How Big is TOO big?

Since I can't seem to get a response from anybody on this maybe someone on here knows,

When sizing a CR injector for a given build, how do you decide what is too big? given the fact custom tuning has come so far, and I really cant seem to find a major issue with going much larger than what you NEED persay, why ever go smaller?

Larger injectors at a shorter pulsewidth seem to make the same power with less heat and less timing(which in my mind means less chance of HG failure most of the time). Rate of injection also seems to be the biggest factor in ability to spool larger turbos (another benefit). The only two negatives I can seem to come up with is a small price difference in some cases, and at about the 250% and above level the truck doesnt like to warm up as fast in cold weather.

lets say someone had a goal of 900rwhp on a 5.9L, this could be accomplished with say 100% injector easily, but why NOT go with a 200%? or if you dont winter drive it, a 300% or 400%?

From what I understand, (no experience) when you start getting into the larger injectors (300%+) they become harder to control at idle with temp changes. They are also less efficient (MPG wise) because you are usually limited to a single injection event.

$.02

I suppose thats a good point, but still at the same time if i was going to slap 300+%s in I probably wouldnt be winter driving and probably wouldnt be overly concerned with MPGs. Just seems more logical that anything less than say 1000hp, just go ahead and put a 200% in, and above that go right to like a 400%. Saves money when you inevitably want more power.

I also remember a video lavon posted of larsons truck idling in cold(er) weather with 400% overs, truck didnt seem overly unhappy.

Not really related per say however what we have been able to do with larger injectors at idle to clean them up from the haze, is make rail pressure higher up to 10k to help. I like you have similar thoughts, I have 150% overs for a 900hp build and only run about 1800US. I find the big single to be more responsive and egts much lower

Justappumped24v said:

Not really related per say however what we have been able to do with larger injectors at idle to clean them up from the haze, is make rail pressure higher up to 10k to help. I like you have similar thoughts, I have 150% overs for a 900hp build and only run about 1800US. I find the big single to be more responsive and egts much lower

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My thoughts exactly. Not that i've done it personally, but from what I can gather those type of benefits seem to be increasing with size. There are a handful of setups i know of that are making some very serious power with as low as 1000uS of max duration and less than 20* timing and a large injector.

wwentzler said:

My thoughts exactly. Not that i've done it personally, but from what I can gather those type of benefits seem to be increasing with size. There are a handful of setups i know of that are making some very serious power with as low as 1000uS of max duration and less than 20* timing and a large injector.

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I believe my timing is about 28 max on my hottest tune. My daily tune is 20

This brings back my want to finish the timing calculator rich had started. Without a CP datalog i think its hard to do anything but speculate. I had sent a few emails around and got nothing back. If nobody else can explain this to me then ill make a little more effort to find an answer from somebody and share on this thread.

Weston might be able to shed some light. He enjoys this kind of discussion. I’m sure contacting Firepunk wouldn’t be a waste of time either. Or perhaps Paul Cato.

A bigger high quality injector is great. Personally the nicest set of injectors that I've tuned have been a set of 500% over King Cobra's from II. That being said, I've tuned some of their older 250% overs that were terrible, Worst injectors I've ever tuned actually! Seems their new stuff is great though.

Also, with those King Cobra's I was able to run a pilot injection event and the truck runs clean and quiet. I was extremely impressed with them.

Dom_c13b said:

A bigger high quality injector is great. Personally the nicest set of injectors that I've tuned have been a set of 500% over King Cobra's from II. That being said, I've tuned some of their older 250% overs that were terrible, Worst injectors I've ever tuned actually! Seems their new stuff is great though.

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Have you ever done any testing on spool with different injector sizes? Would be some fairly easy tests to do on a dyno but id be curious to see if there is a sizable difference in both spool and power per unit fuel flow (much like the mechanical guys talk about making 2hp per cc type deal)