Pulling the inner vac line is like having the solinoid in cold start permenatly. This blocks the vac-retard and thus advances timing.

If your car runs well this way dose not seem to be any risk. However idle timing should come in more like -15 or more, if the dist is advanced to its stop and the vac-retard is disabled.

Running with the vacuum retard line disconnected and the distributor turned clockwise in it's slot all the way makes idle timeing advance too far on my car.
The idle becomes higher of course, but also rough and kind of nasty.

Not knowing what the actual timing under boost would be if you did that could be a very expensive risk.

Yeah, that would probably give you 16 degrees advance (8 from rotating the dizzy, and another 8 gained when disconnecting the vacuum retard). From what I've heard from others, is that it will run choppy at idle and won't really clean up until around 2500. Just too much initial advance. Probably wouldn't cause any harm, provided you have a boost timing retard module to shave it all off before any significant boost.

Jim,

Your car and mine are both running about the same from what you've described, and we're both able to get no more than 8 degrees advance by twisting the distributor to the max (with the vac retard hose connected). And neither of us are using the vacuum retard solenoid.

Your settings: Start retarding at 5psi and the seperate retard slope control knob mounted in the car is currently set to retard timing 2 degrees for each pound of boost.
You should see all 8 degrees of added advance being removed by 9 psi of boost, and another 7 degrees retard by 12.5 psi.

My settings: Start retarding at 2psi, and retard timing 1.5 degrees for each pound of boost. This should result in all 8 degrees of added advance removed by 7 psi of boost, and another 7 degrees retard by 12 psi of boost...for a net total of 15 degrees.

I was being conservative when I first installed the BTM, paranoid to where I wanted all the excess timing removed by the time I was halfway into maximum boost, and I stopped messing with it until gaining a bit more knowledge.
I think your settings are more appropriate, not being concerned with the extra advance until 5psi, then shaving it off quickly after that. And I think you're correct in your observations that more timing on boost doesn't result performance gains, but rather engine damage risks. Get as much timing as your car can stand early on for low/mid range power, and get rid of it by the time you're half way to your maximum boost.

One more thought, that I started experimenting with before I put everything on hold (with a broken foot). The BTM will continue to remove timing as it continues to see boost pressure rise, up to a maximum of 15 degrees. So in both examples above, what we're actually seeing on full boost is probably 7 degrees less advance than running without the BTM. That may not be a bad thing from a safety standpoint, but may leave some power on the table.
I put in-line with the boost pressure line to the BTM, a pressure regulator that won't allow the BTM to see any more than 8 psi of pressure. That way, I still get all the 8 degrees removed by then and no more removed as boost continues to build. Not sure of the impact yet since I've done but one run with it, but in theory it makes sense.

Advancing the timing at idle until the idle becomes choppy can't be good for the rod bearings or piston ring lands.

The choppiness is caused by the mixture being lit off too early before TDC, and that would be loading the rod bearings in a bad way before the piston reaches top dead center.. especially while the oil pressure is low at idle.

I've played with bosch distributors alot on old 4 and 6 cylinder BMW's in the past and advancing the timing at idle too far makes them idle rougher too.

I know you may have put your car away for the winter and you're possibly at work right now but do you remember what psi you set your boost retard start point too, and where you set the retard slope knob?

Thanks, you and Cole are the one's that inspired me to do this and it does make the car a little stronger at low speeds and especially getting away from a stop when the turbo isn't boosting.

See my editted post above. I sent it prematurely and wasn't done typing yet!

MSD recommends setting the 8762 retard start point at 2psi in the beginning of tuning but I think the majority of people installing these things are on supercharged drag racers with higher compression than the 7:1 in our cars, so I think the 2 psi retard start point is conservative for a 930.

With the windows up so I can hear the motor better during full boost acceleration I don't hear any ignition knock sound, pinking or pinging, or detonation of any kind so I think the 5psi start point and slightly steeper retard slope curve works OK for the low compression 930 motor.
I don't know if the final amount of ignition retard is the same though.

When I turned the knob to around 1 degree retard per pound of boost under full throttle, 5000rpm and 1 bar boost I begin to hear what I think is some ignition knock (but none of the higher pitched crackling pinging or pinking noise of detonation) while there doesn't seem to be any more power increase going on, so I quickly turned it back to 2 deg retard per pound of boost and the faint knocking noise goes away while the car seems to keep accelerating just as quickly.
Retard the knob to 3 degrees per pound of boost and I can feel some power go away.

