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Discussion Starter · #1 ·
I currently have a large K&N cone filter with 3" flange and aluminum tube but these filters don't have have a proper bellmouth shape built in, just a basic curve so my plan for now is just to make this more efficient.

I'm looking at 3", not larger because that's the pipe I have and I'm afraid of losing mid range. But if there's good reason to go larger on my setup I will! My teg is standard with the exception of the intake and a 60mm Kakimoto Regu 06R exhaust. Hopefully a year from now I'll source a RBC, header and larger exhaust.

The v stack won't be open in the engine bay, it will be part of a custom box with a cold air feed.

I'm still going to pay shipping and import duties so Spectre and Blox are the best priced and I'm very tempted. Are the pricier filters really better? When I look at my K&N filter I feel like these filters shouldn't cost so much...

The options I've looked at:
Blox at 40$: https://bloxracing.com/collections/...ir-filter-kit-7-filter?variant=37725953622188

K-Tuned at 80$: -K-Tuned Velocity Stack Combo
Spectre at 26$ plus a v stack: HPR0892 Spectre Conical Filter
ITG at 89$: https://www.eurosportacc.com/collections/engine/products/15jc60-73c

Green at 65$ plus a v stack: Green Filter - Part #7214

K&N 6" at 60$ with a vstack: Universal Clamp-On Air Filter
 

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I currently have a large K&N cone filter with 3" flange and aluminum tube but these filters don't have have a proper bellmouth shape built in, just a basic curve so my plan for now is just to make this more efficient.

I'm looking at 3", not larger because that's the pipe I have and I'm afraid of losing mid range. But if there's good reason to go larger on my setup I will! My teg is standard with the exception of the intake and a 60mm Kakimoto Regu 06R exhaust. Hopefully a year from now I'll source a RBC, header and larger exhaust.

The v stack won't be open in the engine bay, it will be part of a custom box with a cold air feed.

I'm still going to pay shipping and import duties so Spectre and Blox are the best priced and I'm very tempted. Are the pricier filters really better? When I look at my K&N filter I feel like these filters shouldn't cost so much...

The options I've looked at:
Blox at 40$: https://bloxracing.com/collections/...ir-filter-kit-7-filter?variant=37725953622188

K-Tuned at 80$: -K-Tuned Velocity Stack Combo
Spectre at 26$ plus a v stack: HPR0892 Spectre Conical Filter
ITG at 89$: https://www.eurosportacc.com/collections/engine/products/15jc60-73c

Green at 65$ plus a v stack: Green Filter - Part #7214

K&N 6" at 60$ with a vstack: Universal Clamp-On Air Filter
I think whichever one you choose will be within 1% of performance compared to the others assuming they are all 3” velocity stack/filter combo. If you changed the size of the pipe or went with a rather large V stack out the bumper you may see more differences but the effect will be negligible. Any filter that doesn’t have the silly little button on the center of the top is good to go in my opinion. The spectre ones with the metal cap in the middle are dangerous, it can be sucked into the motor if it’s wet or compromised.
 

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And I can guarantee you k tuned one is overpriced (although I like their products) anything with that name on it is 15-20% too expensive in my opinion. If you’re looking to save money.
 

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Discussion Starter · #6 ·
I think whichever one you choose will be within 1% of performance compared to the others assuming they are all 3” velocity stack/filter combo. If you changed the size of the pipe or went with a rather large V stack out the bumper you may see more differences but the effect will be negligible. Any filter that doesn’t have the silly little button on the center of the top is good to go in my opinion. The spectre ones with the metal cap in the middle are dangerous, it can be sucked into the motor if it’s wet or compromised.
I've continued reading on since starting this thread and figure I'm going to gain so little from upgrading from my current K&N that it's not worth it. If I were starting from scratch then I'd go for the v stack right away but the K&N has a small inlet radius which research shows is good to within 1-2% of a v stack, so spending another 60-80$ now will only net 1-2hp gain🤷‍♂️.

So I'll put my money on the safety equipment I need instead.
 

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I run an ITG maxogen airbox on the road, too. It provides excellent noise reduction vs an open air filter. Main advantage is you can make it ingest actual cold air.

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I've continued reading on since starting this thread and figure I'm going to gain so little from upgrading from my current K&N that it's not worth it. If I were starting from scratch then I'd go for the v stack right away but the K&N has a small inlet radius which research shows is good to within 1-2% of a v stack, so spending another 60-80$ now will only net 1-2hp gain🤷‍♂️.

So I'll put my money on the safety equipment I need instead.
Good choice , on a stock motor setup you’re better off spending the extra money on suspension, tires, or safety gear as you stated.
 

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this is what I find interesting about the oem air box air supply tube #4 - it is basically a extended concentric reducer. One end is 62mm (2.44") I.D. and the other is basically 3.25" I.D. If you continue to measure the intake supply system from after the #4 tube, the plastic airbox extends the length of the piping tract by 5 inches or so. Still Honda designed the intake to be over 3" closer to the filter.

