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Old 12-30-2010, 06:21 PM   #1
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Default RX7 Injectors vs RX8 Injectors?

Hi guys, I am new here, I don't have a MX-5/Miata, I have a 2nd RX7. However my question is about something that you guys have been doing already. And that is swapping in NA RX7 Injectors, 460cc, into your engines. I was doing some research into upgrading my injectors that I have already for newer modern injectors. From what I've been reading is that 1 or 2 people have installed RX8 secondary injectors, the yellow ones. What I want to know is what generation were these installed. If anybody has the dimensional specs of the RX8 injectors with the proper seals and o-rings, and if the o-rings need to be changed to fit, what are they? Thanks for any information you can provide.

Also if someone has any available data comparing the 2 injectors at same fuel pressure, as well atomization differences, that would be great as well. Any data that you guys have, I could use it.

Last edited by gryffinwings; 12-30-2010 at 06:22 PM. Reason: More questions
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Old 12-30-2010, 09:51 PM   #2
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The new yellow RX8 injectors are 440cc and the ones you want. I'm pretty sure they are all the same (all HI imp) and all fit the same.
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Old 12-30-2010, 10:06 PM   #3
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Whats the reason for switching the injectors and what size are your stock ones I have a 13b miata. I ran the 2 gen red top injectors in my 99 miata. I know 90-05 use the same injector hole sizing.
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Old 12-30-2010, 10:19 PM   #4
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Whats the reason for switching the injectors and what size are your stock ones I have a 13b miata. I ran the 2 gen red top injectors in my 99 miata. I know 90-05 use the same injector hole sizing.
The switch is for the sake of efficiency and possibly more power by better atomization, as well as smoother running.

Stock injectors are 460cc injectors that use 80s technology, or quite possibly 70s technology that was used by Bosch and licensed by Nippon Denso. Changing to the RX8 injectors I get the benefit of current injector technology. Not to mention I'll be refurbishing the fuel rail system at the same time so I figured why not.
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Old 12-30-2010, 10:32 PM   #5
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The switch is for the sake of efficiency and possibly more power by better atomization, as well as smoother running.

Stock injectors are 460cc injectors that use 80s technology, or quite possibly 70s technology that was used by Bosch and licensed by Nippon Denso. Changing to the RX8 injectors I get the benefit of current injector technology. Not to mention I'll be refurbishing the fuel rail system at the same time so I figured why not.
Thats a good reason i some times forget how old the rx7 are some times. Now the other question i have is do you have any fuel controller.
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Old 12-30-2010, 10:45 PM   #6
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Thats a good reason i some times forget how old the rx7 are some times. Now the other question i have is do you have any fuel controller.
Not at this time, I'll most likely need one, but first I'll be picking up some sort of A/F gauge and sensor setup first to be able to see where my AFR ratios are.

Considering how close the cc ratings are, I don't see myself needing a huge adjustment, but it would certainly be nice to pull power out of them.

Now the only problem is, picking the right fuel control. Mainly the one that comes to mind is the Apex'i SAFC, but I'm open to others that could be better and/or easier to use.
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Old 12-30-2010, 10:54 PM   #7
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Not at this time, I'll most likely need one, but first I'll be picking up some sort of A/F gauge and sensor setup first to be able to see where my AFR ratios are.

Considering how close the cc ratings are, I don't see myself needing a huge adjustment, but it would certainly be nice to pull power out of them.

Now the only problem is, picking the right fuel control. Mainly the one that comes to mind is the Apex'i SAFC, but I'm open to others that could be better and/or easier to use.
The best fuel controller i have every used was my AEM FIC as you get a full fuel table and can tune it with a laptop. Along with that you can data log with it to and have 2 maps. Now for a wideband gauge i would go with the AEM easy to use and no setting up. I would go to a 550cc injector from http://www.deatschwerks.com/catalog/...roducts_id=205

If you did the FIC you will be able to control Fuel and ignition. This will be the best for getting every once of power out of your NA 13B.
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Old 12-30-2010, 11:26 PM   #8
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The best fuel controller i have every used was my AEM FIC as you get a full fuel table and can tune it with a laptop. Along with that you can data log with it to and have 2 maps. Now for a wideband gauge i would go with the AEM easy to use and no setting up. I would go to a 550cc injector from http://www.deatschwerks.com/catalog/...roducts_id=205

If you did the FIC you will be able to control Fuel and ignition. This will be the best for getting every once of power out of your NA 13B.
Wow, that seems to be a very robust system for a really nice price, thanks for the info.

