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/van’s 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

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.

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

Four cyl or turbo four with manual transmission has a better chance of improved fe.

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.

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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Hope that covers it.

If the plan is to go 80 mph in a full size van, the fe is going to suck, full stop, end of story.

Agreed, slow down to 60mph and you’ll have better mileage from the beginning before all the modding...

Internal engine mods are literally the last place to look for efficiency gains.

My 2 cents:

Going larger is more likely to hurt economy than to improve it. Building for low end torque (generally speaking) means both that you're going to be able to put more load on the engine before downshifting, but also that you're going to be running at a lower percent load, all else equal. Lower load = worse economy.

I agree with others, you need to carefully balance engine power with gearing such that you're around 75% loaded at your desired cruising speed. Every engine has a peak BSFC, and there's an ideal power output for peak economy. For this reason there's also an ideal engine output for your needs. Maybe it's a 3L engine at 3,000rpm, and maybe it's a 6L at 1,500rpm. It's really hard to say without having driven your vehicle and knowing whether the engine is over- or under-loaded, and whether your target RPM is going to be below peak efficiency and start to hurt economy.

One thing you can say for sure is that, all else equal, a larger engine has more parasitic losses. So, going bigger is only a good idea if everything else lines up perfectly.

Adding a second overdrive to reduce RPM will also increase parasitic losses. I'd probably start by trying to cut those, rather than add to them. Get roller cams, minimize brake drag, synthetic fluids, reduce accessory load, do your aerodynamic optimizations and weight reductions. Maybe after that your existing engine isn't loaded enough, so decrease the final drive to reduce RPM.

Another alternative if you're feeling really adventurous is to de-stroke the motor, which will both move peak BSFC up the rev range *and* cut down on friction losses, since piston speed will be lower. Stroking it combined with a taller rear end may also have the desired effect.

Here's a real world example:

I'm currently in the process of replacing my 1.0L Honda engine with a 2.4L. With the existing 1.0, peak efficiency is around 2000rpm. At 55mph in 5th gear it turns around 2000rpm at 75% load. At this speed I can get 100mpg on a flat road. It's almost perfectly optimized for those conditions.

However, if I wanted to drive at 75mph instead, it's way outside of peak efficiency - spinning too fast, and there isn't enough reserve power for me to gear it taller. Likewise, if I'm climbing a hill (and I live in a mountainous state) I have to downshift, which also hurts efficiency. Normally the hybrid system adds torque with virtually no penalty for the periods where I'm climbing hills, but without it the ideal engine size for my car in the environment it's used is probably a little bigger than 1.0L - maybe 1.2-1.5L. Finding the correct balance of all these factors is a moving target.

The 2.4L engine I'm installing is mostly for fun, but I'm still doing my best to make it efficient. I'm gearing it extremely tall to hopefully get load up, though this will be at the expense of often operating *below* its peak efficient RPM. I suspect it will do worse than the 1.0L engine on flat ground, but might do nearly as well or even a little better if combined with engine-off coasting when driving through mountains and/or at higher speeds.

Efficiency improvements to the 2.4L include significantly reducing rotating mass, helping it to warm up more quickly, deleting accessories where possible, deletion of balance shafts to cut down on parasitic drag, and playing with a lean burn tune to get load up during level ground cruising. I don't think I can out-engineer Honda when it comes to camshafts, stroke, cam angles and that sort of thing. I expect an efficiency loss overall, but I'm trying to minimize it while gaining 400% more horsepower for some laughs.

I forgot why the mission statement is what it is but if it has to be an 80 mph van it would be cheaper and easier to start with a Transport with the 3.8; owners claim 30 mpg at reasonable speeds and I think that's believable.

HP & TQ necessary to move a 6k lb van of X-sq ft frontal area at 60-mph in Direct at sea level. Level ground and no wind.

That’s a basic calculation. Starting point. Dead minimum.

(No, I don’t think you “have it”)

As before, plenty tried it in the 1970s. I’m guessing you weren’t there.

If you're going to do that much work to your engine, you might as well bump compression too to increase thermal efficiency. If you still want to run 87 octane fuel, you can probably set up your engine to do that by doing various things like using colder plugs, retarding timing, etc... Or if your area has e85 you can use that and not worry about all that. The benefits of raising compression start to diminish once you get to about 12.0:1 CR.

You will also need to do some drastic aero mods to your van if you want a "super mpg" vehicle at highway speeds.

Chevy has already did all the work you are thinking is hidden for some reason in a 350 small block designed in the 1950s they tweaked it all the way into the 90s and made it better but completely leapfrogged it with the LS motors. Go find one of the millions of good 5.3s in the junkyard pay $1500 for it, get a standalone computer and harness to run it, and be done. You still will be lucky to get 20 mpg at 65, 16-17 at 80, but it will be a good 20% better than anything you will be spending 3 times as much building designed in the 50's.

Looks like excellent advice.

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You've gotten some good advice. Look for the Caprice wagon thread https://ecomodder.com/forum/showthre...mpg-33961.html. It has a good summary in the first post.

I assume you're attached to the vehicle. My van had a 1600cc flat four, 3/4 ton axles, with sway bars and suspension mods. It got 30 mpg, topped out at 85 and would top the Coast Range at 75, empty.

My idea of a super MPG van would be a Previa with an EV conversion.

