Reading thru few post on site I have noticed a lot of MFI stuff where pressures of systems is around 100 psi(low pressure). I have always worked with numbers based on 150 PSI. Mostly blown engines. That said I have built quite a few systems for others that where in 150 area and seemed to work fine. System I have on FED should be around 200 PSI(never happy and always want more) ,thought being more pressure better atomazation.

Wondering what some others thoughts are on hi vs low pressure system. Like old saying more than one way o skin a cat.

I have ran 150 and more and currently running around 60. Can not tell any performance difference.

I high pressure system with smaller injectors will often idle better and have better low rpm manners. At WOT they all have pretty nice spray patterns. High or low pressure. Low pressure is sure a lot nicer on pumps IMO. I don't see a reason in the world to run 200 psi. That even introduces extra safety issues for that matter, as well as more stress on hose fittings etc.

500 in 871 hi helix blown/wedge mopar, running 8 hat, 8 port nozzles, Enderle 110 pump (way more than I need). I bracket race. Launch at 3200, shift at 6800. Fuel pressure max's at 90 lbs. I have a pump sizer .080, high speed .088, and main at .110. and it's still fat..lol

I'd have to get my log opened up to tell you the pressures my bypasses are at, but they open pretty quick. 15 lbs boost.

I'm with you Chris as I would rather have pressure around 150..

Dave

200 psi system is a test idea. To make it 150 psi its simple nozzle change of .003 and jet change in main.
As for lines I test all lines at 280 psi after assembly. As much as hate to agree with Ed its not a place for Chinese lines or fittings and yes there is difference.How do I know? Lets say when a end comes off at close to 300 psi its moving across the room. LMAO now.

A correction 150 is not high pressure,but rather medium . 500 psi plus on fuel car is HIGH pressure.LOL

All pressures figured at 8000 rpm as are all of my flow numbers.

Thanks for replys.

Its not as simple as higher pressure is always better. I'm not sure of the exact scientific reason why and even if I could explain it if I did. If I was a smart person I could explain why.... Its' sorta like picking the best cam... even the pros don't always get it right... I just know from experience it isn't that simple.

Scott

quote:

Originally posted by David Covey:
500 in 871 hi helix blown/wedge mopar, running 8 hat, 8 port nozzles, Enderle 110 pump (way more than I need). I bracket race. Launch at 3200, shift at 6800. Fuel pressure max's at 90 lbs. I have a pump sizer .080, high speed .088, and main at .110. and it's still fat..lol


I'd have to get my log opened up to tell you the pressures my bypasses are at, but they open pretty quick. 15 lbs boost.



I'm with you Chris as I would rather have pressure around 150..

Dave

David,

If fat and wanting more pressure gradually step the nozzles down little at a time till you get closer to pressure you want.Leaving the by pass pills as they are.

What kind of BV square or K style? K style is lot less drop across it to nozzles. You can run little less pressure on pump while still having more at nozzle itself. But you probably already had that covered,just figured worth pointing out in case you're like me and had occasional brain ****.LOL

You could just pump more air in. throw another 3% blower on her and let her eat that fuel.GO FAST !!!

I'm right at 200#, works for me.

quote:

Originally posted by wideopen231:

quote:

Originally posted by David Covey:
500 in 871 hi helix blown/wedge mopar, running 8 hat, 8 port nozzles, Enderle 110 pump (way more than I need). I bracket race. Launch at 3200, shift at 6800. Fuel pressure max's at 90 lbs. I have a pump sizer .080, high speed .088, and main at .110. and it's still fat..lol


I'd have to get my log opened up to tell you the pressures my bypasses are at, but they open pretty quick. 15 lbs boost.



I'm with you Chris as I would rather have pressure around 150..

Dave

David,

If fat and wanting more pressure gradually step the nozzles down little at a time till you get closer to pressure you want.Leaving the by pass pills as they are.

What kind of BV square or K style? K style is lot less drop across it to nozzles. You can run little less pressure on pump while still having more at nozzle itself. But you probably already had that covered,just figured worth pointing out in case you're like me and had occasional brain ****.LOL

You could just pump more air in. throw another 3% blower on her and let her eat that fuel.GO FAST !!!

After going to a different cam this year the A/F being fat is a little more noticeable on coloring the pipes. Car ran almost exact same as last year with different cam. But then again engine and blower were fresh this year. I do plan to reduce the area of the nozzles. Boost is 14 lbs so with steel rods I don't plan to go any higher although the bearing from last year looked good enough to reuse.
Square Barrel Valve.
I ran across a thread on Inside Top Alcohol talking about spray bars in the hat and how they seemed to pick up a bunch of power. 80-100+ on Rage and Janis dyno's.

I'm still running 8 nozzles in my hat. I asked Aaron Sipple about the spray bar deal and he didn't think it would help me because I bracket race.
I was going to attempt to build my own Janis style.
So instead I just turned the front 6 nozzles up to spray into the airstream instead of down into the blower. Can't say it's made any difference but the hat sure frosts up a lot more than it did. lol

Dave

Not sure I buy difference with spray above blower. Reason its going into rotors and being mashed together until it exits and if delta hole then it has to go to front of blower and be pushed back to rear of intake. Thats a lot going on after the fuel is sprayed into hat. JMO

I am not saying it couldn't show more on dyno,but I wonder what effect t had on fuel system as a whole flow wise and changes else where. Agian just my thoughts.

