HOW BIG OF TB DO YOU NEED FOR YOUR MOTOR? INFO HERE.......

[Faast Ed]

Kind of fits the words Ed E said over on the groove string (whether they help or not):

"Depends on the build".


I too was going back/forth on whether to get a HPI 51 for my build, but I think I am in the same boat as Bagger with not enough cam to benefit from a bigger TB. So I think I shall buy lots of beer instead.

[Don D]

Ed
It would help a little as did the pipe but just at the top and a through retune would be needed. I agree likely not worth it.

[FLTRI]

So, can we all agree that simply bolting a bigger TB onto a build will NOT always produce expected results?

Can we all also agree that simply increasing the ci doesn't necessarily warrant a larger TB?

If so, we can then agree that the entire engine build is what dictates TB size, not individual mods, ie: ci, cams, etc.

If we can all agree with those statements then we know bigger is not always better, no matter who makes it or how much it costs, or how shiney it is.

Just my deduction from this thread,
Bob

[skyhook]

bob I mostly agree...however I've come to believe the one piece t/b's are crap...I would change to hpi 51mm even if I was running a 96" with andrews 21 cams and mild headwork...why?...I just think the area behind the throttle blade is so restrictive that the hpi would significantly improve throttle response...this is something that may not show up on a dyno chart, but is worth doing nonetheless if the customer has the cheese!

[Faast Ed]

...this is something that may not show up on a dyno chart,

I sure wouldn't want to pay for something that won't show on the dyno chart (not a big ticket item).
However, I can see how it would make one feel better about their build (eliminating a known bottleneck) and also it could be helpful if some future mods can benefit from it.

So, can we all agree that simply bolting a bigger TB onto a build will NOT always produce expected results?

I surely agree. (but I still get the urge to consider a bigger TB). LOL   I doubt that it will happen while running this particular cam.
besides, my tuner is likely sick of me taking up all his dyno space!  LOL

[FLTRI]

"however I've come to believe the one piece t/b's are crap...I would change to hpi 51mm even if I was running a 96" with andrews 21 cams and mild headwork...why?...I just think the area behind the throttle blade is so restrictive that the hpi would significantly improve throttle response..."

AKAIK, the smaller the TB the more throttle response.
I have had my 117ci with a stock 2003 TB. Guess what? The throttle response was incredible, however the top end HP was down about 15. When I put a 58mm TB on it the power above 4000 went up considerably but the throttle response (SOP) went down.

I'm going to a 51mm TB because for my touring bike build (big ci, low compression) because I think it will outperfom the 58mm everywhere except where I do not ride (>5500)

So, IMO, the smallest TB that will feed the engine what it wants will outperform a TB that is bigger than necessary.

It's kinda the same as with a carb but the fuel is precisely metered and dictated unlike a velocity sensitive carb.

We discount velocity is still as important with EFI as with a carb for VE quality (cylinder fill)

As always, JMHO, Bob

[GoFast.....]

What's you point? You've got a low mechanical compression and wimpy cam.. Not sure you'd see any difference on the bore.. Max

Let me say it a little nicer than MAX  The small cam and low compression do not have a strong enough signal or is not calling for more air than what a stock TB has. A 31 closings is to small of cam to take advantage and it also is to small of a cam to take advantage of the larger cubic inches. If you keep it like this you mize as well sell the hpi to someone that needs it

[Lovetoride007]

I also am putting together a 107Ci on a 2004 bagger, heads are ported flowing approx 155 cfm on intake ,going with HQ575 cams, compression is 9.9 to 1 , will this set up benefit enough to warrent spending the money for a bigger TB, and how big

[skyhook]

another thing about dyno charts they are at wot...how much time do you spend there?...how much does wot power have to do with normal riding?...my chart with hpi 55 shows I lost a lot of tq at wot, but it is just as strong at 2, 5, and 10% as it was with the stock 50...and the larger throttle blade improves throttle response significantly...so I am not convinced that a smaller t/b with a bad intake(the stocker) is going to work better than a work of art hpi AT ANY throttle position

edit: I'm talking about one piece t/b's being crap...and I believe velocity is controlled by the port and valve, not the tb, especially at part throttle

really not trying to pick a fight with you sir, I do respect your considerable experience with these motors

[GoFast.....]

