I'm looking at possibly changing out my stock cast intake for the 69 RAIV aluminum intake, basically for some perf improvement and mainly to remove the crossover completely due to ethanol's low evap temp. I don't see any block off plates made so I can make those. There's just seems to be no real details about these except they fit most Pontiac V8's. I have a 68 WZ block in a 67. My questions are--
what are the differences between the 69-72 factory aluminum intakes??
what is the RPM range of these manifolds?? can't find that anywhere
has anyone run these? your thoughts?
seen some posts that the copies being produced are not good quality, any feedback?
are they higher than stock and affect hood clearance?, I am running a RAI intake setup
The factory aluminum intakes are just a copy of the cast iron intakes so there isn't any gain except its a bit lighter. If you are looking to go faster start with some tuning of the carburetor and ignition timing first. Then you could move on to a camshaft change or change to an Edelbrock performer RPM.
What I found was -- An essential copy of the cast-iron manifold, the runners were raised about .125 inch to match the cylinder head intake ports and improve airflow. ....so there is some gain.
What I was after is more isolation from the exhaust heat due to ethanol lowering the evap temp of gas. Also I would never think of putting a fuel injection kit with the computer in the throttle body due to Pontiacs hi heat at the intake, computer chips pop at @125-140F.
I fill the heat crossovers with aluminum in all my Pontiac heads. There is no problem installing any EFI system on a Pontiac Pontiac's don't run hotter than any other make engine. When you use any of those throttle body units that have the computer in them, run a return fuel system. We don't have any troubles with those units in AZ, and these guys drive there cars when its over 100 degrees outside.
I did this on my 350HO. The aluminum HO intake was functionally identical except about 1/2" of the port at the intake flange. They put a little more metal there and made the opening slightly taller, but it's not raised. I was able to fill that in with a very small amount of epoxy to eliminate the step. Since the ports are not precisely cast it was not even bigger than a standard port on some of them.
It was nice at first to have a functional choke with the crossover and yet it kept the intake cooler. That helped a lot with modern fuel, hot starts and response. Later on I replaced the carb with an 800cfm unit with an electric choke and put in simple block off plates.
Aside from minor performance and convenience improvements it looks cool. That actually counts for something in the hobby.
Some other notes of consideration, the 69-71 units are the best with the '72 units having a modified plenum floor that reduces volume and flow. It's a measurable difference and unfortunately the reproduction units are modeled after the '72 units. If you check around the internet there's an indepth article about it. Also it's a decent amount of weight reduction if you use blockoff plates instead of the crossover. A stock cast iron intake is about 45 pounds, the Aluminum HO intake complete is about 22 pounds. If you use block off plates with it you get it down to about 13.
Here's the bonus round... because the intakes are essentially the same externally you can modify the cast iron unit to functionally act like an HO intake. Some eye protection and a cutoff wheel, a little grinding and you can remove the cast in exhaust cross over. Then buy a repro cross over for about $150 and drop the whole thing on. Or do the block off plates. I did all this, divorced the water cross over and opened the carb flange. This reduced the cast iron intake to about 27 pounds.
I did this to a factory manifold about 30 years ago and is a great option. At first glance everyone always thought it was a ram air iv and it was only a discerning eye that could tell the difference. When I would tell them I made it from a stock manifold they were usually shocked .
