after all the other discussion is done about the 997.2 IC's, i think it would be nice to see if placing intakes over the intercooler is beneficial or not.

i realize this technique allows the coldest air possible to enter the intakes and then end up right back in the IC. however, the reading i have done on building turbo systems (im no expert), it explains that one of the most important factors in flow across the exchanger (IC) and therefore function is air flow pattern.

placing the intakes in this path and disrupting laminar flow is one thing but removing the duct work all together seems totally counter intuitive. the air has got to be forced across the IC by velocity, there is no vacuum or negative pressure on the other side to pull the air across. getting rid of the duct work will result in nothing but turbulent flow with no way to really direct it once it reaches the fenderwell which is additionally churned up by the wheels.

anyone familliar with the Bernoulli principle can picture fast air moving past the skin of the car creating a low pressure area while the slower moving turbulent air in the fenderwell has a positive pressure. i would expect the faster you go the air is just being sucked out of the well and little is crossing the IC. same thing that makes an airplane fly! fast air moving across the top of the wing creates a low pressure area (sounds backwards, but that physics for ya) while slow moving air under the wing has a positive pressure. the difference causes the lift.

i expect it means there is no way to force the air across the exchanger. but iv been under there and there just isnt anywhere else to put the intakes if you want the blow thru system. i know there is plenty of power being made with these blow thru systems but WHY? is it because the intake charge is colder from the get go cuz its in the path of the snorkle and not in the smoldering engine bay and therefore the IC doesnt have as much "cooling" to do. also you gota figure these guys runnin blow thrus typically have bigger inlets and outlets to the IC, so is the cold intake charge just passing thru and the real benefit to the bigger IC from less pressure drop than stock? i dont really know, im just thinking out loud!

shoot me down guyz

 

I have said this in the past. To make a 1000 on the crank you need to move about 900cfm. The ducting creates a ventoury effect. when you drive your car at say 55 put your hand by the duct, you will feel a strong flow of air going in the duct. You can make all kinds of power on a dyno. Fans in all the right places, ice, bumper off, and so on. You have seen all the tricks before. Trap speed and weight will tell you the true hp of the car and no one will tell you both. I did a 139.9 with my car at 3550 with me in it. the day before the dynojet I use read 700hp, this was a couple of years back. As for no where to get air. if you are using the blow through set up move the turbos. They do not need to be where they are.

 

In testing we have seen a drop of only 5*F on average when we ran the ducts vs taking them out. Our IC's fit in the location very well, and it is not like the air is simply blowing past them, there is only so many routes the air can take once it hits the fender inlet.

If we wanted to, we could easily have made custom inlet ducting, but decided that our customers would be better suited investing the additional funds elsewhere for what would effectively be the same power levels.

 

Neil, I agree. But if I remember correctly you do not pull intake air over the intercooler.

 

Subscribed.

 

Only on the 997TT P800 and R911.

 

tim my intakes are at the intercoolers , i think theres a huge diff then using the stock air box.

 

the large gain on the fenderwell intakes is related to the short distance between the fresh air and the turbo inlet. 1.5 foot versus 4-6ft of intake piping before.

plus being that air is forced into the fenderwells by the ducting it also helps out.

is this the best place for the airfilters? in my mind no but does it produce gains on big HP cars when paired with a nice non restrictive Y pipe.

does it hinder the intercooler cooling ability? maybe so but it is such a small percentage that the gains of removing the restrictions in the inlet piping overcome that of loosing air across the intercooler core.

 

I wouldn't underestimate the amount of air a turbo moves in a given time. 3rd gen RX-7s used a shared air intake/intercooler duct and a high rpm on a stock 255hp car, it would pull engine bay air backwards through the intercooler.

I measured my 996 IC inlet ducts to be around 20 in^2 and, if my math is correct, an 18g compressor at 1.4-1.5 bar will use 85% of available inlet air at 50mph and 43% of it at 100mph -and that's assuming that the outer duct is extremely efficient. Acceptable for the dyno and short sprints perhaps. Anyone log a fenderwell setup on a road course?

