Hmmm

 

Grinding out the separation between the primary and secondary plenums?

I've always wondered if this would be a good idea or not. What about how it would effect power in a NA application? Especially with a ported (or extrude-honed intake). A turbo application?

 

I'm going to find out

My main concern is drivability. The engine spits and sputters when running on only the primary throttle. I tweaked the linkage so that the secondaries open as quickly as possible but it's still not quite good enough.

This tells me that the primary throttle is keeping things from being happy. Not sure what the root cause is, but since reducing the progressive nature of the TB helps things, let's eliminate it altogether.

It's either this or ITBs. This is much easier.

The TB is from a 6.0 liter GM truck. 75mm, built in TPS and IAC. GM does not sell the IAC separately, so when one fails, the entire TB gets replaced. Thus how I happened to have it. A rule of thumb is that small plenums need larger TBs, and the T2 intake has a rather small plenum volume.

The two lower holes just needed to be drilled out and ovalled slightly to fit over the lower TB studs, the upper needed to be drilled/tapped, and I am using a piece of thick plastic to cover the gap where the TB doesn't quite cover the secondary inlets' holes.

 

Very interesting peejay.

I was thinking of cutting the stock UIM open to do it, right at the end of the runners, so I could getto hone the runners with flap wheels and a flex shaft. Maybe even use the bead hones sold at Autozone, Harbor Freight, MSC, or any other supplier. Then welding it shut again, and still use the stock throttle body.

Keep us all informed.

 

I am curious about this mod too...inform us!!!

I also wonder about the TB you are using...it seems to fit quite nice.

And the theory of small plenum big TB. Any expansion on that topic?

 

Updates?

 

Haven't touched it since. Too busy with work.

I would like to hopefully have it on the car by early April. But I also have a LOT of other work that needs to be done on the car and quite frankly I am getting tired of wrenching in my spare time. I drove the car and it needs all four calipers rebuilt AGAIN because they siezed up, things like that.

So, whenever I get around to it, I'll get around to it. More important right now is getting my VW to pass emissions so that I can re-register it. Have all of the parts required, just no time to do it...

 

Move to C-bus Peejay, no more emissions! And our dyno will be closer by

 

After 2011 the VW will be emissions exempt so why bother?

And I may be replacing it with an '86 *something*... exempt after 2010, so I would only have to make it pass once in 2009 and carry the emissions report over to 2010.

The trick is to only drive 24y/o cars.

And the dyno day I am concerned about is in Dayton Need to show up the other WOR guys at Colettis

 

updates... its been quite a while, maybe you got some free time?

i been ding some work to my stock manifolds, and were wondering what your results were?

 

Haven't had time to do much with them.

I did find out that this upper isn't a direct bolt-on to my lower. So one must be Series 4 and the other is Series 5. I don't know which is which. The outer bolt holes on this upper are spaced slightly inboard and away from the engine relative to the upper/lower on the car.

So if I hacked up some rare prized piece, umm... sorry?

 

I did this to a few manifolds several years ago.

 

so what was your results rotarygod?

i will still be using the stock throttle body, but port and polished and knife edged everything. along with removed the secondary plates up front, and made both butterfly sets open at the same time instead of staged...

 

I want to know also. I'm guessing it acts just like a custom intake with a shared plenum.

 

I put it on last night after egging the outer bolt holes out. I used the same S4 N/A throttle body that I have been using.

It's hard to say, but throttle response definitely got worse and while it feels like the 4500rpm stutters that I have are gone at the expense of what feels like less low RPM torque.

I haven't been able to find any papers, but I suspect that the stock upper is designed to have a dynamic cross-chamber resonance like the N/A stuff.

The kicker is I was not able to tune it. I got the idle sorta fixed (had to add 5% more fuel) and I noticed when cruising that it was running at ~16:1 AFR at 60KPa/2800rpm instead of the 15-15.5 that I had tuned it for. Then I went to a gas station to get coffee and set MegaTune up for logging so I could log some on-ramp burns before hitting the dragstrip... and the backlight died. Without tuning, the car seemed to be slower but it was within the margin of driver error, plus I only got two runs in because of some track issues and an unusually busy night.

With no laptop to tune with, and some definite drivability issues (stumbles, etc) I'm just going to throw the old upper back on. I have more important things to worry about, like how my transmission has so much front-back play that it destroyed the speedo gears and I have to be very careful shifting into 3rd or 4th. Or the rearend that is howling more and more. Or the idler arm. Or maybe reattach the oil cooler so it's not flapping in the breeze hanging by the lines.

You know, crap more important than trying to get more power from an engine that already has more power than is useful for the things I care about.

 

I had a perceived loss of low end and part throttle power. Don't try it on a stock ecu! Yes it runs but you'll hate it!

 

wow... i really thought it would of resulted in better results. good thing i didnt already do it.

thanks for sharing both your experiences, i wil NOT being doing this...

 

My current RX-7 is what is basically a bone stock '90 GXL. I have an extra set of S5 manifolds lying around. I just ordered a new long shank non ferrous die grinder bit and it'll be in next week. I'll hollow one out and put it on this car to document what happens. I don't think anyone has actually done this with proof. What I'll do is do a set of runs with the g-tech pro. It'll give me a dyno chart. I'll average the runs together to reduce the margin of error. The actual hp number is irrelevant. All we care about is the shape of the curve. Then I'll do runs with the hollowed out chamber so we can see what changed and where. Keep in mind that these will only be indicitive of full throttle and you'll have to rely on my personal perception and opinion when it comes to drivability and throttle response.

I get pretty consistent mileage in this car. It averages between 21-22 mpg. I drive about 100 freeway miles a day for work so it's easily repeatable. I'll keep the other plenum on long enough to get a couple of tanks worth of info. This assumes the car will run good enough. Keep in mind I am going to do this completely free of any tuning so it will be done on a bone stock car. I can't tweak anything. Since many people don't get into ecu tuning, this should be extremely relevant for those wanting to know what intake mods will work on a stock ecu equipped car. While results may vary with a standalone, I think this is info that most people really want to know as it is a free mod that only takes time. I don't remember liking it in the longterm but I'm always willing to go back and revisit an idea if I get a chance to. Give me a couple of weeks to get this done.

 

Oh yeah, that reminds me. At ~90-95KPa, which is essentially full power even though it takes very little throttle to get there, I noted that the AFRs in the 2000-2500rpm range had dipped into the 12.8:1 range. Thing is, I used to have them tuned to 14.5:1...

So definitely heavy load volumetric efficiency got a lot worse at low RPM!

 

Moving in a different direction. Pics soon.

 

What are the test results?