Bigger Throttle Body
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Road Warrior
Joined: Nov 2007
Posts: 1,984
Likes: 7
Years ago I had a big block Corvette. 1972. Decided to do a lot of work on it and when it came time for the carb I went conservative because I worried about too much carb for the same reason we are talking about.
Holly 750 double pumper. After getting tuned up good car ran very good but got 7.5 miles a gallon. Ran it for awhile and gas got expensive, so I sold it. Really hate that now, usual story.
The guy that bought it decided it could run better so he put a 850 double pumper on. I figured against the rules.
That thing was the fastest street car I was ever in. Ran wonderful with the 850.
Course there is a lot of volicity, even with that, when 472 cubes are pulling.
May try a Kuryakyn just to see. Life is too short.
The heads are OK and cams can change.
Holly 750 double pumper. After getting tuned up good car ran very good but got 7.5 miles a gallon. Ran it for awhile and gas got expensive, so I sold it. Really hate that now, usual story.
The guy that bought it decided it could run better so he put a 850 double pumper on. I figured against the rules.
That thing was the fastest street car I was ever in. Ran wonderful with the 850.
Course there is a lot of volicity, even with that, when 472 cubes are pulling.
May try a Kuryakyn just to see. Life is too short.
The heads are OK and cams can change.
Last edited by Old Gunny; Dec 20, 2008 at 11:30 AM.
Banned
Joined: Oct 2008
Posts: 164
Likes: 0
From: Hollis
Years ago I had a big block Corvette. 1972. Decided to do a lot of work on it and when it came time for the carb I went conservative because I worried about too much carb for the same reason we are talking about.
Holly 750 double pumper. After getting tuned up good car ran very good but got 7.5 miles a gallon. Ran it for awhile and gas got expensive, so I sold it. Really hate that now, usual story.
The guy that bought it decided it could run better so he put a 850 double pumper on. I figured against the rules.
That thing was the fastest street car I was ever in. Ran wonderful with the 850.
Course there is a lot of volicity, even with that, when 472 cubes are pulling.
May try a Kuryakyn just to see. Life is too short.
The heads are OK and cams can change.
Holly 750 double pumper. After getting tuned up good car ran very good but got 7.5 miles a gallon. Ran it for awhile and gas got expensive, so I sold it. Really hate that now, usual story.
The guy that bought it decided it could run better so he put a 850 double pumper on. I figured against the rules.
That thing was the fastest street car I was ever in. Ran wonderful with the 850.
Course there is a lot of volicity, even with that, when 472 cubes are pulling.
May try a Kuryakyn just to see. Life is too short.
The heads are OK and cams can change.
How often does your bike spin at 6000?
Ultimate HDF Member
Joined: Jan 2008
Posts: 6,532
Likes: 132
From: SoCal
I have the SE 58 TB on my 08 SG runs just fine throughout the entire rpm range, you can't label a certain size TB too big or too small without taking all things into consideration and even then sometimes just try it to see if you like it hell you are paying for it. If bigger TB's were so bad why did Harley put the 50's on the touring bikes first? I would cost them less to change nothing so bigger must have had a benefit either in MPG , HP , TQ or a combination of the 3.
Ultimate HDF Member
Joined: Feb 2007
Posts: 7,663
Likes: 7
From: Northeast Ohio
I ran a 50mm all year on my 120 and it was good, although I am "experimenting" going to an HPI 55mm that is sitting on my workbench at this time. I ran a SE 50mm on my 103 with the Woods 400-6 cam (.650 lift) and it was good, but I sure would not have gone any larger.
Banned
Joined: Oct 2008
Posts: 164
Likes: 0
From: Hollis
I have the SE 58 TB on my 08 SG runs just fine throughout the entire rpm range, you can't label a certain size TB too big or too small without taking all things into consideration and even then sometimes just try it to see if you like it hell you are paying for it. If bigger TB's were so bad why did Harley put the 50's on the touring bikes first? I would cost them less to change nothing so bigger must have had a benefit either in MPG , HP , TQ or a combination of the 3.
Got a big powerplant that runs past 6000rpm all day long like what you would find at a drag strip?, sure go get a large TB then. Thats what they are designed for. WOT and fast revs where air VOLUME is now most important. Air volume at lower rpms though is not as important(and wont be hindered with a smaller TB), air velocity IS now what is important, at those lower rpms.
