OS .91 C-spec-PS W/ OMI Viper Head- correct head shim?

[Todd Marsh]

I just spoke with OMI and asked what would be the ideal shims to use for my exact heli set up (OS91 supplied W/ factory pump, & OMI Viper Head using a Curtis Young Muscle II pipe). I wasn't sure of the correct shimming as the OMI VP package that my VP head came in hadn't listed what was to be used for proper shimming with the new PS engine, which hadn't yet come out at the time I got the new VP. OMI said they have just finished extensive testing on the PS engine using Jason Krause as the test pilot, just with-in the last week & here are their findings: .016thous. shimming seemed to work GREAT, with fuel that contained anywhere from 15-30% nitro. Also of important note, OMI noted it seems those people who are using "wildcat" fuel, seem to be getting better performance results with shimming up to .024 thous, as Clint also has noted in a earlier post. OMI suggested using the factory supplied .008 shim, & the extra .008 supplied with the OMI OS V.P. head, to get the optimal internal cylinder volume for proper combustion. He also suggested using 2 OS#8 plugs rather than the #8 & #5 combo. I just talked with OMI April 26th, 2004, and this was the response, given the parameters I am using & I thought helpful it might be to others as this is a popular set-up, and maybe it can prevent frustrating testing to get what they want performance wise. I intend to have a MA company Representative do the final set-up & tune of my helicopter within the next week or so, and will give the results of OMI suggestions in relation to how it performs in the hands of someone able to exploit the helicopter & its abilities to its limits. I would have posted in MA section but I know the new OS/PS is a popular, so I figured I would spread the knowledge to anyone who might benefit.

[Clintstone]

last week & here are their findings: .016thous. shimming seemed to work GREAT, with fuel that contained anywhere from 15-30% nitro. Also of important note, OMI noted it seems those people who are using "wildcat" fuel, seem to be getting better performance results with shimming up to .024 thous, as Clint also has noted in a earlier post

I have been testing the VH with Magnum 30% and an OS 91 PS with the MPII and GV1 with 710 V-Blades. I ran everything on the shims from 8 to 28 thou and the 24 thou on Magnum 30% is a BAD BOY.... I will give credit where it is due and Shannon Davis...... in a conversation was the motivation from prior testing. Shannon really puts alot into the Hobby and he was the motivation behind my testing. I ran in weather from 40' to 93' , high and low humidity, I ran a parrallel test on a stock PS and I had good results there too. I found the best performance on my motors to be the Magnum 30% with OMI VH with 24 thou shims . It is the smoothest and strongest motor I have ever flown. The stock head I found that the stock 8 with a 4 thou which brought it up to 12 thou. ATT>>>>>>>>> the motors start easier too with lower compression, don't be scared to drop compresion as the power goes up.
In a test this passed weekend @ Blacksheep , we tached my motor withthe OMI Head on MAGNUM 30 % and it was running 1870 HS and when I did a hole flight and the lowest the headspeed got was 1860 and that was just for a moment. I flew another flight with 2 degrees more pitch and had the same result.
The stock head made almost the same power on top but wa no match for the OMI VH for smoothness and over all performance. A pleasure to fly the combination. Note : I have tested CP with good results but have conducted no test with WildCat........... The other guys @ BS changed there motors to 24 thou after Shannon completed his testing and everyone there agreed the 24 thou was the best combination. We tried the 16 thou on Magnum and on a cool day did fine but it started going away when outside temps came up. Thanks for reading and I will be happy to share all of my findings. I just want everyone to have the fun I am having.

[Todd Marsh]

Clintstone, what combination of glow plugs are you using & if they are indeed 2 types of differerent plugs, which position is each respective plug inserted? To aquire what you have found to be the best spacing (.024) are you using 3 X .008 shims, or have you found a single .024 shim that works with the application? Would you say .024 gave the best result in performance regaurdless of the type fuel?

In running so many different tests, with all variety of different thickness shims, as you did, what did you say were the disadvantages to running a smaller shim (say .016)? Was pre-detonation a issue with the higher compression that was the result of less shims? What were you able to see in terms of engine temperature variation with the different shimming?

I am suprised to see such varied results in prefered performance ( diffrence in .008), I guess Ill have too see for myself if .016 or .024 is the trick with whatever fuel I decide to run....I am probably going to be using Cool Power 30% & starting with 2X.008= .016 shim. If I can find Wildcat locally, I might give them a try.

Thanks for the infomation Clint.

