Originally Posted by Ish_944

@JRP944 Have you made up your mind regarding the CAD data? Are you still willing to share, or was it kind of sold together with the hardware?

Originally Posted by Tony5

Still putting the miles on, still hoping to get some proper footage.

Ran into my first real issue today. Well, actually it did it just once the day I installed the ITB's then never again, so I chalked it up to a loose wire connection and never looked into it.
Gave it the beans and the engine cut out momentarily. It didn't die, it just acted like it was idling. On a ten mile highway drive, I tried WOT in 3rd, 4th and 5th gear multiple times and it did it at any RPM, and only at WOT, 99% throttle was fine.
I know JRP wasn't entirely satisfied with his TPS design, and it's really the only thing related to the ITB's that my DME is aware of having been changed, so that's where my investigation started. Sure enough, like JRP said, the TPS didn't make contact with the WOT switch when I ran the throttles by hand. His TPS mount design is adjustable so I borrowed some tools from my cruising wingman (in a 69 Datsun pickup, on a Ford Ranger frame, with an LS making 300+ hp with only 2000ish pounds to push, in case you were wondering) and I adjusted it so that it definitely hit the WOT switch at the expense of consistently contacting the idle switch. Didn't help. At all. So for fun I adjusted it so that it never made contact with the WOT switch. Ran perfect. Back at home I realized that if I stick my finger in the TPS and hit the WOT switch at any RPM, the engine falls on its face. So clearly I was pushing the pedal just hard enough to hit WOT today even though it didn't normally make it that far.
The TPS is one of the few remaining systems on the car that I haven't researched at all, so it looks like I've got some homework to do. I really have no clue what my DME wants to know from the TPS, in fact some time ago when I was troubleshooting a problem I ran the car just fine with the TPS unplugged. I know it's not a variable signal through the entire range of throttle angle, more like an on/off switch, but that's all I know.

Originally Posted by thorpeda.

do you still have this ?

Originally Posted by JRP944

I based the TPS design on the simple principle of the ON/OFF switch, but whether or not the voltage through the new TPS versus the stocker is the same or not I can't say. That might be a worthwhile test if you can trace the wire back to the DME and with the engine running, check the voltage input to the DME at the idle and the WOT contact.

Originally Posted by walfreyydo

I believe the TPS has 3 different modes: Idle (open loop), part throttle (closed loop, should hear a click as soon as throttle plate moves from fully closed) and WOT (open loop), with two contacts in the TPS itself (idle and WOT). The DME uses three different fuel/ignition maps to match those three possible conditions. Often the contact inside the TPS gets worn and will not register WOT or idle and these can be easily fixed by carefully opening the TPS and bending the metal spring so it makes contact again. Its an extremely simple design

I was able to pull some tunes from the Rogue Tuning website and open them in TunerPro (free open-source tuning software that I believe will allow you to burn your own chips if you have a burner). Some screenshots from Tuner Pro showing these three states are in the thread I started here towards the end. Seeing this was helpful for me to understand how the stock Motronic system works and how the different states of the TPS correspond to the fueling and ignition maps within the DME. If a chip burner were sourced it could also be a potential alternative to standalone?

FWIW if going full standalone then a variable TPS would be preferred and I think there are BMW variable TPS's that can be used with an adapter plate that is compatible with the TPS's found on our cars. Tony if you have any questions about going the MS route, I can certainly help get you up and running

Originally Posted by JRP944

Hello Everyone-

I want to share something I've been working on for a little while now - as the title says, it's 8v ITBs. I know, I know...we've been down this road before. But I have an interest in them and wanted to design something fun.

So a little background information...I originally started working on some layouts that would utilize the RHD 45mm DCOE throttles. While this would have worked, I didn't like how the DCOE throttles are spaced at 90mm centers and the 944 cylinder head is 122mm centers. I think this works well for the 16v motors that have spark plug access through the valve cover, but on the 8v it just didn't seem like the greatest solution by partially blocking access to two of the spark plugs. So I abandoned this route.

Next I thought about simply using Jenvey SF style throttles. They're proven, they're reasonably priced, they look good and they have a nice catalog of parts to put a system together. I wanted to create a system that utilized the stock throttle cable with a center pull arrangement, so I developed my own linkage and laid out a few concepts to analyze various manufacturing processes. I then 3D printed some parts to check for basic fitment in the engine bay.


Open trumpets. Looks cool, but filtered air is important.


Fully CNC'd plenum with removable plenum spacer for changing internal volume by 0.5L. Center inlet.


Cast and machined plenum with nice, smooth internal radii.


3D printed test assembly. Shown here with an earlier (and not great) version of the center throttle linkage.





Naturally I found a few things that didn't fit exactly how I thought and I discovered some things I didn't like about the overall design. This got me thinking...why not take this to another level and design my own throttle bodies? I decided to make them out of billet aluminum and keep them to 22mm in length. This allows for better fitment of the surrounding components with decent length ram tubes and a good size plenum. The throttle bodies were designed to be modular, so they will work with any cylinder spacing from 88mm and larger. This means they'd be great for use on VW 5-cylinder engines, Porsche flat sixes and even BMW straight sixes as well.


Short throttle bodies with 60mm long ram tubes connected to a machined plenum base.



Center pull throttle linkage, center feed intake plenum.


Throttle layshaft with rigid connecting links and individual throttle return springs.



I have a few different plenum concepts as I'm not sure what I ultimately want to go with. This will be partly dependent on what fits best in the car once the inlet manifold and throttles are actually produced. I've always liked the look of the center feed like BMW used on their M cars back in the day. It packages pretty nicely and lends itself well to being machined from billet and then welded together. I'd love to do some cast components, but it looks like going the machined/welded route is likely the best for small runs. TBD.

