I have 20b ran by microtech that was recently tuned on a dyno. It was running very poorly, so I started adapting numbers from suggestions given by a well known rotary tuner.

One of the setting that I was advised to change is time-based DWELL setting. The previous tuner set the DWELL to 4.25 ms. I was told that was too high for microtech and was advised to set it back down to 3.0-3.25.

I since have not taken it to boost. Now I'm reading on this forum that changing the DWELL setting is a big no-no because it changes timing?

I wanted to ask whether I can decrease the DWELL setting from 4.25 to 3.25 while leaving the timing as is. or do I need to change the timing map all over again?

I also changed the pump1 setting from 0 to 5"Hg without changing much else.

I was also advised to make sure that the timing is staked at 5 degrees. How do I make sure of this?

Thank you.

 

anyone?

 

Around 3mS is the proper dwell for stock coils.

Did the car ever run correctly or is this a new setup? Has it only been tuned for power on the dyno or has it had street tuning?

Rich? Lean? Misfiring?

 

I have MSD blaster ss coils. would it be still 3 ms?

the car put down about 600whp but on 91octane with this new setup with the high dwell time.

it was running lean with AFR in 15-20 range after the last tune in the vacuum cruise, but I fixed it by playing with the matrix setting while driving around town.

it's running whole lot better after I played with the matrix setting on vacuum, but due to lack of microtech experience with the last tuner I want to make sure I have everything sorted out before I take it back into boost.

 

talked with microtech, they say to try 3.5ms for blaster ss coils.

can I lower the DWELL setting safely without changing any other parameters?

 

^

 

Yes, you can lower the dwell. All you are doing is lowering the maximum charge time of the coil. You don't really even see full dwell beyond low RPM as there isn't enough time to charge the coil for that duration.

 

thanks aaron! Microtech should be paying you some commission. You're the only one responding to our questions

Thanks again.

 

dwell is the time that the coils are charging. it works a bit like a fuel injector duty cycle. the coil needs time to charge fully, and it takes a little time for it to fire as well, and when you plot that with time, or RPM, you only have so much time for the coils to charge.

it depends on the coil, and if you're running waste spark or not, but 3.5ms of dwell is about the most you can have running a stockish redline.

 

Microtech should pay all LT8s owners a refund on the ECU because of the bait and switch they did with promises of continuous software improvements. to date, there have been exactly zero software updates for the LT8s.