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Kinda regretting posting this thread without knowing the exact method and size I used because it seems like there is no consistency now. My setup has run great for many kms under both cruise and track conditions but I'm thinking my siphon hole size is smaller than either of the other two on this thread that did it. However , the only thing that will affect is how well the siphon works ...so please monitor this carefully !
Kinda regretting posting this thread without knowing the exact method and size I used because it seems like there is no consistency now. My setup has run great for many kms under both cruise and track conditions but I'm thinking my siphon hole size is smaller than either of the other two on this thread that did it. However , the only thing that will affect is how well the siphon works ...so please monitor this carefully !
Brett, Thank you for making this post because It is better to know about it than not at all, with that in mind either one of us have 2 outcome possibilities and it won't be anything dramatic if this fails so don't let your conscience beat you, there are lessons to be learned here and if anything we all contributed here and time will tell if there is any gain or ill effect, we will know soon about the outcome of what i have done,in few days . Thank you again for sharing the knowledge
it’s all under influence of demand though and forces you to run a way oversize pump to avoid impacting output pressure
that’s why I’m getting rid of all that and instead gutting an S1 module with a low pressure lift pump that can dry run to pump fuel over instead, but I have other reasons for doing it as an overall race car strategy.
the ultimate goal would be an on/off relay operated by the level float signal on that side though, we’ll see ...
I'm having no problems so far. I appreciate any knowledge complete or incomplete. There's certainly no handbook for this stuff. I think in this thread there's now some parameters out there that most people will find themselves within.
yes, it was specifically for a V8 install, but I’d expect that the pump could be exchanged for larger capacity. What’s needed is also going to depend on fuel type, NA vs FI, siphon nozzle or not, and so.
500 hp @ 0.5 bsfc only needs 156 lph on gasoline for the engine, plus safety factor and other considerations. So 255 lph seems about right for their claimed use.
It should also be noted that one thing that’s easy to overlook is that the factory fuel pump is wired to always put power through the fuel pump resistor. Which reduces voltage depending on the actual input voltage, but using some numbers for reference; 13.5V would be reduced to approx. 10.0V, which is going to reduce flow to around 30-35% for low load/speed operation. When the pcm detects a certain engine load it turns on the high speed relay, which allows the battery/alternator to have a path of least resistance around the low speed resistor. The fuel pump then runs at full voltage/speed.
However, if the high speed relay goes bad the system will still function, but always run the pump through the resistor in the low speed mode. I suspect there’ve been a few times over the years that somebody thought they were having a pump issue and maybe the pump was getting tired and a bit worn, but they never thought to check and confirm that the high speed relay was possibly the issue.
A little update to my progress, this mod seems to have fixed my wonky fuel gauge. The needle used to move a lot when I was on boost using lots of fuel. It would dip after being on it for a few minutes and then crawl back up when I think the tanks evened out. Now it seems the siphon is keeping up properly and keeping the levels even. I'm thinking the factory pump wasn't flowing enough through the siphon under high demand.
Not only that, the issue with a siphon system is that when it reaches the point of high output demand like that the output pressure will start dropping significantly. On the OE system that’s why the fuel pressure is up around 60 psig; because the pump is heavily back-pressured by the pressure relief valve(PRV)/siphon assembly. If you go to the S2 section and review the test sheets where I had Deatschwerks flow/pressure test the S2 pump module, the PRV starts activating at around 50 psig. The pump flow is fairly high then, but way higher than an NA Renesis will ever need. It’s the lower flow demand of the engine and then all the excess flow being sent to the PRV/siphon that back-pressures the pump output to 60 psig.
The PRV/siphon is intentionally restricted to create create the high output pressure and then also keep the siphon active. So it entirely makes sense that for a higher flowing pump setup you need to account for higher flow through the PRV/siphon. The extreme between low and high demand are much greater now than the factory system was ever designed for. You need to really think through how the system is going to perform at those extremes. The output pressure dropping at high demand results in a potential variable that may not always be consistent and could unexpectedly result in going lean under a high engine load condition.
So that’s one of the reasons I’m not big on the siphon setup.
Had mine operating for 5 years plus including plenty of track days . I also have a fuel pressure gauge and it stays rock solid at around 58psi at all times ...except when hitting 420ish whp on E60 or when tank is below 1/3rd on high g corners.
So this isn't a mod for serious racers ..... it's for high hp street cars that might want to do the occasional track day and don't mind running over 1/2 tank of gas on those occasions.
I just thought to report back, my fuel tank is below 1/4 tank and with the aforementioned modifications it seems to be working just fine, i will update this thread if I run into any issues
05-01-2020, 04:02 PM
