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hda hda is online now
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Ditching the airbox

I have a cone filter at 5” from the throttle body, which I know it is not optimal.

I have a hot wire setup.

Trying to see which alternatives are out there that maybe include an airbox?
I’d like to have a reservoir of filtered ait between the filter and the throttle body to increase throttle response.

Is there a way to force air towards the filter by using a “scoop”? I removed the spoiler.
Old 02-05-2019, 06:18 AM
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This is for a 964
Old 02-05-2019, 06:44 AM
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What do you have instead of the spoiler ?
993 had an extended snorkel for cars with fixed spoilers , as the grill was higher than than the electric grill in lowered position .
Old 02-06-2019, 07:30 PM
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Quote:
Originally Posted by ian c2 View Post
What do you have instead of the spoiler ?
993 had an extended snorkel for cars with fixed spoilers , as the grill was higher than than the electric grill in lowered position .
For now nothing

Old 02-06-2019, 07:32 PM
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You could fit a French horn .
Old 02-06-2019, 08:00 PM
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You could fit a French horn .
Insightful!
Old 02-06-2019, 08:06 PM
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He's from Houston so a Steer horn would be appropriate
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Old 02-07-2019, 11:24 AM
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Thats’ the technical expertise I am looking for.

Prefer Trombetta if I possible.
Old 02-07-2019, 11:26 AM
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Gotta love the peanut gallery.

Anyway - I remember reading somewhere that the ducktail provided the best aerodynamics for the car, as well as created a low pressure spot for air intake.

You could fit a duck, or go the 993 external snorkel route.

Love to see more pics!
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Old 02-07-2019, 03:05 PM
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Which peanut?

Anyhow is the area of the grill a depressure or pressure on the lid?

I am not mounting no ducktail on the 964.

Without going for a snorkel a la 4Runner offroad truck, looking for ways to catch some “fresh air under pressure...
Old 02-07-2019, 04:20 PM
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Been a while since I sat on a school bench, but I think the concept of a "filter air reservoir" flies slightly in the laws of physics. The filter is still there to restrict flow, and a lets say 7 litre reservoir would be sucked into the engine during two revolutions.
This link might be of more help, though. Upwards pointing snorkel that fits 964 OEM airbox, as used on some 964 RS models.
https://www.*****************/fu/pt697_703_-cma81-cmo107-ct334/Porsche/964--911--1989-94/964--911--C4-1989-93/Air-Induction-Kits/
Think the retractable rear spoiler is one of the 964s coolest features, but I guess a fibreglass fixed spoiler engine lid would save weight.
Old 02-09-2019, 10:57 AM
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Quote:
Originally Posted by Paperboy View Post
Been a while since I sat on a school bench, but I think the concept of a "filter air reservoir" flies slightly in the laws of physics. The filter is still there to restrict flow, and a lets say 7 litre reservoir would be sucked into the engine during two revolutions.
This link might be of more help, though. Upwards pointing snorkel that fits 964 OEM airbox, as used on some 964 RS models.
https://www.*****************/fu/pt697_703_-cma81-cmo107-ct334/Porsche/964--911--1989-94/964--911--C4-1989-93/Air-Induction-Kits/
Think the retractable rear spoiler is one of the 964s coolest features, but I guess a fibreglass fixed spoiler engine lid would save weight.
Can you then elaborate why, since you are better than me at physics, does a closed airbox work better than an open one? Better response, better midrange, etc?

I wouldnt use the cup car as a reference, if you stay always in high rpms then obviously you do not need an airbox.

Unfortunately your link did not work for me, maybe you can post just the picture?

