Water/Meth injection and small turbo
 

Hello hello,

I'm about to turbo my NA and I'm hesitation between a GT2554R and a GT2560R. I really want quick spool as the car is my daily but I would also like to hit 250WHP (which I think is a reasonable limit to keep a reliable car,no?). So my plan was to us the smaller T25 GT2554R up to 10 psi and add the water meth injection above that boost in order to cool the very hot compressed air of the turbo running at low efficiency.
Has anyone done that? What do you think?
I know that injection adds failure point but I think its kind of cool to be able to have a big red switch for high power :idea:
Cheers
Seb

caveat: non-miata experience.

I've only ever run water/meth on my subie. When you compare the meth dyno curve to the non-meth dyno curve, the whole curve is moved up about 15whp/wtq. Like you propose, I did this pushing the limit on the stock relatively small turbo. I gained a bunch of area under the curve, but the high end still feels breathless. While it's punchy down low, it tends to encourage me to shift before redline and makes the power band feel narrow. If I could do it again, I'd go bigger turbo.

Basically this. I have a bunch of experience with the GT2554R (DD'd one for ~30k miles). It's got plenty of midrange and would benefit from more octane up to ~5500rpm or so, but on top it's going to fall off no matter what.

So basically there's no point?
I don't understand I thought the whole point of water and meth was to drop intake temp, wouldn't that offset the low efficiency at high flow?
Btw thanks for the great answers

Water injection stops knock. It doesn't do this by lowering intake temps, it does it by changing phase in the cylinders and other demonic magic.

Water yes, but meth drops then temp by changing phase no? I thought that by mixing both you would get best of both world, less knock with H2O, and less temp with Methanol.

I don't think a 2554 will spool one iota faster than a 2560R. the 2560r will stay on top a little longer too.

Other way around. Water is for intake temps, methanol is for octane. You would ideally want to run more than 50% meth in the system, but at that point it has to be plumbed like a fuel system with an eye towards safety.

Water isn't going to magically produce more air. If you aren't making the most of the air you can move (detonation limited), then water/meth will help, but if your compressor can't move more air, lower intake temps won't help make more power.

Well technically the 2554 can produce more air at high boost, just with a crappy 50ish% efficiency. From what I understand everyone runs the GT2554R at 10-12psi. I would like to push it to 16-18psi.

I shouldn't be detonation limited because I'm still at power level below what the car can do with bigger turbos. Assuming the IAT stays low thanks to injection+intercooler.

I'm not sure I get the point of water/meth for anything that isn't det limited.

I will get a 3" exhaust, Ryan you think both turbos will spool the same way?
Sav, you would rather pick the 2560 if you had to do it again?

I mean, I'd rather have an EFR6258 :)

Agreed, if I had to do it all over again I'd use an EFR

It's my first turbo build, I'm gonna start with a cheap used Garret. When I build the engine then I'll put an EFR, baby steps...
Anyone has a dyno plot?

No, shittard. Nobody has ever posted a dyno plot of the most common turbo on this forum. If they had they definitely wouldn't have posted it in the "dynos and timesheets" thread.

Geez. Am I the only one?

From Florida, I see, that's all I needed to know, "shittard ". I obviously am talking about a methanol injection dyno plot for a 2554 or 2560, because guess what section of the forum we are in...
I did google it but there's not much. Wackbards and Sav do you have some of your old plot?

Sure, call and pay my hourly labor rate and I'll dig it up for you. :party:

Alternatively, type "site:miataturbo.net savington 2554R dyno" into Google and see what turns up.

Here's a freebie. This community has a ton of amazing info, and super low tolerance for spoon feeding. Asking for spoon feeding and insulting mods will not help you acquire said amazing info.

