You certainly have to make sure that you use the proper regulator designed for the amount of fuel that you are flowing....... otherwise you would not be able to keep the pressure down when all 3 pumps are on....... but that is just common sense

 

Certainly, but I wasn't talking about a regulator. I was speaking to the oem lexus venturi you are using with the triple pump setup, and the same concept would apply of proper design for the amount of fuel. A stock oem venturi would be designed for 500hp or less fuel flow.. not 1500-2000hp. So with that small opening my concern is fuel pressure not being stable when multiple pumps are staged in and not all of their fuel is consumed meaning it has to return through the tiny venturi. In the case of APS with the venturi "fix", I have seen cars that can't bring fuel pressure below 55psi with twin pumps. To fully alleviate the unstable fuel pressure concern, the system must be tested at 35-40psi fp with all 3 pumps running with the engine idling/off. I will run this test for you if you need, free of charge

 

Let me measure the size of the orafice in the venturi today.

But...... you would never have all three pumps on at idle or car off...... You only stage the pumps in when the fuel is REQUIRED therefore not all the fuel will go back through the return. 99.5% of the time you are running on ONE pump. The second pump comes on at 20 psi, third one over 30 psi..... so even if the fuel pressure jumped up 2 or 3 psi.... at WOT you would NEVER notice is. Also the ProEFI has a fuel pressure sensor and constantly adjusts pulse widths for any fluctuations in FP.

 

What about ditching the venturi and running a special walbro like in the CJM kit to draw from the other side?

 

Why? The venturi siphon works perfectly.


To add another pump would be complex.... how would you control it?? IF that side of the tank goes dry how would you determine that and shut off the pump??

 

Charles can touch on this more if he wants, but from my understanding the pump is a special walbro model and is always running even if the other side is empty. It will sit in the hanger just like any other walbro and pulls fuel from each side of the tank. I wasnt talking about using a pump on the drivers side, if thats what you thought.

 

Yes that would work but why use a $100 fix on a $2 problem.

As long as you can properly control the pumps (i.e. pro-efi, haltech), the venturi should never be seeing high fuel flow amounts.
And if nissan, toyota, and whatever manufacturers with saddle-style tanks felt the venturi works, then why reinvent the wheel right?

I think your idea will work fine (thought about it myself till talking to Chris and Larry), I was concerned with controlling that pump too, and didn't want it running when there was nothing to draw from the other side.
Best of luck though however you go.

Tom

 

You have to buy the pump anyways, so there is no extra $100. The venturi would seem to be a delicate balance of when to turn on the pumps, so not to increase fuel pressure.

Do you have 2 pumps running at idle or just one? I thought I remember you sayin you had 2, but not sure.

 

All 3 of my pumps are allready in use (I think larry can confirm lol)

But no to 2 pumps at idle. At idle only 1pump is running. At around 18psi or so pump 2 comes on, and 25psi pump 3 also comes on.

I am not positive on the pressures that the 2 pumps come on in my situation, Larry can tell us (he set it up).

We opted for all 3 in mine also because next season we will also be running E85, so when you get up there in the power you definately need 3 pumps on E85....lots of fuel.....

Tom

 

There is no delicate balance.... you turn on the second pump when you need it...... somewhere above 15 psi or so. Then turn on the third later at say maybe 25 psi.... this is all turbo size dependent. We have been staging fuel pumps for YEARS on cars without any issues. The venturi works perfectly.

 

I believe that your 2nd pump comes on at 200 KPa and the 3rd at 300 KPa. Therefore the third probably hasnt been used much!! Your static fuel pressure is ~ 45psi.

 

Are you subtley telling me we need to turn up the boost more?

lol

Tom

 

Enough said.

I don't understand why so many folks here on my350z seem to think that the keys to making big power with the Z/G are so different or special compared to other platforms that have already been down this road before.

