PMO vs. Weber Manifold - better?

vntgspd · 09-20-2006, 08:32 AM

I have both sets of manifolds. The PMO's are a little less than 1/2" taller than the factory Weber manifold.

Anybody know if there is a definite advantage to the PMO unit?

I know the PMO's were made this way for a reason so I suspect there is SOME advantage. I also know they are worth more and I will be selling whatever manifolds I don't use.

So, if anyone has any practical knowledge as to the real world benefit of the taller manifold, I'd love to hear it so I can make an educated decision on which way to go.

Thanks!

David

Steve@Rennsport · 09-20-2006, 08:54 AM

Hi David:

One would need to know all the particulars of your engine to offer any advice, but the taller manifolds do even out the fuel mixtures when using longer duration cams such as "S" cams.

Their job is containing reversion,....

vntgspd · 09-20-2006, 09:13 AM

Okay,

So with my 2.4L with 2.2S pistons and "E" cams, the PMO's would be an advantage, but maybe not as noticeable compared to an engine with more aggressive cams.

My read of your comment is that any performance enhancement at lower or upper rpm may be negligible, but the driveability may be improved as a result of the improved fuel mixture entering the cylinder. Am I on target here?

Thanks.

PS: It looks like I'll owe you a little something nice by the time I'm done with this project. Thanks again for the advice.

Fleming · 06:36 PM

Steve did I hear that the 2ltr. 911S manifold can be "tuned" with the addition of the insulator blocks (bakelite) in one (7mm), two or three high, or was I just dreaming that?

The height of the stock 40mm carb 2ltr. manifold is 68mm and a 46mm PMO manifold I have is about 80mm. (don't know the height of the PMO 40mm manifold but am guessing it is 80mm also - given Vntgspd's 1/2" dif).

So a stock manifold could be "improved" by using two insulators or by using 3 insulators match the equvilant height of a PMO with a single insulator. Any advantage or is passage alignment an issue?

Bob

Steve@Rennsport · 09-21-2006, 06:51 PM

Bob:

I've never tuned the intake with the stock (short) manifolds since the gains we saw on the engine dyno all came from the tall ones as well as some custom 1.5" raisers we made for some race engines,...

IMHO, raising the short ones more than an inch with spacers isn't really a sound idea due to distortion and the ease of vacuum leaks. I do use & recommend the phenolic insulators (.25") to prevent fuel percolation in all carbureted applications.

I think if you have S cams or better, you ought to consider the tall ones instead of stacking thick spacers that can cause you some big-time grief,...

911pcars · 09-21-2006, 08:12 PM

Steve,
I have the insulators under my Webers. Are they bakelite or phenolic resin? I didn't think bakelite was still manufactured.

Sherwood

Steve@Rennsport · 09-21-2006, 09:06 PM

Those are phenolic,...

911pcars · 09-21-2006, 09:30 PM

Thanks Steve. "Phenolic" sounds like a hidden curse word as would be sneeze/muttered at Dean Wormer in Animal House.

Sherwood

Steve@Rennsport · 09-21-2006, 09:59 PM

Very true,...(funny movie and filmed right here in Oregon)...

randywebb · 02:50 PM

Sept. 3 for the Toga Party
http://www.moonstonehotels.com/Cottage_Grove_Events.htm

Exterior was a trashed out frat. house on 11th that was later knocked down

the motorcycle scene was filmed using the staircase in the foyer of Sigma Nu, UO campus

toga party scene -- basement of Sigma Nu

mock homecoming parade and other scenes filmed in downtown Cottage Grove

dilapidated prison halfway house that served as the "Animal House" exterior was torn down in 1986

The Dexter Lake Club (East of Eugene), where Bluto and the boys tangled with local toughs, is now Demeter's Cafe. The former bar is now a craft boutique. But owner Sherrie Sims says the neon sign immortalized in the film still lights up.

exterior of the Sigma Nu house, for instance, served as the sorority where John Belushi's "Bluto" character climbed a ladder to window peep at half-clad co-eds. Also recognizable are UO dormitories and athletic fields, the EMU "fishbowl," Knight Library and Johnson Hall.

Also still intact is the downtown Cottage Grove building - then the Holloman Ford car dealership - where a runaway parade float crashed through the wall and into a car on the showroom floor -- the crew framed a fake front into a rollup door
____________________________________
The properties of phenolic materials make them very well suited to a myriad of industrial applications. Phenolics are the result of polymerization between resin and a base material that can be paper, glass or cotton. The base material used is dependent upon the intended application of the finished product. Paper phenolics are used in the manufacturing of electrical components such as punch-through boards. Glass phenolics are particularly well suited for use in the high speed bearing market.
- from the Wiki entry; an OED can give you the historical derivation of the term

Fleming · 09-22-2006, 01:41 PM

Sorry for using a Trademaked name for a generic product (kind of like calling all those nose tissues "Kleenix").

Wifi is great. They define that "black hard plastic" as "Bakelite is a brand named material based on the thermosetting - phenol - formaldehyde resin polyoxybenzylmethylenglycolanhydride

But this thread sure got the way back machine working.....funny stuff.

Bob