safe timing limits on 930 turbo
 

This question is more of a poll to gather information than anything else related to safe timing advance limits for 930 turbos. This is an attempt to gain a feel for safe timing limits on our cars that still run stock compression ratios but may have upgraded turbos and bigger intercoolers. Sort of a follow up post to a discussion going around on recurving a 930 distributor.

===I would like info on the following 2 scenarios of boost for a 79 930 turbo intercooled 3.3 liter engine running premium street octane 91 or 93:
1) stock 0.8 bar --What is maximum timing advance in degrees BTDC?
2) 1.0 bar W/G spring-- What is maximum timing advance in degrees BTDC?
Basically looking for what experience has taught the tuners out there what is the maximum safe timing limit of degrees BTDC that can be run without detonation at those boost levels.
Once you know the maximum alloweable advance it has to be factored into the amount of mechanical advance and boost retard that you are running to determine the initial static timing points.

Thanks guys......this could be very valueable info to us starting down that slippery road, so let us learn by your mistakes.....

Fredmeister

Fredmeister,

Here's my timing table from my EFI'd K-27 3.3 w/ 8.0 to 1 compression and dual plugs. Note that in the table, you need to add one decimal point (so 300 - 30.0 degrees advance). My max timing (dual plugged, mind you), is 36 degrees.

Best,
Mike

Table RPM Range
[ 0] = 600
[ 1] = 800
[ 2] = 1300
[ 3] = 1700
[ 4] = 2200
[ 5] = 2900
[ 6] = 3700
[ 7] = 4400
[ 8] = 5000
[ 9] = 5700
[ 10] = 6100
[ 11] = 6500
Table Load Range (MAP/Boost in Bars)
[ 0] = .20
[ 1] = .40
[ 2] = .60
[ 3] = .75
[ 4] = .90
[ 5] = 1.05 (1 atmosphere - normal aspiration)
[ 6] = 1.25
[ 7] = 1.40
[ 8] = 1.60
[ 9] = 1.75
[ 10] = 1.90
[ 11] = 2.10 (1.1 bar boost)

Timing Table [
[ 0] [ 1] [ 2] [ 3] [ 4] [ 5] [ 6] [ 7] [ 8] [ 9] [ 10] [ 11] (RPM reference)
[ 0] = 300 148 127 160 169 171 174 240 220 210 190 180
[ 1] = 300 100 120 170 179 181 184 240 220 210 190 180
[ 2] = 300 100 120 174 180 182 185 244 220 210 190 180
[ 3] = 300 220 278 316 334 329 300 255 230 215 200 180
[ 4] = 300 270 310 355 340 340 330 280 240 220 210 190
[ 5] = 300 290 330 360 360 350 340 300 255 230 218 190
[ 6] = 300 270 310 290 290 280 260 258 243 220 212 172
[ 7] = 300 220 240 290 290 270 250 248 235 224 190 170
[ 8] = 305 170 190 160 170 214 220 238 230 200 170 157
[ 9] = 160 160 170 160 160 186 180 180 180 180 160 150
[ 10] = 155 155 155 120 120 155 150 150 150 150 150 150
[ 11] = 150 150 150 120 120 150 150 150 150 150 150 150
(boost ref)

Mike,
Wow - that's quite a bit more timing that I run in non-boost part.

Don't let column 1 (30*) throw you off. I use that to keep the low speed drivability good (when rpms drop towards 600 and throttle is light, more timing kicks in making it less likely to stall). Normally it idles around 1000 rpm and I see about 10*-12* of advance. At around 4000 rpm if I am just cruising (light throttle), I see around 19* advance. At 4000 rpm if I stab the throttle, for the second that the turbo starts to spin up (no real boost) the timing jumps to 35* (row 5 and column 6). Once the boost comes on (row 6 and above) the timing drops back to the 20s and the teens.

Yes understood... I run a max of 30 deg timing @ around 3500 rpm & ~85kpa.
I typically cruise (2800rpm/70kpa from memory) with about 28 deg.
And idle around 10 deg - though I can't get my idle to go below 1200RPM :(
The only explanation is an intake leak but I just can't find it with everything I have tried.

I understand that with twin plug, you don't need to run as much advance?

I appreciate the input but you guys are deviating away from the original question asked:
I am looking for settings for a single plugged, stock compression ratio car at boost levels of 0.8 and 1.0 bar.
I don;t want to loose the focus of this post but want everyone to understand the original question asked as I believe this comprises the majority of the cars out there that are not so heavily modified as dual plug and EFI. In particular this would address my car which is where I want to start.

Sub'd

Hi Fred,
Totally understand your point of view here. However, I would think you might find it interesting how a dyno tuned computer controlled car might be optimally timed. This way you understand what the engine would like to have and see what you have to settle for with a distributer. Just a thought, it's your thread and I tried to start a similar thread when I was tuning my EFI car.

Mike,
I'd love to see this as a thread, separate or otherwise.

EFI optimized would be fine info. That does not impact what I am seeking because CIS could be comparable to a good tuned EFI system.
But dual plug and higher than stock CR (7.0 to 1) gets away from my engine parameters quite a bit. I just want to make sure we have apples to apples here.
Dual plug and high compression could easily be on another thread.....as soon as someone starts one.

Now that thats straight, lets get some feedback posted here guys!.......daylight is a wastin and I have 2 weeks till the first track event. Would be nice to have some good data before hitting Mid Ohio.

US 930 cars 27 btdc, Euro spec 930 says 29 btc @ 4000. Early 930 Euro spec cars have a few better innards/exhaust system to make breathing better. If you go to race gas ( no catalyst ) maybe 30 BTDC. I believe both US and euro cars had 7.5 compression for this factory recommended setting. Old school engine builders/ tuners ( on the forbidden topic of somewhat modified systems ) say another 2 degrees w/ twin plug and extra enrichment using a factory distributer curve w/ race gas. Of course cams, porting, valve size,compression ratio and C I displacement alterations change these parameters.

Since most of our US CIS 930's are modified to breathe better than stock, are we to assume that 29 BTDC at 4000 rpms (with advance and retard lines pulled off dist and plugged) is safely maximizing performance .....1 bar boost? Currently I run 26 BTDC but I am a newbie and my car still ain't tuned properly.

They are talking total advance under all testing conditions that create maximum advance at 4000. Whatever you connect or disconnect do not exceed these parameters for safe operation with relatively stock components. 100 plus leaded fuel ( no catalyst ) helps a lot to slow/cool the burn so a little more advance beyond 27 US and 29 euro @ 4000 should be doable to 1.0 bar with modest upgrades / fuel. The factory timing, fuel delivery and enrichment settings were determined and set for .7/.8 boost for all around usage. There is a tremendous upside in the 930 turbo tuning as Porsche did a lot of leg work with this system before settling on the final street production tune specs.

24 total on my twin plug CIS motor -

Hey "PorschePhd" do you have any thoughts to add to this thread?

In a nutshell, Single plug, stock compression, CIS engine running 0.8 bar and then 1.0 bar safe maximum timing limits.

Was hoping some real world tuners could add valueable info to the thread to help us all out.