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Old 03-24-2003, 11:00 PM   #1
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Default Cutting the header for more top/low end?

just wanted to know how much do i cut of the header,is the difference between a regular and cut header big?
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Old 03-24-2003, 11:09 PM   #2
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what type of engine
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Old 03-25-2003, 01:42 AM   #3
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sts 5 port with a rex pipe
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Old 03-25-2003, 10:18 AM   #4
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Cutting the header makes the total exhaust length shorter which supposedly increases top end at the expense of losing low end torque. There is a point of diminishing returns so I would start with 1/4" (0.25 inch) and then cut a little more at a time until you find the right balance for what you are trying to accomplish. Unfortunately, you'll probably waste a header finding the optimal length but that's all part of fine tuning.
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Old 03-25-2003, 10:44 AM   #5
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Default Cutting the header for more

Guys;

Depends what you want. A shorter Header generally shifts peak Power to a higher RPM. A longer Header the opposite. Sometimes you don't have a choice and you HAVE to cut, just to get everything to fit and accept the consequences.
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Old 03-25-2003, 11:05 AM   #6
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There are a lot of different versions of what this does. I am not going to say what I think it does because it is irrelevant here but one US magazine published that shortening the length of the pipe/header increased the acceleration of a car and not the top end speed.

They also stated that increasing the length of the pipe/header increased top end speed.

Seems to be a lot of controvery on this subject. The magazine in hand was RC Nitro. So who is correct?
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Old 03-25-2003, 11:16 AM   #7
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I am just repeating what Motorman and others have said in the past. Of course, pipe shape and design would probably have some affect on it also. I just think about the NTC3 pipe. Very long with lots of torque. One of the common tuning tips is to cut .5" (half inch) off the header right off the bat. I finally got around to it and it really woke up my MR12.
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Old 03-25-2003, 11:26 AM   #8
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Actually, here's some info from the RCNitro article online:

Quote:

The header's length has a significant impact on performance. It's much like a trombone: you slide it out farther, and it resonates at a lower pitch. Slide it out less, and it resonates at a higher pitch—same thing with tuned pipes. Experiment by cutting 1/8 inch at a time off the header, and run the engine between cuts. The idea is to keep cutting until, as the boys from across the pond say, it's really "on song." That means the engine and exhaust system are in sync and singing in harmony. This is when the engine makes the most power. The rule of thumb is that a longer header is better for bottom-end power, while a shorter header makes your engine scream on the top end. You can go too far in either direction, so don't be reckless; you'll do more harm than good.
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Old 03-25-2003, 11:56 AM   #9
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Yes, and that I agree with.

But while shortening the length of the header increases RPM if you also shorten the length of the pipe you take away from this and increase bottom end torque. They also mentioned this in the actual magazine article.

So, effectively the pipe is the main denominator and decides whether you increase or decrease Torque/RPM.
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Old 03-25-2003, 09:15 PM   #10
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Default Pipes and Headers

Guys;

I would say that the length and shape of the Pipe has a greater impact on powerband than say cutting 1/2" off your Header. Cutting the Header (or extending) is for fine tuning what you have already.
Sport engines seem to benefit more from a Short, Torque Pipe, while Race Engines seem to work better with a Pipe that encourages Power at higher rpms. These have at least been my observations.
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Old 03-25-2003, 09:47 PM   #11
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Modellor: that info is wrong. The shorter the exhaust system the the more HP (RPM) the motor will make. The longer the exhaust system the more torque the motor makes. It does not matter what side you take it from. This is been an undisputed rule for the past 30+ years. It comes from 2 stroke dirtbikes, and was made real common knowledge by the RC Boat guys. The shorter the exhaust system means that the pressure waves have less distance to travel to get from the exhaust port to the end of the pipe and back to the exhaust port to pack back in the fresh chrage. This makes the exhaust system more in-sync with the motor at higher RPM's. But at lower RPM's the motor will not be "on the pipe." The longer the exhuast system means that the motor will be "on the pipe" at lower RPM's. When you go up in nitro % you want to leangthen you exhaust system because the more nitro will make the exhaust charge travel at a higher velocity, thus effectivly shortining the exhaust system so to compensate you must leangthen it. I belive that every 10% means you want .125" longer. ??? I think??? Shape does make a bigger difference than size though. Less belly leangth and more cone leangth makes for a better top end pipe, and more belly and less cone leangth makes for a more bottom end pipe. I have know idea where RCNitro get's its information from, but I have a collection of old boat motor tuning books from the same publisher, Air Age, that came out in the eirly 90's and has the same info that I am writing, so I belive that the RCNItro people just need to do their homework.
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Old 03-26-2003, 11:30 PM   #12
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I usually cut 1/4 of an inch originally and then cut in 1/8 increments after that. If I cut a little too short, than I space the manifold and pipe about 1/8 of an inch by using the coupler. My coupler is strong it doesn't rip or anything. If I make the manifold too short, I buy a new one.

Also, a shorter pipe/manifold combe moves the powerband more rpm-biased because pressure pulses take less time to reach the end of the pipe and rebound than if the manifold and pipe combo were longer in length. This allows the pressure pulses to be more synchronized with the engine at higher rpms.
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Old 03-29-2003, 03:59 AM   #13
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the shorter the pipe, the higher up the power band is,

it is more greatly shown on Go-karts and dirtbikes then on our engines.

we seem to see it more as more rpm with a shorter pipe

and alot of people cut in 1/8" and if u cut a little bit off, just pull the exhaust through the coupler a little bit to compensate


my mate races go-karts and a friend of the family owns 3 dirt bikes, i have seen first hand the adjustments they make.

but with a long pipe, given a long enough straight they will still rev up to the same point.

but a shorter pipe is better on huge long tracks, and a shorter for a track with NO straight away but basically all corners, and a lot of hair pin ones.

also i have had my exhaust come just about off during a race, i lost all speed on the straight, but had plenty more power then required out of the corners.
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Old 03-29-2003, 05:45 AM   #14
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Yeah, I agree with the shorter pipe producing more power. I didnt want to state my own opinions because this type of thread is open to massive agruements.

But I can understand why many people believe that a shorter pipe produces more torque. On a shorter track you always want bottom end power and as a short pipe works better on such a track people tend to associate it with more torque and a longer pipe with more top end power.
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Old 03-29-2003, 05:37 PM   #15
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Default Re: Cutting the header for more top/low end?

Quote:
Originally posted by shortyboy
just wanted to know how much do i cut of the header,is the difference between a regular and cut header big?
Is it a 1-piece or 2-piece pipe

What car is it ?

What plug are you using ?

What fuel are you using ?
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