Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

question on carbs

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Old 08-11-2002, 07:02 AM
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FlooredCOBRA
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Default question on carbs

does anyone know if the OS .46 VX DF carb will fit the MVVS .40 GRRT rear intake engine? Are they close in any way.

http://www2.towerhobbies.com/cgi-bin...=++&search3=Go

here is link to carb

my problem is i have the GRRT and it is set up for WOT full time, no throttle at all. I am looking for a carb that will work with this without loosing any power. Meanning smaller bore and all. So far from the pics the bolt pattern looks the same but not sure, does anyone know for sure.

If anyone has any other ideas on how to set up for a throttle please let me know.

Thanks
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Old 08-12-2002, 07:59 AM
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DerFly
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Default GRRT Carburettor

MVVS has a throttle carb available for the GRRT...
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Old 08-12-2002, 09:49 PM
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Default question on carbs

yes but it is a front intake carb. The but I have the .40 GRRT FAI PYLON rear exhaust, rear intake . The bolt pattern is different.

So thats why i was wondering if anyone knos if anything will fit on my set up.
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Old 08-12-2002, 10:36 PM
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Default MVVS GRRT

The MVVS web site shows a carb for the rear intake GRRT, part#3226.

If MVVS is using the same carb mount dimensions as Nelson (I read somewhere this was the case), the OS carb #40A from the .46VX DF will fit. And it won't choke off your engine. It has an inner diameter of 15 mm!

RR
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Old 08-12-2002, 11:47 PM
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Default question on carbs

i went to the website and fouind this carb and part number
http://morrishobbies.com/product_inf...eec2f38f456823

the bolt pattern is different from that i have with the rear intake.

But good to hear the OS may work with my engine. 15mm is a big and hopefully it matches what i have in there now.

I'm going to try this set up out and see how it goes, thanks for your reply!
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Old 08-12-2002, 11:52 PM
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Default question on carbs

I just found the same carb with same part number on this website and it does say for rear intake rear exhaust. I am just a little confused on how it would fit.

http://www.justhobbies.com/mvvspg3.htm
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Old 08-13-2002, 12:18 AM
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Default They aren't the same..

The OS carb bolts directly to the rear cover..the MVVS uses two bolts to bolt the carb to the engine from a ring around the end of the carb....the mounting methods are completely different. I can't say if the bolt patterns are the same, but the OS has a smooth machined surface that mates to the rear cover, the MVVS is more of a conventional carb but has the long screws along either side.
At any rate, I would imagine the carb for the OS would be as hard to come by and expensive as the VRDX is...

MVVS has a large bore version of the 3226 carb..
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Old 08-13-2002, 12:39 AM
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Default question on carbs

i found this OS carb. It looks about the same , the bolt pattern is similar.
http://www2.towerhobbies.com/cgi-bin...=++&search3=Go

guess only thing i can do is go ahead and purchase it and see if it fits. If not i can always send it back. Hopefully it will work out.
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Old 08-13-2002, 02:04 AM
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RossiRay
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Default GRRT

After going to the Morris web site I can see your confusion. The photo for 3226 is a generic shot of a front rotor engine and carb.

The part number 3226 is correct for the rear intake GRRT. This is according to the MVVS factory web site, www.mvvs.cz . Click on motory, and then click on F3D, you will find the reference to the carb there.

RR
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Old 08-13-2002, 04:37 AM
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Default question on carbs

great! thanks for your help!. I'm going to make my order tommorrow and get that thing in the air.

And the price cant beat it for a carb!
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Old 08-13-2002, 04:58 AM
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Default question on carbs

From what I've been told, the #3226 GRRT R/C carb is too restrictive to produce full power from the GRRT. For maximum output, the #3219 Q500 R/C carb is just the ticket. You will either need to ask Morris Hobbies to remove a bit of the length of the bottom (its too long and rubs on the rotor), or you can do this yourself with a dremel or whatever. You also need to request the longer bolts to go with the carb (tell them you are putting it on a GRRT and they'll fix you up), as the bolts from the venturi are too short.

