Leave the SBC and flat6 conversions out of this.

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

My stock 1.7 would easily get 38-40 mpg on the highway at 70-75mph. Why bother with an engine swap. Just use a 1.7 in good tune and the right tires.

When I am not hard on the Turbo, my Subaru 2.0 WRX motor does 30 MPG highway....

Its good around town, but my foot is always in it so hard to say how efficient it could be.

WOW! those are great numbers!

My 2.0 with a hot cam and carbs was more like 25-28

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

There's at least one VW turbodiesel out there. (Pre-TDI.) That would seem to be a great way to go for fuel economy, but I'd be concerned that the gearing would be too short to really do the diesel justice.

--DD

I had a Honda J35 odyssey engine in my 914 210 hp getting 25 city and 30 highway. One of the smoothest engines i have ever swapped into a 914.

Why not ee20?

Subaru flat 4 - it fits
Get it with the 6 speed trans - gearing good
Diesel - gets 40+ mpgs in the Forester. Heavy and AWD. Imagine the numbers it could make in a 914

Just wondering.
Does anybody really care about the fuel economy of his 914???
It is good, even to today´s standards and 914´s are so much fun to drive. So who cares about a mile less ore more on a tank?
(Just my 2 Cents...)

We need two hundred and fifty 2 cents to buy a gallon

What about an early 1.6/1.8 Miata motor?

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 ). 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 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 and we're back to square one. Same for the 3 cylinder out of the Mini Clubman which is 1.5L and 134 HP.

Nope. 1st generation Miata is roughly the same weight as a 914 (2,000 lbs ish), similar frontal area, etc.

I had one from 1994 - 2018. About 30 MPG on highway, 24 MPG combined fuel economy per EPA.

https://www.fueleconomy.gov/feg/noframes/7490.shtml

A good portion of why the Miata MPG is so low is because of the tires. The messy underbody creating drag, and the poor aero drag due to the body design / convertible top shape don't help at all either.

If you're serious about MPG, you're going to end up having to do the engineering and it's not as simple as just swapping engines.

Note to tie into later post: 1st Gen Miata had a published Cd of 0.38 -- same as what I could find for the 914.

YES!

Fuel economy has always been a big draw for me since I fell in love with these cars in the 70s. Performance and mileage? Not interested Performance and great economy? Sign me up.

I think good mpg is a good measure of engine performance. Just like our cars, doing more with less.

You can have both with a 914 -- respectable fuel economy but MOST importantly great handling.

This was Rich's the original question. If I had to do a different swap I would consider a K series with megasquirt. You could control the VTEC to keep the fuel economy up there but also kick it in early if you wanted some extra ooomph.

Just to play devil's advocate , 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?

Be careful with that logic. You can have a highly efficient engine hauling around two tons of weight and terrible parasitic load . . . you won't get good MPG.

Be careful with "engine performance". That is a meaningless term. Could mean horsepower.

The thing you're talking about is Brake Specific Fuel Consumption which is a measure of how much fuel is needed to produce X amount of HP produced.

https://en.wikipedia.org/wiki/Brake-specifi...uel_consumption

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! )
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).

Click to view attachment
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.

Not sure about MPG focus, but here's one example:

https://www.k20a.org/threads/k24a-powered-7...che-914.228246/

Ron

I also have gotten into the 38's with a stock 1.7
the MPS was not readjusted for today's fuel, so likely running slightly lean
brant

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.

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.

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.

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



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.

@bbrock
There is no free lunch. Any modern engine is going to be a water pumper of some sort. Now start adding the weight . . . engine cradle, engine / trans adapters, radiator, all plumbing, electric fans, coolant weight, etc.

What I think I'm failing to impress upon is that MPG isn't just one thing that is easy to do. Everything has downstream systems engineering implications.


To your point - bang for the buck. I think you are correct -- modern EFI on a 1.7L will be the way to go.

What we are failing to see is that a 1.7L IS a small engine - even by modern standards less yet a 1970's world!

I think it was Len that suggested that a reconfigured 1.7L was the recipe..
Smaller displacement higher revving , better breathing ...

I look at my own hoopdee as an example: Ford Festiva - 0 aero! 1.3L, 1600#'s 14" narrow wheels (upgraded from 12") 200k, I drive like I stole it & it still gets 36-39mpg !
Click to view attachment

Even here the engine is only a piece of the secret sauce.

Smaller engine - check. sub 70 HP I think for the Festiva
Narrow, low inertia wheels, low rolling resistance tires - check

A big piece of the equation is the low weight -- 1600 seems low. Edmund's says 1800 but the point remains. The less weight . . the better.

So in addition to the comment to bbrock on making 1.7L more efficient with modern EFI (via incorporation of decel fuel shutoff) and better fuel control, weight reduction is the order of the day.