[Shannon Davis]

I have been testing the shims for several months now, on both c-spec and c-spec ps. This week end I had two Tempest 3D's w/ identical setups. Bothe PS engines w/ ENYA 4/3 plugs(4 on top). Fuel was CoolPower 30%. One engine had .016" of shim and the other had .024". I did not know which engine had what shims. After tuning both to their best perf. I flew the helis w/ Wayne Ellison and HC watching. We all decided which heli had the most power. The same heli was smoother and easier to tune. We checked the serial number on the head and I checked my notes and the .024" was the winner. I did not know which heli had which motor. So it was a true test.

We then took HC's heli that he had been having trouble with and added .012" of shim. This brought his up to .024" of shim and the difference was noticable. It ran much smoother w/ lots of power. It took about 20 min. to change the shims, so weather changs were not a factor.

I don't think it matters what combo of shims you use-- one of my engines has 1-.008" and 8-.002" shims.

I think I calculated that ever .004" of shim is about 1 point on the comp. ratio. ie. .012"=15:1 then .016"=14:1.


Hope this helps.


Wayne is going to try .028" next week.



ps-- the mixture/comp on my ION was perfect all day!!

[pepper]

what about useing just the standard head. is all the testing just with the viper head??

was their a differance in useing the PS vs the gold head c-spec.

peppper

[WillJames]

Clint tested both. The standard head on a PS is teh Hyper Head. Even the PS with the standard head benefitted with extra shims. Clint can tell you the specifics but I think he added .004 to it if memory serves me correctly.

[Clintstone]

Pepper, this is correct. I added 4 thou to the stock C-spec head and to the PS head. I did not do much witht he stock head but it ran great with 4 thou over stock ( mostly ran Magnum in it ). The stock PS head I tried several combinations of plugs and always when back to the enya 3 althou the OS 8 was about the same but I preffer the enya 3. The PS with 4 thou ran good on CP and Magnum 30. Both fuels benifitted from the 4 thou shim.
The OMI head I found the enya 4 and the enya 3 to be a really good combination with the 3 on the angle. I did like however 2 # 8's OS. The enya 3 and 4 seem to make the needle very broad and with th tach the main needle responded every time you click the needle. I tried the 16 thou and was impressed on a cool day but when the temp got over 80 I was disappointed. I did however like the 16 thou with 20%. I feel for our weather that the 24 thou with the VH is the best combination withthe enya 3 and 4 . Plugs had the smallest effect on the test and the largest was the shimms.
Todd I think I saw you are from Colorado, you referrred to Wildcat Fuel as did someone in an earlier post, I want to be clear again that all my testing has been done with Magnum and Cool Power. Both are top quality fuels and alot of guys get hung on the fence on this one. I say fly what works and they both work well. Cool power works better than Magnum on higher compression but the Magnum bennifits more when the compression is dropped. Yes I feel the Magnum bennifited more but they both run great . Cool power is a top quality fuel and of course it is gonna run well. Todd you seem to be talking around Magnum as are some of the other guys here. That is cool as it is your choice and that is what makes this all fun. I am currently running Magnum because it is working the best for me. I have heard from OMI that the Klien reg. is really doing it with the CP and I have not gotten one of those to test yet but if in the future I get one I will certainly share my info.

Headeed to work..................

[WillJames]

Clint's C-SPEC PS's were running better than the other 10 or so at the field on Sunday. He and Shannon are definitely getting a handle on tuning the C-SPEC. I fly CP 30, and he is right that hte Magnum produces a little better power, especially on a super hot andd humid day like Sunday then the CP 30 does. I saw it with my own two beadie eyes, I have 2 C-SPEC PS's myself. I was running the tach for him, we compared my MA tack against two others at the field Sunday and all 3 were exactly right on each other. We fly CP and Magnum around here in the south eastern US because there is no WC (or any other brands) for sale anywhere. All you ever see is CP and Magnum, so getting other fuel to test is not that easy for us.

[Shannon Davis]

I also played w/ the PS stock head and was the happiest w/ it when I had .016" shims under it--w/ CP30. I run the Viper head because I feel it cools better- it fits the Fury fan shroud perfectly, and it looks really cool.

[Todd Marsh]

I was in error in my earlier post....CLINT runs Magnum fuel not Wildcat. My apologies in advance, for any inconveniences.

I posted that OMI had in fact verified some fuel does run better with shimming as much as .024. They also said current testing showed .016 to be the all around winner, in respect to performance & consistency, although perhaps OMI & JK are in error in these findings. I was confirming what you said W/ regard to the .024, not disputing or dis-respecting anyone, or anything, yourself included. Actually, the company verified they have done testing all the way to a .028 shim. Read the post & verify this fact yourself. I have re- read the post(s) multiple times now & am convinced your screen must read differently than mine, as I cannot see the foul. that was so apparently made on my part.