HMM, interesting you guys mention higher idle timing causes a rough idle. With EFI, the more timing I threw at it - the better (smoother) it idled. I'm at -20* advance at idle right now and my idle rpm moves less than 50rpm while sitting still. When I tried -10* it seemed to be unstable and very sensitive. My cruise timing is around -28*

What is your idle AFR?
A slightly rich idle mixture will be unstable and oscillate up and down with stock igniton timing at idle but advancing the idle timing will even out and stabilize the idle even if it's richer than needed.

I have my idle AFR right around 14:1

steady cruise up to 3000rpms is around 14.5:1

Using the timing change that comes with a loss of vac to accelerate the motor seems like it might be beneficial in it's own right.

Just because a motor can handle more timing at idle w no load dose not mean it can use it under load as it begins to accelerate the motors mass and then the car.

I have reason to believe these motors can take as much as -23 at 1000rpm at idle with no load. However, under load no more than about -16.

By 1500 something like -23 with no load / no boost but only about -20 at .2 bar under load.

Thus something that starts at or jumps to -16 should be good off idle and we should be able to use about -20 by 1500.

----

For those not using MSD I believe there is off idle throttle response and on cruse efficiency to be had from modifying the Boost Retard stop that limits the range of motion of the pot. This would increase the level of boost or vac retard for more advance off idle and more advance on cruse while keeping the same on boost timing value.

Mark and J,

I'm as confused about all this as you two. This Ultimate thread has made me crazy. I'm going back to what I know and what I don't know. One thing for sure is I have no idea what my distributor really does or doesn't do. Then when you add boost anything you thought you knew about timing goes out the window anyway.
I will say I'm pretty confident that at 1 bar your timing needs to be between 18 -22 degrees. But this is also true only if you are still running stock compression. I have looked at numerous equations to see how to figure effective compression ratio at 1 bar and decided it would take a seperate computer to run the correct calculations and then only if you know from another computer what all the 108 variables are as they change under load and boost. Anyway I decided F--- it I'm going back to basics.

When I was told I had cancer everyone around me went nuts. My sons in law even drew straws to see who got to buy the "Old Sled" once I croaked. I thought about it and just figured we're all going to die of something and cancer is pretty simple, it either kills you or it doesn't, and a 50/50 chance is pretty good. You just gather all the information you can and you do everything you can to beat it and either you kick it's ass or you go out swinging.

I happen to be the most bone stubborn SOB on earth and I don't have any quit in me. So I've decided this modding a 930 is much the same, the d--- thing is either going blow up or it's not. If you don't have the balls for it then don't go there. If your going to go there then gather all the information you can and use it to give yourself the best chance of keeping the heads on it. After all the factory ran these motors at 1.4 bar flat out for 24 hours.

After all this s--- it still boils down to one thing, detonation. If you can control detonation you can safley run .9 to 1 bar without incident. We alredy know a lot about controling detonation and we need to put these safegards in place before you start pushing the envelope. (Oh GOD NO .... I just opened the door for another commercial advertisement from John at J&S) Does anyony know if he even owns a Porsche?

If you are even considering changing to a higher compression ratio, know you better be prepared to spend 6-8 grand on preparing block, crank, rods, cams, pistons, and fasteners even before you start looking at heads, ignition, and a fuel system. So before you ever start down this slipery slope you need to determine how you are going to use the car and be realistic about it. Reaper930 has the ultimate weapon when it comes to turbocharged Porsche street cars but I'm betting you could not build it for less than 150K. And once it's build maintaining it is like pouring buckets of bucks off a bridge and it would be awful to drive on the street full time. I think it's the knat's ass but unfortunatly I can't afford one so I just remain green with envy.