Then anything can work better than you think just like the million of ideas that didn't work as thought. I think I tried 1/4 of them. LMAO

quote:

Originally posted by wideopen231:
Not sure I buy difference with spray above blower. Reason its going into rotors and being mashed together until it exits and if delta hole then it has to go to front of blower and be pushed back to rear of intake. Thats a lot going on after the fuel is sprayed into hat. JMO

I am not saying it couldn't show more on dyno,but I wonder what effect t had on fuel system as a whole flow wise and changes else where. Agian just my thoughts.

Then anything can work better than you think just like the million of ideas that didn't work as thought. I think I tried 1/4 of them. LMAO

The difference may be cooling the air and the blower for a more condensed charge. Plus the fuel may help get a better seal for a little more pressure.

quote:

Originally posted by Curly1:

quote:

Originally posted by wideopen231:
Not sure I buy difference with spray above blower. Reason its going into rotors and being mashed together until it exits and if delta hole then it has to go to front of blower and be pushed back to rear of intake. Thats a lot going on after the fuel is sprayed into hat. JMO

I am not saying it couldn't show more on dyno,but I wonder what effect t had on fuel system as a whole flow wise and changes else where. Agian just my thoughts.

Then anything can work better than you think just like the million of ideas that didn't work as thought. I think I tried 1/4 of them. LMAO

The difference may be cooling the air and the blower for a more condensed charge. Plus the fuel may help get a better seal for a little more pressure.

Chris,

It has the delta opening, and when I first started running blower using only hat nozzles I could kill the front 4 plugs after 3 passes they were so fat. Rear plugs A/F looked good. So after 3rd pass I would change the front plugs.
After the first season I pulled the engine, flowed the system using hat and port nozzles. Leaned the hat down a bunch, and tuned at the port. Now I could run same plugs all season.
I can't see any difference in the fuel being "mashed" together into the rotors from 2 inches or 10 I still have to have the tune up right.

Like Curly said, the theory is to pre cool the air as it enters the blower creating a better atmosphere. They do not run hat nozzles with the spray bar, only the nozzles in the spray bar. They also claim to be increasing the amount of fuel by something like .080+ nozzle. Cooler denser air + more fuel = more power.
Jody Stroud said he has 26 nozzles in his spray bar set up from Rage.

I'm looking at it like I have more control over weather from round to round so better consistency. I do not change my fuel from round to round.
I may be totally confused like a crack head though...lol

Dave

I have run 45 psi and over a 100, the only difference is the HS is easier to set. One question, isn't the intake valve closed for 390-400 degrees of rotation? Seems to me that most of the fuel is sitting on the intake valve. So I am not sure how better atomazation takes place.
Joe

This message has been edited. Last edited by: sr4440,

quote:

Originally posted by sr4440:
I run 45 psi and over a 100, the only difference is the HS is easier to set. One question, isn't the intake valve closed for 390-400 degrees of rotation? Seems to me that most of the fuel is sitting on the intake valve. So I not sure how better atomazation takes place.
Joe

All the better atomization takes place above the blower.. Once the fuel hit's the rotors it goes to a liquid basically anyway. All it's trying to do is cool the incoming air as much as possible before hitting the blower the as the blower compresses it doesn't heat up as much.. Cooler/denser A/F.

Dave

Dave, I was responding to wide-open, he's running NA. On your deal it makes perfect sense to cool the air and make it dense before being compressed.
Joe

Ahhhsooo...

lol

Dave

Want cool air go to screw blower. LOL You have to tune to 200 to 300 higher temps because intake charge has much less heat. SOrry bu after you run a screw blower you wonder why they even make a roots. I know guy I am helping runs (wait try's to run) roots in TA/D. Like pissing into a tornado.

I can see where it would help cool air charge coming into blower. Would like to see on track data as to effect on run. Not against it just always skeptical after years of hearing how this or that makes big power gains.Then I have wall full of machined pulleys because holes are suppose to get air out between belt and pulley and allow more contact for ribs. We try anything for power.

This discussion makes me want to find out what pressure I am actually running. I have never checked. My car kept wanting more fuel until we finally found a spot it liked and repeated with.
468 cid
8 stack Enderle
0.5 pump
32 nozzle, 65 pill
tried a 33 nozzle last race of the year, but tuning conditions were very rare for us here so numbers may not be indicative of how that change actually worked.

Chris,

Years ago when Johnny Gray was running TA/FC I know he put a couple of nozzles just behind the butterflies on the injector. He claimed it helped. His old car was running pretty quick at that time so I have no reason to doubt him.

I can see that spray bar helping. It makes sense. Good luck!

My Toilet on the sbc is about 55 psi max.....and it prints slips....5.61, 5.61, 5.61..etc. My Kinsler stuff was supposed to be around 150 psi, but they were WAY off on the tune and after I got it leaned out enough to make passes, the pressure is around 95 psi.