We in Colorado do what others do elsewhere.... We simply buy what fuel is available when we need it. I have no desire to "pump up" any particular brand fuel over the others manufactures, & I honestly couldn't care ANY less. The post was simply to inform people what the OMI manufacture said about shimming the OS/PS engine. Direct from the horses mouth who claimed JK did the recent testing. I am sorry for the misunderstanding, whatever it was, Clint, as apparently you felt it was clearly a attack aimed squarely at you, for what reason I am unsure. Perhaps you could quote from my pasts posts on this subject and post the 'undesirable' portions, so I can better understand what it is that I said to offend you so much.

By the way, I haven't ever even used WILDCAT fuel. The only reason I can say you might have felt I directly disrespected you Clint, MIGHT be because of a simple misunderstanding. There wasn't a bit of disrespect in my tone or words in that post, & if there was lets just re-print in black&while the issue.

In the future I will not quote anything from your posts, & that will nip having these discussions right in the bud. I do not discount your findings at all Clint, in fact I might try your suggested .024 myself. I generally hold a fair bit of prudence to the manufacture claims, especially when the test pilot was Jason Krause & testing results are 'hot off the press' so to speak. That doesn't mean I might not add another .008 shim to my current .016, just to see for myself. Just thought I would start with OMI manufacture suggestions, given the testing & information they provided me that was a day old, (recent) & I intend to start my engine for the first time soon.

[Clintstone]

seems those people who are using "wildcat" fuel, seem to be getting better performance results with shimming up to .024 thous, as Clint also has noted in a earlier post.

Todd , we are square as I read your PM and I sent you another,

I am suprised to see such varied results in prefered performance ( diffrence in .008), I guess Ill have too see for myself if .016 or .024 is the trick with whatever fuel I decide to run....I am probably going to be using Cool Power 30% & starting with 2X.008= .016 shim. If I can find Wildcat locally, I might give them a try.

but these 2 comments made me think you were trying to give me a hard time. I am just trying to justify my PM to you and I understand from your PM it was a misunderstanding so I am over it .

I am sure Jason and Todd did some great testing and are very reputable and I would never dispute anything they bring to the table and they are a great asset to the Hobby, but I am running a PS and they I believe are running a Klien mod Carb. James told me they had had great results but mine is running best on the 24thou with the PS and I am running Magnum 30%. HC is running Cp 30% and his is now running great. Sorry for the misunderstanding.

[Shannon Davis]

Todd, On my FAI it seems to run the best at either .016" or .020"--I'm not sure where I am rught now-lost track . I will let you know. I think the difference is in the head speed and Gear ratio. I run lower HS on my FAI and a "taller" ratio. 7.75 I think on the FAI and 8.18 on the 3D.

I also want to mention that the air in AZ is a lot different than that in NC/SC.

[HeliDriver]

I had trouble running a C-Spec with the Cline and ViperHead with Magnum fuel. I had a stock C-Spec in my other Fury and it ran great so I know it wasn't the fuel. I tried shimming the head but never was happy so I sent Paul the Viperhead back and kept the Cline and shimmed the head, it runs better with the gold head IMO.

[Clintstone]

Heli Driver, are you gonna be @ Sulpher? Hope to see you there.

[pepper]

since we are talking c-spec's, got a problem...

i went to the field to run the pred and my c-spec just wouldn't start. finally it started, moved to the flight line and as soon as i trans. from idle to mid it just died? haven't had a problem until now.. i just could not get the thing to trans. smoothly.. so , i finally got it to run up and as soon as i did it just it over heated and shut off, it ran very lean!! and i didn't do any adjustments. i wound up turning everything from 1/4 turn back to 2 turns and could not get it run? i am useing CP, a TJ pro with perry punp. do you think the pump has anything to do with it?? just the other day it was running great and had not a single problem.


thanks,
pepper

[Shannon Davis]

Are you running any kind of a check valve?? If so I have seen a lot of motors do as you say because the check valve was stuck. Give it a good hard blow

[pepper]

no, just clear filters..

pepper
GOD BLESS

[HeliDriver]

Clint, I will be at LARKS, I'm leaving Dallas tomorrow morning, should be pulling in by mid afternoon. I wil be there through Sunday. I'll have a canopy up and some drinks in the cooler so come on by and visit. I've got a few extra lawn chairs with me!

[HeliDriver]

Pepper, sometimes that hard fuel line can crack or loosen around the backplate or the pump, check it out.

I had hell with mine so I lost the perry pump and went with a Cline. problem solved.

[pepper]

ok guys, got it fixed. replaced the perry pump. i had the one with the brass looking screw on top and replaced it with the one that has the allen screw on top. never noticed i had different ones, wonder if their is a difference??

pepper
GOD BLESS