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[TexasBowhunter]

I'm seeking some info on there HPI intakes and have a question about there latest offering...
its where they offer a 55mm T/B with a 58mm manifold attached to it...vs. the 58mm work of art they have available...
I'm getting all my information together for the 120R crate I plan on getting soon and was curious as the how well this unit performed?
Talking to the rep he mentioned that the 55mm-58mm would allow much more torq down low and in the mid range and with the 58mm it would have more torq at the top and not do near as well in the low end torq area...
with this said from what I have seen the 120R doesn't seem to be inadiquite in the bottom end when we speak torq...
Anybody got any views on this one and/or used it and can show a dyno sheet by chance...
Thanks
paul

[HILLSIDECYCLE.COM]

I'd lean in the direction of the 58mm t/body, with their 62mm manifold, "Max-Flo" set-up, 1.800" manifold I.D.
Scott

[strokerjlk]

Talking to the rep he mentioned that the 55mm-58mm would allow much more torq down low and in the mid range and with the 58mm it would have more torq at the top and not do near as well in the low end torq area...

I think that is correct, more times than not.
 "much more" not so often.
that brings up the question, is it felt on the street or is it just seen on WOT dyno sheets?
when your looking at WOT runs under 2500 on the dyno,it's just that WOT.
 long explanation short. when you wick the throttle on the street you seldom  just wick it to WOT at 2200 rpms.or at least it isnt a good idea in most riding situations. 1st gear or maybe 2nd gear you might do it there but the gearing is much more forgiving and your up on rpms so quick,it isnt like a 1:1 ratio dyno run in 5th or 6th gear. you also wont be dropping back down to 2200 rpms on the next shift if you are at WOT.
Now at cruise....if you shift up through the gears in a manner that you are falling back to 2200 then up again,you will be at partial throttle openings. and either t/b you mention can perform there equally well

[HD Street Performance]

Listen up this is a tuner, he does this for a living
An overly large throttle body may not kill a dyno sheet but it sure will kill the street manors of an otherwise good running motorcycle due to small blade angles now feeding proportionally much more air. Very twitchy on a cable control TB and a tuners challenge with FBW

[fatboi1959]

I'm running the 120R, HPI 58, 1.800 Intake runners, Rev performance EMS. When all was installed the first test rides were a little challenging at maneuvering speeds because of the touchy throttle. My set-up is a cable operated (2007) and decelerating from say 3,500 with the throttle closed (or any higher rpm) you could tell the vacuum was very strong in the intake and as you started bringing your throttle open to meet the speed you were trying to maintain the engine would surge ahead for a split second then run perfect. This can really get your attention charging into a corner! As i continued putting the miles on, and now around 5,000 this symptom has almost completely disappeared. As Don and others have stated the big throttlebodies can and will degrade the driveability of the bike especially at maneuvering speeds. Rev performance said if i sent them my ECM they could make it less touchy but i am now happy with the driveability of my bike and am going to leave it alone. This symptom has repeated itself every time in the exact same spot so you know it's coming. 

[strokerjlk]

An overly large throttle body may not kill a dyno sheet but it sure will kill the street manors of an otherwise good running motorcycle due to small blade angles now feeding proportionally much more air. Very twitchy on a cable control TB and a tuners challenge with FBW

that wasn't exactly what I was saying Don.
so in this case we are talking 120r here ,and 55 mm vs 58 mm. I dont see it giving up anything anywhere with a 58mm. on the street.
on the dyno it wont be any better down low,and all things the same...the 58 will lose on the bottom. but then again we don't normally just wick the throttle to WOT instantly at 2200 rpms in 6 th gear.
I agree with what you are saying, if and when it is overly large. but I believe in the last couple years, more and more  we see that what was once though to be to big is more the norm now. some of that is the manifolds,and some of it is, we are seeing that they can be tuned to run at partial throttle,and still have peak hp/tq gains up higher.
remember when  58MM was taboo for a 103?

[timo482]

this might be considered a thread jack - if so,  apologies.

this kind of behavior with large throttle bodies is why many cars in the days of carbs were set up so that at low speeds only two barrels of carb were working - and the smallest barrels at that - only when the engine was raging along did the other 2 or 4 open up. many 6 packs were set up so that there was mechanical linkage that opened the two other carbs when you mashed on it - if you did that going two slow the car would nearly stall before going, you had to sort of ease into it till the rpms were rising and then mash it. my boss used to break rear ends on a regular basis - mashing the 6 pac too soon. lots of fun though.

with our bikes we only have ONE barrel - so getting it right is important - if we tune for wot at 6000 rpm we can easily make them un drivable on city streets in town.

[HD Street Performance]

we see that what was once though to be to big is more the norm now

Remember when 2.120" valves and ports with bowls that are 2.XXX were taboo. EFI is a game changer, plus let's face it 120" is a big motor.
Thanks for the clarification, I respect your opinion.

TBW can be the redeeming factor, software works with the ECU to act as a damper from overly fast blade opening assuming the tuners adjusts that properly and the user has the proper software.

