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Author Topic: Anybody ever made a homemade air intake?  (Read 3521 times)

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« on: February 25, 2017, 08:59:33 PM »
Just wondering if a good flowing intake can be built from scratch at a fraction of what a kit costs?

Offline broken1

Anybody ever made a homemade air intake?
« Reply #1 on: February 25, 2017, 09:46:55 PM »
I used the OEM boot & electrical PVC & made a bracket & clamp to hold it. PM me your number & I can send you a couple pic's
overkill is an often underrated achievement

Offline Jerry Hall

Anybody ever made a homemade air intake?
« Reply #2 on: February 26, 2017, 11:27:56 AM »
There is some discussion in another thread    http://trx250r.org/threads/6793-New-Project-YFZ-Banshee-Hybrid?p=71802&viewfull=1#post71802     that might keep you from making some of the common mistakes when making home grown intake/air filter engine components.  Honda's engineers have already solved the resonance portion of the design by providing a good pattern in the OEM TRX250R boot to follow in the diameter progression vs distance from the carburetor.  


Remember an engine that makes good power has an intake that flows well and has the resonance of the system correct.  An engine that has a high flowing intake with the resonance wrong will not usually make good power and will have unsolvable jetting issues as well as dips and spikes in the power curve.

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #3 on: February 26, 2017, 01:28:23 PM »
So the pipe on the air intake needs to be the correct Tuned length to reduce resonance issues?
Someone should dyno a Trx250R with different length pipes on the carb and filter to see what it does to the curve. It would be interesting.

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #4 on: February 26, 2017, 01:35:04 PM »
In V8 drag motors a short ram intake usually means shorter intake runners to make more low end torque.A High Ram Intake usually makes More HP in a higher rpm range. Just wondering if the same rule would apply to a tuned intake tube on a Trx250r?

Offline Jerry Hall

Anybody ever made a homemade air intake?
« Reply #5 on: February 26, 2017, 06:06:53 PM »
Quote from: DeathPunch88_250R;71971
So the pipe on the air intake needs to be the correct Tuned length to reduce resonance issues?
Someone should dyno a Trx250R with different length pipes on the carb and filter to see what it does to the curve. It would be interesting.


The pipe on the air intake needs to be the correct tuned length to take advantage of resonance. Resonance can our friend or dreaded enemy. Optimizing resonance is the phenomena of pressure waves arriving at the port, reed tip or valve at a time just before intake closing so the trapped air flow into the engine is maximized.

I have done a lot dyno work on the TRX250R intake length.  ESR, LED and Honda has obviously also done dyno work on the intake length.  The portion of the intake that optimizes resonance on all of the above intakes have tuned lengths that are almost identical.  When Troybult finishes his dyno testing on his new intake system, it will also probably have a similar tuned length to the above systems already in the public domain.  The engine knows what intake length it wants and has not changed since these engine were designed.........it just takes a few devoted developers doing dyno testing to come up  with the same answer.  Different cylinders designs, different carburetor sizes, and pipe designs on the TRX does not change the tuned length of the intake very much but it does have a huge effect of the size of the air filter needed. A flow bench or cad package cannot be used to find the optimum tuned length on the intake or exhaust.

Tuning the intake is not a new concept to us old timers, most of the above builders have been doing it on all of their engine packages for over 25 years.
« Last Edit: February 26, 2017, 08:15:53 PM by Jerry Hall »

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #6 on: February 26, 2017, 06:50:22 PM »



Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #7 on: February 26, 2017, 07:23:55 PM »

Offline Jerry Hall

Anybody ever made a homemade air intake?
« Reply #8 on: February 26, 2017, 07:26:33 PM »
Quote from: DeathPunch88_250R;71972
In V8 drag motors a short ram intake usually means shorter intake runners to make more low end torque.A High Ram Intake usually makes More HP in a higher rpm range. Just wondering if the same rule would apply to a tuned intake tube on a Trx250r?

My v8 testing has showed the opposite to your findings.  Short tuned lengths favor higher RPMs where longer tuned lengths move the power to lower RPMs when the cams are optimized for a given tuned length.  

The tuned length of a intake tract tunnel  in a 4 stroke starts at the valve and ends slightly above the bell mouth of the ram tube.  The optimum tunnel shape starts at the valve and ends at the bell mouth of the ram tube.  The air flow does not really care if the intake tract tunnel is in the head or built into what we usually call the intake manifold.  The engine is just wanting a certain cross-sectional port area vs length from the valve with as few bends as possible.

The old 4 barrel intake manifolds had intake tunnel lengths/tuned lengths that were way too short.  These short tuned lengths were at an RPM that was out of reach of the breathing and mechanical limits of most engines. Then came the tunnel ram type of intake manifolds in the 1970s that had tuned tunnel lengths that were 6" or more longer than the 4 barrel manifolds.  The tunnel ram manifolds typically made more power everywhere in the RPM range.  Engineers found that making the runners real long could make a small block Chevy make big block type power in the mid range but there was not enough space under the hood for these carburetor type manifolds.  

20 to 25 years later when fuel injection became the norm we could make the runners as long as we needed and feed the runners from a large plenum with the throttle body mounted at one end.  Engine power started to escalate without the need for wild cam timings because the tuned length of the intakes were optimized for the cam and RPM range where the engine needed to operate.  This group of intake systems were known as tuned port manifolds.

Engineers are often handcuffed and cannot do what they know will work well because of space confines or marketing will not allow them to introduce certain technologies because of the prejudices of the consumer.

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #9 on: February 26, 2017, 07:31:29 PM »
Someone gave a tip to use Zip Ties in the Chat Box so I used some with good results. I plan to get a Red Filter in place of the blue one.

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #10 on: February 26, 2017, 07:32:53 PM »

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #11 on: February 26, 2017, 07:34:44 PM »
Okay thanks Jerry I ended up Using the stock boot

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #12 on: February 26, 2017, 07:35:26 PM »
Better to go with Whats proven!

Offline Jerry Hall

Anybody ever made a homemade air intake?
« Reply #13 on: February 26, 2017, 07:57:55 PM »
Quote from: DeathPunch88_250R;71977






My testing has shown that the intake pictured is a very good intake for engines with 39mm or smaller carbs and engines that make under 45 hp.  As the power goes above 45 hp, the surface area of the filter needs to increase as well as the inside diameter of the small portion of the intake boot.  The length of the small diameter portion of the intake boot is the portion of the system that should not be changed much.  This is the tuned length portion of the intake NOT THE DISTANCE FROM THE CARB TO THE AIR FILTER!!!!

On the big bore engines that are making over 60 hp the air filter needs twice as much filter surface area as the one pictured above.  Air filters with a lot of surface area helps prevent the engine from sucking dirt through the filter.  Air filters with excess surface area allows the filter to be oiled slightly heavier without hurting the air flow through the air filter.  Excess surface area also reduces the amount of suction the engines places on the particles of dirt that are trying to sucked through the filter.  

If you have room, install an air filter with as large of a diameter and length as possible.  There have been a few rare occasions when a very large filter will cause a drop in power even after re-jetting the carburetor.  When this occurs I usually find when I get the tuned length correct the power is restored and or better.

Offline DeathPunch88_250R

Anybody ever made a homemade air intake?
« Reply #14 on: February 26, 2017, 08:10:34 PM »
Cool Jerry! Thanks for the reply on my Intake.
I will take my old filter to the parts store when I go get the new one and see if they can get Me a longer filter.