88 Distributor on a 97 Block Vortec Timing Question

[bwag575]

I recently converted my Cobra from an 1988 to a 1997 4.3 block. I am running the distributor and 4BBL Carb from my 1988 motor in the 1997 set up now. Any thoughts on where I should set the timing marks? I keep reading 8BTDC for earlier 4.3's and 0-1BTDC for the newer models. I wasn't sure if timing was dependent on the vintage of the distributor or the age of the block. I have started it outside the boat and it runs great. I just want to dial it in a bit before I begin sea trials.

Thanks

 

[Maclin]

Re: 88 Distributor on a 97 Block Vortec Timing Question

You want to match the ignition advance to what the new engine's specs ask for.

It may or may not be possible with the distributor and ignition system you are using. It all depends on the timing advance that is provided by the distributor or computer. You do not want to go past the total advance spec for the new engine, and also need to match the initial (at idle, or "static") advance.

Let's say your "vintage" ignition system is conventional where the distributor controls the timing advance mechanically via weights and springs. The total advance produced can be 24 degrees just for example. Setting the initial advance at 10 BTDC would provide a total advance at higher rpm's of 34 degrees. The advance also has a "curve" of how much comes in at what rpm. Now let's say the engine is designed for 8 degrees initial and total of 34. In order to get the full 34 degrees you would have to set the initial at 10 which may make the engine kickback during starting with too much inital advance.

Likewise if the engine could take 36 degreees but only 8 or 10 initial then you can see where this is going, as the distributor may be locked into an advance setup that may not match up well with the new engine's tuning specs regarding igition advance.

These are just examples, and all depends on the exact type of ignition used, like whether or not a spark computer is involved.

 

[Bondo]

Re: 88 Distributor on a 97 Block Vortec Timing Question

I recently converted my Cobra from an 1988 to a 1997 4.3 block. I am running the distributor and 4BBL Carb from my 1988 motor in the 1997 set up now. Any thoughts on where I should set the timing marks? I keep reading 8BTDC for earlier 4.3's and 0-1BTDC for the newer models. I wasn't sure if timing was dependent on the vintage of the distributor or the age of the block. I have started it outside the boat and it runs great. I just want to dial it in a bit before I begin sea trials.

Thanks

Ayuh,.... While I agree with what Maclin is sayin', I also disagree,...

If yer usin' the entire ignition system off the old motor, use the spec's called for, for That ignition system,...

The other spec's you've been seein' are for totally different Ignition Systems,...

 

[Scott Danforth]

Re: 88 Distributor on a 97 Block Vortec Timing Question

Since your have just updated the long block and not the induction and ignition. Run the distributor just like the 1988 at 8 degrees BTDC.

your new engine should be a vortec block with a balance shaft. The vortec combustion chamber will take a bit more advance prior to detonation. However for discussion purposes, I would stay at the 8 BTDC.

 

[Maclin]

Re: 88 Distributor on a 97 Block Vortec Timing Question

To optimize the tuning I would want to know exactly what you have now as it may not be OEM for 1988. I did not mean to imply a total re-fit would be needed, and if it is the 1988-era setup then I agree it is close enough until you decide to set it on KILL

Of course the gains from "Pretty Good" to "KILL" would only be 1/2 to 1 mph probably...sigh. I kind of forgot for a minute there that it was for a boat. In a performance car or similar that extra timing optimization would make a bigger difference in realized performance.

 

[bwag575]

Re: 88 Distributor on a 97 Block Vortec Timing Question

Thanks for all of the advice. It is the complete '88 ignition set up on a '97 'balance shaft' block. I will go with 8 degrees BTDC and see how it does. Like I said earlier... it started right up, ran smooth, and revved well outside the boat when I got it back from the engine rebuilder. I shouldn't be too far off. Just need to dial it in with the timing light. "Kill" should be pretty easy to attain being as it is replacing the original 2.3l that came with the boat. 2 more cylinders, 2 more liters, and 2 more carburetor barrels should be fun....(I did upsize the outdrive as well). Thanks again!

 

[Scott Danforth]

Re: 88 Distributor on a 97 Block Vortec Timing Question

If you run 91 octane you can go up a few degrees of advance