Timing advance...where's the safe limit

[mark houghton]

I'm full of it this week, spending too much time here - someone tell me to get a life.
I'm contemplating switching to an MSD6BTM to allow programming ignition boost retard, so I can take advantage of some additional timing advance at lower rpms and perhaps gain some bottom-end performance. Memory says that my idle timing is set retarded at factory 1-2 degrees ATDC. I would like to advance that, then retard it back out when on boost. But how much is too much before I need to start worrying about exhaust gas temps and the like? Would say 10 degrees BTDC at idle be too much? Of course that advance would be taken out a like amount on boost, to keep me at around 26-28 ATDC.
Thoughts/experiences? Is this really worth the effort and investment from a performance standpoint, or will I toast my motor into a pile of molten metal by advancing the non-boost timing? This is new territory for me, so excuse my ignorance.

[356-930]

Originally Posted by mark houghton

I'm full of it this week, spending too much time here - someone tell me to get a life.
I'm contemplating switching to an MSD6BTM to allow programming ignition boost retard, so I can take advantage of some additional timing advance at lower rpms and perhaps gain some bottom-end performance. Memory says that my idle timing is set retarded at factory 1-2 degrees ATDC. I would like to advance that, then retard it back out when on boost. But how much is too much before I need to start worrying about exhaust gas temps and the like? Would say 10 degrees BTDC at idle be too much? Of course that advance would be taken out a like amount on boost, to keep me at around 26-28 ATDC.
Thoughts/experiences? Is this really worth the effort and investment from a performance standpoint, or will I toast my motor into a pile of molten metal by advancing the non-boost timing? This is new territory for me, so excuse my ignorance.

Disclaimer: I am a pepper tree mechanic and write from personal experience on only one engine. My knowledge is thus limited and based in part from experience, reading pieces of the 930 tech spec book, reading this forum and talking to real P-car mechanics.
No, you won't toast your engine.
I now run 8-deg BTDC (have run 12 deg without incident but the engine miss-fired unless it was under load) at idle and pull timing back to 20-deg BTDC at 1-bar on a mostly stock CIS 3.3 liter without an intercooler. Street car, time in boost limited to 5-sec B4 shifting, water/meth injection to cool charge air.
With stock (0-deg at idle) timing, my engine is a dog. With +8 deg of timing at idle, it's an eager puppy.
I have seen two timing/map curves on fuel injected 930's and they run 15 deg advance at full boost. The factory timing recommendation of 28 BTDC at 3500 or 4000, (can't remember which) is when all mechanical advance is in, vacuum gone, no boost. Between the mechanical boost retard in the distributor (-8 deg in mine) and the MSD boost retard, you need to pull timing back to 20 deg BTDC or less at full boost. A dyno is a handy device here.
The MSD6BTM facilitates removal/retard of up to 3-deg of timing/psi up to a max of 15-deg. Onset of retard is 1-psi.
To best wake up the low end/no-low boost performance you should consider the MSD6AL with the 8762 Boost retard module. About $75 more but this setup allows you to delay onset of retard (I use 5-psi as my start point) then up to -3 deg per psi and a total of 15 deg of retard. This scheme lets you leave more timing in at low boost levels, a good thing I believe (but have no proof).

[mark houghton]

Thanks Chris, I was hoping you would chime in on this topic. And actually as I started doing more research, I did find that the MSD8762 is available. Since I currently am running with an MSD6AL, that would be an easy add-on.

I think I've got all this timing crap straight in my mind...I think.

Check me on this: By the book I normally set my idle timing at 0 degrees (TDC) with dist. vacuum lines disconnected/plugged, which achieves mechanical advance of 26 BTDC at 4000 rpm.

So, if I advance my idle (with vacuum lines still detatched) to 10 BTDC - and if I DIDN'T retard it back out at higher rpm - then my timing at 4000rpm (lines still disconnected) would be at 36 degrees BTDC (26 degrees stock setup plus the 10 additional I dialed in at idle).

Now, dial in 10 degrees of retard via the MSD and I would theoretically be back at the factory advance when on boost.

Confirm it all by applying air pressure (1.0 bar, since that's what I run) to the MSD and see that the timing at 4000 rpms is indeed at 26 BTDC (no vacuum lines). Reconnect the vacuum lines and go...knowing that the actual advance at boost would be less than 26 because the vacuum retard is now in play as well (I would have to strap someone to the back of the car with timing light in hand and doing WOT on boost to confirm the actual advance...since I don't have a dyno).

Clear as mud, or do I still have this all screwed up? I just want my car to be an "eager puppy" as well!

[cole930]

Mr. Mark,

I am runing that same set up. I went this way for 2 reasons 1. Eliminate detonation on the big end and 2. get the old girl off her fat A-- on the low end.
You are right on as to your understanding of how it will work. 8-10 degrees to start out is a good starting point and then play with it from there. Start retarding as soon as it comes on boost and try 24-26 as a total up top.
Brian may have some timing numbers for you as he has been playing with vacuum advance on his 930.

