Any MPG Fans here??

[L31MaxExpress]

I get 20 to 21.5 pretty consistently with my 91 RCSB K1500. Its a 350 with a HM290, 3.73's and 265/75-16s. I started with a 97 vortec block and TBI heads with the stock roller cam. I used split ratio roller rockers. 1.6 intake and 1.5 exhaust in an attempt to gain more low end torgue to reduce downshifts in the mountains. I'm running a 180 deg thermostat to keep the fan clutch from engaging as often. I have an edlebrock intake with JBL shorty headers and Y-pipe through a single 3 inch pipe and muffler ending before the rear axle. I wanted to reduce back pressure to reduce pumping loss. I have a 14X4 inch open air filter. I also used the old style intake gaskets to block off the heat exchanger under the intake. I installed the coolant block off plates in these gaskets for the rear coolant passage. My tires are Goodyear dura tracs in load range E and I run them at 85 PSI to reduce rolling resistance. I'm running a custom chip from Harris. I explained to him MPG was the main goal and I would be thrilled if it made 180 HP. I have other trucks for towing and hauling so crazy power isn't important here. I also run Mobil 1 5W-30 along with synthetics in the axles. I replaced the leaf spring bushings and all 4 front control arms along with all steering parts before a 4 wheel alignment. I wanted to run as straight as possible to reduce drag. If the front leaf spring bushing are wore the rear axle can shift to one side allowing the truck to YAW like a forklift. This will plow the wind on one side and create a vacuum on the other. That condition will increase wind drag. I haven't found a smoking gun for MPG just a lot of little improvements to get the mileage up.

The only smoking gun I have found that helps consistently in good weather conditions, flat road or downhill is highway lean cruise.

 

[95burban]

I’m more of a smiles per gallon person myself, but getting good MPG out of a brick is neat.

 

[BeXtreme]

I was the systems engineer for the ERAU electric land speed record team while I was a student there. We started out as the Jet Dragster build team and then transitioned into doing our own land speed record car. The real problem with going fast relates to several factors. You can really break it down into three major components. Aero drag due to the vehicle shape. Aero drag due to the required driving downforce. And rolling resistance.

The first one is pretty easy to determine and is mostly dependent on the overall shape and size of the vehicle. Cd is the coefficient of drag and is specific to the shape of the vehicle(all of the talk of removing mirrors, body kits, sealing windows, etc... will have an effect on the Cd of the vehicle). A is the overall frontal area and is fixed(it can be reduced by having venting that will just redirect the airflow through channels and then to the back). That just leaves the velocity as the only variable. As you can see by the equation, the drag value is equal to those items times 1/2 of the velocity squared. It is an exponential curve and it goes up quickly.
https://x-engineer.org/aerodynamic-drag/

The second part is the big limiter for wheel driven vehicles when you want to go VERY fast. Your speed is steady when the drag is equal to the force being applied by the driven wheels. The driven wheels require a certain amount of force on them pressing down in order for them to be able to apply the force necessary to drive the vehicle forward without slipping. This amount of downward force is usually provided by the weight of the vehicle, but it stops being enough by itself above a certain speed(usually above about 100-120mph). This is compensated for by using a wing shape or aerodynamic shapes to generate additional downforce to be able to keep traction on the tires. As the required force to keep accelerating exponentially increases the faster you go, the required downforce to keep the tires from spinning also increases exponentially. Since downforce creation also induces more drag, it quickly becomes a huge issue.

This can be seen by looking at readily available graphs for lift vs drag. Downforce is just aerodynamic lift being generated in the opposite direction, so L/D curves based on forces vs airspeed are very beneficial in visualizing what is happening. With a wheeled vehicle that is needing to generate MORE downforce as the speed increases compared to an aircraft that only needs to generate a fixed lift force to overcome its own weight, you can see how it is a MUCH bigger problem for a car than it is for an aircraft.
https://en.wikipedia.org/wiki/Drag_curve

 

[618 Syndicate]

I was the systems engineer for the ERAU electric land speed record team while I was a student there. We started out as the Jet Dragster build team and then transitioned into doing our own land speed record car. The real problem with going fats relates to several factors. You can really break it down into three major components. Aero drag due to the vehicle shape. Aero drag due to the required driving downforce. And rolling resistance.

