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[Rooster]

I am using Hp Inc's 58mm throttle body with bigger injectors on my 131. Very good quality and flows great. A little pricey compared to boring but worth it IMO.

[Black Diamond]

Hey Howie

HPI said 54mm was a large as they could open up the stock TB. The only changes to Brian's tune was done at the top end. Actually took some fuel away to keep it in line with his tune. This was a quick turn around switch as I was on the road again. I hope to wring it out over the winter as we don't have much motorcycling in Dec - Feb. LOL.

My tuner is going to T-Man's for their tuner class soon.

JW
[/quote  

Its seems odd at first, but a larger TB will indeed send the existing tune to the rich side. The MAP sensor sees more KPA or less vaccum at the same throttle position.
The computer responds with more fuel.

Anybody have a 50mm FBW TB for sale, I'm interested. Sounds like an interesting dyno test.

Steve George

It would be great if someone such as yourself would do a test like this. With your skills, knowledge and insights we could all learn something.

HPI still can not predict when they will have their own fbw units available. I'm not sure why the aftermarket is so far behind on this area.

JW

[Black Diamond]

I am using Hp Inc's 58mm throttle body with bigger injectors on my 131. Very good quality and flows great. A little pricey compared to boring but worth it IMO.

Rooster

Do you have the HD electronic throttle control system on your 131?

JW

[Hoist!]

For my build, I am getting virtually the same results SE 58mm TB ported and polished vs the HD/HPI 54mm TB using the same high flow (5.3) injectors. I am not saying this will be true in all cases. As I posted earlier I do not have the d sheet on this however, I may pick one up in the near future and will share it. As you know, we are extremely limited in our choices at this time. I just wanted to play with this to see if I'm getting all I can from my build. Not saying anyone else should toss their SE 58mm based on my experience. Just want to share what we're seeing.

You are correct, as with any part, eBay is the place to try to recoup some of your investment. After our testing I will be selling one or the other.

JW

You sure about that? I thought the SE's were 4.89.

Did you consider an HPI TB at all in this thought process of changing out TB's? Just curious how you came to the conclusion to go this route with your build.

Hoist!

[Black Diamond]

You sure about that? I thought the SE's were 4.89.

Did you consider an HPI TB at all in this thought process of changing out TB's? Just curious how you came to the conclusion to go this route with your build.

Hoist!

Hi Howie

I have the following injectors

SCREAMIN’ EAGLE PRO HIGH FLOW INJECTOR
KIT – 58MM THROTTLE BODY
Injectors provide fuel delivery at the rate of 5.3 grams/
second, 23% more than Original Equipment injectors.
Recommended for use with engine configurations making
more than 100 rear wheel horsepower. All EFI-equipped
models require ECM calibration (sold separately). For race
application only.
27796-08 $139.95

I talked with HPI. To date they do not make a throttle body that work with the electronic throttle control system (no throttle cable) I have not found any options other than the SE 58mm or modify the stock 50mm to 54mm.

When I had that oil bypass problem due to the valve seals leaking, I discovered I could not get a replacement filter for the 58mm system except from HD. I asked K&N when they would be marketing the 4 hole filter this system uses but they had no answer. Additionally, I had one of the flanges crack on the 58mm on my trip to N.C. creating an air leak.

JW

[Rooster]

Rooster

Do you have the HD electronic throttle control system on your 131?

JW

I don't know as I didn't put it on. All the stock stuff went back on. Mine is an 07 not FBW, anything else I would have to ask.

[Heatwave]

Hey Howie

HPI said 54mm was a large as they could open up the stock TB. The only changes to Brian's tune was done at the top end. Actually took some fuel away to keep it in line with his tune. This was a quick turn around switch as I was on the road again. I hope to wring it out over the winter as we don't have much motorcycling in Dec - Feb. LOL.

My tuner is going to T-Man's for their tuner class soon.

JW
[/quote  

Its seems odd at first, but a larger TB will indeed send the existing tune to the rich side. The MAP sensor sees more KPA or less vaccum at the same throttle position.
The computer responds with more fuel.

