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more volume in a pipe is the enemy of velocity, and velocity is what you want to pack more air in with an NA car. Having said that, flow matching the entire system is always good and steps inside a flow path (up OR down) hurt velocity by making the air swirl and laminar flow detach, depending on speeds.
All that to say - I don't know why Nissan thought to use 2.5" pipe going into 2.75 TBs, unless the throttle shaft takes up enough space that even at full open it's the equivalent of 2.5ID.
I built my LTCAI using 2.5ID pipe and it was fine - noticeable (10ish) power bump on dyno. Then I put something like these in https://mrpmachineshop.wordpress.com...ura-vw-mk5mk6/ which are 2.75 ID, and per Jon at Z1 the larger MAF housing area meant dyno tune rather than street tune (have to recalibrate the air mass for a given flow, since it's now flowing a tad more). The Z1 After-MAF silicone is already 2.75, so I recently redid the filter to MAF housing piping in 2.75ID. It's in my build thread in the most recent pages, if you want to see pics.
The intake is a few decibels quieter now (measured with an app on the iphone, so not giving specifics as I'm sure the measurement isn't accurate, but as a relative thing). I'd say the car doesn't struggle as much at higher RPM, but it sat undriven for so long that my subjective 'feel' isn't really reliable. It will need to go back on a dyno to be sure - BUT - with the ecu already tuned for the 2.75 MAF housings it shouldn't be much. I don't see much of an AFR difference, but I haven't investigated short and long term trim changes yet.
On the other hand, 2.75 through the radiator support requires removing a LOT of material and bending sheet metal, which might be the reason the kits are generally smaller than that. And any of them have to flow better than OEM with the bellows tubing creating turbulence.
I built my LTCAI using 2.5ID pipe and it was fine - noticeable (10ish) power bump on dyno. Then I put something like these in https://mrpmachineshop.wordpress.com...ura-vw-mk5mk6/ which are 2.75 ID, and per Jon at Z1 the larger MAF housing area meant dyno tune rather than street tune (have to recalibrate the air mass for a given flow, since it's now flowing a tad more). The Z1 After-MAF silicone is already 2.75, so I recently redid the filter to MAF housing piping in 2.75ID. It's in my build thread in the most recent pages, if you want to see pics.
The AFM straighteners are neat but its a little odd they dont mention cross sectional area which is king. If you moved to 2.75" then added the flow straightener you are likely below OEM level of xsection. Lots of OEMs use Airflow straighteners but they are usually just two blades of plastic vs a honeycomb.
the honeycomb is barely thicker than foil; if I'm calculating cross sectional area correctly, 2.5 is 4.91 sqin, the 2.75 is 5.94 sqin, a 20ish% increase. The frontal area of the honeycomb would need to be almost 1 sq inch.
I've been searching for these two old pics I took before I had my throttle bodies ported and finally found them. The stock size is 2.5" (63.5mm) and it tapers down to 2.375"(60mm). You're incorrect about them being 2.75".
Oh yeah and of course I have to add the eye candy to show what they looked like after porting. IIRC they ported them up to 65mm with a slight taper to 63.5mm. Good enough for me while keeping OEM reliability.
Last edited by backman_66; 06-19-2023 at 09:21 PM.
I've been searching for these two old pics I took before I had my throttle bodies ported and finally found them. The stock size is 2.5" (63.5mm) and it tapers down to 2.375"(60mm). You're incorrect about them being 2.75".
Oh yeah and of course I have to add the eye candy to show what they looked like after porting. IIRC they ported them up to 65mm with a slight taper to 63.5mm. Good enough for me while keeping OEM reliability.
damn, well scratch everything I just said an now I’m more confused 😵💫. Haha I guess all my outer diameters are the same now as the Takeda intakes are 2.75 OD. I I guess I don’t know what I’m talking about 😂 anyways, I hope my car is a little faster now that I got rid of the necked down section. LOL
damn, well scratch everything I just said an now I’m more confused 😵💫. Haha I guess all my outer diameters are the same now as the Takeda intakes are 2.75 OD. I I guess I don’t know what I’m talking about 😂 anyways, I hope my car is a little faster now that I got rid of the necked down section. LOL
No issue @Josh South . We're all here figuring **** out and trying to help one another. Thanks to @backman_66 ,we now know the diameter of the throttle body inlet.
