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This is what they call the remote mounted water pump. What you see in the picture is the water pump housing delete manifold. So there is a pump somewhere in the engine bay that it is not visible from the picture
Is this mod worth the weight savings? What does all the stock water pump stuff weigh?
Looking at pictures of the factory water pump set up it does look quite substantial and is placed rather high in the engine bay.
How reliable are these "electric" pumps?
As much as i prefer simple mechanical things, I do like the idea removing all that weight from that high of an area in the engine bay. And I guess there's some power to be gained by not driving the water pump off the crank.
IMO the advantage to the electric water pump is that the pump is at the bottom (hopefully). one of the problems with the rotary is that the pump is up high, so air bubbles are a problem.
two you can run the pump at the most efficient place, vs having it go with rpm
it seems like the packaging is more flexible, which is nice when you're trying to package big radiators and intercoolers and stuff.
The air bubble problem I'm assuming is only when bleeding the system when it is filled/drained like all other vehicles? Is there something special about 13Bs where they have a problem with water consumption and/or loss where they need to be bled often?
Interesting point regarding running the pump at an efficient pace, whether that be variable or fixed and not be dependant on engine RPM. I'm guessing if variable that's something an aftermarket ECU can control.
I'm leaning towards a carb'd street NA setup though and am really trying to keep things simple. Is cooling really be a problem for me with the stock mechanical set up? I do plan to beat the crap out of it, but no turbo.
Yeah, I don't like that you create another possible point of failure with an electric pump. Could be wiring, relay, fuse, or failure of the electric pump. I really prefer keeping things simple. I'm not going to lie though, I really like how "visually" simple the electric pump can make the engine bay look.
I'm still not discounting the benefit of removing all that weight from such a high spot in the engine bay, that to me seems like the biggest advantage for my application. So I'm still curious how much all the stock water pump parts weigh if anyone knows. Also still curious how much HP the water mechanical pump robs from an NA street port.
Last edited by brapbrapbrapbrap; Jul 21, 2023 at 09:51 PM.
Is this mod worth the weight savings? What does all the stock water pump stuff weigh?
It isn't about saving weight, and an EWP setup probably weighs more than a standard iron water pump housing, let alone an aluminum one. (Don't forget the alternator bracket that you now need!)
The stock Mazda water pump setup kinda sucks, the belt drive is a glancing blow off of the slack side of the belt so it slips a lot, and the stock water pumps cavitate at a fairly low RPM (anywhere from 6000-7000), and when it cavitates it basically stops pumping coolant and the engine overheats rapidly. To prevent that you either need to slow the water pump down a lot with a small crank pulley, which also means your alternator doesn't work worth a flip at low speeds anymore, or you need a water pump that doesn't pump water as a function of engine speed.
The other thing is, a lot of people who go to EWPs do it in part so they can run a common 6" or so trigger wheel. The stock lower crank pulley is about 4.5" and runs very close to the water pump housing, cannot put a common trigger wheel on there.
In this case, I also suspect that they needed to get more hood clearance at the front of the engine, given that is a Miata we are looking at.
Which motors got the iron water pump housing? Which ones the aluminum one? Are they interchangeable? Is one preferred over the other?
Good to know regarding the pump cavitation issue. I'm surprised the pump cavitation issue presents at such a low RPM given stock redline limits on NA S4 and S5 FCs were about that RPM if not higher correct?
Is there a go-to unersized pulley that's preferrred that will still turn the alternator at a high enough RPM for street use?
Regarding trigger wheel clearance I assume I guess I don't need to run an aftermarket one if I'm going with carbs and a distrubutor? If I do decide to go EFI is there another common feasible way to get the crank position wthout running a 6" trigger wheel?
I don't think hood clearance was a in issue with this car, I've seen plenty of stock Miatas with the stock 13B alternator position without any clearance issues. This car looks like it was going for the "shaved/clean" look, and I think that had more to do with it than anything to be honest. Found more pictures of the car, there was a hood cut out for the carb filter, so hood clearance was definately not an issue, lol.
The alternator pulley is not likely to slip, at least not that I've heard. The water pump pulley on FD generation RX7's depends on the factory air pump pulley being present for belt contact. When people remove the air pump pulley, they are left with less than 90 degrees of belt contact to the water pump pulley, as shown in this photo:
On the FD engine, the water pump housing doubles as one of the alternator mounts. Some aftermarket water pump adapters have provisions for the alternator mounting, but some people prefer to relocate the alternator down low.
The non reverse rotation pumps have even less belt contact than that to the water pump pulley. What is more, on both belts the pump is only a glancing blow on the slack side of the belt, so it is extremely likely to slip.
This is why I still have an air pump on my '81. Besides being required by the rules for the series I compete in, it also serves as the main water pump drive. All the same I only get about 5000mi out of a set of belts. Cavitation sucks.
Which motors got the iron water pump housing? Which ones the aluminum one? Are they interchangeable? Is one preferred over the other?
up to 1985 are iron housing
1986+ are aluminum housing
i think they all share the same bolt pattern, but the housings differ enough for them to require getting the right combination of parts to convert between Rx-7 chassis' (depending on what you're trying to do). some are fairly straightforward, others get more complicated.
They have sort of the same bolt pattern to the block. The aluminum pump housings share the same four mounting studs as the iron ones, but there is a fifth stud (might be a bolt?) on the '86-up engines that is not used on the '85-down. And, the water pump bolt pattern changed slightly, so IIRC you have to use the alternator bracket that goes with the water pump housing. Or do what I did and spend three hours hacking up a 12A bracket to work. Then that boss needs to get tapped 1/8 NPT on the engine side and a plug installed, then tapped 10x1.50 on the water pump side, for use with a 10x1.50 bolt. I forget if I used that side because 1.25 would not have deep enough engagement in the existing hole, or if long, all-threaded 10x1.50 bolts are easy to find because Chrysler used that thread pitch and was far too cheap to use shanked bolts anywhere.
Also, the aluminum housing has a different sized hole for the coolant temp sender vs. the carbureted cars' choke switch. Not a big deal unless you want to use a 1st gen RX-7's autochoke.
If I do decide to go EFI is there another common feasible way to get the crank position wthout running a 6" trigger wheel?
Depends upon which engine you end up using.FC you can use the Stock crank angle sensor. 13B-REW you can use the stock setup from that as well. Which you can see in the picture of the FD water pump setup.
