Why choose correct sized injectors?

[Andy0912]

First post so please, if I'm breaking any rules or making myself look stupid because I missed something in my all of my searching, my apologies. I have read alot about picking injectors based on flow, IDC, measured airflow it is intended to support, and so on. For example:

http://www.dsmtuners.com/threads/injector-and-fuel-pump-supported-airflow.366003/

I've found several reasons that one may choose a specific injector size to match their engines airflow such as needing 650's or smaller for SAFC, price difference, "it was a good deal", or any other reason of the sort. While planning my build, im having trouble deciding on several sized turbos. Between the 14b, 16g, and 68HTA. (I fully understand they are not exactly in the same power range, my dillema is what my end goal is, not which one performs better.)

With each turbo choice, there is a significant difference in airflow, leading to a different size injector to match. For example, the FP 68HTA is advertised as 51 lbs/min on their website which, according to the link I listed earlier, would require around 1000cc injectors to run around 80% IDC. However, a 14b (the easiest to acquire, tune for, and build for) flows anywhere around the low 30's as I've seen (please correct me if I'm wrong) which would require around the 600cc range. So now to my real question, if I can afford them, and I'm going to be tuning with Link, is there a reason not to go with the biggest sized injector? Another way to out it is, as long as I can properly tune them, could you run 1000's for a 14b turbo in order to leave room to grow?

The ECU bases its injector control off of percentage of the injector size right? My thinking is that since 1% of the stock 450s and 1% of 1000 are significantly different, there may be some aspect of accuracy and smoothing that is lost with oversized injectors. I'm nowhere near an expert, and to be honest, I'm not too confident in my knowledge about injectors in particular, so any information you could give me would be great!

 

[wolf alchemy]

I don't know much on injectors so wait for some to confirm my theory. But with injectors they all have different, lows and highs. So let's say you do use 1000cc with a 14b. Even with tuning their low output, may be too high during idle which will cause a rich idle, even with tuning. But then again I could be wrong so wait till someone else either confirms this or states I'm a dumbass. XD either way I tried to help, but also posted to bring attention to your post. Good luck.

 

[Vegas Smith]

Many people experience tuning difficulties as you increase the injector size on older injectors. However, newer injectors like the FIC hi-z line have gotten great reviews even 1650s etc. In short, there isn't much a reason to not go big as long as you have the tuning capability to compensate. You will pay more for a larger injector though...FIC-hi-z 1650s aren't cheap.

 

[Mello]

Big injectors are thoertically harder to tune at idle (when little fuel is needed). The injector can open & close (respond) in a certain amount of time. As the injector get larger the hole for the fuel is larger & when trying open close quickly more fuel passes through. Larger injector have a decrease in resolution or fine tuning. Good injectors respond quicker than cheap injectors too. Not all injectors of the same size are equal in response. But in your situation & the sizes you mentioned you are looking at you will most likely be okay & not really see much difference for future growing room. You would notice if you jumped to 2200cc injectors.

 

[Andy0912]

Many people experience tuning difficulties as you increase the injector size on older injectors. However, newer injectors like the FIC hi-z line have gotten great reviews even 1650s etc. In short, there isn't much a reason to not go big as long as you have the tuning capability to compensate. You will pay more for a larger injector though...FIC-hi-z 1650s aren't cheap.

Awesome! FIC hi-z line is actually what I'm considering. Don't foresee wanting to go bigger than 1000cc in anything less than a few years. Just out of curiosity, what is it you meant by people having trouble with tuning the older injectors?

 

[Andy0912]

Big injectors are thoertically harder to tune at idle (when little fuel is needed). The injector can open & close (respond) in a certain amount of time. As the injector get larger the hole for the fuel is larger & when trying open close quickly more fuel passes through. Larger injector have a decrease in resolution or fine tuning. Good injectors respond quicker than cheap injectors too. Not all injectors of the same size are equal in response. But in your situation & the sizes you mentioned you are looking at you will most likely be okay & not really see much difference for future growing room. You would notice if you jumped to 2200cc injectors.

Okay that makes alot of sense. I suppose I was on the right track, just a bit off in my prediction. I really appreciate the help!

 

[1990TSIAWDTALON]

I have a set of OLDER FIC Blue Max 1650's. They work GREAT at WOT but are a bi*** to tune mid-throttle because of transition issues. Go with Hi Impedance injectors if you upgrade to any injector over 1000cc for sure. If you ever plan to run E85, then get even bigger injectors since they need more fuel to do the same thing. Just my .02

 

[Andy0912]

I have a set of OLDER FIC Blue Max 1650's. They work GREAT at WOT but are a bi*** to tune mid-throttle because of transition issues. Go with Hi Impedance injectors if you upgrade to any injector over 1000cc for sure. If you ever plan to run E85, then get even bigger injectors since they need more fuel to do the same thing. Just my .02

E85 is an option for me, but id have to do some more research. Thanks for the input!

 

[Spades]

Im one that doesnt like the idea of over-injectoring. Reason being atomization... A correctly sized injector will spray a finer mist and have better combustion and knock prevention than a setup with overly large injectors that are choked down using less pulse-width. When tuning on the edge every little bit counts

 

[Andy0912]

Yeah, atomization is something I didn't even consider. I agree I would like to pick the right size, but I was curious and saw that this topic hadn't been covered very much. Plus I like disecting things further than what someone says will work b

 

[1990TSIAWDTALON]

BUT....you can NEVER make a small injector bigger but you can always tame the beast on larger injectors. I'm the one (of many) that don't like to have a set of injectors for every mod that I do. I've never tuned a car down, only up, for the past 40 years. Still just my .02 on planning for the future.

 

[Andy0912]

Ever had any issues? What's the biggest injector size you've had compared to the smallest turbo?

 

[1990TSIAWDTALON]

1120's on a 16G then went up to a 20g, then went up to a Holset, then went up to 1650's then went with E85 and now have 2150's. So see the money wasted? If you ever taste E85 and how your car runs, I would say 1120's would work and give you room, or any injector of similar size.

 

[Andy0912]

1120's on a 16G then went up to a 20g, then went up to a Holset, then went up to 1650's then went with E85 and now have 2150's. So see the money wasted? If you ever taste E85 and how your car runs, I would say 1120's would work and give you room, or any injector of similar size.

Hmmm interesting. You've got me thinking I'll have to look into e85 a bit more. Thanks for the injectors advice too!