another thing about dyno charts they are at wot...how much time do you spend there?...how much does wot power have to do with normal riding?...my chart with hpi 55 shows I lost a lot of tq at wot, but it is just as strong at 2, 5, and 10% as it was with the stock 50...and the larger throttle blade improves throttle response significantly...so I am not convinced that a smaller t/b with a bad intake(the stocker) is going to work better than a work of art hpi AT ANY throttle position

edit: I'm talking about one piece t/b's being crap...and I believe velocity is controlled by the port and valve, not the tb, especially at part throttle

really not trying to pick a fight with you sir, I do respect your considerable experience with these motors

I think we also have to remember that the stock head is going to restrict flow also

[skyhook]

yes, definitely depends on the build...I also believe in running baby cams in '06 and later motors unless you upgrade EVERYTHING

but I still believe throttle response will improve with a totally stock, correctly tuned motor with a 48 or 51 hpi

I'm not selling anything here, do not work for hpi, just voicing my opinion

[Bagger]

GoFast, IMHO a HPI 48mm - 51mm versus stock TB IMHO would complement your build and provide quick and smooth throttle response.  It would not be over throttle bodying your build.  The HPI TB is a quality piece of workmanship.  To some it may not be cost effective, but for me, it was money I didn't mind spending. 

Well, I agree with what FLTRI said about velocity and cylinder fill relating to throttle response - don't want to over TB a build for the sake of a few HPs in an rpm range not ridden in.   

In my bagger build, the throttle response is immediate and smooth, no high revving to get it moving.  This bagger with it's wimpy cam (9.0:1 corrected CR), immediate acceleration and the 1700 to 3000 rpm TQ is well suited for an annual ride from Florida to Maine and on into Canada.  It's ideal for riding up through the Smokey and Pocono Mountains, pulling out of corners on winding back country roads, accelerating past semi-truck on the interstate and riding through the streets of Manhattan.   And after I put 100,000 miles on the bike, I may take the engine to 106" or 107", and the 48mm TB will be ideal match IMHO.

[GoFast.....]

yes, definitely depends on the build...I also believe in running baby cams in '06 and later motors unless you upgrade EVERYTHING

but I still believe throttle response will improve with a totally stock, correctly tuned motor with a 48 or 51 hpi

I'm not selling anything here, do not work for hpi, just voicing my opinion

I was talking to Eric at HPI and he reminded me of something I had forgot about earlier than 06 stock TBs.The throddle plate is 44mm but they are really 38 mm because they are two pieces. The intake manifold behind the the throttle plate norrows to 38 mm restricting the flow. To see this all you have to do is take a flash light and open up the throddle and as you look down the TB you will see it choke down behind the Throddle plate. Someone shold be able to post a picture of it here on HTT.These TBs really need improved as the cfm increases with High perfomance upgrades. Trying to make serious horsepower with these is really like beating a dead.......

[Bagger]

To beat  just a bit more, here's some additional V-Twin Forum comments made by a respected engineer.  Although comments primarily relate to a 95", the same philosophy can be applied to larger cubic inch builds.  Increased velocity seems to be objective.

05-24-2004, 02:56 PM 
GRock 
Premium Member   Join Date: Apr 2004
Location: connecticut
Posts: 1,897

http://www.v-twinforum.com/forums/showthread.php?t=37459&highlight=48mm
clive,
You are probably ok, but I've tuned a few EFI's in my time and we are finding that stock delphi is marginal for 95". Your cam is not too radical, but as long as you are headed to the dyno I will give you a hint. Record MAP readings on Race Tuner while doing 4th gear roll on. If graph starts to get jumpy in higher RPM range (4700 RPM and up), motor needs more air. For 95" you probably only need to have stock throttle body bored out. It's cheaper than whole new unit and air box. However, if you are going to continue the quest for more power by going larger cubes, you will absolutely require more air. Zeus, with all due respect anything above 100" benefits from larger than stock. My 107" was limited in HP with bored delphi. Went to dual runner and just re-tuned and gained 6 HP and about 8 lbs TQ. And got smoooooother running in the lower ranges. By the way I have a couple BC Gerolamy re-worked Dephi units with manifolds that I'll sell cheap if you find you need one.

I've been researching V-Twin, HP Inc and others for opinions on upgrading TB.  HP Inc recommended their 48mm for the 98" kit.  I'll be running this to the ground to learn pros/cons, especially to low end TQ.

http://www.v-twinforum.com/forums/showthread.php?t=65094&highlight=48mm

11-04-2005, 01:03 AM 
GRock 
Premium Member   Join Date: Apr 2004
Location: connecticut
Posts: 1,897


Just to let you guys and the rest that are considering EFI builds know.....

