ITB Recommendations

[rcguerena33]

Hi -

I’m nearly done freshening up my 9M 3.8 engine and need/want new ITB’s to replace the somewhat outdated 9M ITB’s. The engine specs, briefly are -

964 case
993 crankshaft
Carrillo rods
102 mm 993 Clubsport Pistons
102mm x 107mm slip fit cylinders
9M intake valves
9M exhaust valves
9M retainers/springs
9M Billet heads
9M Intake manifolds
9M Race cam
9M Headers
Motec M130
Coil on plug

Rev limiter is set at 7,800 RPMs and this setup was putting out north of 400 HP on 95 (we’ll be testing and tuning with the current setup in the coming months).

Any suggestions?

[winders]

The best are the AT Power ITBs...I would go with the 48mm size. That is what I had on my 3.8L race engine that produced 450 HP....

[Nk993]

Originally Posted by rcguerena33

this setup was putting out north of 400 HP on 95

was that your own testing or 9ms imaginary testing? (sorry I just have a very low opinion of them)

[JoeMag]

I also have AT Power's ...48mm, I like them. You note intake manifolds. Do you mean an actual intake or stacks? From a long time ago I recall 9M's heads had 42mm intake port, is that what yours are.

[rcguerena33]

@nk993 - the old dyno was 9m's.... No idea if it's close/accurate but just trying to get a ballpark out there for conversations sake. We'll run our own dyno and numbers in the coming weeks but honestly don't care about 400 vs 375 hp etc. I just want it setup to maximize what I have and hope we can have a fun conversations/debates about what it puts out!

@joeMag - just stacks (the language was from an old post so easy to copy and paste). I have 42 mm intake ports.

[winders]

I had Xtreme heads with 45mm ports....I would prefer the smaller ports with the 48mm ITBs for a street engine.

Regardless, the AT Power ITBs are the best but I not a fan of their drive by wire setup. I did my own with dual Bosch actuators in a custom setup from EFI Australia.

[Henry Schmidt]

"Best" is always an interesting claim.
There are a number of nice systems on the market that fulfill most normal use applications. Jenvey, Clewett, Rasant, PMO, Rothsport and even Supertec have systems that will meet most needs, sometimes at very reasonable prices

[Henry Schmidt]

Kinsler, in a partnership with Ed Pink (Singer), make a system that offers a progressive linkage that improves the driving experience. Well tested, sexy and made in America is always a great selling point.

[Henry Schmidt]

Rasant on a 2.8 SS built by Supertec 20 years ago.

[Henry Schmidt]

Let's not ignore the Heritage systems offered by Jenvey. A great way to maintain that "period correct" Porsche aesthetics. Throttle bodies that replicate Weber IDA carburetors. They fit stock early air filter housings.

[Henry Schmidt]

Rothsport/Singer ITB fitted to a 3.8 engine for the street.

[Henry Schmidt]

Supertec ITB. Jenvey throttles on a manifold we cast in a friends garage using old Mahle Volvo pistons. State of the art? hell no but it was a fun project.



They can be sized for any 911 engine. Here they are fitted to a 340hp street car 3.9 engine.

[JoeMag]

Robert -- My reasoning for picking the AT powers was that they have a blade for the throttle plate and not a shaft with a throttle plate through it. The blade is ~1.5mm thick. Comparing area down the throttle of a 1.5mm blade and 6mm shaft, you'll see that you basically can go down a size of throttle and the air faces the have same area. 45mm w 1.5mm blade is equiv to 48mm with 6mm shaft. They also have cam'ed mechanism on their 993 actuator that gives progressive response. there's a bearing thats attached to the blue part that fits into a groove in the red part that provides the throttle motion.

If I recall correctly the Rasants have a port for idle air control port for don't touch the gas pedal warmups.

Henry -- Nice set of pics.

[JoeMag]

[stephen1070]

This is a cool set up for an owner wanting this airbox configuration - the best for me too!

Thank you!

https://www.youtube.com/watch?v=8Afffdv5Tfg&list=RD8Afffdv5Tfg&start_radio=1

Originally Posted by Henry Schmidt

Who are you again? My post is not about you. Get a life.
My post suggests that "best" is subjective. It always is. My post shows many different options based on many different criteria. Not everyone is about maximum performance, in fact most people playing with these old engines have different criteria base on things as simple as esthetics, cost or even manufacture.

I just built a high butterfly intake for a customer who whats to run the stock air filter housing on an ITB system. AT Power doesn't offer it so obviously AT Power is not "best" for him.

[AintGotNoGasInI]

Topper performance tuning makes a pretty good ITB set up, pretty affordable as well. I'm installing them on my car currently. Dual DBW in my opinion is a massive benefit in ITB'S. for my purposes I wouldn't purchase ITB's without them

Tyler, the owner of the company is very helpful. I'm sure if you contacted him, he'd help you out

[Turbo_pro]

Back on topic after the silly trip down obsession lane: WTF is that?

Race Head has some pretty cool options. I saw a set on 3.8 engine in a transplant to an 87 Carrera. Carbon Rain hats are stellar.

https://racehead.com.au/product/porsche-964-993-itb-kit/

[Nk993]

Theres also some guy in denmark producing barrel throttle ITBs... DRS developments installed them on their to replace the AT power ones, but havent seen any updates from them in a long time, so dont know if they tested it yet.

they mention it here: https://youtu.be/HvX98EC3SIM?si=8EyplpJjClxBbk4n&t=667

[rcguerena33]

ITB talk gets everyone fired up! Ha.

I'm really leaning towards the AT Power ITB's based on some of the above info and their overall adaptablity. Kinsler is a close second... with the M130 I'm running we can only do a single DBW motor setup. 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.

We'll see how testing looks next week and figure out next steps from there. Thanks all for the help and keep you posted.

[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