Hadn't it been for the sake of emissions certification being a PITA to deal with, I'd be tempted to work around a Cummins 4BT, even if it would involve a conversion to spark ignition just like Cummins did to the CNG/LNG or LPG versions of the 6BT mostly fitted to shuttle buses and some school buses.

This is where I would start for a fuel efficient van build.
 

I have a 2003 Dodge Sprinter. I accidentally won it in an auction for 595 dollars. Didn't run well. A few hundred in parts and my labor and I had a short, low roof van that got 28 mpg on the freeway at 65 mph.

Then we could get into the downsizing vs. downrevving issue, comparing the 2.7L from the Sprinter and a 4BT. When it comes to spark-ignition on the other hand, I'm not so sure if some downsized gasser from Mercedes-Benz cars would fare so well in a Sprinter as they're reported to do in the sedans.

This is to up date this post:

OMG The news just keeps on coming it:

Well after all these years of they saying it cannot be done…I have found proof I was on the right track, or that at least it can be done.

Full sized vans CAN GET 29/30MPG any highway speeds.

THAT blows all the "you cannot get a big box like a van to do 30MPG..."

GM Has TWO models of vans that do just that.

From https://www.dieselplace.com/.../2-8-...press-vans.../

28 Expressvan
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Joined Jun 17, 2018
13 Posts

We are typically running about 7500 lbs GVW in Chicago traffic and also 100 mile runs on the highway. The little motor launches the van quite well, since it has way more bottom end than typical gas v-8's (325 ft lbs @ 1500 rpm, 370 @2000).

This van runs a Turbocharged 2.8 Diesel that makes 360FtLbs @ 2000 and 185 HP @ 3200RPMs, and a 8 speed automatic.

In the city, it drives about the same as the 5.4 E 250 it replaced. On the highway, no trouble merging and accelerating while loaded. It’s no race car, but it’s fine.
Fuel Economy is exceptional when heavily loaded. We run about 20 to 21 mpg city, and holding a steady 66 mph (at 65 it will downshift to 7th) we just got 33.3 mpg in humid 90 weather with A/C on over 60 miles. On open road without trailing a semi, we get a little over 30.

The other one is a 2019 Chevy Express Passenger RWD 3500 155” wheel base custom outfitted running 4.3L V6 with Direct Injection and variable Valve Timing making 298ft-lbs@3,900rpm, and 276hp @ 5,200rpm though a 8 speed automatic.

This large buzz bomb can make 19 City and 29 Highway MPG.

REALLY!

The diesel is closes to my plans for my 383.

Here is the latest update on the van engine build.

The Engine is all figured out and built.

The current question is how to feed her. What kind of intake will work best, especially at my projected low 1500 to 2000RPM operating speeds.

Ever sense I discovered the 3Rd. Gen Camaro site I was sure I wanted to run a TPI intake.

This idea came into question with my switching from a 350 to a 383 and because nearly everyone felt that the TPI was made to work best any 2800 RPMs and that it would not work with my 1500/2000RPMs.

So many were so sure of this “FACT” I was persuaded to buy and plan on using the Van’s TBI on an adapter.

It took some time for a thought to work its self up to the forefront: OMG everyone is saying a TPI peaks at 2800RPMs….SO DOES an standard Cam used in these cars!!!
It’s NOT the intake it’s the cam….

So a new research was done and I found Ken Schueneman at FIRST Performance LLC a person whom REALLY knows the TPI intakes. And he agreed with my findings of the cam making the Torque Peak at 2800RPMs not the intake.

So I had a long talk with Ken, we concluded that with my main interest is LOW RPM operation and plan of gearing my van to run between 1500 and 2000 at highway speeds like 70 to 85MPH and my hope and belief that doing such will very likely to give me 20MPG Plus and PERHAPS even reach 30MPG on level roads with no wind.

I am very much aware in other conitions I will not get those MPG, BUT then I will have the power to clime those mountians at any speed I want to run, and if slowed down be able to regain that speed again thanks to having the real power a large engine gives. I believe it is know as power to wheight ratio.

Taking how my engine is built, the specs allow all the above and that everything does indeed lean towards making my goals happen and all of this: the 193 Stock heads, the cam, the crank and rods, my engine will almost never run over 5000RPMs.
Ken said that a stock TPI system will match my engine very well. It will majorly improve its performance over the performer intake.

Now the major questions are what PCM: Do I modify my current Vans PCM to run the injectors as a dual batch injection system…and do I really need the Dynamic EFI add in board or can I reach my tuning goals the old fashion way with a Tunercat and have chips burned….?

OR run a second PCM more suited to allow better tuning and run the van’s PCM piggy back to operate the 4L60E transmission?

After all I have read and Ken has done we concluded how the fuel is fed to the engine, either TBI, 87 TPI all at once, later dual batched (4 +4) or even sequential has shown very little difference in MPG, Ken has seen the most improvements with tight ING timing.

He has not done any work with Lean Burn Highway Modes and was not a fan of my idea of using EGR to help maximize MPG but we did agree I will most likely get the best use of EGR with his external EGR add on system and to close off the factory system.

One last question will be MAF VS MAP. This will depend on the fuel system’s PCM. I have long leaned towards MAF but it can be a bit harder to install and sadly the older MAF sensors seem to have a poor history. My research has shown MAF is a little more sensitive to engine running…

It is nice to at last be able to use parts I bought around the year of 2000 and to finish an engine I started in 2005.

The Research continues….