Hello everyone. I'm copying this from another forum where instead of helping people were just questioning why I'd do it. So please before you start just having a go at me just understand that I've got the EWP and it's going in regardless.

So, I am looking at installing a Davies Craig EWP (and controller), and I've been told by a very respected and knowledgeable friend that I need to install a reroute to avoid over heating. I'm in Australia and I have taken the car to trackdays in 90-100* weather and had no issues with over heating. Neither in gridlock traffic on such days so I have never considered getting a re-route. The argument put forward is that by putting the pump on the bottom radiator hose it changes the flow through the heater core and so doesn't pull as much hot water out the back of the engine.

I don't know much about fluid dynamics, but I think by having the pump on the bottom radiator hose the flow past the heater outlet mouth will pull water out of the heater hose. Thoughts on this also?

Anyone care to contribute any thoughts to this please? Particularly if you've gone down the road of an EWP and you are with or without a re-route.

Further to this, when I do put the EWP in, I will be removing the stock water pump impeller, as well as the thermostat and the thermostat housing. I have an NA6 B6 so the idle air control valve (IACV) is attached to the thermostat housing. My understanding of the IACV is that it boosts the revs when the car is cold so that it warms up faster. Being that the EWP controller will now be controlling pump speed in order to warm car up faster, can I now delete this IACV?

Image for reference

 

Keeping the heater routing stock and switching from a stock water pump to a lower rad hose EWP will:

1. Reverse the flow through the heater
2. Weaken it somewhat

That being said, it’s going to be hard to find advice. Few people run EWPs and those that do tend not to run heater cores. Presumably you would want to go through the effort of plumbing the heater outlet back to the EWP inlet to make it work well.

Also, you want a reroute for more even cooling, regardless of EWPs or heater cores. If you use one end of the head as the water outlet, it should be the back.

 

I would look at this more from a pressure differential standpoint than fluid dynamics. The stock water pump creates very high pressure inside the block on the heater core supply side, and very low pressure at the water pump inlet where the heater core returns. This pressure differential causes significant flow on its own. When you move the water pump into the lower rad hose, the pressures on each side of the heater core will be very close to equal and you’ll be relying on the fluid dynamics alone to create flow. The stock lower water inlet doesn’t look like an efficient enough shape to me to create a good pressure drop on the heater core return line. Definitely not the pressure drop created by the stock mechanical water pump at that point. Coolant reroute is probably a good idea in this case, unless you’re willing to do the testing yourself and maybe lose a motor in the process. Like afm said, it’s pretty unlikely that you’re going to find anyone who’s dealt with this exact problem before.

 

I suspect "somewhat" is an understatement. With an EWP in the lower hose, you will presumably have positive pressure throughout the cooling system, from the exit of the EWP all the way through to the radiator inlet. That now includes both the heater core inlet and outlet, so you're relying on whatever pressure drop occurs through the mixing manifold and block to create flow through the heater core. I'm going to approximate that flow at "essentially zero".

Now you have an engine which has the water inlet at the front, the water outlet at the front, and zero flow through the heater core. I would expect this motor to overheat and fail dramatically faster than a stock engine would. With the stock engine, the stock water pump draws water from the heater core into the mixing manifold, so at least there's some flow. Your setup will get rid of all of that.

I would do two things:

1. Absolutely install a reroute of some sort. With an EWP, IMO, you no longer have the option of feeding the water out the front of the head.

2. Reroute your heater core so that it returns to the lower hose upstream of the EWP. This will retain normal heater core function.

 

Also, the IACV will still be required if you want the car to idle like a street car. Don't delete it.

 

Afm, I'm not sure I understand how it will reverse the flow through the heater. There's going to be a negative pressure of the water flowing past the exit of the heater hose going towards the old position of the mechanical water pump. I don't understand how it would reverse? In terms of plumbing the heater outlet upstream of the EWP, if I do the bypass surely that won't be necessary. As the flow will be front of block to back. As such (I assume) there will be an even flow between top radiator hose (now at back of head) and heater inlet. So it will now be a positive pressure driving flow rather than a negative pressure (I assume with mechanical water pump it was pulling water from the outlet with the location as it is).

