mostly city and semi-rural. At 50 MPH it gets 23.
When it was my daily, it got 14.2 average.

 

[rumblefish360]

Considering the older less efficient trans and non lock up converter, it’ll take a little more power to run at any given speed and so hence RAMM did state, manual transmission which I like best myself. Unless it is rush hour traffic for 2 hours each way. Then I’ll take the slush box thank you very much.

 

[RAMM]

Sorry fellas, I will get back to this but my excuse is 12 hr night shift and being on my long stretch right now. Might be a couple of days. It is starting to get interesting though. Free discussion of ideas is important especially in this political climate. J.Rob

p.s. NO I do not think 30mpg is possible with an old school LA.

 

[moper]

What if I told you an LA engine that was carb'd , solid flat tappet, vac distributor going down the highway @ 2800-3200 rpm could make 450-500HP and still knock down 18-20 mpg?

I'd tell you I did it around 2008. Engine has 20K on it, 4" stroke, ported iron 596 heads, and a hydraulic flat tappet under .530" lift. Oh, and it's in a 3800lbs E body... Not an A body. It's got about 20K miles on it now.

 

[nm9stheham]

The heads don't have have to be iron but I happen to believe the iron head CAN be more efficient than aluminum because of thermal efficiency. You have less energy in BTU's escaping the combustion chamber where you want them to expand the Nitrogen in the air/fuel charge.

FWIW.... My comments here are not directed at anyone in particular. I just want to comment on the idea above as it shows up from time to time, and is an interesting question IMHO.

Here is one thing to know: Power extraction can't be predicted from absolute temperature in the chamber at the start of the combustion process, or even during the power stroke. Hotter temps at the start of the cycle may intuitively make one think that the pressure is also higher all through the burn and power cycle (hence more torque/power), but it is the burn process that dictates the pressure profile which sets power output. In fact, there is direct test info that says that a higher charge temperature in the cylinder can actually result in slowing of the combustion process and a lowering of peak cylinder pressures. So that is the problem with trying to equate head temps to power output: it misses the effects of the most critical part of the situation: the actual burn process.

And looking at just the heat flow through the heads to the coolant is only a partial picture of the direct heat losses. Since the exhaust heat loss and cooling system loss are comparable in magnitude, the cooling system heat outflow alone can't be used to reach any valid conclusions; you have to look at the whole heat outflow picture. A slower or delayed burn ends up with a hotter exhaust, and that jives with the lower output of a delayed burn; think of the hot exhaust from too much ignition timing retard.

For hot-rodders IMHO, the best answers so far comes from actual testing that has been done with AL vs Iron heads on the same engine. So far from the very few test articles I have found, the 2 are a wash.

BTW, here is that paper.... from Oak Ridge Labs.... you know, the atomic energy guys. This one is a headache-maker, and takes a lot of time to understand and get anything out of; I'm getting ready to hit it for a 3rd time, and still have a lot details to digest. Figures 10 and 11 illustrate the slower pressure profile and the slower heat release rate with increasing intake charge temps.
https://www.sciencedirect.com/science/article/pii/S0010218016303650

 

[ir3333]

I'd tell you I did it around 2008. Engine has 20K on it, 4" stroke, ported iron 596 heads, and a hydraulic flat tappet under .530" lift. Oh, and it's in a 3800lbs E body... Not an A body. It's got about 20K miles on it now.

i know a few 408's with stock j heads.Ton's of torque but dreadful mileage.
They are in trucks where the torque is very useful.

 

[RAMM]

I'd tell you I did it around 2008. Engine has 20K on it, 4" stroke, ported iron 596 heads, and a hydraulic flat tappet under .530" lift. Oh, and it's in a 3800lbs E body... Not an A body. It's got about 20K miles on it now.

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

 

[MopaR&D]

i know a few 408's with stock j heads.Ton's of torque but dreadful mileage.
They are in trucks where the torque is very useful.

What's the gearing like on those trucks? I'm curious how the mileage would be if they were turning really slow, like 1500 RPM at cruise with a mild enough cam to keep the cylinders filling well at that speed? A 2000 Durango 5.9 I worked on cruised at barely 2000 RPM on the freeway at 75 MPH with that fat overdrive in the 46RE trans and still had plenty of torque for getting up hills and such.

 

[rumblefish360]

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

LMAO! Tell me About it.

Between the state of tune, carb and ignition, the next mileage getter is your friend overdrive. Figuring where to land the cruise rpm’s (tire size and gear ratio combination) are the final hurdle.

This is the difficult parts since knowing how efficient the engine is without a dyno test can cause a long and expensive search.

Mileage be dammed!
Make mine smiles per mile.

 

[ir3333]

What's the gearing like on those trucks?

3.91 with an overdrive trans.
Comp musclecar replacement cam i think .226 and .234 duration at around .470 lift. Owned by mopar mechanic \ racer with 30 years experience.