detonation, timing and fuel mixture advice

[twin plugged targa]

Hi I know I have touched on this before but I have been doing a bit of research since and want a bit of confirmation if possible.
My 2.7 twin plugged 10:1 system (weber carb) is pinging only above 4K rpm when under full acceleration.
I rotated the distributor (twin distributor setup similar to 964) and beleive retarded it somewhat. Result was reduced pinging and performance.

I have since located some race gas and will try that on next trial.

The car has been used with original timing settings in Florida with no noticable pinging. But when used in the UK and Northern France, pinging was evident.
I have read that in colder climates, the fuel mixture is leaner due to denser air?.

So might my 1st step be to try and adjust the Webers to run richer and leave the ignition as original?.

I this easy?
Do I need weber adjusting/tuning tools?
If so where can I get some?

I would like to try to resolve/improve this myself as the car is in Normandy, France and have had no success in locating good local garages.

Any help advice appreciated.
rgds
Ben

[Formerly Steve Wilkinson]

Sounds like your first step ought to be to buy a timing light.

Stephan

[twin plugged targa]

I guess the next step after that would be for me to figure out how to use it

Are they easy to use or is it an area I should leave to the professionals?
Thanks
Ben

[jluetjen]

Yes, you're going to need to learn to use the timing light (pretty easy) and then determine the correct adjustment (not so easy). It may be just as easy as advancing or retarding the spark, but it may involve recurving the distributor to get maximum performance. What's the rest of your ignition like, is it stock or is there a computer that can be remapped or rechipped.

Alternatively I'd recommend finding a local dyno and take the car in and have them tune it while on the dyno.

BTW, In colder climates, I believe the engine is tuned richer to take into account the denser air.

[twin plugged targa]

Sounds like the tuning with the timing light may be beyond my expertese.
I may take the car back to the UK to somewhere like Auto farm or similar to have an oil cooler fitted and have the timing set up same time.

As for the ignition setup I believe it has been done as described here from a Rennlist article:

"964 Dual-distributor converted for 2.4-2.7-3.0-3.2 litre Engines. This one is done by installing a trigger from a donor SC distributor and using the appropriate crank gear, depending upon the engine being used. This unit will not fit the Turbos' due to interference with the boost plumbing. Again, these can be triggered by OEM Bosch CD boxes, Permatune's, MSD's or a proprietary splitter unit for Motronic-equipped engines. This setup is ideal for any Motronic motor and works very well in carbureted or MFI-equipped engines."

So there is no electronic ignition and so no ECU/chip. Therefore I still believe that with the colder air that she could be running too lean as there is no built in compensation?
Please feel free to correct me and advise as necc.

I was kind hoping that I could get away with some minor carb adjustment and not get into the timing setup.
This engine was running fine in Florida

Maybe I should just ship it back!!!


Thanks again for any advice/input
Ben

[RoninLB]

Originally posted by twin plugged targa
. Therefore I still believe that with the colder air that she could be running too lean as there is no built in compensation?
Please feel free to correct me and advise as necc.

colder air is more dense. thinner air would cause a lean.

[Formerly Steve Wilkinson]

Using a timing light is about as easy as using an electric shaver, but you do have to at least have a basic understanding of _why_ you're using it and what it's accomplishing. If you're up for learning that, we can probably walk you through it.

Stephan

[dean]

Back in the dark ages I used to jet carbs. You are going to need to go to a larger main jet for WOT richness. If I were you, I would see what you have for main jets now and buy a few larger sizes. Then try them out. Keep a jounal of what you do and how it runs. Change one thing at a time. Boy do I wish they had EFI back then.

[911pcars]

Different fuel octane or fuel blends might have a bearing on pinging at different locations. Altitude the same? Higher altitude = less spark advance necessary.

High compression and excess spark advance cannot coexist w/o potential engine damage from detonation. Be careful.

Twin plugs makes this less of an issue, but still needs oversight.

I suggest some chassis dyno time to sort out tolerable spark advance throughout the entire rpm range, then recurve the ignition advance accordingly. If one isn't local, find the closest one. In the meantime, retard the static timing (using timing light) so you're safely out of the pinging range.

Sherwood Lee
http://members.rennlist.org/911pcars

[twin plugged targa]

Thanks for the advice guys and merry xmas!.

I will contact you guys again when I am next with the car if I have the opportunity to use a timing light.
It still confuses me how the performance of the car can change between Florida and N. France?.
I used up the gas and put new stuff in with some octane booster, with no change.
As I mentioned, I did rotate the distributor assembly which I believe changes the timing?. I believe I retarded the ignition as the idle dropped along with overall performance and pinging.
The car sounds fine under normal usage, so I may drive it gently back to the UK and source a good tuning P -Garage to tune /adjust it properley as I do not want to melt a piston!.
I do tend to drive my cars 'like I stole them' so I will get this sorted properly.

Wish I had the luxury of time, internet hookup, and you guys assisting as it would have been nice to fix this myself. But I am missing the ingredient of time for the moment.
PLus the issue that I am on the other side of the 'the Pond'.

Thanks once again and happy holidays
Ben

[dean]

I bet it has to do with the air density. The air is warmer in FL so it is less dense. So your motor is getting less air. In colder weather just the opposite. More air in the motor with the same amount of fuel means a leaner mixture.

[Oldporsche]

Back in the last century, I happened to be stationed in Germany. They had crap pump gas. It smelled like varnish. My VW didn't care however.

There are plenty of go fast types in UK or France for that matter. I believe that there is a PCA group in france. If I remember correctly they have a website. You might find some help there.

Good luck,
David Duffield

[twin plugged targa]

Hi Dean,
I read aniother thread where Turbo guys were debating the aspect of colder air = denser air= leaner burn.
But Ronin stated the opposite.
I may try and turn the webers before I change the timing.

I will try and do some research online with regard to french porsche sites, but my written french is not great esp. when it come to auto terminology!.

Thanks
Ben

[beepbeep]

Well, you run Webers and that's unmetered system so yes, it leans out when cold, as you draw more air and squirt equal amount of fuel.

Is there particular reason for carbs?

[dean]

The best thing to do would be to tune your carbs while on a dyno. Then you would know what your air/fuel is and what is going on with the power. Another way would be to install a wide band O2 sensor