Can someone explain the difference?

Can someone explain the difference?

    The 35fp has about 3x the power and can pull small ST46 airplanes with good authority. The 35s runs nicely if you get the venturi small enough, and has the power of a Fox or slightly better.

   Brett

Well, I scored a NIB OS Max FP35 on ebarf a couple of hours ago.  Time will tell if I made a good investment.

I don't know the specs on the piston and liner yet.  I hope to have the engine in a few days.  I probably spent too much, but that ebay bidding process can make a sane man do crazy things.

Hi Dick. Is it a steel piston or abn? We ran several 35's back when they first came out. There wasn't a pressing need at the time for a smaller alternative to the 40 so we just used them up or sold them off. We modded them the same way we did the 40 as in: filled boost transfer and wedge head. The power was really good and we were able to use venturi's as large a .30 with ST needles. With the large vents the 35 would swing an 11x6 Super M. Normal vent size was .281.

Hi Dave,
Some questions, since your clan has lotsa expertise with these engines, if you don't mind answering:

1.  Is it true that the ABN 35FPs all have a smoothly curved bypass where the OS MAX FP is stamped, and that steel pistons all have a raised "bump" (there's probably a better engineering term, but senility is setting in) to the left of the OS MAX FP?

2.  Did your mods allow a breaking run?  The 6" prop usually indicates this.

3.  If Dick wants to run his 35FP stock, would you recommend that he run a 4" pitch prop in a more or less constant 2-stroke?  As we all know, back in the day, folks experienced no end of grief trying to get the FPs to run like Foxes and "cure" the tendency to "run away", which was really just the engine seeking the RPM range it was designed for. And thus Dick could save himself from repeating history?

4.  My experience with stock 35FPs is they are powerhouses well suited to stunt if run with the lower pitch prop.  Would you agree?

Thanks.

Hi Dave,
Some questions, since your clan has lotsa expertise with these engines, if you don't mind answering:

1.  Is it true that the ABN 35FPs all have a smoothly curved bypass where the OS MAX FP is stamped, and that steel pistons all have a raised "bump" (there's probably a better engineering term, but senility is setting in) to the left of the OS MAX FP?

They both have full length transfers

2.  Did your mods allow a breaking run?  The 6" prop usually indicates this.

Yes - see below

3.  If Dick wants to run his 35FP stock, would you recommend that he run a 4" pitch prop in a more or less constant 2-stroke?  As we all know, back in the day, folks experienced no end of grief trying to get the FPs to run like Foxes and "cure" the tendency to "run away", which was really just the engine seeking the RPM range it was designed for. And thus Dick could save himself from repeating history?

I believe that people have had success doing this

4.  My experience with stock 35FPs is they are powerhouses well suited to stunt if run with the lower pitch prop.  Would you agree?

I'm not a fan of low pitch props. Just a personal thing. The first 4" pitch prop that I've flown that I like is the carbon prop I got from Bobby Mac. It's a 13.25x4.25 with an under-camber. Very nice prop.

Thanks.

Hi Kim. Yes the mods were made to make the engine 4-2. It was early in the fp's lifetime and 4-2 was what we did. The planes we were flying were large and needed a larger prop. I don't believe in a lot of head clearance when there is a squish band. I generally set the clearance to 0.007" - 0.012". If the compression ratio gets too high I either add exhaust timing (which lowers the "trapped" compression ratio) or open the chamber bowl. Large squish clearances isolate a large portion of the charge in a area that doesn't burn. On a 35 to 40 size engine with a squish area of 35% of the bore a 0.020" clearance is just less than 10% of the total charge in the squish volume. You take the time to trap the charge, you might as well burn it. Blocking off the boost lowers the angle/area of the intake ports to make them trap better at lower speeds necessitated by the large prop. I'm not saying there isn't another way, because there are, this is what we  did.

This along with the added power and people still wanting to use 6 pitch props was a recipe for lots of speed when the motor broke.

   Bingo on that one!  The stock venturi was close to workable *but not if you wanted to run it at 8500 rpm*. Mine worked pretty well stock here at sea level with a Tai-Pan 11-4 most of the time.

  I would also note that the 35 was a lot closer to working, stock, than the 40FP.

   Trying to run almost any of these engines with 6" of pitch is an exercise in frustration, which is why everybody thinks they need to be reworked.

