Data Recorder Shows 300 rpm 'droop' After Car Launches???

[Don Whitmore]

The data recorder is showing a significant rpm 'droop' (300 rpm - 400 rpm) after the car launches (converter flash)...sort of like a 'camel hump' in the run trace.

The car is a 350 ci SS/JA weighing about 3100 lb. The 60 ft times are good for this type car but wondering if they can be improved if the 'droop' is reduced???

I've noticed the Comp cars don't seem to have this issue, so is it something we're doing or just a characteristic of a Super Stock car???

What can be done to reduce or eliminate the 'droop?' Converter swap? Gearing? You just gotta live with it???

[KRatcliff]

That is the converter loading. It is normal to see that in a car like yours.

[BlueOval Ralph]

Getting the fuel curve right will help that!

[Ed Wright]

Mine shows a couple hundred if it turns the tires a little. Dead hooks don't show it.

[Don Whitmore]

All...thanks for the input.

@KRatcliff....what is different that the Comp cars don't see to have the 'droop?'

@BlueOval Ralph...would you go leaner / richer in this area? I forgot to mention it is a fuel injected combo.

Thanks for the help!!

[KRatcliff]

I cannot answer the question on the Comp cars due to zero experience with them. I can only surmise that the ones you may have seen may be leaving at a significantly higher RPM, the converter may be smaller (ie 7"), and the engine isn't pulled down as much or at all when the converter fully engages.

I have looked at the graphs of many fuel injected stockers and super stockers. Every one of them had the same hump. Even our super stocker with a carb combo has a hump. Most were 2 step cars, but a few were foot brake stockers.

Any tuning that you do for this event is basically behind a curtain and you are not exactly sure what the A/F ratios are due to the action of the 2 step. I have a certain pattern of attack for that event, but that is just for my stuff and I have a lot to learn before I come close to getting these tunes right.

Listen to the others with more experience than me on this. I was just giving you my experience.

[BlueOval Ralph]

A little richer at peak torque if EFI give it a little pump shot

Originally Posted by Don Whitmore

All...thanks for the input.

@KRatcliff....what is different that the Comp cars don't see to have the 'droop?'

@BlueOval Ralph...would you go leaner / richer in this area? I forgot to mention it is a fuel injected combo.

Thanks for the help!!

[Chris Hill]

..

[BlueOval Ralph]

Don't thinks it's converter, the issue is the converter and engine, fuel curve are not happy together as Marv Ripes would say.

[Ed Wright]

Marv would know.