Looking for long term/higher mileage ITB experiences
 

I'm thinking of switching from CIS to ITB, and as there are quite a few different systems out there, I'm wondering which ones need the least maintenance/fiddling when doing higher miles per year.
Please only comment if you have real world experience, not hearsay or internet wisdom...

Currently looking at:
-AT Power
-RHD
-Jenvey
-PMO

Arlo: I will follow this post with interest and also share 2 things to consider if not already considered. First, will you keep air conditioning and compressor? If so, make sure the new intake arrangement allows space for compressor. Second, does the new intake allow for a good rain shield? I know Belgium gets rain, and even if you get caught by mistake in a storm, you want to effectively avoid breathing it into your intakes. Forgive me if you have already considered these.

All the ITB brands listed are respected.

Choosing a good EFI system is also very important, preferably one that your local tuner knows well. EFI/ITBs take a lot of effort to get tuned correctly, but once dialled in shouldn't require fiddling.

I'm running Megasquirt with repurposed Triumph ITBs. I would not use either of them again, instead opting for one of the shiny new ITB sets you listed and a different ECU. I had to do considerable on the road tuning to get the setup really spot-on for real-world driving, but after that I haven't touched it.

You didn't say what year is your car or the engine/CIS. Since you mentioned "higher miles per year," I think you drive the car regularly as a street car. Are you planning an engine rebuild with more compression and more aggressive cams? If not, then ITB's will not net you a big increase in power. If you are planning a performance rebuild, then the ITB's will give the cams more air than CIS.

My real world experience with CIS over many years and different brands of cars:

CIS is extremely reliable. It is an analog hydro-mechanical system that develops running problems gradually, thus giving you plenty of warning that it needs adjustment or attention. You may develop problems with cold starting or poor running, but in almost all cases it will start and run. Earlier CIS is slightly more reliable and easy to troubleshoot than the 1980-83 OXS systems in the USA. CIS does not like to sit for long periods. The problems most people have with CIS are on cars that don't get driven frequently or have been sitting for a long period, and the owners are trying to get them running again.

In theory, a digitally controlled ITB EFI system should be extremely reliable once you get it correctly adjusted. However, many people here have to keep messing with them to get them to run right and stay that way. If an EFI system has an electrical problem, it can happen immediately or intermittently without warning and cause the car not to start or run.

I will defer to those who have got ITB/EFI running well on their cars for years.

Review this thread: https://forums.pelicanparts.com/porsche-911-technical-forum/925845-post-your-itb-setup-32.html

I have a 75 Carrera that I bought in 2006 and ran with CIS on the original 2.7 engine for 16 1/2 years without trouble other than a little hard starting on cold early spring mornings. The car ran good, but I grew up around my uncle's 64 356C and I really liked the dual carburetor look so I decided to explore a CIS to ITB EFI conversion.

I looked around to see if anyone had already worked out the conversion process and was selling a conversion kit. I found Al Kosmal and x-faktory.com on an internet search and made contact. Long story short, I bought one of Al's conversion kits with RHD ITB's and a MegaSquirt 2 ECM plus an MSD Streetfire CDI box to control the fuel injection and the ignition timing (I am still running my original Bosch distributor with a Pertronix ignitor and the mechanical advance locked).

From the beginning of the project I decided to use a dyno tuning shop to tune and quantify the results of my conversion. I ran a baseline pull to see what the CIS 2.7 was running to start. Then I removed the CIS and installed the ITB EFI system and started up the motor set the ignition timing offset and balanced the ITB's followed by dyno tuning. At this point the car ran great at WOT and max power at the wheels went from 175 with CIS to 192 with ITB EFI (9.7% gain). I soon found the tune was not quite right at part throttle / moderate load, but I was able to improve this situation by making a couple of tuning runs using Tune Analyze Now! the VE table auto-tuning feature in the Tuner Studio MS Ultra app.

In January of this year I decided to rebuild my 2.7 into a 2.8 with bigger cams, etc, so I repeated the process above with the rebuilt engine. Because I am using bigger cams with more overlap and less vacuum signal, I had to modify the MegaSquirt ECU program to use throttle position instead of intake vacuum for the load sensing signal, but the rest of the start up process was the same: set timing offset, balance the ITB's, and dyno tune and test followed by auto-tuning on the street.

Since I installed the ITB EFI in June 2023, I have logged over 3700 miles. During that time, I have not had to re-adjust the ignition timing nor re-balance the ITB's (I have checked the air flow at idle before auto-tune test runs).

The RHD units are high build quality, but the ITB balance fine adjust screw and locking nut on the cylinder #1 / #4 ITB are very close to the idle speed adjust screw on the cylinder #2 / #5 ITB, so close I couldn't get a wrench in to tighten the locking nuts. I remedied the situation by replacing the locking nut with a spring on the #2 and #5 idle speed adjustment screws (think idle speed or idle air / fuel mixture screws on carburetors).