That's not a small amount and I would gladly get it back for the slightly higher pressure drop of an upgraded set of stock location inlet pipes. Even several feet of 2.75" pipe with bends does not drop much pressure at 500 cfm (per side).

The MAF is another issue but I don't see why you couldn't run a blowthrough setup with the factory style inlet routing, not as sexy but I doubt much sacrifice in effectiveness. In fact, there have been several threads alluding to mininal or virtually nil gains in testing -I'll have to dig to find out the power levels though.

Just my .02

 

we move the filter towards the body so not to obstruct the core....
here is what we do....

 

I have some direct experience with this, as well as track testing. I went to a blow-thru fender well intake system and back to the OEM style intake with enlarged hard pipes/ modified plenum and actually dynoed higher with the OEM style intake (different tune though). As for performance, the car ran the same 1/4 mile ET and trap speeds with both systems, so the power was literally the same. This was with K24/18G turbos and full supporting mods. My experience is that there is no difference - they both work equally well at the 700 HP level. Also, I am pretty certain that Joe's Porsche record setting 231 MPH run at the Texas mile was with an OEM style intake.

 

yeh i agree with the short distance and the restrictions being negated is a huge factor, not to mention it gets rid of some lag and increases low end torque and throttle response. placing the MAF closer in line to the TB is great performance wise. the further the MAF is from the TB, the poorer the throttle response is. from the time the TB opens to the time the low pressure pulse movement reaches the MAF is elongated in stock configuration. the MAF cant correct air/fule mixture until it senses air movement. the old speed density EFI or MAFless systems, this doesnt matter at all! your tube can be as long as mine

another point, are these cars making big power becausee the intakes are in the fenders or because they have $15000 in other parts. it may be the icing on the cake, or cake in your face!

the air is certainly being forced into the fender and most likely the best place to put the intakes, but at what cost to IC? also keep in mind air is not forced into the intake its only introduced to it. it will only pull in what the motor demands, but again its nice to have this cooler/denser air on first pass to the IC.

these 800+ HP cars are running big thick IC's too and this thickness is a slippery slope and up for debate. its a fact that the second half of the core only does 1/4 of the work. so the thicker you make these cores, the harder it is to pass the ambient air through. this idea coupled with the lack of ducting may be a more of an issue than realized. air is going to take the path of least resistance. a direct quote from one of turbocharging's experts is "when viewing IC's design, regard thick cores as less than thought out." so whats the maximum? again im no expert, 3.5, 4.5 may even be optimal! the single most important factor to IC design is low pressure loss from inlet to outlet (inlet/outlet diameter and internal flow design). there is a crap load of math you can do to come up with some theoretical values and maybe someday il sit down and do it.

ur right the power loss may be minimal, but thats what remains to be seen i think. i just want people to think about it. i dont know anything about neils results or testing, but just for example if you do one reading in december at 30 degrees you may not see much drop from pre to post at all. but if its 100 in august you just might at least expect to see more variant and frankly, august is when we need the IC's to work. this just may be one of those issues that never gets resolved and in the end it may not matter that much. its just food for thought, and generally i just like to argue....ask my lady friend!

 

Joe's car that ran the mile does not have a stock air box.... at least the pic I have seen.... the Y pipe with the BOVs on top... I have a feeling they scooped up the air from above the ICs or simply put a filter right on the turbo inlet... all the 1000 plus HP cars are rerouting.
On a 18 car it will not make a difference as long as you have a good filter, intake, and ICs....
I only suggest such set ups for 30r and up type turbos...

 

Mark,

I'm pretty sure Joes car went to the fender style after that run, later that year and then went back in the fall with the new blow-thru system, but had problems which prevented a clean attempt to break the record...not positive, but pretty sure. Also, about the filter / sock trick - I think I do recall some talk of that, too - possibly on the fall run with the new intake, but not sure...Anyhow, that was a hell of a run! I wouldn't want to be driving that thing at 231 MPH!

 

we just saw the difference ona local Proto car in houston

had aftermarket inlet pipes with 3076's and it was choking the setup couldn't make the power it should.

put the blow through system on it and really woke the car up.

but on small turbo cars you wouldn't notice it