Tom F

I'm sorting out my newly rebuilt 3.0 Turbo motor - stock except SC cams, K27 and later exhaust. I have seen (with help from Chet930) that the ignition timing on these cars is not right. Mine runs a vacuum retard unit, which is all wrong with a super low compression motor, like this one. The retard is probably there to light off the wretched thermal reactors, which are gone now. The easiest fix is to simply disconnect the retard. I did, and it helps, but it doesn't completely fix it.

It seems to me that what I need is a simple centrifugal advance with around 20 crankshaft degrees initial timing, and around 30 degrees at 4000 crankshaft rpm, with a gradual retard from there. This is what the original 3.0 Turbo in Europe ran, according to the diagram I found in the shop manual. My '77 US distributor centrifugal advance runs from around 10 crankshaft degrees initial advance to around 30 at 4000 rpm. So, I think that I would gain by altering my distributor to match the Euro spec., in other words, cut the total centrifugal advance by half to get a more advanced intial setting while not going too far advanced on boost.

Has anyone else tried this? Can anyone recommend a shop who can recurve this somewhat exotic distributor? (The only cars to use the clockwise rotation with an 8-pin CD box are the 3.0 Turbos.) My impression is that ignition timing is more of an issue in optimizing the performance of these engines than is the CIS that everyone curses. This engine is just begging for a crankfire ignition setup, with computer control to adjust ignition advance for boost level. Is there such a thing?

P.S. According to McInnes' book, the original Corvair turbo did something like this, but GM added a turbo boost retard - the car would run something like 40 degrees centrifugal advance, but back off to around 30 with a boost operated device. Good idea, until the retard unit fails, at which point your motor would likely turn to shrapnel.

I also notice that the later Turbo 3.3 runs a total centrifugal advance of just 10 crankshaft degrees, yielding timing under load that should be close to what I want for my 3.0.

nathanUK '81 930 G50

Stephen of www.imagineauto.com sells a gadget that does that. It is too technical for me to give you any advice other than for you to get in contact with Stephen Kasper.
I have heard that if set up correctly there will be a performance advantage for 3.0 or 3.3 930.

DeanM

If you can replace the springs in your dist. you can do it yourself. All you need is a set of aftermarket springs and a timing light. Try some springs out with the timing light and if they are not correct try some other ones. Or there is a guy in Harvard MA who has a dist mach.

FLYN930

Tom,

I would recommend contacting Henry Schmidt at Supertec. He can hook you up with what you are after.

http://www.supertecperformance.com/

Brian

mmastro

Hi,
I have a Euro 77 930 with SC cams, K27, Garrettson intercooler and headers and run Euro timing settings with no problems...Couldn't you just Euro-time it (as written in the factory manual) or must your US distributor be recurved to mimick the Euro one to achieve this?

I'm sorry, I don't really know enough about this subject to have an intelligent conversation.

Tom F

I think that Euro timing means 10 crankshaft degrees of centrifugal advance, in total. So, if the vacuum unit is disengaged, the timing would vary from around 20 degrees BTDC at idle to around 30 degrees BTDC at 4000 rpm, and taper off (retard) slightly from 4000 up to 6000 rpm. With my US distributor, if I set maximum advance at 30 degrees BTDC at 4000 rpm (vacuum disconnected), then I get around 10 degrees BTDC at idle, which is too far advanced for an engine with 6.5 compression ratio, in my opinion.

So, I think that my distributor must be recurved to acheive "Euro timing."

Tom F

Has no one experimented with different advance curves for this motor? It think that there must be room for improvement, because the 76-79 cars were set up with ignition retard to enhance the thermal reactors. I should have said in my last post that 10 BTDC is too far retarded for a car with 6.5 CR, not too advance. Thanks.

nathanUK '81 930 G50

I would guess that nobody wants to advise you because they do not want to advise you wrongly and for you to damage your engine. This sort of things needs to be done on a dyno and would take a lot of time.

Maybe you should buy a euro dizzy from a breaker in the UK ???

Oh, if you do, do NOT get it from Douglas Valley Breakers... DON'T ask me how I know...

A930Rocket

I'm sure Stephen (IA) or Steve (Rennsport) can help. Give them a shout.

Chet 930

I got 10 degrees BTDC (from what I remember) at idle and 29 at 4000 rpms. That worked great. It was when it was at 10 retarded at idle and who knows what at 4000 rpms that it ran crappy and was backfiring.

Stephen is doing the EFI on mine and it will be interesting to see what the ignition curve looks like after its tuned on the dyno.

sand_man

As for a source, I'd try one of our spnsors first - Imagine Auto. If no luck, then I'm confident Henry Schmidt (Supertec Performance) could hook you up. Honestly, I've found that there wasn't anything that Imagine Auto couldn't or wouldn't get for me! Prices were always fair, too!

Tom F

Chet930, it sounds like you're a few branches ahead of me on the early 930 evolutionary tree. Why did you go to EFI? Did you just get restless with the CIS? I like the CIS, personally, though I can see that it has its limitations.

I have comparable ignition timing to what you had, but I have some minor surging between idle and 2,000 rpm. Another Rennlister (thank you, Jim!) sent me some used injectors, which I will probably try after they're tested.

Chet 930

Several reasons for the EFI......first one being the strict Smog program in California. I know that the motor could be tuned better so that it should pass smog without having to be choked back on the CO output and ignition timing to the point where it will barely even run on the dyno at the smog station.And then its still a 50/50 chance it will pass. A lot of that is driven by the lack of an engine management system. Secondly, I feel that there is still more power hiding in the motor due again to a lack of an ECU of some sort. Third is that I personally think the motor can deliver the first two reasons with a friendlier powerband too than it had. It does come on pretty hard when the boost comes up although I know the bigger intake ports and cam timing are playing a part in that as well.

I'm wondering if the surging you have is the result of the fuel mixture being too lean or rich in that rev range?

Tom F

My control pressure is good (2.9 bar warm), my CO setting at idle is 3.1%, which is on the rich side, I think. The manual says 1-3% for a Euro car, which is close to my configuration. I had it at 2.5%, and it felt about the same.

Chet930, all your reasons for the EFI make sense.

My car never ran right with the LDZ for reasons other than the turbo itself, so I don't have a good baseline to compare the K27 against. I am not impressed with the boost below 3000 rpm with the K27. The thing comes on like gangbusters at 4000-4500. My sense is that the LDZ, being a smaller unit, would actually be more responsive, but produce less high end power. UPS lost my LDZ, so I can't put it back. Does everyone agree that I would be disappointed with the LDZ after running the K27?