New 914 owner Questions - Tire Sizes & Crankcase Vent

[PropellerHead]

Longtime lurker and occasional poster on the 911 forums, I joined the 914 crowd this past fall with the purchase of a '74 2.0L. The car has me learning new Porsche tricks and exploring more sections of the valuable Tech Forums. Good to see there is nearly the same level in the 914 sections I've come to appreciate on the 911 sections.

I have some 914 specific questions for this group however. Yes, I know how to use the archives and I've done so already but some questions remain and/or a revisit might be required because information found was several years old and things can change (such as tire availability).

Question 1)
Tire sizes. Specifically I am *not* interested in significantly altering fender width/lips on this car. I've lowered cars in the past, stretched, rolled fenders, etc. and I'd like to avoid that if possible here. The body is un-modified, straight and need not have an amateur like me mucking with it.
I have 15x5-1/2" wheels, OE Mahle versions. They are in good shape and I'd like to keep them. Current tire size appears non-original but is a 195/65-15. Tires have a date code of 1997.......so I would like to replace them! That said, tire availability in that size stinks. I'm not an all-season touring tire kind of guy. I'd prefer something far softer and stickier.

Alternate sizes which might be of interest:
205/60-15 (BFG Radial T/A (all-season) is about it here)
205/55-15 (Dunlop DZ102 is about the only thing worth consideration)
195/60-15 (almost nothing available here of interest)
195/55-15 (lots of good options, BFG g-force sport comp-2 is a nice tire for this car, Toyo R1R, etc)

I have space to the outside on the rear fender lips (see, I did read the archives ) which varies from side to side but should allow a 205 width as long as I don't get too greedy with ride height and tire sidewall height.
I don't want a tire which is extremely short. This isn't an auto-x car for me and it won't see track use (the 911 and BMW are fine for that). It isn't a daily driver.

Has anyone been running a 195/55-15 tire? Is this 'too short'? The diameter is about 1.5" smaller than the 195/65-15 I'm running and the car sits plenty low already. Photos would be helpful if you're running a 195/55-15 tire!

Question 2:
Crankcase ventilation - I have Dellorto 40mm twin carbs (FI was long gone on this car when I bought it) and they don't seem to have a vacuum source to connect to the PCV valve on the oil filler set-up. I've researched the original system and also found some KrankVent references but that's not a vacuum source either and is more appropriate for racing use (on throttle) rather than street use.
My car has the vents in the cylinder head (early 2.0L) and I also have a spare engine (a later 2.0L) which doesn't have the same vent ports in the head.
Anyone here done Dellorto carbs with the early 2.0L crankcase vent system?


Ubiquitous car photo:



Cheers,
Chet

[John Rogers]

Hummmm, on here and the other two 914 sites there are lots of pictures of four cylinder engines with carb conversions. Generally the head connections are capped or blocked off and a line with no PCV valve in it is run to some sort of puke take. On the VW sites they show and sell pretty cast aluminum ones that bolt to the firewall or you can use some sort of jug with a holder so you can dump it now and then. BO NOT put the oil back in the engine.

If there are leaks at the valve covers, see the tech article I wrote on here for fixing the slipping gaskets and run a vent from each cover to the vent tank.

Do not try to run a line into one of the intake manifolds or there will lots of smoke.

[Dave at Pelican Parts]

Originally Posted by PropellerHead

Has anyone been running a 195/55-15 tire? Is this 'too short'?

I know that 195/50 is too short! I didn't think so in the past, but I have changed my mind on that. Something about running 4000 RPM to keep up with freeway traffic may have had some influence there...

There should be a number of fairly grippy 205/60-15s out there. At least, there were a year or two back. I'd suggest looking at 205 width, and anywhere from 50 to 70 aspect ratio. Some will probably not offer much choice, but the 50- or 60-series should.

Question 2:
Crankcase ventilation - I have Dellorto 40mm twin carbs (FI was long gone on this car when I bought it) and they don't seem to have a vacuum source to connect to the PCV valve on the oil filler set-up.

As John said, with carbs you don't run a vacuum to the PCV system. Just run the lines into a breather box of some sort, and then either into a puke tank or (probably after additional oil separation) into an air cleaner.

--DD

[PropellerHead]

Thanks both Dave & John,

PCV:
Car has one of the breather box/puke tanks mounted on the firewall. When I bought the car it wasn't properly connected but was present.
I'm confused about the absence of a vacuum source though. PCV systems of old ('Merican cars) that I'm used to had carbs and a manifold vacuum source for PCV. Early cars used a crude draft pipe but since the 60's at least used manifold vacuum to draw vapor. The 2.0L FI system did the same. Had a fresh/filtered air source and a vacuum draw (post throttle) with check valve on the filler neck console. I guess I don't understand why it would be advantageous to *not* actively draw vapors from the crankcase via vacuum.

