Have a quick question about the three hoses connected to the airbox on my '73 1.7 FI. Can I pull the hoses off the airbox and just cap them with a breather filter? The reason I'm asking is I want to remove the airbox and put on a dual-stage Uni foam air filter, using a silicone coupler and elbow piece at the TB. So that leaves these two hoses that connect to the airbox (non-oil bath), and the one that connects down at the bottom of the elbow between the airbox and TB, with nothing to connect to. The two shorter hoses on the driver's side terminate into these short metal fittings that I could probably just put a breather filter on top of, and the much longer hose that connects to the rear of the airbox I could probably just put a breather filter on the end of that one.

Am I risking destroying the engine or greatly ruining it's ability to run properly by doing this?

Here's a picture of where two of the hoses originate. The one on the far left terminates in the airbox, and the one on the right terminates down at the rubber elbow right before the TB. So can I just put a crankcase breather filter where the yellow circles are, or am I asking for trouble?

Anyone, anyone? Bueller? Bueller? Almost 50 views and nothing?

The left hose is your crankcase breather and should be vented into the intake air. This is so the oil vapors are sucked into the engine and burned and not spewing the oil fumes into the air and your engine compartment.
The hose to the right is the intake side of you auxiliary air valve. This needs to be pumbed down stream of your air filter so the air sucked into the engine thru this hose is clean filtered air. You don't want dirt being sucked in here.

So both of these hoses should be hooked in between the throttle body and your new air filter.

Jim

Short Answer: You can, yes.

Right Answer:There are two reasons people don't normally do this:
1. The filters you put on there will weep/blow oil vapor around your engine compartment.
2. The stock air filter is better than what you have planned and you're not going to 'unlock some horsepower' my doing it.

Okay, the fitting on the left blows air out, and the one on the right sucks air in, correct? This is my first air-cooled engine, so you'll have to excuse my ignorance of how these things work. So again, in theory, with a crankcase breather filter attached to these hard points, they'll still work, with the exception of possibly oily vapors getting out of the fitting on the left. I could fix this by running a hose with a loop, and put the filter up high. That way, air can still get out, but any mist/vapor will get stuck in the loop and drain back down. Used to do this on some Italian motorcycles I used to own. As for the airbox, when I compare the small inlet on the stock airbox versus the much larger surface area of a cone or barrel-type filter, I can't help but think that more air is better, and the FI system will adjust for it?

I realize it's not a hp beast, only having like 80hp or so. But I would think just about anything that would give it a few more ponies, without hurting the engine, is a good thing. Also, I'm not such a Porsche purist that I feel like I have to keep everything like it rolled out of the factory. Besides, this 914 isn't a "true" Porsche anyway, right?!

My 914 is at the shop getting a new fuel pump installed, so when I get it back I'll check what's inside the airbox to see how oily and grungy it is. If these two hoses do like you say, the inside of the airbox should show some oily residue somewhere. Lucky for me this car is so old, that it's exempt from any emissions testing and inspections!

It won't give you "a few ponies" but it will most certainly give you a headache.

These engines aren't starved of fresh air. Without modifying the rest of the engine, adding more intake air will do next to nothing for performance.

Now, if you were thinking about adding a good 4-1 exhaust header, that would actually do something for your HP.

I'm pretty sure it doesn't have the stock exhaust, sort of looks like one of those Burch systems, but not completely sure. Again, don't know a whole lot about these cars. In what way would removing those two hoses and capping the fittings with breather filters give me a headache? Will it stumble and bumble because those hoses aren't attached and routed to the airbox?

My other current project car is a 1991 Mercury Capri turbo, which is an absolute hoot to drive, very zippy for being 25 years old and only having 53K miles. I put on a 2.25" exhaust with a free-flow cat, resonator, and dual tip; swapped in a set of Audi TT leather seats; replaced the rear sway bar bushings, brake rotors, and pads; etc. Going to leave the intake alone though, because of how the airbox and MAF sensor is set up. Have a 15x6.5 set of wheels and 205/50 tires in mind for it, along with painting the bumpers black and that should just about do it on that car (it has a new convertible top, and a new headliner in the removable hardtop). My other project, which is more or less done, is a 2000 GMC Sonoma with an LT4 and T56 trans. Bought it with the conversion already done, with the correct wiring harness and computer, one-piece aluminum driveshaft, limited slip rear end, coil overs on the front, cal-tracs on the back with lowering blocks, etc. I changed the wheels and tires, swapped in a set of Cobalt SS Recaro seats, and replaced the mufflers with a pair of Summit chambered ovals. Only thing I did in the engine compartment was replace the cone filter with a dual-stage Uni foam filter.

So you can see with these other projects, I'm finding it a real challenge to not molest this 914, and to leave it pretty much stock. I was thinking of replacing the seats with something more adjustable, but that thought passed, lol! Maybe I'll concentrate on more functional things, like s/s braided brake lines, and getting the darn stereo system to work...that's it, this will be the completely stock, unmolested car!

Oh boy, you really need to do some more reading before you dive into it.


If Cap'n Krusty wasn't dead already he would have ripped you a new one for that comment alone ...

The D-Jetronic system on your 1.7 is cranky and old, some of us here have been working on them for ages (see my web page). They like things to be pretty much exactly they way it came from the factory. Start pulling stuff off without fully understanding it can lead to problems.

If you really want to mod your 1.7 to get more horsepower, changing the air or exhaust system while retaining the D-Jet isn't going to do much, as the existing systems are reasonably optimized. Your best bet is to increase compression and displacement (i.e. overbore kits), and go to either Webers/Delortos, or aftermarket FI. If you don't care about "orginality", get rid of the motor and put in a V8 conversion kit or a Subie kit.