As for the lid, i am looking to shed weight. I am unsure if I will re install the spoiler or not. Car tops at 140mph so unsure on how much I need it
Old 02-09-2019, 02:54 PM
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Hi hda.
Regarding the link. Google Fibreglass intake snorkel porsche 964 and you will find several links from there.
Re intake. Maybe we were talking past each other. Of course a set up with a sports filter or no filter at all will be less restrictive than a standard set up. However, what ever restriction that is there is there all the time, if that makes sense.
On an internet show called Engine Masters , on Motor Trend on Demand, poss on youtube, they dyno tested 19 diff combos of air cleaner/filter on a modified V8 giving about 700 hp. Three interesting findings.1. The worst combo, a time period correct OEM aircleaner robbed 50 hp. 2. 3 combos were slightly better than no filter at all, all were of the vertical stack type, the best one w/o any filter. 3. All the losses/gains happened at and above 5000-5500 rpm.
I guess this proves the old engine air pump analogy is correct. Any filter restriction/improvement is most likely noticeable only at high rpm, and really doesn't effect mid range. Also, directing the air is just as important as restriction. Hence the velocity stack on old 1960s Gasser dragsters. Also, pictures of the top of the range N/A 964 engine, the RSR 3,8 seems to show a metal trumpet type air inlet.
What other mods does your engine have? This is a complete amateur opinion in this black arts matter,but unless an engine doesn't have any interior mods such as porting, large valves or modified intake runners or some advanced re-chipping I guess a low restriction filter in the standard set up is ok. Happy for any opinions you might have.

A rear spoiler is def part of the aero package on the car at higher speeds. Saw this figure. On an earlier non rear spoiler 911 the high speed rear lift was above 200. With a duck spoiler it was down to about 70.
Old 02-10-2019, 08:52 AM
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Quote:
Originally Posted by Paperboy View Post
Hi hda.
Regarding the link. Google Fibreglass intake snorkel porsche 964 and you will find several links from there.
Re intake. Maybe we were talking past each other. Of course a set up with a sports filter or no filter at all will be less restrictive than a standard set up. However, what ever restriction that is there is there all the time, if that makes sense.
On an internet show called Engine Masters , on Motor Trend on Demand, poss on youtube, they dyno tested 19 diff combos of air cleaner/filter on a modified V8 giving about 700 hp. Three interesting findings.1. The worst combo, a time period correct OEM aircleaner robbed 50 hp. 2. 3 combos were slightly better than no filter at all, all were of the vertical stack type, the best one w/o any filter. 3. All the losses/gains happened at and above 5000-5500 rpm.
I guess this proves the old engine air pump analogy is correct. Any filter restriction/improvement is most likely noticeable only at high rpm, and really doesn't effect mid range. Also, directing the air is just as important as restriction. Hence the velocity stack on old 1960s Gasser dragsters. Also, pictures of the top of the range N/A 964 engine, the RSR 3,8 seems to show a metal trumpet type air inlet.
What other mods does your engine have? This is a complete amateur opinion in this black arts matter,but unless an engine doesn't have any interior mods such as porting, large valves or modified intake runners or some advanced re-chipping I guess a low restriction filter in the standard set up is ok. Happy for any opinions you might have.

A rear spoiler is def part of the aero package on the car at higher speeds. Saw this figure. On an earlier non rear spoiler 911 the high speed rear lift was above 200. With a duck spoiler it was down to about 70.
Hey paperboy - thanks for the reply.
Indeed a "less filtrating" filter will be less restricting and allow more air to go through at the cost of more dirt going in as well.

As for the test, I am not surprised to see the gains losses happening at high RPMS (I assume high since 5,000rpms must be so for a modified V8). However the difference between a good airbox and a bad one is in the midrange torque.

My opinion is that an open/RS style airbox is not efficient and does not produce more power. I don't care if that's what they used in the 90s on the cup cars, an open box sucks hot air.

I actually did a test with open vs. close airbox and the power difference coming out of turns was incredible. Yes, it was on a Honda S2000 and not a 911 but we are still talking about a naturally aspirated engine - and one of the best ones. Laptimes were as a consequence in favor of the closed airbox.

I then developed an intake called Puffo that was actually convey air under pressure towards the stock filter (to maintain best filtration). That alone resulted in a +13whps (!!!) and an increase of 4mph top speed at the track (same day, same car, same driver).

Hence my idea of developing a similar airbox intake for the 964. Problem: it is pretty tight back there! And I am not sure if the area above the grill if of pressure of depressure.
Old 02-12-2019, 06:33 PM
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Did you research the 993 snorkel I mentioned earlier that was used on fixed-spoiler cars ?
Get it up high . It doesn’t have to be in the airflow just closer to the grill .
You’re going to get little ram-air effect .
Seeing as your not even running a grill , you could use a BMC can-filter and tube to naca ducts ?, or even have a cone stitching out of the top ?

There was an expensive aftermarket option available that took the snorkel and upsized it to be placed right under the stock grill with a cone-filter inside .

I’ll look it up for you .