Also those injectors that you recommended aren't going to be great, those are of an older design, I'll be sticking with the RX8 injectors, those should be more than enough.
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Old 12-30-2010, 11:37 PM   #9
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deatschwerks are not factory stock injectors if i remember correctly and they are up to date too. I could be wrong but those are the people to contact for your injector question.
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Old 12-30-2010, 11:51 PM   #10
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deatschwerks are not factory stock injectors if i remember correctly and they are up to date too. I could be wrong but those are the people to contact for your injector question.
Hmmmmmm.... sorry if I may seem ignorant, but visually they look like the old style, maybe this could mean that the injector is a modified older style which still means it's older tech which isn't really what I'm after, but I could be mistaken.

I've heard that apparently aftermarket injectors are years behind OEM injector manufacturers, mind you this could be wrong, but I'm more inclined to use OEM Denso units that are of new tech, then use an aftermarket injector that looks like an old design. Mind you I know my thought process could be flawed. But personally I think this is the safer route, going with new type OEM injectors.
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Old 12-31-2010, 12:19 AM   #11
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Since we are on the topic of fuel injectors from the RX7 and the RX8, would I need a change in FPR and Fuel Pump?
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Old 12-31-2010, 12:29 AM   #12
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Hmmmmmm.... sorry if I may seem ignorant, but visually they look like the old style, maybe this could mean that the injector is a modified older style which still means it's older tech which isn't really what I'm after, but I could be mistaken.

I've heard that apparently aftermarket injectors are years behind OEM injector manufacturers, mind you this could be wrong, but I'm more inclined to use OEM Denso units that are of new tech, then use an aftermarket injector that looks like an old design. Mind you I know my thought process could be flawed. But personally I think this is the safer route, going with new type OEM injectors.
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Since we are on the topic of fuel injectors from the RX7 and the RX8, would I need a change in FPR and Fuel Pump?
From what i know is they used the old style body and not the new slim style that you are looking for but that doesn't mean they are old tech. They change the insides and they also change the nozzles witch gives you the spray pattern. If you want the best for injectors i would go with injector dynamics injectors. not sure how small they go but evos and sti's run them with a solid 14.0 air fuel idle. Those from what i know are the best you can get for injectors but will coast a pretty penny.

As for FPR and pump no real need to change unless you plan to flow 50% more fuel.
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Old 12-31-2010, 12:41 AM   #13
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From what i know is they used the old style body and not the new slim style that you are looking for but that doesn't mean they are old tech. They change the insides and they also change the nozzles witch gives you the spray pattern. If you want the best for injectors i would go with injector dynamics injectors. not sure how small they go but evos and sti's run them with a solid 14.0 air fuel idle. Those from what i know are the best you can get for injectors but will coast a pretty penny.

