Turbo timming recommendation?

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kevin1969

kevin1969

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This is my first forced induction mopar so sorry for all the questions. What timming are you guys running? I plan on running my curve through my holly 950 comander efi box with a 3 bar map and pump gas only plan on running 6 to 8 psi for now. Thanks guys.
 
What do you know about your current existing timing?

I assume you are going to use a MSD 6530 box with a locked out distributor?

The general rule of thumb with Turbo Boost is alot like Nitrous use....

Retard 2* for every + psi.....so 8 psi = -16* out of your total advance....then, slowly step it up ....till you find the sweet spot.

Some setups are running -1* per psi

Everyone says they want to run pump gas.....

Pump Gas is the Devil....:twisted:

most times you get some decent stuff, other times you get leftover bottom of the barrel who-knows-what.
Dont jeoprodize your setup and then blow it up and come back and tell us "I was just running pumpgas".

:wack:
 
I'm planning on using a locked out disributor and according to the holley commander 950 wiring diagram the pickup runs through my holly computer then out to my msd 6a box. From what I understand the timing curve and Rev limited will be controlled by the holley box. I hear you on the pump gas I plan to run a conservative tune on the street and load a tune for race gas when playing. I'm very new to all this efi and turbo stuff
 
I add a bit more advance under vacuum at light load. It helps overcome the low end losses before the turbo spins up. Retarding timing throws more heat to exhaust, increasing turbo drive, but also reduces efficiency. Having knock detection is benificial. Fuel mixture plays a large part too. To me a turbo is smoother and easier to tune than a high compression N/A engine. EFI is a great help in tuning a turbo.
 
I do plan on running a knock sensor. The commander 950 computer has an input. I have to order a gm knock sensor module and the matching sensor but that is in the plans as well.
 
2* per psi is way too much to pull.


I ended up with 25* locked out(.9 per psi), drove it for a while like that.

Picked up a 6530 with a 3 bar map, now running 35 and pulling 10*starting at 5psi to 25 at 10psi. And this isn't an exageration, it picked up probably 50whp under the curve just by doing that.


.7-1.0 per psi is a good start.



What engine?


What heads? Closed or open chamber?
 
That engine is probably wanting 35ish na timing, if you're on pump fuel , I'd pull 8* for that boost level and start there, it will probably want a tad more tho. If you throw some q16 or a good fuel in I wouldn't even pull any timing on 8lbs with your setup




Pull too much timing and you'll lift the ringlands.



I'd ditch that pump fuel and put it on e85 if it's avaliable in your area.
 
Already fat tune up, will become fatter with less timing, which could lift the lands especially with a turbo or nitrous combo. Granted it's less likely then damage occurring from pre ignition, it's still very much possible. Just something to think about.
 
kevin1969 said:
It's a 340 sb with 10 to 1 compression with 202 J heads. I plan to build another motor in the future.
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My 340 is also high compression 10.2:1 but with eddy heads and running e85. My timing at 10 psi is 23 to 24. All the tuning was done on a dyno, adding more timing than this didn't make any more power in my case.

Other factors that may come in to play, my turbo is on the smaller end and probably makes higher EGT's. I am also at high altitude, so dynamic compression might be lower.
 
MrMoparMan said:
My 340 is also high compression 10.2:1 but with eddy heads and running e85. My timing at 10 psi is 23 to 24. All the tuning was done on a dyno, adding more timing than this didn't make any more power in my case.

Other factors that may come in to play, my turbo is on the smaller end and probably makes higher EGT's. I am also at high altitude, so dynamic compression might be lower.
Click to expand...

I'm at 11.9:1 on 10lbs 25* blow through e85 compression makes the biggest difference in how a turbo works.
 
1980volare said:
Already fat tune up, will become fatter with less timing, which could lift the lands especially with a turbo or nitrous combo. Granted it's less likely then damage occurring from pre ignition, it's still very much possible. Just something to think about.
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I am ignorant about how this scenario of "lifting the ring lands" occurs..... Please explain...
 
When the tune up becomes fatter because of low timing or for whatever reason, fuel will seep past the rings and ignite, hence lifting the ring lands.
 
1980volare said:
When the tune up becomes fatter because of low timing or for whatever reason, fuel will seep past the rings and ignite, hence lifting the ring lands.
Click to expand...

I never heard of anything like that. I am new to forced induction, so, I am woefully ignorant of the whole scenario, but I have been around fast cars with modified engines since 1955 (no typo) and retarded timing was never a factor in the mixture's rich/lean scenario as far as I ever heard, and the only "lifting of ring lands" I have ever experienced (or, seen, or heard of,) was the result of too little end gap on a supercharged or turbocharged engine, which resulted in the ends of the ring coming together, making it impossible for the captured ring to grow in length any further, so then, when additional heat tries to expand it further, it becomes forcibly locked in position in the bore, and the next trip down, the crank pulls bottom of the piston pulls so hard that the piston separates and the ring land is "lifted" off the piston.

I don't understand the dynamics of combustion BELOW the ring land making that happen.

Please educate this old-timer, who obviously doesn't "get it.":eek:ops:
 
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