Thanks for the comparison photo.

So the S2 impeller is the one with the "inverted" blades? If so, it looks like it requires more torque but less RPM to move the same amount of liquid.

 

^It's got a much wider operating range with better flow and the underdrive pulley only helps with that at high revs as it stops the pump getting into heavy cavitation.

The S2 pump does fit on the S1 engine with a small modification to the casing (Mazda altered one of the bolt locations by 1/2D on the S2 to the S1 engine.
To be honest, you could just leave that bolt out with a new o-ring, it seals fine.

To be honest, I thought I'd mentioned this last year when we stuck the S2 engine in, but might have forgotten, or it's buried in a thread somewhere.

 

Thanks. Good to know.

 

so swapping out S1 for S2 water pump would be a good mod and we should not bother with drilling the extra hole in order to get the all bolt holes to line up.

 

^Nothing wrong with opening the hole to suit, 2 minutes with a file sorts it out.
Used it without the bolt in for a while with no issue though.

 

To follow up. My water pump started leaking so I decided to upgrade to the S2 pump.

Few notes for people who decide to do the same. As Phillipm mentioned S2 water pump is not perfect fit to S1 engine. Bottom left hole does not align with stud and there is not enough 'meat to file it down enough to fit the pump so you have to pull the stud out. Also don't forget to order S2 pulley since S1 will not fit.

 

So therefore if you are fixing the S2 pump on S1 with one less stud or nut, are you not risking a coolant leak @ pump?

 

You can file the hole into a slot and even though you break through the outside of the casting there's still plenty to clamp down on, but like I say, I used it for a long time with the bolt missing with no issue.

 

thanks for stating it again for those who missed it the first time

 

Thanks Phillip..

You also need to replace Pump Pulley with S2 one.
Plus how did you go with the S1 Pulley Belt (vvvvv) as Mazda changed it on S2's at the same time and made it specific with these changes to Pump and Pulley...or do you use a different drive belt to the S2 OE for your RE (Renny II) powered buggy?

I have not made a direct physical comparison between the S1 (N3H1-18-381A) and S2 (N3R1-18-381) vvvvv Belt , AFAIK it is only in Belt Length (shorter or longer, not their Belt profiles)?.

My take to use an S2 Water Pump on an S1 would need the following Mod and Parts changes.

N3R1-15-100 Water Pump (Must File OUT Stud Hole)
N3R1-15-131 Water Pump Pulley
N3R1-18-381 V Belt??

 

hmmmm im gonna try this when im back to nyc.

 

Just curious, have you or anyone under driven your water pump?

Was it worthwhile or not a good idea?

Thinking about picking up the SuperNow Pulleys and didn't want any issue with your waterpump

 

underdrive? yes

 

Actally you have to file toward inside where the rubber seal is. Problem is that to line it up properly with the bottom left stud you would have to file into the rubber seal. The only way to make the pump work is by pulling that stud out and using the silicone as a gasket. It will leak without silicone!

I didnt have time to monkey with silicone so i just put in new s1 pump. Maybe next time.

 

let's try it one more time

.

 

I never had an issue with it, seems Nad is after a few PM's, I'm not sure why, but I haven't got that engine any more to have a look and see what might be the issue there.