I've always known what I wanted. A neat, clean 930 with 375-400 HP that's fun and easy to drive on the street and fast when you want it to be. I have also known what I needed to do to get there, starting with controling detonation. I bought the car with 52,000 miles, SC cams, light porting, and a K27 7200. I immediatly bought a better intercooler, 964 bov set up, a good set of headers and I always run the highest octane fuel I can find, without exception. The intercooler, headers, and fuel octane are three of the four, must do, things to control detonation. The fourth and most difficult is fuel system control. You HAVE to know where your Afr's are at and you Have to be able to control them. I've gone with an Innovate LM1 and I'm going to be monitoring afrs, rpm, MAP for boost and vacumme, EGT at the collector Y, MAT for intercooler and manifold temp, CIS system pressure, CIS control pressure, and on board afr readout. As near to an in car dyno as I could get. I can download all the information and tune accordingly. The tuning is the tough one, you HAVE to be able to control the afr's, so here comes the dwur, adjustable wur, or andial with a clamp. If you don't have one of the latter all is for nothing.

At this time I'm not going to worry about timing because there is no way to get it right without a Dyno. I'm going to start with 10o of advance and 18-22 o at .8bar, once I get the afr map done I will play with timing. I bought a MityVac and I took a blood pressure cuff and a 15 lb go kart tire gage to make a boost simulator. I have a digital timing light with adv and retard dial. I can screw with the timing then without worrying about detonation.

Don't know of any better way to do this but I'm always open for suggestions.

Cole

Cole,
I feel your pain and I am with you 100%. The factory pieces were designed and manufactured to do one thing......work very effectively and reliably with a stock engine. Change fueling, boost, VE, ignition without safeguards or monitoring and you're "dancin' with the devil" my friends.

David,

I get such a kick out of all this, I try to read everything I can and then sift through it to get the fly s--- out of the pepper. Always assuming I'm going to walk away with some valid enlightenment; that's what makes this site so great. All you bums kept me going when I was doing 6 mo. of chemo and sitting here at 3 am with a bucket between my legs and I love every one of ya so don't take this wrong. I have read 333 posts and still don't know exactly what my factory distributor specs. are and have no real idea what the timing curve should look like.

But hay !!! Keith is way to serious, Mark is as twisted as I am, and J keeps me grounded but all in all it keeps me from robbing banks or something.

Cole

well, i've been playing with fuel pressure and injector pulse widths to get the 60# injectors to play nice at idle. If I drop the inj. duty cycle below 1.5 the idle begins to hunt (at any timing number) but with the fuel pressure where it was my a/f was 12.4 at idle. I've been lowering the fuel pressure to lean the mixture but i'm sure there is a threshold where the injectors won't tolerate to low of a pressure. The cold race plugs we put in the motor will have to come out as they foul easily which adds to the tuning stress.

Last night I started the car after 7 days and before i could back it out of the shop a plug fouled :( as it was warming up in the high 11's a/f (still haven't fine tuned that)

What AFR's are you guys seeing with acceleration off idle and cruse?

Are you seeing a lean surge with first throttle?

I believe off idle there would be more TQ at around 13/1. Same off curse till boost comes on.

That is one of the reasons why 3 to 3.5 CO seems to work well. Not great for MPG though.

Just an idea but, in cold start, cold a engine situation, could it be the cold start idle valve needs to be adjusted/programmed? Seems your plugs are fouling to an over-rich condition due to the lack of air fed to the engine in a cold start? Maybe the IAT programming could be the root of the problem.

14.2 to 14.4 at idle, depening on engine temperature, air temperature, and the WUR's mood of the day. I do not see a lean surge when stepping on the throttle from idle...usually drops to about 13.8 at that point....most of the time. I don't think that CIS is capable of delivering extremely repeatable AFR's as you might see with EFI; thus my results differ somewhat day to day.

Which #60s do you use? Mototrons have become problematic after the change of manufacturer. The quality has gone and IIRC they follow the spec only at 3bar.

I love ya' man, and couldn't have said it any better. I've got so much f---ing information rambling around in my head that I'm at risk of confusing myself as well as others.

For us Boost Timing Module MSD junkies, 10* advance with vacuum retard active/5 psi threshold/2* for each psi retard curve, adjustable or DWUR, mandatory AFR monitoring, larger intercooler, 1.0 boost max, 92 and above octane - and I think we've taken as much risk out of the additional timing equation as possible for street draggers. The only remaining piece that I want to see to fill in a blank spot is: What is the timing at 4000 rpm's with .8 to 1.0 bar of pressure applied to the BTM? If either of you haven't put your baby to bed yet this year, that little pice of info will help us sleep at night.

Accept the risk with eyes wide open, enjoy the ride, or sit on the porch with the old dogs and watch the world go by.

I'll buy you a cyber beer after work tonight.