I see this quite a bit and wanted to share my opinions on non-stock fuel filters. There are a ton of reasons the people would install different fuel filters, ranging from installing carbs, to relocating the fuel pump, to running aftermarket FI, engine swaps, upgrading to modern technology, etc.

The #1 thing to look at when choosing an aftermarket filter is the filter element size. These are measured in microns. Fuel Injection should have a 10 micron filter, carbs can get away with something larger, up to 40 microns (but that's getting pretty big).

The #2 thing to look at is the actual filter body size. Here's you're trying to make sure you have a filter unit that fits where you want it to, but also has enough size to deal with contamination over time. A tiny filter body has a tiny filter inside, and a tiny filter will start to lose flow sooner as contaminants collect in the filter element.

One rule-of-thumb that I start off with when trying to select a filter is starting my search with OE filters for newer cars. These are all built to for fuel injection (<10micron) and built to last for a reasonable life span (years). This is a bit of a complicated way to search, because you have to look at a lot of pictures. A lot of these filters don't explicitly call out the micron rating, but if it's made for modern FI and it's a reputable brand (FRAM is not reputable, for example) you can pretty safely assume it's a good filter.

Most people start their filter search on eBay, Amazon, or Summit (etc). A lot of these aftermarket filters are washable, billet aluminum, and lots of other fancy features. And a LOT of them are built to attract uninformed bargain hunters, who buy what's cheap, looks neat and says 'fuel filter' in the name.

Here's a filter I just pulled off a car. It's a Sniper Motorsports (a division of Holley) filter. It's rated at 30microns (way too coarse for FI) and it's tiny. I'm installing a Mahle KL 65 filter which is used on some Boxsters, have correct 5/16" nipples on either end, Mahle mentions 'up to 1 micron' filtration (doubtful, but I'm confident it's <10microns), and it's HUGE. This filter will do it's job well and will last for a long time.

One final note, clear plastic filters are 'neat' to look at, but are always not-great filters. The 'lowest' quality filter I would put on any 914 is the stock 914 filter. But this KL 65 is a better choice as long as it fits where you want to put it.

Hopefully this is helpful knowledge.

Great info! Would the size of the filter (volume) impact the fuel pressure?

It may be perceived that the small filters don't decease the flow...

The volume of the filter body won't affect fuel pressure, all other things being equal.

A smaller filter (especially as it starts to clog) will impede fuel flow. If the rate of flow through the (clogged) filter begins to drop, this can cause the fuel pressure to dip, especially as RPM increases and you're flowing more fuel out the injectors. If filter-flow < injector-flow then pressure at the injector will drop.

I won't know until I install the KL 65, but I'm pretty sure that's the scenario I was running into on this car. The car would idle fine and run fine at cruise, but higher RPM would go lean, no matter how much I tuned in more fuel.

Great information.
Thank you.
AFAIK a 6 had the sock in the tank and nothing else.
So...... for carbs, simple works for me.
Provides an immediate visual every time I'm in the engine compartment.
Neat, readily available, easy install.

I had a relatively small (2" wide by 8" long") 10 micron filter that I used for my system. It was rated at 600hp so I figured I would be OK for my sub 600hp setup, It clogged up after about 500 miles where my 100 micron pre pump filter was completely clear.

I havent replaced it yet... I am confident I dont want to go back to a 10 micron filter that isnt cleanable (My 100 micron is able to be cleaned)


So just know small and compact isnt always good...



I had the same type of issues you had Mark with tuning, my 044 pump would scream like crazy which I thought was normal as I know they are loud pumps and I even replaced it thinking it was going bad as I would lean out over 10psi then after about 50 miles of troubleshooting we finally pulled the filter and figured out that was the issues. No issues now! We'll see what 20-30psi feels like

I have carbs and relocated my fuel pump up front with a filter before the pump but I also added one in the engine bay for flow verification. I know I added another point of failure but it is easy to maintain.

Good information. I also added a cut-off valve in front of the filter for changing out the filter (s) / 3 in all........ w/o putting fuel everywhere.....

Thanks

That looks strikingly similar to the fuel filter in my car ...

I would be suspicious of any fine filter that is cleanable. I am not confident of my personal ability to clean out 11-micron debris from a filter without something like an ultrasonic cleaner. I'd just opt for a replaceable filter, or at very least a filter with a replaceable element.

And the large filters, as the one McMark shows, should last any of us for quite a few years. I can live with throwing away a filter a couple of times a decade...

--DD

Which reminds me, mine has been on the car for over 10 years now.

What model filter are you using ?

I am using a Pierburg type pump mounted up front which has its' own self contained filter, with a petcock and a big Mahle in the back.

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I havent been able to find a 10 micron filter for under $250 that was large enough for me to think it would last more than 3 months. The one I did buy was $100, which IMHO is to expensive to be replacing that quickly. I specifically need one I can hook up with a 10AN line due to my fuel supply demands and pressure.

The KL 21 that's in Andy's and Lawrence's cars have fittings on the end that can be unscrewed. I THINK the threads are 14x1.5. They have threadlocker from the factory, so they're a bit of a pain to unscrew. Pull out the fittings that come on it, screw on a couple AN-10 to 14x1.5 adapter fittings and you're set. For about $45.

https://www.summitracing.com/parts/vpe-16633/overview/

This is the same filter (KL 21) that's on the 1996 911 3.6 Turbo. So I think it's plenty for your little 1.8.

You would think... Right now Im making about as much power as a 3.6 turbo on pump gas at about 17psi... Im going to push it to at least 25psi on 100 octane this year. We'll see how far, but the turbo will take 35psi efficiently and my engine will handle it just fine. The bigger question is will I destroy my trans or "500hp" cv joints in the process. My boost map is set for a slower onset to reduce torque spikes to try and save that stuff.. The bigger thing here for fueling is that I plan on running E85 which means I need 30% more fuel. Long story short I need 1300cc injectors for a reason...

I'll see about giving that filter a try! Price is decent and I can certainly do that price as a consumable. Hell swap the filter every oil change. I have an electric pressure guage that I'll hook up engine side to make sure I am getting enough pressure at the rail.

Not keen on any fuel filter in the engine space for obvious reasons,the filter needs to be @ at the source of suction ,anyone keen to tell me otherwise go ahead,but suction @ the point of supply is where you have a filter...period.
Many pumps used are great @ suction but most pumps are crap @ drawing fuel from an indirect source ,funny how Porsche moved the pump to the front,folks think it was vapour lock not really the full story.
Its fine to add a second filter in the engine space as Mark has shown,just don't like plastic stuff around that heat and environment ..asking for serious issues IMO.

You say'n it could be a problem ?

I suppose if you run into a flow issue you could run 2 in parallel.

If this is referencing me, I'm not suggesting any location vs another. Generally I'm putting pumps and filters under the tank or in the steering rack pocket.

Does the Mahle KL65 fit into the place a 1.8 normally sits ? I've found the stock square filters to hang up on the steering shaft and make R/R a messy operation

Under the tank on the driver's side? Sometimes, but it won't fit through the access port. So you'd have to pull the tank each time.

The KL 14 filter is a little bigger than the KL 11 that I would normally install in a stock setup and should still fit through the 'window' based on the dimensions on the Mahle web site.

Can you share the link to Mahle that Has the filter dimensions; looked, but no find