PSI Screw which one

Part 1:
I thought I had a "C" rotor PSI screw, now I am told I have a "D" rotor. The size of the lobe ends on the trailing rotor is how you tell?
Is that correct?
Part 2:
What is most commonly used in Pro Mod C or D, what is ideal?

CHeers

 

psi c or d

Take the injector body out of the rear hole from both sides, if you can see straight through it is a D and if you can't see out the other side it is a C. Out law pro mod definately a C rotor!

 

blower

So does alky dragster!

 

Also anyone running ORSCA this year due to there being scared of Gil Mobley's Camaro

Mike, I know your comment was not all inclusive and I am talking about a 10.5 car here. I just wanted to take this opportunity to jab at ORSCA for banning the C-rotor....

Richard Gavle

 

A d-series can make 58-60 at the proper overdrive
i've heard one racer switched and didnt see a increase

 

The C Rotor is definitely the prefered between the 2. The output is higher per revolution. But both are better than a roots blower IMO as far as a total package.

As far as the C rotor banned from ORSCA, that's ridiculous. Talk about reacting before you even have an event. But whatever, Gil and the guys will just put a D on it and still beat the guys that were calling for the change to begin with.

 

While I agree with most of the stuff you say, Mike, saying you cant use high speeds to pull fuel on a screw car is not true in ALL instances. There are numerous cars that do, but its all about how the fuel system is done. I know a bunch of cars that do and run very fast too. Not trying to start an argument. Just saying I see it different.

 

For what it's worth, we never take any fuel away from a roots. At least at low OD it doesn't help.

 

Mike. Your not serious are you????????? Because if you are, everybody please send all fuel management systems to me, and I will buy for 30 cents on the dollar. Please private message me for more contact info.

Lonnie Houde

 

We may have a little misunderstanding here. What I was talking about was high speed type lean outs which we don't use, not about managing the overall fuel system going down the track, which we do a lot of.

 

I think any injected alcohol or gas car can benefit from taking fuel out in the lower gears. It's really no secret : http://www.dmpeinc.com/ explains how it might be done on his website.

Top Alcohol Funny Car / Supercharged Pro Mod

(In our example we will use a 3 stage jet log with a .080"jet in Position 1, a .060" jet in position 2, and a .030"jet in position 3)
A funny car normally runs a 3 speed transmission. Each gear loads the motor differently. It is easy to consider there is less load on the engine in low gear than there is when the car is in high gear. (Less gear multiplier) Therefore it’s easier to understand that the engine will require more fuel in high gear than in low gear.
In this situation we would have a 3 jet log installed (jets as indicated above) and the fuel system set rich allowing for the burn out and also staging the car.
We will have a switch under the clutch pedal "or" under the throttle peddle telling our fuel control the run has started. (We will call this W.O.T. for wide open throttle).
At W.O.T. we will open the first jet. Knowing the motor is rich and needs to be cleaned up we will open jet #1 (.080" jet)
At the fuel log the .080 jet is opened and fuel bypassed from the engine and leans the fuel curve. Cleaning the motor up and allowing it to accelerate freely.
Now as the car is shifted into 2nd gear we will close the .080 jet and open the next jet in the log order (jet #2).
In our example we have an .060 jet in the 2nd jet position. Now we have richened the motor by .020". We did this to give the motor fuel back knowing it is under a greater load than previously seen in low gear. Also, we know that cylinder head chamber temperature is rising as well and this will require fuel to control.
Now the car is shifted into high gear. We now close the .060 and open a .030 jet. Again we have richened the motor knowing the load has again increased. The multiplier in the trans in now 1 to 1 (no multiplication) and we are also aware that we have plenty of chamber temperature we need to deal with, and lastly aerodynamic drag is at its greatest point as the car is well past 200mph.
In this example we used the fuel log to control the engines fuel requirements as the car progresses down the race track. It allows us to have a "tune up" for each gear as we can see each gear gives us a new situation we need to tune about.
Many experienced alcohol tuners will use 4 and 5 jets on top of the 3 jet system allowing them to lean and or richen specific areas within each gear as they see necessary on there specific situation. This gives tuners control to control the fuel flow in as many ways as they feel necessary.


You dont even really need a timer if you use a high enough check pressure and shut the jets off with the gears.
My dads gas carbureted car picks up two tenths turning the notched floats around backwards in the back carburetor. The notches keep g-forces from pinching the fuel off and it wants some fuel out of it in the bottom of low. Notched floats can slow a tunnel rammed small block car a full quarter second, they really overfuel in low gear for the correct a/f ratio under load in high gear.
A high speed as its called can benefit a roots blown car by putting enough fuel in it staging and leaving and then cleaning it up once its on step. If it doesnt improve the 330' its useless.

I almost forgot, so could c rotors in a d case sneak past tech?

 

C and D rotor case externally are the same, rotor bore is larger on the C and unless you take the rear injector body out you can't tell, usually the performance difference will be the tell tale espesially the MPH at the stripe.

 

Amazing what comes out of what you think is a simple question.
Thanks gentlemen.

 

To clarify, when i said i've heard one one racer switch and not see a difference, i was talking from a d to a c series.
I know plenty d's fast in outlaw trim, we spin mine less than 125
with 11 mm belts, the belts hold up better than on the roots.
Somebody pm me some boost levels off a c rotor i would like to compare to mine

 

Isn't there also a visible difference in the width of the flat section between the female rotors, D versus C, with the D being wider and the C being narrower? All I have here is a C to look at.........