When you go to nicely ported heads like Baisley and keep the stock TB, you are definitely holding back the flow.

MAP almost always will start to drop from anywhere from 4100 to 4700 on a decent 95 and higher build with the Delphi. BUT.... the difference in HP is maybe 3 to 4 HP with a cam like the 37. And some of that may be caused by front to rear fuel reversion at high R's. So not a big deal on the TB size. Remember that you aren't hanging around in the 4000 to 5000 rpm range for very long anyway. The most that you can bore out of the stock Delphi is about 3mm MAX, and although that will move your MAP drop up a few hundred R's, it doesn't completely solve the issue you are having. Again, I'm not calling it a problem because it really isn't on a cam like the 37. This is for up to 2005 models.

The 06's have their own problems in this arena, but some of those are influenced more by the smaller injector size that simply will not support high HP engines because of the limited pulse width. This, COMBINED with the TB bore, WILL cause problems on 06's that are trying to make big power.

Anyway, don't everyone go crazy buying big TB's, because in most cases you will never feel the difference. Really a nice alternative is to send them out to a guy like Dakota Kid who will not only increase the bore but also increase intake velocity due to his re-work. And that, my friends, is the real key!

As for the quote from Daytona Twintec on the inadequecy of the stock TB, while Chris Schroeder is a pretty sharp guy, his numbers on the limitations of the Delphi show that it is inadequate to maintain MAP gain. But it really does not affect streetability of most 95" builds. And his limitation on the HP number is really not a limitation at all. (BTW, you can get more that 105). MOST 95" street builds are not making too much more than 105 HP anyway. And TQ is always on the way down by the time that MAP drop occurs anyway. So what are you losing? Not much.
Take that quote with a grain of salt!

FYI

All the best

03-23-2005, 08:32 PM 
GRock 
Premium Member   Join Date: Apr 2004
Location: connecticut
Posts: 1,897 

Quote:
Originally Posted by SYCLONE
Do you think with the numbers he's already making now with his build that a larger T-B will make improvements worth the cost. Seems pretty stout right now. You have fooled with these as much as anybody...where and what kinds of gains do you think he'll see. Especially interested in what you have found to be the advantages/disadvantages of dual vs siamese manifolds when you have run them on the same motor. I would guess that a properly sized dual runner would be easier to tune, make more torque sooner, and be less prone to reversion with big cams running lots of overlap. Grock..time to spill the beans !!

Unfortunately, with the price of these things it is rarely worth the cost for this mod on a 95". Your gains are only going to be in the higher rpm ranges anyway, as the MAP pressures begin to go a little squirrely when you hit aroung 5200 - 5400 RPM. You will get a few more ponies out of a build like this, but, like SYCLONE says you are running real nice for a 95 and nothing will be noticed in the normal riding ranges with the TB mod.. If mores cubes and bigger HP numbers are in the future, then look into it, otherwise it is a want item and not necessarily a need item.

SYCLONE,
You make a good point, but I was simply giving the poster where to's on getting a larger throttle body. I would think that the money should stay in his pocket OR, if he likes to spend, have his TB bored for around $325 at a couple of different shops that I know of. But the 48mm bore is really nominal for the build he has and will not hold up for bigger mods later. As for your assessment of dual runner vs. siamese, yes, I do prefer the dual runner design for larger motors and cams with long duration and high overlap where they definitely are easier to tune and eliminate front to rear fuel reversion. Seems to give smoother running and when larger injectors are used, low speed operation and idle are easier to control. In short, for all you guys and gals that have done the 95's, it is rarely worth the cost of a new TB to justify the cost unless the 95 build is just temporary medicine for the performance fever.

[Bagger]

FWIW, J.E.T comments regarding velocity.  The J.E.T website shows their dyno testing results.


http://www.cyclespot.com/forums/showthread.php?t=14729

Modified Throttle Body??? Thoughts?

--------------------------------------------------------------------------------

I was checking this out on the J.E.T. website and was thinking about this as a mod but wanted to hear from some of the wrench experts...Below is their performance claims. The 48mm is $170.00 and the 51mm is $366.00 Thoughts please...

