PMO EFI Throttle Bodies vs Alternatives

[WP0ZZZ]

I've noticed that PMO is making its ITBs for EFI in a dark finish which I find quite attractive. Is there any data about how these ITBs perform compared to other alternatives? I imagine that AT Power's shaftless ITBs perform better, but by how much?



https://www.youtube.com/watch?v=Iyl57J_-R8U

[colingreene]

I think that the shaftless are also a different price category

[rswannabe]

PMO’s are not an optimal design for best performance. They evolved from pmo carbs, which evolved from Weber carbs. The offset/different length runners lead to slight flow variations compared to others. Shafts impede airflow more than shaftless. That being said, I like their slightly vintage look, harkening back to carbs and mfi throttle bodies. I like you can run them with the old carb/mfi air boxes. I like that they use the same factory linkage systems (easy to get parts or swap systems). I like that they are easy to adjust and don't need frequent readjustment. And while the design is not optimal, I believe it would have to be a highly tuned and refined motor build to see big differences between pmo and other throttle bodies. My built 3.8 made 372 hp (crank) on the dyno with pmo 46’s. I doubt it would have made a lot more with a more optimized design.

Gratuitous pic of the PMO’s in my ‘74.

[nospiners]

rswannabe , that's a pretty girl !!!

[winders]

The AT Power ITBs are significantly better than the PMO stuff...they make more power using smaller diameter intakes which greatly improves low end and midrange torque.

[WP0ZZZ]

As you guys say, there are probably other options that give more performance but has someone quantified it? Are we talking 5 hp or 25 hp?

@rswannabe your engine looks amazing! I agree with everything you say. The vintage look is a big plus for me and I'm ready to leave some performance on the table but before making a decision I would like to know how much performance I would be losing!

[rswannabe]

@nospiners - Thank you!

@wpozzz - Thanks! Unfortunately I don’t have quantifiable data for you. Nor have I seen any real back to back tests to point you towards.

[WP0ZZZ]

I understand that making a proper test is hard and uncommon…

I’m wondering if there are any air flow bench tests of ITBs. (Not sure if the results from such a test would be a good indicator of real-world performance though...)

[eastbay]

So they finally are ready to sell them, was wondering if they would ever reappear. Suppose they will double the price like the carbs?

edit. they sure are pretty

[Cloggie]

I agree that some real data comparing ITB's against the standards would be great, trouble is that one will not just put in ITB's.

You are likely to upgrade to some sort of engine management system, likely tuned tighter than the stock.
You are definitely going to have to change cams to fit the changed characteristics of the engine, so that is also something that will make a big difference.
You are also likely to have a better exhaust system than stock...

....so back to back comparisons are tough.

But one data point from my past. I used to have a 240Z with the standard SU carburetors and exhaust. I replaced the SU's that were driving me crazy with triple 42DCOE Webers - no other change. The Webers were not all that well tuned, but well enough.

Well, my friend with a Ford Capri V6 which pretty well an even match with my 240Z with SU's was suddenly and definitively outclassed with the 240Z/Weber combo. In the impromptu 0-100km races we had, it used to be within a car length or so between the two cars. The Webers gave me minimum 4 car length advantage ....and going away.

Since then I have been an ITB fan...

D.

[mepstein]

I was told by a top engine builder that pmo itb’s are better for race engines than street. The position of the injectors and a couple details makes it harder to get a good idle and low rpm performance. Fine for the track but not as great for the street. I’m sure people make it work but it’s worth keeping it in mind.

[Jeff Alton]

Have not used the AT Power ones, but they do look very well engineered. Shaftless design in very good.

We have built almost identical motors, one using Jenvey (which we used for years) and one with PMO ITB's. The difference was the PMO car was a 3.5 vs 3.4 for the Jenvey. The Jenvey engine made more power and torque everywhere despite a very slight displacement advantage. Not a true apples to apples as there are many many variables. But, a data point none the less.

The new PMO finishes look great.

The Jenvey "Heritage" ones are very unique in the look is important. Have not tried those kits yet, just their standard tapered throttles.

We have used Clewetts as well. Seemed to work ok, but the design is a bit industrial. Have a 2.7 with RHD that will be going for tuning in a couple of months as well and will report back.

Then there are the Kinsler, JSR, Borla etc.

Cheers

[Mahler9th]

Hey there... just discovering this post.

Hope all is well.

My friends at Reno Rennsport worked with AT on their Porsche applications:

https://renorennsport.com/team/

You have seen my car-- Mat Lowrance built it and has built my engines for years.

He has a lot of experience with flow work and extensive knowledge...

I suggest giving his son Brian a call.

many of my friends have experience with the AT products as a result of the work done by Reno Rennsport... one of them has a 3.6 putting out north of 400 bhp. This is a Motect-equipped engine with DBW and I was there at the dyno-- same dyno is used by a pro Formula D competitor.

My friend with the 3.6 engaged Oscar Zelaya to tune his engine-- Oscar is in pro racing and provides services tio several team, including the Action Express IMSA team that just finished #2 at Daytona.

In any case, if you want some perspective on ITBs, I suggest contacting Brian at Reno Rennsport.

Feel free to shoot me an e-mail if you want to discuss further...

Would love to catch up and hear how you have been doing!

- Mike

[lateapex911]

I just toured the PMO facility...I can't comment on their performance vs other ITBs, but I will say that their quality and construction appear to be quite nice. Just my 2 cents

[3literpwr]

Just had this conversation with a buddy who has a 911 (CIS) and was a EFI engineer for a few companies, including Saleen and a supercar company called Kepler. He had mentioned wanting to design he own system and stressed the importance of pointing the injector directly at the intake valve, not runner, like on the PMOs.

[JWest]

The quality has remained after the Empi purchase of PMO, but they are leaving out details and small parts. No TPS, forgotten spacers for the fuel rails, etc. Not a huge deal, but a pain if you are expecting them to be as complete as they were from PMO in the past.

I doubt most people would notice the differences mentioned here between manifold designs, but PMOs do have the vintage look that many desire.

Just finished this one with Empi PMOs. Rock solid idle and zero tuning issues.

[MrBonus]

Originally Posted by JWest

The quality has remained after the Empi purchase of PMO, but they are leaving out details and small parts. No TPS, forgotten spacers for the fuel rails, etc. Not a huge deal, but a pain if you are expecting them to be as complete as they were from PMO in the past.

I doubt most people would notice the differences mentioned here between manifold designs, but PMOs do have the vintage look that many desire.

Just finished this one with Empi PMOs. Rock solid idle and zero tuning issues.

Nice, those do, in fact, look very proper and vintage.