Cole

[fredmeister]

What are you guys using to apply boost pressures to the distributor during the timing process in the driveway? I use a Mityvac for vacuum but don't have a good tool to use to get the 14psi of pressure I need to check boost of the distributor.
Thanks

[mark houghton]

I just use my air compressor and dial the regulator way down, then check the output with a separate pressure/vacuum gauge to get it where I want it. Then just roll the compressor over, hook up the hose, and press the trigger (note: I let the first rush of air bleed to atmosphere because it spikes higher than desired until the regulator does it's thing). I use the same setup for checking WUR control pressure changes on boost. It's cumbersome but works. Actually, I've been looking to by a Mityvac for this reason. What....they don't do pressure, only vacuum??

[cole930]

I use the same Ace Hardware lawn sprayer I use for pressure bleeding brakes.

Cole

[fredmeister]

Originally Posted by mark houghton

I just use my air compressor and dial the regulator way down, then check the output with a separate pressure/vacuum gauge to get it where I want it. Then just roll the compressor over, hook up the hose, and press the trigger (note: I let the first rush of air bleed to atmosphere because it spikes higher than desired until the regulator does it's thing). I use the same setup for checking WUR control pressure changes on boost. It's cumbersome but works. Actually, I've been looking to by a Mityvac for this reason. What....they don't do pressure, only vacuum??

yep Mityvac only does vacuum. At least mine doesn't.
I thought of using the Speed Bleeder I have but don;t want to get brake fluid residue in the vacuum/boost lines to the dizzy.
I just wonder how accurate the regulator is on my sears 30 gallon compressor, they are not good at such a low range like 14 psi .

[mark houghton]

Originally Posted by fredmeister

I just wonder how accurate the regulator is on my sears 30 gallon compressor, they are not good at such a low range like 14 psi .

Agreed, that's why I use a stand-alone pressure gauge to set my Monkey Wards air compressor output. Don't trust the regulator until you know it's outputing what you want.

[911st]

I suspect the safe sweet spot on every motor is a bit different depending on factors such as AFR, turbo, exhaust design, inter-cooler efficiency, and changing environmental factors.

Great idea using the MSD boost retard. I have proposed that idea from time to time over the years as there is opportunity and risk left on the table w the stock spark system. However, ignition's are not really my area as that part was not adjustable on my 91 Turbo with its sealed and mapped system.

Please verify but I have heard about 24 deg at one bar is safe w a modified 930 at one bar however, that is just a rule of thumb.

As you know generally the richer the AFR the slower the combustion process. The higher the boost, the faster the burn. The hotter the temp of the charge, the faster the burn. The risk point is typically at peak HQ where combustion pressures are there highest.

As we do not have programmable ignition where we can pull advance near TQ peak and put it back, we might however be able to play the natural fuel curve against timing so we are a bit rich at TQ peak.

I good dyno tune by someone that knows what they are doing is valuable to find the ideal and get the most out of a given 930 build. I believe they advance timing little at a time until HP starts to peak and go flat and then pulls back some to keep it safe w/o losing power. EGT monitoring can help with this to.

Sounds like you will end up with one of the best running 930's around.

The best.

[mark houghton]

Originally Posted by 911st

I suspect the safe sweet spot on every motor is a bit different depending on factors such as AFR, turbo, exhaust design, inter-cooler efficiency, and changing environmental factors.

Great idea using the MSD boost retard. I have proposed that idea from time to time over the years as there is opportunity and risk left on the table w the stock spark system. However, ignition's are not really my area as that part was not adjustable on my 91 Turbo with its sealed and mapped system.

Please verify but I have heard about 24 deg at one bar is safe w a modified 930 at one bar however, that is just a rule of thumb.

As you know generally the richer the AFR the slower the combustion process. The higher the boost, the faster the burn. The hotter the temp of the charge, the faster the burn. The risk point is typically at peak HQ where combustion pressures are there highest.

As we do not have programmable ignition where we can pull advance near TQ peak and put it back, we might however be able to play the natural fuel curve against timing so we are a bit rich at TQ peak.

I good dyno tune by someone that knows what they are doing is valuable to find the ideal and get the most out of a given 930 build. I believe they advance timing little at a time until HP starts to peak and go flat and then pulls back some to keep it safe w/o losing power. EGT monitoring can help with this to.

Sounds like you will end up with one of the best running 930's around.

The best.

The MSD retard module is on the way and I'll probably have her all hooked up and going in a couple of weeks.

My goal is to start with advanced timing around 8 degrees BTDC, then sequentially retard the timing as boost builds in order to maintain the factory specified maximum 26 degrees BTDC at full boost (I run 1.0 bar with a cool air charge and generally slightly less than 12.0 AFR at boost).