I know with a dual carb set-up that I would want to draw equally from all 4 ports, not use a single port as that would cause fuel balance problems. Interested in ideas!

Tires:
Data below is from tirerack as it has easy access to data and a good selection. Other options may exist as well and I will do some additional searching once I narrow a size down.
In the 205/60-15 size, nearly everything available is a 'touring' class all-season tire. Nothing exciting except the Yoko r-comp tire (which is a little over the edge and $$ for a small street tire!).
The 205/55-15 has only one performance tire (Dunlop Direzza) but is some 1-1/4" smaller diameter than above.
205/50-15 has lots of good options but is another 1/2" smaller in diameter than the above making it almost 2" difference from the 195/65 on the car.

The 195/55-15 is taller than the 205/50 (*almost* as tall as the 205/55) and has a bunch of exciting options and quite inexpensive and exciting options for tires.
Since this car went almost 20 years on the last set of tires......while I expect to drive it more than the prior owners did in that span, I don't really care about tire life.

[John Rogers]

No vacuum source is needed with carbs as you mentioned, what you have is the same as old US cars had many years ago. On these air cooled engines you will have some pressure build up in the case section and a 3/4 inch or so line from the breather box location to the vent tank is all that is needed. No PCV valve or intake connection should be used.

[Dave at Pelican Parts]

Most of the original D-jet setups did use manifold vacuum on the PCV system. Some did not. (I think the 75+ did not?) Unfortunately, you wind up mucking with some of the assumptions that the system was designed to work under when you switch over to carbs. So most people just set up something to deal with blow-by and ditch the original functionality. That's where the lack of PCV valve, lack of vacuum, and presence of a puke tank come in.

Note that the PCV valve in the D-jet setup was only supposed to open at moderate vacuum conditions, to make sure that you wouldn't pull too much oil in when at WOT. See Brad Anders' dissection of a stock PCV valve for more info: PCV.

I think the main reasons not to use a vacuum source on the PCV system with carbs are:
- Lack of a good place to get a clean vacuum signal
- Possibility of sucking oil into the intake under certain driving conditions
- Lack of desire to re-engineer the PCV system to take the above into consideration

--DD

[PropellerHead]

Thanks again guys. As always, our host has created a valuable resource for enthusiast Porsche owners.
Cheers,
Chet

[porschetub]

Originally Posted by PropellerHead

Thanks both Dave & John,

PCV:
Car has one of the breather box/puke tanks mounted on the firewall. When I bought the car it wasn't properly connected but was present.
I'm confused about the absence of a vacuum source though. PCV systems of old ('Merican cars) that I'm used to had carbs and a manifold vacuum source for PCV. Early cars used a crude draft pipe but since the 60's at least used manifold vacuum to draw vapor. The 2.0L FI system did the same. Had a fresh/filtered air source and a vacuum draw (post throttle) with check valve on the filler neck console. I guess I don't understand why it would be advantageous to *not* actively draw vapors from the crankcase via vacuum.

I know with a dual carb set-up that I would want to draw equally from all 4 ports, not use a single port as that would cause fuel balance problems. Interested in ideas!

Tires:
Data below is from tirerack as it has easy access to data and a good selection. Other options may exist as well and I will do some additional searching once I narrow a size down.
In the 205/60-15 size, nearly everything available is a 'touring' class all-season tire. Nothing exciting except the Yoko r-comp tire (which is a little over the edge and $$ for a small street tire!).
The 205/55-15 has only one performance tire (Dunlop Direzza) but is some 1-1/4" smaller diameter than above.
205/50-15 has lots of good options but is another 1/2" smaller in diameter than the above making it almost 2" difference from the 195/65 on the car.

The 195/55-15 is taller than the 205/50 (*almost* as tall as the 205/55) and has a bunch of exciting options and quite inexpensive and exciting options for tires.
Since this car went almost 20 years on the last set of tires......while I expect to drive it more than the prior owners did in that span, I don't really care about tire life.

Dave makes good points over tyre choice,its a trade off however ,go small and get the engine on the boil cooling wise (always good in the summer) and have speedo error to deal with.
I strictly use tyre calculators on the net and strive for no less that 3% error,you can't go too wrong with this ,be aware that a 205 series tyre is a little big for the rim in the lower profiles...the sidewalls tend to move around a bit under heavy cornering,up to the owner really
As regards to your crankcase breathing,if your engine is in good health you can vent to the one of the air cleaners without much issue,if your motor is worn with more than healthy blowby a "puke can" as Dave suggested is the only way to catch the vented oil which will require cleaning often.

[porschetub]

Sorry Chet forgot by the way looks like a nice car,hope all will go well for you and nice to see another member "on board" here,cheers.