marco_chevy

I need to know what is the best timing curve i can send to my MSD box 6012. I did not run the MAP advance now. It,s better to have it or not? If yes, where i can connect it on my GMPP carburator intake! I have one hole for the booster brake, but i can put in a Tee and connect de MAP sensor on it ? The vac go to about 25 on my brake vaccum gauge.

If i dont use it, i need to send a new timing curve to the MSD box. If not, vac advance will be always 20 deg.I know that i need to start about 18 at 0rpm, and go to 32-34 to 3000 rpm until the end, but it's now very precise.

Someone have a good timing curve for my Alluminium 6.0L whit L92, carb intake, and 54-469-11 comp cam. Supposed to have 9.6:1 comp.

3pedals

iTrader: (3)

If Edelbrock ever makes my L92 intake,and sends it to me, I'll be able to share my tuning experiences. I've ben waiting since mid march for my frickin intake!

chris-m

i once waited 6 months+ for them to give me my performer ls1 intake manifold i had ordered.... numerous foundry/casting type issues and no stock. after numerous calls and emails i eventually gave up and bought a GMPP unit.

marco_chevy

It's what i have, a GMPP carb intake for L92 heads!

Tunink

iTrader: (3)

just order it from jegs?

I ordered mine and it was here in about 10 days.

Mike454SS

iTrader: (4)

Since I don't know what carburetor you're running, I guess I'll ask if you have any vacuum nipples on the carb that are currently capped off, that do indeed see whatever vacuum is below the throttle plates?

If you do, you can run a GM MAP sensor with a vacuum line from one of those nipples.

Full throttle timing will not be affected by the MAP sensor, as at full throttle, there shouldn't be any vacuum, but the part throttle driveability/efficiency (gas mileage) will probably be a lot nicer if you use a MAP sensor.

As for which curve to run in the MSD box with those heads, I don't know. I don't know how adjustable the timing curves are in those boxes. I am pretty sure the harness to plug into the MAP sensor is already there with the MSD controller though, so it should be very easy to add it to the system once you find a good vacuum source.

marco_chevy

OK... like i can see, i'm better run the vac advance, for have better gaz millage! I will chek this evening where i can take this vacuum. I also have the GM MAP sensor that i can connect it whit the harness supplied whit the msd box.. If i dont send i new timing map in the MSD box, and run whit 1, 2, 3, 4, 5 or 6 pre-programed pills, they are all pre-programed whit the same MAP advance, as you can see the picture.. If i dont connect the MAP sensor, and run the pills, i will always have +20 degre more at each RPM, it's that? more vacuum i have, more the timing will drop!



If i well understand, at Wide open trottle, at 3500 rpm, will pills #4, i will have about 21deg + about 0-10 more degre whit vac advance( more vaccum)...total of about 21-31, and if i run on the highway at the same rpm ,3500 , whit the same pills #4, i will have 21deg + about 20 degre (minus vacuum) total of 41.... it's that?..

What is the maximum degre i can run the car on the cruise ? I can set the minimum and maximum degre! It's pre-set at 5 and 45. At 45 degre, it's not too high timing for detonation?

Here are the pills 4, by MSD

3pedals

iTrader: (3)

you are confusing psia ( psi absolute) for vacuum. at WOT the psia will be roughly equal to atmospheric pressure which is ~ 14psia, and at idle the psia will be alot lower #, closer to 0psia depending on your engine setup
you need to convert your vacuum readings to psia.
Barrett

marco_chevy

Ok.. i understand better, but more the motor is WOT, more the vaccum i have, less the timing advance i have!...

I chek my carb, and have 1 small vaccum line in the front.... and a screw in the back, under the pump... tomorow, i will take off my 1inch phoenolic spacer, make a hole and insert a 1/8 pipe fitting whit 1/8 hose barb, for connect my MAP sensor... i will have a good vaccum! and will be easy!

marco_chevy

That's what i made this evening...

i will have a good vacuum at this place.. my carb has no vac port in the back.



I use the MAP sensor that was on the plastic intake when i receive motor from the junk yard.

marco_chevy

i try to run the car, and the timing is very bad... i have trouble to start the car.. very hard to run whit it... i put a pill on, remove the pills, and always have very bad timing. I disconnect the MAP, and all return to normal curve whit 0 advance that i send to the msd box whit my PC... i take off the sensor, i i see that it have some gaz on it... may-be the sensor need to me upper than the inlet in the spacer ? I need a new MAP sensor.. what is the best ? GM.. 09359409 like the one i have ? Next week i will have adapter for connect my laptop on the msd box, for see the timing live.!

