Timing help
06-29-2010, 05:22 AM
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Timing help
I have recently rebuilt 2 small blocks with thunder bolt iv ignitions. I wanted to make sure the timing was set correctly to the specific cam I bought for it. I have currently have the timing set to 8 btdc when the engine is at idle. Which i believe is the stock setup. I set this using a timing light flashing at the harmonic balancer and using the timing tab. Is this the correct way to time the engine with the specs from the cam? Or can I advance it to gain some more power. It runs good now but I think it could have more.
06-29-2010, 05:55 AM
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cam card means nothing for ign timing, you need to ck the timing at full advance at 3500 rpm, should try 28-32 deg total, heads, pistons, cam, intake all have a effect on where you need to be, just have to experiment...
06-29-2010, 06:07 AM
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Timing the cam and timing the ignition are two different things.
Timing a cam is setting the lobe centerline to a specific point, either advanced or retarded from TDC. Your lobe centerline is ground into the cam, and in this case is 110*. You can't change this.
You do, however, control the position of the cam on installation. Cam grinders figure you are going to use a "standard" timing set which is "supposed" to index the cam to a baseline position, and they position the dowel hole on the cam so that it "should" pretty much be in the same position on installation from engine to engine. Your cam card shows that your dowel is positioned to place the cam at 4* advanced position. You determine this by taking the lobe centerline (110*) and comparing to the intake centerline (106*). "Straight up" would put the intake centerline at 110*.
We know that stock crankshaft to stock crankshaft, the snout key can vary a few degrees. Timing gear to timing gear, the key position can vary. For this reason, it is recommended to CHECK your cam position at the time of install and to use offset keys, offset bushings, etc to make certain that your cam is installed in the position indicated on the cam card (or in a position that you want it in).
Timing the ignition is twisting the distributor to get the timing light to flash where you want to see it. Oh, when timing a cam, you usually also double check the position of the timing tab on the motor..
Anyhow, your cam is probably more or less where Comp wanted it. Your ignition timing at 8* gives you around 32* full advance (i believe you have a 24* module in your TBIV). Many can stand to bump to 10-11* static, which gives you 34-35* full. Depends on your fuel and your motor's dynamic cylinder pressure under load. You can bump it, and listen closely for any evidence of "pinging". If it runs better and you get NO pinging under any load conditions, then run it that way for a while and yank the plugs to look closely for evidence of "chicken tracks" on the plugs. If none, then continue.
If, however, you bump the timing and see/feel no benefit, then back it back to where it was.
MC
Timing a cam is setting the lobe centerline to a specific point, either advanced or retarded from TDC. Your lobe centerline is ground into the cam, and in this case is 110*. You can't change this.
You do, however, control the position of the cam on installation. Cam grinders figure you are going to use a "standard" timing set which is "supposed" to index the cam to a baseline position, and they position the dowel hole on the cam so that it "should" pretty much be in the same position on installation from engine to engine. Your cam card shows that your dowel is positioned to place the cam at 4* advanced position. You determine this by taking the lobe centerline (110*) and comparing to the intake centerline (106*). "Straight up" would put the intake centerline at 110*.
We know that stock crankshaft to stock crankshaft, the snout key can vary a few degrees. Timing gear to timing gear, the key position can vary. For this reason, it is recommended to CHECK your cam position at the time of install and to use offset keys, offset bushings, etc to make certain that your cam is installed in the position indicated on the cam card (or in a position that you want it in).
Timing the ignition is twisting the distributor to get the timing light to flash where you want to see it. Oh, when timing a cam, you usually also double check the position of the timing tab on the motor..
Anyhow, your cam is probably more or less where Comp wanted it. Your ignition timing at 8* gives you around 32* full advance (i believe you have a 24* module in your TBIV). Many can stand to bump to 10-11* static, which gives you 34-35* full. Depends on your fuel and your motor's dynamic cylinder pressure under load. You can bump it, and listen closely for any evidence of "pinging". If it runs better and you get NO pinging under any load conditions, then run it that way for a while and yank the plugs to look closely for evidence of "chicken tracks" on the plugs. If none, then continue.
If, however, you bump the timing and see/feel no benefit, then back it back to where it was.
MC
06-29-2010, 12:54 PM
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Thanks for the quick replys guys. That was almost instant. I will try messing with the ignition timing this weekend. Would it be good to adjust the distributor while it is at full advanced(around 3500) and then advance it until it starts pinging?
