Mutilated Stock Intake Manifold
 

So... much... grinding...

https://i.ibb.co/hBrmPc2/20221101-105707.jpg
https://i.ibb.co/cYP1PQX/20221101-105716.jpg
https://i.ibb.co/VYY0rNv/20221101-105728.jpg
https://i.ibb.co/DWcvkdJ/20221101-105722.jpg

I wanted a spreadbore intake manifold that flows well, fits under the low profile shaker of my '77 Trans Am, has the required bolt holes for an OEM-style AC compressor, accommodates my Q-jet throttle linkage, looks nice, and weighs less than stock.

I agonized endlessly, went back and forth multiple times, even bought multiple intake manifolds. I have a Performer, a Ram-Air IV/HO-replica, and a Crosswind on hand. So much money spent. NONE of these alternatives met all my requirements. Some were missing bolt holes to accommodate the AC or the throttle bracket, some were too tall and couldn't easily be shortened, some were horrendously bad casting quality, some weren't conducive to the power levels I was aiming for.

So finally I just chose to mutilate my stock manifold. I know it fits, all the bolt holes are there, and it can be ported to flow more than enough to meet my needs. With all the grinding and cutting, I've removed over 15 pounds of weight. And I can pair it with an aluminum water crossover, which weighs less than a pound. It's still significantly heavier than the all-aluminum manifolds, but that's a trade-off I can live with.

I wish someone would produce one of these exactly like this in aluminum and good quality casting.

Now it's off to SD Performance for CNC porting!

Grind away! Holy crap. That had to have taken at least 6 hours...

Interesting solution...
Kinda like it.

I'll be getting it cleaned and blasted so the surface is more even. But I'm really happy with the result.

Nice work.

I remember reading in the H-O Racing engine book where they said often the best intake for your Pontiac performance engine is the stock one.

For the majority of street Pontiacs this rings true.

Yes, but maybe not that one. It has the restricted secondaries.

EVERY flow test has shown that those make no actual difference in real life. And anyways, they'll be ported away

Intake Uptake '75-'78 Edition
Do You Need to Modify Your'75-'78 Pontiac Four-Barrel Intake Manifold for Best Performance?

https://www.motortrend.com/how-to/hp...take-manifold/



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That 75 and later intake you spent so much time on I believe the floor of the port is higher to accommodate the EGR circuit.

I had great results with the old fat runner Edelbrock P4B QJ and according to Rocky Rotella the flow is better than a stock intake.

Wow. That was a lot of work if you did that with a grinder. Looking good. I wondered what one of those would look like with the cross over removed.

I did one of those intake’s earlier this year. When I first started I wasn’t sure what I was getting myself into. I have to say, after I opened up the secondaries and ported matched it to RA4 sized 1014s felpro’s I was shocked how cavernous that intake is. The plenums are a little deeper than all the earlier Qjet intakes I have a seen. When PMD re-engineered the plenum for the second generation EGR after 1975 they dropped the plenum down and made it deeper to make room for the exh port running up to the top. All you have to do is grind and blend where the egr was coming into the plenum, connect the primaries and secondaries, and it really opens up. When you port match the exits and open up a couple places where the boss’s for the intake bolts are it becomes a totally different intake. I don’t how much or if the secondaries are actually a restriction, Rocky’s article indicated that they are not. I opened mine up anyway.

Looks like it will perform, even though the interior still looks as-cast. I'd use it.

The EGR causes the side wall to tuck in a little bit, as can be seen on the top view picture, but the floor is actually slightly lower than non-EGR manifolds to make up for that. Actual volume remains the same, but there's slightly less room on that side between the manifold and the valley pan as a result. I compared the floor with the one on my RA-IV/HO reproduction, and this one is definitely lower than that.

The Edelbrock Performer intake that I have on hand has tiny runners, and some of them have huge bosses running through them that would make porting difficult. The casting itself is excellent quality, but its design is crippled.

why did you cut through the center of the front bolt holes?
how do you plan to block off the exhaust cross over in the heads?

That's why I use the earlier Edelbrock PB4 QJ

I wanted the aluminum water crossover to be attached with 4 bolts rather than 2, that one will also have 2 half-holes so that 2 of the bolts are shared between the two parts but they're still separate and the water crossover will no longer dictate where the intake manifold must exist.

I'm running KRE D-ports. No exhaust crossover holes.

I used an acetylene torch to remove the water crossover (the casting is THICK there), a chop saw with abrasive cutting disc for a couple of longer cuts (see the tiny knick on the left side of the carb flange where I cut too far), a 5" corded angle grinder with a thick wheel, and 2 air die grinders with metal bits (one straight, one angled).

These are in-progress shots where I just got done removing the exhaust crossover:

https://i.ibb.co/d4M8zBK/process-1.jpg
https://i.ibb.co/7WG9H4q/knick-on-plenum.jpg
https://i.ibb.co/9GBZjBb/shaved-4.jpg

You can see how thick the casting is in places. I ended up removing those fins on the bottom of the plenum and grinding that whole outside surface smooth.

keep in mind the RA/HO repro intakes plenum floor is not as deep as GM intakes, rocky rotella measured them & showed about 1/8-3/16 less depth, i compared my 1970 iron intake to a 71 HO GM intake & the HO is not as deep, both were fully ported by SD.

In my case it's a full 1/4" difference on the short side. That HO intake manifold is one of the worst casting jobs I've ever seen in my life. There's no obvious core shift in mine, the quality is just horrendous on both the inside and outside. I refuse to use it. I don't even want its water crossover, it looks awful. I'll likely take the one from the Crosswind. I have an older one that has the water crossover still attached so I can cut it off where I need to.

Shaker455 do you have any thoughts on the effect of the gap under the primaries on the carb signal? It seems backwards to me too have the divider drop on the primaries instead of the secondaries? I am running the drop on the primaries like the pictures show. But I wonder if I shouldn’t put the EGR plate under the carb back in, cover the EGR holes in the plate and cut down the divider on the secondaries?

I recall Rocky flowing the PB4. It did really well.

From what I've read elsewhere, they don't have a noticeable effect, but I was planning to build that back up with a spacer after the porting is done