J.E.T Website:  http://www.johnsonenginetechnology.com/JETPAGES/parts/twin-cam-throttle-body.html

Our goal when we started our project was to offer our customer’s a high horsepower throttle body option for a lower cost than what is currently available. Right now, big throttle bodies are available from Screamin’ Eagle and other aftermarket manufacturers at costs between $400 and $800. They all produce good results, but the total cost of installation and tuning can be over $1000. For just a small increase in performance, this can seem a little expensive to many people. Instead of having to purchase an expensive new unit, we set out to see what we could accomplish by some simple inexpensive modifications to the stock unit.

All ’05 and later Twin Cams (except for ’08 FLH’s) come with a one piece 46 mm throttle body. Upon testing we found that this 46mm unit was limiting customers to about 92-98 HP depending on displacement and the level of performance work. We found the overall design of the part to be a little lacking (it was clearly designed without performance in mind). The port runner increases in diameter from 1.900” to over 2” after the butterfly and still gets larger in area until the port exit at the cylinder head which is 1.640.” Any intake manifold that is designed to increase engine performance has port runners that are smaller then the butterfly, which also has a constant taper to the cylinder head. This is done so that the air in the throttle-body is constantly increasing in speed (this reduces reversion and increased throttle response, it also helps prevent detonation by keeping the fuel in suspension (low velocity and reversion cause fuel to fall out of suspension which increases the likely hood of detonation).

We flow tested the stock throttle body and found out that it flowed 219 CFM at 28.” We then bored it out to 48mm (.090” bigger than stock). The manifold was flow tested with just the bigger 48mm butterfly and we saw an increase of 13 CFM (232 @28”) We then did a little bit of clean up porting and re-flow tested the throttle body with results showing an increase of 22 CFM (241 CFM @ 28”). After flowing the throttle body we installed the unit on a 103 cu” TC with a mild camshaft and 9.8:1 compression ratio (baseline power of 92 HP and 104 ft lbs torque). Upon installation of the 48mm High-Flow throttle body and proper tuning; the HP increased to 96 HP and the torque increased to 106 ft lbs. SEE DYNO

Seeing as the 48mm worked so well, we thought we would push it a little further and try going to 51mm. After re-boring the throttle-body to 51mm (an increase of .196” over stock), we flowed the throttle body and that’s when the bad news started. The 51mm throttle body only flowed 243 CFM @28” an increase of only 2 CFM over the 48mm unit. Seeing as the flow bench is not always a tell-all in performance, we then installed the part on the same 103 cu” TC as before and proceeded to test and tune the 51mm throttle body. The results were not good; the HP and Torque both went down about 3-4 units in the low and midrange RPMs, but the power above 4750 RPM increased by about 4. SEE DYNO

All in all I would say that the 51mm ported stock throttle body was a failure, because not many people spend a lot of time riding above 4750 RPM, but we were determined to make the 51mm throttle-body work. We thought about what we could do to increase the velocity behind the butterfly. Increasing the velocity and the CFM would increase the power everywhere and make better use of the big butterfly. The port runners were then cleaned up and some very high-tech epoxy was used of fill the ports (to replicate the port runners of our J.E.T. intake manifolds). After the manifold was epoxied and ported, we tested it on the flow bench and it flowed a lot more with the epoxy, 257 CFM @28”. Now we were faced with a manifold that was about 15% smaller, had the proper taper that an intake should have, and it flowed 14 more CFM (38 more CFM than stock!!!!) This could only mean that the port velocity was much higher in the manifold with the epoxy. So we took the 51mm High-Velocity throttle-body to the dyno.

Unfortunately, we were unable to retest the epoxied 51mm High-Velocity throttle body on the same 103 cu” TC, so we took advantage of a very mild 106 cu” TC with a very good baseline on it and a stock throttle body. The 51mm epoxy unit was installed and properly tuned in. This is where the results turned for the better… way better. SEE DYNO

The HP went from 100 HP to 107 HP and the torque went form 110 ftlbs to 115 ftlbs of torque. We also noticed the power increases were produced throughout the entire RPM range and not just in the higher RPM areas. These results were very encouraging find and could only mean one thing; we accomplish our original goal.
As a result, Johnson Engine Technology, Inc. can now offer a service that will take the stock throttle body of a potential customer and modify it for optimum performance without the high cost of the aftermarket part.
__________________
Life Blows... Enjoy the Breeze

Semper Fi

[GoFast.....]

FWIW, J.E.T comments regarding velocity.  The J.E.T website shows their dyno testing results.


http://www.cyclespot.com/forums/showthread.php?t=14729

Modified Throttle Body??? Thoughts?

