[moto_bruce]

Esteemed Forum Members,

Been cruising this forum. I like that there is a place to talk IRTBs, something that has been on my mind for a few years now. I have finally decided to dive in and would like to ignite a discussion about the pros and cons for an intake plenum.

From what I've gathered from looking at a couple of forums, websites, etc, I haven't really found a good reason one way or the other. Some people assert that a plenum defeats the purpose of IRTBs to some extent (because of the mass of air in the plenum), some assert that being able to take the intake air from a cooler part of the engine bay is worth more horsepower.

I've also seen comments that the individual foam filters on each throttle body are bad for laminar flow into the throttle (although I wouldn't want to expose my motor to unfiltered air).

It would be great if we could build a thread that was a good reference for IRTB plenums.

Bruce

 

[renesisdrms]

i don't think plenums necessarily hurt power. if any, proper length helps air flow into the engine. think of it same as for the headers. individual throttle body with plenums on them i'm sure is purpose in its own. could be for the vacuum pulses that increases air flow speed and/or for the valve overlap characteristics.
if bmw's are running it that style with plenum and gets 300hp... it can't be wrong.

 

[moto_bruce]

Here's a link from m.net that talks about filter socks and plenums. There are some good real work observations in the thread.

http://forum.miata.net/vb/showthread.php?t=168089&highlight=irtb+plenum

I'll initially use socks, but I think I will revisit plenums after I've lived with IRTBs for a little bit. I can guess that they will make an incredible noise (glory), but might bother my neighbots :twisted: . I'll be installing a FR kit on a 95, just waiting on the socks.

Bruce

 

[Bryan]

Let us know how it comes out. Firsthand experience is always best

Which kit are you installing.

 

[moto_bruce]

I'll be installing the Fuji Racing Kit w/ Freedom ECU. I have parts in hand, just waiting on filter socks, but I've been looking into plenums because I suspect a plenum will be more livable day to day.

 

[Bryan]

I'll be installing the Fuji Racing Kit w/ Freedom ECU. I have parts in hand, just waiting on filter socks, but I've been looking into plenums because I suspect a plenum will be more livable day to day.

Cool

Don't forget to post some reviews and impressions once everything's all set up!

 

[timallen]

Yes! I too am interested in how a plenum will work for daily driving.

I'll be getting the Fuji kit very soon!

 

[90_mx]

Is the Fujikit now more complete as per rjthomsons thread? What ever happened to his setup anyways does anybody know if he got it running reliably with the piggyback? That seemed to be the first real serious install I`ve read on but left alot of us short on reviews and updates.

 

[turbored]

I'm excitedly waiting for more info on the fuji kit. Heard it runs too rich on the subcon for the 1.6. If there's an easy cost effective (read: no Standalone) I'd dump my GReddy and buy it in a heartbeat.

 

[Bryan]

If there's an easy cost effective (read: no Standalone) I'd dump my GReddy and buy it in a heartbeat.

Why?

You're going to at least need a piggyback...

 

[turbored]

piggyback is fine if it works good.
I just want a bolt in kit that I don't have to tweak a lot to get running.

 

[Bryan]

"Running" and "Running Well" are two very different things. To get the car running optimally, you are going to need to do some tuning at least after initial installation. No two cars will act exactly alike even with the same kit.

For all that trouble, why not get a standalone and get it professionally tuned to where you like it, then leave it at those settings until something goes wrong?

 

[moto_bruce]

The install on my car will be stand alone ECU. It is the Freedom ECU. I think this install and the piggy back installs aren't comparable, except when it comes to the hardware under the hood.

The engine management is going to be totally different. Nothing wrong with a piggy back, especially when the sub-con comes with the kit for less than what most tuners are charging for the throttle bodies alone. It is actually a good way to get into IRTB without having to spend $3500 all at once. Get it up and running then go with the stand alone of your choice, when you are ready. Beats leaving it in the box until you buy a standalone (then save up enough ducks to get it programmed).

Hopefully, I'll start the install this weekend. Still gathering some small parts that I think I will need to get it all done:

vacuum hose
a donated catch can from a friend
new spark plugs
caps for coolant system
hose clamps
etc.

I think the install is going to be pretty straight forward. But I think a lot of us have the impression that an IRTB install is like installing a monster flow intake, simply bolt it in. I think we have to remember that we are monkeying with several different systems in the car (fuel, cooling, vacuum, PVC, etc) and making a small mistake in any one part can lead to problems.

