Looking for feedback on my 3.3 ITB EFI + Haltech R3 plan (1979 911SC)

[911Ren20]

Hi everyone,

I have spent way too many late nights reading old threads and watching videos, and I think I finally have a plan. Before I lock parts in, I would really appreciate a sanity check and ideas on where I can save some money. All of this slippery slope started with engine out to deal with Triagnle of death last month. Now I already got my feet wet.

Car / engine / Itb:

1979 911SC - big port car

3.3 liter, twin plug

PMO 50 mm ITBs on manifolds stepped to match the 38 mm ports (already purchased)

Stock heat exchangers and exhaust for now

Goal:
Reliable, clean running daily street car that feels sharp and period correct.Not chasing every last horsepower, just good drivability, easy cold start, and solid data for safety.

ECU and ignition

After going in circles between Elite 2500, MS3, Microsquirt and a few harness builders' opinions, I landed on:

Haltech Nexus R3

Enough I/O and logging to do it right

PDM Build in

Feels like a good middle ground on price vs capability

Ignition plan:

Keep stock twin plug CDI setup for now, leave option to upgrade to COP

Use Haltech to control timing, fed by:

Clewett crank trigger kit with hall effect sensor

Later on I might go coil packs, but for now I am trying not to blow the budget completely.

Hardware and sensors plan

Using Clewett for the air cooled specific bits:

Clewett crank trigger kit (hall sensor)
Clewett Cam sensor

Sensors - I am happy to use generic or Bosch style sensors as long as they are reliable and play nice with the R3. Current list:

MAP sensor with a small vacuum manifold / balance rail for the PMO runners

IAT in the intake plumbing

CHT on at least one cylinder

Oil temp (replace the stock unit) to ECU, ECU to Gauge

Oil pressure (replace the stock unit) to ECU to Gauge

Fuel pressure sensor

Wideband O2 (single sensor)

Idle control valve (already part of the PMO kit)

TPS on the PMOs (already part of the PMO kit)

Knock sensors, is single sensor effective at the throttle linkage bracket position?

What I am hoping to learn from you

This is a summary of a lot of nights of reading and trying to connect the dots, but I am definitely open to changing things if I am overbuilding or spending in the wrong places.

I would love feedback on:

Sensor list

For a NA 3.3 street motor, what would you consider must-have vs nice-to-have


Budget friendly choices

Any favorite non-ECU-branded sensors that are proven on these cars (oil press, fuel press, temp, MAP, etc.)

Smart places to reuse OEM hardware or existing senders

Places where people tried to save money and later regretted it

Any issues running a Nexus R3 with Clewett crank trigger and stock CDI

MAP plumbing tips for PMO ITBs to get a clean load signal

Trying to keep this project realistic without doing it twice. Any real world experience, “if I did it again” stories, or parts suggestions would help a lot.

Thanks in advance.

[Showdown]

Seems like you have a good handle on the project and everything you've listed looks good. I would recommend that if you're thinking of COP, just do it now. Consider that if you wanted to do it in the future, you'd still have to pin and run all the wires and stow them away somewhere in the engine bay for later... you're already doing the most difficult part of the conversion. Audi 1.8T coils can be had for $30 or so which is only ~$400 And you specifically mentioned not wanting to do it twice.

I'm also for picking all the fruit once you start- you're doing a major conversion, so why not do everything you can- there's no way you're going to be excited about having to pull the motor and rebuild a wiring harness in a year because you forgot X, skimped on Y.

Other things that you may consider:

Dual wideband sensors- Haltech makes a dual controller for $150 more than the single controller.
Flex fuel sensor - Haltech's is $200 (!!!) but they can be had for a lot less; they're all the same and a GM one works just the same bit for a lot less.
Dual knock sensors- cheap and no reason to not, if you can.

[911Ren20]

Gotcha, Totally understand your perspective. it's truly a slipper slope.

I will look into expanding the o2 to dual band. Knock sensor adds a bit more effort. will need to get those bridges. Do you have mounting recommendations besides the 993 bridge?

Regarding COP, I just serviced the CDI stuff not long ago. just keep hating myself for double spending. the plan still as you describe. future proof the harness and Stow away until COP. Do you have more info on the audi 1.8t coils?