My K-Tuned 3.5" velocity stack is not 3.5" I.D., it is 3.35" I.D. So technically speaking, a 3.5" velocity stack put at the end of #4 is what I did for a cheap (SRI). There was a small obstruction lip inside until I ended up making a custom transition piece to smooth out the difference of the inside dia's. Which added 3" in length.

I just wanted to share that if you buy a 3" velocity stack ,the I.D. could end up being smaller than the 3" intake pipe you are using now. Going with a 3.5" velocity stack would prevent that I.D. line up from being unmanageable and it would better suit Honda's original design.

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Discussion Starter · #12 ·
this is what I find interesting about the oem air box air supply tube #4 - it is basically a extended concentric reducer. One end is 62mm (2.44") I.D. and the other is basically 3.25" I.D. If you continue to measure the intake supply system from after the #4 tube, the plastic airbox extends the length of the piping tract by 5 inches or so. Still Honda designed the intake to be over 3" closer to the filter.

My K-Tuned 3.5" velocity stack is not 3.5" I.D., it is 3.35" I.D. So technically speaking, a 3.5" velocity stack put at the end of #4 is what I did for a cheap (SRI). There was a small obstruction lip inside until I ended up making a custom transition piece to smooth out the difference of the inside dia's. Which added 3" in length.

I just wanted to share that if you buy a 3" velocity stack ,the I.D. could end up being smaller than the 3" intake pipe you are using now. Going with a 3.5" velocity stack would prevent that I.D. line up from being unmanageable and it would better suit Honda's original design.
Advertising 3.5in when it's not is nonsense. Even the cheap stuff on AliExpress gives ID measurements..

Honda does design well but there's always room for more performance. When I'm done I'll post up my custom cai and box, it's very similar to the Mugen just doesn't look the part!
 

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The dimensions of their various air boxes are on their website.
It is hard to see in pictures as it sits underneath the rear clam.


 

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Discussion Starter · #15 ·
The dimensions of their various air boxes are on their website.
It is hard to see in pictures as it sits underneath the rear clam.


That's a big box actually. Your lotus must be a blast!
 

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you need a decent sized filter to avoid large pressure drops and then a sized box around it for smooth airflow and decent noise suppression. SC is not that loud on the intake side, but all motor needs decent noise suppression.
 

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Discussion Starter · #17 · (Edited)
you need a decent sized filter to avoid large pressure drops and then a sized box around it for smooth airflow and decent noise suppression. SC is not that loud on the intake side, but all motor needs decent noise suppression.
Why the need for noise suppression? This reminds me of Audi bragging their Le Mans prototypes were so quiet and efficient.

For size, I got the biggest cone filter I could walk out the shop with, the larger the surface area the the easier the engine will breath right. It's a K&N RX-3990-1, 152mm wide and 220mm long, fitment turned out to be an issue! I do like that it has a shoulder in the ID for the intake pipe, but for a 99$ filter it should have a better design with some bellmouth built in.
 

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because a naturally aspirated k20 with an open air filter in a Lotus Elise makes your ears bleed. There is no sound deadening in the car and your head is right in front of the air filter with a thin GRP wall in between. They are painfully loud.
Next the intake noise is so loud that you fail to pass the drive-by noise limit on many race tracks in Europe.
With an Eaton blower and a cone filter, the engine sounds like a circular blade saw behind you head grinding through hardwood. The airbox makes this noise much more subtle and bearable.
Next, the open air filters commonly suck in lot’s of hot air from the engine bay. For every 10°C increased IAT you lose about 1.5-2% power (3% reduction in air density). I commonly saw 20-30°C above ambient IATs of folks running open air filters. 2-4% power loss or 5 to 10HP. Sorry, but the added noise of an open cone filter is not worth 5 to 10HP for me.
 

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Discussion Starter · #19 ·
because a naturally aspirated k20 with an open air filter in a Lotus Elise makes your ears bleed. There is no sound deadening in the car and your head is right in front of the air filter with a thin GRP wall in between. They are painfully loud.
Next the intake noise is so loud that you fail to pass the drive-by noise limit on many race tracks in Europe.
With an Eaton blower and a cone filter, the engine sounds like a circular blade saw behind you head grinding through hardwood. The airbox makes this noise much more subtle and bearable.
Next, the open air filters commonly suck in lot’s of hot air from the engine bay. For every 10°C increased IAT you lose about 1.5-2% power (3% reduction in air density). I commonly saw 20-30°C above ambient IATs of folks running open air filters. 2-4% power loss or 5 to 10HP. Sorry, but the added noise of an open cone filter is not worth 5 to 10HP for me.
Hahaha your case is very specific. I expected a response regarding power loss due to harmonics or something of the sort but I agree with you that losing your hearing isn't worth it.
 
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