Quote: <TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD cl***=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Originally Posted by Russco I run 22 initial and 34 total and use the BTM box to pull timing out under boost to prevent detonation </TD></TR></TBODY></TABLE> Try this: sit in rush hour traffic on a 90+ degree day until the coolant is at 220F, then shut down the engine and try to restart it, I bet that 22 initial will make your starter happy... >>>but since he has the MSD box all he needs is a Start / Redard plug in and the starter will never see the 22 initial.... <!-- / message --><!-- sig -->
Realitively simple to add a vac*** port if you have a3/4" or so adapter plate between carb and blower . Just drill and tap the plate.
My CR on my Stock 291 DeSoto is 7.5:1, and the boost is 3-4lbs, so I shouldn't have many problems..I'll bet I could get away with 87, too...especially with a vacuum advance...
VA really only helps turn the moter over when starting, then advances when it starts....On a race or blown motor I want the timeing perfect. You cant be perfect with all that movement.If you dont run VA, you want it locked so it cant move.Blown motors are usually low comp, and start well with out va.Race engines usually spin the motor then hit ign on to fire.
There are several ways to skin a cat, MSD start retard box works great retards timing 20* while starter is cranking
Back in the good ol daze, didn't guys with a lot of initial advance spin the motor up on the starter and then flip the ignition toggle on?
forget any timing in the distributor and run it with locked dist. Ask D.W. how much hell we had with his trying to use variable advance. his is locked at 34 total and initial if I remember correctly, with a retard built into the msd based on boost.
I think I have 20 or 21 degrees of initial timing and it never drags the starter at all. It isn't high compression. 345 - have you seen the SW wings vac boost gauge? it's pretty sharp looking compared to others.
I was going to stay out of this one, but now I can't resist stirring the pot So MSD got a boost retard device? Using electronics with a pressure interface to do what the simple vac advance would do if you left it on the dist.
funny, isn't it? But then everything new is that way....all those fully adequate old springs/orifices/whatnot being replaced by millions of lines of code.
Stir away, but I dont think it can be nearly as accurate as boost referanced retard to prevent detonation. It seems to me that under varying cir***stances you could have the same vacuum signal at the distributor but different boost pressures, maybe Im wrong but after breaking a bunch of pistons in the past and being able to run 9to1 compression and 7psi of boost now on pump gas and by simply turning a knob under my dash to change the timing and run race gas I think thats a good thing
you could have the same vacuum signal at the distributor but different boost pressures Only if the distributor is connected to the wrong place.
Wow, 345 DeSoto...thanks for asking this question! It's like you opened up a valve, and all this info started gushing from these guys! Thanks to all who replied. Almost every one of you guys is a genious penious! (something my wife sometimes calls me...when she's not calling me other things) Man!...I just cannot believe the ammount of info here. - Rick
not easily....when you can see all the gages, each one is too small to read. And there's the lighting thing too. Making movies is a pain in the ***.
Im finding this really interesting and certainly dont claim to have the knowledge some of you guys do but Im always willing to learn. So in Squirrels video at 11 seconds in the vac gauge is reading about 2" while boost is at 5 PSI and at 59 seconds vac is about 7" and boost is at 5 PSI with the BTM box those two instances would have the same amount of total timing but with the vac advance they would not to me thats where the vac advance falls short or am I missing something here
Vacuum advance starts coming in @ around 10" on many cars so it shouldn't be a problem with the vacuum at the 2" level.
SQUIRREL - "....when you can see all the gages, each one is too small to read." That's exactly why all my gauges are bunched up together in front of me, rather than strung out the whole length of my dash. Getting old and scary is hell...
To fully grasp what's going on here first you gotta realize there's 2 thing in play. First is vacuum advance on a street engine, which is good and the question normally asked here. Then there's vacuum advance on a blown street engine which is generally considered bad by blower people due to the ping = death nature of blower motors. Usually the amount of timing added by the vac advance will make a street fueled blower motor detonate/ping. For what it's worth squirrel is the first guy I've ever hear run a vac unit on a blower motor, but then again he's Squirrel and able to do what normal humans can't. My personal experience using vac and a blower (not knowing any better) produced huge ping even with initial cranked way down. Removing the vac unit allower higher initial for better start/idle and actually ran better on the street. The huge blower torque curve more than covers for the tiny amount of part throttle torque lost by not running the vac unit. If you're still hooked on using the vac unit, look into getting one that doesn't add a lot. They're available in a range of amounts with emission era versions adding the most. Another angle to consider......if you're so unsensitive to detonation that you can run a vac unit.....maybe it's a sign to crank the boost up til you can't run the vac unit good luck!
The instance at 59 seconds is where I was backing off the throttle, and it does look like it still had boost and carb vacuum was going up. If you are running a lot of boost or compression then you could possibly get in trouble with vacuum advance....again, each engine is different, and I can sure understand guys with more cylinder pressure not wanting to run vacuum advance from above the blower. I've run the same pistons in mine for 20 yrs and 80+k miles....not enough compression/boost to cause problems?
I would have to agree with the guys here. I had to ask that question myself during the time I was building the custom intake manifold for our 291 Desoto and 6V53 blower. I talked to several people who run blower motors in there rides and have done so for years. They all said the same thing. Run the vacuum above the blower and the boost gauge below.
Someday when you have about a year or two to do it, search boost or blower and you will find all kinds of stuff, lots of great info, plenty of opinions, some great debates and of course some drama. Boost or blower question always a good thread.
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