It's your car, do what you want with it, but understand what you're doing and the limitations, and how much money you've got to make it happen. Have fun with it...

Considering I was in 8th grade when this car was produced, I really do appreciate the advice and suggestions. I'm guilty of believing in the old-school hot rod trick of increasing airflow and exhaust to get some hp, so naturally I'm thinking this should work on the 914. I realize the FI system is over 40 years old, but from what I heard from a local 914 owner who has a '71 1.7L with dual carbs and a '72 1.7L with a sorted out FI, he said hands down the FI car runs better throughout the entire rpm range, and that's in completely stock configuration.

I'm definitely going more for daily driver reliability, so I'm hoping once I get the car back with the new fuel pump, it'll run like it's supposed to. But if the FI system starts going out, since there are so many parts involved with it (injectors, ECU, sensors, etc), I may just get one of those Weber 32/36 conversion kits and a hi vol / low pressure fuel pump and call it a day.

If you guys see me making a train wreck, by all means chime in...don't just sit there and watch, lol...

You do realize this is the same conversation we've all had 100 times when new people join the group, right? I appreciate your enthusiasm, but I guarantee there are better places to spend your time and money on that car.

The 914 is an extremely well built and capable car in completely stock form. There are very few 'upgrades' that make the car better. One of those is a front sway bar. Do you have one of those?

If you need an old hot-rod adage to hook onto, try this one... "There's no replacement for displacement." Get a bigger engine.

And the single-carb setup is about the worst possible way to get air and fuel into the engine. Duals or FI are the only way to go.

--DD

Yup...something similar, "there's no substitute for cubic inches"...or one of my favorites, "injection is nice, but I'd rather be blown"...!

Again, in all seriousness, thanks for being courteous and constructive with the suggestions and advice. Having never owned anything like this before, I certainly don't want to do anything foolish with it that would impact it's performance, as nominal as it might be. I'm thinking of getting a 944 console, and with some imagination, I think I could get it to work in this car, i.e. using the stock shifter cutout as a storage cubby instead, making the ashtray opening bigger and putting the 914 shifter thru there, cutting a slot just behind it for the heater handle, putting gauges in the upper part of the console (oil temp, volts, clock), etc. That should take my mind off doing any mods to the intake system, lol...

What ever you decide on, ensure you don't build in a vacuum leak. Your car won't idle correctly.

By removing the three hoses from the airbox, I don't see how that would create a vacuum leak? One blows air out, the other sucks air in, and not sure what the third one does (the long hose that connects on the backside of the airbox). The airbox isn't pressurized, so I don't see the difference, other than temperature, between leaving them hooked up to the airbox or just popping a breather filter on the end?

Yeah, I know, the VW/Porsche engineers are all geniuses, and who am I to question how they have hoses routed/connected to the airbox, lol...

The third line is probably the vent from the charcoal canister. Air from the engine blower is routed up the driver side of the car (hoses under the rocker) to the charcoal canister on top of the fuel tank and then flows through the charcoal canister and back to the air cleaner in the engine compartment.

The charcoal canister and engine breather are vented to teh air cleaner so the fumes from them are burned by the engine. It is an emissions device but neither of them cause ANY lose in performance, fuel mileage, HP, etc... So there is absolutely NO reason to disconnect them or vent them to the air. Connecting a "breather filter" to either of these will not harm your car but you gain nothing and you add to the emissions put out by your car.

A "breather filter" is not a small particle filter, so putting a "breather filter" on the Aux Air Valve intake hose will allow dirt into the valve that would never get there through the stock (or after market) air filter. Probably would not be a big deal but the Aux Air Valves for the D-jet cars are no longer available and the commonly gunk up and stick. Adding any additional dirt to the normal gunk won't help.

In My Opinion the restriction to the intake is the throttle body not the air cleaner or air filter.

I don't see any harm in changing to an aftermarket air filter but I would add the 3 fitting to the connector between the throttle body and the air filer and connect your crankcase breather, aux air valve and charcoal canister vent hoses. Simple to do and it keep your engine compartment cleaner.

I also found the changing the stock heat exchangers (the exhaust attached to the heads) to SSI heat exchangers and adding a Bursch exhaust added some pep to my 71 1.7.
The SSI heat exchangers have slightly larger inside diameter pipes, so they flow a little better without being too much for the little 1.7.
My 2.0L engine has a complete header system (no heat) similar to Tangerine Racing's beautiful system, these make a bigger difference but i think you need a bit more engine that a stock 1.7 to get the benefit.

What ever you end up doing, go in small steps so if you run into a problem you don't have a bunch of changes to sort through to figure out which cause it.

Also get out and drive it before you take it apart, 914's seem to have a hard time getting back out of the garage or off their jack stands.

Take care
Jim

Oh Ya

Jim - thanks for the detailed and informative response. At least I have a much better idea now of what these three hoses out of the airbox do. Seems like the only one that is of concern is the one that goes down to that valve you mentioned, since the other two seem strictly for venting purposes. I'll take a closer look once I get the car back, and go from there. Maybe changing the plugs / wires / dist cap / rotor / coil will scratch that itch instead!

A word about air filters. I decided my old 2L didn't have enough air. I ditched the stock filter and fabbed my own intake using a k&n filter. That engine went south rather quickly after that. Nothing filters like the stock filter and introducing more air does no good. The exhaust valves will only expel so much of that air. I now have a raby inspired 2056 and still use the stock filter. Its the best option in my experience.

Thanks for the feedback, exactly what I was looking for regarding the stock airbox.