Hi-speed bypass

Hi guys, just wondering what most of you prefer as im setting up an engine for the first time, do the majority run the hi-speed off the barrell valve on the hat or on the loop line from the shut off putting the fuel back into the input and not to tank? i appreciate any input thanks

 

till you get a good base line I wouldn't run any hi speeds yet..Dave

 

agree with dave i run mine without till we got a hold on it then came off the bv back to the tank

 

ahead of the BV works more as a "pump sizer" after the BV works as a high speed

 

head of the BV makes the whole system more equal when pulling fuel from it.dave

 

thanks guys, my plan was to run its first like sugested and then run the hi-speed, i was just plumbing everything up on the weekend making lines up etc...and while i was on a role i thought i'd set it up for it and just block it off, until i have some id of where the tunup is. i just have heard so many different ideas for setting it up and mixed opinions and can see the logic in both. keep the input coming guys thanks

 

Blank pill or just flip it up side down

 

Are you also running port nozzles as well as hat nozzles? If so you can take off from the ports as not to change so much of the fuel system.

 

You know, i've never really even considered that. good idea. thanks

 

Hi Speed

First, I'm no expert (at all) just trying to learn all this. But wouldn't just pulling fuel from your port nozzels run the risk of melting things. I guess it depends on your nozzle size, but a hi-speed pulls fuel and drops system pressure correct? I would think a hi-speed that pulls fuel from the entire system be a bit less of an abrupt change in the fuel system. If you remove fuel and pressure from the ports only you would be removing x amount of fuel (depending on the orfice in the hi-speed) over 8 nozzels, instead of 16 nozzels. I guess if you just put a generally smaller orfice in the hi speed it wouldn't pull as much out, but won't this defeat the overall purpose?

Sorry for the longwinded question.
Corey

 

It shouldnt matter where you plumb in the high speed, it regulates pressure, thats it. If its set to open at say 130 psi it will limit your system pressure to 130psi maybe a few more. Say you put a .050 pill in it, its going to let the pressure rise some, but its still the whole system pressure.

 

Hi Speed

Ok, I'm with you on that, one more question then, if it has nothing to do with flow then why worry about what jet size then? Not trying to be a dick, again just trying to learn all this. As far as my nozzel question think I was incorrect because all the nozzels would see the hi-speed's effect equally, no matter where in the system it is.

Sorry to the OP if I hyjacked your thread.

Corey

 

My simple thinking on this subject has always been:

The pressure you set the high speed poppet at determines when you want it to open.

The orfice size determines how much you want to bleed off at that pressure (time).

You can have multiple high speeds set at different pressures with different orfice sizes to control fuel volume at different points in the run.

Greg

 

Hi Speed

Sorry one more question about this, this sounds more like a pressure regulator than a hi speed, by this thinking the pump could build no additional pressure? Could the pump not build pressure above the high speed crack pressure? As G Martin stated it would almost have to or the multiple hi-speed concept would not work, once the lowest one popped than that would be it? Does not the collective orfice sizes in the system regulate your total system pressure?

I think I may be making this way more complicated than it has to be.

Corey

 

Corey,

You are thinking too absolute. When a high speed poppet opens at a certain pressure, the volume being bled off is much smaller than the pump volume so the pressure continues to rise but at a little smaller rate.

As an example, on a roots car you need more fuel to launch the car. We have a high speed poppet that opens in the 60-70 PSI range to bleed off some fuel at about 50-60 feet out. The fuel system pressure and volume continue to rise but the orfice in the high speed is acting like another main jet bleeding off fuel in the system, taking out fuel when the engine doesn't need it. At about 100 PSI there is another high speed poppet that opens to bleed off some fuel at the top of first gear and towards the end of the pass. This 2nd high speed closes at the gear change when the system pressure drops below 100 PSI putting fuel back in the engine when it has more load after the gear change.

Theoretically you could put a bunch of poppets in the system to bleed off fuel at different points, one type of fuel management.

Hope this makes sense.

Greg

 

Hi Speed

Thanks Greg:

I'm a Millwright so I was trained in hydraulic systems and I'm trying to think of the fuel system as such. Its helping in some respects but there are still a few grey areas that I am getting my head around. Plus trying to convey what I'm thinking onto the screen by typing it is not one of my strong points. What you stated helped alot.

Corey

 

Thanks to everyone posting on this thread its really helped me get my head around it, with everyones input. cheers

 

Hi speed

Thanks for letting me ride on your back through this thread as well

Corey

 

Good one!!!

 

When you change the main jet , doesn't this also change the system pressure ?

When the system pressure changes, then the poppet pressure of opening/rpm will change to ??????

Correct , yes/no ?