What size injectors?
 

Hey...

I am in the process of using Gary Schuhart of Trackdog Racing in Dallas to re-tune my turbo (FM2 not hydra, FM intercooler, koyo rad, 600cc Deatschwerks injectors, MS PNP, 95 1.8)...

Gary's strong first response on talking to me about how to get the car right was that the 600cc injectors needed to go for more like 350cc injectors.

The car has always had a really bad cold start issue since i picked it up already built/tuned, and even once warmed up, it would idle poorly and die very easily from a stoplight. It never felt (even at 10psi) nearly as fast as i would think i turbo should feel, compared to other turbos i have been in...

It has also had an awful noise coming from under the hood that i figured was either the turbo itself or the KN filter on a turbo being extra loud, now wondering if it has not been detonation. See this thread from the last few days:

https://www.miataturbo.net/general-miata-chat-9/help-quiet-awful-intake-fm2-sound-61997/

Gary is going to tear into tuning the car and figuring out exactly what is going on this week, but was talking to someone on miata.net today and he told me to post on this forum and ask about the 600cc injectors before replacing them with smaller ones.

So, my question is:

Should I keep the 600cc injectors and tune it with them, or should i go with Gary's advice and downgrade the injector size? I am loath to go against Gary's advice as 1) he seems very knowledgeable and 2) he is the one helping me get the car right, don't want to go against his advice lightly.

Thanks
Randy
:)

If you're going to never make more than like 250whp, I'd put in smaller injectors.
In fact...
I will trade you my RX-8 425cc injectors, which would be PNP for a miata...straight up for your 600's. I'll even pay for shipping both ways.

My old-tech Rx7 purple 580cc injectors (actual flow) idle and perform just fine and I'm running MS1, batch fire. 20cc more is not a big deal. What injector do you have?

600cc is a tad large for a GT2560 on an NA engine, especially if you're only tooling around in the 10PSI range. I'm not sure if I'd go all the way down to 350cc, but something in the 450cc neighborhood would be about right.

So you're saying the car won't drive "right" on 600cc injectors? I don't see why he needs to change, IAC settings or over-run may need to change, but I think he can idle the car on 600cc injectors just fine. What's wrong with squirting 50% duty all the time like I've been running at 250whp?

Unless those injectors need cleaning you should be able to get em to idle decently just fine. At least the same as 350/460cc injectors anyway. IMO

I had rx7 460's and they idled like complete dogshit. No amount of tuning/tweaking I did to them could get them to be consistent so I had to run em rich to keep em happy.
Running ID1000's (that's right, 1000cc) was a complete joy, on both pump gas and e85. I could get em to stay between 14.7-15.5 without oscillating very much.
Currently running ID1000's on my subaru as well, and also not having issues.

If you want the best quality switch to ev14 injectors.
Otherwise the old style will all perform very similar to one another. AT least the 400-600 range ones anyway.

Would RX-8 425cc injectors not work well then either? The guy above was offering a trade, and that's about the cc that others are recommending also...

I will ask Gary about the ev14 injectors also...

Thanks
Randy

What size would work best on a 10psi older style FM2 with MS?

It seems on researching a little that the smallest they make are 550cc, and Gary at Trackdog is going to want to go smaller than that no doubt...

Randy
:)

I mean what size EV14s would work best on a 10psi older style FM2 with MS?

Randy
:)

Deatschwerks

Any of them will work good
From 550 all the way to 1000.

Like I said, when you're using a higher end, more advanced technology injector, the whole "big size compromises idle/driveability" goes out the window. That only applied to old dinosaur injectors lol

There are buttloads of threads/articles about new vs old.
Here's one:
http://www.rx7club.com/showthread.php?t=974696

Do some research, you'll be surprised to learn that xxcc injector =/= xxcc injector

If you want the best of the best, get ID's and a good afpr, run it at like 70 base pressure. Tune the fueling to perfection

Rx8 425's would work best for you. I truly believe that Bosch type injectors work way better than pintle type.

BTW, I have no IAC valve and not TPS sensor for the record...this is not rocket science.

No, but all else being equal, it's easier to establish a stable, smog-passing idle with smaller injectors.

Unless I missed it somewhere, the OP hasn't old us specifically what ECU he has, only that it's a pre-Hydra FM2. So I assume he has a Link, which is comparable to an MS1 in terms of fuel PW resolution. For those using older ECUs with fairly limited resolution, injector size is absolutely a criteria in determining whether an engine will be able to achieve a steady idle and good low-load performance, regardless of what modern trickery has been done vis-a-vis the mechanical design of the injector itself.

I'm pretty sure he's running mspnp.

You should have no issues getting those injectors to idle smoothly. There are people here who idle 1000's smoothly.

It's MSPNP. Rainman, if you have any questions about what is going on with the car, PM me and I may be able to help you.

Thanks Will...and thanks for all the advice everyone...

Passing smog is a big deal at this point, now that i am in Texas and not Oklahoma...

I will forward this thread to Gary at Trackdog...

Sounds like either RX8 425s might be the best of the older type, but the newer types sound interesting...i will see what Gary suggests...

Randy
:)

I will ask Gary about doing this swap and get back to you...

Randy
:)