MSD timing computer question

[bb]

I have installed the following on my 76' 2.7 turbo.

MSD-6abtm (boost control)
MSD timing computer.
Pertronix igniter.

I did this due to the fact that the car broke down twice due to ignition problems. Car runs good now but here is the question:

**On the timing box you get 20 degrees of advance, and you can retard for easier starting. You can control how fast the total timing is put in to the car, and at what poing the advance comes on.

The problem is that you have to set the car at 15 degrees when idle since you only have 20 degrees total on the box.

Is there any advantage, or problem with this?

Thanks
Oscar

[bb]

also, has anyone run this type of setup?

Oscar

[911pcars]

I haven't used this box, but are you sure the 20 degrees is crankshaft degrees? Seems a little restricted in terms of adjustability. Could it be that this device provides 20 degrees of distributor advance? That would work out to be 40 degrees of timing range at the crank.

Another thought is of using the MSD remote retard switch. Crane also has an equivalent device (basically a potentiometer, I think). This has a range of 20 degrees of retard, but if you set it at a midway position before adjusting basic timing, you should have +/– 10 degrees of advance/retard at your disposal for fine tuning, on a dyno for example.

Sherwood

[Hatari]

Oscar,
What's the timing computer part number you have? I am running an MSD 8981 timing computer on a highly tweaked 3.2. I set the maximum timing at 35 degrees and adjusted the retard for different (under 3,500) rpm ranges. It has worked great thus far. I think you may need to start from the max desired advance and adjust the pots to reduce the timing and slope (up to 15 degrees max retard) from there if you have a similar unit to mine.

Jack

[rfng]

The boost timing master, I have one and have used it on my SC Turbo Kit. The BTM only operates or starts to retard the time after 3 psi. So you can set the timing up to start retarding the timing between 1-3 degrees per psi after 3 psi. So if the switch is on 1 then at 4 psi it retard total timing 1 degree and so on.

I would bet with your compression ratio stock you can run it at stock time or 5 degree less for a total 9 degrees less timing if you run 8 psi.

[A Quiet Boom]

I'm running the timing computer on my carbed SC motor. Yes it's only 20 degrees "advance" I run 34 total and use all 20 degrees to get it down to 14 at idle. All of my advance is in by 3300 and it works really well for me. For a turbo car I'd recommend the BTM since it'll allow more boost without detonation, they are widely used by guys running aftermarket blower setups on all types of cars. BTW the start retard function can be used in other ways. The most common use is in drag racing as a high speed retard, basically it's wired to a switch on the shifter and once you're in high gear you hit the switch for a few extra MPH at the traps. It can also be hooked up to work with a nitrous system or through a pressure switch as a crude boost retard. On my old tow vehicle I used it with a dash switch to prevent detonation on long hill climbs or in the event of poor gasoline. It's only useful as a start retard if you're running really high compression like 11:1 of higher.

[iamchappy]

rfng, I have been installing a turbo on my 79sc engine and I too have a MSD BTM. What is your idle advance set at (5) Have you altered the mechanical advance weights in your distributor, I plan on running 8psi can I get by with the stock advance setting at total 45 using the BTM at the 3 setting -15 degrees of total advance with a total then of 30. Or will I also need to retard the distributor abit.

[rfng]

Your compression ratio is about 8.5. , I would start by retarting the static timing by 5-8 degrees. At 8 psi your compression ratio should be almost 11 to 1. Set the btm at 1 or 1/2. The problem with the btms irrespective of the boost pressure, the engine needs a lot of timing under non boost conditions, however at full boost 15 degrees on the top will make the car somewhat sluggest as it is building boost. You'll have to play with it. total timing should not be more than 22-28.

My distributor was an early modified 930, which would advance slightly less and advance later, but I was running a little more than 8 psi, with almost a full point more of compression.

[bb]

I'll get the number tonight from the MSD box. But is there any advantage on running the car at 15 degrees rather than the stock setting?

thanks
Oscar

[rfng]

It just depends on your boost level etc. Optimally you want as much advance as possible without detonation.

[rfng]

It just depends on your boost level etc. Optimally you want as much advance as possible without detonation.