Higher Water Temps - Higher HP #'s on the dyno...WHY?

[MambaViper]

Just had my 2nd ever dyno session with my '05 Srt yesterday and i am just curious as to why the Viper keeps pumping up HP/TQ #'s the hoter the car keeps getting on the dyno making run after run. When the water tems were 180 and oil around 200 it put down about 15Hp/Tq less than after the 3rd pull in a series of 3 when the water temps were pushing 210 and oil 200-210 range.....i have never seen this before and asked the dyno owner if he ever has and replyed that the only other cars he sees like this are new GM's also.....Weird?? My only guess is Emission's Crap.....Is that right??? This car must be set up to run at a constant 210 water temp wise?? I thought that was a bit high?? My other turbo cars put down peak #'s at 170-180 temp range.

The hotter it got TQ #'s down low at about 2-3k were noticably higher.....and then HP #'s jumped between 10-15 HP from 5k up to redline and the A/F seemed to lean out a bit. Does anyone know for sure WHY??

[The Former PFR]

Did you play with the ignition on the dyno? I suppose if the car was running pretty much the same ignition advance, the engine gets more efficient the hotter it gets. Fuel atomization probably also gets a little better which *may* explain the lower A/F seen by the O2 sensor. Still....this is not something I would have predicted, but that is what me thinks may allow this to happen. The Viper has a deaf engine management system IIRC, so its not like it tries to optimize ignition timing and would consequently make more power. Lastly, with a deaf system, the ignition map is most likely based on the engine running 210. With the fuel a little warmer than it would be with the engine running 185, the activation time would decrease, effectively adding a smidgen of ignition timing (and this is why they tune at the higher temp). Turbo cars make more power when cold because they are SO intake air temp limited, but N/A isn't as much and might swing the other way due to the higher efficiency of a hot engine as well as the other factors listed.



BTW, did outside temp and barometric pressure stay the same throughout the day?

[MambaViper]

that makes perfect sense now

the 3 pulls were done back to back to back.

and by the 3rd pull i couldn't even put my hand on the intake manifold and i heard the fans kick on as the pull was being sampled.....water was above 210+....both sessions were the same result......the 3rd pull yeilding 15 peak Hp more than the 1st pull......and TQ around 2-3k was up almost 15ft.lbs

when i go to the drag strip next time i am not taking ice paks to put on the manifold.....i'm leaving it alone

now as far as my turbo DSM......compareing water temps from 180 to 210 it lost 45 hp and 40 ft.lbs throught the entire pull with the hotter temps....the viper is just the opposite

[MikeR]

Thats part of the reason i didnt put in a lower temp thermostsat. Everytime I was at dyno my last few runs yield the most power.
At my last dyno session, my first run was 494rwhp and last pull was 507rwhp. This was after 5 consecutive runs.