I race a 400 engine in a 350 frame. Looking to experiment with pipes. Will 350 pipes fit the 400 engine? I assume the mounts will be out to lunch.
the header is shorter on the 350 pipes , so you'll gain more lowerend power and mid .. I was taught the longer the header pipe the more power at topend range.. break that down into thirds.. low mid and high...
The pipes will be all wrong. The header flange has the wrong bolt pattern size and the rear mounts will be wrong. Both those can be fixed. The tuned length and pipe cone angles and diameters are wrong and that can't be fixed. If this is your first year racing and you are learning, they will work; just not well. Probably OK on a tight course where even stock exhaust would be OK. You would be smart to get a set of good 400 pipes. In 2 stroke race bike modification the emphasis should be: tires, suspension, brakes, ignition, exhaust, intake, engine modification, appearance. Lyn Garland
Thanks for the comments guys. Actually what I am looking to do is knock about 500 rpm+ off the top since spinning this thing as tight as I have the last few years has shortened it's life somewhat between rebuilds. I actually am turning it tighter than I ever turned a 250 or 350 back in the day and this is a big motor, a 430. It spins up like the pipe may be a bit short. I've thought of adding some length to the headpipe or belly but I wanted to do something first I could easily undo. I have several sets of relatively mellow 350 race pipes (sub 10,000 rpm) with the same headpipe size that would fit right on ( I figure lashing up temporary rear mounts is no problem) and what I am mainly wondering about is pipe to frame clearance underneath since the 400 engine is taller. Don't want to send a set of pipes down if I can't get them on. Incidentally, I just installed my new custom 1 x 2 chromoly swingarm, adjustable up to 19 inch, with 3/4 inch axle. More rigid and more weight on the front. Interested to see how it works.
If you add one inch to the down pipe (header) you will drop your RPM and probably give you clearance to mount the pipe. You should actually buy new pipes. Swarbricks are the best. Lyn
that is the general idea, but I will proably be a bit more precise than that and use formulas. Something very similar to Swarbricks is what I am using now. So, does anyone know if 350 pipes will fit the 400 engine? my main concern is whether they will clear underneath.
Lyn- Linker is running full blown Barlow set-up....very fast, high strung rd motor. (probably more high strung than any of the WERA guys...) Not sure if he's ever raced w WERA, but he's been running AHRMA for a long time... It sounds like he wants to add a little service life, without decreasing too much power... Linker- As Lyn suggests, adding an inch to the header will shift the powerband down 500 rpm and is probably your best bet. you already have a killer set-up, putting 350 pipes on it will hobble it in more ways than just lowering peak rpm. That being said...I took my tz350 swarbricks off my rd375 and ran them on my rd 400 with no modifications or problems, but I'm sure I would have been better off with 400 pipes. (now that I think of it, I did have to make new rear sets...)
You might want to put it on a dyno and see where it peaks. Harry usually sets up most of his 400's to peak just over 9000, but a few of his riders (like maybe that Spray-n-go character) that he knows can hold higher corner speed, he actually gives them 1/2 inch or so SHORTER than his normal header to get more revs and power. PS- to the fellow who was told a longer header would give more topend- I'd take tuning info with a grain of salt. Plenty of people are willing to give advice, only a portion of them know what they are talking about.
Carl, good to hear from you. Sorry I will miss Savannah, have a good time. I think you nailed it, I am pretty sure I have some of Harry's shorter pipes. Chuck Quenzler mentioned to me he had several pairs of Harry's pipes, and his description of the shorter pipes squares with what I have. They feel like they peak at about 10.5 to 10.7, with maybe 500 rpm of strong overrev. It takes conscious effort and some tach watching to shift at or just below 10, with the engine still climbing sharply to the power peak, whereas shifting by feel once it gets to or just past the peak naturally takes it to 10.5 or 10.7 at least. Geared more or less normally, coming onto a long straight, it needs more than 10K revs to continue to pull hard. When I asked him about this, Harry once told me to just hold it open until it wouldn't rev anymore coming out of the infield at Daytona, for instance, and that is right at or just above 11. At first I thought the 11,000 thing was just tacho error, but I put another little Tinytach digital tacho on it, and it read the same. At Miller, geared very short, I could shift at 10 and it would pull strongly across the gear splits, but without the short gearing, I more or less need to spin it up farther. I am NOT complaining about the result, the thing is a jet and I love it, I just want to move the whole curve down about 500-750 rpm for more crank longevity. I just don't want to add any length until I have a good feel for what I am going to end up with. As to my question about 350 pipes (which started this thread), I have a couple pairs of wrong, 350 pipes with the right length and the same headpipe and stinger diameters, and I just wanted to try them first, before I changed the pipes I am using, to get a feel. I won't use them to race, just want to see what the effect on rpm is. I am still wondering if they will clear under the engine, mounted to the taller 400 cylinders. I think I will just take them south and see. And RZRacer, good to hear from you. You are right, added pipe length is where I am going.