The first one is pretty easy to determine and is mostly dependent on the overall shape and size of the vehicle. Cd is the coefficient of drag and is specific to the shape of the vehicle(all of the talk of removing mirrors, body kits, sealing windows, etc... will have an effect on the Cd of the vehicle). A is the overall frontal area and is fixed(it can be reduced by having venting that will just redirect the airflow through channels and then to the back). That just leaves the velocity as the only variable. As you can see by the equation, the drag value is equal to those items times 1/2 of the velocity squared. It is an exponential curve and it goes up quickly.
https://x-engineer.org/aerodynamic-drag/

The second part is the big limiter for wheel driven vehicles when you want to go VERY fast. Your speed is steady when the drag is equal to the force being applied by the driven wheels. The driven wheels require a certain amount of force on them pressing down in order for them to be able to apply the force necessary to drive the vehicle forward without slipping. This amount of downward force is usually provided by the weight of the vehicle, but it stops being enough by itself above a certain speed(usually above about 100-120mph). This is compensated for by using a wing shape or aerodynamic shapes to generate additional downforce to be able to keep traction on the tires. As the required force to keep accelerating exponentially increases the faster you go, the required downforce to keep the tires from spinning also increases exponentially. Since downforce creation also induces more drag, it quickly becomes a huge issue.

This can be seen by looking at readily available graphs for lift vs drag. Downforce is just aerodynamic lift being generated in the opposite direction, so L/D curves based on forces vs airspeed are very beneficial in visualizing what is happening. With a wheeled vehicle that is needing to generate MORE downforce as the speed increases compared to an aircraft that only needs to generate a fixed lift force to overcome its own weight, you can see how it is a MUCH bigger problem for a car than it is for an aircraft.
https://en.wikipedia.org/wiki/Drag_curve

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[df2x4]

The real problem with going fats relates to several factors.

Mostly junk food.

I'm done, sorry.

 

[BeXtreme]

Mostly junk food.

I'm done, sorry.

damn fat fingers

 

[GrimsterGMC]

Mostly junk food.

I'm done, sorry.

Never apologize for making humour, for some of us that's all that is keeping us sane.

 

[Caman96]

I was the systems engineer for the ERAU electric land speed record team while I was a student there. We started out as the Jet Dragster build team and then transitioned into doing our own land speed record car.

So using a 90’s Van was never considered?

 

[Pinger]

The second part is the big limiter for wheel driven vehicles when you want to go VERY fast. Your speed is steady when the drag is equal to the force being applied by the driven wheels. The driven wheels require a certain amount of force on them pressing down in order for them to be able to apply the force necessary to drive the vehicle forward without slipping. This amount of downward force is usually provided by the weight of the vehicle, but it stops being enough by itself above a certain speed(usually above about 100-120mph). This is compensated for by using a wing shape or aerodynamic shapes to generate additional downforce to be able to keep traction on the tires. As the required force to keep accelerating exponentially increases the faster you go, the required downforce to keep the tires from spinning also increases exponentially. Since downforce creation also induces more drag, it quickly becomes a huge issue.

What's been overlooked there is the torque around the rear wheels due to drag. The drag force acting horizontally acts on the vehicle above ground level (and can be defined as having a 'centre of pressure' - in the same way a 'centre of mass' can be defined).
As this force acts at a height above ground level, above the driven (I assume RWD here) wheels a torque is applied around the rear tyre contact patches and the front of the vehicle tries to rear up (note, no vertical forces due to aero effects) which transfers weight to the rear wheels to the benefit of traction. It is easier visualised by considering a dragster deploying its parachute at speed.

There are too many vehicles capable of in excess of 100-120 mph generating zero downforce - in all probability lift - for there not to be another factor at play.

 

[eXo0us]

Only because of the difficulties associated with introducing the fuel and it finding air to combust with. Try running a SI engine on a fuel with octane rating as low as diesel's and combustion will be uncontrollably fast - spontaneous. We call it detonation.

I've built once a very fast TDI engine to run on Vegetable Oil. Held the land speed record for alternative fuels for a brief period in Germany. (146mph)

Looked very deep into how the combustion in a Diesel behaves. With a DI injection you have the combustion starting at various points in the cylinder (where the injector sprays)- from there the flame travels outward. That expands the gases and we get the pressure wave which is making power.

Diesel has a longer molecule then gasoline - it takes some time to attach enough Oxygen to completely take it apart to make CO2.

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Further like you mentioned in a DI the mixture is not as good - so the chain has to find the O2 modules floating around - more time requiered.

We experimented with different fuels and mixtures and found that when we use 10% Diesel to start the combustion and a rapeseed oil you have- which contains a few oxygen atoms - we can rev pretty high. 5300 rpm.

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If you don't have the Diesel in the veggie oil - cold start sucks. You need to preheat the combustion chamber with glow plugs and preheat the fuel