As for FPR and pump no real need to change unless you plan to flow 50% more fuel.
Yeah I checked out Injector Dynamics, very knowledgeable people, I talked to them already to see if they carried anything below 725cc, which they don't. However the ID 725cc injectors are incredibly linear and can control fuel all the way down to 15cc, which is pretty amazing if you ask me. However the reason I decided RX8 injectors because the tech is new for one reason, cheaper to obtain, they are reasonably new injectors. The problem I have with deatschwerks injectors is the fact that they use the injector cores and modify them, to me this isn't exactly the same as new tech injectors like the RX8 ones or the new Bosch EV14 injectors (these require more work to work with), which I looked into, however this doesn't mean I think it's a bad product, it's just that I'd rather use something far newer and is also a drop in replacement from what my research has revealed to me from what others have done. What I mean by that is that, I found one person that had used RX7 FC 460cc injectors and then dropped in a set of RX8 Yellow Injectors and the fit just like the RX7 injectors including electrically.
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Old 12-31-2010, 12:57 AM   #14
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Yeah I checked out Injector Dynamics, very knowledgeable people, I talked to them already to see if they carried anything below 725cc, which they don't. However the ID 725cc injectors are incredibly linear and can control fuel all the way down to 15cc, which is pretty amazing if you ask me. However the reason I decided RX8 injectors because the tech is new for one reason, cheaper to obtain, they are reasonably new injectors. The problem I have with deatschwerks injectors is the fact that they use the injector cores and modify them, to me this isn't exactly the same as new tech injectors like the RX8 ones or the new Bosch EV14 injectors (these require more work to work with), which I looked into, however this doesn't mean I think it's a bad product, it's just that I'd rather use something far newer and is also a drop in replacement from what my research has revealed to me from what others have done. What I mean by that is that, I found one person that had used RX7 FC 460cc injectors and then dropped in a set of RX8 Yellow Injectors and the fit just like the RX7 injectors including electrically.
If they fit go for it i was just pointing out those to company's as deatschwerks are a good price and injector dynamics are just some of the best. What is the flow on the rx8 injectors, if its less then a fuel controller and FPR would be in need, and if they flow more then just do some sort of fuel control. Also top on the list would be a wideband gauge.
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Old 12-31-2010, 01:25 AM   #15
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If they fit go for it i was just pointing out those to company's as deatschwerks are a good price and injector dynamics are just some of the best. What is the flow on the rx8 injectors, if its less then a fuel controller and FPR would be in need, and if they flow more then just do some sort of fuel control. Also top on the list would be a wideband gauge.
Well according to one guy using these RX8 yellow injectors, the fuel rating was 450cc at 43.5psi when he sent them off to cruzin performance:

http://forum.miata.net/vb/showthread.php?t=223699

Which is a bit less than what stock RX7 NA injectors run at which is 460cc at 43.5psi. The fuel pressure being what WitchHunter Performance says. Personally I don't think I'll have to many problems though even if I don't get all the items I need right away. However that wideband would be a good idea anyways to have a peace of mind on how much fuel I'm burning.
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Old 12-31-2010, 01:36 AM   #16
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Hmm so i see from what there saying is you could have a set that flows less and you could have a set that flows more. I also forgot about begi having the injectors you want look into these two from them. http://www.bellengineering.net/produ...roducts_id=585
http://www.bellengineering.net/produ...roducts_id=586

These will be plug and play for you.
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Old 12-31-2010, 02:15 AM   #17
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Hmm so i see from what there saying is you could have a set that flows less and you could have a set that flows more. I also forgot about begi having the injectors you want look into these two from them. http://www.bellengineering.net/produ...roducts_id=585
http://www.bellengineering.net/produ...roducts_id=586

These will be plug and play for you.
Wow, sweet, thanks for the information, and also in the 550cc configuration I need when I decide to turbo charge my non-turbo 13b rotary engine.
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Old 12-31-2010, 02:44 AM   #18
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Glad to help, also i don't know if the NA 6 port motors have the coolant port behind the intake manifold but if they do i would plug the with freeze plugs as the oring fail and every time you take the manifold off you drain the coolant. The freeze plugs are 20mm freeze plugs.



the last pic is just a teaser but the first one shows the freeze plugs installed.
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Old 12-31-2010, 04:07 PM   #19
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I'm looking into the coolant port behind the intake manifold, if they are indeed there I'm not sure what I'll do, what do you mean they o-ring fail every time? To be honest I don't think they serve much of a function.

Anyways I have been able to secure a set of rx8 yellow injectors, now I wait for them and get them checked out at some fuel injector place.
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Old 12-31-2010, 04:51 PM   #20
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The o-rings that seal the water ports to the manifold are known on the turbo motors to leak. Also when you unbolt your intake manifold you drain the coolant out of the engine witch means you now have to bleed the coolant out. On the FD rx7s the ports are blocked from the factory when there cast. They found there is no real need for them.
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