Performance mixed with fuel economy!?

[rumblefish360]

I was about to suggest a TQ. But…. There not always easy to find a good one for use. It is an unknown if the OP is ready for a TQ rebuilding and parts search for tuning parts.

 

[318willrun]

I'm attempting to do this myself. I've set goals. 20 mpg, cruise at highway speeds without issue (70 mph) and relaxing, and run a 13.99. I'm using a 904, 2.94 gears, and a 318 magnum. If I achieve it all is yet to be seen, still working on the build

 

[MopaR&D]

I outlined a performance+gas mileage 318 build a while ago I may build some day...

Get the compression up in the mid-to-high 9s. Run Magnum heads or something with closed chambers, iirc KB flat-tops in a 318 with Eddy heads puts compression around 9.7:1 and you'd have good quench. The key there is you can then run a leaner cruise mixture before getting into misfires and hesitation. And with that compression and good quench you might be able to run regular gas especially if the heads are aluminum.

Put a good dual-plane on top but not an Air-Gap those are too inconsistent with temperature and usually run too cold for efficient part-throttle fuel vaporization. And either an Edelbrock or Street Demon carb in the 600cfm-range.

1-5/8" headers into 2-1/4" or 2-1/2" duals... tuned exhaust helps part-throttle efficiency and MPG.

Run a good MSD-type ignition system to ensure as complete a burn as possible.

Lastly hook it up to a manual transmission of some sort, our old-school autos suck a lot of power. Whether OD or not try to set it up with a top gear final drive ratio no higher (numerically) than 3.23.

With that complete setup in an A-body I'd see 20 MPG would be a piece of cake. I had an '88 M-body with a roller-cam 318; after converting to 4-bbl, duals, ditching lean-burn computer and adding MSD box, and swapping to 3.08 gears in an 8-1/4" rear end I was still averaging around 20 MPG and that car weighed at least 3800 lbs. Acceleration was no longer a "floor it and pray you don't get rear-ended by a semi while merging onto the freeway" affair, about enough to keep up with modern traffic lmao.

 

[Steve Cotter]

YY1- the vin starts BH29P9B, so it is a 340 car
318 WR- I prefer spaghetti also, am watching your challenge
Guys, thanks again; I don't want a hotrod, just a nice cruiser, I want to be able to take the grandkids for a ride and not make their parents worry. BUT the occasional burn out is still required. Therefore, I'm leaning towards a 360 with magnum heads, a mild stock type cam, and the 4-speed manual OD gearbox.
P.S. Just drove by our local gas station: 4.099 for regular, 4.999 for premium!

 

[318willrun]

318 WR- I prefer spaghetti also,

^^ ^^^

 

[RustyRatRod]

The compression is really a big deal. Normally, Chrysler engines of this era blueprint down into the 7s. They are never actually as high as they are rated. Never. If you can get compression to somewhere between 8.8 - 9:1, that's really the sweet spot for MPG and performance mixed. Ant more and the risk for detonation during heat soak is there. Any less and mileage and performance take a hit.

 

[MopaR&D]

The compression is really a big deal. Normally, Chrysler engines of this era blueprint down into the 7s. They are never actually as high as they are rated. Never. If you can get compression to somewhere between 8.8 - 9:1, that's really the sweet spot for MPG and performance mixed. Ant more and the risk for detonation during heat soak is there. Any less and mileage and performance take a hit.

The rough-cast open chamber heads sure don't help either. The 360 in my truck is right around 8:1 with stock heads and it'll ping with more than about 34 degrees of total advance at WOT. Whereas my Duster's 360 is at 9:1 but has Edelbrock heads (the quasi-open-chamber ones but aluminum and with much better surface finish), max power timing is 40 degrees (confirmed on a chassis dyno) and I've never once heard it ping.

 

[Rat Bastid]

The rough-cast open chamber heads sure don't help either. The 360 in my truck is right around 8:1 with stock heads and it'll ping with more than about 34 degrees of total advance at WOT. Whereas my Duster's 360 is at 9:1 but has Edelbrock heads (the quasi-open-chamber ones but aluminum and with much better surface finish), max power timing is 40 degrees (confirmed on a chassis dyno) and I've never once heard it ping.

After years of screwing with this stuff, I can say unequivocally that the surface finish of the combustion chamber has zero effect on detonation or detonation resistance. In fact, I can (and do) suggest that you polish the chambers to get them to equal size and then use a burr finish on them.

 

[YY1]

Magnum 5.2 and 5.9 are pretty spot on at their OEM rated compression, and apparently the roller LA versions are pretty dang close as well.

 

[66fs]

doesnt matter much what the criteria is, if he wants 300 or 500 hp
a 360 making a certain amount of hp will always be more streetable then a 318, or even a 340 making the same hp

especially since he has the 360 allready

Well 300 hp is a piece of cake with any small block Mopar. I have never swapped a 360, in favor of a 273, 318, or 340, let alone think of one as the only high performance option. But I do agree to use what you have. Unfortunately his 360 is of unknown condition. With 360 heads, Edelbrock carb, 4 barrel intake, dual exhaust and a cam in the 268 duration ball park any small block will easily do all that he is looking for. Especially with 3.91 gears and the 833 O/D manual trans. First gear gives a torque multiplication of 3.91 x 3.09 = 12.08 and a high gear equivalent of 3.91 x .73 = 2.85. Even my 273 would spin the tires through 1st and 2nd with 4.10 gears.

