vforce reeds

[iamjasyn]

I don't know if anyone here can help. I did some searching but haven't found a clear answer kinda.

I did some calculations and discovered that the vforce2 reed cage has an opening area about 40% larger than a 38mm carb. AG Bell says you shouldn't have any cross section of the intake track between the reed tips and the carb exceeding 15% of the bore area of the carb, so that the suction signal to the carb remains adequate and the proper amount of fuel gets into the crankcase before the reeds close. This would mean the delta2 cage is huge! The older CR cage I have with stuffer is about 15% larger than 38mm and lines up perfect with an 86 CR boot.

The cage works well for my money, especially on top. However, I've seen some pictures of hte vforce3 on ebay supposedly used on a TRX and the intake window looks quite a bit smaller than the delta2.

Has anyone seen any numbers between these two setups? Also, the part numbers between the CR and TRX are different. Any idea why?

[C-LEIGH RACING]

In your calcs did you figure the stiffness of those reed petals. Even though the opening is larger you might not be getting that much more flow.

Wasnt it Ahood on Mac Dizzy that was testing some reed stuffers he was making a good while back.
Neil

[iamjasyn]

Well, I quickly typed up what Bell says about it. I think you're misunderstanding my question. I'm saying that the area is too large, and that's a bad thing. I gather than stiffness of reed tips is more of a factor when comparing the trade off between low end response and high rpm petal stability. Overly stiff reeds won't eliminate problems caused by an overly large intake tract. In fact I'd guess they'd compound it. Read this:

AG Bell:
One area where I see modern high flow reeds causing big tuning problems is a result of the massive increase which they produce in inlet tract volume immediately after the carburetor. On passing from the carburetor the inlet tract area typically increases in a short length to almost double that of the carburetor bore. This reduces air speed, and as a consequence it also reduces the pressure differential existing between the carburetor side of the reed valve and that in the crankcase. Remembering that it is the pressure differential which determines how soon and how rapidly the reed petals lift you can being to appreciate why this is more undesirable. That big volume delays the reed opening by several degrees and it slows the rate of opening. In practice it is akin to tying a 6ft length of elastic cord to a door and tugging the cord to open the door. The time delay from the initial tug to when the door opens is quite considerable, the result being that the initial flow into the crankcase is reduced.

…My conviction is that the cross-sectional area of the inlet tract at any point between the carburetor and the crankcase end of the reed block with the reeds at full tilt, should ideally not be more than 10-15 percent greater than that of the carburetor bore. Therefore if we were running a 38mm carburetor with a cross-sectional area of 1,134 square millimeters, then the flow area at any point between the carb and the tips of the reeds should not exceed 1,250-1,300 square millimeters.

[iamjasyn]

A 39mm carb has an area of 1194 sq mm, and the delta2 cage has an inlet area of about 1874 sq mm, or about 40% larger than the 38mm carb.

So from here, I'm wondering if anyone has dyno'd these vforce cages next to each other. It surprises me that moto-tasunari doesn't give up any clue about this role with their design. You don't even get a picture of it. I guess they figure flashy pics of their 8 petal design sells better. :rolleyes:

I don't remember about ole Ahood. It wouldn't surprise me though. There have been some bright guys on that site. I wish I'd known to ask these questions a few years ago.

[C-LEIGH RACING]

I see what its saying now.
Thats kinda in line with how I was thinking when I mentioned the reed stuffer.
I guess the best design would be to have a constant size opening from the carb bore to the face of the reed petals.
It might be, after that reading the reason Duncan produced the pyrimid reed cage. That cage has a lot of petal space but maintaines the same size up to the face of the petals.
Neil

[iamjasyn]

I guess the demand from the crankcase is going to effect how wide those petals open, but yea it sounds and seems reasonable that a consistent chamber size from the carb is going to give flow that the carb was designed to give. I thought the elastic cord analogy was a good one. Air compresses or decompresses before it travels, so if your demand is not high, you aren't doing yourself a favor sucking it through a larger chamber. Another interesting analogy he gives is that of sipping liquid through a straw. True you get less of your soda from drinking it though a regular straw, but you're going to have suck a lot harder if you decide drinking through a piece of garden hose is a better way to get more to drink.

I think I read on tasunari's site that the reason they doubled the reed tip area was to allow the same amount of fluid to pass with a smaller opening which prevents the reeds from having to make as much travel. In my imagination I'm thinking this allows lower pulse signals to get the fuel it needs from a stiffer petal while allowing the same stiff petal to work well at higher rpm's. I guess the pyramid is a similar concept but with 6 petals instead of 8.

I wish I owned a dyno. But even if I did, I couldn't try to charge for dyno runs in my garage without feeling guilty about the noise and traffic... Do you know what is considered a good dyno these days and how much it might cost me to do some runs on it? I think there is a shop with a dynojet not too far from me here in Temecula...

[iamjasyn]

By the way Neil, if you care to answer this, do you think one of the other sites is better for technical stuff like this? I see some familiar faces over at .net. It's odd that Mr Mac's site isn't up after several days for maintenance...

[CorvetteZ06]

iamjasyn, not sure if this would help ya out, but on my current R motor, CT/Pro-X 310, I have tried 3 different reed valves. The Duncan Pyramid, ESR, and the delta force 3. I think they all mostly felt the same, but I will say, the delta had a bit of an edge. So I just stuck with that one and I have never had any problems. Goodluck on your research! :cool:

[iamjasyn]

Originally posted by CorvetteZ06
iamjasyn, not sure if this would help ya out, but on my current R motor, CT/Pro-X 310, I have tried 3 different reed valves. The Duncan Pyramid, ESR, and the delta force 3. I think they all mostly felt the same, but I will say, the delta had a bit of an edge. So I just stuck with that one and I have never had any problems. Goodluck on your research! :cool:

Thanks. Good to know. I thought I remember reading people having problems with the reeds on the delta3 early on. I'm thinking about trying it for the butt dyno. I'm all but convinced the delta2 has too large of an opening for a 38mm 250 gas motor - I'm just wondering how much and where.

It would be nice to have someone post the width and height of the opening, and if its oval or square of the delta3 if they had one handy.

[parttime]

has anyone run the g3 reed cage?how did you like it. here is there website www.1dirracing.com