Bigger Throttle Body More Power?
Tourer
Joined: Jan 2008
Posts: 274
Likes: 0
From: South Texas
I am building a 113" and headquarters recommends leaving the throttle body stock. they have reported issues with loss in torque or something like that going to a larger throttle body and with an 850+ pound motorcycle, the more torque the better.
Tourer
Joined: Mar 2009
Posts: 299
Likes: 1
To big of a TB will make your bike lazy and run like a pig. You need a big inch motor to use a 58mm. I have a 55mm HPI worked by Tman with a match ported 58mm pro manifold on my 124" motor with Tman stage 4 thumper heads and it is just rite for it talk to a good Tuner or motor man for advice because it will make a big difference in performance.
Outstanding HDF Member
Joined: Oct 2007
Posts: 3,450
Likes: 4
From: El Cajon Ca.
Got to agree with bigger isn't always better. Same goes for exhaust. You will lose your bottom end torque for sure. Some of the best head porters use small reshaped ports rather then hogging them out real big. It's all about velocity.
Member
Joined: Jul 2009
Posts: 4,310
Likes: 1,079
Depends what engine work you're having done. I have the 58mm on my build (2010 SE Ultra 110 FBW) which includes headwork by Hillside. They strongly recommend adding the larger TB to go with their headwork. I also have larger injectors, roller rockers, FatCat, Ventilator A/C and Woods 408-6 cam. I couldn't be happier. The engine is explosive from a dead stop so don't let others convince you you're going to have lag and reduced velocity because of the larger TB. Not true.
I will say that the engine is alot more sensitive to tuning changes. The "window" of max performance at low rpms is a very narrow band and you'll need to get it right or you can have lag. But once you get it right, you'll have outstanding performance down low and boundless power in the upper rpms.
It all comes down to a build that can take advantage of the higher flow of the 58mm TB and a tuner that has the skill and patience to tune the map to fully utilize it without losing low-end performance. I for one wouldn't go back to my stock 50mm FBW TB (which I still have). Talk to Scott at Hillside Heads for more info on why the 58mm makes sense on the proper build (even on a 110). http://www.hillsidecycle.com/
I will say that the engine is alot more sensitive to tuning changes. The "window" of max performance at low rpms is a very narrow band and you'll need to get it right or you can have lag. But once you get it right, you'll have outstanding performance down low and boundless power in the upper rpms.
It all comes down to a build that can take advantage of the higher flow of the 58mm TB and a tuner that has the skill and patience to tune the map to fully utilize it without losing low-end performance. I for one wouldn't go back to my stock 50mm FBW TB (which I still have). Talk to Scott at Hillside Heads for more info on why the 58mm makes sense on the proper build (even on a 110). http://www.hillsidecycle.com/
Last edited by Heatwave; Jul 31, 2010 at 08:19 AM.
6th Gear
Joined: Apr 2009
Posts: 14
Likes: 0
50MM vs 58MM ??
Some insight please - I have a 09 RKC, 98 motor that has:
107" headquarter kit
Polished and ported
Compression release
Kirker slip on's
High Flow Air
SE race tuner
current dyno run 104hp / 115 TQ
pulls like a freight train - very happy with current build but we are always wanting more.....
I'm being told that the next phase for more power would be to move to a 58mm throttle bottle versus my current 50mm ?
2 into 1 exhaust ( recommended D&D )
Would the above make much of a difference?
107" headquarter kit
Polished and ported
Compression release
Kirker slip on's
High Flow Air
SE race tuner
current dyno run 104hp / 115 TQ
pulls like a freight train - very happy with current build but we are always wanting more.....
I'm being told that the next phase for more power would be to move to a 58mm throttle bottle versus my current 50mm ?
2 into 1 exhaust ( recommended D&D )
Would the above make much of a difference?
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