Anybody have a 50mm FBW TB for sale, I'm interested. Sounds like an interesting dyno test.

Steve George

I will be completing my engine upgrade this coming week ( http://www.cvoharley.com/smf/index.php?topic=40465.0 ) and will have my stock 50mm throttle-by-wire TB available for sale. I will also have the stock injectors, stock A/C back plate, stock A/C, 255 cams, stock rocker arms and stock pushrods from my 2010 110" SEUC available for sale. PM me if you're interested.

[Steve Cole]

There is a lot of talk about larger throttle bodies but we have found they are not necessary on engine builds 103 cu in. and smaller. If you would like to check to see if you need one there is a simple test that can and should be done prior to replacing one. With a Scantool you need to first check the MAP reading with both switches turned on and engine off. This will give you the Baro pressure where you are at. Next you need to do a WOT run up through the engine RPM range, again checking the MAP reading. An example would be you got 100 kPa in the first test and 100 kPa in the second test. No need for a larger Throttle Body. Now if your second test gets you 85 kPa when you started with 100 kPa then you MAY need a larger throttle body. The reason I say may is because you are showing an intake restriction and you need to find out why. Could be nothing more than an air filter issue but it needs to be checked to know what it is. As with any changes you have to retune the ECM to properly function with the changes you've made and I've seen it many times where a change got made and the tuning was not corrected.

[Heatwave]

Facts are always a helpful input to a discussion like this. When looking at almost all of the stronger performing 103 engines, they almost always have a throttlebody larger than 50mm http://www.woodcarbs.com/dynoruns.htm

[Steve Cole]

Having one and needing one do not always go hand in hand. Having a larger than needed throttle body takes away some of the velocity at lower engine speeds which reduces throttle response. So if your after nothing but bragging rights from the dyno at high engine RPM then bigger is better..............  Another test one can preform would be to watch with a scantool and see how much throttle is required to drive MAP to it's limit as described in my prior post. When you only need to give it 25% throttle at 2500 RPM to get you to max kPa you will begin to see what I mean.

[SBB]

You sure about that? I thought the SE's were 4.89.

Hoist!

4.89 are for Cable operated TB's.
5.3's are for TBW TB's.
That is per the 2010 SE catalog.
Why there is a difference I haven't a clue.

 

SBB

[SBB]

If a 110 or 117 run equal or better with as 54mmTB instead of the 58mmTB then why does Hoist and sadunbar's bike have 62TB on them?

What I'm reading makes sense but I see conflicting info as to size requirements for a 110/117.

SBB

[sadunbar]

If a 110 or 117 run equal or better with as 54mmTB instead of the 58mmTB then why does Hoist and sadunbar's bike have 62TB on them?

What I'm reading makes sense but I see conflicting info as to size requirements for a 110/117.

SBB

The cubic inch of a motor is not the overriding factor to consider when choosing throttle body size...  The capacity of a motor to flow air is the most significant factor to consider - air cleaner - intake - heads - cams - exhaust.....you want your throttle to be sized to take full advantage of the rest of the package - not just the cubic inch of the motor .  There is more performance downside to having to small of throttle body than there is performance downside of having to large of throttle body.... 

[SBB]

The cubic inch of a motor is not the overriding factor to consider when choosing throttle body size...  The capacity of a motor to flow air is the most significant factor to consider - air cleaner - intake - heads - cams - exhaust.....you want your throttle to be sized to take full advantage of the rest of the package - not just the cubic inch of the motor .  There is more performance downside to having to small of throttle body than there is performance downside of having to large of throttle body.... 

Thanks.

   

[sadunbar]

If a TB is 58mm feeds sufficient air to your motor combination - a 62mm TB will only make the small throttle positions more sensitive - which in turn will make the "drivability" of the bike less desireable.

To large of throttle body will not result in less power....Having to large of thottle body will make the bike harder to ride smoothly at parking lot speeds.

But having to small of throttle body will result in less power...

Given those choices - I would prefer a slightly oversize throttle body vs. a undersized throttle body...  But the sizing of your throttle body should be based on your motors overall package - heads and cams being the most important factors - not your motor's cubic inch....