For more details see the thread I reference in my signature block below.

There is really no point in going to ITB's if you're not doing other engine mods to take advantage of it, especially cams. Before and after CIS to ITB's on an otherwise unchanged engine will net you very little power. But of course very worth doing if you're eventually going to do a build.

Before/after
 

Dan,
Thanks for posting your experience with EFI/ITBs. Opinions differ, but you present facts/data clearly showing that decent power increases can be made on a stock engines with no other changes made..... and EFI/ITBs, combined with modern engine management offers superior tuning and....they are very cool

You might get limited power increase but I do think you would see an improvement in driveablilty if you drive your car year-round and live in a climate with that varies the seasons. I'm a hard-core CIS guy (I like CIS) but keep thinking about doing an upgrade just to improve cold weather performance in Oregon. I think that EFI with a common intake plenum may be the way to go in my case, but ITB's do just look mechanically-easier to implement.

That's my thought as well. Why spend $15K just to possibly get another 10-15hp from a stock engine. ITB's and EFI let you tune a non stock engine with an aggressive cam to it's best potential.

15k? You can build a Megasquirt/RHD EFI/ITB kit for about 4k.

Yeah, the sky is the limit and the difference between a MoTec AT Power setup and a cheaper one is likely negligible, particularly on a stock motor.


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The ITB setups we’ve built for our customers have been in the $15k + range. Motec, custom harness, higher end systems. But before we even talk about induction, we are building a rock solid long block. The induction is the icing on the cake, not the main event. It’s that age old saying about building a strong foundation…

Sky is the limit on what one can spend- and for some applications/people it may make sense to drop $15k+ on induction after $40k on a motor build and 50k on paint etc…

The reality is that’s not the only option and the big question is what the end goal is- a $200k build to cruise around on weekends might make as much sense as a $4k DIY induction setup on a thoroughbred race car.

Different strokes for different folks and knowing the function of the car and owner is the starting point and North Star.

Perhaps the OP should spend some time defining what they want/need out of the car and their budget before asking for opinions on products.


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dannichols1474's experience with dyno tuning highlights the need to use a well-educated tuner that has the proper equipment to provide more than just a wide open throttle "tune" if you are looking for a comprehensive calibration.

As a professional efi calibration specialist along with a being a carb tuner I can tell you that doing a full street map without a load controlled dyno is impossible to do, accurately. All the fuel modeling setup, driveablity and part throttle tuning will take up 90% of the tuning time

There is nothing like DIY and self learning, but if you do contract a professional, make sure they will be able to provide the service you expect.

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To the OP, I think it’s totally worth doing.
I own two Carrera’s, one with original Motronic and the other one with an ITB injection intake system. … granted the non-stock car is a 3.5…but the difference in throttle response is significant. Although horsepower gains might be modest, I’d expect it to FEEL a lot stronger. These cars are all about feel, so I think it would be totally worthwhile.

In my opinion, the character of the motor is more important than the power figure, and the throttle response and sound you get from ITB’s and a lightened flywheel is worth the cost and effort. The immediate throttle response throughout the power band and liveliness when blipping the throttle are incredibly satisfying to me.

Exactly.......

umm

really?

This.

Looking for long term/higher mileage ITB experiences
 

Yes.

RHD ITBs are $2300
Megasquirt 2 is $525
Wiring harness is $100
14.7 O2 sensor is $82
Fuse panel is $15
Oil temp sensor is $20
TPS sensor is $50

Allow $100 for hoses
Allow $100 for wiring accessories

There you go. About $3500 or so. Add MSD street fire and pertronix if you want to get rid of the CDI and points (that’s another $300)

You can add sensors to your liking/need.

This of course is wasted spark and wasted fuel but it does achieve an ITB system for under 4k. The throttle response is crisp and as others have demonstrated with pre and post conversion dyno charts, there are gains in the range of 5-10% hp.

Now if you go with MS3pro mini and add in denso coils and a clewett cam sensor, and a MAT sensor for about $1200 more you now can have sequential fuel and semi wasted spark.

Jump up to MS3Pro for $1200 as opposed to the MS3ProMini at $600 and you have full sequential fuel and spark, knock sensors and a bajillion other features that aren’t needed.

So, for about $4k you have EFI/ITB.

And if you don’t want to roll your own, buy one from Al for about $5200-5500; everything you need in one box.

The myth that an EFI/ITB system must cost $10,000+ is ridiculous.


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I'm not sure why a properly setup ITB/EFI system would require ongoing maintenance. Since I've had mine installed in early 2022, the only issue I've had a idle control valve hose come loose but that took 5 seconds to fix.

The largest hurdle for getting mine running right has been proper tuning, not at WOT or normal operation but sorting idle and cold start issues.