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Pretty much as title says. I wanted to go to 550cc injectors and stay around low 300whp, but if I find say 1000cc injectors for cheaper, is there a downside to getting those instead?
 

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Yes you can run different injectors...Think of injectors as a time thing (which I’m sure you know)... whenever a said duty cycle sprays fuel the “hole” or pental opens up doing its thing, so you get... more fuel... however unless you have a proper ecu (preferably a stand alone) the ecu you have doesn’t know you stuck 1000cc in there and that will be a bit abrupt and without control it won’t run very well.. Try this place, I’ve bought from Marren Motorsports lots of times www.injector.com
 

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The most important thing about running big injectors is getting them characterized for flow rate and dead time, and then having an ECU that can support dead time over battery voltage compensation. Injector Dynamics is ~the best at this, their 2000cc injectors will run a 2 liter engine at idle with zero fueling issues.

Dead time is the time that it takes the injector to open and close, mostly off the shelf injectors have a value around 0.5 to 1.0 ms. Not having dead time correct or compensated will lead to a ton of issues with idle fueling and weather compensation correction, especially with large injectors.

Do not fall into the trap of cheap, high flow rate injectors. They are very frequently lower flow rate units that have been hacked up and had the orifice drilled bigger. They will be garbage full stop. Be extremely wary of high flow injectors like that if they don't have each unit flow tested and dead time measured. You will have a very frustrating time getting ****** injectors to run right.
 

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What fuel rail are you using? Top feed side feed? And I have the same question as the guy above what ECU.
 

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Discussion Starter #7
What fuel rail are you using? Top feed side feed? And I have the same question as the guy above what ECU.
What ECU you running?
Stock. I’m planning on dropping a ton of money at once when I have it and getting a turbo (gt3071r?), a fuel pump, downpipe, injectors, a stand-alone ecu, and a tune all at once.

I now have two questions.

Why bother with a lower flow injector like 550cc? Why not just get a 2000cc and not use it to its full potential.

What is the difference between the types of fuel rails (side, top)?
 

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Stock. I’m planning on dropping a ton of money at once when I have it and getting a turbo (gt3071r?), a fuel pump, downpipe, injectors, a stand-alone ecu, and a tune all at once.

I now have two questions.

Why bother with a lower flow injector like 550cc? Why not just get a 2000cc and not use it to its full potential.

What is the difference between the types of fuel rails (side, top)?
Side feed is the old style of injector, top feed is more modern usually. You get the type of fuel rail to match the injectors you want.

You want to size the injector for the power you want because injectors have a minimum amount of fuel they can accurately deliver. If that minimum amount is greater than the fuel demand at idle your engine will run horrendously.

The other thing to think about is spray pattern and droplet size. You have a 4 valve, DOHC head. If you get a pencil spray injector you will be spraying right into the divider between the two valves. This is mentioned by Adaptronic's experiences with transient fuel tuning: Transient Throttle Conditions and How to Set it Up on Modular ECUs
Dr Cowart mentioned in his video that the Ford Duratec engines he was calibrating had X of about 30%, and Tau of about 400ms at idle. I’ve found with most Japanese engines that X is only about 15% with standard injectors – although if you have a narrow spray pattern injector like an Injector Dynamics one, and a dual inlet valve head, then often the injector stream points right at the divider wall between the two runners, and a lot of fuel ends up on the divider. This has the effect of increasing X; so an engine that might be 15% on factory injectors might increase to 40% or so with upgraded injectors.
If you only need 550cc injectors and you want the "best" possible injectors, you would want to figure out how to get the OEM R35 GTR injectors to work with the 3S-GTE. Those are designed to spray directly into the back of the intake valve for 4V DOHC heads for better transient fueling and have very fine droplet size.

If you just want something that works and you have no plans for E85 then just run the 540cc gen 4/4.5 fueling system. Those are fairly modern injectors and shouldn't be too bad.

Modern injectors are pretty good, you can get 1000cc injectors that work great in your car but it will still be better with 540-570cc injectors.
 

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Can't change injectors without changing the ECU. The stock ECU is set to one injector size. If you put in a different size the duty cycle for that injector will put in more or less fuel than the OEM set injector. A 1000cc will net you plenty of flow for the power goals.

Use this calculator to see what you actually need.
 

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I can't imagine most people realistically needing more than 600-700cc injectors. Just choose a reputable brand, ID1000 come up a lot. I am going with seimens top feed.
 

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I can't imagine most people realistically needing more than 600-700cc injectors. Just choose a reputable brand, ID1000 come up a lot. I am going with seimens top feed.
You can get SARD 800cc side feeds so fit the stock rail. The ID1000 or ID1050X only downside is they are top feed meaning a new rail.
 

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You just have to ask yourself how big do you need (horse power).. I ran 800/1680cc in my RX7... it was a crazy mess... lots of roads untraveled back in 1997...
 

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1000 cc injectors idle fine on a 3S-GTE with modern engine management. A stock ECU is probably pushing it, but if they're a well matched set it'll probably work ok. Just for reference, you'll go from like 10-15% IDC at low load to like 3-6% with the much bigger injectors. This doesn't leave much room for error, and the older ECUs aren't the most accurate.

That said, a modern EV14 style injector is so much better than an old early 90's sidefeed, or even late 90's top feed (which are like EV6 vintage).
 

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1000 cc injectors idle fine on a 3S-GTE with modern engine management. A stock ECU is probably pushing it, but if they're a well matched set it'll probably work ok. Just for reference, you'll go from like 10-15% IDC at low load to like 3-6% with the much bigger injectors. This doesn't leave much room for error, and the older ECUs aren't the most accurate.
How does a stock ECU control a bigger injector?
 

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How does a stock ECU control a bigger injector?
A stock ecu doesn’t know you changed the injectors, so since it’s a time thing and the “hole” is larger it sprays more Fuel.. I believe that’s where it gets tricky... long ago (late 90’s) on my rotary I went through all this.. I ran 550’s on primary and added 850’s on the secondary with added boost, it didn’t run super smooth through the curve, but
It was manageable, especially under WOT.... but it didn’t lean out which is super crucial on rotary motors under boost... The issue still lies with the stock Mickey Mouse ecu’s, you can’t control timing and that’s where the running quality gets goofy.. I first did all this when there was no road map and all we had was the alphabet soup part numbers from HKS and Trust... that’s when I bought a MoTec stand alone... that solved everything...
 

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A stock ecu doesn’t know you changed the injectors, so since it’s a time thing and the “hole” is larger it sprays more Fuel.. I believe that’s where it gets tricky... long ago (late 90’s) on my rotary I went through all this.. I ran 550’s on primary and added 850’s on the secondary with added boost, it didn’t run super smooth through the curve, but
It was manageable, especially under WOT.... but it didn’t lean out which is super crucial on rotary motors under boost... The issue still lies with the stock Mickey Mouse ecu’s, you can’t control timing and that’s where the running quality gets goofy.. I first did all this when there was no road map and all we had was the alphabet soup part numbers from HKS and Trust... that’s when I bought a MoTec stand alone... that solved everything...
So it didn't actually work and you had to get a tuneable ECU to get it running properly.
 
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