do i need injectors

[sxynerd]

We don't play with minimum numbers here Cliff, lol. j/p Op and anyone looking to ever "eventually" go up in power; Always by the maximum injector you think you'll ever think you'll need and if you're not up to the 60#ers then make the leap to the 60's. lol Brand new they are about $330 but you wont have to buy injectors again. Unless you supply fuel the right ($$) way the 42's are going to run out before 450rw.

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[sainthk]

Sxynerd,
So let say you buy 60lb injectors, you only use what you need and not the whole 60lbs? and i'm guessing thats why you need a re-tune so the comp knows what to support?

[sxynerd]

Originally Posted by sainthk

Sxynerd,
So let say you buy 60lb injectors, you only use what you need and not the whole 60lbs? and i'm guessing thats why you need a re-tune so the comp knows what to support?

Essentially that's right. It's a little more complicated but yeah you only tune in what you need.

[sainthk]

Alright I get it now, Thanks for the info.

[cliffyk]

Injectors can be too big, and for any n/a application 60lb/h would be too big (30lb/h are adequate for any n/a 4.6L 2V or 4V application) as you would only be using the lower 40% to 50% of their range. This will make properly tuning idle, part throttle, and low load fueling quite difficult if not impossible.

Read Greg's book to find out more...

[sxynerd]

I didn't think of that cliff, damn sure glad you're here. Do the math for us Cliff, at what point should a person who's going to eventually make more power step into 60's? It's very possible to hit the 280-300 mark with stock injectors but at those numbers 60's would still be in range to tune, correct? buying 42's is a waist if you're going to ever want to make more than 450 without converting to higher flow fuel lines. (Since the pumps usually isn't the poop factor)

[cliffyk]

Originally Posted by sxynerd

I didn't think of that cliff, damn sure glad you're here. Do the math for us Cliff, at what point should a person who's going to eventually make more power step into 60's? It's very possible to hit the 280-300 mark with stock injectors but at those numbers 60's would still be in range to tune, correct? buying 42's is a waist if you're going to ever want to make more than 450 without converting to higher flow fuel lines. (Since the pumps usually isn't the poop factor)

Injectors should always be selected so that their fuel delivery, at 75% to 85% duty cycle, matches the engine's peak HP--if the maximum duty cycle is much less than 70% you will have fuel control problems at idle and low loads, much more than 90% and you are flirting with their going static at high rpms and loads.

Here's a table showing what the ranges are for some common injector ratings for our cars:



The formula is:


This is similar to MAF sizing in that MAF selection also needs to be made so that the engine's air flow requirements will cover 85% to 90% of the MAFs total range. If a MAF is too small it will "peg" and stop reporting any further flow increases (can you say LEAN!), if it's too large you will only be using a small portion of the lower part of the total air flow range the MAF can support.

Here's a chart of the flow bench data we got when testing the OEM MAF from my car:


We ran it right up to the bench's limit, you can see that at the low end there's a lot of change in output voltage for small changes in air flow (a good thing for idling and low loads).

However at the high end, at greater than 5.0V output, there is little change in voltage for big changes in flow. This is bad for any sort of precise fuel control in the range above 5.0V out (BTW, it's the PCM that imposes the 5V limit, the MAF will output higher voltages as you can see).

99.44% of difficult/impossible fueling related tuning issues are due to improper injector and/or MAF sizing.

It's true that by playing with the low and high injector slopes, injector breakpoint, and the MAF transfer function almost any combination within reason can be made to run. But if you seriously undersize injectors or MAFs you'll reach their upper limits before being properly tuned--and if you oversize them you'll be operating over only a small portion of their usable range, limiting the resolution of their use.

Add a so-called "calibrated" MAF with an unknown, goofy, not-even-close to linear, transfer function and things really go to crap fast.

Hope this helps...

---------------------------------------------------
See what happens when you retire and have too much time on your hands...

[teej281]

So running around N/A, 42lbs would be the max you'd ever wanna go with hopes for the future??? What about running a really built 4v with ported cobra r heads and healthy cams???

[Black_GT_02]

I plan on circa 550rwhp next summer. I'm on 42lb injectors now. Would I be okay just upgrading my fuel rails?

[sxynerd]

I always love asking cliff to explain or elaborate on an idea. Thanks Cliff. Not only is it technical, it's understandable. Why don't you rewrite Banish's book? LOL