Dyno Results after swapping 2 1/2 Mac to 3 inch........

[03DarkShadow]

Well i swapped in the 3 in Mac cat-back about 2 weeks ago and put on the 2.75 ultra-grip in place of the 2.80. My best with the 2 1/2 and 2.80 was 458.6HP and 512LB-FT SAE. The outside temp that day was 67 degrees. I also sprayed a lil giggle gas(39 jet) after that run and netted a 515HP and 537LB-FT and that was spraying at 4500 rpms. A/F's stayed around 12-1 w/ a spot between 4000-5200 rpms going off the charts rich on both the NOS and Regular runs. Now the results, Temperature today at dyno time was 91 degrees. 442HP and 475LB-FT SAE only pull made off the bottle. Engine temp was at 188 degrees. Now i wanted to see what the larger 46 jet would yield. 512HP and 550LB-FT, he let off at 5500 because the A/F was starting to go lean. I put the 39 jet back in and ran again. 490HP and 552LB-FT and A/Fs were the same as before. steady around 12-1 going off the charts rich between 4000-5200. Im not disappointed at all considering the temp today. Only ting that concerns me is that Power starts falling off at 5500 whereas before power would not fall off until 6000. ???? Any ideas or suggestions?? Thanks for the space Jamie

 

[03DarkShadow]

BTW, not that it matters bottle pressure was at 900psi today and it was over 1000 on the previously made runs. Jamie

 

[jonas]

your supercharger is becoming inefficient at that range and that pully. This isnt from my own experience just from feedback ive been getting from people on this and other boards. anything above 293 doesnt make a great deal more power.

 

[trey193]

Looks to me like that was a lose lose situation. Maybe a tuner can get it all back and then some with a dyno tune! I have heard several reputable tuners say the 3inch catback is overkill unless you have a KB and a bunch more boost! Good Luck!

 

[jleews6]

Low bottle pressure didnt help.
The weather didnt help
and you might be over spinning the blower.

Try changing the fuel filter.
Good luck:beer:

 

[03DarkShadow]

I changed the fuel filter this past weekend. Thanks Jamie

 

[Corner-Carver]

My gut feeling is that the 2.75 is just too small of a pulley for the Eaton. The bottle pressure is a touch low, but no that bad. Plus the fact it was 91 degrees... ughhhhhh

 

[lguerra1]

To me, it looks like the temp. is what killed your numbers more than anything else. While using SAE numbers does correct somewhat, it cannot correct the increase in boost and lower boost temps you get with colder air. That alone increases power substantially.

Also, with the cat-back, going from a 2 1/2 to 3" will not necc. give you any difference, if you havent changed anything before the mufflers. If you are still using stock logs or some sort of 2 1/2 inch x pipe, changing the cat-back only will not really affect your numbers.

 

[03DarkShadow]

ttt

 

[Fast01Cobra]

I have also heard that the 2.75 is too small. My question would be, what if you dyno with the 2.80 pulley again?? Also what was the diff in barometric pressure?? That has an effect as well. Also was it the same dyno?? Dynos are great, but seems like no two are the same. Just my 2 cents.