Tony5

Plenty of production cars out there equipped with ITB's. Multiple BMW M cars come to mind. Obviously none of us have that kind of R&D budget, but it must not be impossible.

Zirconocene

@Noahs944 : A lot of the BMW M cars (all of them?) use ITBs as standard equipment, so you can definitely DD motors with them. I don't totally understand why Porsche hasn't really offered ITBs for their "standard" cars; even some (most, all?) of the GT3s have a single throttle body. The beastly, famous race cars have ITBs, of course.

I don't have a great overview of where Porsche has and has not included ITBs on a motor, but even just looking at the intake spacing on a modern flat 6, I can't see a commercially available ITB that looks like it would bolt up easily. More knowledgeable people will, hopefully, chime in. I just love the idea of ITBs on these 4 cylinder engines but the reality is that I'm just a dabbler, at this point.

Cheers

JRP944

E30, E36 (Euro), E46 and E90 M3s used ITBs. E28, E34, E39 and E60 M5s used ITBs.
Nissan Skyline R32, R33 and R34s used them as well and those were turbo motors.
The new 992 GT3 and 718 GT4RS use ITBs and I think the 991 Speedster did as well.

I don't profess to be an expert on any of this stuff. I just think ITBs are cool and I like a good engineering challenge.

JRP

Zirconocene

@JRP944 : Interesting to hear about the newer Porsche engines and ITBs; I'm going to go download the PET catalogs for those and see what I can see. I think it makes sense that Porsche had to move to ITBs at some point, given the power gains some of their new motors are making. Maybe that's totally wrong but I'm with you, I also think ITBs are super cool and like to believe that they make good engines great.

ETA: Wow, pretty hard to find pictures or documentation of the actual parts that Porsche used on the factory motors with ITBs. Curious.

Cheers

V2Rocket

ITBs are almost entirely for throttle response. They don’t just make power by themselves.

The concept of reflected pulse tuning works the same with an ITB and trumpet or a conventional single TB/plenum with multiple runners. The same runner length/design will tune at the same RPM regardless of where the TB is in the system.

They do allow easier fine tuning and idle control for really big camshafts that might otherwise struggle with a single TB. But in the last few decades cylinder heads have gotten so good and VVT so prevalent that “big” cams aren’t really necessary anymore to make power. So less incentive for the cost and complexity of ITBs there.

Additionally, Drive by wire is universal now so it’s even more of a cost/packaging problem to get 4-6-8 DBW TBs onto an engine.

They do sound super cool with open trumpets.

While lots of cool cars use ITBs, lots of very high specific output cars don’t. S2000, several Ferrari, current Corvette Z06, Mustang GT350. Even a junkyard Coyote 5.0 engine with stock cams, Boss intake (one big TB), headers, and a tune will make 450whp from 5.0L.

JRP944

There was an article in a semi-recent PCA Panorama that was called "10 Things You Didn't Know About the 911 GT3" or something like that written by Manny Alban and it pointed out the use of the ITBs on the 992 cars. I'll have to dig through the digital back issues as I currently can't remember what month it was from.

JRP

JRP944

As usual, quality information presented to the masses. Thanks!

JRP

sonnier

Very interesting. My original plans were to go V8 with my 944 but after much thought it would be better to just buy a Corvette and don't really want to do that. I'd rather keep the the stock engine but play around with it and ITBs are something I've wanted to mess around with. Sure there are better ways to make power but I also don't want to break transaxles and such. I've looked at the danST Engineering kit and thought that was the way to go, but I've also thought it isn't the best design, yours looks much more promising. I like the fuel injectors/rail on top for better serviceability plus the design looks nicer. I'm in the process of fixing old wiring, probably just going to bite the bullet and go PDM and stand-alone so after that anything is possible. Keep up the good work, I can't wait to see what you come up with.

Tiger03447

What brand PDM are you going to go to? I’ve got to rewire my entire dash and would like to get rid of my entire fuse and relay panel on my ‘83. I have purchased a later model fuse panel in case that I have to use it, but would rather upgrade the entire system with transistors to do the protection and switching instead of relays. TIA😀

Tony5

So maybe I missed it somewhere above, but what are we doing with the AOS in our hypothetical ITB world?

JRP944

Have to cut it down and relocate it or use V2's Oil Filler Relocate using a combo of other stock parts.

JRP

Tony5

And your plenum design incorporates a hose bung to keep the AOS plumbed in? Or are you thinking a catch can is the way?

JRP944

Yep, the back of the plenum has (2) 1/4"NPT ports and (1) 3/8"NPT port. The 1/4"NPTs can be used for the IAC valve and the AOS vent while the 3/8"NPT can be used for an IAT sensor.



Perhaps I'll make all the ports 3/8"NPT if it seems like there are better fitting options available for the larger size versus 1/4"NPT, but I haven't fully decided yet.

I run a catch can on my current setup that is recirculating so I plumb the return line back to the intake manifold. I was planning to do this same thing on the ITB design.

JRP

T&T Racing

IMO, 1- 1/4" bung, 1- 3/8" bung for AOS, and 1 - metric bung of proper diameter for IAT. Maybe all bungs should be metric because all other fittings on car are metric. Check McMasters for fittings

JRP944

I like the 3/8"NPT for use with the standard GM IAT sensor that everyone seems to use. I do know that a version of it is available with either an M12 or M14 thread though.

The thinking for using all NPT threads is that you can get NPT x metric hose barbs to get the correct sizes for the hoses.

JRP