I'm going to use a MIP Stinger. I used another 'pipe designer' program. Fed in my engine's specs, header diameter and a few other variables, and it spit out a design that looked very close to the Stinger. Called Moore's for some measurements, and sure enough, it's "right on the money". All I have to do is get the engine to spin up to 26,000 to 28,000 RPM.
The program recommended a header length of 4.3". I've also heard that a longer header produces better top end. I gave myself about 8" to play with--I'll probably start with 6" and cut it down incrementally to fine tune.
Macs makes a header and pipe for .12 to .15 marine engines-the header looks the same as mine, but the pipe is a good bit longer.
I just went down and measured the pipes on my .21 twin. they are 20cm (less than 8inches)from the widest point of the Macs tuned pipe to the plug, that is going around the header with the measuring tape. Your header at 6 inches will leave you no room for a tuned pipe.
I don't run .15s but, I think that they would be considerably shorter than a .21.
MikeP!!! How long is yours?
Oh! By the way, I have always believed that a longer pipe will give you more torque, but less rpm. The with the shorter the pipe, the faster the boat will go when it winds out, and the longer the pipe, the quicker it will respond with a bigger prop. Shorter pipes seem to eat plugs though. There is a limit to how short you can go, but I think it is best for racing to go as short as you can. Short enough that the plug's filiment gets a little crystalized and pulled down a bit.
seems kinda big, but i guess i should get used to it. [the engine manual reccomends this prop] i emailed Al's Hobby Shop and some others about a tuned pipe three days ago, but they havent responded..... :-[ :'( i should be able to extend the header i get, since that doesn't change diameter like the tuned pipe... though i havent given up on that either. i'll try to fill in that chart u gave me, see what it tells me. bummer we cant race these things when they're finished......when i get it going and join IMPBA i'm gonna try to get the "local scene" or the district to make an amatuer A-B class w/ everything between .12s and .21s in it.....the bigger engines can just use less nitro. i'm sure there are enough poeple out there that want to race boats like this that it could happen, it's just a matter of getting it done. you should ask around at the next race about it. have u got a prop yet?
uh oh, good ol' tower hobbies doesn't have any pipes .18 size.......from what i've seen the really nice pipes just come in race-class sizes too [.12, .21, etc] would it be better to downsize to .15 pipes, or go up to the larger ones [MAC has a .19-.21 size]?? :-[ :-
Hey Hammer...I think the MIP pipe was designed for nitro trucks--they come with headers for all the popular models.
On the length, what diameter header are you using on your .21? The program I used said the header length depends on a bunch of stuff, but given the pipe dimensions, if I used a header with .30" diameter, it should be 2.6" long. I'm using 1/2" pipe instead, and the program said 4.3" long for that diameter. You thinkin' I should use a smaller diameter?
Overall length's not a prob--the pipe is only 5 3/8" long.
Lax--I don't know about the size...this is my first tuned pipe project.
Anybody else have an idea?
BTW--I'm starting with an Octura V937 prop (Tom's suggestion)
I measured my pipes and header and stuff on my .15 here is what I ended up with. The header is 3" long, The rossi car pipe is 6.5" from the glow plug to the weld(center of the fattest part of the pipe) following the path of the header and pipe. The mac's pipe is 7.5" from the glow plug to the center of the fat part of the pipe. I know I could go shorter. The inside diameter of the header is .45". For best performance the header needs to be a certian I.D. depending on the size of the exaust port of the engine. I don't know how to calculate it but it seems that bigger than .45 is too big. The proper size for most .21's is .48 I.D. I also run the v937 and haven't found anything better. That's all I know about that.
i'll take a look @ new era. 'bout those car pipes, towers got some .21 headers that connect to two pipes, they look pretty sweet. Ron said it wouldn't hurt to use a .21, so i might go w/ the MAC .21 marine and fit it to a standard .15 header, im pretty sure i can do that. b.t.w., that K-90 looks like a REALLY nice ride, u should be able to have some fun w/ that!!
i went to my local shop today, for the 1st time ever they were actually not rude to me even though i'm not over 21....they also told me that since my engine had bearings, the thrust of the prop would push the crankshaft back into the crankplate [which would be bad news] unless i got a put a thrust bearing on my drive shaft. is this true?
wonder why they're selling the K&B .18 car/buggy for only 65 bucks, factory direct is 85... how much of an improvement would the MAC .21 give me over one of those .18 car pipes.....it's a 20$ difference so i'm not too sure which. they also have a big-bore carb for .18, that sounds pretty tempting, even for a 37$ price tag.
not sure if u mean unsharpened/balanced/polished, or if u mean un-customized.......if u mean the first, no, if u mean the second, yes. do you know anything about bushing engines and hafting to put thrust-bearings on them?
sounds like it could be true, but i would think K&B woulda told me that or something. ??? b.t.w., u should look at the link Hammer put on, i think there's a big-bore carb for .15s... that might a good thing to smash the budget a little farther with!!
could i out a loose washer behind the drive dog, in front of the strut, with the drive dog pushed back up against the strut, with just enough room for the washer, so there is no room for the shaft to push back?
Joe--also leave a little extra 'slop' (1/32-1/16")--flex shafts shorten themselves slightly when twisted hard. You don't want to bind the engine up under hard acceleration.
Mike P--what mods did you have done to your V937?
Hammer--they're small, light, cheap, 'just for fun' models. Did you notice mine has electric start and a clutch? It's not a full tilt race rig--just fun. I've got about $115 invested so far. You really ought to get one!
i did some work on the drive shaft this weekend, soldered a piece of tubing w/ a 1/8" bore and a 3/16" diameter onto my 1/8" shaft, so all i need now is a 3/16" drive dog. i'll try to get some pics on here later......do you have any of your outdrive?
b.t.w..
i wish i could say i've only spent 115$ on mine, but since it's being converted from elec., i spent alot on the elec. stuff before switching.
it looks great, cant wait to get it running......the only problem is that they put the engine head on wrong, with the water-cooling outlets over the carb's air intake, where i'll be installing a big ol' air filter. not a big deal, since i'm planning on taking everything apart [except for the crankcase, piston, etc] and checking it over.
roject 'Hydro-therapy'
