Dyno/exhaust Crisis

[topfuel67]

I took my car to an exhaust shop today to have the center mufflers removed. Only other thing I have is a mopar CAI. I've read that removing that muffler alone gives a nice boost. Next door to the muffler shop is an OLD school dyno shop. The guy had never dyno'd a srt8 before. His dyno had no electornic read out. Just the old needle guage on the wall. Anyways I went to him and had him dyno my car before the exhaust removal and then afterwards to see the gain. Now this guys dyno needed to be "loaded up" (whatever that means) before it got an accurate reading. The rpms needed to be held for about 10-15sec and then he'd hit a button to get the reading. With the new trans tcb on my car it did not cooperate. It would shift every gear at 6100 or so and he couldn't get a good read since the rpms needed to stay constant for about 15 seconds. When the car got to 5th the governor would cut it at 160MPH. So the best run we were able to get was my car made 340 hp at 5000 and 380 hp at 5500 rpm (he could not get it to hold 6000 long enough to get a reading without the rpm spiking-or shutting down). After the mufflers were removed I went back. This time the car seemed to be grumpier. Everytime he held the rpms to get a reading he'd hit the dyno button (I guess after the dyno was "loaded up") and then the rpms would spike causing it to hit the rev limiter. So the after results were 320 hp at 5000 rpm and 360 hp at 5500. We even took the car for a cool down drive, let it sit and tried again. Still the 360 hp peak (peak before it spiked and shut down).

So my question is to anyone who is experienced with these cars on a dyno: Does this old school dyno seem totally off and my car could not have possibly lost 20hp from removing that center muffler? It was 60 degrees for all dyno runs, cloudy and slight drizzle. I still have the stock resonators on. Anyone hear of a dyno that has to be "loaded up" and hold the rpms for a good 15 sec or so and then once he hits the button for the guage to work it allows the rpms to spike like that? It just all seems backwards to me. Part of me wants to put a stock exhaust back on and the other just wants assurance that his dyno was a joke. Anyone know a good dyno shop?
Thanks!

[crhemi]

Did you pull fuse 11 or disconect the battery and let the computer relearn it's new self?

[srt8danno]

Sounds like an antique dyno was needing more than a “load up” (whatever that was) I wouldn’t worry a thing about it and take it to a nice modern facility that can handle a mighty beast like the SRT8.

[topfuel67]

I tried disconnecting the battery. Dyno'd again. And then pulled fuse 11. Tried dynoing it several times. After the exhaust it just didn't make 380 hp again. After whining about this to friends I think the problem was the electronics interferring on a "load up" dyno. I've checked out vidoes on various websites and their dynos pull for about 15 seconds total and have a full read out. Each run was over 30 seconds on this with the end result being the rev limiter or governor cutting out as the needle on the wall was trying to register the power. At least my computer's first new lesson was GOTO 6000 rpm...

[topfuel67]

I had my car Dyno'd at Granatelli's Motorsports in Oxnard, CA on a Mustang dyno. With the same setup (deleted "suitcase" and CAI) the car made 354hp on their dyno at 5950 rpm. I'm going to put the stock exhaust back on and take it back to see if the hp goes up.

[Chrispy]

Good luck! Remember Mustang dynos are 12-15% lower in their reading than dynojet.

[vipnathan]

30 sec a dyno? You are going to lose hp from the heat. I am glad you are taking it back to stock though. I am curious to see if your hp increases or decreases from the added back pressure.

[Chase023]

Maybe due to heatsoak??

I know mine was a bit hot when it ran, it was like 357 HP and like 358 TQ.

With the mods now I hope I am close to 390 to 400+

[topfuel67]

At Granatelli's it made 339hp the first pass when it was cold-190 engine temp. Then made about 345hp the second time-200+ and then 354 the third run-210+. It improved with heat, so I don't think heat soak was the issue.