Need timing suggestions at altitude...

Hey guys,

I need opinions on where to set my timing to start tuning. Obviously I want to start a little low, and bring it in as we tune, but I don't want it so far back that it creates headaches. The setup is pretty common, 511 hemi, fuel heads, Mert hh14 retro at 32%, 11.5:1, MSD 44, in a TD at 2100. The twist is the altitude. We run at 6,600' above sea level. A typical day here is about 3.5lbs down on inlet pressure from sea level, 8500-9500 density.

I'm thinking about 29 degrees.

Whaddya think?

-Scouder

 

I haven't run that exact setup, but with a roots blower and a 44 amp mag in a hemi, I haven't ever gone over 29 degrees. I think you should start off at 26 and just play with the blower and fuel system.

 

what 1 does the other might not want to...I run fuel heads with a 14-71 hh retro littlefield 526ci.4.310 bore 2 mallory mags at the hit I have 36 leed at the 1 2 it takes timing out to 34 then to 32 I never have a bearing issue if you run fat heads you wanna run a LOT LESS leed..Dave

 

Isn't the lead difference between the Mallory and the MSD about 5-6 degrees?

 

Scouder,
In my experience you can run 29 degrees to start but you don't say what cyl heads you have (fuel should be large chamber). To make this car run well ( how fast do you want to go) you will need have your fuel system flowed and make sure that you let them know that is your normal corrected altitude. You will have to be more aggressive with tranny ratios too. Mike Canter has an excellent article on reading sparkplugs on this forum that deals with timing and fuel. But you need to get close with the fuel system(nozzle size will be much smaller or it will have a huge main jet). Over time you can deal with adding blower or compression once you have confidence in your program.

A serious word of advice, if you ever go to good air you really need to rethink the program so you don't knock the rods out of it. My home track has fantastic air and I have watched so many people come to town and knock the rods out on the first run. You have a really unique situation that calls for a different program. If you tell us what you are trying to do maybe someone from the Denver area can help with some advise that will save you thousands of dollars. Ralph Gorr has a ton of tune ups from around North America under all conditions with some one off vehicles.
Thanks
Dale

 

Your original question

Personally I've never seen a reason to change the ignition timing for different altitudes, have any of you?

 

I think mostly you can compensate for altitude by taking fuel away, but going from sea level to 4 or 6 thousand feet you can get away with a bit more timing. It can put you on the ragged edge though.

 

i helped a friend in texas with his car alt between 4500-6500 i have never raced that kind of air fuel system will play a major roll in tunning if the fuel system is right for that kind of air 28* to 30* depending on how the track is went 4.06 just messing around and the track was shit no real high dollar pieces its better to start with less timing as to have to much and burn something up but say if i brought my car there i would just leave my timing at 30* and look at my formula fuel take away a little fuel and a gram off each finger but i wouldnt jack the timing way up thats for sure

 

Thanks guys. I really appreciate the help.

I think I'll set it at 26 for the initial setup just to be safe, but I'll bet it'll like a little more than that. I don't want to be too far off because fuel and timing chase each other.

I'm sure you guys are right, that the timing on the blown engines is not as affected by altitude as a normally aspirated deal. I just wanted to see what you more experienced guys thought.

Spud Miller is gonna flow my stuff and set me up with a tuneup for our local track and the one "down the hill" in Salt Lake City, so the fuel should be fairly close right out of the box. I shouldn't have to worry to much about dumping it's spleen on the track.

Hopefully I can learn how to drive this thing and get it tuned in enough to go play the Top Dragster game in SLC.

-Scouder

 

Spud does great work. You're in good hands