Velocity Stacks vs Airbox

[9kracing]

So I'm relatively new to the forum, and I'm sure a lot of this info has been discussed ad nauseum, but I'm not able to find any past threads with good info in them, most likely because some old forums are missing.

My question is, why do people even run air boxes on these cars? From everything I've seen my entire life, properly sized trumpets will make significantly more top end power every time. The Honda guys have done countless dynos with and without... and you don't see any of them running air boxes do you.

I understand why the stock cars have them, and the CSL, but why would someone who's putting in cams and headers and going for max power want to rob themselves of potential power?

[oceansize]

Induction noise that emanates from a carbon fiber box rather than a trumpet shaped trumpet .

Also see below, probably the best answer I ever found when I was considering box vs stacks vs FI.

https://forums.m3cutters.co.uk/threa...3#post-2266239

[Slideways]

Properly filtered cold air via sealed carbon airbox with internal velocity stacks versus poorly filtered hot air with open velocity stacks

It seems that open stacks were common in the 70s 80s race cars because complex carbon fiber parts, such as an intake manifold, were still being developed. By the time the McF1 and E36 M3 came into production in the 90s, carbon fiber intakes were more common and seen used on race cars such as the LMR V12. Nothing will damage a cylinder, piston, cylinder head or valve like an open or poorly filtered velocity stack.

[9kracing]

Nothing will damage a cylinder, piston, cylinder head or valve like an open or poorly filtered velocity stack.

Agreed, and that's why the factory cars run them.

We aren't talking about factory cars that get driven 15,000 miles a year.

We're talking about cars trying to make max power.

[Tbonem3]

Agreed, and that's why the factory cars run them.

We aren't talking about factory cars that get driven 15,000 miles a year.

We're talking about cars trying to make max power.

I don't see how that's actually the case. Trying to make max power would be building an engine for competition that you hope will last hours (versus tens of thousands of miles if not hundreds).

Not removing the intake plenum. Stacks don't make more power or better sound or look better than the CSL airbox.

They belong in the same mod camp as -5 camber, chynacoils, ebay CF lips & gruppe m rep "mufflers."

[9kracing]

Stacks don't make more power ... than the CSL airbox.

What I'm asking for is dynos to back this up. Because I see this trumpeted all over the forums with zero evidence shown.

Also, I'm not talking about sound, which everyone seems very hung up on.

An airbox is a restriction when you're moving large amounts of air. There's no way it makes more power on the high end. What it does it provide better low end throttle for daily driven cars.

Even the companies that make velocity stacks for the S54 don't show any dyno charts or talk about power numbers.

I'm sure at some point someone tested stacks vs a box with no other changes while on the dyno, right?

[oceansize]

What I'm asking for is dynos to back this up. Because I see this trumpeted all over the forums with zero evidence shown.

Also, I'm not talking about sound, which everyone seems very hung up on.

An airbox is a restriction when you're moving large amounts of air. There's no way it makes more power on the high end. What it does it provide better low end throttle for daily driven cars.

Even the companies that make velocity stacks for the S54 don't show any dyno charts or talk about power numbers.

I'm sure at some point someone tested stacks vs a box with no other changes while on the dyno, right?

To me the biggest issue is lack of cold air. I don't know that can be overcome but here is a dyno from Kassell.

320 HP and 236 ft-lbs

[9kracing]

40 wheel HP is nothing to sneeze at, thanks for that. I also think that sounds great.

Does anyone know the current throttle body size on these cars, or what Dinan bores them out to?



I realize this is a Honda, but it's an inline high compression motor with variable valve timing that has an 8k+ redline, so not really that different.

They showed massive gains by using a properly sized and designed ITB setup, all over the RPM range.

https://honda-tech.com/forums/all-mo...sting-2841539/

[EthanolTurbo]

To me the biggest issue is lack of cold air. I don't know that can be overcome but here is a dyno from Kassell.

320 HP and 236 ft-lbs

And this guy still got rid of this heat soaker setup and switched to a CSL airbox. Stacks are wack if you want consistent power.

[heinzboehmer]

40 wheel HP is nothing to sneeze at, thanks for that. I also think that sounds great.

That's 40 whp with the stacks, headers and tune.

I tried my best to be scientific when I did airbox and headers to try and quantify the gains. At the end of the day, I did the mods over the course of a year or so (so didn't exactly have a controlled environment), but I still think I managed to produce a decent reference for them. These were the results:

Stock: 269 whp, 230 WTQ
Airbox + canned tune: 294 whp, 245 WTQ
Airbox + SSV1s + dyno tune: 315 whp, 252 WTQ

Airbox alone was worth 25 WHP and everything combined came out to 46 WHP, so similar results to that video. As mentioned above, my biggest concerns with stacks would be heat and the hacking up of all the lines that run to the manifold. Don't think the stacks have any benefit over the airbox.

