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Old 04-10-2019, 11:31 AM   #1 (permalink)
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My ideas of a super MPG Van:

This is a three step plan.

First is a 350 or 383 engine built for LOW RPM operation and MAX torque.

Second using a 80's TPI system.

Third adding a second overdrive transmission behind the stock 4 Speed automatic transmission.

First is the engine: questions come up:

I have searched a dozen times for what I plan on building.

I cannot find any one is doing for what I am going for: IE:

A low rpm 383. My plan is for this motor to spend most of its life running at 1700 RPMs and operate from 500 to 4000. Everyone builds a Hot Rod version.

I am trying to build as much torque as possible using a mild RV TPI Cam, and plan on advancing it 4 degrees. I am much more interested in LOW RPM Torque than house power, Torque is better at low RPMs than HP which is made at higher gas using RPMs.

The combo I want is: Aftermarket 400 crank for a 350. Stock 400 rods so I can keep my KB D shaped pistons. I am aware of the side loading on the bore, one as I do not plan on running over 5000 max, is this major problem?? Is there any piston skirt coating or treatment that can help with this that can be applied to my KB pistons?

Cam will be grounded for RV TPI Operation. Lifters are stock 350 roller lifter set up.

Heads are 1970 early swirl port 192s, and other that major cleanup and 3 angled seats, springs tested and Perfect Circle Street Running (Oiling) valve seals, all rest left stock. I only plan of light grinding to ports to match.

I will also run stock ratio roller tip rocker arms to lower the scuffing of the valves in the guilds.

I plan on feeding this with a 80s Camaro/Corvette TPI running MAF controls. I plan on having the stock Highway Mode turned on until I can get a special add on board to the PCM which allow greater tuning.

Everything is built counter wise to common Hot Rodding standards. Stock heads, no opening the ports, no polishing them, (Everything I have read says the textured surfaces of stock ports HELP low RPM power, polished and opened (larger) ports are for HIGH RPM air flow and HARM lower RPM power) same for the heads. Low RPM cam that will not shift to higher RPM power curves, (the way most cams make more power, move the power curve up the RPM range)

Now we come to the big questions.

One will the improvement in torque add MPG in my appreciation?

Will this torque off set the extra fueling needed to keep this engine running correctly??

Any idea what amount of extra torque this will make over my stock 350?? (Say a stock 350 VS a stock 350 with the 400 crank making a 383??)

So bottom line will this help my car make MPG??

Is it worth the extra cost to convert my 350 to this 383??

Next is the TPI System and only a couple of questions have come up, intake runners/tubes:

I have are the two different runners for my TPI setup, stock tubes and one set of aluminum Siamese pairs with larger bores.


The stock tubes are 1.52 inches, the stock intake manifold is 1.45 (inside) so there is already a slight compression happening, so the aftermarket tubes are 1.62 will they increase this ramming effect or worsen it??


I wonder IF the large runners to the intake might produce more of a ram effect when they hit the stock manifold over the stock smaller tubes.


Could there be an efficiency loss as the air is going to compress and heat up as it does.


Then again that might work better, A) this compression could raise the pressure a little and B ) hot air is supposed to help cause more vaporization of the gasoline?


The casted aluminum Siamese large set has a light sand casting texture where the factory seems slightly smoother.


Also there is the opening between pairs at the face, more like a opened premium four barrel manifold...I wonder what effect that would have??


I would think that will allow cross breathing and perhaps lower the controlled force induction allowing them to share like that.


I would be of the opinion that the relieved port might actually be to benefit larger camshafts but I plan on running a stock or near stock cam.


In theory the slots would provide a smoothing of vacuum across the ports, I assume is a concern when the cam is aggressive and potentially not great for vacuum.


So as I will be using a smaller cam should I have them filled in??


The $64,000 question is will they (the larger tubes)harm or help my MPG running a small cam??


Or will these throw off the whole idea of TUNED port injections air flow at low RPMs??

Last is the Overdrive:

I am thinking that a second overdrive added to a stock 4 speed auto with a OD gear can work and in fact greatly increase a stock car/vans MPG, just by lowing the cruse RPMS from around 2400 RPMs to 1700 RPMs.

This seems to be the best of all worlds, stock gearing until the added Over Drive is engaged the the advantage of super highway gearing.

Your thoughts and knowledge is invited.

