Ignition timing issues for blocks with different heads.
When it comes to these swaps, there is lots of power to be made, but we often see questions to the affect of:
“I am having ignition timing issues on my LS VTEC Swap. When trying to sync the timing I can’t even get close to the 3 timing marks on the crank pulley. When I line up the TDC mark I’m only at 8 degrees. The distributor is retarded all the way it can go(rotating it towards the radiator support). My mechanical timing is spot on, I am not sure what to do next?”
Answer:
This is often caused by different distances between the cams and the crank then OEM tolerances allow for, whether it be from deck height, different heads, and in other cases crank modifications, including pulley replacement.
This will often lead to the situation where with the Dizzy at both extremities you will not get timing marks to line up.
While there are several acceptable methodologies to remedy this, our preferred solution is to reconfirm everything to leave no room for error, this means we will:
1) Confirm TDC on the crank pulley, verify it is indeed TDC (0 Degrees). Confirm Cyl #1 is indeed at Top Dead Center mechanically with a feeler gauge. Then confirm the pulley white 0 degree mark supports this. If not, remark 0 degrees with a new timing mark.
2) Confirm cam timing is indeed “centered” when timing is at the proper TDC. If not, you may need adjustable cam gears to correct/account for.
3) Set timing to 0 degrees in the SManager. The car may have trouble idling at this low ignition, have a colleague add some extra throttle if necessary (which is why Hondas normally use 12-16 degree marks).
4) Using a timing light confirm the TDC 0 degree mark on the pulley lines up with timing case mark when the light is strobing.
Lastly… IF… the dizzy can not be adjusted to account for these changes some may just ignore it and just completely redo the map based on dyno results, after all if the numbers work the dyno will show it, however, if your working with a known good dyno tuned basemap and you want to “keep” some of those ideal ignition values without scrapping everything, one could “offset” the timing in the basemap for the difference between the MAX dizzy position and the needed dizzy position. As in, if fully advanced on a good “keyed” dizzy that is non adjustable if true timing is still off 5 degrees short, one could add 5 degrees to the basemap (mark the new basemap as non transferable to another car) and keep going from there.
The difference is “missing” timing can be measured by advancing the timing in Smanager from the “0” to the necessary number needed to get the marks to line up, when the Dizzy was maxed. It would be more ideal to get things to match, but if you or your customer is stuck then this is a good “patch” to get things rolling.
Again there are other acceptable ways to rectify this situation, but given the variety of builds we see, especially ones where we don’t know the history of the motors or parts used, this procedure works for us.
Hope that helps,
The Etunez Tuning Team