timing on SBO

K

kartboy63

Member
i run tillotson 3" with a 58mm crank,on methanol with a 28mm flatslide, 310-246 cam, i run 34* timing, if i go to 36* would that give more bottom end or top end, or say i went to 32* what would that do?
 
Generally speaking more timing equals more bottom end and less top end. Less timing equals less bottom end and more top end. Hope this helps.
 
Sorry but for my own good I need to question that rule of thumb.
Lets say if the "ideal time" to light the fire with gas is 1 second BTDC @ 3500 RPM's, then when the engine is turning 7,000 RPM's the trigger that was lighting the fire @ 1 second BTDC is now actually lighting the fire at 1/2 of a second BTDC.
Seems to me that the more RPM the engine is turning would require a sooner time to light the fire. Much like old car distributors that had centrifugal advancement weights in them that would advance the timing as the RPM's increased.
If the fire is started too late it is still burning after the downward power stroke and exiting out the exhaust stroke.
 
If the timing was set correctly for a wide rpm range lets say 35 degrees then dropping the timing to 33 degrees would help the bottom end and hurt the top end adding timing say 37 degrees would hurt the bottom and help the top
 
I stand by my original statement because I have tested and play with timing on big cars as well as go karts. If my big car is spinning coming out the corner we take timing out to kill some bottom end and I know for a fact it helps. I have a personal tuner that goes with me and he has forgot more than I know. I asked him to make sure I didn’t have it backwards and he said I was spot on. So to the OP this is my personal experience. To the other posters believe whatever you want.
 
Hobbs, You are correct. Oh, and there is a little problem that can be caused by adding a bunch of timing, it is known as detonation.
 
Obviously 50* is not going to work .
Late 60's early 70's .
Using vacuum it was always adjust for highest vacuum then back off one # .
 
Kartboy, You don't indicate how much compression you are running, so I am assuming that it is fairly high. So do yourself a favor and set your timing at around 34 degrees, save your engine from exploding and don't listen to the theorist on this forum. Most of them don't know how an engine even runs, they only know how to operate a keybourd. 34 degrees will give you the best all around power and be the least harmful to the engine.
 
As you well know the number of factors involved all affect this .
If it creates an explosion the pistons on the wrong side of the stroke so any possible gain is negated by the engine having to overcome the expanding gases .
Funny thing , I never said you were wrong only provided an alternate view .
Quote:
(. 34 degrees will give you the best all around power and be the least harmful to the engine.)
Now thats, a. Epiphany.
So 38* will increase the bottom end powe and 30* will increase the top end power ?
 
tecbigdog said:
Kartboy, You don't indicate how much compression you are running, so I am assuming that it is fairly high. So do yourself a favor and set your timing at around 34 degrees, save your engine from exploding and don't listen to the theorist on this forum. Most of them don't know how an engine even runs, they only know how to operate a keybourd. 34 degrees will give you the best all around power and be the least harmful to the engine.
Click to expand...
thats where i set most of the engines at (34*) i was just wondering what way to go for more bottom end, and now im still confused LOL
 
Timing is kind of like bird hunting. You have to lead the bird (piston TDC) with the barrel so that when you pull the trigger (ignition fires) the bullet gets to the bird at the right time. Faster the bird flies, the more you lead it. Thing is with ignition timing you would rather miss behind the bird than infront of it.
 
Many people dont understand that ignition timing is the start of the ignition of the fuel, the energy does not happen at that time or of course it would knock, spin the motor backwards, etc. Since the engine is rotating you are trying to ignite the fuel early enough that once the energy is produced from the fuel igniting, the piston has made it to atleast 1* past TDC. The closer to TDC that the energy is released, the smaller the combustion chamber, higher the cylinder pressure, and usually more torque is produced. If you lower the ignition timing, the further past TDC the charge happens, the greater the combustion chamber, lower cylinder pressure, etc, usually the more hp.

You got to remember we are talking milliseconds and moving targets. Also crank angle is changing on these firing positions which is a factor
 
flattop1 said:
As you well know the number of factors involved all affect this .
If it creates an explosion the pistons on the wrong side of the stroke so any possible gain is negated by the engine having to overcome the expanding gases .
Funny thing , I never said you were wrong only provided an alternate view .
Quote:
(. 34 degrees will give you the best all around power and be the least harmful to the engine.)
Now thats, a. Epiphany.
So 38* will increase the bottom end powe and 30* will increase the top end power ?
Click to expand...
When you move the timing, all you do is re-position the power curve at a different RPM. There is very little or no power gain. It just changes the ROA. A few minutes on a Dyno will prove that me and Hobbs are correct.
 
tecbigdog said:
Kartboy, You don't indicate how much compression you are running, so I am assuming that it is fairly high. So do yourself a favor and set your timing at around 34 degrees, save your engine from exploding and don't listen to the theorist on this forum. Most of them don't know how an engine even runs, they only know how to operate a keybourd. 34 degrees will give you the best all around power and be the least harmful to the engine.
Click to expand...
I take your snide remarks personally Mr. Big Dog of 4cycle.com. Even though I don't disagree with most of your advice given to Kartboy myself and others contributing to the topic didn't need to hear your BS opinion you have about us. Tell us just where did that theorist keyboard operator touch you in such a way that hurt so bad?
Flattop thanks for posting a couple of relevant links.
 
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