Ultimate HDF Member
Joined: Jan 2008
Posts: 6,532
Likes: 132
From: SoCal
I love my 58mm TB and would not go back to the 50mm , I do not go to the drag strip , I ride a Street Glide not a Dyna , I weigh 200 lbs and have the standard gearing which equates to about a 2.80 not the 3.17 or the even higher revving 3.37 so if 58mm being too big were an issue it would rear it's ugly head on my bike. I am not speculating on how a 58mm TB works, I can tell you how it works from experience , I am running one not just talking about theories and the theories I have heard here are sound one's they just haven't proven to be true in my case.
Tourer
Joined: Mar 2007
Posts: 431
Likes: 0
just can't let it be!...maybe I'm trying to make myself feel better about the money I spent and am not being realistic, BUT I'd do it again...just like the stock heads and cams, the stock t/b is not a pure performance design, and thus has limitations...I don't know why they put a restrictive manifold on the stock, se50, and se58, but that is the choke...you could put a 100mm throttle blade in front of it and it's still not an optimal design
the fine folks at kuryakyn wild things and horsepower inc have proven that low/mid torque isn't compromised by too large throttle body...ntrat it's time for you to discard your old carburetor/velocity ideas, join the new millenium ha ha ha
I've always said that I represent the minority of performance riders...I want my power 3500 to 6000 rpm...and for me, the moco stuff doesn't cut it
ok, I'm thru ranting and raving
ps ntrat: how's that slow softail holding up?
the fine folks at kuryakyn wild things and horsepower inc have proven that low/mid torque isn't compromised by too large throttle body...ntrat it's time for you to discard your old carburetor/velocity ideas, join the new millenium ha ha ha
I've always said that I represent the minority of performance riders...I want my power 3500 to 6000 rpm...and for me, the moco stuff doesn't cut it
ok, I'm thru ranting and raving
ps ntrat: how's that slow softail holding up?
Banned
Joined: Oct 2008
Posts: 164
Likes: 0
From: Hollis
I love my 58mm TB and would not go back to the 50mm , I do not go to the drag strip , I ride a Street Glide not a Dyna , I weigh 200 lbs and have the standard gearing which equates to about a 2.80 not the 3.17 or the even higher revving 3.37 so if 58mm being too big were an issue it would rear it's ugly head on my bike. I am not speculating on how a 58mm TB works, I can tell you how it works from experience , I am running one not just talking about theories and the theories I have heard here are sound one's they just haven't proven to be true in my case.
I can tell you this too. There are larger street engines tuned for double duty street/strip performance running much smaller throttlebodies that put down significantly more power than what your running under foot.
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Banned
Joined: Oct 2008
Posts: 164
Likes: 0
From: Hollis
just can't let it be!...maybe I'm trying to make myself feel better about the money I spent and am not being realistic, BUT I'd do it again...just like the stock heads and cams, the stock t/b is not a pure performance design, and thus has limitations...I don't know why they put a restrictive manifold on the stock, se50, and se58, but that is the choke...you could put a 100mm throttle blade in front of it and it's still not an optimal design
the fine folks at kuryakyn wild things and horsepower inc have proven that low/mid torque isn't compromised by too large throttle body...ntrat it's time for you to discard your old carburetor/velocity ideas, join the new millenium ha ha ha
I've always said that I represent the minority of performance riders...I want my power 3500 to 6000 rpm...and for me, the moco stuff doesn't cut it
ok, I'm thru ranting and raving
ps ntrat: how's that slow softail holding up?
the fine folks at kuryakyn wild things and horsepower inc have proven that low/mid torque isn't compromised by too large throttle body...ntrat it's time for you to discard your old carburetor/velocity ideas, join the new millenium ha ha ha
I've always said that I represent the minority of performance riders...I want my power 3500 to 6000 rpm...and for me, the moco stuff doesn't cut it
ok, I'm thru ranting and raving
ps ntrat: how's that slow softail holding up?
People seem to forget, the intake runner diameter needs to be accounted for. I probably should have mentioned that at first, but wanted to keep this conversation simple. The problem with alot of the stock HD intakes delas with the runners choking down too much. They can be modified though to flow the needed air.
So with this information now presented with more in depth explanation Im still going to stick with my original statement that the Kuryakyn 57mm TB is too big, that includes the intake runners which I know are over sized at 1.8". Just too big for a 107" street build. You would be much better off looking at an HPI 48mm or 51mm with a 1.66" intake runner.
SEDELUXE: Trust me, my specialty is FI tuning, not old school carb jibberish.
Tourer
Joined: Mar 2007
Posts: 431
Likes: 0
with fuel metered electronically (not by air velocity) and sprayed directly at the valve, the port velocity argument is diminished...also isn't port velocity governed by the port/bowl/valve, not the induction module?
don't pizz me off or I'll sic my guru on ya! lol
don't pizz me off or I'll sic my guru on ya! lol