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Exhaust Back Pressure Myth (a Good Read)


New Member

A very good read.

our stock powerband is @ 5,500RPM and I believe the best pipe diameter for Stock engine is in between the stock pipe and AHM M1 diameter. Modified Engine is a different story. :)

I think this is the reason why YYPang is better on stock and mid-modified engine.
What do you mean about mid modified engine, sir? Stock bore and stroke?
How about gas consumption, sir? Will it lessen GC?
Racing CDI modifies the powerband of your engine without engine modification. It increases your horsepower because it over revs your MC to the stock modification (at the expense of durability with prolonged over revving). Mid Modification means changing to Racing CDI, 57mm Vixion/JVT block, stiffer valve spring and exhaust modification. Increasing your bore size increases HP but a little bit of torque, increasing your stroke will do the opposite. Max engine mod (like Traxxis) is the mother of all modification. :)

Take note, the rule of thumb is you need 30% increase in HP to gain 10% Topspeed. The only main advantage of increasing your HP is acceleration which is what we are always using 99% of the time. We don't use topspeed daily right? :D


New Member
You mean to say sir, if you have a high lift crankshaft, you will lose some of hp and gain torque? I thought they are directly proportional... by changing the pipe to an aftermarket sir, does it save gas comp or more gas comp? Coz some say it lessen, some say it increases. What is ig really, sir?
Sir, you may read a good info below. I am more into car tuning which was my past life. :) but i think it is the same.

Now do you have a high lift long duration cam? High lift will just push the valve deeper into cyclinder for efficiency. This will increase torque and HP. Bore and stroke doesn't involve your Cylinder head. You may read differences between oversquare, square and undersquare engine. T135 is undersquare engine which is on the torque side. :)
for camshaft.
Fuel Consumption isn't affected by open pipe or any exhaust mods. however there are theory's behind it which backed by experience from myself and my colleagues.

1.) High Fuel Consumption due to sungaw pipe - big diameter pipe like GP Elbows with unmodified engine. This happens when your powerband or max torque shifts to higher RPM requiring you to rev it higher to attain max torque since exhaust velocity is slow affecting low RPM torque. The more you use high RPM, the more fuel it consumes.
2.) High Fuel Consumption due to waswas mode always on - you like the bassy sound of your engine, revving it a hundred times (stop light, starting it up, parking it, during cruise mode you intend to press the clutch and rev and rev it.) thus consuming more fuel.

We should have stage upgrades just like car, what the motorcycle industry is doing is like creating frankenstein. Ex: Racing Cam without chaing air filter and exhaust and etc...)

Staged Upgrade:

Stage 1: Power Intake Filter, Power Exhaust, Sticky Wider Tires and fine tuned Carb (non FI) - all engines are built with stuffy nose. This will increase your power by 5%-20% depending on the tuning. Example is that you breath through your stuffy nose(Intake Filter) and then breath out to your mouth (Open Exhaust). You have to satisfy both... Stage 1 is more of a very popular tuning aiming almost all consumers for increased fuel efficiency with the Stock Durability. Vixion Kit is also an option since it is a stock part but bigger piston.

Stage 2: Stage 1+ High Lift Cam + Port and Polish head + Racing CDI+Stiffer Spring + Bigger brakes - A tuner's second stage upgrade.
Stage 3: Stage 1+ Stage 2 + Suspension Upgrades+ Bigger Bore kit - Racing setup starts here.
Stage 4 -infinity depending on budget. :D


THATS WHY MY MOTORCYCLE BECAME SLOW> HAHA!! ANW, I'll change it back to its origal pipe. Im using nob1 pipe not that loud :(
one thing... I noticed our aftermarket pipe diameter is really big, if you look at Bigbikes specially motoGP bikes exhaust, the pipe elbow diameter isn't that big and that is producing 236HP on 4 Cylinder HIGH RPM Engine comparing it our UB with less than 10% of the power :)


Super Veteran
very informative on the read..... bro @Francisco N. Maristela i need some advice & your opinion. i'm in the process of upgrading to the FZ150/vixion kit.. and just planning to modified the stock exhaust as sample picture below. having trouble finding the 26mm front manifold for the exhaust. is it wise to use the 28mm manifold or wait till i can find the 26mm manifold and do the modification for exhaust.. 28mm seems really big to me and might not be efficient for the exhaust gases to exit the chamber and flow speed at the highest velocity possible... thanks in advanced.

Sir we got the same project for daily commute and not so loud pipe. My plan after upgrading to Vixion is...

1.) Buy a new 26MM exhaust manifold (I see a lot in Caloocan)
2.) Weld it in the original Canister Without removing the Catalytic Converter.

or go To QC Kamias and have it kalkaled. :D


the reason why Sniper MX is slow because of it's Catalytic Converter. All Cars have a term De-Cat so it would be faster but not environmentally friendly. SNIPER MX complies to Euro 3 Standard which is not bad for a Carb engine. :D
26mm - Remove filter cage and you may have a larger exhaust outlet - exhaust velocity is still good due to smaller diameter elbow
28mm- Remove Filter cage but retain the exhaust outlet. - the key here is free flowing exhaust with velocity.
this is good for Vixion upgrade, Power intake filter, RCDI and Valve spring.

sorry Kojack, i thought you are from the Philippines, what you want to do is called "kalkal Pipe" here. :)

We have special shops that does a very good job in modifying exhaust.



Super Veteran
nice one bro @Francisco N. Maristela hopefully we all can get it up & running asap with the vixion kit :)... back home the road transport department is kinda strict and the mr policemen, they really love giving away fines tickets so need these not so loud "kalkal Pipe" and keep a low profile...

26mm - Remove filter cage and you may have a larger exhaust outlet - exhaust velocity is still good due to smaller diameter elbow
28mm- Remove Filter cage but retain the exhaust outlet. - the key here is free flowing exhaust with velocity.
i'm having trouble finding the 26mm manifold and there are a lot of 28mm manifold. seems like replacing the front manifold with 28mm makes more sense and less work than 26mm, removing the filter cage inside and still retaining the exhaust outlet as is. need to do these exhaust mods soon and move on to the other to do list. thanks bro ...