I have a question about the fuel pumps used in the surge tank setup, in this case the Radium setup? Should you match the main feed pump and the lift pump? It looks like most people do, but why do they?

I question this since IMHO, the lift pump is obviously always running at a very low load pressure and would only require a lower output (and less expensive) pump and draw way less amperage on the wiring. A higher output pump lift pump would be more expensive and would be running way below its rated output, but would likely still draw more amperage due to its overall beefier design? I'm I right about that conclusion or I'm I misguided? As I see it, as long as the lift pump is reliable, all you need is a lower cost, lower overall output lift pump and in turn this would result in less of an overall amperage draw on your wiring, with less heat. This would then also allow the main feed pump to draw more amperage, if needed, without potentially taxing the overall wiring.
Any opinions?
Thanks
Mike

 

Idk about sizing the pumps. But from a wiring perspective I would have each one on its own circuit.

 

I agree. I have the main pump coming directly from the battery (did the wiring mod years ago) and for the lift pump I planned on using the existing stock wiring.
Mike

 

Mike, they talk about it here when selecting a surge tank.

https://www.radiumauto.com/Blog/Post...Fuel-Pumps-101



I have the Radium setup and its a nice piece.. I just wish it wasn’t such a huge PIA to install. My only gripe about it.


Steve

 

Steve,
Thanks for the link. This is exactly what I needed to decide what to do.
Mike

 

I ran 10 gauge wire to each pump. Btw Its a nightmare to install and once i got it in i realized that i broke my fuel level sender and had to replace it. Im nervous about breaking the new one so i still have it in a box lol.

 

I'm fighting hot fuel issues with the radium setup and a walbro 450 pressure and lift pump. But I also have high ambient temps here, something to keep in mind. Might be swapping the longer fuel lines from rubber back to a metal pipe to lose some heat

 

Mike,

Check this out first. To hit my HP goal, I was going to have to do similar with the Radium and multiple pumps. I think the new series of Brushless might solve a lot of issues.

https://fuelab.com/c-1389277-fuel-pu...-pump-kit.html

In this case, it looks like you can run 1 single pump. Which for me means less gas lines, wires, and electrical load on the car. Rob Dahm just made 700rwp on his Tii with one of these pumps.

Eric

 

The Radium setup is also a sump, just slapping in a brushless pump doesn't solve that issue.

I'd love to upgrade my radium setup to a Ti pump, might help with the fuel heat issues. But I can't justify the cost at the moment.

 

Curious - are you saying that some attribute/s of the radium kit is heating up your fuel? Or that the dual Walbro 450 pumps are heating the fuel? The 2x pumps raising fuel temp I can understand but checking whether you're saying there is something about the radium setup contributing.

 

I did come across a paper by Radium themselves several years ago about the heating of the fuel. It does happen but causes a negligeable effect on performance since the fuel temp only rises 20-30 degrees C and the fuel volume is so much smaller than air volume in the combustion chamber, the effect makes very little difference in the overall temp of the charge.
Mike

 

The trick is leverage with a small flathead screw driver between the fuel level assembly mounting point and the tank opening. That pushes in the fuel level assembly about 2mm and enough to clear the opening.

 

its definitely getting heated up due to the design of the radium kit, you have to realize that the sump pump heats up the fuel then it goes to the sump where its picked up by another pump which heats it more then is sent to the rail and returned directly to the sump not the fuel tank. Since the already heated fuel goes back into the sump and not the tank it doesnt have a chance to cool off. This cycle repeating itself over and over is why their system has fuel heating issues.

 

What size line are you running out of curiosity?

This is also why I was leaning hard toward the single Fuel Lab pump. If I am reading it correctly it will replace the lift and dual Walboro's altogether. Less pump(s) heat, tubes and power wires.

Eric

 

I'm trying to conceptualize this. Isn't this how all surge tanks are designed? The lift pump should be running at close to 0 pressure so heating from this pump should be as minimal as possible with the given pump.

 

The lift pump heating will be minimal since it is at very low pressure, as you stated. Also, the lift pump lies in the main tank itself and therefore would be cooled by all the tank's fuel, assuming you're not running your tank around empty or even close to empty, which is 95% of the time.

Also, as far as the surge tank itself, yes, the fuel will heat up from the main pump in the tank and the returning heated fuel from the engine return line. But there is a counter to this heated fuel from the cooler lift pump fuel coming from the main tank. Remember also, the lift pump will be supplying around twice the fuel needed in the surge tank by itself from the low-pressure free flow, and in combination with the return line fuel, it will likely be almost 3X or more the amount of fuel needed particularly at idle and while cruising. Tons of fuel will be overflowing or pouring over the top of the surge tank back into the main tank, cooling the remaining surge tank fuel. If racing the car, particularly on road courses (not straight line drag racing), the fuel heating will be more of a problem over time out on the course since you will be using much more fuel and less extra fuel will be overflowing the surge tank.

Lastly, look at my earlier post concerning the paper from Radium looking at this. They found the fuel heating to have a negligible impact on performance again due to the very small volume of fuel as compared to the volume of air in the combustion chamber. I would worry much more your heat management in the engine and engine bay. Your intake air temp, your intercooler efficiently, your coolant temp efficiently, heat barriers, and your oil cooling efficiently, will have a far greater impact on performance than simply your fuel temp. IMHO, the fuel temp issue is a non-issue.
Mike

 

it's my understanding that having warm fuel has at least one potential benefit, which is improved atomization.

 

apparently when you get rid of the fuel temp sensor, the variation is like 3-4% in afr, so its a thing, but its not huge

 

Ive been running the Radium FST w/3 walbro pumps.
so I have, 1 lift, 1 prim. and 1 Aux(comes on at 8psi)… installed about a year now.
I’m logging fuel temp( sensor is located on the feed line, right before the primary rail) via Haltech and it’s never presented itself as an issue.. fuel temps might raise a couple of degrees after a handful of hard pulls(20-22psi) but nothing crazy.
Also STFT will adjust for variances in the fuel temp being colder or warmer(fuel density) as @j9fd3s suggested.
I can post some logs too.


Steve

 

I agree, but again compare fuel temp to charge air temp for differences in overall performance. Charge temp is way more important. Again, much more air than fuel in the combustion chamber. I have seen stats that state every 10 degree F drop in charge temp will add at least 1% more HP or as much as 1.5-1.8% more HP in a rotary (Can anyone confirm this?). On my own car, my extensive modifications to control heat dramatically dropped my charge temp while cruising and especially in boost. Again, I believe concentrating on heat or thermal management with the engine and under the hood is way more important than fuel temp. Look at this older thread below.
Mike

Thermal management - RX7Club.com - Mazda RX7 Forum
My Posts #2, #13, #15, #19