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I'm No Expert
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Curious, whats the point of these with a dist? I can understand a crank trigger setup were each cylinder was firing a coil pack or somthing but if you have a crank trigger with a dist, then i'm confused what the point/advantage is? Just seams like now you have to line up both the crank trigger and the dist perfectly.

I'm sure there's a good reason, i just saw a crank trigger deal in my Jegs catalog with a dist and i dont understand the advantage.
 
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The crank trigger is the same thing that was inside the dizzy. Only thing the dizzy does is direct the spark to the proper plug. Once the dizzy is installed and the rotor lined up with the terminal you for get it. All timing adjustments are done at the crank. The advantage is a more steady signal.

Tim
 

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Sit N' Spin
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Locked out. What ever you set the timing at is where it is at all rpm. You can add an MSD timing control if you want an advance curve.

Tim
The advantage of triggering off the crank is that you eliminate the variance in your timing caused by the slack in the timing chain without having to run a gear drive. On Chevys the "cam twist" factor is also eliminated. However, as River Rat 005 said, you have to lock out your timing as the crank trigger has no idea what your mech advance is doing in the dizzy.

With a coil pack ignition you obviously would have no choice but to trigger off the crank.

With a cam sync, coil pack ignition and a crank trigger, you have the ultimate setup for an EFI motor as the computer can control EVERYTHING the engine is doing.
 

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WHY cant you run mechanical or vacuum advance??

would you not just phase your rotor to 1/2 of the total advance?

grant it most just lock them out.
With a crank trigger the timing is triggered by a wheel on the crank monitoring position. By using a mechanical or vacuam advance in the distributor, the only thing you would be changing is the rotor phasing and not the actual spark event.
 

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Sit N' Spin
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WHY cant you run mechanical or vacuum advance??
Just as you said in your post above, with a crank trigger, rotor phase comes into play bigtime. If you did not lock out the mech or the vac advance, rotor phase would change with RPM. This alone would cause a timing nightmare just as bad as a sexual remark in the workplace would cause an HR nightmare. :D :D
 

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crank trigger

Yopu can move your crank trigger +/- 1-degrees and not change your distributor phasing. Spark has a way of finding the right post, some times.

Jerry
 

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After discussing this recently, it was interesting to learn there are problems even beyond the cam and timing chain. One of the more extreme examples was the fact that the distributor (in a chevy-type block) is bolted down to an aluminum surface (intake manifold) which is bolted to the block. The aluminum manifold is less stable as a mounting surface, than say the block itself, and also contributes to timing variance. (this was a tip from Warp).

When you think about the numerous deficiencies with a distributor vs. crank trigger it's a no-brainer. Keeping in mind, however, that the difference only comes into play, from a practical standpoint, in a racing/very high performance application where EVERYTHING matters. For example, a dry sump oiling system is the "best" choice for consistent oil delivery in race conditions, but its complexity and cost is not a viable trade off for low RPM applications.
 
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