Desirable jetting for Porsche 356c at high altitudes

[mmorrison]

I currently have a 1964 Porsche 356C, with Zenith 32 NDIX carbs, stock main jets (130) and idle jets (55). Altitude at my location (Kerrville, TX) is about 1,600 ft. I am considering driving the car to Colorado Springs, CO, maybe in June of next year. CS altitude is about 6,000 ft. Question...I am sure that the car will run much better at the higher altitude with different main/idle jets. Can anyone tell me what size jets you are using at the higher altitudes in your Zenith carbs?? Also, if you have the name of a vendor who can supply those size jets. Thanks

[Slip356]

Several yrs back, had a 356 tour of about 15 cars, started in Colorado Springs, down the east side of the Rockies, over them & then up the west side to Denver. This was a 10 day wonderful trip.
In preparation we had lots of discussion on carb jetting. I live in N Wi, likely about the same elevation as you. One guy from Mpls shipped his car to CarQuip in CS I believe & had them change jets for the elevation. Big mistake. Lasted about a day, he changed back in the hotel parking lot not fun!
I spoke with my trusted mechanic (who rebuilt my engine) he said unless you’re moving there permanently, don’t touch the jets. Learn to live somewhat erratic idle & loss of about 10% power. He was right. That’s what the other 13 cars did. My 62 cab still has the throttle cable for warm up so I just left it slightly pulled to compensate for rough idle.
All worked fine. Don’t fool with the jets unless you’re an expert and like fiddling with carbs.

[Jon Schmid]

One thing to be mindful of if you leave the jetting alone (I would): when releasing the accelerator to go downhill at altitude, expect the engine to backfire. My '64 C coupe with the 75HP 32NDIX carbs isn't so bad; my son's now 1960 1600S Roadster with the same carbs sounded like a war zone. No big deal--once we got/get out of the SoCal mountains the cars ran/run fine. Have fun!!

[Starbucket]

Don't mess with the jets, it won't be that bad, if anything bring a spare set of plugs incase you foul one.

[Bulli Klinik]

For a trip, it's not worth changing the jets. You may want to consider advancing the timing if you're here for a few days. Most air-cooled cars add about 5 degrees for our 6000+ feet. Most definitely add some timing if you're going up Pikes Peak.

Feel free to contact me if you need some tourist tips or want to stop by my shop. I restore 356's, among other things.
_________________
I've never met a Bus I didn't like.
Mike K
Bulli Klinik
Colorado Springs

[mmorrison]

No, this wont be just a trip to Colorado Springs....my son will take possession of the car and I don't know how long he will choose to live there, He may be moving back to Texas some day, but who knows? Considering the vehicle will likely be operated at the higher altitudes where he lives for an unknown period of time, I'd rather set him up with a jetting combination more likely to succeed in those circumstances. I've only driven the car in Texas for the 15 years of my ownership and have no experience or knowledge of how the higher altitude will (if any) affect the engine (i.e. performance, maintenance, etc.). Thanks for your input.

[Starbucket]

If you plan to drive the car there don't changes the jets before you go or you might be too lean and burn a valve or two, wait until you get there to change the jets. The main jets go down to 115 and cost about $15 each, idle jets cost about the same. www.dellortoshop.com has them in stock. As far as what size you need to know if you are lean or rich at your altitude to know how many steps to go down. You can take a plug wrench with you and take a 10 min. drive at 50-60 mph down the hwy. then put the clutch in and switch off the motor (don't let it idle) safely pull off the road and pull a plug and read it, White=lean, tan=Good, and Black=rich.

[Bulli Klinik]

[mmorrison]

Thanks to all for the info...I spoke with Carb Rescue and got a rough idea of the size jets (main/idle) that might work for the higher altitude of C.S. Ordered from Alfa 1750 in Italy and requested 125 main and 52 idle jets. I'm thinking that I will probably trailer the car to C.S. this summer and change out the jets once I get there and see how it performs. Got good recommendations on Alfa 1750....he appears to have cornered the Zenith carb parts world market...will post the final results when we get to Colorado.

[mmorrison]

FWIW....I ordered main/idle jets on Feb. 15th and received them today (Feb. 19th)...brand new and sized as requested. Kudos to Alfa 1750