Engine swaps, Mpg focused Options

[r_towle]

Leave the SBC and flat6 conversions out of this.

Who has swapped a different engine into a 914?
Something Japanese, great mpg?

[r_towle]

I got 48 mpg from my tuned 1.7 with djet….and I really learned djet that year.
And I learned all about low roll resistant tires….which are great for mpg but suck for traction
But I digress.
Just curious if anyone put a newer FI engine like a Toyota or Honda into a 914

[Superhawk996]

And I learned all about low roll resistant tires….which are great for mpg but suck for traction
But I digress.
Just curious if anyone put a newer FI engine like a Toyota or Honda into a 914

You're on the wrong track with an engine swap. You were on the right track with low rolling resistance tires.

Fuel economy is a function of rolling resistance, aero dynamic drag, and parasitic drag.

Aero drag is almost a fixed variable based on body shape. 914 is already surprisingly good with flat underbody, small frontal area, and small side mirrors, you'll largely need a wind tunnel to tweak it any further. Someone did a nice CFD on 914 aero. If you are serious about trying to improve MPG, you can't ignore aerodynamics.

Here: http://www.cassidy-online.com/porsche914/a...aids/index.html

Tire are ABSOLUTELY the the largest rolling resistance variable you can easily affect. Look at Honda Insight (165/65R14) - skinny, low rolling resistance tires. Sounds a lot like stock 914 tires. But notice, the Insight went 14". That is to reduce inertia of the wheels vs. stock 914 on 15". The larger diameter wheel requires more energy (i.e. lower MPG) to accelerate the wheel up to speed after each stop. You'll also want to keep wheel mass as low as possible (carbon fiber would be ideal (IMG:style_emoticons/default/laugh.gif)). Big meats that look cool and provide awesome handling aren't going to get good MPG.

After that, you're chasing parasitic drag. Need to go to high roll back brake calipers (makes brakes feel crappy), low drag bearings and seals (differential, wheel bearings, etc.).

The actual engine has very little to do with MPG other than it needs to overcome rolling resistance, aero drag, and parasitic drag. As noted by Mark as well as your own claimed MPG, a stock 1.7L driven gently is going to be pretty respectable.

I'm curious if you got 48 mpg; what target MPG are you hoping for and for what purpose? How much gas could you buy with the money spent on the engine swap and/or pursuit of lowering parasitic loads?

If you want more fuel efficiency out of an engine, you're going to end up looking at something like 1.0 - 1.2L, 3 cylinder turbo charged engines.

The Mitsubishi Mirage 3 cylinder is 1.2L - about 76 HP. Sounds suspisciously like a stock 1.7L (IMG:style_emoticons/default/happy11.gif) but will have better Brake Specific Fuel Consumption than a 50 year old air cooled motor.

Or, there is the Ford Fiesta 1.0L 3 cylinder EcoBoost that is good for 123 HP. But if you're on the turbo and making 123 HP, you won't be getting best fuel economy (IMG:style_emoticons/default/av-943.gif) and we're back to square one. Same for the 3 cylinder out of the Mini Clubman which is 1.5L and 134 HP.

[bbrock]

The actual engine has very little to do with MPG other than it needs to overcome rolling resistance, aero drag, and parasitic drag.

Just to play devil's advocate (IMG:style_emoticons/default/happy11.gif) , how are boxy crossover SUVs getting high 30s and low 40s mpg? Surely they have more drag and rolling resistance than our tiny little 914s. Haven't all the advances such as variable valve timing, tuned combustion chambers, and precise fuel management allowed engines to make more power to overcome rolling resistance with less fuel?

[Superhawk996]

The actual engine has very little to do with MPG other than it needs to overcome rolling resistance, aero drag, and parasitic drag.

Just to play devil's advocate (IMG:style_emoticons/default/happy11.gif) , how are boxy crossover SUVs getting high 30s and low 40s mpg? Surely they have more drag and rolling resistance than our tiny little 914s. Haven't all the advances such as variable valve timing, tuned combustion chambers, and precise fuel management allowed engines to make more power to overcome rolling resistance with less fuel?

Let's talk specifics. Most boxy SUV's approaching 40 MPG are hybrids so a little bit apples to oranges comparison there.

https://www.kbb.com/suv/most-fuel-efficient-suvs/

Conventional Honda CRV - 30 MPG combined
https://www.fueleconomy.gov/feg/bymodel/202...onda_CR-V.shtml

Conventional Toyota RAV4 - 30 MPG combined
https://www.fueleconomy.gov/feg/bymodel/202...yota_RAV4.shtml

Here's an interesting one: Nissan Rogue - 33 MPG combined but doing it on a 1.5L, 3 cylinder turbo - 201 HP!
https://www.fueleconomy.gov/feg/PowerSearch...amp;rowLimit=50

You'd also be surprised at the aero numbers on what otherwise looks "boxy". The generic turd / jelly bean shapes are low drag and there is an lot of engineering done to reduce aero drag which is why you find so much plastic under these cars. Underbody shields, tire spats to reduce aero loss at the tire frontal area, automatic grille shutters to reduce drag though the radiator when you don't need full radiator frontal area, variable ride heights to reduce drag at highway speed. Lot's of cool technology being applied to reduce rolling resistance and parasitic losses that most folks don't even know about.

