Maximum Effort Motor TB Requirements

[Ohio HD]

I'm collecting new parts to build another 124" from the ground up for my 2008 Twin cam SG. What I mean by maximum effort is I'm not concerned with what the left side of the sheet does, it'll land where it lands. I'm staying relatively moderate for cams for an application like this as the bike needs to be street-able and mechanically dependable.

My main question for those that have built big motors and are familiar with HPI TB's, will the 62/64mm I have be enough to keep from being a choking point in the induction? I have no idea what the TB is capable of flowing. HPI won't give the information out, and I realize it all depends on what the TB is attached to. I guess one has to ask as well is the airbreather enough?

Would going to the HPI 68mm TBW be too much or make tuning for low speed difficult? I anticipate reaching over the 160 hp line, but one never knows.

Below is the basic motor data.


124" Twin Cam
Static compression - 12.2:1
Cams - S&S 640
110 Heads with 1.800" intake port - flows 343cfm @ 28in
Air breather HPI V2 - flows 429cfm @ 28in
Throttle body - HPI 62/64mm 1.800" runners - flow ?
Exhaust - Burns stainless

[kd]

Did you discuss the TB with Jimmy?  HPI initially built 9 62/64 throttle bodies and had 8 out for testing for months.  They were just completed and confirmed when I spoke to him and bought number 9.  They then went into production. He told me then it outflowed the 66 Throttle Hog.  The HPI is smooth and as well mannered as a stock engine until you twist it up. Then it performs. My sheet for the 120 it went on is in the dyno section and includes a Burns exhaust.  That pipe is the first prototype All Holds Barred system and the head pipes are 6 - 8" longer by my request to help hold some torque.  It's not a 640 (it's a 660SM) because I wanted more left side torque and I do believe the 640 would give up more on the right. Dan Baisley did my MVA heads (and port matched the 1.8 manifold) for the cam and the torque I wanted so not really a good comparison but they do flow well.     My compression is set at 11.3 to your 12.2:1.

The 120 makes 148 power / 144 tq with the Burns exhaust and 62/64 HPI. I seem to remember a version of Ray's barn built 124 hit the 160+ using the 640, similar compression, Larry's heads, his home built Burns exhaust and 66 Throttle Hog. IMO your recipe with the extra compression should get you easily on target.

https://harleytechtalk.com/htt/index.php?action=dlattach;ts=1542728950;topic=99409.0;attach=81713

[Ohio HD]

Ray did hit the 160 mark with the 640's, his 66mm has been worked on, it's flow is more than out of the box. My head porter tells me that the HPI 62 will outflow the S&S 66mm as they come out of the box. I believe him. I suspect the 62/64mm will give enough air, but I don't want to cut myself close if it's marginal. I don't mind investing in the 68mm and a V2 breather for it. I just don't want a combination that's not going to tune well in the low end.

I've been using a 62/64mm since 2017, I have one of the early TB's they made. I never get any exact answers from HPI. Just some could be and should be. I tried to find out more about their stainless exhaust systems, it was futile. So I did the logical thing and called Burns.

[04 SE Deuce]

 Glad to see you're not planning on slowing down any as you head toward retirement. 

Your head guy and a flow bench should answer your throttlebody question, right?

[kd]

One of the differences with the 62/64 is more volume behind the throttle valve.(hence the 64)  I spoke to jimmy about that and got a subsequent read from strokerjlk.  I asked Jimmy and Jim if it would benefit tuning by softening the pulse in the short intake tract.  They both agreed there would be a benefit tuning.  The larger volume plenum and 1.8 runner also contributes to runner shape (as would any other larger design) with less negative flow characteristics up to the intake valve.

[hrdtail78]

I hit 160 plus /w 124 and 640 cams with a HPI 58 on my own street bike, S&S stealth /w taller filter and rain sock.  Have seen 200 plus with their 62 cable driven on 135 true max effort engine.  15:1, B2's, E90.....  TBW has a huge advantage with throttle blade control and will help the low speed manner of the 68, but I don't think it is necessary for your goals.

[Don D]

Consider that the throttle body is a part that can be changed during a tuning session. By doing a few runs at WOT and logging the MAP pressure you should have an answer about what is needed . The shape of the curves, where the power line noses over, and the look of the intake port (borescope) will matter too, an indicator of reversion being present or not.
Just a thought as the HP goals go up, S&S didn't miss the mark with the larger exhaust port and valve on the B2 heads. Have some Hurricanes here that are the case and point and poster child of the exhaust side needing help too. They flow as much as worked M8 heads on the intake side FWIW.

[kd]

Consider that the throttle body is a part that can be changed during a tuning session. By doing a few runs at WOT and logging the MAP pressure you should have an answer about what is needed . The shape of the curves, where the power line noses over, and the look of the intake port (borescope) will matter too, an indicator of reversion being present or not.
Just a thought as the HP goals go up, S&S didn't miss the mark with the larger exhaust port and valve on the B2 heads. Have some Hurricanes here that are the case and point and poster child of the exhaust side needing help too. They flow as much as worked M8 heads on the intake side FWIW.

  Don, you may recall the PM conversation we had over the exhaust valve size and port work on my MVA heads. It seems to be contrary to common belief but works in the right circumstances.

[Ohio HD]

Glad to see you're not planning on slowing down any as you head toward retirement. 

Your head guy and a flow bench should answer your throttlebody question, right?