--------------------------------------------------------------------------------

I was checking this out on the J.E.T. website and was thinking about this as a mod but wanted to hear from some of the wrench experts...Below is their performance claims. The 48mm is $170.00 and the 51mm is $366.00 Thoughts please...

J.E.T Website:  http://www.johnsonenginetechnology.com/JETPAGES/parts/twin-cam-throttle-body.html

Our goal when we started our project was to offer our customer’s a high horsepower throttle body option for a lower cost than what is currently available. Right now, big throttle bodies are available from Screamin’ Eagle and other aftermarket manufacturers at costs between $400 and $800. They all produce good results, but the total cost of installation and tuning can be over $1000. For just a small increase in performance, this can seem a little expensive to many people. Instead of having to purchase an expensive new unit, we set out to see what we could accomplish by some simple inexpensive modifications to the stock unit.

All ’05 and later Twin Cams (except for ’08 FLH’s) come with a one piece 46 mm throttle body. Upon testing we found that this 46mm unit was limiting customers to about 92-98 HP depending on displacement and the level of performance work. We found the overall design of the part to be a little lacking (it was clearly designed without performance in mind). The port runner increases in diameter from 1.900” to over 2” after the butterfly and still gets larger in area until the port exit at the cylinder head which is 1.640.” Any intake manifold that is designed to increase engine performance has port runners that are smaller then the butterfly, which also has a constant taper to the cylinder head. This is done so that the air in the throttle-body is constantly increasing in speed (this reduces reversion and increased throttle response, it also helps prevent detonation by keeping the fuel in suspension (low velocity and reversion cause fuel to fall out of suspension which increases the likely hood of detonation).

We flow tested the stock throttle body and found out that it flowed 219 CFM at 28.” We then bored it out to 48mm (.090” bigger than stock). The manifold was flow tested with just the bigger 48mm butterfly and we saw an increase of 13 CFM (232 @28”) We then did a little bit of clean up porting and re-flow tested the throttle body with results showing an increase of 22 CFM (241 CFM @ 28”). After flowing the throttle body we installed the unit on a 103 cu” TC with a mild camshaft and 9.8:1 compression ratio (baseline power of 92 HP and 104 ft lbs torque). Upon installation of the 48mm High-Flow throttle body and proper tuning; the HP increased to 96 HP and the torque increased to 106 ft lbs. SEE DYNO

Seeing as the 48mm worked so well, we thought we would push it a little further and try going to 51mm. After re-boring the throttle-body to 51mm (an increase of .196” over stock), we flowed the throttle body and that’s when the bad news started. The 51mm throttle body only flowed 243 CFM @28” an increase of only 2 CFM over the 48mm unit. Seeing as the flow bench is not always a tell-all in performance, we then installed the part on the same 103 cu” TC as before and proceeded to test and tune the 51mm throttle body. The results were not good; the HP and Torque both went down about 3-4 units in the low and midrange RPMs, but the power above 4750 RPM increased by about 4. SEE DYNO

All in all I would say that the 51mm ported stock throttle body was a failure, because not many people spend a lot of time riding above 4750 RPM, but we were determined to make the 51mm throttle-body work. We thought about what we could do to increase the velocity behind the butterfly. Increasing the velocity and the CFM would increase the power everywhere and make better use of the big butterfly. The port runners were then cleaned up and some very high-tech epoxy was used of fill the ports (to replicate the port runners of our J.E.T. intake manifolds). After the manifold was epoxied and ported, we tested it on the flow bench and it flowed a lot more with the epoxy, 257 CFM @28”. Now we were faced with a manifold that was about 15% smaller, had the proper taper that an intake should have, and it flowed 14 more CFM (38 more CFM than stock!!!!) This could only mean that the port velocity was much higher in the manifold with the epoxy. So we took the 51mm High-Velocity throttle-body to the dyno.

Unfortunately, we were unable to retest the epoxied 51mm High-Velocity throttle body on the same 103 cu” TC, so we took advantage of a very mild 106 cu” TC with a very good baseline on it and a stock throttle body. The 51mm epoxy unit was installed and properly tuned in. This is where the results turned for the better… way better. SEE DYNO

The HP went from 100 HP to 107 HP and the torque went form 110 ftlbs to 115 ftlbs of torque. We also noticed the power increases were produced throughout the entire RPM range and not just in the higher RPM areas. These results were very encouraging find and could only mean one thing; we accomplish our original goal.
As a result, Johnson Engine Technology, Inc. can now offer a service that will take the stock throttle body of a potential customer and modify it for optimum performance without the high cost of the aftermarket part.
__________________
Life Blows... Enjoy the Breeze

Semper Fi

This confirms what Eric AT HPI said to me about the turn into the port. It is to abrupt and by adding something to smooth it out it flows better.  My only question would be I would hate for that expoxy to come lose and suck it down the engine.

