Mazdaspeed injectors are 265cc, I thought NB's had 245cc?. I was running 14psi with them just fine, once I hit 15psi I ran into fuel cut.
This is on the MSM IHI Rh55 turbo. A true piece of ****.

So why is everyone saying his stock injectors can't handle 8psi?

OP, Why didn't you just use a NA base map to tune for boost? Worked for my MSM motor on 99 base map.

 

i know nb1 injectors are 245s, i thought nb2 were bigger, 265?

 

I was using the base megasquirt ve map for 96-97 without MAF. I now realize that I really jumped the gun on the ignition map, and should have left it alone until getting fuel mapping right. Again, live and learn. I'll get it back together, and do it right this time.

Thanks,

Jason

 

That's why. All of the discussion on NB injectors is interesting but irrelevant to OPs dilemna.

OP, bottom line on the science is this:

You have a barrier between two chambers. The chambers contain fluids at different pressures. If you make a hole in the barrier, fluid will flow from the chamber with higher pressure into the chamber with lower pressure. How much fluid flows depends upon two things:
1. The pressure difference between the chambers; and
2. The size of the hole.

So, if you need more fuel, you've got a choice: increase the pressure difference, increase the size of the hole or both. Doing nothing burns pistons as you inevitably go lean.

For most of us that use MS, increasing the size of the hole is the most expedient answer and leaves the rest of the system per Mazda design (including materials, resistance to leaks, etc.). The injectors you mentioned (ID725s) will work beautifully for your application.

 

I never stated what size the NB's stock injectors were, just gave an example of how any one specific injector would perform in the two different fuel systems (MAP-references vs. static.)

This was in response to someone who had said "The NB runs higher fuel pressure than the NA."

Well, yes, sort of. But not by much, and the NB's fuel pressure does not rise as MAP rises, so at moderate levels of boost, the NA is actually quite close to the NB in terms of fuel pressure (and will exceed it after a certain point.)

 

Whats the size of OPs stock injectors?
if his fuel pressure also raises and eventually surpasses an NBs it effectively raises the size on the injector as well.

If the stock injectors are very small I can understand why it blew because of fuel. but right now I'm just understanding aggressive timing.

I'm just trying to understand this further, sorry for inconvenience.

 

Personally i believe it blew because of both. If the op was running 8 psi there isnt enough fuel to feed it and of course that timing.

 

This page lays things out nicely:

Fuel Injectors - Miata Turbo FAQ

 

This may be the dumbest reply, but...
since the 20, 34, and 55 rows in the AFR table are [almost identical
why not fewer rows below 100 KPa and more above? this is where you need more contol

 

Because low resolution map sucks ***** to drive on.

 

Actually, you need more in lower KPA regions. That's where you do all your part throttle driving, above 100kpa, you're generally at WOT, don't have large changes in VE and therefore don't need many breakpoints at that point in the table.

Remember all cells are interpolated in between each other, so the 'lack of resolution' isn't technically correct, there's a lack of breakpoints, but not resolution.

 

Thank you

 

sorta pointless, you dont need the resolution there and that table is pretty good.

I just think he may have tip-in issues or issues climbing hills when targeting 15-15.5:1 between 2000-3000 RPM. That's a little too early to go THAT lean. I'd bring that back to 14.7 and reserve the 15s for cruise areas only, like above 3500.

 

Thanks for the info Brain.

Jason

 

Thanks,

with that in mind, what about these as break points

KPa = 20, 28, 40, 57, 81, 115, 164, 230

rpm = 700, 1000, 1400, 1900, 2600, 3600, 5000, 6800


In a generic sense, are there certain "events" at which you want to align your KPa or rpm breakpoints?
Any guidelines on percent change between?

 

I would leave it as is.

 

In a generic sense, are there certain "events" at which you want to align your KPa or rpm breakpoints?
Any guidelines on percent change between?

 

Yes, where there is a large change in VE.

 

Its mostly personal preference, but certain rpm and kpa breakpoints are definitely helpful.

IMO:

You want at least one row in high vacuum, 10-20kpa
You want as many rows in the part throttle and cruise areas because that's where you'll be most of the time
You want at least one row over your target kpa in case you overshoot target

You want 1 rpm row lower than your idle target, 1 at target, and 1 slightly over
You want to stagger them evenly in the midrange/cruise
You want 1 rpm row at or a little past your redline/fuel cut

That's how I try to set mine up anyways

 

It has been said before, but I will say it again. Whatever your maps say is fine, BUT your fuel system must be able to supply enough fuel to do what the map asks.