Yes, and that may be a step in all of this, ship it, a head and the V2 breather to him when it arrives in a few weeks. Need to see how busy he is. I also need to determine just how far open the TBW plate is at WFO. I don't know that it opens at full 90° to the port. 

[Ohio HD]

I hit 160 plus /w 124 and 640 cams with a HPI 58 on my own street bike, S&S stealth /w taller filter and rain sock.  Have seen 200 plus with their 62 cable driven on 135 true max effort engine.  15:1, B2's, E90.....  TBW has a huge advantage with throttle blade control and will help the low speed manner of the 68, but I don't think it is necessary for your goals.

Jason I appreciate your tuning (and motor building) experiences giving feedback on this. Let me pose a few scenarios of what I may be  performing, and get your input if you don't mind. This is scenarios for my two bikes.

Bike 1 gets the new 124" for maximum output.
Bike 2 gets the existing 124" that's currently in Bike 1.

I have an HPI 62/64
I need a new TB for one of the bikes above,


Scenarios
Bike 1 is getting the new 124 as above.
Bike 2 will need a TB setup when the 124 from bike 1 goes there.

Option 1
Send the HPI 62/64 that's on bike 1 along with the 124 to bike 2, buy a new TB for bike 1.


Option 2
Bike 1 gets a new TB, a 68mm, or another 62/64 unit
Bike 2 gets the 62/64 that I have.


Option 3
Bike 1 keeps the 62/64 TB on and is used on the new 124 motor.
Bike 2 I buy an HPI 55/58 MAX flow or a 58mm elliptical.


I guess assuming the HPI 62/64 is ok for the Bike 1 new motor. A new HPI 55/58 would work well on bike 2. Bike 2 is less compression and less cam.

[Ohio HD]

One of the differences with the 62/64 is more volume behind the throttle valve.(hence the 64)  I spoke to jimmy about that and got a subsequent read from strokerjlk.  I asked Jimmy and Jim if it would benefit tuning by softening the pulse in the short intake tract.  They both agreed there would be a benefit tuning.  The larger volume plenum and 1.8 runner also contributes to runner shape (as would any other larger design) with less negative flow characteristics up to the intake valve.

As Jason mentioned, being a TBW there is control over the butterfly characteristics that a cable TB doesn't have. Up to some point it's tunable, until the TB is just too large for the application.

[hrdtail78]

What years are the bikes and what level of calibrations?  The difference being how much control you will have over the blade.  Earlier TBW cals gave you control of blade up to 2500 and later levels give control up to around 4500.  More control is always better.   

For a 124 shooting for somewhere in the 140's.   I recommend 55/58.  I haven't seen it choke down any power.  No modified or special backing plates required.   Great steerable manners and easier to tune. 

Obviously the best way to know is testing as mentioned.   But my recommendation would be 62 for your big power and 55 for your tame one.  These recommendations come with my assumption of both being street ridden and manners are wanted. 

That 135 with 62 is a ground up purpose built Mega Flo engine.   The 62 is cable and it's a B2 manifold.  With that cubic inch, .700 plus lift, and the flow sheets I have seen.  A 62 flows well. 

   

[Ohio HD]

The bike I'm building a new 124" for is a 2008. It'll be tuned with TTS.

The calibration used by the tuner on the milder 124" in the 2008 now was an FUF205. This motor will go into a 2009, but I want to tune it with PV simply because of the ABS. It's less hassle to use my Twin Scan 2 with the PV tune.

And yes, these will be ridden on the street. Just that the 2008 with the new 124" will be more of the play around bike.

[kd]

What years are the bikes and what level of calibrations?  The difference being how much control you will have over the blade.  Earlier TBW cals gave you control of blade up to 2500 and later levels give control up to around 4500. More control is always better.   

For a 124 shooting for somewhere in the 140's.   I recommend 55/58.  I haven't seen it choke down any power.  No modified or special backing plates required.   Great steerable manners and easier to tune. 

Obviously the best way to know is testing as mentioned.   But my recommendation would be 62 for your big power and 55 for your tame one.  These recommendations come with my assumption of both being street ridden and manners are wanted. 

That 135 with 62 is a ground up purpose built Mega Flo engine.   The 62 is cable and it's a B2 manifold.  With that cubic inch, .700 plus lift, and the flow sheets I have seen.  A 62 flows well. 

   

That's interesting.  What's the cutoff year between the "early" and "later" TBW control levels?  I can see that being important with a hot rod build intended for street use.

[Ohio HD]

Model years up to 2013 have a table that stops at 2,500 rpm. After that they stop at 4,000 rpm.

[kd]

Thanks. My 2011 RGU is not a problem but was built with consideration for parking lot manners.  With a left side angry cam it could matter.

[Barrett]

There's a few MegaFlo builds in the dyno section using the HPI55/58 with nice results.
They were sure happy with the throttle response.
https://harleytechtalk.com/htt/index.php/topic,90369.msg1038689.html#msg1038689
I would go with option 3.

[Ohio HD]

I was able to get Jimmy on the phone today, I think the trick is get him first thing in the morning.

So he was pretty much in line with what was suggested by Jason and Ed. He said use the 62/64mm on the larger build, and the 124" I have now with the 62/64mm, he said drop down to the 58mm. He said the 58mm will give the same overall results on that 124" I have now, but will enhance low end.

He said the higher compression 124 could handle the 68mm, but he said it'll rob me of low end that the cam would normally supply. He said the 62/64 would flow enough for it on the top.

So the plan will be to get an HPI 58 Elliptical and V2 breather for that one as well.