 

[Oldmanmopar]

2005 single wheel 3500 6 spd. cummins I bought new . It reminds Me of the Torque of my old 440 4 spd. R/T. It gets anywhere from 20 up to 30 mpg depending on how you drive. Since I bought it we have been in almost every state towing a race car trailer. It now has almost 290,000 miles on it We also have the identical truck but a dual wheel. It gets only 15-20 mpg but it has twice the power after serious up grades. A little over 100,000 miles We use it for very heavy towing.

Diesels are the way to go and can be run on almost anything Home heating oil, vegetable oil and mixes, When my wife and I go to my daughters we always take the truck. 2 1/2 hour drive an the fuel needle barely moves. Our Explorer uses a 1/2 tank of gas.

The single compared to the dual wheel is this. The miles to empty readout on the overhead console when filled reads somewhere around 360 -380 on the dual wheel truck. The single wheel truck reads 620 - 640. We cannot figure it out but we use that truck due to its mileage on fuel all the time now.

The only thing I can contribute to this is since new this truck has had a tuner and has been on "Crazy larry"since. It smokes black so bad I pity the people behind me on a hill. The one day I was at an intersection on a 4 laner and when I took off the lady next to me had her window open and when I looked back she got out of her car and let the smoke clear from inside

Long story short . Power and Mileage, Buy a Diesel. To have fun and show off like I like to do , Buy a V8 gas and run race fuel mixed with Methanol or Nitro Methane and go a quarter mile at a time. LOL

 

[YY1]

If you understand gross HP vs net HP 300 is really easy as the 5.9 Magnum is dang near 300 from the factory.

 

[MopaR&D]

After years of screwing with this stuff, I can say unequivocally that the surface finish of the combustion chamber has zero effect on detonation or detonation resistance. In fact, I can (and do) suggest that you polish the chambers to get them to equal size and then use a burr finish on them.

Interesting, guess I was thinking about potential hot spots but typical open-chamber LA heads don't really have any pointy edges sticking out (compared to say a 302 318 head). What is the benefit of the burr finish, does it help improve mixing of the intake charge during the compression stroke?

My understanding is aluminum heads are more detonation-resistance because the much faster heat transfer makes the combustion chamber surface "cooler" between power cycles and doesn't transfer as much heat into the intake charge as the piston comes up on the compression stroke. But you don't actually lose any combustion efficiency like the old myth claims because there simply isn't enough time in a power stroke above about 2200 RPM to allow any real amount of heat transfer to take place while the mixture is burning. I just figured the smoother and more consistent machined surface finish aided in minimizing heat transfer partly due to the *slightly* reduced surface area.

 

[MopaR&D]

If you understand gross HP vs net HP 300 is really easy as the 5.9 Magnum is dang near 300 from the factory.

The old MP 300hp Magnum crate engine was essentially a stock 5.9L with a 4-bbl carb intake, everything else is stock including the cam iirc.

 

[diymirage]

Well 300 hp is a piece of cake with any small block Mopar. I have never swapped a 360, in favor of a 273, 318, or 340, let alone think of one as the only high performance option. But I do agree to use what you have. Unfortunately his 360 is of unknown condition. With 360 heads, Edelbrock carb, 4 barrel intake, dual exhaust and a cam in the 268 duration ball park any small block will easily do all that he is looking for. Especially with 3.91 gears and the 833 O/D manual trans. First gear gives a torque multiplication of 3.91 x 3.09 = 12.08 and a high gear equivalent of 3.91 x .73 = 2.85. Even my 273 would spin the tires through 1st and 2nd.

But we're not talking replacing a good running engine, we're basically talking starting from scratch

 

[YY1]

The old MP 300hp Magnum crate engine was essentially a stock 5.9L with a 4-bbl carb intake, everything else is stock including the cam iirc.

That's where I was goin'

 

[66fs]

But we're not talking replacing a good running engine, we're basically talking starting from scratch

True, I am all about using what you have or get your hands on. As far as I'm concerned they are about equal if built the same. I personally prefer the others before the 360. Hopefully there is not much to getting his 360 going. As my grandfather used to say, "If you have compression, spark at the right time, and fuel it will run".

 

[AJ/FormS]

Trying to stay with the LA engine to keep the 340 hope alive.
Forgot to mention that I was planning on swapping to a 4 speed also; then I could use the much maligned OD manual. Upper teens for mileage is tolerable, I want to drive the wheels off it in retirement (12 months left of 12 hour rotating shifts!).

I have everything you need, and a recipe. If I can ever get across the border without being vaxxed, I may be heading for Virginia in spring. Pm me if interested.