I looked at doing similar years ago on a turbo-rear narrow-bodied n/a car .
Got talked out of it by an expert as not worth the work .
Iirc , removing the engine cover let some hot stuff out and made the stock snorkel less hot .

Or , you could just fit a French horn

Last edited by ian c2; 02-12-2019 at 08:55 PM..
Old 02-12-2019, 08:28 PM
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Hey paperboy - thanks for the reply.


As for the test, I am not surprised to see the gains losses happening at high RPMS (I assume high since 5,000rpms must be so for a modified V8). However the difference between a good airbox and a bad one is in the midrange torque.

My opinion is that an open/RS style airbox is not efficient and does not produce more power. I don't care if that's what they used in the 90s on the cup cars, an open box sucks hot air.

I actually did a test with open vs. close airbox and the power difference coming out of turns was incredible. Yes, it was on a Honda S2000 and not a 911 but we are still talking about a naturally aspirated engine - and one of the best ones. Laptimes were as a consequence in favor of the closed airbox.
There is really no such thing as a “closed air box”. Any air box has an opening, the “air box” of an open filter element is the engine bay above the motor, with its opening being the grille in the engine lid. The air box as you are calling it, being on the outside of the throttle, is not considered a tuned part of the intake tract. It’s purpose is only to provide a necessary volume of air with no restriction at a reasonable temperature. On a production car the air box is also used for sound control.

Speaking of temperature, the engine bay of a 911 is essentially the same temperature as the ambient outside air due to the large volume of air being drawn in by the cooling fan. Think of it as if the intake was completely in front of the radiator on the s2000 you were using as an example.
Old 02-16-2019, 07:26 AM
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I developed this intake for my 993 a few years ago:





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Old 02-18-2019, 03:40 AM
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I'm just passing through this thread, but I'll add a couple of small notes:
1) air pump is not an analogy, that is exactly what the intake side of the motor is
2) the intake is a long tube - the single biggest thing to tune (if you want power) is the resonant frequency. It's just like a trumpet/speaker bass tube/pick your favorite wind instrument. Every air volume and length of tube between the filter and the intake valve is part of that tuning. Manufacturers try to tune the intake so that the intake resonance leaves a standing high pressure at the intake port. The 964 has two resonance points (flapper switches from one to the other). The 993 has at least 3 with the vram system.
3) because the intake is a big tuned pipe, adding a volume after the filter just changes the resonant frequency. Sort of like making a speaker box twice as big with the same driver; not necessarily good for the output.
4) the filter box is big, with the filter spaced in the middle, just to make space for a lot of filter surface area.
5) High efficiency normally-aspirated motors have to be *very* tightly tuned to get the specific power output. That's why your s2000 (>100hp/L NA) ran worse when you messed with the intake. To get 240 peak HP from such a small motor required Honda to tune the whole system really well.

You can definitely do better than the stock 964 intake but it won't be by just putting a snorkel on it. The 993 vram adds another fat resonant peak for midrange without losing much, if any, of the high-rpm peak. ITBs let you tune for specific RPMs using different length trumpets. Some of the factory cars used fully-variable trumpets, like a tombone, that would slide longer or shorter as the motor revs. Complicated though.

You can also just knock the rough edges off the current design: take it all apart, match the intake runners to the ports, extrude-hone the inside, smooth out all the joints, and replace any leaking rubber bits. That's on my list but haven't gotten to it yet. Look for Goughary's "Intake Madness" thread on rennlist for an example.
Old 02-18-2019, 07:14 AM
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To reiterate what was mentioned above, the air temperature at the filter is essentially ambient above 10mph (or less). There's no hot intake air to worry about.

Steve Weiner has commented several times that he's measured a 2-3hp gain from the cup car airbox. That's the best you can expect without pressurizing the incoming air.

You can roughly calculate the effect of a ram air intake vs mph. I think the gain is usually less than 5hp at 100mph.

Outside of that, you're getting into changing the intake manifolds and throttle body. That will change the shape of the torque curve but not necessarily add to it.

Exhaust and ignition advance are the low-hanging fruit for the 964. After that, the $/hp is exponential.
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Old 02-21-2019, 09:03 AM
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Thank you for the last 2 inputs.

At the moment I have the open cone filter there for my hot wite setup. I would like to put a “box” around it but from reading above, it seems that the temperature is not a worry item.
Old 02-21-2019, 09:43 AM
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