Recent 500 efi injector test vs another claimed replacement
 

I recently had a customer from.new York message me about a replacement injector for his 500 efis that requires no tuning changes. I have yet to find THAT injector, it doesnt exist to.my knowledge. I have relegated to using a bigger, more commknly available injector and developing a tune that works on stock 500s. By time I spoke to him he had found a business that sold him a "direct fit" injector, claimed to be very close to his stock 500 efis. Well, always anxious to see this mystical replacement I graciously volunteered to test 4 of them against 4 average, good 500 injectors on my modern , accurate ASNU machine. No, they were NOT remotely close. I'll post more later,Smitty
https://cimg6.ibsrv.net/gimg/www.off...3014df3be0.jpg
https://cimg2.ibsrv.net/gimg/www.off...6bdb02b42e.jpg
https://cimg4.ibsrv.net/gimg/www.off...a42774ecf8.jpg
https://cimg5.ibsrv.net/gimg/www.off...fb504fc3cc.jpg
https://cimg9.ibsrv.net/gimg/www.off...2a48d71498.jpg
https://cimg2.ibsrv.net/gimg/www.off...23b45f9945.jpg
https://cimg0.ibsrv.net/gimg/www.off...8a808fc9f9.jpg
https://cimg9.ibsrv.net/gimg/www.off...12e7042641.jpg

https://youtu.be/a4tr9Z6j5bU

So heres a little injector trivia/math for those that care, stock 500 efi, 36 lb, lucas 42 lb, sounds pretty "close", right, well, alot more to the picture than just static flow numbers. At static flow, yes the test yielded a average of 76 cc (42 lb) vs 68 cc, doesn't sound like alot BUT, still12%. Sooo, if your engine previously ran at 12.0-1 afr, it would now run at 10.56, oh, not good at all. BUT, it gets MUCH worse when you move away from static, go down to 2500 rpm /6 millisecond area in test, 100 cc average vs 66, now your talking FIFTY TWO %, so, just about there cruising at 3000 rpms, your cruise AFR would now go from 13.0 to about 7 to 1, yeah, not gonna work. I printed off a copy of the full test sheet , I will post it tomorrow, there were areas approaching 60+% more. Even another 36 lb injector, with DIFFERENT characteristics, may flow close at static but since voltage bias tables in tune do NOT change on a "stock" ecu for a different injector, there will be areas where the latency/dead band will make flow wildly different either lean or rich. Ive said this before, I purchased several 34, 36, 38 lb injectors and ran them against stock 500 injectors and only pace they were remotely close was at static (100 % flow powered wide open ). I tested a set of supposed "dead match" Bosch 36 lb a year ago that were worse then the 36 lbs ones I bought to compare. Moral of story, people are more interested in selling you something and making a buck then anything, be careful what you buy, boating seasons short, no one wants to be down with a melted piston or a hurt short block from a pig rich tune, Smitty

Very cool info!

This is great info and I have been learning a lot from Smitty and you other mechanics on here that chime in with input/advice! Thanks to you guys for helping your OSO brothers out. I normally would look for some replacements thinking new is the way to go, but after reading several threads on here, I contacted Smitty over the weekend, my injectors will be heading his way soon.

so,what your saying is I won't need whipples extra injectors w/ these bad boys shoveling in fuel to my big whippled motor.:D
good info.

I am assuming (and I dont know that much about injectors) that the listing of the injector i.e. 42 lbs or 36 lbs is what they flow at 100% duty cycle? if so, no injector is ever run at that level in an engine so it would really be a meaningless number would it not? why are they not rated at something like 70% or 80% the way camshaft duration is rated at .050 to give a more accurate measure of what is useful to the engine.

My take away, when I rebuild my motors I might as well add tuning into it.

I have to wonder since I will most likely go up to 540's if it is even worth keeping the stock MEFI and maybe moving to a Holly FI.

Then of course change intake or not.

All injectors (as far as I understand) are rated at static flow, ie, 100% flow with full voltage, usually at 3 bar (43,5 psi), sometimes at 4 bar, 58 psi. the thing most people dont understand which is why I put these test results up, different injectors have different characteristics. These are a prime example, although they "only" flow 12% more at static, they flow 50,60% more at lower settings (more like theyd run in a boat). In my previous testing, even 36 lb aftermarket injectors although they flowed close at static, flowed far different at the lower settings. A misconception on mefi engines is that somehow the computer adjust for this, it does NOT. There is no 02 feedback, no MAF sensor so its simply blind speed density, it just opens the injector a amount based on map reading and a "lookup" table with some modifiers for ect, iat, tps etc. So, if a injectors flows 10, 20, 50% more at 4000 rpms and 10 ms of open time, engine will simply run pig rich, or in some cases lean if the injector flows LESS somewhere. Then throw in voltage bias, in a recent post discussing using bosch 36 lb injectors the voltage bias that was supplied showed injector needed 1.3. 1.4., m1.5 milliseconds of added fuel on top of the normal fuel table where the stock bias table was in the .35, .50 range at normal voltages you'd see in boat. So, the aftermarket injectors would require a EXTRA millisecond or so of opening time to correct for deadband/latency, (the amount of time injector is energized and no fuel flows. I offered the OP in the bosch injector thread my services for FREE to nsee how different they really were but since I never heard from him I assume he just instalkked them and hoped they worked right, Smitty

If you have mefi3, Id just use it and have it tuned. I recently dynoed a 540, AFR 325 heads, mefi3 controller, extrude honed/modified intake, a tb I bored out and made throttle blades for and with a fairly small cam from Bob M it made over 700 ft lbs of tq and 650 hp, Smitty