Engine Intake Temperature Dyno Difference

Most gear heads know that letting the motor cool can have a positive effect on performance at the track, but how much can it really make a difference? I thought some of you might find this interesting.

I got a chance a couple of weeks ago to dyno "black jack," see sig. I was concerned that since my fuel system is only runing around 30 psi w/o vacuum that the car may be running to lean. So we hooked up the wide band and went to work.

I drove the car in off the street and put it right up on the dynojet chassis dyno (will have to ask about the model number). I honestly believed that the car would make in the neighborhood of 270rwhp, because I've had a nearly identical combo with shorty headers that made 270rwhp in the past, and this combo is running BBK 1 5/8" long-tube headers. So, I expected a bit more.

While hot, the first pass laid down a disappointing 260rwhp. I honestly thought something was wrong. Maybe the motor is old and there's some blow by... no idea really, but you wouldn't know it from driving it. The shop owner and I are friends, and I was helping him with a project. So we let the car sit for around an hour and cool. Now the car was so cool, it didn't even register on the stock temp gauge, and on pass number 2, the power came up to 265rwhp, just over a 5rwhp improvement.

We immediately followed up with another pass. This time the temp gauge was at around the lowest white line, and it again showed about another 5 rwhp improvement. to a total of 270.6 rwhp.

We immediately ran it again, and on the final pass got another rwhp, but lost about 4rwtq at peak. Unfortunately, I didn't peak at the temp gauge this time. Now that performance was starting to turn back around, we called it a day.

The thing that stands out to me is the air fuel ratio during each run. The first and hottest, full operating temperature, run shows a vast departure to the rich side from the other runs. The leanest run also made the most low-end torque. At peak power, each of the three last runs were within .02 AFR of each other, a perfect place to really see the effect of the temperature difference, assuming timing was also close.

Just a little food for thought! Hope it helps one of you in your tuning and racing endeavors!

Perhaps the most interesting part of the experiment to me was that there's a happy medium. When the car was its coldest, it was 6rwhp under peak. This is obviously not due to the density of air, but to the adjustments that the computer made to timing and fuel. At the vertical line, the AFR was identical and we still see that the coldest (red) run made less power. I think that the computer must be pulling timing for whatever reason.