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I'm going to make a hard pipe to the throttle body and am mulling how to design it. I've notice most designs are just a straight pipe with a J shape on the TB end, like the one in the (poached) picture below. The factory pipe actually has more of an S-shape, because the intercooler outlet doesn't point straight at the TB, but rather points more toward the center of the engine bay. See the second picture of the over-sized SFR pipe, and notice how the pipe first bends to the right, then back to the left to mate with the TB. Obviously, the J version will be easier to make, but my question for those with that style pipe is how well it fits at the intercooler? Seems like it may not line up straight with the intercooler outlet and instead uses the coupler to fudge the angle needed? True? If so, anyone ever notice any practical issues with that design, like a higher tendency for the couple to come apart or tear?
Simple pipe with one bend at TB end...
More complicated s-shape. Harder to make, but is it needed?
I’d suggest spending the time getting the angles correct at both ends. Laminar flow can be a funny thing and an odd angle at a point of entry can do weird things to the volume and pressure, it’s much less critical in the middle of a channel as it has a chance to normalize. Plus, I have seen people fight with the fitment of some of the aftermarket intercooler pipes and seen the occasional coupling pop off under boost.
The factory had the right idea, in my opinion. I look forward to seeing what you come up with.
Pipe shape itself doesn't matter that much, look at any factory turbo car and see how crazy the pipes are shaped to package better.
there's a lot of junk in the 944 bay to plumb around like headlight brackets... probably the reason for the S bend.
now one thing to consider, most folks with the simple straight j pipe use aftermarket couplers which are twice as long as the factory ones, so they may have enough 'give' to deal with the misalignment.
I’d suggest spending the time getting the angles correct at both ends. Laminar flow can be a funny thing and an odd angle at a point of entry can do weird things to the volume and pressure, it’s much less critical in the middle of a channel as it has a chance to normalize. Plus, I have seen people fight with the fitment of some of the aftermarket intercooler pipes and seen the occasional coupling pop off under boost.
The factory had the right idea, in my opinion. I look forward to seeing what you come up with.
On the other hand, would an S-shaped pipe with straight-on inlet and outlet angles flow better than a straight pipe with the inlet slightly canted vs the intercooler outlet?
Originally Posted by gruhsy
Would a gradual curve work as an option with entrance and exit being straight on?
That's essentially what SFR did with the big pipe in my second picture above. All things equal, it "feels" like a better design because the inlet and outlet line-up straight, and the curves are smoother inside than if made up of pipes coupled together at an angle.
Originally Posted by V2Rocket
Pipe shape itself doesn't matter that much, look at any factory turbo car and see how crazy the pipes are shaped to package better.
there's a lot of junk in the 944 bay to plumb around like headlight brackets... probably the reason for the S bend.
now one thing to consider, most folks with the simple straight j pipe use aftermarket couplers which are twice as long as the factory ones, so they may have enough 'give' to deal with the misalignment.
best option- hump hose
The factory pipe definitely is contoured to fit under the intake air snorkel and around the air box, but even with that out of the way, the intercooler outlet just points to the left so much that you either need some way to aim it back toward the throttle body. A hump hose would work, or a 30 degree coupler even better probably, though I suspect most with the straight LR style just use clamp the pipe at a slight angle and add a little more angle with a slightly longer coupler.
When I get to cutting metal, I'll see how things work out. Feels like the s-shape is a lot of effort, but the straight pipe is a bit under-engineered...
easy way to make an S pipe is to get a 90 and cut it halfway through the bend (make 2x 45s).
flip one leg around and weld the 45 cuts together
. . . . . . _
_| -> _/
looking at photos the main obstacle of straightening the S curve is the AFM housing, but also the headlight mechanism as i said before at the IC end.
in the midst of my own plumbing project and i'm going as far as modifying the headlight mounting outwards to give the IC pipe a straight shot, but you don't have that flexibility in a stock chassis.
Here it is. You could use it straight out of the box I'm sure, as it lines up at least as well as a straight pipe, but I'll probably make a small pie cut to line it up straight. Also need to put the ISV and Bypass valve pipes in, along with boost braces, but these S-pipes will save me hours I'm sure.
Nearly perfect length too, with beads on both ends!
So I ended up using half of the pipe Dave suggested and attached a straight pipe at about a 20 degree angle to line up with the intercooler. It all lines up pretty well now. Just have to add the ISV and BOV ports.
To make the 20 degree angle, you have to cut both pipes at 10 degrees and combine them for the full 20. If you cut one straight and the other at 20 degrees, you'll end up trying to weld an oval to a circle...
Are you going to try and fit the bigger throttle body as well? It looks like you’d need a funnel at that end to match it, or are you going to use a rubber adapter hose?
Are you going to try and fit the bigger throttle body as well? It looks like you’d need a funnel at that end to match it, or are you going to use a rubber adapter hose?
That 65mm TB I posted has the same 70mm mouth as the factory one, and my plan is to use a 2.5" to 2.75" silicon coupler, kind of like the factory but with less of a transition. I'm going to add boost braces all around to prevent the hoses from blowing off.
08-04-2018, 01:49 PM
Hard Pipe shape question
