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HelicopterEngines Plugs Mufflers Fuel › Most reliable/smooth/powerful 90 engine
09-07-2003 12:42 PM  14 years agoPost 1
spurry

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Reading, UK

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I'm planning on running a 91 motor in a raptor 90. My plan was to go straight for the OS C-Spec, because it is 'OS' of course ! But I've done loads of reading about the choices I have and would like to hear what you think of them. I'm now leaning towards the YS for it's fuel system and power.

I'm a bit concerned by the C-Spec's needing any mods done to have great power and be reliable and also reading of their shakes at a certain rpm. Do they come with the backplate nipple as stock? Are they at their best with the cline-regulator?

The YS91ST for an extra $25 comes with a great fuel system apparently, similar to the C-Spec with the Cline fitted? Same performance as the OS without the need for any mods like the OMI carb, perry pump or cline? Anyone know the stock power of this engine?

Webra 91 P5 AAR doesn't seem as popular, but it has a power output of 3.6bhp.

TT90, Also doesn't seem to be the choice of many, 2.75bhp. Was used by Alan Szabo but sounds like he's doing some testing with the C-Spec.

I'll probably be fitting a MPII to whatever I get although the SB16 also sounds great. TOO MANY CHOICES!!!

James

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09-07-2003 12:55 PM  14 years agoPost 2
G.Man

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Bristol

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James

The webra is a beastie but is also a pain to tune, you will need uniflow almost for certain to get a consistent run once tuned. The AAR is built like a proper 2-stroke engine so is very tolerant of abuse.

The YS has the next most grunt stock and is IMHO the smoothest, but it is at its best on 30%.

The OS is a great engine stock but does not fit anything properly with that rediculous head. The viperhead cures this in the main. Cline regs improve the fueling but I have seen excellent results with both perry pumps and uniflow. All have disadvantages but only uniflow does not decrease the power (it does not lower crankcase compression)...

If you like to tinker and are good with engine setup my choice would be the webra, if not then depends whether you want to run 30% or not...

If not go with a uniflowed OS

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09-07-2003 01:11 PM  14 years agoPost 3
DOKEY

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Northamptonshire UK

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YS, the end !!!


Ryan.

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09-07-2003 01:21 PM  14 years agoPost 4
spurry

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Reading, UK

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Many thanks for the great reply Galifrey. Who would of thought I'd be shopping for a 90 sized ship, not me that's for sure. Great feeling tho!

I'm not one for tinkering and tuning, actually it bloody pees me off when I have to constantly fiddle with the needles and I'm always longing for one of those engines that you see other people have and once set right...just fly! So I think that rules out the Webra.

Will the YS fit the rappy better than the OS? It seems as the OS runs best with the cline or perry+uni but it's things that one will save the hassle of doing when they could just get the YS in the 1st place.

The YS being at its best on 30% will cost me an extra £20 per case, an extra £15 for 20% or just the usual £65 a case for 15%. I thought about getting the YS, starting off on 15% for a case and then increases to 20% keeping the 30% for the butt-lashing days!

I'll keep an eye here and make my choice by the end of the week, but I think it might take some really bad news about the hassle-free YS and good about the OS to change my mind.

James

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09-07-2003 01:26 PM  14 years agoPost 5
spurry

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Reading, UK

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Oh, must keep it a fair comp. I've read about a bad case on the YS91 which often cracks when using a MPII.But the lighter SB16 lets it last a little longer. Hopefully it was a bad batch and it's old news.

The MPII on the OS is supposed to bring an increase of .5bhp. I haven't seen any info about the power increase on the even more powerfull YS yet.

James

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09-07-2003 02:02 PM  14 years agoPost 6
Andi G

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Switzerland

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Hi,

I don't think YS needs 30%, with an MP2 you should have more than enough power at 15%... of course you can always go higher.

Mine has not enough fuel though to say definitely but I think 15% is great - I use the Funtech muffler, seems to be good. Not as expensive as the SB16, that should be made out of gold for the price you pay! I got mine from waka model in Japan for 13500yen or similiar (waka model [wk-model@yomogi.or.jp]) I think the YS was 28800yen.
http://www.fun-tech.info/Line_UP/si..._hn90type-f.htm

Ask the FAI guys here, it looks like the YS runs with most fuels even with lower oil content. The mp2 should give it more power than a muffler but it looks ugly. Shure a nice choice for 3D but for FAI the muffler will probably run a bit sweeter.

My main reason for the YS was the fuel and fly once it's set in. I don't want the max power but a smooth engine that doesn't need constant fiddling!

Regards,

Andi

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09-07-2003 02:05 PM  14 years agoPost 7
Andi G

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Switzerland

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I forgot one thing, you might need spacers for the funtech. Mine touched the tank on the Nova, I installed 4.5mm between engine and muffler.

