This post is very timely. I have just completed two separate sessions (7 pulls) on a dyno with a Gen I. The following info should interest all Viper owners, especially Gen 1's.
What made my experience valuable was the quality of the dyno sessions. Dynotech, who evaluated my car is also the manufacturer of Dynojet dynamometers. He also was involved in dynamometer testing for the GTS factory racing program. He has data for over 100 vipers in his data base. He manufactured the unit doing the testing at Mid-Ohio this weekend.
He walked up and actually knew how to open the hood and than asked at the end if I wanted to close the hood. They were a wealth of knowledge, here are a few items:
1. As you shift thru the gears to get into fourth, do so very cautiously (short shift), the dyno is tough on the half-shafts.
2. The vipers heat soak very quickly, therefore, no more than two pulls prior to a 20-30 minute cool down, then additional pulls.
3. Use a high flow external fan during pulls and during cool down. Keep hood down during the pulls.
4. The airflow sensor heats up and the computer adjusts to an environmentally favorable map and reduces horsepower. I haven't tried it yet, but, he suggests putting the airflow sensor in front of the radiator to always get that cold morning power.
5. When working with the factory racing program they told him that the losses across the drive train were 14% new and as the car approached life end, the losses would increase to 17% and yes I heard him correctly.
To back that up, he said that in every case the club racers that he dynos have about 12% losses and that is with a very efficient drive train and no half shafts.
6. If the dyno operator is skilled enough at the end of the pull he can reset the dyno, push in the clutch and get a reading of the horsepower that that the drivetrain is exerting on the dyno drum, in other words, obtain the losses across the drivetrain.
Now for the power data, my gen I has the following:
1994 w/10,000 miles
Balanger Headers thru BTR
Roe's oval cats
Dynomax mufflers - all exhaust components @3"
BTR Cones & Smooth Tubes (I dyno'ed both)
Roe VEC1 controller.
The best run was 404 rwhp and 471 ft lbs torque. The curve is very smooth and flat throughout the power curve. If I use the 14% number for losses the car is 469 hp and 548 ft-lb of torque.
If you have noticed there has been a recent discussion of smooth tubes/KN's versus the cones. The cones pulled 7 hp more than the smooth tubes and KN's. It should improve in a moving vehicle, since the cones are at a disadvantage when not moving.
It was interesting that with stock air box and filters removed the engine pulled less hp, however, the air fuel ratio turned very lean and I didn't have time to adjust the VEC1 to offset the lean condition. He also indicated that some of the new KN's were so heavily oiled that they actually restrict airflow. He suggested cleaning the filters (degreasing), then applying a more sensible amount of oil.
If you are a viper owner and have not dealt with Sean Roe and Tom Welch - you are missing out.
