How big is too big?

bad360rt · Post by **bad360rt** » Mon Apr 10, 2006 10:41 am

I'm looking to run MS for fuel only on my blown '02 Dakota 5.9 R/T. My last dyno was 592rwhp 547rwtq. Based off of ~20% drivetrain loss and using the injector calculation with .60 bsfc and 85% dc, I'm looking at needing 63lb injectors to support the power I'm making now. Of course with plans for future growth I would like to only buy injectors once. My question is how big is too big? Can I run 72lb injectors and still be able to trim them enough at idle and part throttle? What about 75lb or even 83lb injectors? Thanks for the help!

I'm looking forward to my MS install and tuning, I can't wait to finally have full control over my fuel curve

Bernard Fife · Post by **Bernard Fife** » Mon Apr 10, 2006 2:33 pm

bad360rt,

Check this out: http://www.megasquirt.info/v22manual/minj.htm#size there's a section to help you estimate the maximum injector size you can run.

However, you can be much more lenient with MS-II than MS-I, becuase it has 100 times the pulse width resolution (0.001 millisecond versus 0.1 millisecond), allowing finer control even at very short pulsewidths.

I run 72 lb/hr injectors on my 406, idle is no problem at all with MS-II.

Lance.

Clifton · Post by **Clifton** » Mon Apr 10, 2006 7:36 pm

I know I need to run a 72 lb injector. The 550's I have now are maxed with the stock piggy backed ecu. How can you tell if it will be too much at idle if I haven't set up the MSII yet? It is 180ci 6 cyl.

bad360rt · Post by **bad360rt** » Tue Apr 11, 2006 11:40 am

Thanks Lance. Looks like I'll be going with the MS-II

Since my truck is already EFI, everything else is already in place, and I've already upgraded to a full return fuel setup, just need to be able to run big injectors and control them and I didn't want to fork over $3K for the standalones that are available. Hopefully I'll be posting in the success stories section in about a month, until then it's more

-Dave