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Discussion in 'PSI Superchargers Tech Questions' started by racecar1517, Jul 7, 2020.
Who has used a dribbler setup, and what worked vs what didn't work?
I have used it because it came on the car when it was bought. Later took it off and in looking back saw no real valid reason for it. It makes tuning complicated unless you use Alky Pro software. Why do you want to use it?
Yes, I'm interested. The temperature spread at idle is roughly 500 degrees. The coldest 2 cylinders lag behind for the first half of the run.
I have listen to many people say that idle egts don't matter.
At this point I'm willing to try something new. Just because it's hard doesn't mean it won't work, or doesn't have value.
Remember that thermocouples are extremely slow to react, can really fool you.
The dual nozzle system works best in clutch cars, specifically TAD's.
Tom Conway pioneered this system in the early 90's and it became pretty standard after that in TAD. The goal is to have the port checks set high enough they are just starting to crack at stage and the dribblers are set on a low pressure check so they are cracking open at idle.
At stage rpm (part throttle with a clutch, no WOT 2 step), you use the dribblers to try to cool off or heat up cylinders to have them all even.
You have to be smart with this system or you can get out of whack real quick. If you richen a dribbler to bring a cylinder down at stage, you need to lean the port nozzle 1 in that cylinder. If not, pretty soon you are just richening, richening, richening until your nozzle area becomes all out of whack.
For the 16 nozzle system to be truly effective, all cylinders must be 'lit' at stage. When this happens you are usually looking at a staging egt average of 600+. This is common with TAD's because of their smaller CID and easier weight transfer vs a FC.
Most TAFC systems are 8 nozzle because for many years, having 1 or 2 holes out at stage was a method of power management. It is still not uncommon to see this today on many cars.
In regards to idle, if you have a clutch car, I did experiment with a 16 nozzle system on a TAFC a few years back, with the idea that if I could keep all the cylinders idling the same, they would be closer at stage. But the screw blower really loads some holes up with fuel at stage, so the idea did not work. We ran really fast with that set up, so we never went back, but the concept didn't pan out.
That said I had a roots 481x I was tuning that the only way we could get the back 4 holes cooled off at idle was to add dribblers to those holes. I did this by splitting the nozzle area of the single nozzle into whatever it took to get the hole cooled off at idle. I was able to get the cylinders a lot closer at idle, then I could get the barrel valve back 'normal' since I wasn't chasing the back four cylinders over 800.
Most people have gotten away from running a real lean idle set up in the heads up world. A lean barrel valve/idle mixture with a hot cylinder head temp can obviously be very 'responsive' and result in good 60' times. However what we have found is the trade off is more cylinder head heat can lead to detonation down track, so you have to somewhat crutch it with more fuel than what you could run with a cooler head. Also with power management, most cars pull timing out early and are trying to use ratio to make the car 60', rather than have the motor set on wreck.
I will run my dial in Top Dragster cars leaner at idle since I'm not pushing the tune up down track. This is primarily so that they don't have to change the oil every run. My heads up cars (screw) are rich enough at idle you need to change the oil after a pass.
Another way to do similar is to run a port line off the high pressure poppet port to a distribution bloac and have BV drilled so it aligns when at full throttle. You run a smaller nozzle of port block as you normally would and a larger nozzle off the hat line feed. Spike Gorr did this in mid 90's. I still have the sheets on the system.