Been having cavitation issues with a large single. I’ve long been torn on a big single setup for simplicity or dual smaller pumps. Just throwing out some ideas, since I’m M6 and would be using a Hobbs switch, are any of you manual guys using a timed relay to keep the secondary pump on between shifts etc? Kind of just chewing on the idea

For ease, I have the Hotwire FPWK-017A which is rated for 30 amps. I could probably just tie into the main power right in the rear of the car for a secondary relay instead of running a whole new power wire to power dual 255s. Racetronix 255s only draw 10/12 amps at 58/80 PSI. Thoughts on this and the timed relay? Has anyone considered this method before? My concern would be with a manual, I can go from 0-10PSI in during a shift and I’d imagine I’d have some funky stuff in the transitions with a single pump and then a surge when the second pumps kicks on again, just from my experience limping along a overwhelmed pump with methanol the tune doesn’t track AFR nearly as well as it does with my bigger pump, it’s safe but it’s rather inconsistent gear to gear and how long the pull is etc. I can’t help but think this would be exacerbated by having an even smaller primary pump and then a second pump kicking on and off every 2 seconds

 

NO lift shift---- kidding
I don't like two pumps because you can be wot and one pump fails, you are in a lean condition---boom. With a large single, if the pump quits, the engine dies.
Is your single inside the tank or external? If it is inside, then maybe Holley hydromat is something to look at to avoid cavitation. It flows a lot of fuel.
Maybe some manual guys will post.

 

I don’t really like the idea either but it’s where I’m at. But a 525 pump flowed too much and would slowly overheat the fuel. Making it cavitate, it would start sending my stfts lean etc. A 340 I’m going static on my injectors to account for the pressure drop. So I’m kind of stuck. I did find a time delay relay I plan to use. Once it activates it stays on for 2 seconds after trigger coil deactivates. This car is meth injection dependent as it is. So if something goes it’s gonna go bad lmao.

 

Let us know how that relay works out.

 

I will be sure to. It’s a BU-509TD 20/30 amp relay. I’m kicking around the idea of wiring up a standard relay in line with it so if it does fail I’ll atleast have the traditional on/off setup that most people use but that’s easily done afterwards on the lift, would just be tapping into all the wires to run to an identical relay. I only wanted the timed delay since I’m a manual so it would constantly be cycling the pump. I’ll be sure to leave a little extra wire to tap into. Right now I’m on jackstands so I’m just trying to get it up and going. If I wasn’t so dumb I’d have ran my methanol second injection stage wire but I never planned on using it so I snipped it and wrapped it up behind my A pillar… I could’ve triggered my second pump off of KPA reading rather than a Hobbs / setup a redundant fail safe

 

Honeywell makes a Hobbs that is triggered at 2-3# of boost. Do you think that when you are racing that your boost drops below that level between gear shifts?
Do you have a boost referenced regulator?

 

I’m procharged so I drop to like 30 kpa between shifts when the bypass opens up. And yes boost refd and all that. I have a 4 PSI Hobbs, believe it’s a Honeywell, I installed in my inline vac/boost manifold on my brake booster hose. Had to tap a npt hole for it.

 

Just an update. Timed delay relay works really well just jumping out the Hobbs plug. Still have the car torn down but I don’t foresee any issues with it. I ended up just putting my relay inside the trunk behind the drivers side speaker panel thing that you pop out to pull the carpet back. I drilled out the rubber drain plug ontop of the rear deck to run my wire loom through. Sprayed it down with some contact cleaner and will seal it up tomorrow night.
here is a video demonstrating the delay off. Both pumps are running in start of video