On the Fury/Vigor it should work, but it's quite long and I don't know if it will work without cutting the canopy. Give me a shout if I should measure something for you but be aware that I measure in mm not inches

See you have a Raptor, with that clutch assembly you should take a smooth running engine. Go for YS

Andi

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09-07-2003 02:50 PM  14 years agoPost 8
spurry

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Reading, UK

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Thanks Andi, also an interesting post, but I actually like the look of the MPII on the rappies. Ther fuel that I'll be gulping is Wildcat 15/20/30% which has an 18% oil content.

Come on you YS! It's galloping ahead by a staggering amount so far, with the Webra only inches behind it and the C-Spec trotting along in the distance! My money's on the YS.

James

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09-07-2003 04:45 PM  14 years agoPost 9
Dr.Ben

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Richmond, VA, USA

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The YS is very smooth, even in bone stock form. It does NOT need 30% fuel to make ton of power or to run well. We run them in AMA/FAI contest work on about 20% nitro, and they still make a lot of useable power. For numbers, I can pull at or just over 10 degrees at 1900 rpm in FFF, which is plenty to do most anything you'd like. I do not anticipate the power will be unacceptable on 15% fuel, either.

There is the issue of the stock rear bearing in the YS. If you buy one new, changing out that bearing to the one from the C-Spec may ease your concerns for minimal additional expense.

With the full Cline/Viperhead package, the C-Spec is a piece of performance art. You need to decide if you want to spend that amount of money to have about the most powerful combo versus just a simple, reliable, and smooth combo that runs well bone stock and only makes A LOT of power (namely, the YS). Yamada/YS has spent the better part of twenty years perfecting that fuel system. They've got it pretty well worked out.

Ben Minor

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09-07-2003 05:14 PM  14 years agoPost 10
Andi G

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Switzerland

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Ben,

I guess most FAI pilots use the SB16 right? I guess the power on an mp2/15% should be at least as good as with a muffler and 20%, just take care to chose the right gearing.

I think 7.5 instead of 8.5 will make a much higher difference than 15% or 20%. I went with 7.86 as the next higher on the Nova is 8.18 which is louder and sucks more fuel. I'm not into 3D but I want to start with FAI one day so this will suit me better.

I think the Raptor has 7.9:1 which should have it's sweet spot around 1800 with mp2 and 15%.

The mp2 is a tuned exhaust, so nitro content will change the powerband. With less nitro and oil the engine should have peak power at higher rpm.

Yes, a C-Spec is probably great with all the add ons. But after paying a lot of money for the original 91sx I felt like an idiot... I just didn't want to pay them another 300$ to get what the original engine should have been. And then add lots of dollars for Hyperhead and pump...

Problem is just that I'm about to get a 50, and it looks like OS is the best there - well, after dremeling the crank and adding another carb (luckily I can get a 60B at 20$). I hate this idea, how about you?

Get the engine that runs great stock (well maybe with OS bearings anybody got a part number? ) .... it's a ys...

Regards,

Andi

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09-07-2003 07:53 PM  14 years agoPost 11
G.Man

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Bristol

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I spoke to JK at our club about his Viperheaded clined c-spec and he reckoned the YS still had the power edge, especially with its own viperhead...

who knows tho

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09-07-2003 08:12 PM  14 years agoPost 12
Will B

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Bicester, Near Oxford, UK.

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I'm running a YS91 with a Viperhead and SB16.

Its unbelievably smooth and has gobs of power.

Its the best engine setup I've used so far. You wont be dissappointed going with the YS91.... its the dogs bollocks.

Cheers, Will.

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09-07-2003 08:42 PM  14 years agoPost 13
spurry

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Reading, UK

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It's all sounding good! Where did you buy the Viperhead from Will?
You need to decide if you want to spend that amount of money to have about the most powerful combo versus just a simple, reliable, and smooth combo that runs well bone stock and only makes A LOT of power (namely, the YS).
The YS sounds brilliant! The C-Spec's votes are coming up now, basically it is a choice between the YS91St or the OS91C-Spec with Viperhead and pump/cline. It's a whole different ball-game shopping for the 90's, but it's fun and I can't wait for the first few flights with a 3bhp motor whizzing the 710's round at 1800 ready for flight of fury.

Only one for the TT ? Does anyone know the power output of the YS? With the MPII and the SB16 will be good.

James

PS: Will, have you watched that 'A Chopper Is Born' series on Discovery with Mark Evans, that wasp-looking heli really was the dog's cahoonas!

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09-07-2003 10:05 PM  14 years agoPost 14
spurry

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Reading, UK

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Are the crankshaft threads different on the YS91st and OS91Sc-H C-Spec? Just wondering as my Quick UK fan that I have for the OS70 may not fit if so.