 

just to clear up a misunderstanding, the cjm pump does NOT use a pump for the siphon, it uses a venturi as well. so there is no need to determine a time to shut it off.

the cjm pump was built focusing on a drop in, as PnP as possible, oem like solution. the stock siphon line plugs right in without having to chop it, and you drive the car like you would have on the stock unit. we did not do a third pump because we felt the surge can was more important... everyone has different priorities... and over 1000rwhp there is little concern for a surge can anymore because its not like you will be road racing a car at that type of power. even professional time attack cars dont run anywhere near that type of power. i did testing on my car on a surge-can less setup and it definately had its starvation issues, but it was easiest enough to avoid and if i was building a car with 1500hp i wouldnt mind that.

i tested with a stock 300zx assembly. it bolts right up to the 350Z tank you just hve to adjust the pump height because the 300Z tank is deeper and it includes a siphon too since its tank was setup just like the 350z. i was going to just use that and clamp another pump to it but i ended up not liking it without the can... and thats when the cjm twin pump became a project.

 

Because it isnt the same in every aspect. I dont mess with others cars that much, nor study them like I do the Z. The more I know about it, what works, and WHY it works the better I am. Someone can say it works all day long, but I want to know why it works like it does.

 

tyler i think one you finish yoru reserach you will understand the abilities each system offers....
IF the questioning end up being about trusting SPs years of experience testing susch systems successfully then there is no other way for you to find out if its true unless you try it. Personally I dont see the problem in the case of SP since most of the driving works through just 1 pump with idle conditions same as stock. THe fact that you will be running a superior ems should give you a piece of mind on controlling fuel delivery also.

 

bumping an older thread as my question falls along these lines.

So is there a reason why one should have a CJM twin pump setup running all the time vs having the second pump kick on a set boost level, via a boost pressure switch?

Just seems there would be no reason for the extra wear/tear and noise to have both pumps running when just cruising. Or do these pumps not like being cycled on and off (which would be the case durinng like a drag race...)

Easy enough to wire in the switch, so just curious..

 

That is the way I would and have my setup.

The pro-efi controls mine (SP triple in tank too). 1 pump is on all the time, at about 15psi the second pump comes on, and at about 26psi the third. As long as you are monitoring/controlling fuel pressure all should be good.

tom

 

i dont recommend doing that but mostly just because it hasnt been tested. shutting off the driver side pump will kill the over-tank siphon. it would be like running a custom RFS with no return correction kit. so killing that one isnt a great idea.

the passenger side pump has a surge can fill assist on it... it helps keep the surge can full by pulling in fuel from the bottom of the can. now, there are already 3 holes in the bottom of the can, so it should be fine anyway under regular driving. but the theory goes a little like this... without the 3 holes, under full throttle, both pumps are relying on the one pumps fill assist to pull in enough fuel for both pumps... now, the other factor there is the consideration that the can is only so tall, and fuel will fill over the top of it anyway if you have a decent level of fuel in the tank.. but we ignore that for the sake of considering the performance of the unit at various tank levels.

if you had a full tank, then the passenger side pump could be totally shut off and i guarentee no problem because fuel will be flowing in over the side of the can anyway. on top of that, the siphon line should be bringing in enough fuel anyway for regular driving until the tank falls low enough that the drivers side is empty and no more fuel is coming in from the siphon. when the siphon is dry, and fuel is too low to come over the side of the can... the 3 holes should bring in enough fuel for regular driving without the pump with fill assist running. but, i never tested that, so i cannot promise it.

the 3 holes are there and we also consider them somewhat "pilot holes". i have told people that if they get to a point where they are starving the pumps under full throttle, then enlarging these 3 holes is the place to start... but of course the larger those holes are, the more worthless the entire point of having the surge can becomes.

there is basically this huge pandoras box of possible scenarios and we did our best to get the unit to meet most peoples needs. yes it would have better fuel control to not have the 3 holes... but then it could have issues with max power... ya the holes can be larger to ensure no starvation at higher HP, but then the fuel control goes down. if someone who has one has a good understanding of why things are there and how the unit works... i would go as far as to say that its "tuneable" to meet your needs... but we suggest most users run it as we instructed.

if somebody needs it to do something a little different then it already is, i would gladly consult with ideas on how to tailor the twin pump closer to their goals.

so to summarize that way long post... what you are asking about doing... if you do it, shut off the pump that has the large hole with blue oring coming out the bottom of the canister... it should be the passenger side pump if your unit is correctly assembled and orientated. this SHOULD work just fine... let me know if it doesnt. If it has pump starvation issues when tank levels start getting low AND you are not turning hard or braking hard... opening up the 3 holes will resolve that, but at sacrifice of fuel control.. basically rendering the canister surrounding it all purposeless.

 

ya i guess i'll just leave both running

Thanks Charles!