[Showdown]

I'll be using the 993 bridges, there are some threads here on mounting them:

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/960640-another-aem-efi-conversion.html

Probably easier with the engine out and heads off, but doable in-situ.

I used the Audi (VAG) coils on my current engine with wasted COP spark which put more load on them than they'd see in full sequential mode and they didn't blink once. they're ubiquitous and affordable as well so it's no big deal to cary a few extras just in case and you can pick them up at NAPA and Pep Boys, etc. if needed.

Another option is Denso coils which some folks have had luck with- I didn't so I switched.

FWIW, you don't NEED dual O2, but the Nexus R3 can utilize it and you'll bet more/better data than just relying on one bank.

[911Ren20]

My engine is out, adding the bridges should be simple.

Correct on the dual o2. I do plan on for upgrading to headers and full exhaust in the future. just working with the budget this year. so 1 bung for now. Hopefully we will pick up a few extra hp then

Appreciate the info on the Audi coils. will look into it.

Its really coming together.

[ToySnakePMC]

Not ITB, but common plenum with single EFI throttle body on this new 3.2SS.
Using ECU Master Black ECM with sequential fuel, sequential dual Audi COP spark, and Hella DBW pedal using this Bosch 996/997 throttle body. I agree - update the "operating system" now with whatever features you're looking to do in the near future.
Got about 180 break-in miles on this new engine build - and it is a different beast than what I had 9 months ago! Best of luck to you on this new endeavor. Patrick

[rwest]

You say you want good cold starts. How are you planning on doing it? If you use the ports on the PMOs for a MAP signal, you can’t feed idle air into them too. DBW can control idle speed, but that doesn’t sound like something you want to do (me either).

Also keep in mind that your CDI setup likely has some value to someone else, so you can sell it and do the COP without feeling too bad...

Good luck, so many choices out there and not a lot of readily available information on pros and cons.

[911Ren20]

I’ve thought about going to DBW in the future. I’ve seen some info on using an E46/E90 M3 throttle actuator connected to the factory throttle rod on these cars, and possibly running it with a 997 pedal as the input. I haven’t gone too far down that rabbit hole yet, but I’d like to keep the option open.

My idea is to leave a few modular connectors at the ECU side for future expansion. That way, if I decide to add DBW or need another input later, I can just build a small branch harness off those connectors instead of reopening the main loom.

to get cold start, im thinking tuning base on the follow parameter.

Using IACV to add air during cranking and warm-up.

in theory on the R3:

PWM duty cycle during cranking

Warm-up table (coolant/CHT based)

Idle target table (CHT based)

Idle ignition control (timing-based stabilization)

if I am simplifying things too much. please correct me. I am a beginner on this subject.


@patrick, That's a great looking engine. congrats!

[zaphodtheprez]

I went to COPs directly and never thought of keeping the CDI because I wanted sequential firing, a 3D ignition advance table, PID idle timing control, over rev cutoff etc. The ECU should handle all those functions and more. My only other consideration was a Bosch six channel ingnition trigger by the ECU and/or a six port coil pack depending on the ECU's capabilities. I felt the weight of a six in one coil pack, sold it, and decided on COPS.

I may not be getting your design but how will you distribute the spark trigger to the required channel/cylinders with the CDI? Are you also keeping the distributor?
It was the first time building a harness for me too and I chose modular also. I found several benefits from this - I didn't have to lock in my design from the start, I could focus on one subsystem at a time and if I messed up it would be an easy fix. This helped my confidence and I could get though the build without anxiety. My next build will be a much cleaner harness but I'll keep the subsections - also helps with easy disconnects to work on or test one section or you can count the few disconnects you need to drop the engine.

I also added hydraulic quick disconnect to the fuel line going to the fuel rails. Makes for fuel spill free engine drops.

With ITBs, the IAV method of idle control was not ideal. I was never happy with it because as Julian pointed out, MAP and idle control in the same system compromise both. I use Alpha-N+MAP hybrid strategy with the EMU Black and it works great now that the idle controller uses a combination of DBW PID and ignition PID. No interference with the map signal under idle. Will you use vacuum assist for brakes? I have a separate pedal triggered pump.