So ultimately I wanted to share this with you folks to see if there is any interest in the 944 community for some 8v assemblies like this. It would be nice to produce 8-10 sets of parts (or more) that would include the following:

• Inlet manifold (machined and welded)
• Throttle bodies (Black anodized, ball bearings and lip seals on throttle shafts, AL2024 throttle plates, 1215 steel throttle shafts with zinc plate)
• Custom linkage (Individual throttle return springs and throttle linkage arms with bushings)
• Intake plenum with ram tube extensions

This is kind of a feeler before I have anything machined. Naturally, I would prototype on my own to make sure everything worked first. Let me know your thoughts on the overall design, if you'd ever consider buying something like this and if so, how much is something like this worth. I have my own thoughts on pricing based on quoting parts, but curious how that aligns with the market.

Have a great Saturday.

JRP

Originally Posted by David Mabee

Did you get this up and running. I'am interested. Also what engine management system are you using

Originally Posted by Tony5

So 200 miles later, I've got some thoughts on these ITB's.

But we'll start from the beginning.
If anyone ever has the opportunity to deal with @JRP944 do so with confidence. Great communication, fast shipping and he packaged the kit up to be bombproof.
Upon first inspection, it's a work of art. It's exactly what I would've dreamt up myself, but brought to life better than I could have done. Attention to detail, finish and futureproofing are all top notch. Everything works smoothly, no binding, no rough spots. Everyone whose seen it in person so far immediately thought that it was a thoroughly engineered product being made by some name brand company for retail sale. Even the hose clamps he sent with are nice yellow zinc plated pieces.

Install was very straightforward. If I had a late car it probably would've taken me less than 1.5 hours. I had to cut down my early AOS and install the late AOS top cap on it for clearance. I have plugs in the two 1/4" NPT holes and a 90° elbow to 3/4" barbed hose fitting in the 3/8" NPT hole, I was able to spin my old AOS hose upside down, cut 2" off and reuse it. Single 1/2" hose to my brake booster, one small vacuum line to a T running my FPR/FPD. I had to heat up and re shape my S bend fuel in hardline that originally went over the plenum, I made it more of a hockey stick and ran it under. My throttle cable is too long for the cable stop to slot in to the throttle cam, so zip tie to the rescue till the new set screw cable stop arrives.
At this point the car started right up, idled great, revved easily. Then I smelled the gas. Loosening the stubborn S shaped fuel line cracked my fuel rail. It took two hours up to this point.
Day 2, I buy some longer fuel hose and install a spare fuel rail off of a 1984 car, where the fuel comes in at the rear of the rail. Again, car starts right up and runs great.

Maiden voyage, the exhaust immediately sounds different. Lower tone at low RPM's and some of the raspiness is gone. You can hear more intake noise and some whistling that sounds kinda vacuum leakish, but nothing drastic while I make my way to some open roads and let the car warm up.

Then I finally get to let it rip. Huge disappointment. It sounded cool, but i spent the next ten miles trying to decide how I was going to convince my friends that cool sounds were a good trade for massive power loss. By the time I got home I decided that the throttle wasn't getting to 100% open. It had to be that, because I couldn't accept that the car was so slow. I had one of my kids step on the go pedal while I watched underhood. Nope, it was going wide open. More disappointment. Then I noticed the gold paint on throttle linkage #1. And then the gold paint missing from the underside of my hood. So I closed the hood, pushed the pedal as far as it would go and popped the hood release. The pedal went probably another 30% further. What a relief.
This hood is scheduled to be replaced by an FG one when my paint guy finally gets caught up, so I had no qualms about cutting a chunk of the under hood bracing material out for clearance. Throttle feels like it's working now. Test drive 2# starts off well enough. Way more power when I have all the pedal travel. But I didn't cut out enough hood bracing and my throttle occasionally sticks at WOT. That's not a great experience in case you were wondering.
A little more clearancing, everything works now and day 2 comes to an end.

Day 3 and I can really start laying on some miles. The sound is great. The car is definitely louder, but not from the exhaust. The pedal feel takes some serious recalibration to get used to. It's stiffer, but not linear, it's also got quite a bit more travel. It gets stiff enough at 3/4 travel that between the stiffness and the increased travel, I often think I'm at WOT and I'm not even close. And that's important, because unlike with the standard manifold where 80% throttle seems to get you 95% of the ponies, it's now much more of a 1:1 ratio, if you have the pedal at 90%, adding the last 10% gives you noticeably more power. The one other person that's driven it so far thought I was being pedantic when I told him this. Then he ended up describing it the exact same way.
Speaking of power, I do believe there is more of it up top. There's also less torque down low. I'm fine with the trade, I only own this car for fun and I'm not sure if I've ever shifted below 4k rpm, so more fun up top is great.

But the sound is the real star of the show.
I'm gonna warn you up front, I've made multiple in car and drive by videos, and the in car ones are terrible. It doesnt do the ITB's any justice.
I thought the drive by videos did better but my cameraman said they were garbage. A day later I was able to be the cameraman, and yes, the videos I got on my phone do not capture half of what you hear in person.
Seriously, if someone with quality recording equipment in the northern IL or southern WI area wants to do right by the music the car makes, hit me up and we'll get some real footage.

I made a quick before/after video, and the difference is there but I feel like I need to delete it now after hearing it properly from outside the car.

https://youtu.be/SuUW0TmhQQE?si=tMLBD8Tbb1jBjGwo