Dyno Tune

Since the day I bought the Banzai Runner it's run very rich. If you stood anywhere near the rear of the car while it was idling, your eyes would begin to burn from the fuel-rich exhaust gases.

I had recently completed my partial tune-up and installed an electronic ignition. All that was left is to do was dial in the carburetor and timing to complete the tuning process. I don't know a whole lot about Holley carburetor tuning so I decided that would be best left to an expert while on a chassis dyno to ensure optimum performance and economy.

I got dyno-tune quotes from The Speed Merchant and Mustang Ranch in San Jose, and made an appointment to have the Pantera dyno-tuned at The Speed Merchant. It turned out that the Holley carburetor that was on the Pantera when I bought it was leaking gas internally and was already running the next to smallest jets available for it. At the very least, a rebuild was in order.

The carburetor on the car was an OLD Holley 1850/4160 model with side-hung floats - not necessarily a performance oriented carburetor. And, I've generally heard on the DeTomaso Mail List that this style of carburetor tends to starve the engine for fuel under hard-cornering - an environment the Pantera is sure to be found. For $50 more than the cost of rebuilding the old carburetor I purchased a brand new Holley Avenger 670cfm carburetor. I had the carb installed at The Speed Merchant and the car was then tuned on the dyno.

I was a little disappointed with the final results of the dyno-tuning. At WOT the engine runs great! But under normal driving conditions when gently easing onto the throttle, it demonstrated a lag in response. The car also idles at 1,100 rpm now too.

After soliciting the advice of a number of club members, as well as input from everyone on the DeTomaso Mail List, I decided to adjust the accelerator pump linkage. I made minor adjustments, counting each turn of the adjusting nut so I could back-out any changes if necessary and return to my starting point. This adjustment improved driveability tremendously! I think I still need to increase the gain slightly on the accelerator pump, but the car is a pleasure to drive again.

As for the engine idling at 1,100 rpm at normal operating temperature, I suspect there's a vacuum leak. The throttle stop adjusting screw does not even make contact with the throttle linkage presently. I just got off the phone with one of the guys down at The Speed Merchant and he agrees that it sounds like a vacuum leak is causing the fast idle. I need to call the manager on Monday.

The results of the dyno pulls were a little lower than I had expected. Although, they were done in fourth gear rather than third gear. I don't know if that would account for the lower results. I recommended the shop do the pulls in 3rd gear because it's closer to a 1:1 ratio, but they did them in 4th gear. Anyway, the Banzai Runner Pantera produces 249.8 hp at the rear wheels. I don't have the printout handy while I'm typing this, so I'll add the torque figures in the next update. Bear in mind that this is with the original engine that has over 88,000 original miles on it. It's never been rebuilt or opened. The only modifications are the new carburetor, an Edelbrock Performer intake manifold, and headers. All in all, I guess 250hp to the rear wheels isn't that bad for an original stocker.

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