Mike454SS

iTrader: (4)

The spacer you adapted the MAP sensor too looks exactly like what you need as long as the vacuum tube to it doesn't fill with fuel...which it probably won't do.

Are you sure that the cam and crank sensors are connected to the MSD Box properly?

Are you sure that the ignition coils are ok, and plugged into the correct harness connectors?

marco_chevy

all run good whitout map connected.. i ran the car about 200 miles... all ran good also whit pills on it, but not great performance... I see somewhere that 0vac HG is 14.7 PSIa ( motor off), and about 29 HG vac, it's go to 0 PSIa( opposite)... it's mean that at WOT, it'S about 29HG and about 0PSIa, and at idle, it'S about 10-15 HG, that mean about 7-8PSIa. At WOT, it's 0 PSIa = +20 deg timing, give about 39 at 6000 rpm whit pills 4. at idle, 1000 rpm, it's about 4 deg + 7-8 PSIa, give + 12-13 deg for total of 16-17 deg.

When cruise on highway at 3500 rpm, HG is about 20, give about 4PSIa, + 20deg added to the 3500rpm timing that is 21... give total of about 41 deg timing, it's not too lot of timing?

It's the way to understand this box?

marco_chevy

i need a new MAP sensor... if i have in mind that i would go whit a supercharger next year, whit a blow thru carb, can i go whit a 2bar MAP sensor now or i can't run the motor whit this.?... if i bought a 2 bar, i only have to change de setting in the msd box for a 2 bar and all is ok? If ever i go whit a blower, i will have the good sensor!

Whitch one i must buy?

LS1MCSS

iTrader: (18)

Are you sure the engine has more vacuum at WOT?

marco_chevy

Yes, the motor has more vacuum at WOT ...more HG vacuum.., near 29-30, but have about less pressure, about 0 PSIa... At idle, HG is about 15, but PSIa is about 7-8... whit motor Off, HG is 0, and PSIa is 14.7.. it's to different reading! not easy to understand, but i think i'm ok whit this.. like the number i give in my post #13. Vacuum in HG is a aspirated air, and PSIa is pressure. The normal pressure is about 14.7. When motor creat vacuum, pressure go down, and at WOT, the vacuum of the motor is higher, and reduce the air pressure near 0.

Whit a supercharger, air is forced in the intake, and pressure go more than 14.7.. may be go to 30-40psia...i think we can set a map whit negative psia, for have timing retard when boost is high. i'm not sure.

Let me know if i'm wrong !

marco_chevy

no body have an anser for me?

Mike454SS

iTrader: (4)

I don't think you understand vacuum...you have pretty much no vacuum at WOT as the throttle plate is...wide open...the only time a car really see's much vacuum at WOT is when there's a restriction somewhere, like a restrictor plate, or a horrible air filter or something like that.

The 41 degrees you mentioned at 3500 RPM cruise (throttle mostly closed) makes complete sense...39 degrees at 6000 RPM and WOT seems like WAY too much (10 degrees too much) timing to me.

marco_chevy

can you explain me how read the vaccum... I would like to know!

What is the PSIa whit motor OFF ?:
PSIa whit motor at idle 1000 rpm ?:
PSIa whit motor at WOT 6000 rpm ?:

what will be the timing degre whit pill no 4, and vac advance,if i use the picture in the post # 7

idle 1000 rpm:
cruise at 3500 rpm:
WOT at 3500 rpm:
cruise at 5000 rpm:
WOT at 5000 rpm:
WOT at 6000 rpm:

i found conversion table...but it have 2 Hg possibility.
Hg is what i read on my vacuum gauge, and PSIa is what MSD box read!

What is the good table:

14.7 psia - 29.9292 Hg or 0 Hg standard atmosphere
1.1 psia - 2.2396 Hg or 27.6896 standard atmosphere

It's may-be the reason why i dont understand.

I also see:
•Standard Atmospheric Pressure 1 atm = 101.325 kN/m2 = 1.01325 bar = 101.325 kPa = 14.7 psia = 0 psig = 29.92 in Hg = 760 torr = 33.95 Ft.H2O = 407.2 In.W.G (Water Gauge) = 2116.8 Lbs./Sq.Ft.

Finally, i thinks 1 PSIa is 2.036 Hg ( gauge)...

It's mean that motor off, PSIa is 0 ( 0 Hg).... and at WOT, PSIa is about 14-15 ( 28-29 Hg). ?

DCx

iTrader: (12)

on my ls1 with a hefty cam and ported heads i run a holley 750 HP street 70/80 jets and my timing curve looks like this.

0-1000 15*

1000- 3000 is a steady ramp to 29* total at 3000.

runs excellent.