Andial twin plug conversion . No advance ? Help
 

I recentely purchased a pre built 2.6 RSR spec engine . It came with a Andial converted SC distributor for twin plug applications . The engine has roughly 11:1 comp and pings when the rpm is below 3000 . I pulled the cap to see what was wrong with the advance circuit and found nothing but a pickup and trigger wheel . What did andial expect the consumer to do with this ? I certainly dont want to retard the timing . Power on top is incredable . Unfortunetly the engine is not always run between 5-8000 rpm . Im using 93 octane pump gas right now . Does anyone have a suggestion ? Does MSD make something for me ? I guess I would need 2 of them as well . My timing is set at 25 deg btdc . Of course that is my base setting as well as high rpm . Hopefully someone has an answer . Those 92mm RSR pistons are not cheap .

Kurt Williams

http://forums.pelicanparts.com/uploa...1111983363.jpg

Blended race gas :confused:

Wouldnt more advance cause more pinging? I didnt think these distributors were supposed to advance much. Ive never heard the number for max advance on one of the RSR distributors, but isnt max advance for a modded 964 distributor ~24 degrees? It doesnt sound like yours is advancing at all. I know you said you dont want to, but have you tried retarding the timing to see if the pinging goes away?

friggin awesome motor, BTW. Are those cold start injectors in the aircleaners? :cool:

Thanks Sherman, yes they are cold start injectors . This engine actually makes more power that the BAE turbocharged engine it replaced . Thats a real 019 RS pump on there too . It was built by Al Bass on an aluminum 67S case . 2.0 S nitrated crank and rods with RSR 2.8 pistons and cylinders. Thats 66mm x 92mm . It revs to the moon and sounds like no other porsche engine ive owned .

Now back to my question . Anyone ????

Kurt Williams

Quantify a few things, there might a an ECU mounted somewhere in the system that controls advance (somehing must be handling it). Look for a flywheel sensor and use a timing light to see if there is any RPM related change in advance.

No . And No

Kurt, sorry for the going off on a tangent right off the bat :) check out the edit I made to my earlier post.

Have you tried retarding the timing to see when the pinging goes away? Isnt 25 degrees close to or exceeding max advance for twin plugs?

I havent yet retarded the timing any . I suppose turning it back a few deg is worth a shot . Im still wondering what Adial was thinking and better yet why would this be purchased at the price they charge . I do notice that the pinging does not start until the engine is fully warmed up . So maybe it will go away . However I really dont want to settle for this . I think is a crude compromise . Where is Grady when you need em ?

Kurt Williams

Do you have a CHT sensor? Maybe pull the fan and make sure there is not a rats nest or anything else obstructing airflow to the top of the cylinders and then switch to a '78-'79 SC fan with the 1.82:1 turn ratio. Block off that heater output also. Here is a link for Grady's 'Rubbermaid Solution'

Oil temps have not yet gone past 195 deg f . And I drive it hard . The heater outputs are capped off and not leaking . I will be swapping on a set of SSI`s and removing the RSR headers this coming fall . So they will stay that way until then (yes thats an eyesore)
The inside under the shroud is 100% clean . I realize the engine kinda looks like crap since I paid no attention to detail yet . But its certainly free of any rats nest . I actually did shine a light in there last week because it was resting for the last 3 months in my garage . It was still free of any leaves or nests .
I dont have a cht . I figure its not experiencing high head temps since it only ping`s at low rpm . Actually when it starts pinging I can make it go away by pushing the pedal down a little more . I believe thats because the mfi puts more fuel and that cools the combustion charge a little . I should also note that an engine(at normal running temp) with the base timing set at 25deg btdc would normally be hard to crank/start due to the advanced timing . Mine does not . It starts normally even with the 11:1 ratio .


Kurt Williams

why not give Andial a ring?:D

Is it possible that the engine is running a little lean at low rpms and that is causing the pinging? Based on what you stated above this might make sense. Good Luck, Sam

Sam no dought you make a good point . But until I just the timing issue corrected I dont plan to touch what appears to be a perfect working MFI system . And I dont think that the mfi design allows you to alter the mixture at different given engine speeds . As far as I know its a progressive enrichment altered only by rpm , temp, and throttle position . But im new to the mfi world as far as tuning goes .