I'm still looking for the "official" Cd for a 914 -- per old link 0.38 is referenced
(Note: Cd=0.38 was an amazing number for a car designed in the late 60's! (IMG:style_emoticons/default/piratenanner.gif) )
http://www.914world.com/bbs2/index.php?sho...ag++coefficient

http://forums.pelicanparts.com/porsche-914...drag-914-a.html

https://www.early911sregistry.org/forums/sh...rag-coefficient

Many modern SUV's are playing in the realm of Cd of 0.33 that is LOWER than a 914 if the number above is correct (per 3 sources).


https://www.researchgate.net/profile/Adrian...lication_detail

With respect to rolling resistance, anything approaching high 30's and low 40's will be on low rolling resistance tires. Likewise, all major OEM's have been playing with low drag components (i.e. brakes, drive line disconnects, etc.). Drive line disconnects allow you to get rid of the need to accelerate rotational inertia (like AWD driveshafts, PTU, and 1/2 shafts) unless it's needed for tractive effort. It's cool technology, but adds weight, which in and of itself, then reduces MPG. It's a delicate balance but everything is tipped toward MPG numbers.

Electronic Power Assisted Steering -- this is a great example of newer technology (electric driven rack & pinion) replacing old school hydraulic power assist steering. It was done to reduce parasitic load on engines to improve MPG. Was not initially done for the tuning potential it offers.

The advances in engines (i.e. good Brake Specific Fuel Consumption) have largely been offset by the increasing weight of these pigs incurred by all the safety mandates, feature gee gaws, and NVH treatments.

[bbrock]

Let's talk specifics. Most boxy SUV's approaching 40 MPG are hybrids so a little bit apples to oranges comparison there.

But wait, why are we eliminating hybrids? Ultimately every mile driven is power by ICE. Maybe more complicated of a swap than OP is looking for but it's still an example of how technology has advanced to squeeze more out of a gallon of gas.

Also, the new RAV4 Prime gets 38 mpg on gasoline only. I knew calling SUVs "boxy" would get me into trouble due to Cd improvements. I should have said "heavy." Those slugs are getting respectable fuel economy with well over a third more weight than our little 914s.

BTW, I regularly got 36 mpg highway in my stock 2 liter. That was in the 55 mph speed limit days though and the city mileage sucked.

Finally, sure advances in engine technology have been offset by the behemoth vehicles they are powering, but I fail to see how transplanting that tech into a featherweight and aerodynamic (even by today's standards) car couldn't yield some screaming fuel economy.

[Superhawk996]

Let's talk specifics. Most boxy SUV's approaching 40 MPG are hybrids so a little bit apples to oranges comparison there.

But wait, why are we eliminating hybrids? . . . . I fail to see how transplanting that tech into a featherweight and aerodynamic (even by today's standards) car couldn't yield some screaming fuel economy.

Because of the complexity - by the time you transplant a hybrid powertrain, battery, power electronics, and cooling systems you will no longer have a featherweight car. Then don’t forget to update the body, suspension, and brakes to handle the new weight from the powertrain “upgrade” all of which add yet more weight.

There is a reason they have grown to 3400 - 3700 lbs pigs. (IMG:style_emoticons/default/laugh.gif)

As stated earlier - you’ll need to do the engineering. Won’t be a simple powertrain swap and in the end, you’ll be hard pressed to beat the stock 1.7l and you’ll have incurred all the expense associated with the “upgrade”. A simple engine swap isn’t going to do it.

I assume the purpose of the OP proposed swap was to save gas money. Point being - unless the engine “upgrade”, all labor, and all materials used are free - there will be no savings.

I suspect @bbrock you’re more concerned about emissions which is a whole different game.

[bbrock]

I assume the purpose of the OP proposed swap was to save gas money. Point being - unless the engine “upgrade”, all labor, and all materials used are free - there will be no savings.

Or the challenge? Why do any of us fiddle with these cars?

I suspect @bbrock you’re more concerned about emissions which is a whole different game.

Don't mean to hijack, but big assumption and mostly wrong. My personal interest for my 914 is mostly on fuel economy because my car should be the cheapest and most fun way for me to travel the long distances through amazing country needed for my job. I want to minimize the emissions my car produces in doing so, but the practical gains to be had in cleaning up vintage sports cars don't add up to much. Now if we are talking about the global fleet of ICE vehicles overall, sure, emissions and economy are important.

But back to the subject. I find this a fascinating question from the challenge perspective. What does modern technology offer this vintage platform to improve efficiency? My hunch is that converting a stock engine to modern EFI may provide biggest bang for the buck, but it is a fun question to ponder. Surely there are modern engines out there that could improve efficiency and performance.