im taken my 95 inch up to the 107 doin head work and ruin head quaters 580 lift gear driven cams with the thunder max and fat cat exhaust. was thinkin of sending my stock throtle body to house power inc to have bored to the 48 mil. the guy at there shop sugested going with there 51 mil. says i would gain more . dose this sound right to you guys ? is it worth the investment?

thanks

 

you say h-q cams with .580 lift...do you mean hq-0039?...if so, that is more of a torque cam which doesn't benefit very much from a big throttle body...unless you are racing or you rev the motor above 4500 rpm a lot, you probably won't gain much by modifying or changing throttle bodies

 

Call HPI!!! They know the flow rates and performance gains for their products. They will take into acct your motor, cam, riding style, bike etc and recommend one for ya. I agree with Skyhook, don't go too big, it will KILL your bottom end torque. I'm in the process of building a 98" motor. I went with HQ's ST kit. I talked to Eric at HPI and he suggested I stay with my OEM or one of theirr 48mm throttle bodies if I want to keep my low end grunt. He said anything more on a 98" would hurt my low end. Sure, I would gain some hp up top with a larger setup, but it would be doggy down low. In the end I sent them my OEM intake/throttle body and had them clean it up. They were running a special last week or so and it was only $170 shipped back to me! It looks really good! Eric said I should see about 5% increase in power from the modification. I would have seen a total of 7-8% increase with one of their setups. But at $700, I wasn't sure it was worth it. He did say if I were to go bigger in cubic inches, then I would benefit from a bigger throttle body. Prolly one of their 48 or 51mm setups with the small runner size is a good option for ya..?
Jason

 

yes there the 0039 . so your saying going to the 51 or boring the stock out want change much. i was wondering if the guy was blowing smoke. just trying to gain as much as i can. any other sugestions ?

 

talked to them this mornin and it was $200 to bore the stock TB he sugested the 51 with my set up. just throughing out there to you guys to see what all thought.

 

that cam makes great power from 2000 to 4500...and 4500 is about the point where a bigger throttle body begins to have an advantage over the stock unit...so you might see a small gain on a dyno sheet, but I doubt you'd feel it in normal riding

 

With the 0039 I would have your stock TB reworked and bored to 48mm. You will have really snappy throttle response. I wouldnt wast money on the 51mm unit. Too big with that cam choice and unecessary.