[HILLSIDECYCLE.COM]

We use 62mm's on 124"ers, without any issues.
And have 58/62 combos on 120"s.
No ill manners.
Scott

[Dan_Lockwood]

I'm not sure if this is relevant or not, but back in about 2001 I was looking for a nostalgic intake system for a new 540" BBC I was going to use in a '55 Nomad gasser.  I wanted to look at the 8-stack injection systems of days gone by.  There are lots of companies now that convert them over from mechanical to electronic and also make new retro looking 8-stack systems.

Okay, now to the comments.

When doing my checking around it was common that most had butterflies in the 2" and up range, more than I thought I really needed for 650 hp.  I was told, unlike a carb that requires air velocity to maintain a good atomization of the fuel with the air, direct port induction system of today will only use what they need.  The all said that going too large on butterflies was not detrimental to performance and the electronics would do their thing based on the "tune" to make it work.

So with the new larger throttle bodies here under discussion, does it really matter if they are on the just a bit large size?  I'm sure perfectly tuned volume is best, but for our purposes, would you just not get a 60'ish diameter throttle body and tune accordingly?

Comments on this thought process would be greatly appreciated.

Thanks and this is a great thread...

[HD Street Performance]

When doing my checking around it was common that most had butterflies in the 2" and up range, more than I thought I really needed for 650 hp.

IR VS paired cylinders changes the requirement. Single cylinders (yes 8 of them) have a lot of pulsation

[strokerjlk]

we see that what was once though to be to big is more the norm now

Remember when 2.120" valves and ports with bowls that are 2.XXX were taboo. EFI is a game changer, plus let's face it 120" is a big motor.
Thanks for the clarification, I respect your opinion.

TBW can be the redeeming factor, software works with the ECU to act as a damper from overly fast blade opening assuming the tuners adjusts that properly and the user has the proper software.

EFI certainly is the game change. it can make a great combo shine. and it can cover a multitude of sins.
I think the TBW redeeming factor is, Lambda based fueling. while T/P has advandages,Lambda based fueling can really calm and smooth out a dirty motor or one with a lot of overlap.

[HILLSIDECYCLE.COM]

HPI has also whipped up plenum spacers for us in the past, which the length is dictated by the cam used.
Scott

[GMR-PERFORMANCE]

Many times it will come down to real testing.  We swapped a stock t/b on a 107 kit with a 54 cam and the larger 55 t/b from HPI picked up in the low and mid range area. SO one might think that it will always do this. Not the always the case. If a unit is too small to start with then of course the gain will be there.

Just finished another 107 HP Kit engine build. Ran the HPI 55 FBW , it made the same power as my own bike with a 58FBW and the HPI manifold.  SO did I find the point where larger does not work, or do the two units flow the same??

With proper tuning it seems hard today to install a t/b that is too large. Mike Rolland did some testing a while back with 57MM( I think it was 57mm)  t/b on stock engines and could not create any issues, gains where almost nothing as I recall. The air pump will only use what it can, being that you are firing the fuel into the intake port at 59-60 psi hard to mess that up. Even the stock units can get the job done, adding volume may be useful, or it may not. Again what you see on paper may turn out to be nothing under normal riding. I know that if I was racing or laying into the engine hard, I am not going to pull a tall gear and low rpm. Drop it down a gear or two ,  get the R's up and run the engine up to peak hp point.

WOT pull is a dyno test, not how one rides on the street.

I do not think you are going to hurt the over all set up by running a larger plenum.  I plan on running a 64MM on my 120 I am putting together. Why not,.. who would have thought I could get a 58 to work correctly with no downsides on a 107. It will come down to the tune being correct. It may require a bit more work in the low rpm areas to ensure great drivablity but it can is is done on a regular basis.

[sadunbar]

I'm running the 120R, HPI 58, 1.800 Intake runners, Rev performance EMS. When all was installed the first test rides were a little challenging at maneuvering speeds because of the touchy throttle. My set-up is a cable operated (2007) and decelerating from say 3,500 with the throttle closed (or any higher rpm) you could tell the vacuum was very strong in the intake and as you started bringing your throttle open to meet the speed you were trying to maintain the engine would surge ahead for a split second then run perfect. This can really get your attention charging into a corner! As i continued putting the miles on, and now around 5,000 this symptom has almost completely disappeared. As Don and others have stated the big throttlebodies can and will degrade the driveability of the bike especially at maneuvering speeds. Rev performance said if i sent them my ECM they could make it less touchy but i am now happy with the driveability of my bike and am going to leave it alone. This symptom has repeated itself every time in the exact same spot so you know it's coming. 

I started with a HPI 62mm/1.800 runner throttle body on my 120r (with T Man 662-1 cams/Rev. Perf. EMS).  I also was unhappy with the low speed parking lot maneuvering.  I installed a HPI 55mm/1.800 throttle body.  It calmed down the low speed maneuvering nicely.   I'm very pleased with the result.