Bigger Bore Etc

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tony.mon
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Re: Bigger Bore Etc

Post by tony.mon »

The front stack receiving lower pressure is also why there is a deflector blade in the lid aiming air at the front intake.....
It's not falling off, it's an upgrade opportunity.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

"Actually if this is what you mean, which I guess it is, that totally makes sense now as to why you'd run the front cylinder with leaner settings: it runs with a slightly lower air pressure at the intake!"

!!Yes, that's it...in a nut shell.


"Big bang configuration, nice. Is it revving freely to the redline and can you share your airbox and carb setup?"

I don't currently run it twingled, but if I were to do that again I would make my rear cylinder 180 out and I would use two long trumpets with no airbox at all, just a v-stack filter. Jetting is almost unchanged and it'll be particular to your bike. Sprockets need to be changed though. I would look closely at CRF 450 gearing hint hint, nudge nudge. In fact, we have a lot in common with the CRF and other dirt track stuff. And thank you, that motor is music to my ears. I'll post a vid soon with the new valves and porting, sounds even better...somehow.

AV
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

tony.mon wrote: Fri Feb 28, 2020 7:55 pm The front stack receiving lower pressure is also why there is a deflector blade in the lid aiming air at the front intake.....
Yes indeedy! I love it when old topics get cleared up.

AV
tony.mon
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Re: Bigger Bore Etc

Post by tony.mon »

I looked long and hard at a similar setup to yours running big bang, and even made a larger oversized airbox which not only extended under the carbs but down into the vee between the cylinders, after re-siting the coolant reservoir.
If I had only divided that into two separate airboxes, each with its own filter and intake, I think it would have worked for a big bang configuration.
In terms of volume, you would need around 2/3 of the std airbox each cylinder, I think.

But running with pod filters is always very difficult in terms of jetting, so I would recommend using an airbox.
You can upset vtr's really easily messing with the airbox and intake routing. I think it's that the throat size is so large, almost any change disturbs the air enough to generate detrimental swirl which results in poor fuelling.

I put a thread up years back with all of my airbox mod attempts, if that helps at all, including dyno back to backs for accurate comparison of the results.
It's not falling off, it's an upgrade opportunity.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

Oh without a doubt it is sensitive. But...as you pointed out the airbox needs to be much bigger. The airbox is really an air capacitor and is drained far faster than it can be refilled. The key is getting the v-stack correct and this is fairly easy to configure. What I would do is use the intake tubes from a BMW R1150rt that are made by RB racing. I think having an individual tube with a K&N on the end is probably the best way to go. One of my pipe dreams is to make a Baja bike out of a VTR/Varadero with a twingled powerplant :beer:


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tony.mon
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Re: Bigger Bore Etc

Post by tony.mon »

An interesting point is that, with VTR's, when you increase the flow of air into the engine, the normal expectation is that you would need to up mainl jet sizes to give a commensurate increase in fuel, to maintain the stiochiometric ratio.
In practice, the opposite applies..... Smaller mains are needed.
It's counter-intuitive.
It's not falling off, it's an upgrade opportunity.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

What that would indicate to me is that the flow increase would have been an increase in Velocity thus allowing the incoming air to draw more fuel through the main jets. Another possibility is that the tumble/swirl aspect in the combustion chamber is improved along with VE. If that were so, it could do more with less fuel. I remember reading somewhere long ago and far away, an article by an engine builder, who lamented on the sad state of affairs when he noticed the trend toward adding fuel to make power. He insisted that if the engine were more efficient at making power it would need less fuel. I know the guys at RB racing always make sure to post the fuel mileage gains they achieve with their performance upgrades right next to HP and Tq #'s. Interestingly, they also show improvements in 0-60 times which indicate real world power gains more accurately than bogus dyno#'s which change with the tides.

AV
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freeridenick
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Re: Bigger Bore Etc

Post by freeridenick »

Ace VenTRa wrote: Sun Mar 01, 2020 12:06 am What that would indicate to me is that the flow increase would have been an increase in Velocity thus allowing the incoming air to draw more fuel through the main jets.
I've always assumed the plastic 'heatshield' was there to try and moderate the velocity to make it easier to set the bike up from the factory. Knowing that it can be ditched or the whole snorkel/lid assembly removed and the bike can be setup to run effectively. Also knowing that others have done this but their setups are not the same as mine got me thinking this way. IMHO it's definitely not there to prevent hot air getting into the airbox.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

Mos def not for prevention of hot air. The incoming air temp is fairly constant if all the other pieces of kit on the bike are in place. They can be tuned with the lid off etc., but without starting a war here...most people will agree that the lid needs to be on with the filter and divider in place as god intended them to be. At least as an oem setup that is.

AV
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freeridenick
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Re: Bigger Bore Etc

Post by freeridenick »

Ace VenTRa wrote: Sun Mar 01, 2020 4:44 pm Mos def not for prevention of hot air. The incoming air temp is fairly constant if all the other pieces of kit on the bike are in place. They can be tuned with the lid off etc., but without starting a war here...most people will agree that the lid needs to be on with the filter and divider in place as god intended them to be. At least as an oem setup that is.

AV
It's not oem, not even close :wink:.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

DO tell....?
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freeridenick
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Re: Bigger Bore Etc

Post by freeridenick »

Ace VenTRa wrote: Sun Mar 01, 2020 5:36 pm DO tell....?
http://vtr1000.org/phpBB3/viewtopic.php ... 9b615b9ef4
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

Nice...I dig it.
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freeridenick
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Re: Bigger Bore Etc

Post by freeridenick »

Ace VenTRa wrote: Sun Mar 01, 2020 6:06 pm Nice...I dig it.
:thumbup: thanks. It's faster than I am and that's all that matters at the moment.
Ace VenTRa
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Re: Bigger Bore Etc

Post by Ace VenTRa »

Whether we admit it or not, I believe that to be the case with most, if not all.

AV
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