Kurt Williams

This doesnt help the fact that your distributor is not advancing, but I did find an old thread from Grady saying that Max advance on a twin plug distributor should be 20-26 degrees.

http://forums.pelicanparts.com/porsche-911-technical-forum/161001-twin-plug-dist-tdc.html

I agree, doesnt sound like you have a reason to touch the MFI

Kurt,
Perhaps that's the way the factory did it for a RACE engine on race gas. I don't know.

However, you obviously have too much low end advance for your driving and operating conditions. Good thing you discovered it before any damage was done. In the meantime, I'd retard the timing so you don't burn a hole in anything expensive. The power will go away until you find a solution, but that's only temporary.

MSD and Crane sell electronic advance boxes that allow you to customize an advance curve within their design parameters and max. advance limits. With one of these, you'd adjust the timing at idle to 5ºBTDC or whatever works best by manually adjusting the distributor, then the box takes care of the rest with the help of a laptop computer. You could optimize the advance curve with this box on a chassis dyno. Not sure whether you'd need one or two sets of spark and ignition control boxes.

Another option would be to sell the twin plug distributor and change to a crank fire system and electronic control. I'm sure you'd be dollars ahead due to the resale value of the rare Marelli distributor. The Marelli looks period correct, but you may or may not care as long as it's low maintenance, consistent and flies. I'm sure you'll have other suggestions as well.

Sherwood

Sounds like you may have a 935 style distributor, which has no provision for variable advance. Maybe?

Kurt - I have a new Andial-converted twin-plug distributor based on an SC unit with Bosch twin-plug cap & rotor which I bought on ebay last year.

I contacted Peter Sanchez at Andial to seek his advice as it too seemed to have no visible method of advancing the timing - this was his (partial) reply:

"...The SC distributor is used because it has the proper electronics inside while having the most useful advance curve for most applications. The turbo distributors are used also but only on turbos.

We do not tamper with the advance curves, if it has been done it was by the customer.

The vacuum advance should still be intact on the distributor unless the owner instructed us or took it upon themselves to remove it. The advance plate needs to be locked down also though so it doesn't move all over the place and advance the timing randomly".

Well, I don't know how the ANDIAL guys do it, but it seems that a pretty common high performance modification is to have a distributor thats had the timing locked out at the high RPM setting and then to use a retarding device to get the engine to start and perform at low RPM. This is, in fact, the way airplane engines are set up (except they use an "impulse coupling" or "shower of sparks device" to retard timing for starting.")

MSD and others make such boxes. Having said that, the folks at ANDIAL certainly know what they are doing and I would inquire with them directly for the solution.

Wow thats good news . I will call andial tommorow morning . Thanks,


Kurt Williams

Hi Kurt, what did you find out here?

Your original post is very confusing:

"I pulled the cap to see what was wrong with the advance circuit and found nothing but a pickup and trigger wheel"

You need to remove all of the guts of the distributor to see the centrifugal weights at the bottom. Doesn't sound like you did this?

The RSR distributors originally came without advance mechanisms. This is because they ran in a relatively narrow RPM band all the time on the track and did not need them.

I would suspect that your distributor (if it indeed is a converted SC one) has the mechanical advance way down in the bottom. It's probably stuck or not working completely.

-Wayne

Wayne:

A correction is needed here,...:)

RSR distributors (2.8 Marelli & 3.0 Bosch) ALL have advance mechanisms. They need that for starting a high compression race engine as well as running decently below 5000 RPM.

935 distributors (Bosch) did NOT have any advance mechanism since starting a low compression engine at 25-26 deg total works fine. BTDT in both cases for many years. :) :) These motors are well known for some uneven running below 5000 RPM from that early spark and are pretty jerky to drive slowly (exacerbated by a TALL 1st gear).

Kurt's Marelli does indeed have an advance mechanism (below the trigger plate)and I'd kindly suggest that he get that checked on a distributor machine to make sure that its working correctly.

Lastly,......even with twin-ignition, you cannot use any pump gasolines at 11:1 CR. :) Run 100 octane unleaded race gas to prevent risking those ultra-rare and now dreadfully expensive 92mm RSR P/C's.