Thunder Tiger GP.42 vs Tower .40

Tower Hobbies has the Tower .40 engine for $49.99 and the Thunder Tiger GP .42 engine for $52.99. Has anybody used the TT GP .42 engine? How does it compare to the Tower .40? Can the GP .42 be modified like the Tower .40 for a C/L application? Leonard, do you have any experience with the GP .42? If I was going to purchase one or the other which would be the better engine? I have a Tower catalog that has a $10 off coupon in it and I was considering purchasing one of these engines. Thanks for any information.

They are both good engines. I have converted both. I have both in stock in case anybody wants a modified and converted engine. The Tower 40 is an EXACT FP clone, except that it has slightly less head depth and uses, instead, a .010 head shim as compared to the .016 used on the FP.

Both the Tower 40 and the Thunder Tiger engines--including the TT .42--use a fully machined crankshaft, while the current OS offerings are cast and have only two machining operations.

The Tower .40 is a true ABC engine (it uses a chrome cylinder) while the Thunder Tiger is nickel plated. The plating is quite thick on the Thunder Tiger, however, and not a negative at all.

They both fit in the same .35/.40 FP mounts and have the same crankshaft length.

As an unmodified engine, they should both be run in a higher rpm mode using less prop pitch. There probably wouldn't be a whole lot of difference between them because the .42 is only slightly larger. If you follow AMA guidelines (read that "rules" in a contest) you would need to use .018 lines on the .42, but they stretch less and are easier to handle, so that is not all bad.

When I modify them the way I do, the .40 has a "burp" in the intersections that I consider objectionable if mounted upright or inverted. None of the other engines I modify, including the TT .42, have this particular malady. I, therefore, recommend my modified .40 version for side mounting (as on a profile) only. The modified .42 can be used either way.

The TT .42 is an "oddball", however, in the way they mount their carburetor. It bolts onto the case with two flanges and these are rather "delicate" in that the carb will probably break in a crash. This is a problem for RC use only, but it does mean we have to do something different when converting them to CL use. What I do is make a "normal" venturi and then drill through the venturi and case together for the needle. I can then install an OS needle in the "normal" fashion EXCEPT it will end up about 1/16 inch below the "normal" 1/2 inch height. For an inverted engine you will need to mount the tank that much higher in the plane. If you do that, it will work fine.

The .42, by the way, uses a larger outside bore on the sleeve as well as a larger inside bore for the larger piston, so you cannot swap parts with the OS or Tower .40.

I didn't check the weight of those engines so I don't know how they compare. I assume they are close. Since the TT .42 doesn't burp in the upright or inverted mounting it may allow additional airplane designs to be used other than just a profile. I forgot that the wire size goes up from .015 diameter to .018. If I had you modify the TT .42 would it be be compareable in power to your SSW .40? What size plane, in terms of wing area, weight would this size engine haul around? Is the fuel consumption about the same for both engines? As far as the nickle versus chrome plating, since it has a thick nickle plating it should wear as well as chrome?

I have done several of these engines for others, and they seem to work well. Power should be slightly better than the 35/40 FP. I usually figure the 40 FP has 200 rpm gain over the 35 with the large prop, but, when turning the same prop, there is little difference because you end up setting them at the same rpm for the same lap time. The .42 should give you a little more flexibility over the .40.

I charge the same for either engine: $20 for venturi and needle. $40 for modification. $105 for the complete engine, converted and modified.