Macs Pipe speed

[t3NHRacer]

If I got a Macs pipe for my nitro hammer how big a speed difference would it make. And would it require any other modifications to the boat when putting it in? Any other mods I need a few more mph to race my friends. :cool:

[Ron Olson]

you will probably have to shorten the pipe to get the right length. A tubing cutter does a really nice job on that.

[t3NHRacer]

Ok I can do that. But what about the speed difference. I need to know if it is worth it.

[Ron Olson]

Put it this way, I've got 3 of them for my .12 boats. I haven't found a better pipe yet. I'm always looking and I've got an assortment of other ones that I've tried that don't seem to work as well.
I'd like to try one out in a NH as well as a Miss Bud. Bugfanatic has a Miss Bud that I may try one out in if we ever get together again yet this year.
I'd try to shorten the header as much as possible because it is way too long in stock form then add on a length of tubing to the exhaust side to dump the fumes.
One other trick up my sleeve they I have is a larger carb that someone modded for me. It's a Nova Rossi .21 carb with the base turned down to fit into the intake. The 5mm bore carb opening comes from ROAR mandated rules that don't apply to us. The carb change alone added a good 5+MPH to my boats.

[water dog]

Smart idea Ron !.

[BurnZ]

Hey Ron,
Just received a Mac's pipe. Where is the best place to put the pressure fitting? Or does it matter? Chris

[BoatDoc]

you will notice quite a difference in speed with that pipe. it's worth it. it's worth it. it's worth it. does that answer the question??? ron may have a better answer for this, but as far as where the pressure fitting goes...my limited experience with inboards has shown me that the closer to the engine they are the higher fuel pressure you get.

[BurnZ]

Is it better to have higher fuel pressure? Chris

[BoatDoc]

i would have to say yes. it will change your needle settings, however. if the fuel pressure is higher, it will push more fuel through the carb. to my understanding it will also atomize better at higher pressure. i run one of my outboards with the pressure fitting on the crankcase...that thing has crazy fuel pressure. i think a supercharged 454 gets better mileage than that engine. but like i said, my experience with inboards is fairly limited. i've been around outboards mostly, and only got my first inboard about a year ago.

[BurnZ]

Never been around or seen an outboard in person. Only in mags. I guess it totally changes the characteristics of a boat since the weight is shifted back.

[BurnZ]

What if you put the fitting on the header? Then you'd never have to add one to any new pipes. Or is it more likely to throw more oil in the lines?

[BoatDoc]

to me, nothing can match the sound of a K&B 3.5ob with an exhaust throttle and a mini-pipe. they are obnoxious as hell :D and i like noise!! most races won't allow that set-up because they are WAY over the noise limits.

[BurnZ]

I just measured the pipe length. If I cut it to 7" to the widest part, then I'll have to shorten the header also and it will like about 1.25 to 1.5" too short to go out the exhaust exit out the back of the boat.

[BoatDoc]

you can use a piece of tubing on the end of the pipe to make it dump out the transom. you shouldn't cut the pipe itself, usually you would only want to cut the header.

[Hydro Junkie]

In the inboard hull, the pressure fitting on a tuned pipe is normally best at the widest point of the pipe. This is due to the pressure waves going both directions most consistantly at that point. You won't get quite as high of pressure as in Boat Doc's case(and no offence intended, Doc), but it will be more consistant pressure. One thing you DON''T want to do is put a pressure fitting on the header. the header will have the unburned fuel the pipe is trying to push back into the engine in it. It will lessen the effect of the tuned pipe, how much?????????????????

[BoatDoc]

good point HJ, never thought of it like that.

[Watercadet]

Wait on that durastic legnth chop. I shortened mine by an inch and it would not let the motor get on the pipe. Go slow. Test, adjust, test, adjust...etc. 1/4 in at a time is OK. Get a pipe cutter from Pep Boys of the plumbing supply to cut it and the headder.
Adam

[BoatDoc]

hey HJ...i just feel like adding more fuel to the fire...your favorite boat (the pro boat miss bud 1/12) has the fuel pressure fitting on the header. if what you say is right (and it makes sense to me) then that means that we've found yet another thing wrong with the buddy. i think we should start a slogan for the pro-boat bud..."THE BOAT THAT WE LOVE TO HATE." i've had one...so i can say that :D

[BurnZ]

Finally got to run it today. Man, with that pipe I definately need larger turn fins! She's certainly loud now. Has a popin sound like my old 2stroke 4-wheeler had with an aftermarket pipe and silencer. When it hits its power band its gone.

I still had the shorter ep versions rudder on it today. It didn't turn very well.