I chose not to replace the sensors for the dash gauges. The only one the ECU feeds is the tach. I have separate sensors for CLT/Oil temp, IAT, Crank and Cam trigger (the Adapt Motorsport one), one wideband directly (the other is through a Spartan controller to an analog input), fuel pressure, gps receiver for vehicle speed. Most of the sensors I ordered had an available calibration curve.
No CHT or knock sensors - I have lower compression.

For DBW, I have the BMW/Hella pedal and EFI Hardware throttle actuator. With DBW, I also mapped in progressive throttle response. The hard wired throttle had much less resolution at smaller openings and lower engine speeds. DBW tunes out the jerkiness.
I use the Bosch VAG COPS.
Next time, I want to build one with a plenum and single throttle on Speed Density...and a Rotrex supercharger where the AC compressor goes...and an intercooler that uses up some of the empty space under the Carrera tail...we can all keep dreaming right?

A couple Pelican members helped me quite a bit. I reached out to one directly and a couple others reached out to me to make sure I had what I needed or offered to provide feedback. Such a great community here.

[911Ren20]

Great feedback, guys - seriously appreciate all the insight.

I’ve already learned a ton just from this thread, and I’m really glad I came here before smashing the buy button. It also helps knowing there are a couple Haltech tuners in San Diego, so local support won’t be a problem.

I ended up spending the evening digging into COP setups. Looks like the R8 red coils are really all I need is 12 for the twin setup, and they’re surprisingly cheap. Not sure why my brain was still hanging onto the CDI idea. With the R3 handling PDM and sequential ignition directly, the smart coils plug right in without needing separate ignitors. Definitely simplifies the whole plan.

One thing I’m still on the fence about is the wiring harness. How daunting was it for those of you who built your own from scratch? I’m debating whether to tackle it myself or hand it off to a pro. Would love to hear what you guys experienced.

@zaphodtheprez great tip on the quick disconnects. Gonna look more into Map and IAV. You guys have planted the DBW seed in me. My small brain thought brake boost hose can connect to vacuum manifold? But research also indicates ITB vacuum isn't strong enough. some owners run a separate vacuum pump, noisy?

[montauk]

I converted my 1980 911 using PMO ITB’s and a Haltech R3. If you search my posts, you’ll find more info and photos. Off the top of my head:

Go DBW from the start. It eliminates the need for a separate idle control or manual throttle lever, since the ECU uses the throttle motor to manage idle. Plus, it’s a fun system to experiment with.
I used a BMW pedal ($250). Wiring is straightforward:
• The pedal has built-in redundant hall sensors. ($30)
• At the engine, remove the TPS from the throttle motor and install a Eurosensor.
• You’ll need brackets for both pedal and motor (Toptuning sells a pedal kit).
Don’t worry about brand names — most of this hardware is Bosch, and it all works the same way.

The built-in PDU offers a lot of flexibility:
• Standard outputs handle injectors and COPs. – do the COP now as Julian suggested. I’m using Denso COP’s.
• The four high-output lines can drive heavier loads. I run the fuel pump from one and the starter solenoid from another.
• I may use another high-output for the AC solenoid – not sure about that yet.
This gives the ECU direct control and lets you eliminate old wiring.

I’m using the PWM feature to drive the original oil pressure and temperature gauges. The input is a Bosch sensor. The ECU is also triggering the low oil pressure light. I used another Bosch sensor for fuel pressure input. Tach is ECU-driven.
For temperature input, I used a spark plug thermocouple with a conversion board — much cheaper than Haltech’s CAN adaptor if you only need a single channel.

[zaphodtheprez]

I found the idea of building a harness daunting also. I watched too many pro level videos with concentric twisted looms and race grade quality. I had to remind myself I’m not building a race car. Even a modern 911 does not have that grade of wiring.

If you hire a pro make sure you’ve made all your design decisions before they start. If you’re building it yourself use quality materials - Deutsch connectors with barrel crimps, quality crimps for wire joins, correct wire gauge for use and temp range, same for sheathing and boots. Test each section as you build - for strength and correct electrical continuity.

Take good measurements and build it out on a 4x8 peg board. My friend and I built ours at the same time. He drew and pinned it up on a plywood board with accurate measurements and I used the dinning table. I had to use a spreadsheet to track my continuity pin outs and wire colours - he just wrote it on the board. There’s no contest which one looks and fits better. Don’t use the dinner table even if your wife is a trooper.