Also, there is an art in how the system is finished. No two installs will be identical and the instructions aren't so specific on how you solve some of the problems, like where do you put the FRP or plumb the catch can, etc. Its up to the installer to solve. But that is what is totally cool about this type of mod. The end work shows the ideas of the tuner and the installer.

On plenums (the subject line of this thread!) there are several options out there, according to Chris Chu, it looks like 6L of volume or more is desirable. There don't look to be too many options out there in that volume, but I need to do more homework. Fitment can be a problem also, I'll have to look at that later, obviously. I think his setup was TWM, where the thottle bodies are built into the manifold. Pretty trick. The more I think about a plenum, the more I like the idea. Much study to do....

 

[jesseclee]

I've also heard that the individual socks kill velocity.

So why not use K&N filters? Looking at the Fuji's air horn bolt pattern, it looks similar to the sidedraft Weber DCOE's. K&N makes filters of various sizes for this bolt pattern:

Another option is the Piper Cross large filter

These are made in DCOE bolt paterns as well as in blank plate form, so you can create your own openings and bolt patterns.

 

[moto_bruce]

Nice pics. I wonder how much volume is inside the Piper-x. I would guess that there is some internal framing to hold the filter and give it shape. I'll have to check if the Fuji is the same as a DCOE pattern, not sure, but it would make sense to build the throttle body pairs to be compatible with DCOE for people with carbs to switch to injection. If they are a DCOE pattern, that simplifies things greatly as there seems to be much available in a DCOE pattern in plenums, and I wouldn't have to jack up a blank trying to get the spacing and bold patter right.

I had also heard that socks may hurt flow (Chris Chu again). I think Keith at FM uses an ITG on his Seven (the big ITG like the Piper-x pictured above, not the individual socks), and has stated he saw no difference on the dyno between filter on and off.

Attached is a pic of a manifold for dual carb setup from mazda motorsports. Looks similar to the mani with the Fuji kit, but you never know until you have it in front of you. Expensive at over $750, even with the racer price. When you see the cost of these parts by themselves, you quickly realize that the package ain't a bad deal at all.

I was thinking about dynos and a lot of people use the dyno numbers as the foundation for comparison and I agree that it has a lot of merit. But it is also only one data point. Here is a link from FM's site that shows the same car with 2 separate dyno runs. The lower number was a 2k-7k pass at 15 seconds, the higher curve was 25 seconds.

http://www.flyinmiata.com/tech/dyno_runs/NC_sweep_times.pdf

The guess from FM is that this graph may be showing lower inertial losses and may explain the extra zip that a car with a lightened flywheel might show. I would suppose that IRTBs have a similar gain due to the reduced inertia of the air column. Maybe not easy to capture on a dyno. I just think there is more to IRTB power than the simple 15-20 hp gain you see on a dyno. There is more to it and the dyno isn't capturing it.

Bruce

 

[moto_bruce]

Here are some filters for carbs. The 400 CFM series are "perfect for DCOE 40mm and 45mm sidedraft kits..."

http://www.racetep.com/ramflolynx.html#Neck

 

[timallen]

The Fuji Kit has TBs made by OER Japan, which also produce carbs licensed by Weber. The TBs have the DCOE bolt pattern, so yes, the filters described above will fit.

 

[moto_bruce]

Tim,

Thanks for the confirmation, saves me some homework and greatly simplifies fitment since I won't have to hack my own base plate.

 

[moto_bruce]

Here is a link to TWM Induction's website:

http://www.twminduction.com/airbox.htm

and pic below. This box measures about 3 liters.

[/img]

 

[gibbp]

Plenums, when correctly designed, make power. Simple as that. If we had had the time we would have fabricated one for my street motor. Just never got around to it.

TWM sells a nice ITG filter kit for DCOE based IRTB kits. It cost us roughly 1-2 hp on the dyno versus 10-15 with "socks" They absolutely DO kill flow and power. We dynoed it extensively years ago.

The GT3 motor has what is basically a cold air box around the TBs that tapers to a large cone filter. This setup loses 5 hp on the engine dyno. BTW, that little 1.8 makes well over 265 HP with VERY small restrictors.....and 0ver 180 lb/ft of torque. Doesn't like to idle though....

If you have the time and knowledge, build a plenum and get the largest filter you can.

Gibb