Jump to content
Sign in to follow this  

Exhaust in front, intake in back.

Recommended Posts

This is something that has pegged my interest since I got into riding all those years ago.

Why is it that every single cylinder or any inline engine built so that the exhaust exits the front and the intake air needs to enter out of the airflow tucked in behind the head? I'm sure there is some reason I don't understand, otherwise they wouldn't all be this way, but what exactly is it?

Just wondering:ride:

Share this post


Link to post
Share on other sites

Cannondale (now ATK) designed an engine back in the day that had the exhaust in the back. It created a very short powerband that wasn't up to par with the competition. The fact is you need your exhaust pipe to have a certain length to produce a broad powerband, and having the exhaust on the back won't allow it.

Also, it forces the air filter to be placed under the gas tank. Not very practical...

Share this post


Link to post
Share on other sites

It would probably also throw off the weight distribution. The top end would have to rotate and move back to make room for the intake setup in the front of the frame.

Share this post


Link to post
Share on other sites

The reason the exhaust typically exits from the front is so that the engineers can maintain the proper exhaust tube length and to accommodate the carb/intake packaging requirements. Most air filter boxes pull air from the back to limit the hot air hot air off the engine from entering the intake.

Share this post


Link to post
Share on other sites

I would agree with CamP and add that there's a lot less dirt at the back of the motor where the intake is.

If you want to try it the other way around - google search "ICC Motors"

icc-tm_548x480-64c.jpg

We go-kart guys have been using these for several years now. 125cc two-stroke w/integrated six-speed gearbox. Intake in front and exhaust in the rear. Not cheap, either, which is why I still run a CR125 on my kart.

Edit: almost forgot - no water pump (kart axle-driven). Not sure how you would handle that on a bike...

Share this post


Link to post
Share on other sites

well for our application in particular i can see intake in the front making the induction of water mud dirt etc even more likely due to the front tire flinging it everywhere. the exhaust would also be very very short, making a usable power range that is the fraction of what our bikes have.

however, Honda's K-series engines, (or the k20 at least) which are used in the Acura RSX, and the most recent Honda Civic use the setup you describe, where the exhaust exits from the rear of the engine, and the intake manifold is on the front.

Share this post


Link to post
Share on other sites

this is a turboed k20 but was the best example of what im talking about.

turbo and exhaust in the back, intercooler piping traveling up front to the intercooler, the forced in through the front.

130_0708_12_z1999_honda_civic_hatch.jpg

Share this post


Link to post
Share on other sites
I would agree with CamP and add that there's a lot less dirt at the back of the motor where the intake is.

If you want to try it the other way around - google search "ICC Motors"

icc-tm_548x480-64c.jpg

We go-kart guys have been using these for several years now. 125cc two-stroke w/integrated six-speed gearbox. Intake in front and exhaust in the rear. Not cheap, either, which is why I still run a CR125 on my kart.

Edit: almost forgot - no water pump (kart axle-driven). Not sure how you would handle that on a bike...

Chain driven maybe? or runoff the front sprocket somehow?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×