I am upgrading to a 4 injector style TB soon (I hope) and was wondering what size injectors to go with.
It will be on my 12a for now, but after I get the bugs worked out I will port it to my 13b so I want something that'll work on both.
I am looking at High-Z 42.29# injectors. I have two now and they work well. 4 will be plenty for my stock 12a I should think.. For the 13b I was curious: What is the max duty cycle you s4 guys see with the stock injectors? 42# is pretty close to the ~430cc, IIRC.
I would like to use the stock s4 injectors when I switch over, but I am fairly sure they won't fit on the new rail..

60# Mototronic High-Z injectors look good as well but are about $20 more each than the 42# and I get a much better deal to get them in quantities of 4 instead of two, so I don't want to buy two now, then two later when I go to 13b. Or maybe two 60# would work on a 13b?

I have used the calculator on the megasquirt.info site in the past and even doubling the engine size, it still underestimated the size I needed and I ended up wasting some money, so this time I'd rather not.

 

2 750s get me 167 RWHP off a decently equipped 12A (2x50 TB, fairly open exhaust, streetported) and still have some headroom. You don't want to get too big, idle and low end become problematic and not as smooth as you'd like.

-Mike

 

with 4 stock NA 460cc fuel injectors on an S5 NA we hit around 80% at 13.2:1 AFR at 7500 rpms, after that it drops off a bit to 9000 rpms.