Jpreston, thanks I didn't think of it in terms of fluid pressure. See above

Savington, you make a very good point I didn't think of it terms of now having positive pressure at the front of the block. I guess with the mechanical pump it had the pressure from the blades of the pump pushing it front to back, and without those blades directing flow with just purely water pressure that would surely be disrupted. Again not sure why it's necessary to reroute the heater core outlet (as above). Also please explain why you think it's necessary to retain the AICV.

Guys thank you so much, was not expecting such an intellectual discussion on this. It's super helpful

 

The issue is less about pressure in the block and more about the pressure at the mixing manifold. You are relying on the flow through the mixing manifold to draw water into the manifold. I think that's ambitious. If you're wrong, and the flow reverses, you will have no flow through the heater core, and you will nuke the motor. If you move the heater core return into the lower hose, you ensure that the heater core flow remains as it was originally. You can try it your way, but the stakes are awfully high.

Because the car won't idle correctly when hot AND cold without it.

 

We run my freind's car with both the warm up air valve and idle valve removed. Have to give it a little gas for about 15s after start up, after that it is fine. We just set a staric idle with the bypass screw.

That said, he doesn't have PS or AC and the fan is always on (PO screwed the wiring up), so the only varying large load is if the headlights are on or not.

 

I run a EWP on my race engine. It's awesome. Mine is set up in reverse flow pumping from the bottom of the radiator into both the front and the back of the head. The stock pump is blocked off by a billet plate and runs straight to the top of the radiator.

To run a heater just redirect the feed to the back of the head through the heater and you are done.

Just get two blanking plates for the head and get 12AN fittings welded on. I'm getting a couple done soon for a spare engine if you want me to make them at the same time. You'll just need a Y fitting to split the feed out of the EWP.

My EWP thread is on here somewhere.

edit: might be 10AN... I'll check.
edit2: yup 12AN EWP Install

 

Savington, I'm not sure if you are describing the situation with or without the bypass. Just to be clear through this discussion it's become more clear that I'm going to need one so I'm sticking to a with bypass situation. And so, with the bypass with the water outlet (going to top of radiator) coming from the back of the head, and also the heater intake coming form back of the head, I assume that there would be a roughly even flow through both being that it's a positive pressure pushing through and not a negative pressure pulling either. I assume the positive pressure would then complete the path through the heater into the stock return location?

Also please can you explain the IACV situation a bit more. My understanding of it's function was that it induces a higher idle and as water passing through it heats up and moves the piston inside closing off the air path to the idle control valve under the throttle body. Which would then return the idle to a normal level. So by removing the IACV it would thus just idle at a normal level even when cold. Which wouldn't be an issue because the EWP controller just wouldn't turn the pump on until water temp started rising and then it would only turn it on slowly rather than the mechanical pump being on constantly.

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You're making a lot of assumptions and all the replies tell you to design it so that you aren't making any assumptions.

Dann

 

This

 

Totally wrong. Research how the IACV works first, then leave it on the car so your car idles correctly.

 

Sorry for the delay in reply.

Just to be clear, we're all talking about this one:


If so I've been reading this https://www.miata.net/garage/isc.html . And what I've taken away from that is that it's only useful when the engine is cold, after that it's open and there is no use to it. Thus if I remove it I would only notice a difference when it's cold when I assume it would idle weird until it gets to operating temperature. But actually when I blank it off it still idle's the same (when hot), so that's telling me it isn't doing much. Please tell me where I'm wrong.

 

Fair enough, but I mean tell me it doesn't sound right, that if the coolant flow is now front to back, and the outlets for the top radiator hose and the heater hose are in the same housing there would be a roughly even flow. Reason being I want to make this as plug and play as possible without too many modifications.