Port Nozzel pressure

Mike -

So is it a good idea to run it that way, I haven't seen that many cars doing it that way.

Ron

 

I appreciate the information!

Thanks,

Ron

 

Hi Guys,

Thought I better jump on this thread, rather than starting a new one, we run a Hi-Helix 16-71 Blown BBC and we seem to have a problem with the fuel system backing up or building up pressure on the start line and then the port poppet opens and starts to flood the engine, If the engine is in stage for only a short time i.e. 3-4 seconds it leaves hard if we get hung out or it is a particular long stage the fuel pressure starts to build up and the port nozzles come into play.

At idle the temps are close and around the 600 -800 'F mark when the engine revs up to staging rpm (6000rpm) after a little while some of the cylinder temps take a dive, we started with a Nozzle Poppet sets at 15psi but we are up to about 40psi at the moment it seems to make it better but it is not perfect

Any advice would br much appreciatted

Cheers
Marc

 

No. Because the barrel valve is closed. Remember, you are on the backside of the spool. There is barely enough fuel flowing thru the system to even turn the turbine in the flow meter at idle.

 

Could we have some more information? is it a k style b.v.? Idle return pressure? pump loop pressure? Hat Nozzle area? What fuel pump? Is the b.v. spool in backwards(slot @ the front instead of the back)?
Think of the b.v. leakdown as a jet; 75% leakdown= .075jet 80%=.080jet. A pete jackson b.v. uses a jet to set the leak and a idle mixture screw for fine tuning.
To small of hat nozzle area can open the port check to soon staging. Opening a pump loop with a lower pressure could help by lowering the pressure before the b.v.
I haven't heard of an alky fuel system with much more than 25 pounds port nozzle check ;though I've done it because I was trying to put too much fuel beneath the blower and your problem sounds like the same problem I was having. Roots blowers like at least 50%-50% if not 60% in the hat 40% in the ports.

 

Hi Creech,

K style BV
Idle Pressure 5psi
Pump Loop 160psi
990 pump

Will post the other stuff when I confirm and check the Spool

Cheers
Marc

 

160psi pump loop? Are you talking about the pump saver on the top of the b.v.? The loop would be down by the pump (sometimes called a high speed).
I call it a loop if its between 15 or less and 45psi. A high speed is usually tapped off the line going to the ports 65 to 95+ psi depending on location and were you want it to come in.

Another question how much overdrive and boost, blower set back(not to big of deal ,just wondering)? Is it dropping #2 and #4 cylinders? And how much compression? A 990 pump is about 15.9 gallons @ 4000 pump speed so sounds right. I had a 14:1 comp BBC with a 14/71 hh on it when I dropped the compression to 10.5:1 I had a similar problem. I didn't have a computer so I put a couple gauges on it; one off the pump one off the distribution block with lines up to one of those things you mount the gauges on the dash with. I held it in one hand and watched it while I brought the motor to 5000 with the other, Crude put it worked.

 

Hi Marty

We do not run a high speed, sorry yes I was talking about the pump saver

33% OD & 46 pounds of boost @ 9500

Normal set back nothing huge

I was mistaken it is a 110 pump

To me it seems it cannot return the fuel to the tank quick enough during stage and the pressure is building up rather than a steady pressure

Cheers
Marc

 

Could there be a restriction in that line somewhere, like the fittings or something? What size line are you using for the return?

Paul.

 

pressure

how about using the pump saver port as a secondary by pass.. lower the ps pressure to around 40 psi and it should relieve your stage issues and close off at wot...of coarse you need to dump it rather than plumb it to the block.
just a thought.

 

A110 pump is kind of small (13.6 if I remember right) put I suppose it would work if you dont return much.
On screw blown motors we replace the -6 idle check with a -6-8 adapter. http://www.goodvibesracing.com/orb_fittings.htm and use a -8 idle check. If thats not enough you can drill out the 1/4' hole in the spool too, up to 5/16' .

 

Hi Guys,

More Info

BV LD is 75%
Idle check was set at 9psi (maybe a bit high? and causing a system build up)
Scroll is at the back of housing
The pump has 110 cast in it and 990 stamped on it, it flowed 12.62GPM @ 4000 as a complete hat / nozzle fuel system
Hat area is 0.04072
Port area is 0.01873
Which is 55/45 ratio if my brain is working right

We use a -6 poppet and -6 line, I pulled the spring out of the poppet and used the leakdown tester to blow air back to the tank using the current set up and the % was the same with or without poppet / fuel line attached, but that was with air and not a fluid, might try the -8 upgrade.

Looking at the data, it just seems to build up a back pressure while holding quite stable staging rpm,

Cheers
Marc

 

Thats 68.5% hat 31.5% port. Its gonna hall ass! Bring the ports back to 25 psi when you first try that -8 idle . It might sound crazy but if it works try droppin' the port check to 5 psi you might have to raise the idle pressure to lower the idle: It'll Heat Up Quick But EVIL WICKED AND NASTY !!!

 

Hi Marty

We are running this weekend, best so far is 6.06 @ 225mph 2250lb altered,normal runs are around the 6.20's Not sure if I will get the -8 bits before the weekend, do you think the pump saver idea has merit?, talking about it today it would work in theory

Cheers
Marc

 

The pump saver port is just like a idle port, so I cant think of any reason why not.

 

hello teenracer....this is just a shot in the dark!!!! but check to see if you have a big enough vent in the tank it could be pressurising the tank..good luck...
also to the guy that sell the leak down here on insidetopalcohol..if you want the trickest of all tricks buy from this guy..Mr. mogonagal.hope I spelled his name right is a wizard...dave
www.myspace.com/daveloweswr

 

Hi Dave,

The internal tank vent is a 5/8" pipe and I guess if the tank was pressurising fuel would come out of it?, comparing all data for a a couple of seasons, we did some blower mods this year and we have more boost now than before, we have moved our tuning "window" from 100 - 110 pills to 80 - 90 pills I guess this would cause some back up I would not have thought this would matter but maybe on our deal it is enough, I guess I will increase port nozzle sizes accross the engine and remove fuel by going back to 100 pills? and see if that fixes the problem

Cheers
Marc

 

Is the main in the barrel valve? If so it's returning though the idle/secondary check anyway.

 

egt's dropping at stage.

Hello,
There is a return slot on the bottom side of the spool, This return closes as you open the butterflies. This slot can be modified to continue to return fuel as you open the butterflies. If you have any questions, Contact me, I will explain how this is done. Ken 216 390 4561