Lol it's all good man. Its good to have a small taper going from the intake through the tb because that keeps the velocity up. So 2.75" intakes are still a great upgrade! And there comes a point where you're limited by how much the head can flow regardless.
That's why I think 3" intakes are a bit overkill, although they may make a few more HP in the upper rpm's, i feel like it hurts you where you daily drive it most of the time. 2.75" is the sweet spot that I like.
Did some data logs and a few maps yesterday. Still tuning with the modified intakes today, so hopefully will have it buttoned up by the end of the day. Those are some beautifully machined TBs! After cleaning my TBs the other day I saw a significant change in how the car ran as they were starting to get pretty gunked up. Also used a little polishing paste on a rag to shine up everything.
That's why I think 3" intakes are a bit overkill, although they may make a few more HP in the upper rpm's, i feel like it hurts you where you daily drive it most of the time. 2.75" is the sweet spot that I like.
That's what I would think as well but a lot of places sell them strictly for NA cars. Admin tuning claims 3inch is the best and recommends stock throttle bodies lol.
Of course he claims it's best because he produces and sells the intake. From a pure numbers perspective, yeah it will probably hit the highest HP by a few points so I guess there's no argument there. It would be nice to see a comparison between 2.5, 2.75, and 3" to see how the power looks throughout the entire band. If you're 5 HP higher at 7000+rpm but 5 HP lower from 800-7000, which one would you prefer to use? (just guessing)
Of course he claims it's best because he produces and sells the intake. From a pure numbers perspective, yeah it will probably hit the highest HP by a few points so I guess there's no argument there. It would be nice to see a comparison between 2.5, 2.75, and 3" to see how the power looks throughout the entire band. If you're 5 HP higher at 7000+rpm but 5 HP lower from 800-7000, which one would you prefer to use? (just guessing)
Agree that usable HP and Torque is more important for a Daily Driver. I wish there was more discussion on this topic as most seem to focus on peak power.
Of course he claims it's best because he produces and sells the intake. From a pure numbers perspective, yeah it will probably hit the highest HP by a few points so I guess there's no argument there. It would be nice to see a comparison between 2.5, 2.75, and 3" to see how the power looks throughout the entire band. If you're 5 HP higher at 7000+rpm but 5 HP lower from 800-7000, which one would you prefer to use? (just guessing)
Everything he just said.
I suppose it depends how you use the car. If you live at the quarter mile, then sure, go for every ounce of peak HP you can squeeze out of it. Or if your hobby is all about numbers and bragging right, then shoot for that moon. But if you're driving the car, you know... like a normal person in traffic with other cars, then you want mid-range gains, because that's where you live.
I've always thought this was a strange argument. So much that I never bothered to get my car on the dyno. My completely unmeasured opinion is that the short rear gears, taut suspension and sticky tires all combine to give me low-end response. The intake & exhaust mods were initially providing top-end gains, until the tune cleaned things up and moved those gains into the mid-range.
IDK... not an engineer, but that's always been my thoughts on the matter. We live under the curve, not on it.
the honeycomb is barely thicker than foil; if I'm calculating cross sectional area correctly, 2.5 is 4.91 sqin, the 2.75 is 5.94 sqin, a 20ish% increase. The frontal area of the honeycomb would need to be almost 1 sq inch.
Granted I do not know the specs of your Honeycomb looks can be deceiving. Just to touch on an example, https://www.mcmaster.com/92725T1/ Blocks 21% of airflow.
06-19-2023, 11:36 AM