Original dyno post: https://nam3forum.com/forums/forum/m...185#post140185

[George Hill]

I had just stacks on my car for a little bit as they are certainly fun. At that time I had the IAT mounted on the strut tower. I found that after coming from a stop that the IAT read much higher than ambient, but would eventually make it down to just slightly above ambient. So if I was cruising down the highway for 2 miles and went WOT the stacks were not sucking a ton of "heat" as read by the IAT.

I had a Karb plenum on my car and when I was drag racing it if we hot lapped it we could see the car slowing down, taking the hood off netted me 3 tenths in the quarter. Maybe some of that was inconsistency in the driver, but still my takeaway was that an unducted CSL style plenum is not THAT much better at controlling under hood heat ingestion from a stop.

[oceansize]

I had just stacks on my car for a little bit as they are certainly fun. At that time I had the IAT mounted on the strut tower. I found that after coming from a stop that the IAT read much higher than ambient, but would eventually make it down to just slightly above ambient. So if I was cruising down the highway for 2 miles and went WOT the stacks were not sucking a ton of "heat" as read by the IAT.

I had a Karb plenum on my car and when I was drag racing it if we hot lapped it we could see the car slowing down, taking the hood off netted me 3 tenths in the quarter. Maybe some of that was inconsistency in the driver, but still my takeaway was that an unducted CSL style plenum is not THAT much better at controlling under hood heat ingestion from a stop.

Makes sense. Come to a stop, heat builds up, you take off and a bunch of hot air is sucked in at that moment in time, then less and less hot air as the car moves along. You are probably one of the few people on the board with first hand experience.

[BBRTuning]

What I'm asking for is dynos to back this up. Because I see this trumpeted all over the forums with zero evidence shown.

Also, I'm not talking about sound, which everyone seems very hung up on.

An airbox is a restriction when you're moving large amounts of air. There's no way it makes more power on the high end. What it does it provide better low end throttle for daily driven cars.

Even the companies that make velocity stacks for the S54 don't show any dyno charts or talk about power numbers.

I'm sure at some point someone tested stacks vs a box with no other changes while on the dyno, right?

Yeah, done this test a few times in a few different ways. You just won't beat the CSL airbox with any sort of open velocity stacks, even for peak power. It gets even worse if you then add individual filters for each stack. The absolute worst thing you can do is run those "rock stopper" stainless mesh filters on each stack. Not only do you have almost zero filtration, you actually have very little flow surface area. The filtration surface area of the CSL filter is massive in comparison, and remember that only one cylinder at a time is in the meat of its intake stroke, so you essentially have the entire CSL filter area providing airflow for each cylinder.

Recently had a pretty serious S54 on the dyno 12:1 (limited by racing class), 296/288 high lift cams, Emtron standalone ECU. We made a genuine ~385whp SAE @ 8600 RPM with a Turner airbox on this car. Since it's a proper race car, we knew we'd never run actual open stacks because that's just silly unless it's a show car when things like carbon airboxes exist, but we WERE interested in figuring out if there was a better trumpet length for this engine setup than what the Turner CSL box comes with, so we decided to dyno the car with various length open trumpets, starting with one that matches the CSL box length. Each time I adjusted the tune to match the trumpets. The results were so bad that I didn't even bother to take pictures of the dyno graphs. Peak power with the open trumpet "CSL length" was almost the same, but low and midrange torque suffered significantly. Additionally, both the shorter and longer trumpet lengths not only lost low/midrange, but the top end was also worse, showing losses between 5-10whp depending on the configuration, and up to 20 ft-lbs. We were shocked as we expected the shorter runner length to provide some top-end benefit at the expense of low-end. It either told us that the open stacks are just straight up worse in every way, or that there was no advantage for the RPM range we're running in to go any shorter than the Turner CSL runner length.

Since this topic comes up often and no one seems to believe that engineers (and all motorsport/race teams) know what they're doing, I guess I'll need to export all the graphs from this test, once I get back to that particular dyno and post it for everyone's enjoyment..

[bigjae46]

I installed a heat shield which seals against the hood (almost) for my Injen intake which lowered IATs by about 20 degrees. I'm sure some sort of heat shield would help with IATs when running the Karb box.

There is also a fan shroud which seals off the intake that is missing. I've debating putting that back on although it is a minor PIA to remove.

[digger]

I don't believe the airbox detracts when done correctly and in reality provides notable benefits. Also 6 cyl on a common plenum vs 4 is different animal.

Years ago i tested itb with open trumpets vs itb with identical trumpets with a large airbox with open hood (not on a s54) the airbox wins simply due to density improvements from being able to to duct cooler air.
the gains on the street are even more notable because the hood closed exacerbates heat issues. i know of two others who have found the same thing.

The airbox needs to be large so it basically acts like open trumpets it is not introducing large pressure variations (i.e. no plenum volume tuning effects as with 6 cyl drawing from a common plenum its almost a waste of time due to too many closely spaced pulses) and in effect the airbox is just a large shield keeping air from the rad and other heat sources from being ingested.

I cant say I've ever seen a high end pro race team running ITB with open stacks they seem to have quite elaborate CF ducts that are enormous.