Timing a BLOWN engine ??

OK, I'm getting dieseling and glowing headers

Blown BBC underdriven, MSD 6AL and magnetic pickup dizzy..


Need advice on how to time this beast.


Thanks

 

What is the timing set at now ?

 

Well.. Thats a good question.

Lets just say... I would like to start from scratch...

I have a good timing light that can be advanced.

 

The engine will tell you what it needs, but to get it dead nuts, it is nice to have some dyno time...

But, there are some rules of thumb...Roots blown motors like lots of initial advance, maybe 18-25 or so, and not much total, maybe 25-35 ish. The timing numbers vary greatly with your combination...for example, my blown Pontiac with aluminum heads likes 38 degrees of total. Most Chevvie guys would **** themselves with 38 degrees at 10lbs of boost, but that is what she wants.

Tell us more about the combination....and remember, detonation kills...so does a lean air/fuel mixture.

-Abone.

 

Are you sure your carburetors will deliver enough CFM to feed the CID you have? If not it will run hot no mater what timing you put in it. JC

 

Find Top Dead center # 1 first. If you don't have a timing tape or crank degree hub, grab a 6'' steel ruler out of your tool box, bend it into a curve, make a mounting bracket matching the edge of the ruler at the TDC mark. With your dial adjust timing light, see what ruler marks line up at 5*, 10*, 15*, 20" etc so you can set the timing. Sounds like it needs more Advance or more fuel. What plugs are you running?

 

Go to www.blowerdriveservice.com.... then to FAQ's... lots of good info.

 

i'd get rid of the 6al and get a 6 btm...

http://www.msdignition.com/Products...*og/6462_-_MSD_6-BTM_Boost_Timing_Master.aspx

 

Pictures? This confuses me.

 

If your carburetor is too lean, it will cause detonation, which
can destroy your motor. How do you know if it’s too lean?
You’ll have several obvious indications, like glowing red
headers, audible “lean pop,” or engine surging. Even if you
don’t experience these conditions, you should still read your
spark plugs for proper color. You want to see a medium to​

dark tan color.

Most blown engines operate best on 28 to 34º of total timing.
Running more total advance will not provide any performance​

increase.

http://www.aa1car.com/library/weiand_superchargers.pdf

 

I think that's more a question of jetting isn't it? I have a feeling he's not picking on it hard enough to run out of carb...yet.

Chopper, just for kicks run some good race gas thru it and see if that helps the problem. If NOT, you've got cooling or other issues

 

Yes, CFM is a RPM limting factor, jetting sounds way lean. Also, MSD recomends no advance timming lights and either self powered or use a seperate battery to power up the light as these will effect the actual timming.

 

Depends on if this is a street engine. The simple trick is to lock out the dizzy and set total timing to 30*. That should get you in the ballpark and running. try getting a BTM unit for the 6AL and pull timing as boost increases. Read plugs and repeat.

Also, the headers will be hotter than a NA engine. Usually, the cam profiles on blown engines place more raw fuel in the exhaust stream.

 

Why don't you know what the timing is set at now ?
No timing marks ? No TDC mark ?



Figure out your ignition timing before changing jetting or buying more parts.

 

I'm looking better.

I'm all in at 32* now.

Gonna have to play with a a bit more, but I feel alot better. Thanks for the tips guys.