James

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09-07-2003 10:14 PM  14 years agoPost 15
DOKEY

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Northamptonshire UK

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Yup there different threads, Quick UK do one for OS and one for YS

Ryan.

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09-08-2003 01:46 AM  14 years agoPost 16
Dr.Ben

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Richmond, VA, USA

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Andi,

If you want to see a nifty debate, put Curtis and Todd in a room and ask each which exhaust makes more power. Curits has apparently run the numbers to prove his point, and Todd did the R&D for the SB-16. Whatever.

Don't expect to see a marked difference in engine performance with a MPII vs SB-16. The MPII is far from being a classic tuned exhaust. The reason I know this is that it will work with a YS, which by design tolerate a true tuned exhaust about as well as a vampire tolerates light and garlic. We all like the Hatoris because they aren't so butt ugly, are more aerodynamic nestled behind the canopy, sound wonderful in hover, and are wholly tolerant of needle settings. I will NOT run ANY one piece exhaust unless forced to do so at gunpointd/t issues of engine damage in a crash. But that's just me.

I fully agree with you on the need to carefully choose your gearing for the lower nitro fuels. Less nitro is going to give you less torque and less tolerance for turning big blades in hover at contest hovering rpms. You gotta get it back somewhere, and a bit shorter ratio at or in the low eights should help a great deal.

Ben Minor

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09-08-2003 02:42 AM  14 years agoPost 17
Chris.C

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Hong Kong

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Me too found the YSs are very smooth and powerful. In pod-n-boom form, I run it with 20% nitro fuel and in a body, I ran it with 30% nitro. I replace the bearing with OS's after the engine is run in.

We don't have two piece Hatori muffler in Hong Kong so most of us changed to FunTech's except my ships. I guess the MPII give more top end power but we need smooth running in both hovering and top end. Besides, the "happy" rpm range of MPII may not be as wide as the muffler.

Good news is the Hatori comes up with a new #999 muffler which sits on a dampened mount with double O rings.

Cheers

Chris

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09-08-2003 07:49 AM  14 years agoPost 18
Andi G

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Switzerland

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Hi,

the 999 won't fit on a Milli, the mounting system will interfere with the L frame braces. Might make trouble on other helis too...

Ben, there was an mp2 test in the German Rotor magazine with the mp2 put on an x-ray or something. You could clearly see the internal structure and it reminded me a bit of the mp1.

I think you're comments on hovering sound/smoothness and muffler are right on, the engine is designed for mufflers and won't run as sweet with a tuned exhaust or whatever you call the mp2. But looking at the inside of the mp2 I can't see why it wouldn't increase power on any 2 stroke, but then the YS has a special fuel system and I heard porting times are really different from OS/Webra too. As they influence the lenght of a tuned pipe it seems strange that a fixed length thing like the mp2 should work on both with the same gearing ratio...
Looking at the way tuned exhaust work it makes somehow sense that it can't be as good as with a normal carb (sorry I can't explain why in English), I just wonder what an OS with cline will do...

The Funtech is not one piece but with dampening, however it has no supports to the frame. I think that might be better with helis that have flex in the frame, the Hatori sb16 is mounted to engine and frames and will put a lot of stress on the engine if the frames flex. I wouldn't use that on a Raptor!

You can see the 999 by going to http://www.hatori-models.co.jp and clicking on english, there will be a "news" popup with a link to the 999. Nice website, not even an email if you have questions...

Regards,

Andi

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09-08-2003 09:47 AM  14 years agoPost 19
Will B

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Bicester, Near Oxford, UK.

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Where did you buy the Viperhead from Will
Directly from Omi in the USA. However I just saw that in this months MHW Motors and Rotors are advertising them so they must have them in stock.

Cheers, Will.

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09-08-2003 06:13 PM  14 years agoPost 20
spurry

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Reading, UK

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Thanks to you all for the info, it's been great reading it all. I had absolutely no idea that the YS91 is as good as it must be.

I think the reason for that is you get a great engine stock with plenty of power, great fuel system and all in all, a nice smooth motor. But on the C-Spec, to get the same smoothness, more power and to improve the fuel system, you'll need the viperhead/cline parts on it.

And the only problem I've heard of the YS is the stock rear bearings. Andi, the part number to replace the stock YS with the OS is:

OS part number 27930000
17mmX35mmx8MM

Here's a great LINK with all the info for anyone else to read. I think I'll exchange the bearing to start off with. I'll keep the stock head on for now, but keep the Viperhead head in mind for a future upgrade.

Doesn't Alan Szabo Jr. use the TT90? I know he's doing some testing with the C-Spec, but is the TT his 'general' every-day flying engine?

I think I've decided now. YS sounds brilliant!

James

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HelicopterEngines Plugs Mufflers Fuel › Most reliable/smooth/powerful 90 engine
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