Restrictor Plates in Intake Boot

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sirch345
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Re: Restrictor Plates in Intake Boot

Post by sirch345 » Fri Jun 01, 2018 9:40 pm

jchesshyre wrote:
Fri Jun 01, 2018 9:30 pm
sirch345 wrote:
Fri Jun 01, 2018 9:24 pm
I was really referring to the original Honda OEM inlet rubbers. Thinking about what you said "they seem very securely held in place" I wonder if the Tourmax ones are not so pliable as the original ones would have been when they were new.
I know from experience cheaper rubber motor parts are often more of a plastic type material that doesn't have the flexibility of better quality rubber. Can you not see if you can remove the metal rings from the old ones first :?:

I'm not sure how the ratings of 72Kw and 98PS work, unless 98PS is meant to be 98bhp,

Chris.
I know what you mean about plasticky parts, but actually they are quite rubbery! I just mean I can't see how or which way you'd bend them and which way the metal part would come out.

Re. the power figures, google says 72 kW = 96.5 bhp = 97.9 PS.
That's interesting. IIRC back in the day motorcycle magazines road test reports on the Honda Firestorm were quoting around 103bhp for the earlier bikes (16ltr fuel tank models) at the rear wheel. When the later bikes came out (19ltr fuel tank models) the mags were then stating around 98bhp at the rear wheel.

I'll admit I've never pulled the metal rings out of the inlet rubbers myself, but I have heard of one or two on here who have removed the restrictions (I think Virt was one of them). I don't remember them saying they had to buy new inlet rubbers to make the bike unrestricted.

I think VTRDark had removed the metal rings in his inlet rubbers, but I could be wrong on that.

May be the Dremel will be getting a good work out tomorrow after all :wink:

Chris.
A closed mouth gathers no foot. :thumbup:

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Re: Restrictor Plates in Intake Boot

Post by jchesshyre » Fri Jun 01, 2018 9:46 pm

Yeah, I think perhaps something else must be different in the inlet tract to tune for the restrictor in the later models, but don't know what as the carbs are pretty similar between the early and late models - IIRC the later ones got slightly leaner needles (as per US spec) but otherwise I'm not aware of any differences.

Perhaps it's going rich up top - it did feel more vibey than usual up there as well which I know can indicate high-end richness. Maybe...given what we know about these carbs usually operating in a 'turbulent' rather than 'laminar' flow and that changes that you'd expect to cause leanness can actually cause richness, perhaps the higher inlet speed caused by the restriction changes the flow through the carbs such that leaner needles are necessary? Hmmmm...

But also if I'm completely used to it revving nice and freely up to 9k and above then even the seven bhp difference might be noticeable. I've never used a dyno so have never had the experience of feeling for specific bhp output differences when tuning a bike, so don't really have a reference.

In any case, they're coming out tomorrow!

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Re: Restrictor Plates in Intake Boot

Post by sirch345 » Fri Jun 01, 2018 9:49 pm

Good luck with them :)

Chris.
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Re: Restrictor Plates in Intake Boot

Post by VTRDark » Sat Jun 02, 2018 12:19 am

They definitely are restrictors and it definitely is restricted to 78 kW. Horrible! Gets weaker over 7k rpm instead of stronger and struggles as redline approaches.
Now that is very intresting thanks for the info as that is good to know and puts a diffrent perspective on things. What you have to remember is that you can't gain on top without loosing somewhere else. Everything is a compromise so you may just find out that you loose a little on the botton end and it may or may not have an effect on intake reversion depending on if my theory is right or wrong. Saying that I quite fancy going the other way and installing them as I have never had them :lol: I can always do with more bottom end :biggrin

See the following link for more info on reversion and note that
Reversion refers to the movement of exhaust gases in the reverse direction, backing up through the intake flow path
Which is basically describing what we call a carb fart. So hopfully you can understand how I came to the previous conclusion.

