does changing to a larger injector require a new dynotune?
 

I'm currently running 450cc injectors and the tuner said that they were pretty near maxed out. I'd like to change to a higher flow; perhaps the 1000's that many of you run. Is this as simple as changing the injector selection in the megasquirt-3? or is it advisable to re-dyno tune? 2004 nb/turbo/ms3

it depends on what style injectors.
ev6 to ev14 you'll need to update a lot of the tune

You will need to retune. Injectors have different characteristics, its not all linear. And they act differently at different flow rates.

On a street car you might be able to get away with just throwing something together. But on a racecar I would want everything just right.

You will need a re-tune beyond just req_fuel change, but if you know your way around VE analyze live and reading data logs, then tuning fuel doesn't require a dyno.

If you are working with solid deadtime data and reliable flow figures, you can change between two injectors of the same style with just a req_fuel change and a watchful eye on AFRs during your first couple days of driving. Low-speed driveability may require some retuning due to linearity differences but highway cruise and in-boost should be the same.

If you are changing between two different types of injectors, you need a full retune.

Kitty for you! Was just about to swap my Seimens Deka 60's for some ID750's. I thought I could lower fuel pressure and match the current injectors output and avoid a re-tune. Clearly there is more to it that that. That makes my decision easy. Gonna stay with the 60's.

This is is on another car I own. Retuning the stock ECU is not easy and best avoided.

The fuel probably needs to be retuned, yes, but assuming it's a street-legal car with a wideband & MS you can retune that on the street.

Dynos are for tuning ignition, for figuring out the shape of the spark curve as limited by either MBT or detonation, depending on how much octane you have. Changing injectors is not going to change the MBT curve, and while it is theoretically possible that an injector with a better spray pattern might help with knock resistance, I doubt there's much to gain there.

--Ian

:likecat: for posting truth