ITB Recommendations

[Henry Schmidt]

Originally Posted by Jeff Alton

We have used many over the years. Not going to say what is best...

For a traditional butterfly style, we like Jenvey. Used them countless times with great results every time. We have also used PMO, Clewett, TWM (borla now?) Hargett (did some testing for them and not even sure if they are around?) and RHD.

Our go to is the Jenvey, high quality, easy to adjust and maintain their adjustment. We adapt the throttle set up a little to our liking. On same engines, they made more power than the PMO's but the PMO looks like a weber.

Jenvey also offers their heritage line, which looks amazing if you want a carb look, as injectors are hidden. We have not tested those. The Clewetts are very functional, everything is well thought out mechanically, just aestetically, they are a little "cludgy".

Was not impressed with the RHD at all. Too many pieces involved (I get it, modular to fit many applications) the linkage seems a little "light" for the appplication and they had a complete lack of instructions/tips with the kit. Client really wanted them, so we got a set.... They perofrmed well, but just not quite what we were looking for.

Not tried the AT Power ones, may some day soon. The clients we have built motor for with the all of the listed ITB's have been thrilled with the performance, driveability and throttle response. So we are happy.

Your ECU choice and tuner choice are likely more important to get good performance and driveability.

Cheers

Great information! Thanks Jeff
ITB is not in our wheelhouse so your expert input based on actual experience is invaluable.

[Henry Schmidt]

One of the very first versions of Richard Clewett's ITBs on a 2.7 RS replica built by Supertec. Easy to use, great performance.

[Rivet]

Originally Posted by Jeff Alton

We have used many over the years. Not going to say what is best...

For a traditional butterfly style, we like Jenvey. Used them countless times with great results every time. We have also used PMO, Clewett, TWM (borla now?) Hargett (did some testing for them and not even sure if they are around?) and RHD.

Our go to is the Jenvey, high quality, easy to adjust and maintain their adjustment. We adapt the throttle set up a little to our liking. On same engines, they made more power than the PMO's but the PMO looks like a weber.

Jenvey also offers their heritage line, which looks amazing if you want a carb look, as injectors are hidden. We have not tested those. The Clewetts are very functional, everything is well thought out mechanically, just aestetically, they are a little "cludgy".

Was not impressed with the RHD at all. Too many pieces involved (I get it, modular to fit many applications) the linkage seems a little "light" for the appplication and they had a complete lack of instructions/tips with the kit. Client really wanted them, so we got a set.... They perofrmed well, but just not quite what we were looking for.

Not tried the AT Power ones, may some day soon. The clients we have built motor for with the all of the listed ITB's have been thrilled with the performance, driveability and throttle response. So we are happy.

Your ECU choice and tuner choice are likely more important to get good performance and driveability.

Cheers

Just as a small update on the RHD ITB's. They have since made a small revision on the linkage and now include a full published instruction manual with tips.

[Henry Schmidt]

Some people might find this to be the "best"!
3.5 EFI using RSR high butterfly built by Ruff for Jerry Seinfeld.

[targa72e]

Last option is to convert the existing 9M to a DBW but I'd still be out of idle air control monitoring throught the ECU

You do not need Idle air control with DBW. You can use the ECU to open the throttle to get what ever Idle you want.

John

[Turbo_pro]

Originally Posted by targa72e

Last option is to convert the existing 9M to a DBW but I'd still be out of idle air control monitoring throught the ECU

You do not need Idle air control with DBW. You can use the ECU to open the throttle to get what ever Idle you want.

John

Your "last" option should be the first option. Whenever you have money invested in a "custom" build, trying to modify the parts you own is a great starting point.
My experience with EFI is so limited that I wouldn't begin to understand issues with the 9M system but if you can figure out what is missing, mitigating the issues by modifying what you own seems reasonable. Throwing money at a problem is rarely the "best" way to proceed.

General rule, not aimed at you John. I am agreeing with your suggestion.

[Jeff Alton]

Originally Posted by Rivet

Just as a small update on the RHD ITB's. They have since made a small revision on the linkage and now include a full published instruction manual with tips.

Thank you for the info. I should have also noted, the owner/contact was always responsive and easy to deal with.

Cheers

[Henry Schmidt]

For anyone looking for a cost effective forey into the ITB world, I have a stellar set of 50mm PMO ITB for sale. These will fit any size 911 but probably should be used on a 3.0 and larger.

https://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1184687-quick-sale-stellar-set-pmo-50-mm-itbs.html



These ITBs tend to give you project a more "period correct" aesthetics and still offer the modern convenience of programmable induction.
You can even use a factory early 811 air filter housing to maintain an even more authentic aesthetic.

[Henry Schmidt]

Here's another exciting option I stumbled across in my research.
This system is remarkably similar to the fuel delivery system used on some the NPTI GTP cars of the late 80s / early 90s.
I only know this because I owned 11 of the GTP engines as well as one of the cars.

[JoeMag]

Another consideration is length of intake...

Graph of harmonics for various intake lengths. Length is total length of intake; top of stack to back of intake valve.

A cut of dyno graphs with an intake manifold and straight velocity stacks, a reference stack length, then adding to it in approx 1" increments.

[TimT]

Years ago we built a 3.8 using dual staged injectors with Haltech EFI. The intake, ITBs, intercooler, headers were all sourced from MODE

The engine made impressive power..

I have other pictures ..... somewhere....

[TimT]

[Neil Harvey]

This has been interesting to read. Some really good ideas and comments about what has been done in the past. All good info to take in. What has worked is really good to know.

Project 24 includes an new ITB system. Too early to say or show what it is. We have tested both Barrels and Butterfly types on the flow bench. The Barrels certainly show better flow and speed once opened fully but the Butterflies still beat out the Barrels at part throttle. Just turning the air twice I assume is the issue.

Our magnesium based 911 Project 24 is all about weight, engine speed and acceleration so air volume and speed are major factors. Anything not needed is removed, anything that can be made thinner and stronger is, the goal is to see how light we can make this engine. Cost is not the driver in this project, weight is. Hopefully some of these weight saving ideas can used by others in the future.

[stephen1070]

Henry - this car is on auction now and listed with a "3.4" - do you know the bore and the stroke that RUF used?

Also - what do you think of the exhaust on this car?

Thank you
Steve

Originally Posted by Henry Schmidt

Some people might find this to be the "best"!
3.5 EFI using RSR high butterfly built by Ruff for Jerry Seinfeld.

[Henry Schmidt]

Originally Posted by stephen1070

Henry - this car is on auction now and listed with a "3.4" - do you know the bore and the stroke that RUF used?

Also - what do you think of the exhaust on this car?

Thank you
Steve

3.4 seems right. Ruff did use the 98mm short skirt Mahle pistons in many of their builds. Quite often the customers would complain of cold start piston slap.
Half of the exhaust looks great, the primary half uses a flat collector and I'm not a fan. With this engine, I would prefer to use a header system with shorter primaries.
Something more like these.