Reversion redirection device for an internal combustion engine

Now this I'm not entirly convinced by but is a theory I have. A lot of folk suffer from carb farts as well as the bike suddenly stalling and often it is said to increase the idle speed. Not the aproach I would take as I see that as masking over the issue but it gets those less mechanically minded out of trouble. If you think about the inlet throat and plates (restrictors), having the half moon shape makes it smaller so in theory this should increase the velocity of the mix which is kind of like the same effect as increasing the idle speed. One can turn up the idle which shoves more mix in or do you give the mix a higher velocity shoving the mix in faster which in turn is pushing against the exhaust gases trying to escape out the wrong valve during overlap. :think: A reason why I think the restrictors may have been Honda's way to try to eliminate / minimise reversion (carb farts) and possibley the stalling as things spit back.

Another theory but I maybe wrong and it's related to above. It maybe that velocity is not increased and they do act as a restrictor but pausing the flow and the plate being there acts as a barrier to help prevent / minimise any spit back getting past that point and back up through the carbs and airbox. It's all very complex when you start to dig into things like porting. Some folk are happy to smooth off the inlet track and remove the textured surface but that is there to create a Golf Ball affect. The same reason a Golf Ball is pitted. It would be great if somone with an engine flow meter could measure things with and without the restrictor. I wonder if there is anyone on the forum with access to such tools. It would be good to get a true reading of the differances with and without.

The question has to be asked why would Honda restrict later bikes. Yes they are restrictors of sort but for what purpose and how much real world effect does this have. If they wanted a true restrictor they could have done as they did with the Jap bikes and IIRC do it on the ECU side of things which is another reason why I think they serve a purrpose. They may even have changed the mapping slightly to compensate for these restrictors, a slight advancement has said to have been added in later models so no point in a Factory Pro +4 advancer. One things for sure it's cause and affect and when you change one thing it has an affect on another. The question is where.

Let us know your findings. Intresting indeed but if you want more top end oomph then change your cam profiles at the sacrifice of loosing it somewhere else. :wink:

That PS measurment is a new one on me.
PS explained

Though it’s still commonly used by carmakers, PS or Pferdestärke (horse-strength in German) was actually replaced by kW as the EU's ‘legal’ measurement of engine power in 1992.

One PS is about 98.6% of a brake horsepower – the two are virtually interchangeable, and PS is sometimes referred to as 'metric horsepower'.
https://www.which.co.uk/reviews/new-and ... -ps-and-kw
[BBvideo=560,315]https://www.youtube.com/watch?v=3lQ6e0npIKs[/BBvideo]

:lol: :lol:
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tony.mon
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Re: Restrictor Plates in Intake Boot

Post by tony.mon » Sat Jun 02, 2018 6:52 am

You can simply pull the restrictor out with pliers.
It's held in with small pins in the recessed section.
Ideally you then fill in the thin channel that's left but tbh I've never bothered.
It's not falling off, it's an upgrade opportunity.

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Re: Restrictor Plates in Intake Boot

Post by jchesshyre » Sat Jun 02, 2018 10:55 am

Well, wemoto.com have got straight back to me with many apologies and are sending the unrestricted ones out to me pronto.

FWIW the Tourmax part numbers are CHH-25 for the '98 PS' ones (that I received) and CHH-26 for '110 PS' (the right ones).

They've said I can chuck the restricted ones – anyone want them? DIdn't think so :thumbdown:

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Re: Restrictor Plates in Intake Boot

Post by 8541Hawk » Sat Jun 02, 2018 2:48 pm

Well as I stated before the intake restrictions where for the Euro 100hp limit that was in place when the bike came out.
The first 2-3 years of production the bike were rated at 105HP.
The easiest and cheapest way to met the HP requirements is an inlet restriction.
They have no other purpose.

This is different than the Japan restrictions. In that case it is a top speed restriction. That is the reason for the Japan market limiter to be in the ECU.

Yes you can pull out the metal bits and I have run isolators like that but I can say the carbs "feel" like they seat better with the metal bits left in place.
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Re: Restrictor Plates in Intake Boot

Post by sirch345 » Sat Jun 02, 2018 4:14 pm

jchesshyre wrote:
Sat Jun 02, 2018 10:55 am
Well, wemoto.com have got straight back to me with many apologies and are sending the unrestricted ones out to me pronto.