There will undoubtedly be some trial and error, but I expect to gain performance at low and midrange off-boost where these low compression engines seem to suffer the most, and as a result maybe get a jump on how quickly the boost will build as well. Right now the only thing that gnaws at the back of my mind is the affect of more advance on the EGT's. Guess we'll see how it all goes!

[911st]

Again, not my area but sounds like a valid plan. I have heard others have found increased efficiencies by making the off boost ignition and AFR more ideal and I am excited to see you are doing this. Most get so hung up on the fuel side.

Increased EGT's of idle and at cruse will help your turbo spool. EGT's should be the same on boost if same advance is maintained.

In Bruce Anderson's book he recommends 25 deg advance. I understand when you get near the max TQ/HP point, there is little to no loss with pulling timing back some.

---As noted elsewhere, I also found faster spool and response modifying my compressor bypass so it stayed open at idle and cruse to keep my turbo spinning in reserve for when I accelerated.

[mark houghton]

Originally Posted by 911st

---As noted elsewhere, I also found faster spool and response modifying my compressor bypass so it stayed open at idle and cruse to keep my turbo spinning in reserve for when I accelerated.

I read your post on that awhile back but wasn't able to make any sense of it....perhaps because your '91 doesn't have the same boost recirculation valve that earlier 930's do. Maybe I missed something in your description.

[911st]

Mark,

That is why I keep bringing this and my fueling ideas up from time to time. Just hoping someone else will get it, do it, and enjoy there cars more. It worked for me.

The 91-4 Turbos and most after market inter-coolers have a different bypass valve. Usually it is a black plastic elbow style made by Bosch. My change involved changing to an aftermarket alloy unit with a piston in it and adjustable spring tension. It also involved changing the orientation of the unit. Air pressure in the IC and intake manifold vac would keep it open. Arrival of Boost in the manifold and the larger upper piston area in the unit would push it close. Adjusting the units spring tension effected keeping it open and how fast it closed.

930's came from the factory with a boost valve built into the manifold. I have not done it nor have taken the time to figure out how to change that style to stay open at idle and cruse but from reading about a couple of tricks of other 930 tuners over the years I believe that it can be done to those to.

Here are some links that show a new valve that came out recently that dose what my system achieved.

http://www.youtube.com/watch?v=M2--IIMSa9A&feature=related

Note the normal BOV stays closed at idle and opens only on closing of the throttle. The new valve stays open at idle and is only closed with acceleration and then reopens on throttle lift. The difference is the new valve is also open at idle and cruse.

On our cars, when the valve is open, it is bypassing air around the turbo compressor. Not to atmosphere.

Hope this helps.

[911st]

Sorry, left this one ou: http://www.youtube.com/watch?v=gvnBDlXyheI

[mark houghton]

[QUOTE=911st;4646219]The 91-4 Turbos and most after market inter-coolers have a different bypass valve. Usually it is a black plastic elbow style made by Bosch. QUOTE]

I understand the theory of operation in using a modified BOV, but unfortunately I'm stuck with the stock piston recirculation valve that's built into the intake manifold - and which is held open by manifold vacuum anytime the throttle is closed.

It could be a simple matter of reversing the direction of travel of the piston by swapping the position of the spring - thus keeping the valve open regardless of manifold vacuum. In other words, instead of using mainfold vacuum to keep the valve open, you would use spring tension. Then, in place of the vacuum line, install a tap to the intercooler to provide boost to the valve and force it to close against the spring pressure.

If this sounds too simple, then undoubtedly it's much more involved. I need to look at the assembly and picture the air flow pathways (I'm a visual kind of person). I'm not really sure this can be configured to work oposite it's original design.

[911st]

I do not know the stock valves operation. I have seen hints in articals on tuning a 930 by some very major tuners that they did somthing there that increased boost response.

It may be as simple as playing w the spring tension to ensure it is open at idle and cruse and closes freely and as quickly as possable under acceleration. Could be come change in the porting to the valve.

The aftermarket vavles do not work this way. They stay closed except on overrun. That is how I belived the stock 930 valve worked.

[356-930]

Originally Posted by fredmeister

What are you guys using to apply boost pressures to the distributor during the timing process in the driveway?

Made using a blood pressure cuff bulb ($12.00- local sick room supply co), 15-psi gage and brass fittings ($25.00 local hardware store) and vac hose.
Works well for testing (including leak test) distributor's pressure retard rate/level, setting MSD boost retard onset pressure, rate of retard and, in conjunction with fuel system control pressure test gage, WUR's "boost Pressure"control pressure drop.

[NathanUK]

Hi Chris.

How much pressure can one of those pump to?

[356-930]

Originally Posted by NathanUK

How much pressure can one of those pump to?

Readily gets to 15-psi (1.05-bar) with a few stiff squeezes of the bulb. Ultimate pressure level depends on one's hand strength and integrity of the rubber bulb.