2 questions for the tunning experts

[Dmichels]

1 does the torque curve move or change with timing adjustment. When trying to dial in my timing I noticed I had more power down low with the timing retard ( could brake the tires loose easily) but the acceleration suffered.
2 I am using 100ll AV gas now and it seems like I am running a little lean as compared to pump gas is this possible.
These are separate issues
Thank you for your insight

[c00nhunterjoe]

More power retarding the timing doesnt make sense. Especially running avgas.  Many questions. Why are you runni g av gas? What initial/curve and total timing and at what max rpm advance?

[Dmichels]

Distributor has 18 advance all in at 2000. Runs nice about 36 to 38 total advance. It seamed like I had more low-end power with it retarded. maybe Running av gas because its easy for me to get I have 10 to 1 comp and it runs better

[firefighter3931]

The shape of the combustion chamber determines the advance curve required. Smaller closed chambers are more efficient than larger "open" chambers and as such require less total timing to make the best power. 

If the torque increased with less base timing at idle then that is what the engine wants. You could go in and add some mechanical advance to get back up to the 38* sweet spot and see if the top end charge comes back. 

Generally speaking ; engines will perform best with the least amount of octane required to prevent spark knock. Throwing 110 octane in an engine that only requires 93 will actually slow the car down. Seen this happen many times at the track over the years. 


Ron

[Dmichels]

thanks for the info
from what I understand the 100 LL avgas is equivalent to 97 street gas

[flyinlow]

100LL is higher octane , is 100% gasoline and a good quality fuel for Cessna's .   It is blended  not to boil off at lower air pressures  in the fuel tanks that aircraft fly at.  I don't think it vaporizes as well as car gas.

Auto or stick?

All in 38* at 2000 rpm might be to quick with a stick or with your particular build with an auto.

Not an expert ,just my   

[Dmichels]

car is a stick So you think I should raise the RPM where full advance is? Car is a street car I do not race but I do like to get on it now and then
I have read a fair amount on AV gas From what i gather it works fine at ground presure and temperature. It has to work very well you need MAX power and reliability during takeoff you can cruise at lower power
Thanks for everyone's input.
Dave

[BSB67]

Distributor has 18 advance all in at 2000. Runs nice about 36 to 38 total advance. It seamed like I had more low-end power with it retarded. maybe Running av gas because its easy for me to get I have 10 to 1 comp and it runs better

I'm not quite sure what you are saying here.  Initial at 18°, total at 36°, all in at 2000?

Generally, timing changes will either help everywhere, or hurt everywhere.  So what you are describing, (helping at initial hit, but poor acceleration), if I understand it correctly does not make sense to me unless you have multiple things going on.  Also, butt meter and "my tire spins better" is usally a very poor gauge for performance changes.

And like Ron said, if you are not having detonation, the higher octane fuel is a waste.

[Dmichels]

the distributor has 18 degrees of mech advance that comes all in at 2000 rpm. I set idle timing at 18 degrees for a total of 36

[c00nhunterjoe]

Is your 10:1 measured? What cam specs. What cranking compression? I have a 10:1 383 , 4 speed running 28 initial, 42 total on 93 pump gas. Im not following all of your concerns, questions and measurements on power still.

[Dmichels]

I was "told" that the compression would be 10-1 I was working with a guy that had been building MOPAR engines since the 70,s Cam is the old style 509 hydraulic Mopar performance
My question was 2 part but not necessary related
I was wondering if you could move the torque curve with timing as it seamed like I had more with retarded timing
second unrelated was if AV gas runs leaner for some reason because I think I detect a lean surge at cruise when I switched gas
thanks Dave

[BSB67]

1) yes
2) maybe

[c00nhunterjoe]

the purple 509 will like more initial and in a stick car should be tons of fun. With the timing, you probably have a lean surge with either fuel. I dont know the properties of that av gas so i cant tell you much about it. If it is a 10:1 static engine, you are wasting money on 100 octane av gas,that engine doesnt need it. You shouldnt have any detonation with the timing numbers posted on 93. Jet up a size on the primaries and see if the lean surge goes away. Knowing the cam, all we need is a cranking compression test and your altitude to tell you your static compression.

[flyinlow]

Are you running vacuum advance? If yes, unplug it and see if that stops the "lean surging".