[montauk]

I used the Haltech wiring loom, which is well-designed and easy to follow thanks to its color-coded layout. I added heat-shrink labels where needed to keep things organized.

I did make one mistake with the injector wiring—accidentally swapped cylinders 1, 2, 3 with 4, 5, 6. Unfortunately, the software didn’t allow reassignment of those channels, which would’ve been a simple fix. Luckily, the ECU connector is easy to work with, so I was able to swap the pins manually in just a few minutes.

One tip I picked up from Haltech’s YouTube videos: always check each crimp as you go by giving it a firm pull. A few of mine failed, but because I tested them during assembly, it wasn’t a big issue.

Regarding the harness, the standard 8-foot length worked well overall—except for the left side of the engine. I had to extend the injector and coil-on-plug (COP) wiring to reach that side. In hindsight, I should’ve built sub-harnesses for the injectors and COPs from the start, as someone here rightly suggested.

Final note: use Deutsch connectors wherever possible. They’re easy to work with and reliably watertight.

Originally Posted by zaphodtheprez

I found the idea of building a harness daunting also. I watched too many pro level videos with concentric twisted looms and race grade quality. I had to remind myself I’m not building a race car. Even a modern 911 does not have that grade of wiring.

If you hire a pro make sure you’ve made all your design decisions before they start. If you’re building it yourself use quality materials - Deutsch connectors with barrel crimps, quality crimps for wire joins, correct wire gauge for use and temp range, same for sheathing and boots. Test each section as you build - for strength and correct electrical continuity.

Take good measurements and build it out on a 4x8 peg board. My friend and I built ours at the same time. He drew and pinned it up on a plywood board with accurate measurements and I used the dinning table. I had to use a spreadsheet to track my continuity pin outs and wire colours - he just wrote it on the board. There’s no contest which one looks and fits better. Don’t use the dinner table even if your wife is a trooper.

[Showdown]

Building a wiring harness is, much like anything, dependent on good organization, preparation and meticulous process.

Make spreadsheets with pins, wire color, function, etc... keep yourself organized on paper and make sure you fully understand and know what's going where and why.

Lay things out on a flat surface- I like to put paper or cardboard down on a 4'x8' table so I can tape wires in their path, make notes and see everything laid out. This allows for measuring runs, organizing branches and sub harnesses.

Make sure that every sensor, COP, or device has a connector or sub- harness separating it from the engine harness. This enables you to remove the device if you suspect it has failed without cutting the engine harness. Make sure that the harness form the ECU to the engine has a connector so that you can drop the engine by disconnecting one main connector (I like the Deutsch HDP series- they come in various configurations).

And most of all, think ahead- shrink wrap tubing has to go on before the connectors... wire sleeving before that... etc...

[911Ren20]

@montauk - thanks for dropping into the thread. Your responses in the other discussions actually played a big part in pushing me toward the R3. Are you still happy with yours so far? I spoke with Alex at Haltech and he mentioned the R3 has dual-channel knock inputs, so I can run two knock sensors. I’m curious how you approached knock control on your setup.

Looks like I’ll be pulling another late-night session going through your posts.

And to everyone else - really appreciate the wiring feedback. For those of you who build sub-looms, would you recommend having a connection panel on the left side of the engine bay/firewall so each branch can be disconnected cleanly? I’m thinking something like a small panel of Deutsch connectors so the engine can drop out without undoing the whole harness.

Would love to hear how you guys approached it.

[Showdown]

I can't say what works for others but my approach to wiring is as follows:

-ECU and electronics under the passenger seat
-ECU harness running into the tunnel and out and over the torsion tube and up the right side of the tub where the factory harness is, entering the engine bay on the right side where it terminates into a Deutsch HDP connector that's mounted to a small housing/panel.
-Engine harness connects to ECU harness with mating Deutsch connector.
-Engine harness lives on the engine and stays there- it never comes off once installed.
-From the engine harness, multiple wire runs branch off to the various components like sensors, etc...
-Each sensor, etc... has a connector at the wire termination point (the wires run from the engine harness to the sensor where there's a connector. Nothing is hardwired in.) Thus enabling the sensor to be separated from the engine harness if it needs to be removed/replaced.
-Each bank of injectors has a sub harness that connects to the engine harness on one end and the injectors on the other.
-Each bank of COP has the same. This is done so that if injectors or COPs need to be changed to a different brand or rating in the case of injectors, the engine harness doesn't have to be rebuilt- just the sub harness which is much easier. Also helpful to diagnose potential issues and isolate wiring out of the mix.