This is a '04 STI on stock turbo, bolt ons, & '91 oct.
https://cimg1.ibsrv.net/gimg/www.mia...61625f4984.jpg

Well there was no way for me to see your plot wackbards without asking. And Sixshooter misunderstood my question and insulted me, admin or Jesus himself that's no excuse. I get it, we're on the internet and all, still doesn't hurt to be polite. Admin should show the standard, not lower it.:magna:

Anyways from what I see it seems like injection isn't the right idea for a small turbo.
FYI for future reference Sav plot is post #37 here:
https://www.miataturbo.net/dynos-tim...i-49948/page2/

Sav, correct me if I'm wrong but that is not water injected,is it?

You have been a member for a year and you don't know yet that us mods are assholes?

Haha good point, I'll aspire to be like you then :party:
Nice turbo kit btw, I almost bought it!

Yep, started drinking early yesterday because the surgical pain was making me testy. Welcome to the forum.

you can run -50F IAT's (let's just dream here) and disconnect the wastegate running ALLOFIT, and the 2554 still aint gonna magically start flowing more than it does or being any more efficient at it. I just tuned a 2554 on a 1.6 on e85 a little bit ago. past 10psi aint not much happenin, and that's with corn where I can get creative with timing.

I'm thinking about playing around with water meth on my turbo build as well. I'd expect it to be most beneficial on knock limited engine/turbo configurations.


My internal through process on water's cooling effects on air density (this is not full thought out and might be very wrong, just generating ideas to spark some conversation on the subject):

You injected water-meth post turbo at say 15 psig (29.6 psia) and 150F (610 R). The water vaporizes and absorbs some heat. Maybe 30 F taking the IAT down to 120F (580 R). The mass of the air doesn't change at all from this reduction of IAT, and by using the ideal gas law then P2 = P1 * (T2/T1) so the Pressure of the boosted air should decrease to 13.5 psig according to my napkin math...
PS: I know this is very over simplified.

The decrease in temperature will not add extra oxygen molecules to your air charge. However, it will help some with auto ignition detonation so if that is limiting your spark advance the decrease in temperature will help overall power.



The other weird piece of the puzzle is that methanol is a fuel that reacts with oxygen during combustion. Methanol and gasoline are both competing with the available air.
Methanol makes best power around 4:1 AFR and gas at 12:5:1.
If you inject 15% methanol of your gas volume then in order to achieve a 12:5 AFR for your GAS reaction your overall AFR needs to be 10.8:1

https://cimg0.ibsrv.net/gimg/www.mia...893aaaccfb.jpg

Basically, richen up your target AFR tables when you add methanol.



I'm I making stuff up or is this logic on the right track.

Sort of. True AFR, yes. Gas-scale gauge AFR, no. Since the gas-scale gauge is converting from lambda, it will automatically compensate for the difference in stoich ratios between methanol and gas. IOW, your target AFRs on a gas-scale gauge won't change.

The really curious thing about water injection is that the water you inject displaces air molecules that could have been there. As a result, water injection is really only beneficial if you're detonation limited the whole way through. If you are det limited, you can't take advantage of the air you already have anyway, so replacing some of it with water to make better use of the air that's left is a good idea. If you can get to MBT without WI, then water will just decrease power. As such, running water on a turbo like a 2554R will result in midrange gains where you were detonation limited before, but no top-end power gains.

Methanol is a little different because it contains an oxygen molecule, so you end up making more power by displacing some air with the volume of methanol. Taken to its extreme, replacing all the gas with methanol will result in a huge power bump (and a fuel system twice as big as the one you had on gas).

ahh, good point, they are lambda sensors... not AFR sensors.

Thanks for the explanation. My cooling the charge air you reduce its pressure, effectively reducing the turbo pressure ratio (you dropped the pressure after the turbo). But I guess that even at a lower pressure the 2554 can't flow much more (it might just be more efficient, cf turbo map).

I just wanted a fun system with a big red button :-)

I think you'd still have the same pressure ratio across the turbo compressor wheel. The WM injection cooling of the air charge typically happens down stream after the charge air cooler.

Yep. The only way you change the p/r is by injecting pre-compressor, and that wreaks havoc on the compressor wheel.