pontiac baron , thats not 3psi , its actually about 23" of vacuum . 0psia is about 14.5 at sea level .




lets say 14.5 = 0 ( sea level )

3 is 11.5 less than 14.5 .

11.5 = 23" of vac since every point under 14.5 will be 2" of vac .

 

ah, you're very right. I wasn't paying attention: I'll modify that post and change the picture
14.5 or so would be atmosphere

and no, i haven't ran it
I just plugged that in real quick as a demonstration.
A poorly done demonstration


Here is a bit more appropriate

 

The pic below is an example of this timing curve :

40º until 10" of vac

At 10" of vac it starts pulling timing back to 36º at 0psia .

It stays at 36º until 4psi , then pulls it back to 33º by 6psi .

then from 33º at 6psi it then pulls the timing back to 26º at 20psi ............... basicaly .5 degrees per pound of boost . ( starting at 36º at 0psia )

HOPE THIS MAKES SENSE .

#ad

 

Mine is very much like Blown385. I use what is left of the 25* retard to pull timing fast at 1psi over target boost. It is a straight down line to 25* retard. I don't know it it would save the engine if the waste gate failed to keep boost where I want it, but I don't think it would hurt.

Blown385, why is the red line at 2psia? The only time mine is there is if the map sensor is unplugged or when I close the throttle quickly.

 

i thought you could run a map sensor with this to pull timing?

 

Indeed...
It's the map sensor that tells what the vacuum or boost is doing
Without the map sensor - the box wouldn't retard.

The map sensor sends a scaled 5v charge to the MSD box, which the MSD box scales according to a chart and whether you're using a 1bar, 2bar or 3bar map sensor (you tell the box which one)

 

I've never noticed it before ................. It wasnt plugged in though , when I did the example .

 

blown385,

I must be REALLY missing something because I don't understand your description of the timing curve. The X axis is PSI of boost and starts with 0. There is NO provision for altering timing under vacuum. I called MSD and they verified that for me.

In the picture it looks like the MSD will pull no timing until 9.5 PSi boost. It then curves down until it is pulling 4* at 14.5 PSI. It stays flat until 18.5 PSI boost then starts down again. The curve in the picture ultimately pulls 14* timing at 34.5 lbs of boost.

The software is NOT calibrated to atmospheric pressure where 14.5 is Zero boost. 14.5 on the X axis represents 14.5 lbs of boost.

Again, I called MSD and that is how they explained it to me but maybe I am still missing something?

 

I'm confuddled


http://www.msdignition.com/forum/showthread.php?t=14765


I asked MSD this not long ago.

But I've had others swear to me it's the other route

 

I still need to buy an ignition...I am using a PMS piggy back tuner that can retard timing with boost already. Would the 6530 just be overkill?

 

34.5 - 14.5 = 20 lbs of boost. Key on engine off and looking at the graph will show you what 0 is for your car in your area. Anything below 14.5 is vac and anything over 14.5 is boost. Hope that makes sense. 0 is not 0 boost on the ignition box. 14.5 in my example would be 0 boost and 0 vac.

It is showing 2.00 in his example because his computer is not hooked to his igntion box.

MSD is correct if I understand your question to them. But I don't think it was the correct question. If you have 14.5 with key on engine off (depends on where you map sensor gets it source from, in carb hat, will not see vac with engine running, if under the car will see vac engine running at idle) and you set timing to be pulled at anything under that value (14.5) you are pulling timing while still in vac.

Ok, MSD was correct if your an engineer. Real World, you will never be at absolute 0 for a starting point, unless you were in the space shuttle. Your starting point will be between 13 - 15, and that is a huge range that no one will ever see. Again to find out your actual 0 for your location, key (ignition on) lap top hooked to the box, and make note of where the red line is.

Hope that helps.

 

Racesloth, if you don't have a data log feature with the PMS, I would get a 7531 because it provides great data.

Ask Brian about the data from the 7531. If they would offer the data log feature in a lesser box, I would sugget that but they don't.

 

Like Tim said . 0 psi is actually 14.5 were I live . ( Basicaly sea level ) Anything under 14.5 is vacuum . But you have to remember , every point under 14.5 will be 2" of vacuum . Example : 13.5 is 2" , 12.5 is 4" ect , ect .

The box can not add timing only pull timing , so you would have to lock the dizzy at the most timing you want the motor to see , then pull it from there . In the pic i posted , the timing would be locked at 40º then at 10" of vacuum it starts pulling timing back to 36º at 0psia . The flat spot is at 36º and 0psia ( 14.5 ) until 4psi ( 18.5 ) then it starts pulling more .

I'm really surprised MSD couldn't explain that to you . Well , I take that back .................. I guess it all depends on who you talk to at MSD .

 

I found the post from MSD on their Site, They answered it but like an Engieneer would answer it.

 

Tim, Thanks for the reply. It led me to call tech at MSD again and they contradicted what you are saying. They say there is an ambient pressure sensor inside the box itself (nothing to do with the MAP sensor) that automatically figures what your local ambient is and calculates that into the curve. Therefor, if you set up your graph to start pulling timing at 14.5 on the X axis, you will not start to pull timing until you hit 14.5 lbs. of boost on your boost guage.

I am really confused becasue I feel sure you and Blown385 have done it like you explain in the real world but that is not how MSD says it works.

I am no way trying to argue with anyone as I am a self described novice, but this is important stuff. If someone sets their curve to pull 10* timing at 24.5 because they think it is 10 on the boost gauge, they will be running full timing at 10 PSI and may blow something up.

I even asked them if their other product lines may be different and he said no, all have the ambient sensor in the box.

Can you give them a call as I may still be asking the wrong question? I'd be interested to hear what they tell you.

 

Every time I've ever e-mailed or posted on the forums, they answer it as complicated as possible.
They use as many big words, technical terms, etc....as possible.


I rarely understand the answer, when a 'yes' or 'no' could easily suffice.

It's like they're purposely trying to make it difficult. .....on a high horse being obnoxious or something

 

I can assure you that 14psi of boost is actually 28.5psia on the MSD graph . ( at about sea level ) It cant work like they said , because when I put 10psi on the MAP and put a timing light on the motor it works just like we are describing it . I would recommend doing this anytime you install a box like this , just to make sure you have everything right . Just make sure you use regulated air or you could accidentally kill your MAP sensor . I usually put a tee in the line with a gauge so I can monitor exactly what I'm putting to the MAP .

I usually use 10psi and set it to pull 10º when testing . Nice round numbers .





http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

 

Greg,

That is something I have never heard and don't understand. If that was the case then why do you need a map sensor for the box. I am wondering if that individual was talking about the boost timing master that you hook a line up too.

If that was true I would of been running timing on Brian's motor (40) at 36 lbs of boost! I do not beleive what you just explained as ture. I am checking with a friend who works for MSD to make sure I am correct, but cause I do not want to be responsible for making little parts out of your big parts.

 

I have to agree.

 

I just double checked the instructions for a 6530 box and it states a map sensor is to be used for the boost curve feature. So it does not have an internal vac/boost sensor like a BTM. So it should work like a Digital 7. Wanted to make sure I was not giving bad information.

Waiting for a call back from my friend at MSD.