Recent 500 efi injector test vs another claimed replacement
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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://youtu.be/a4tr9Z6j5bU
https://youtu.be/a4tr9Z6j5bU
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08-09-2022, 09:35 PM
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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
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#3
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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
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articfriends (08-09-2022)
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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.
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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
good info.
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articfriends (08-11-2022)
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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.
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articfriends (07-28-2023)
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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.
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.
#9
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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.
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SB (08-11-2022)
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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
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Gimme Fuel (08-12-2022)