Rule of thumb on modern cars is that every 100 lbs of weight reduction is good for 1-2% fuel economy improvement. The problem is that a 914 is already starting off very light end of the automotive spectrum.

But you could do the easy stuff:
Do fiberglass hood & trunk
Get rid of all OEM tar
Get rid of rear bulkhead insulation / mass dampers both interior and exterior
Get rid of the back pad . . . and all carpet for that matter!
Get rid of all radio/stereo amps/speakers
Set of Oscar's GT style lightened hinges ( )
Use 14" wheels (914/6 came on 14's -- Empi, etc. as 14" alternatives for /4's)
Use 911 aluminum front cross member
Use smaller Li-ion battery and deal with the potential disadvantages
GT style door pulls - eliminate door pockets & door cards
Glove box door - who needs one. Bin it
Shift knob -- bin it. Just grab the metal shift rod.
Seats -- can definitely put some lightening holes in the fiberglass shells.
Dash top and bottom cosmetics - appearance only - we're going for MPG here

Harder stuff:
Go ahead and have Titanium headers and muffler made (huge weight save over OEM)
Fabricate hollow Titanium engine cross bar instead of the cast iron OEM part
Fabricate Titanium intake system plenum / runners / airbox
You get the picture . . . .

Now that we have a bunch of weight out, now you can go back to those sub 100lb/in OEM springs and they will be plenty. Lower rate springs = less weight.

Might as well drill the rotors - we can get some weight out there too. Ditch the rotor backing plates / dust shields / fasteners too!

Starting to sound a lot like race car prep


But no where in this are you going to take a 914 to some sort of 60 MPG miracle even with your best hypermiling tricks.

I had a snotty 2056 in the 'BB' and it was a lot of fun, but gas was reasonably priced at the time too. Not that I was clairvoyant about future gas prices or anything, but I'm more into fuel economy these days

We rebuilt the tired 1.7L motor from my '71 into a 1.9L with stock D-jet, 2L injectors, SSI HEs and 2.0L banana muffler. It'll be running on ATS Classics with 180/70-15 tires. It'll still be fast enough for this old man and I'm expecting decent fuel economy

If you want really insane mileage and reasonable performance, look into freevalve technology. If you don't know what it is, it is simply a 4 stroke motor with no cams. The camshafts have been virtualized, and the valves are opened and closed with air pressure controlled by the ECU. You can have any cam profile you want, dynamically while driving. So at cruising speed, you have a cam profile that makes the best mileage, but the cam profile can change to improve acceleration.

This is a video of a guy that put it in a Miata.

https://www.youtube.com/watch?v=E9KJ_f7REGw

I think this would be really cool on a 911 engine.

Mine had 195x65x15 all season tires. I'm sure with some better tires, some weight reduction and careful driving, it would have been a 42 ish mpg car. Which really isn't bad considering it's not hard to find a stock 1.7 for ~$500. For most people, greater than 40 mpg isn't really an issue because very few people will use a 914 as a daily driver. So if you drive it a couple thousand miles per year, the difference in gas expense won't add up to much.

I love this I haven't seen a Festiva on the road in the longest time. That is the way to walk the talk when we are talking about MPG and reduced emissions!

It is very cool but . . .

Lots of cost for very little MPG gain. The idea has been circulated within the industry for decades where OEM's fight tooth and nail for every last 0.1 MPG.

The cost / benefit is not sufficient . . . yet. Probably never will be now that the political agenda is to push EV's. Just made that ICE based technology obsolete

Ok so 1700 who needs a back seat!

with modern fuel injection....

why not 1600cc's
they made an industrial type 4 of that displacement
and my race shop has one running in a super Vee....
makes plenty of power when built correctly.


as long as were just spit balling and bench talking...
you could likely pull a few more MPG out of a bolt in type 4 that way

brant

My 2 cents...

Weight is not a factor in highway mileage, just stop-n-go. Modern cars go into 'lean burn' to get the 40mpg, which can't be done on our aircooled motors. Also tech like VVT that reduces pumping losses by adjusting the exhaust cam. Plus more efficient trans.
So a modern engine swap won't necessarily get us the same results without ALL the components swapped over.

My Nissan 3.0 v6 190hp measured 24/29 on it's last WCR trip. A stock 1997 Maxima is rated 22/27 and weights 1,000 lbs more.

All the water pumper additions weigh less that 100lbs, so really not a factor in mpgs.

A Rav4 awd is up to 4400lbs. Talk about a porker...

A stock 1.7 with a well tuned MS might get you over 40mph highway. ECO focus tires would be a good start. But for long trips a Prius or that Fiesta makes sense and would be more comfortable I would think.