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A dummy's guide to Intake Manifolds.

Note: written by a dummy.

Mark from Weldspeed

I am lucky to work for a business where I am surrounded by creative people who take pride in making their products the best they can be. Yes, I am the turkey among eagles.

I understand this is not the reality for most car enthusiasts. Many of you have jobs that have little or nothing to do with your car modification hobby, so it's natural that concepts like "what makes a good intake manifold" may not be immediately apparent.

Weldspeed Intake Manifold

So, come with me if you want to LEARN!

Let's just call this a crash-course of Intake Manifold practical design considerations.

By the end of this blog, I hope to help you make a somewhat educated visual design comparison of Intake Manifold options based on the topics we will touch on. BUT FIRST, a note on aesthetics... It has been said that "beauty is in the eye of the beholder", so if you're installing an intake manifold mainly for aesthetic purposes, then the world is your oyster! Just choose the one that appeals to you the most and enjoy!

Intake Manifold runner length


What's a runner? The runner is the length of tube that connects the plenum chamber to the cylinder head flange & intake port. One of the most significant impacts on the way an engine makes power comes from the length & design of the intake manifold runners, which direct air into the ports.

Generally speaking, shorter runners favour a narrow power band higher in the RPM range, whereas longer runners favour midrange torque/power. There are of course limits either way, and nothing is free when it comes to torque production...going one way usually means losing out at the other end. So what does that mean for you? Well, if your particular motorsport favours a narrow powerband high in the RPM range (like drag racing), then short runners may work well.

BUT, for the majority of car enthusiasts who use and enjoy their cars on public roads and in scenarios where responsiveness and midrange torque matter, runner length is KING!

In our own testing we have also seen that longer runners, by increasing overall peak torque production, usually increase power everywhere (more area under the curve), including higher peak power. So you may ask; then WHY do modern OEM designs commonly favour short runners? More linear/smooth power delivery, packaging/servicing size constraints, emissions considerations, fuel economy...the list goes on. I think it's safe to say that making the absolute most torque & power out of an engine platform is not always the top priority of vehicle manufacturers.

Taper? Tapering of the runner from the plenum down to the cylinder head is something that is commonly seen on many popular aftermarket intake manifolds. This style of design has been shown in testing to have the same effect as shortening the runner; ie. a loss in midrange torque in favour for a narrow power band higher in the RPM.

There are other factors in runner design that should also be considered, including smoothness of transitions, sudden changes in volume, bell-mouth openings, etc. Many of which factors may not be visible on external visual inspection of an intake manifold. TWILIGHT ZONE?: There is actually scientific evidence that indicates a step (sudden change in cross-sectional area) inside the runner can have a positive effect on torque production compared to tapered or parallel runners...*head explodes*

This shows you just how counter-intuitive the science of optimal intake manifold design can be.

Weldspeed Intake Manifold plenum


What's a plenum? The plenum is the chamber between the throttle body and the runners (on a single-throttle setup), which functions to evenly distribute adequate air volume to each of the intake runners.

One of primary considerations in relation to the size and shape of a plenum chamber has to do with the relationship between pressure and velocity (specifically, the fluid dynamics concept of Bernoulli's Principle - Enjoy that rabbit hole).

The importance of plenum size may have been over-exaggerated within aftermarket intake manifold circles. Studies have shown that changes in plenum size across a large spectrum showed little to no difference in torque production, except at extremely large proportions (so large you could never fit them in an engine bay). Granted, most research in this area is conducted on naturally aspirated engines.


The question of what material is "best" comes down to what your goals are for the vehicle/engine; aesthetics, weight considerations and of course let's not forget COST, both of production and at point-of-sale.


"That's what she said!"

Being in the business of Intake Manifold design and production, you quickly realise that physically fitting an intake manifold can often mean compromising on optimal design due to the available engine bay space. So even with the best of intentions and relevant knowledge, you will always be limited to the reality of space.

Of course, all of the factors that affect performance are pieces in a puzzle that fit to achieve a common goal. No one factor will make a positive difference without being able to work in harmony with the others.

So, which Intake Manifold is best for you? The WELDSPEED one of course!😜

As always, if you have any questions feel free to contact us on socials/email/website.

Happy modifying!

Mark Weldspeed Sales & Media

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