FWIW the Tourmax part numbers are CHH-25 for the '98 PS' ones (that I received) and CHH-26 for '110 PS' (the right ones).

They've said I can chuck the restricted ones – anyone want them? DIdn't think so :thumbdown:
That's good news, very good service as well,

Chris.
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Re: Restrictor Plates in Intake Boot

Post by VTRDark » Sat Jun 02, 2018 4:24 pm

Well as I stated before the intake restrictions where for the Euro 100hp limit that was in place when the bike came out.
That don't make sense. There's been plenty of bikes over the years that can go over 100hp, what about the SP's, there is no limit...yet. Though there where tests in some countries but no widespread limit. It's only in recent years that they have been talking about putting a 100 bhp limit on things as we move towards an even more screwed up society where everything is designed to push money up the chain and into the mainstream manufacturer's and major corporations hands.

And the following article was written in 2010 for proposed European Union regulations way after production of the last VTR.
https://rideapart.com/articles/the-fact ... ycle-limit

Emissions is something else and it may possibly be an emissions thing to go along with the PAIR.
Well, wemoto.com have got straight back to me with many apologies and are sending the unrestricted ones out to me pronto.
Wemoto are a very good company. Never had any issues with them over the years. Which reminds me I must put an order in with them for some coolant and few other little bits.
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Re: Restrictor Plates in Intake Boot

Post by jchesshyre » Sat Jun 02, 2018 4:29 pm

I think by 'Euro' Hawk means 'some European countries' perhaps, rather than all of Europe? As far as I know France has had a 100 bhp limit on bikes for a while. And I recall reading somewhere a post about maybe Sweden having restricted Firestorms?

However, looking at parts fiches from 1998, the English and French bikes have the same part for the inlet stubs (16210-MBB-950 and 16220-MBB-950, front and rear respectively). The restricted stubs are 16210-MBB-610 and 16220-MBB-610, and a search reveals that they were fitted to German, Austrian and Japanese bikes from 1997, and other European countries (and Australia) from various years in the early 00s depending on country.

See here https://www.bike-parts-honda.com/microf ... B-610.html (restricted) and here https://www.bike-parts-honda.com/microf ... B-950.html (unrestricted) for lists of models for each type.

Getting a bit geeky here, but I notice in the workshop manual that the restricted bikes also run leaner needles and stayed on #45 pilots when the others were changed to #48 in 1998. I have a hunch that this was not just for emissions but because the restriction in the inlet actually causes the bike to run richer...

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Re: Restrictor Plates in Intake Boot

Post by 8541Hawk » Sat Jun 02, 2018 5:41 pm

Sorry for the vague Euro comment....didn't mean anything by it....

I believe the main offender was Germany actually with a few others joining in.

In my defense, you know you all look the same to us 'mericans....... :Ball Kick: :lol:
Though with things like the EU coming and going and all a lot of folks around here being very bad at geography it is easy to get in the lazy habit of just referring to things and specs as "Euro".
Sorry for any offense. :angel:
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Re: Restrictor Plates in Intake Boot

Post by 8541Hawk » Sat Jun 02, 2018 5:48 pm

Back to the topic.
The restrictors can only change the flow of the intake tract after the slides are all the way open.
That is why the bike "feels" normal until you get to the top end, then it falls on its face.

Why they make the bike run richer is smaller port = higher velocity through the carb..... that transition into laminar flow which increases the efficiency of the jets.
So yes technically you can pick up a little on the bottom end with them but it in no way makes up for the loses up top.

In the end, the only reason for them is to limit HP. There are no gains to be had by running them IMHO. :thumbup:
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Re: Restrictor Plates in Intake Boot

Post by VTRDark » Sun Jun 03, 2018 1:38 pm

Intresting.....thanks guys always good to learn something new. :thumbup: Does that mean we can blame the French. It's always their fault. :lol:
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