joepenoso

I was looking through the Pontiac engine section (web site) along with Pontiac high performance magazine at the news stand and they compared a stock OEM cast iron intake manifold to a single plane and a dual plain aftermarkets.
Average horsepower to 5,500 rpm was less with a horse power gain right at the top end with single plane aluminum manifolds. Surprisingly torque was less and the stock GM manifold won hands down. It seems the bigger aftermarket intake ports hurt hurt power below 5K. The Pontiac manifold used was a pre 1972 cast iron. Are Olds manifolds that good?
Thanks
joepenoso

rustyroger

Seems like Pontiac got their manifold right first time. When an engine is designed performance and efficiency have to be compromised by production costs, I guess when you want to uprate a Poncho engine you don't start with the intake manifold but address an area where Pontiacs weren't very good in the first place.

The best intake manifold for the old British Ford kent engine was made by.... Ford!, just about the worst intake manifold for the British BMC A series (Mini) engine was made by.... BMC!.

Roger.

MDchanic

First of all, what were you doing looking at those nasty Poncho magazines?
I hope you washed your hands afterward.

Not surprising at all.
Smaller (and longer) intake runners aid low-end torque while larger (and shorter) runners aid high-end HP. That's why lots of fancy modern computerized cars have variable-length intake runners, which are switched depending on RPM. I think Porsche had one of the first of these in the late eighties.

The reason is inertia: everything with mass has inertia, and that includes air.
You dont notice it while walking through it, but when it's blowing through a tube at potentially hundreds of miles an hour, it matters a lot.
A smaller, longer tube gives the moving air more inertia, which serves to blow the exhaust fumes out and the fresh mixture in, kind of like supercharging.
As the flow increases with higher RPMs, smaller tubes get too restrictive, but at lower RPMs they help.

Remember, a factory manifold was designed to work under factory conditions, with reasonable RPM ranges.
So long as you don't change the rev band too much, it should be among the best you can use.

- Eric

edit: I realized in the shower that while inertia isn't exactly the wrong term, it isn't completely right. What I was referring to is kinetic energy, which is geometrically related to velocity (it's ½mv squared, where m=mass and v=velocity, or where mv=inertia).
As velocity increases, energy increases a lot, and that energy is what helps blow the mixture into the cylinder. You make the runners bigger and the mixture slows down and loses energy. On the other hand, if they're too small, they restrict flow. All depends on desired RPM band.

joepenoso

After reading about the OEM Pontiac intake manifold I was asking if this has any relationship to our beloved olds 4bbl manifolds.
Of course I'm talking about the pre EGR type. I was wondering what type of experience have people had with single plane or dual plane Holley, Edelbrock, manifolds compared to stock.
Did it take away bottom end and only go bang( Turn on like a light switch) on the top end?
Riggles the guy with quadrajet and gm overdrive transmission books strongly argues using stock manifolds on Pontiacs. Looking at Poncho/Olds manifolds there is a similarity although Pontiac had much more development on their cylinder heads.
Thanks
joepenoso

Tony72Cutlass'S'

Unless it's supersonic, then everything is... Backwards..

Although, diving into the world of the possible and impossible, Imagine a converging/diverging nozzel that allowed the mixture to speed up past mach 1.

I'm sure it's been tried somewhere along the line. I'd be curious to see the write up if there is one.

MDchanic

You'd need a lot of pressure.

And you might accidentally make the car go back in time .

- Eric

Run to Rund

Back in 1975, I tested the Edelbrock Torker with Holley 800 spread bore; it was about .15 sec. slower than Tri Carbs on their stock iron manifold.

Tony72Cutlass'S'

So THAT'S how they made the flux capacitor. Gee, and i was wondering all these years

firefrost gold

cliff has said a performer rpm on a bigger pontiac will pick up if cammed right.
the 1967 to 72 intake was a copy of the sd program pontiac had in the early 60's
They did do some cool heads back then . ram air two's and fours and five's
with the round port ware some cool iron.

cutlassefi

On what? What was the gear, compression, engine size? Could you be a little more vague?

First of all look at a newer Performer vs the older ones and a stock intake. On the newer ones, the runners go right out from the plenum. On the older ones and a stock intake, they go out in one runner then split into 2.

Remember this, fuel/air doesn't like to do 2 major things, change shape and change direction. That stocker or early one may be fine at wot vs the newer ones but I'm willing to bet the newer one will drive better, less chance for the fuel to drop out of suspension at lower engine speeds from less turns. There are also 2 other factors, runner length as mentioned, and cross sectional area. Those along with the right head/cam will optimize performance, if the combo is wrong it's a compromise.

Jmo

Run to Rund

In 1975 I ran a 425 in my 66 W30 with Cam Dynamics solid cam, 255/266 deg at .050", .576/.570 lift, home ported heads, 3.90 gears in a N 9" Ford diff that I modified to fit the GM A body, 2.78 first gear Top Loader. I had 1.87" Headers by Ed, car ran 12.30s.

oldcutlass

Usually, and I state usually, most dual plane manifolds are good from idle to 5500 rpm. Single plane are generally good from 1500 - 6000 +. Then you get into the hi-rise which can up your top end rpm from there! The biggest advantage of going from a stock intake to an aluminum stock replacement is generally weight. The performance gain with manifold only is generally negligable unless cam, headers and/ or free flowing exhaust are added.

joepenoso

At what RPM do you think the aftermarket manifold surpasses the OEM cast iron one? Which aftermarket aluminim manifold fits under a cold air package in a 1971 442.

oldcutlass

I'll let the other guys chime in to what will and won't work with the 71 hood. If your not planning any additional mods to your engine, I would just clean up the manifold you have!

507OLDS

We can't compare the Olds intake to the Pontiacs.Two completely different engines.You need to look at the angle of port entry,into the Olds head,with the stock intake,and the aftermarket intakes.The stock 455 intakes are pretty much flat when your mix comes out of the runner,then it has to turn & go downward into the head & combustion chamber.The aftermarket intakes are taller,making the angle less severe,but then you also need to find a balance between volume & velocity,depending on what type of engine you are building.
If you did a similar comparison test with the Olds intakes,like what they did with the Pontiac,the results will not be the same.

joepenoso

Thanks for your insight....
How do you think the Chineseum air gap Pro Comp manifold with it's expanding inlet diametre before entering the head will do compared to original Olds flat manifold with OEM 442 automatic cam?
Thanks
joepenoso

507OLDS

If you are running the stock 40yr old cam,you won't get much benefit from a modern intake,but some. The enlarged port runners on the intake will not do much good when it gets bottle-necked into the head.Port-matching the openings is thought to do a lot,but not really.You can smooth the transition from the intake to the head,but then the size of the port inside the head shrinks,unless you do some porting & open it up.

Axeni

Not robbing the thread here. But I found a nice aliminum intake fairly inexpensive but it states it is an Inch and 1/4 higher. I have a 69 and was wondering what is the easiest way to measure with the hood down.

MDchanic

Give a squirrel a few nuts and have him hold a tape measure under there.

If the squirrels in your area aren't cooperative, or charge too much, you can use a compressible, non-resilient material on top of the air cleaner: put in place, close hood, open hood, measure.

The classic substance is modeling clay, but for this purpose, slightly wadded tin foil should work just fine - cover the whole air cleaner to be sure you don't miss any spots.

- Eric

Tony72Cutlass'S'

Eric,

Which one

Alvin, Simon or Theodore?

**Cue Music**

MDchanic

Just make sure it's not these guys:

squirrelsinthehood.jpg

- Eric

Axeni

Thanks guys.