Is a cold air intake worth it for a Mazda MX-5 ND2 …

… with headers, a free-flowing exhaust, Port Water/Meth Injection and a tune?

I'm not sure about the ND, but on this NC we gained a good 22bhp at the hubs with the new inlet manifold and intake. It had the exhaust manifold, exhaust and cams installed previous to coming in for the initial tests

Thank you, that’s significant! But with what inlet manifold and intake?

Thank you again Chris250 for the info, albeit from a 49 year ago dyno run on an NC. Note also that Mazda had made a major upgrade to the engine for the ND MX-5s: a modified CX-3 engine over the NC and earlier versions of the MX-5: where Sake Bomb Garage/MiataSpeed in Fremont California told me that the motor had already been pretty much maxed-out by this time. Of course, that was when they were trying to sell me an Edelbrock Supercharger: $7,000+ just for the kit. With their installation I guess the total would have to be over $10,000. Christian gave me a test ride in their 12 psi boosted car, with its necessary water/meth injection, and it was impressive! But I just wanted a little more grunt with fewer dollars, and wanted to keep the benefit of it being naturally aspirated as well.

Also, I see from HPA’s Introduction to Engine Tuning course, that I’ve just purchased along with their Tuners Starter Package, where Andre had stated that using a high octane fuel like VP’s Racing's with a 120 octane rating can add 50% to 100% more power to even a stock engine! Of course, that’s what Water/Meth Injection can also do as it can raise the octane rating of even 87 octane pump gas to over 118 octane—the power increase coming in both cases from advancing the ignition timing.

Which leads me to my next post: “How To Tune For Water/Meth Injection And Not Blow Up Your Engine!” Note that with Water/Meth Injection I will be able to match, or exceed the power gains of forced induction without the added expense, and not have to walnut shell-blast clean the intake ports every 15,000 miles—the need for which I've eliminated in my naturally aspirated car that otherwise would still need to be cleaned-out every 30,000 miles (topic for another post)!

Hi Steven,

I'm sorry if my 3-week-old dyno graph is a little out of date for you.

I know that Mazda have changed their core engine, but what normally happens is a lot of designs are carried over, inlet runner flaps etc, which are designed for torque and driveability will be used time and time again. Still, for people like ourselves who are after the maximum airflow through an engine, it is sometimes worth changing the full inlet, especially if you are trying to match the power of a boosted engine whilst keeping it N/A.

I'll mark this post as resolved and follow up in your other post

Thank you again for the reply Chris. But firstly, you still haven't answered my question from November 19, 2025 at 16:33: "But with what inlet manifold and intake?": where you stated that "We gained a good 22bhp at the hubs with the new inlet manifold and intake"

And secondly, you wrote today that "I'm sorry if my 3-week-old dyno graph is a little out of date for you." No, not unless I'm going blind and can't read the date of DIN 700200 (1976) from the dyno graph you’ve attached in this post, making this dyno run … 49 years old! Just where on the internet did you dredge this up from? Please see a cropped image of your (supposed) dyno run, attached, and tell me if you can read what’s written there …

Thirdly, you also wrote that "I'll mark this post as resolved and follow up in your other post"

“I don't think this post has been resolved, Chris.” Therefore I've reopened “my” post here. Not only to seek answers to unanswered questions, but to seek clarification for the date of your dyno run (Was 1976 is the model year of the dyno then?).

Sorry Steven,

I've been trying to reply and post a picture from my phone, and after a lot of failed attempts, I'll just type the info.

The inlet manifold is a FAB9 Performance inlet, which has a larger throttle and then a Subaru intake pipe was used to hold the MAF and to ensure some even air flow, with a flexi-pipe leading to a bumper-mounted filter. I'm not sure which one, as it was a customer build. I'll try and post a picture in a separate post.

The date that you are looking at is the industry-standardised correction factor that the dyno is operating on for environmental conditions, German Institute for Standardisation (Deutsches Institut für Normung) (DIN). 1976 is an older standard that has been superseded, but is still a relevant standardisation for dyno work.

If you open the image I posted and scroll down, you'll see dead centre at the bottom of the screen the date that the dyno work was carried out, 2025/10/31, 31/10/2025 or 10/31/2025 for people who lay out their dates month first, either which way, 31st October 2025.

Here's the engine bay picture

Thank you for the clarification Chris! I apologize for my mistake about the date of the dyno run you showed: I’ve never done a dyno run, and have never scrutinized the ones that I’ve seen online for a date; hence I just fell upon the first date that I saw in your posted file.

I did look at the Fab9 Elite NC MX-5 Performance Intake Manifold that you noted, and the Subaru Aluminum Intake Tube WRX 2022-2025 as shown in your engine bay picture also attached. I like this very clean installation.

Fab9 says in their expected results for their NC intake manifold that for a “2.0L in a fairly stock configuration you can expect substantial gains - 14whp.” That means an extra 8whp (22bhp at the hubs is an apparent typo, although a dyno can be set to discount whp 85% to approximate bhp) gained with the addition of an exhaust manifold, exhaust, and cams.

This, as I was wanting to know despite the unequal comparison here—as the NC and the ND do not even use the same base engine—was to get an approximate idea from actual results of what effect I might expect from a cold air intake, alone, on my ND. Since the ND already has a quite good intake manifold, discounting the Fab9 NC intake manifold's stated 14whp gain on an NC, and further I have to extrapolate that perhaps I could realize an increase of 3 to 5 hp (what I have also seen estimated in some aftermarket solutions that are actually cold air intakes).

That is, with replacing the stock MAF inlet tube and ducting the intake directly out of the hot air of the engine compartment to an external air filter for a $350 to $450 aftermarket upgrade. That's something that I could do for the couple of extra horsepower (maybe 2 Tq to 4 Tq more) by simply running an insulated tube from the stock MAF inlet tube out under the right side headlight to a free-flowing (not a K&N which is the same, as I've found in test results, as no air cleaner at all!) air filter.

This was an engineering exercise, as a Mechanical Design Engineer, to thoroughly evaluate the idea of a cold air intake here, where I had previously discounted the idea as not at all cost effective (not to mention the addition of undesirable loud intake noise).

And it's not cost effective when my Water/Meth Injection (see post) can increase the octane of pump gas to 118+ which, according to Andre, can add 50% to 100% more power all by itself!