Hey guys,

So I've been wondering, what would theoretically make for the most efficient slant? My thought is that there is a trade off between fuel economy and power. I'm wondering what build would be the best of both worlds?

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76 Dodge Aspen
225 Super Six w/ Dutra True Dual Exhaust

http://i1245.photobucket.com/albums/gg5 ... AG0095.jpg
http://www.youtube.com/user/BZuko1?feature=guide

Is the question: Which SL6 combo will make the best "VE"? (Volumetric efficiency )

I think that would probably be the correct way to word it, in the scientific field.... Ok Doc whats the verdict?

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MRO....

Cheap, Fast, Reliable.... Pick 2...

I suppose I should have worded it a little different. What combination of modifications (piston size, camshaft, etc) and parts (i.e exhaust manifolds, carb, EFI, ect) would create the most efficient slant six (most mpg per horsepower) theoretically.

I'm probably dead off but I imagine the trade-off between horsepower and mpg to look something like this.

I'm asking what it would take to reach the peak of that graph, if that makes any sense. Harder to describe what I'm thinking then it is to think it. If it's VE I'm describing them just ignore

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76 Dodge Aspen
225 Super Six w/ Dutra True Dual Exhaust

http://i1245.photobucket.com/albums/gg5 ... AG0095.jpg
http://www.youtube.com/user/BZuko1?feature=guide

yes VE measures how efficiently the engine is operating even with adders or ram-tuning you can go over the 100% mark. Typical slant six in best tune is about 69-70% efficient. add some compression and components that work together it can go up to about 85% in street trim...

Because you can 'bend the rules' (hard to do that with hard physics and math...but there is an art to some things in the auto world)...I can say that your graph would be off since I was able to get a 3400 lb duster to do 24 mpg 100% Higway at about 196HP (estimated from track 1/4 mile)...in a 10:1 compression engine...I wish I had a dyno sheet it would have been interesting to see the VE numbers on the build(probably in the 90% range).

One of the automotive tech teachers here in town always says that good gas mileage is related to your useable torque band, the engine above had a good wide torque band from 1500-5500 rpm...

-D.Idiot

How much money do you want to throw at the problem?

The most efficient would be a picture of a slant on the dash board of a modern FWD four banger, probably from Korea.

Given as light an A-body as possible:

There are a few ways to get there.

170 slant six, 1 bbl, geared to operate at torque peak while at cruise. Manual transmission, moderate cam, good exhaust flow, optimized distributor curve. Operated between 45 and 60 mph. Lower is better.

170 slant six, progressive 2 bbl. then all of the above so that cruise occurs in the primary.

170 slant six, small four barrel, see above.

EFI can deliver good results, but added complexity may become a life long hobby.

Watch EGT's. Avoid detonation. Be meticulous. It would have been interesting to see what a Dart Lite/Feather Duster would have been in an early A-Body, optimised around the 170 engine.

I feel that a small primary progressive or vacuum secondary 2 bbl could be ideal. The problem would be getting one tuned to run appropriately. Very doable though.

It would be very challenging to match the economy of some of the new cars available today.

Just my 2¢

CJ

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Part of Tyrde-Browne Racing

Except this graph shows an increase of HP on a slant does not increase MPG.
I'm just saying this graph shows an 15 HP increase over early stock engines to comparable 18 highway MPG ratings. I've seen numbers show decreasing differential gear (by a matter of one) say 3.25 to 2.23 increases MPG by 5. May I quote this from The Peterson book. Decrease (numerically) your rear gear size, add a turbo to the engine with 4-7 pounds boost, smaller carburetor jet/s. That's a general guideline for any fuel efficient car. Well Agressive_ted's slant does 25 mpg which is comparable to today's cars that are made with super light materials but overloaded with technology just to make the same MPG as cars 30 years ago.

For instance the new mustang; it's like 1/4 bigger than the original 1965 Mustang and it's loaded with plastic and technology that just makes it as heavy as the original if not more. they engine management computer technology allows it to get slight better mpg. Rediculous.

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'73 Scamp (the girlfriend): 225ci super/6 2BBL conversion (Almost done!)
'90 Subaru, wagon (the wife): H4-cyl 2.2L

1977 Mercedes-Benz 300D, 5cyl diesel(For sale!)

New cars are way heavier, for equivalent size. Aero is much better on new cars, though.

My best so far is 25-27 MPG hwy (1100 mile trip) on my '64 Dart with 240 crank HP, 5spd, TBI, and some aero mods (garbage can front spoiler). I am working towards 25 MPG on my '68 Dart with 290 crank HP on 9psi boost. 23 MPG so far, but more aero mods and tming curving in the works. EFI, lockup auto, timing control. I think the '64 Dart body is better than the 68, and a Duster or 2nd gen Barracuda would be best.

It's not about how much peak HP you make, it's how efficient the engine is at cruising speed. I think I can do 25 MPG with 350+ HP on about 10-12 psi boost.

Lou

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Home of Slant6-powered fun machines since 1988

Operating an engine at it's torque peak is not the path to best fuel economy. You're not operating an engine for maximum efficiency you're operating a group of sub systems which together form a car. If you make the engine do less work through aerodynamic improvements, weight reduction and better driving habits you will get better fuel economy without changing the engine at all. If you do want to change the engine for higher efficiency, and you should, have fully optimized spark and fuel delivery. With the technology available for a reasonable price this means port EFI and crank trigger ignition. This will allow a large increase in compression ratio which will further improve engine efficiency. But you know what? After all that work to an F-body you could have saved yourself a lot of time and broken even on the money to just buy a Neon or similar car. The Neon will kick an F-bodies sorry behind in most every performance metric too. Just so you know, a bone stock Neon with a 5-speed will do the 1/4 mile in 16.6 seconds, about 28 MPG city and 36 MPG cruising the highway at 75 MPH.

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Joshua

Aspen76,
Forget max power and do the "torque build" and drive it at peak torque as much as possible. Watch the vacuum gauge and keep it at 16 to 18" as much as possible, recurve the distributor for max punch at peak torque. Don't run the engine too cold either......the slant gets it's best mileage when at temp. The sooner it reaches that point the better mileage you get and that includes short hops! Tune the rear end gear ratio and tire size to match peak torque.

Best mileage and power to date has been with a 2.25" head pipe to 2.5" and a FlowMaster 70 all the way out the back with a square MOPAR tip.

A torque motor makes for a fun ride.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG