Discussion Forum - Northstar Chevelle Club

Rolled in for my chassis dyno session this morning at TPIS in Chaska. They use an axle dyno vs roller drum style. Nice since there's no chance of slipping. They have adapters that bolt to your axles, and then the sides mount to that. Some would call them portable, but they're more like moveable.

When it was converted to EFI, we did about an hour or so of test driving and tuning to get it good enough, and the plan at that point was to go on the Power Tour in a couple weeks and tune on the fly. Lost my job, didn't dare spend the money on the trip, then got a job in 2 days but then I didn't have time off. That was back in '08. Fast forward to this morning where I finally got my chance to see if my seat of the pants dyno was still in tune. I always thought it was rich, and it felt like there was a timing issue.

After hooking my car up, Jim @ TPIS asked if I knew of any issues, so I relayed those to him and he looked at my program on his laptop. Background: Chris P still had my initial program saved to his Flintstone laptop and somehow got it into email form so I could open it up and save it to Jim's laptop where he could mess with it before the car ever turned the dyno. He fixed a couple small fuel map issues he saw (mostly transitioning through the RPMs and initial start up richness), and quickly made a new chip. We're talking less than 5 minutes to do. He puts in the new chip and hits the rollers for a trial run. Initial run was good, made sure everything was good to go and then pushed it a little. 249.8hp at 5500 at the wheels. not bad, at least I know. (i'm also doing some basic reverse parasitic loss calculations in my head to see what that might be in at the crank numbers). run #2 focused on timing, which showed mine actually decreasing over the pull. Fix that. #3 added 6 degrees timing (mine was apparently off a bunch) 268.8 @ 5600rpm. #4 bumped it to 9 degrees base timing, 280.5hp @ 5800rpm. #5 went to 11 degrees, 289.7 at 5800 and 5900rpm. Pull #6 bumped it to 14 degrees and we peaked at 290.9 at 5800rpm, 282.2 lbs-ft at 5200 (266.4 at 3300 up and then down to 246.7 at 6100rpm. Done, no more gain but it sounds really good being wound up. The graph is a nice line up at almost 45 degrees, and the torque "curve" is very flat and slightly uphill. To recap, 40 FREAKING HORSEPOWER INCREASE AT THE WHEELS and it was already there, we just had to find it.

Here's a bad video of it:

Thanks to Jim Hall at TPIS, it shows how much a chassis dyno can help tune a car--especially EFI. It was quite easy with the only real wrench work for tuning being done on the distributor hold-down.

-- Edited by bowtie on Wednesday 8th of August 2012 07:17:20 PM