[FLTRI]

"After the manifold was epoxied and ported, we tested it on the flow bench and it flowed a lot more with the epoxy, 257 CFM @28”. Now we were faced with a manifold that was about 15% smaller, had the proper taper that an intake should have, and it flowed 14 more CFM (38 more CFM than stock!!!!) This could only mean that the port velocity was much higher in the manifold with the epoxy."

"The HP went from 100 HP to 107 HP and the torque went form 110 ftlbs to 115 ftlbs of torque. We also noticed the power increases were produced throughout the entire RPM range and not just in the higher RPM areas."

So, once again it's not the size but how you use it, and bigger is not always better.

[Bagger]

So, once again it's not the size but how you use it, and bigger is not always better.

FLTRI, you may have read these articles before, if not here's Robert Johnson's (JET) take on port size and velocity.

http://cycledoctor.com/Articles/JET.htm
http://cycledoctor.com/Articles/head2head.htm

[Don D]

"If so, we can then agree that the entire engine build is what dictates TB size, not individual mods, ie: ci, cams, etc."

You could substitute the word "pipe" or "cam" or whatever part of the build for the word "TB". I see too much of this and not viewing the motor as an engineered system rather than picks off a menu.

Regarding the JET philosophy, it did have merit in the EVO days and reducing the ports did help mild builds with 80" motors. Today if we want to have a torque monster that stops at 5K it will work too on a 95" motor. If it were mine though I would prefer a little more top end and sacrafice a small amount down low. Cams and cam timing and exhaust can be coordinated to fine tune these things without pulling the heads or just Blueprinting them.

Good thread!

Agree with most all said here.

[FLTRI]

"FLTRI, you may have read these articles before, if not here's Robert Johnson's (JET) take on port size and velocity."

Interesting to note how few listen to, and take the advice from, those who do not subscibe to the bigger is better misconception.
Bob

[GoFast.....]

"FLTRI, you may have read these articles before, if not here's Robert Johnson's (JET) take on port size and velocity."

Interesting to note how few listen to, and take the advice from, those who do not subscibe to the bigger is better misconception.
Bob

Bob, It because it is a half truth. Bigger is always better if you have the combination to flow it without losing velocity

[FLTRI]

"without losing velocity"
There enlies the key to TB sizing rather than just assuming because it's bigger it wants/needs more air.
I mean there a folks with $700+ HPI TB, 95ci with se203, tw6, tw26, etc, and stock heads, even when the dyno confirms no power improvement.

[Faast Ed]

Bob, It because it is a half truth. Bigger is always better if you have the combination to flow it without losing velocity

Not every build involves "the combination to flow it without losing velocity".  Hello? Very many builds do not fit that catagory.

Soooooo.....,   "Bigger is NOT always better".  Whole truth, not half truth.

[FLTRI]

"I never put a Tb that is too big for the combination of build no matter if it is a small block chevy or a Harley"

How can you be sure? EFI is not quite the same as a carb when it comes to determining what is too big.

It is much easier to determine if a carb is too big because it won't feed fuel properly.

EFI systems dictate the fuel quantity and timing so it becomes much more subjective as to what is too big for a TB.

This is why, for the street, I like to error on the side of smaller rather than larger. This attitude assures excellent throttle response and low rpm smoothness.
If it was a race bike my attitude would be much different, as the upper rpms (>4000) are the most important so bigger could be better.

I guess if I were selling TBs I would always reccomend bigger than what the customer currently had mainly because the engine will run just fine with a bigger-than-necessary TB, maybe just down a bit in the response and low rpm manners.
A carb salesman could not get away with selling bigger than necessary because the engine would run like crap.
JMHO, Bob

[fuzznut5197]

This confirms what Eric AT HPI said to me about the turn into the port. It is to abrupt and by adding something to smooth it out it flows better.  My only question would be I would hate for that expoxy to come lose and suck it down the engine.

While JET is mentioned, has anyone ever seen this:

http://www.veta.com.au/pages/applications/lotus%5B1%5D.pdf

I was surfing around looking for why you would put golf ball dimples in the intake (from VTF), and stumbled across it. Looks like a JET or R&R port. But my pea brain still doesn't understand it.