Racing Fuel Systems

Before another thread gets hijacked I thought I would start a stand alone one.

A discussion has come about from another thread regarding the calibration of a carburetor and engine specs were given but no car weight, gearing, converter etc. it was stated these are needed.

What effects do these have on the calibration?

If hours upon hours are spent on an engine dyno changing up jets, air bleeds, emulsion etc to get the best power curve & BSFC numbers then how relevant is that tune in a 3350lb car with 3.5:1 final drive and 3000rpm converter v 2800lb car with 4.11:1 final drive and 5500rpm converter?

I am thinking the gearing and converter have to fall inline with the engines torque/power curve and carburetor calibration would be a very close baseline wise from the dyno that may need track jetting when in the car.

How would gearing, weight and converter influence emulsion, air bleeds, IFR etc over and above engine specs?

I’m all ears an hope to learn something here.

IMHO,

I think spending alot of time of the dyno fine tuning the carb is not the best place to spend time. Yes you can get things close, but tuning for the conditions the car sees at the track in my opinion is better.

How the carb is loaded and accelerated on the dyno will be different than how it is loaded and accelerates on the track.

How much heat the carb/engine see on the dyno vs in the carb can potentially be different.

Gforces will effect things in the car.

In my limited experience, I have tuned the carb in the car, then had it on the dyno, and appeared to makes some gains, but then when the engine went back in the car, I lost performance and usually ended back up where I was at. Same thing when I did tuning on a chassis dyno.

The things the engine wants on a dyno may not necessarily be the same as it wants going down the track.

I agree with the above mentioned. The hardest i have ever seen a motor work is in offshore boats, tied to a huge water brake on a engine stand, and climbing sand dunes. A chassi and engine dyno are only as good as the knowledge of the operation. I have seen a few let go in these controlled situations, i have seen pump lines blow, and ceiling tiles sucked in, and blown out. some times the operator's lack of knowledge causing the destruction, some times the water pump can not hold the torque and the K-factor. That is the stall to torque ratio of the hydraulic coupling device, AKA the torque converter.

title of this thread should be .... "Car gearing and weight effect's on tuning .... the .... Torque Converter. "

You are all over the place, and not very specific, so I am not going to speculate about any of that.

The greater the load, the greater air fuel charge it takes to carry that load.

Trans brake and take off are the greatest load, followed by the gear changes, and high RPM.

A 9 inch converter with a 1.59 ratio compared to 9 inch with 1.95 ratio.....same gear, same car, same cam, carb, and everything else you want to speculate.....is not going to tune the same, and will typically make most grown men cry themselves to sleep at night.

I understand the intentions of this thread
"Lets say you stopped sending that car down the quarter and just wanted to cruise around so diff gearing changed to 3.25: and converter 2.5-3k. How would that change the tune or calibration of the carb? There would be more time in the lower revs and throttle position may change to maintain certain speeds but wouldn't fuel qty delivered at that throttle position be the same as with the same throttle position with race type gearing?"

An excersise for everyone. below is my combo:

Engine: SBC 383
11.4:1 comp
245* & 252* @.050 int/exh cam
Trickflow twisted wedge g1 heads flowing 271@ .500”
Super Victor intake
1-3/4” headers
110 gp/h mechanical fuel pump
MSD Digital 6 ignition 20* initial 34* total

I think you need to start with a better example for a combo. In all practicality who would want to cruise around with a race spec engine. 245@.050 camshaft SBC
A true street car doesn't resemble a race car. Thats why specifics are important.

"Spec a carby for me with:" What carb ? you could have hundreds of combos here

A dyno tune may more resemble a track tune ,I don't know, but I do know it may not resemble a true street car tune either in carb or camshaft drivability.