In addition, I separate my power wires from the main harness and run them in a separate harness from the fuse/relay panel under the seat to the engine to minimize the possibility of noise and to make the already fat ECU harness more manageable. They connect to the engine harness with a Deutsch HDP connector in the same spot at the engine harness.

All of this will be detailed in my build (and was last winter when I rewired the car for the second time )

This approach has been great for keeping wiring clean and organized, and for engine drops. Disconnect the main Deutcsch connector and the power Deutsch connector, the two vacuum lines to the manifold and the fuel feed and return line and the engine comes out. Takes less than 10 mins to disconnect everything and it's all neat and organized making the drop and later install super easy.

[montauk]

Originally Posted by 911Ren20

@montauk - thanks for dropping into the thread. Your responses in the other discussions actually played a big part in pushing me toward the R3. Are you still happy with yours so far? I spoke with Alex at Haltech and he mentioned the R3 has dual-channel knock inputs, so I can run two knock sensors. I’m curious how you approached knock control on your setup.

Looks like I’ll be pulling another late-night session going through your posts.

And to everyone else - really appreciate the wiring feedback. For those of you who build sub-looms, would you recommend having a connection panel on the left side of the engine bay/firewall so each branch can be disconnected cleanly? I’m thinking something like a small panel of Deutsch connectors so the engine can drop out without undoing the whole harness.

Would love to hear how you guys approached it.

Still happy with the R3 setup.
I’m running a single knock sensor mounted to the throttle bracket boss — about the only spot that works without drilling into the heads or case. If you want to run two knock sensors, the 964-style setup seems to be the best option.

As for the harness: don’t overthink it. A big single connector or a bunch seems like it would be nice, but it’s not essential. The shielded wires (knock, cam, crank) should go straight to the ECU without splices - that's extremely important, and they have plugs on the ends — same with the sensor wires, injectors, and COPs. Unplugging everything and snipping a few zip ties is quick. Ten minutes, call it an hour tops.

Unless you’re dropping the engine monthly, you’ll spend more time adding connectors than you’ll ever save. And every connector is a potential failure point.

[montauk]

I ran my wiring through the hole left for the old Lambda/O2 system. I had to enlarge the hole but it worked well. If you closely at the second photo, you may notice the sliver knit (it's original) carpet has a slight bulge. The coco mat behind the passenger seat is about an inch higher than the one behind the driver.

[Showdown]

Originally Posted by montauk

As for the harness: don’t overthink it. A big single connector or a bunch seems like it would be nice, but it’s not essential. The shielded wires (knock, cam, crank) should go straight to the ECU without splices - that's extremely important, and they have plugs on the ends — same with the sensor wires, injectors, and COPs. Unplugging everything and snipping a few zip ties is quick. Ten minutes, call it an hour tops.

Unless you’re dropping the engine monthly, you’ll spend more time adding connectors than you’ll ever save. And every connector is a potential failure point.

Respectfully, I strongly disagree with this.

First time I did it, I wired everything directly to the ECU, no connectors anywhere because it was easy and when it came time to modify the harness in the engine it was a royal pain, to say nothing of trying to drop the engine with wires everywhere. When I had to replace my COPs not having a sub-harness resulted in the swap being hours long inside the engine bay not snip snip 10 mins.

It's so easy to future proof and make your future life easier now while the engine is out and you're building from scratch, it begs the question why wouldn't you?

[rwest]

I mounted an Deutsch connector on a custom bracket that I made that used the old cruise control mounting points and then put all the engine stuff on a plug for ease of engine removal (agreed that it doesn’t happen that much) and it made it much easier to build a custom harness that just snakes it self around the engine instead of from the passenger compartment.

I’ve decided to source my power and put fuses/relays where the old CDI box would have been mounted.