Question on Lean Outs

I have a question on how do you set up several lean outs at different poppet pressures to arrive at a smooth AFR through out your RPM range? With one lean out you can watch the plugs; but with several lean outs how would one know which lean out is wrong?
Thanks, Joe

 

With lots of runs/testing. If you have one opening early in the run and closing and then opening another later in the run, the only way to tell how happy it is on the first timer would be to make a hit and shut it off before your next timer kicks in. Check your plugs and bearings. If it looks good, run it a little further and repeat. Of course if the car likes the changes it is going to run faster. The quicker and often times cheaper in the long run option is to have a credible person setup and flow your system where they can give you a 'ball park' that is competitive. Testing is still needed to maximize your combo. If you take a look at things and you 'think' that the engine is running up through detonation, it probably is, and it may not show up on your egts or your O2 sensor if you run one. Things may happen that you may not understand or may seem trivial at the time, but be patient and listen to what the engine is telling you.

 

Thanks for the replay rb0804.
Are you saying I should use timers instead of relying on poppet pressures?
Joe

 

If you rely on regular poppets you have to get creative to maintain the same opening point if you make a change to the fuel system that effects entire system pressure. An example would be adjusting the main jet for weather changes. If the weather gets worse and you install a larger main jet to compensate and try to maintain your targeted a/f ratio, it is going to bypass more fuel and your total system pressure goes down a tad bit. Unless you changed your poppet pressures, they are now going to open a little later in the run in this example. If you jockey around nozzle area along with the main jet it is possible to maintain the same operating pressure while maintaining the fuel reduction you were shooting for. Doing it this way you don't have to worry about changing poppet opening pressure and hope you get it correct. If you were to use a timer it is going to operate at the same point in the run regardless of your system pressure. You can also open and close the jet so you have better control of the a/f ratio throughout the RPM range. Once you open a pressure poppet, it's open and you may run up through a lean spot somewhere. Wonder where Mike Canter is hiding, he usually chimes in by now.

 

Precisely - save yourself money in the long run and outfit the car with timed controllers.

Brandon Booher
NHRA TAD #3
Torque MGMT. - Owner

 

Thanks for the replies guys.

My motor is a 548ci BBC with a roots 14-71 Littlefield in a drag boat. I rev limit the launch to the tree were the motor picks up the load at about 7500 rpm in about 1.5 sec. The motor stays very close to this rpm (+/- 100 rpm) for the entire run. I have used a lean out in the past with a .055 jet set at 90 psi and I have seen a slight increase in the rpm of about 75 rpm. My port line pressure after the BV and before the port check is ~100 psi. The port check was set 18 psi and the egt's showed a drop ~100 deg. I have since moved the port pressure sensor after the port check to give a more accurate port pressure reading and lowered the port check to 12 psi to try to keep the temp. from dropping so much at launch. The hottest plugs have ~90% of the cadmium still on them at 32 deg timing. The egt's tell me a different story then the plugs do; I have since ignored the egt's, now I am only looking at the plug readings.

Currently the boost is at 21.2 psi at 7400 rpm; the blower needs to be stripped again. I believe the motor has lot more in her, but I want to proceed with caution. I would appreciate any advice that you may have to improve my ET's. Right now I am running 4.2 at 660ft, 6.01 in the 1/8 and 7.60 in the 1/4. I would like to lower my 660 times if possible.

Thanks again, Joe

 

Joe , what type hull, setup are you running ? To only pickup a small amount of RPM like that isn't normal ---that kind of cu in and blown setup should be at 7.0 pretty easy -

 

Mark,
The hull is a Cheyenne, open boat, with a jet pump in it. Jets take a lot more power then V-drives do.
Thanks, Joe

 

I'm just confused by the above because I don't know anything about drag boats. In my world 660' and 1/8th mile are the same. And are you really covering from 1/8th mile to the 1/4 mile in 1.6 seconds? I run a 6.2x 1/4 mile and I'm still 2.2 seconds from the 1/8th to the 1/4. So either I'm not understanding something right, or you are holy smokes hauling on that back half.

 

Maybe Joe can state the whole situation so that it would be easier to help him--- instead of a piece at a time ? I agree a jet boat is a lot harder to push down the track than a prop setup in a Hydro or a Flatbottom --

 

Sorry guys I made a mistake. The 6.01 sec time is for 1000 ft not for the 1/8 mile. Yes I agree that would be confusing.
Thanks, Joe