View Single Post
  #30  
Old 9th December 2008
Don Burton's Avatar
Don Burton Don Burton is offline
Senior Master Custom Bike Builder
 
Join Date: Apr 2006
Location: The Warm Southeast! U.S.A.
Posts: 7,256
Reputation: 395253
Don Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond reputeDon Burton has a reputation beyond repute
Default

Quote:
Originally Posted by Bob F View Post
I did the Gronk Mod making the holes larger than his instruction and added a few rows. Then I opened up the AC and installed a K&N filter. When I did another baseline Dyno pull I gained 2 HP. The Dyno tech said he could have tuned some more power out of it but he wanted to schedule it for a different day. The sound was more what I wanted. I decided to save my money for upgrades so you're right, my testing was limited.

I went back and checked an old post written by Rider1951. He said he did the Gronk Mod on his 05 1200C but only drilled out some of the holes and only drilled them out to less than 1/4 inch so he didn't get all of the flow or performance of the full Gronk Modded U.S mufflers. Still, with a slightly richer than stock N65A needle, richer than stock 45 pilot jet and a leaner than stock 175 main jet in the carb for both tests, he ran 62.48 HP and 67.52 ft. lb. of torque with the stock tapered mufflers and 65.45 HP and 72.55 ft. lb of torque with his half-way Gronk Modded mufflers. I would expect that with all of the baffle tube holes drilled to 1/4 inch for a full Gronk Mod, he would pick up a couple more HP and a couple more ft. lb. of torque. That's not bad for a relatively quiet muffler that won't attract undue attention anywhere when ridden moderately, while it still sounds like a Harley. He did say that he was a little rich above 5,200 rpm and was running only 13.5:1 between 3,700 and 4,500 rpm so he could have tweaked it a little (perhaps by shimming the needle and using a little smaller main jet).

I suspect that you could have gotten more power out of your Gronk Mod if the bike had been run long enough for the EFI to adjust itself to the changes and also perhaps had the dyno operator done more runs.
__________________
"The day soldiers stop bringing you their problems is the day you have stopped leading them. They have either lost confidence that you can help them or concluded that you do not care. Either case is a failure of leadership." Lt. General Colin Powell, U.S.A., ret.
Reply With Quote