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ASP FS91AR

Tuning assistance

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Ralph Yeates29/07/2008 14:01:00
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Hi all I have an ASP 91 4 stroke  engine I put it on the new model that recommends 70-100 so should work fine had a hairy take off and had to fly around on full throttle to keep the plane up. This tells me that the engine is not giving enough power for the model as the model is ARTF then the engine should be fine. Searched on just engines web site and found the review changed the prop for a less pitchy one 16*10 down to a 16*6 put the tacho on and I am not getting the recommended 8400 rpm only getting 6400rpm missing some 2000rpm. I have checked the valve clearance again and this as recommended 0.1mm but still no increase in rpm.any suggestions appreciated.
I tacho'd a SC 120 FS and the RPM is 8500 so I am not in the same ball park yet.

Tim Mackey29/07/2008 14:13:00
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IMO thats too large a prop for a 91 4T

The following are the guidelines for my SC 91 ( identical engine to yours from the same factory even )

IDEAL PROP 14 X 7

RANGE 13 X 8-11, 14 X 7-9, 15 X 5-7.

3 BLADER 12 X 8, or 13 X 6

I use the 14 X 7 on my 8.5Lbs Spitfire and it flys very well indeed. Typical max RPM is 8500

Steve Hargreaves - Moderator29/07/2008 15:31:00
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I agree with Timbo......a 16" is way too big for a 91 4 stroke.....a 120 maybe. A 14x6 would be a good start point methinks

Personally I wonder if the review on the JE site contains a printing mistake....I've emailed Jenny to check.

You don't say what sort of model your'e flying..sport, aerobatic, scale? Different models would need different props....also does the box recommend a  70-100 2-Stroke?? This would make a huge difference as 2 strokes are generally more powerful than 4 strokes (twice the bangs you see!!!)

Myron Beaumont29/07/2008 16:00:00
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Steve  Re twice the bangs)-Not quite as simple as that & you mustn't generalise like that You wont confuse me but you might send out the wrong message to beginners ! ( I've just done a " Timbo"
Steve Hargreaves - Moderator29/07/2008 16:09:00
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Hi Myron....I thought you'd gone all sparky these days...good to see you in the ic section!!!

Not sure what you mean matey....2-strokes DO have twice the bangs (firing strokes) as 4 strokes & 2 strokes DO (generally) produce more power (size for size)....how could that confuse anyone??? If I'd gone on about volumetric efficiency, cylinder filling, relative & absolute torque values & brake mean effective pressures then I could understand people being confused.....especially me!!!!

Ralph Yeates29/07/2008 16:54:00
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I'll pop to the local Model shop and get some of the smaller props and post the results but the just engines review does post prop sizes and rpm ratings. That was the next cheapest port of call prop sizing.
Steve Hargreaves - Moderator29/07/2008 17:05:00
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Sounds good Ralph...its all about finding the sweet-spot!!!
Tim Mackey29/07/2008 17:28:00
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Myron Beaumont wrote (see)
Steve  Re twice the bangs)-Not quite as simple as that & you mustn't generalise like that You wont confuse me but you might send out the wrong message to beginners ! ( I've just done a " Timbo"
No you havent...you have criticised someone for an error they didnt make - I dont generally do that grumpy!
Ralph Yeates29/07/2008 19:40:00
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Steve the model is a hanger 9 spitfire and it recommends 60 2s and 70-1004s  but you dont put 2 strokes on scale spitfires its just not done. 

Steve Hargreaves - Moderator30/07/2008 09:11:00
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Couldn't agree more Ralph.....a 2T in a scale aircraft just doesn't do it for me either. A model 4 stroke doesn't sound much like a Merlin either but it's definitely better!!!!!!!

Didn't David Ashby review the H9 Spit recently?? I seem to recall he stuck a Saito 100 in his...??

Steve Hargreaves - Moderator30/07/2008 09:20:00
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Just got a reply from Jenny Landels at Just Engines....she writes:-

 "Hi Steve

Thanks for your email,I have just gone and checked the review and yes the 16" props are mentioned. I must admit to a little surprise in that 16" is well outside of the recommended range - although magazine reviewers do tend to try very large ones. We recommend between 12x8 and 14x8 for this engine. It is a tricky subject because people sometimes will get upset if they don't achieve exactly what a reviewer achieved but obviously we do like to publish the reviews for information. The 13" prop figures on the review are in line with ours here so I would use those as more of a reference point. Feel free to quote me if you like.

Regards

Jenny"

Hope this helps

Tim Mackey30/07/2008 09:32:00
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Ralph Yeates30/07/2008 10:29:00
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Steve thanks for your help it's just that I was far off the mark from the review I'll drop it down to a 14" and that should fix it as long as I get the rpm I should be fine otherwise I'll have to look at a larger engine if I still don't get the correct pull from the 91. Yes David did and I see on different forums that they also use Satios as they seem to be the only people that make the 100 I just wanted to utilise what I had before buying a new engine.
Ralph Yeates30/07/2008 18:06:00
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Ok been to the model shop {very poor selection of props} so got what I could and here are the results
APC 14*6  8,000 rpm  ish  Just engines review says  9,800 that is still almost 2000 away
master airscrew 13*6 8,600  again JE say 10,400   same again off the mark
This brings me back to my original question I am 2000 rpm off the reported rpm for the size & pitch of the props, isit that JE review contains errors maybe ?
Malc Pinnock could maybe comment on why he is getting better rpm from the same engine and same prop as I can get nowhere near his quoted figures.
I am using Model Technics Fuel and Anderson Hobby smart Tacho.
As far as I know there is no other options of tuning the engine to get more RPM.

Tim Mackey30/07/2008 18:41:00
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Well as long as the main needle is set correctly ( and mine is around1.5 turns out only ) a good plug and proper tappet setting.... no , there aint much else to tweek !
Ralph Yeates31/07/2008 09:57:00
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just odered a satio FA100  from Inwood
thanks for all your help guys
Steve Hargreaves - Moderator31/07/2008 21:06:00
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Seems very strange.....ASP are usually very good motors. Is it new? Run in? My thoughts might be to send it back to JE for advice....they will run it up for you & pronounce it a good or bad 'un. Tell them what fuel & prop & plug you are using so they can replicate the same conditions. It does seem down on power but without knowing the history of the engine its difficult to know the cause.....

Enjoy the Saito...I believe they are brilliant motors...never had one though....my pockets aren't deep enough!!!

Ralph Yeates01/08/2008 06:02:00
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I'll speak to Jenny and send it back and see what they find out interesting to know the out come.
Ralph Yeates04/10/2008 11:22:00
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From Just Engines

We found your tappets overtight and the timing on the cam gear out, we have tested the engine on a 13x7 APC at 9700 and a 14x6 at 9200, our ‘office figure’ is 10300 on a 13x6 so we believe your engine to now be within the normal range.

Your engine is in the post today, you might be kind enough to send a fiver for our coffee fund to help towards the postage, we will not charge for the labour or anything. Generally the timing should not be touched but there is a dot on the cam gear that is lined up in line with the pushrods when the piston is at TDC.

If you want great service from friendly people I can not recommend Just engines enough Customer service is super.
Steve great advice.
Happy Bunny & the fiver is in the post

Frank Skilbeck05/10/2008 13:25:00
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My ASP 91 FS does 9,200 rpm on a 14 x 6 on 10% nitro. I had some problems with mine cutting out initially and it does seem sensitive to the fuel used, but in the last 3 models it's been very good.

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