Supercharged Miata: where to place the nozzle?

Franco · #1 01-03-2004, 11:20 PM

I have a supercharged Miata with no intercooler. I want to use water injection to decrease detonation and advance timing accordingly. My two options for the location of the water nozzle are:

a) Right at the entrance of the intake manifold. I'm afraid with this setup, since there is very little time for the water to mix with the air, the cylinders might receive different amounts of water. Also, it seems that the water going to cylinder #4 (farthest from the nozzle) would have more time to evaporate than the water going to cylinder #1.

b) Right after the supercharger. This would give the water more time to mix with the air and to evaporate before getting to the cylinders, so it seems that the water would be distributed more evenly to each cylinder. The downside would be that, for knock supression, you want the water to enter the combustion chamber in liquid form.

So what do you recommend?

robbilau · #2 02-03-2004, 12:02 AM

With the JRSC you have both heat and (depending where you live) bad gasoline to contend with.

I think you should first treat for heat. Put the jet as far away from the dummy TB as possible and reduce temps. That will help with detonation by reducing intake temps and depending on how much you end up injecting there may be some left over for the combustion chamber too.

Some people have been injecting before the sc with M45s with good results as well. They claim it helps seal the rotors in addition to cooling the unit. I would leave this to subsequent experimentation, though. YMMV etc.

As far as injecting at the manifold I have seen recommendations of about 3 inches from the inlet being a good point for decent dispersion to the cylinders. I plan on using WI for a non-intercooled FM turbo and will have two jets: one at the tb for detonation adn one right after the turbo for cooling.

mx5 · #3 02-03-2004, 12:06 AM

I installed the nozzle in mine before the supercharger

cmetzner · #4 02-03-2004, 04:17 AM

I have an M62 sc on my 99 Miata. I am in Calif so can only get 91 octane. I mounted the nozzle in the outlet of the sc. I do not have a way of measuring the temp of the air charge. However, I am able to add 20% more timing with no ping with this set up compared to no water injection at all.

-- Chuck