    Brett

Certainly, but after they were reworked they ran great on 6" pitch props in large heavy planes.... Which is what we wanted at the time....

    But you give up so much performance that way you lose a lot of the advantage. Even bogged down that way, and stock, it was still close to an ST46 in performance on smallish 46 airplanes. 11.5 or 12-4, and the performance goes through the roof. The difference in shaft HP between 9000 and maybe 11,500 (in-air rpm with similar diameter) is tremendous.

     Brett

I hope you guys keep this up.  I know nothing about the FP35 I just bought.

In our club we setup FP35s and 40s as follows:

FP needle, 101/2x41/2 apc, free flowing exhaust (usually a tongue muffler with a lot of holes), .283 venturi, one or two extra head gaskets, Enya #3 plug, or Thunderbolt RC, Powermaster 22%(50/50) 5%. Needle is set to run a medium 2 stroke in flight which will break to a hard 2 stroke in maneuvers. If it take about 4.5 ounces of fuel to do the pattern, you're in the ball park. Sufficient fuel needs to be run through the engine to keep it cool and controllable. Or so we theorize. If the break is too hard an extra head gasket or two, usually solves the issue. Please note that head gaskets vary. Stock OS gaskets are .015, aftermarket gaskets from Leonard Neuman, RSM (I believe) or Tower, if you can find them, run .010. 2 OS means 3 Tower. Buy the gaskets from Leonard, very reasonable cost. Many many times we have found that a balky runaway engine is caused by the usual gremlins: clogged filter, leaky tank (even a pinhole leak raises havoc with uniflo), airplane vibration, poor choice of fuel, worn plug or wrong plug, venturi seal or back plate leak, worn front bushing, in other words the setup works when the plumbing etc. is as it should be. Vibration problems plague profiles, of course, and can be a factor in full fues planes as well. A solid front end is essential, it seems to me, to establishing a reliable and useful tune.

Needle valve adjustment can be critical and sensitive. A click or two either way can mean the difference between usable, predictable power, and over lean jet speed. These engines need to be tuned for performance in flight. Ground setting may or may not be an accurate predictor of in flight engine run. This is especially true on profiles, since vibe issues are common. If engine runs too rich when flying I add a click or two next flight. If too lean, the opposite. It usually works out better, when tuning a new engine/plane combo, to start with an overly rich setting gradually leaning a click or two each flight. The sweet spot may be narrow. Solid front end planes tends to provide more latitude in adjusting for the sweet spot.

Tower 40s are handled similarly and perform similarly in my experience.  The Tower 40 is a near FP clone. The cylinder is chrome plated vs. nickel plated. The head appears to have deeper fining and the combustion chamber looks a bit more shallow (or visa/versa, I forget.) When tuned correctly we've found FPs to be powerful effective stunt power. Members have used them successfully in Advanced Pampa and Expert profile at local contests and Brodak. So far FPs and Towers with re-timed sleeves, that we've observed, are down on power. I have seen a Byron Barker modded engine that ran well. It's my understanding that BB does not re-time the engines. Hemi heads reduce the squish band and lower compression. I've seen them work. It's been our experience that adding head gaskets produces a similar effect while allowing for flexible adjustment.

35S run a traditional 2x4 break out of the box. Mild mannered. Run great when in good repair. Soft break. Predictable. East to setup. Considerably down on power IMHO compared to hyper FPs. 35s (es) have a non-bushed rod and, I think, no oil slit in the lower end. Will wear out a rod after a while. Leonard sells fully bushed replacement rods for $16. All 35s are cast iron piston in a steel liner. Over lean runs can cause damage and/or premature wear.

"Leonard sells fully bushed replacement rods for $16. All 35s are cast iron piston in a steel liner. Over lean runs can cause damage and/or premature wear.  "

Correction  he does not sale fully bushed rods for 16.00
I have the same rods for sale, they are made of much harder Alum. but they are not bushed
Also the sleeves are soft in the motors and the metal wrist pins pads cut grooves into the sides of the sleeve


Randy

Yep you should replace the pin pads with teflon... Man the old motors were a lot of work.....

Ok, I understand Randy Smith is the source for the better connecting rods for the OS Max .35S.  Does any one know a source for wrist pin teflon pads for the Max .35S.........TDurrill