IPD "competition" Plenum - Mea Culpa

Hey all, I decided to give the IPD plenum another shot, and wanted to say that my earlier comments on this site may have been misplaced. I think it is a good product. I had previously installed an IPD competition plenum and a 82mm GT3 throttle body on a 3.4 liter 2000 996 Carerra, with 200 cell cats and a Gemballa exhaust. The results were underwhelming - more intake noise, but no noticeable difference in power, delivery or performance. After using it for 500 miles or so, I removed it and sold it to another Rennlister. I put the idea to bed as a good experiment, but the bang for the buck wasn't there. I didn't recommend it, and in fact, discouraged people based on my experience. I recently decided to give the IPD plenum another shot when I found one on eBay for an amazing price (mental note, do not go on ebay or set up notifications...). As a result, I picked up another IPD "competition" plenum and 82mm GT3 throttle body and installed it on my 3.6 liter 2002 996 Carerra, recalibrated the throttle, and gave it some miles to let the system adapt. This car also has 200 cell cats and (the same) Gemballa exhaust as the 2000 (I moved it over). In all fairness, and much to my surprise, I've noticed a difference in the smoothness, acceleration and power delivery. A noticeable difference... Especially in the smoothness and rate of acceleration. Why is it so different? I have absolutely no idea. 3.4 vs 3.6? Different brand of 200 cell cats? Different version of Motronic in the DME? Who knows... In terms of "facts", I don't have any. I don't have before/after instrumentation. I don't have access to a dyno. I can't reflect on actual hp or torque differences. I can only reflect the perspective from the driver's seat. It adds a subtle but noticeable change to the way the car drives. Much like my comments about some other products (like the Numeric shifter), this takes a 9/10 experience to a 10/10 experience. I still wonder whether this is worth $1175 or whatever full retail price is, but if you can get one for a price that feels good, it may be a worthwhile experiment. It wouldn't be in my top 5 things to do, but if you've already done everything else, this may be a good one to add to the list. I feel like I have to update my comments to make sure I'm not passing along unfair information. Hopefully this balances out the prior comments. Disclaimer: I do not have anything to do with IPD or any other tuning company, I wasn't given anything in exchange for posting this, I don't have any vested interest, or anything else like that. Just trying to clear the air.

Tiptronic? I had ipd comp plenum installed on a tiptronic car. Together with some exhaust modifications, like 200cell (x-pipe) The lock-up of the torque converter started slipping/loosening and locking irregularly causing lame throttle response and shaking during driving. The slipping caused the ATF getting very hot contributing further to the detrimental driving behaviour.

The PO of my (3.6 motor swore by it, but he had it dyno'd and tuned. I was on a budget and couldn't buy it with the motor anyway...

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Both are 6 speed manuals.

Thanks. The 2 questions implied are whether a dyno would show gains and why with the 3.6, not the 3.4 motor. Sounds like some of the other variables were constant, cats, mufflers. Hmmm.

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Did you do a ECU tune on either car? From what I understood when building mine, the tune needs to be altered with more ignition timing coming faster and more fuel to utilize the increase in air. You made improvements on the exhaust as well, which is pretty important if you are increasing air/fuel intake. Did you by any chance go with an underdrive pulley to take advantage of the increased flow?

IPD says that no ECU tune is required. They also say that gains from the competition plenum are influenced by the level of exhaust modification. Their marketing, not my opinion. No, I did not do an ECU tune on either car, but I can't rule out that a prior owner did. Is there any way to know? I'd love to find out... Can the Durametric tell me? I do not have an underdrive pulley on either car (although I do have two underdrive pulleys of different diameters sitting on the shelf with new crank bolts waiting for the right time to test them). I haven't done it because I've been hesitant to grind the lock pin boss on the block (and I like having the ability to lock the crank). Yes, the exhaust has been modified, but it was essentially the same on both vehicles. Yes, different brands of 200 cell cats, but same otherwise. Note that I also do not have headers on either car. I think that could potentially eke more out of it with that addition. I'm just too cheap to buy them, and if I do put them on, I want good ones, not knockoffs.

the competition plenum allows you to run a larger throttle body (82 mm ID vs 76 mm ID). all the other stuff that ipd provides (dimples, splitters) are, imho, of little value. with the larger diameter throttle body, think water: if you have a 1" water line and but a 1/2" faucet on it, the faucet will be a restriction to the flow of water even when full open (but the water will come out at a higher pressure; stepping out of the analogy, this means better cylinder fill in low rpm situations and resultant torque increase - called tuning the intake). however, if you put a 2" faucet on a 1" water line, you would have full flow of water when the faucet is only partially open. again stepping out of the analogy, this would result in a mechanical throttle re-mapping similar to a sprint booster; no increase in power, just change in where you get full power relative to throttle position (which might result in a perception of power increase). so what are the benefits of the bigger faucet? well, not so much more air, as less work to get air. if you look at your current intake, diameters slowly decrease as the air moves through the system; throttle body is slightly smaller diameter than the maf holder at the exit of the airbox. this requires the air to accelerate (the same amount of air passing through the maf holder has to pass through the throttle body which requires it to compress/accelerate; pv=nrt from chem class). this fast air is better for low rpm performance (cylinder fill) however it requires work/energy to accelerate this air. the amount of work increases as the airflow increases, to the point that it limits the max hp you can make through what is for all intents and purposes a parasitic loss. so, nothing is free: do you want low rpm torque or max hp? this is where exhaust comes into play. the exhaust is designed similar to the intake - it is tuned to provide some back pressure so as to scavenge air out of the cylinders (if you get the back pressure just right, the air rushing out of once cylinder will help draw the air out of the subsequent cylinder). but again, this back pressure forms a restriction to high rpm airflow - another parasitic loss. to get full benefit from removing the restrictions at the intake you have to remove the restrictions from the exhaust. and sacrifice some more low rpm torque in the process. otherwise, the ecu just looks at the amount of air coming in and adds the appropriate amount of fuel using a graph of rpm/fuel/air. the ipd plenum just makes it easier to draw in air, it doesn't move more air except at max hp. and the + 5 hp increase at max is not so significant that you fall of the graph; the oem tuning is more than able to manage that small increase. so, back to the op, probably the 3.4 works just fine with the oem throttle body and the larger 82 mm unit just gives the sprint booster effect (ie, the 2" faucet on a 1" line) however the 3.6 with the higher power output was limited by the oem throttle body and got some benefit from the decrease in restriction of airflow (the 1/2" faucet on a 1" line).

Ref the Radium King: But doesn’t the AFR the ECU commands keep the butterfly valve on the 82mm almost closed at low demand? I would think a stock ECU with 3.4 or 3.6 displacement would have a hard time managing the low end air flow because of the smaller aperture of the large TB and increased turbulence from that airflow displacing around the smaller area.

you are referring to idle mode, which the ecu can trim (the rkat values you get from the durametric). i am running a 76mm 996 throttle body on my boxster (oem is 67mm) and rkat trims are at 2% where you get a cel at 4% so well within the adaption capacity of the ecu.

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My Indy that I switched to a few years ago, could tell there was a ECU tune, not sure how, my guess is durametric. I talked to the folks at IPD a couple times at length before I purchased my set-up, also with the tuner ( Evolution Motorsports, ie, Evoms). You are exactly right about the larger Plenum and Throttle Body needing exhaust modifications or it will not perform as well as the design intended. As many people have stated here, these engines are pretty well maxed out from the factory, so to squeak out a broader power band or more torque / HP, is going to be difficult and pricey. They also need to work together. That's why I love the term "Well Sorted".