Rich

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Old 04-10-2019, 01:42 PM   #2 (permalink)
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It takes so much horsepower to move so much aero drag and rolling resistance at different speeds. So what you need is the best thermal efficiency to make that horsepower. Better yet lower drag so you don't need as much horsepower. In a way the torque is a meaningless number as it is a force without motion. I can put my 200 pounds on a 10' lever and put 2000 ft lbs on a wheel and not move it an inch. Force but no work. Now say I do move a giant van slowly up a hill, I make more torque than a Cummins diesel but moving the van at 12 inches a minute I still am only making a 1/4 horsepower and 2000 ft lbs of torque (I'm just guessing at the HP number). If max economy is the goal I don't see how increasing the size of the engine helps. I would think going the other way would be the way to go and turbos or diesels or both is what improves thermal efficiency. You want it so you are running 3/4 throttle for your cruise speed, not choking down a powerful motor with lots of reserve hp. Torque does help of course in the real world and makes the van more enjoyable to drive, it just isn't going to be a majic bullet in economy.

As far as Chevy motors, do an LS swap and you will be amazed. The LS is so much better than any Chevy motor that came before it and it bolts right in where the 350 was. They are like big block power with small block weight and efficiency.
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Old 04-10-2019, 02:06 PM   #3 (permalink)
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Well first to answer your main point I had a 94 chevy van, swapped in a 350 OLDs, ran good until it lost two rocker studs, my friend who sold me the 350 was out of 350s so we put in a 305 OLDs, OMG what a POS that was, worst MPG and Semis honked for me to get out of the way on hills, in that case big was better.

I know this lower RPM motor will produce less HP and Torque that a higher spinning engine with its power curve up in the RPMs.

This is one reason for the 383, more Torque thanks to the stroke to put a little more torque at say 1500RPMs than I will get with a 350.

I figure to have enough torque so that can pull the Van with out lugging at speed.

Rich
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Old 04-10-2019, 04:23 PM   #4 (permalink)
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Four cyl or turbo four with manual transmission has a better chance of improved fe.
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Old 04-10-2019, 05:35 PM   #5 (permalink)
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Run a roller cam setup.
When GM switched to roller cams in sbc cars they said it was good for +1.5mpg.
It's probably the only +1.5mpg engine mods you can do.
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Old 04-10-2019, 10:39 PM   #6 (permalink)
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The rpm range that matters is for highway. Pulling a load. That, out of OD it is cruising at 60-mph just below peak torque is the operating environment. (Miss this and everything else goes bye-bye)

Lots of guys tried your way in the 1970s. Not good results.

Take the van and get a TARE weight. Real numbers. Driver + max fuel. Then extrapolate our to axle limits. (A van is pretty much a 6,000-lb vehicle when used per design).

Same for tires. Measure the real thing as installed. Not numbers from factory brochure.
Tire rolling height is the first decision. A CRITICAL number if FE matters.

All the ducks have to line up.

I’d investigate what rear gear ratios were available in late 1970s vans. 3.55 and 3.73 were common.

Engine power comes from rpms. Not otherwise.

.

.
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Old 04-10-2019, 11:24 PM   #7 (permalink)
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Quote:
Originally Posted by slowmover View Post
The rpm range that matters is for highway. Pulling a load. That, out of OD it is cruising at 60-mph just below peak torque is the operating environment. (Miss this and everything else goes bye-bye)

And again I am building engine that has a Low RPM range so that when I am going 80 MPH at 1600 RPMs my engine is built for it.

Lots of guys tried your way in the 1970s. Not good results.

They did not have engines built for low RPM operation so was lugging.

Take the van and get a TARE weight. Real numbers. Driver + max fuel. Then extrapolate our to axle limits. (A van is pretty much a 6,000-lb vehicle when used per design).

Same for tires. Measure the real thing as installed. Not numbers from factory brochure.
Tire rolling height is the first decision. A CRITICAL number if FE matters.

My van has a real ground effects skirts that really work.

All the ducks have to line up.

Id investigate what rear gear ratios were available in late 1970s vans. 3.55 and 3.73 were common.

Mine is a 93 and I believe it has 343s.

Engine power comes from rpms. Not otherwise.

Many engines were built for LOW RPMs, OLDs 403, peek torque was at 2000 RPMs, the 80s Caddy 350 2200 RPMs.

.

.
Hope that covers it.
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Old 04-11-2019, 12:18 AM   #8 (permalink)
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If the plan is to go 80 mph in a full size van, the fe is going to suck, full stop, end of story.
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Old 04-11-2019, 04:09 AM   #9 (permalink)
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Agreed, slow down to 60mph and you’ll have better mileage from the beginning before all the modding...
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Old 04-11-2019, 09:13 AM   #10 (permalink)
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Internal engine mods are literally the last place to look for efficiency gains.

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Quote:
Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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