Mine turns an APC 7.2x8.6 racing prop at 22k on the ground and well over 24k in the air. I like it. I do wish they'd come up with a better way to hold the tuned pipe on. Otherwise its a great engine!

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Old 08-13-2002, 09:56 PM
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Default question on carbs

I just took a pic of my engine from rear. Only thing is i cant get it to work on here for some reason.

But i was looking at the rear of thr GRRT w/ Q500 carb and comparing it to what i have on mine. Even though I dont not have throttle i see another difference also. Seems the intake bore on my non throttled set up is alot larger. By looking at it from rear my intake is almost as large as the exhaust port.

Now i am wondering do you sacrafice size of intake bore when you add a throttled carb?
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Old 08-14-2002, 01:11 AM
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Default It depends on what you want....

The FAI pylon guys like to go as fast as possible, so they run a big venturi without a throttle. If you want to run as fast as possible, then this would be what you would want.

If you want to be able to control the RPMs via a throttle, you will have to make a few compromises. The Q500 carb uses a venturi diameter which allows for fuel draw at settings other than full throttle..
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Old 08-14-2002, 01:56 AM
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Default question on carbs

I wish I could find the thread where Pe Reivers (I think) talked about it, and gave actual dimensions of things... but it must be on the old RCO or already purged from Google. If I remember it correctly, the Q500 carb provides a bit more intake area than the GRRT actually needs. Having an opening bigger than needed doesn't add anything to the power output. The engine will only draw as much air as it will, even if the venturi is a foot in diameter.

I agree with ChuckAuger, whatever small amount may or may not be lost by going to the R/C carb is made up for in spades if you desire control over the throttle. If you decide you don't, then you can always use fuel tank size (or how much you put in it) to limit the length of the flight. The GRRT sucks fuel like nothing I'd seen before in a 40-46 engine. The 6oz tank recommended for the Dust only lasts for 2.0-2.5 minutes of full-throttle flight. That's a lot of glow-puke.
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Old 08-14-2002, 04:41 AM
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Default question on carbs

man talk about a nitro guzzler. I figured 4 mins at least.

As for the size of the venturi I would sacrafice down to a .25 if i have to so i can control thottle. I was just curious about if the size changed with or without throttle control. I love speed but I ghave to have that control to slow down when I want to so I can land. I am not to big into dead sticks, especially when i have no idea when its going to run out of fuel. Now if it was a trainer plane, hey all for it! I will putt one of them things around for days.
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Old 08-14-2002, 06:40 AM
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Default question on carbs

Only one flight did we shut down the engine with the carb before the fuel tank was empty... otherwise, EVERY landing of my Dust(s) have been deadsticks. We haven't found it to be a problem, because it does give you some warning that its about to run out. You will be doing a turn or some other medium-G maneuver and you will hear the engine bobble from sucking air. Then you know you have 10-20 seconds before the engine quits. That's normally plenty of time to get setup for a landing. 10 seconds is a long time with a 175mph+ model.
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Old 08-14-2002, 09:43 PM
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Default question on carbs

That is a good point about having enough time to land. I know what you mean when you hear that sound in the engine right before it dies. I noticed that the DD was pretty predictable at low speeds, i didnt expect it to be. I always figured it was come in hot and you have to pin it down quik before stall.

Also about the carb, well when I ordered my engine we ordered the GRRT rear intake and Ex and the GRRT FAI rear intake and rear round ex. Te other GRRT came with a carb that at the time looked like it was impossible to install on that engine. I called Morris Hobbies about it and the carb was ment to fit with the GRRT but was missing the bolts and adapter ring they said. If i would have known this i would have went ahead and got the carb with it. Only thing now is that adapter plate is out of stock and wont be in untill next week somtime, this is no biggie though.

And another thing is the carb the sent we are not sure wich one it is. The GRRT RC carb or the Q500 carb. This I'll have to find out. They did tell me that the Q500 carb was the optimal setup for the GRRT and was bigger than the regular GRRT RC carb. I asked about the size and they said that there is not much difference in size compared to the WOT venturi and peformance is not lost. So now I am pretty excited about getting it setup and on my DD. My OS46 FX I have in it flies okay but I want all out speed. Now only its just a UPS shipment away!
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