Engine swaps, Mpg focused Options

[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]

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

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

[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.

[jrmdir]

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

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

Ron

[brant]

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.

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

[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.

[Superhawk996]

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!

[914werke]

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 !

[Superhawk996]

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 hoopie a 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 !

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 ( (IMG:style_emoticons/default/first.gif) )
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. (IMG:style_emoticons/default/lol-2.gif)
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 (IMG:style_emoticons/default/av-943.gif)


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. (IMG:style_emoticons/default/shades.gif)

[euro911]

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 (IMG:style_emoticons/default/idea.gif)

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 (IMG:style_emoticons/default/shades.gif)

[ClayPerrine]

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.

(IMG:style_emoticons/default/idea.gif)

[mepstein]

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.

[Superhawk996]

I look at my own hoopdee as an example: Ford Festiva

I love this (IMG:style_emoticons/default/smilie_pokal.gif) 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!

[Superhawk996]

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.

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/smilie_pokal.gif)

[Superhawk996]

If you want really insane mileage and reasonable performance, look into freevalve technology.
(IMG:style_emoticons/default/idea.gif)

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 (IMG:style_emoticons/default/sad.gif)

[914werke]

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.

Ok so 1700 (IMG:style_emoticons/default/biggrin.gif) who needs a back seat!

[brant]

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

[Chris914n6]

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.