Extrude honed intake manifold

[69427]

I've been trying to figure out some winter projects for the '69 (and to be honest, it's getting harder to come up with some significantly productive modifications), and I got to thinking of anything that would give me additional high RPM power. Replacing the 780 VS carb with the 850 DP last year was very productive, and that got me thinking of tweaking the intake manifold. I've got an old Edelbrock intake on it (with the logo ground off to look like a stock Chevy hi-rise) and I'd like to keep it (but tweak it). As I've mentioned before, my engine rarely gets a second glance, and I like the sleeper look. I thought that perhaps having the intake hogged out a touch (via an extrude hone) might be productive, but damn that process ain't cheap. I looked at one of the sites that came up on a search and it was over five hundred bucks to do this type of manifold. I can't justify that kind of expense for an unknown magnitude of improvement ($/hp). So, looks like I may have to settle for a bit of port matching improvements instead.

 

[TimAT]

Are you running an open plenum or a dual plane manifold? GM had a thing to cut the center divider down to 1/4" of the floor, stagger the jetting to compensate for the divider, and made some more ponies on the cheap. I've got the stuff on it at home. (jet sizes, dimensions). Kind of a poor mans open plenum.

 

[69427]

Are you running an open plenum or a dual plane manifold? GM had a thing to cut the center divider down to 1/4" of the floor, stagger the jetting to compensate for the divider, and made some more ponies on the cheap. I've got the stuff on it at home. (jet sizes, dimensions). Kind of a poor mans open plenum.

It's a regular dual plane manifold. The plenum divider is shortened a bit (I believe as machined by Edelbrock). I have heard about stagger jetting for quite a long time, but I never understood how you dial it in without an O2 sensor in each exhaust port.

Do you know if any of this info is in the old Chevy Power books (which I have packed away somewhere)?

 

[phantomjock]

Check out the Downloads Section:
http://www.vettemod.com/forum/downloads.php?do=file&id=3

Chevy Power is there for Members.

And if you want to start from SCRATCH; this looks interesting:
http://horsepowercalculators.net/intake-manifold-design/intake-manifold-design

and an overview:
http://victorylibrary.com/mopar/intake-tech-c.htm#ir




Cheers - Jim

 

[TimAT]

The Chevy Power manual link does not have the engine section- only the suspension.

And yes, the engine stagger jetting is in the BB engine section. Exact readings without the 02 sensor as you guessed would be impossible. The recommended jets in the book are listed as a starting point, but I suspect GM's "starting point" is going to be nearly right on. That section if I recall, also has the height of the divider after trimming.

 

[69427]

The Chevy Power manual link does not have the engine section- only the suspension.

And yes, the engine stagger jetting is in the BB engine section. Exact readings without the 02 sensor as you guessed would be impossible. The recommended jets in the book are listed as a starting point, but I suspect GM's "starting point" is going to be nearly right on. That section if I recall, also has the height of the divider after trimming.

I managed to find my old copy of the Power Manual. You are correct that there are recommendations for the divider height and jet sizes. I think I'll probably give it all a try over the winter.

I have a spare Edelbrock manifold sitting on the old original engine, so I took a picture of it to show the present shape of the plenum divider.



In addition to the plenum and port matching tweaks, it would sure be nice to be able to take a bit of weight off this manifold. Sixteen pounds is more than I thought these things weighed (and of course, it's up high and up front).

 

[redvetracr]

Edelbrock doesn`t do sloppy work like that, your notch looks home made. cutting one full inch out of the plenum ala the #198 ZL-1 GM intake might help but to be honest it will take a whole lot more than $500 to get a dual plane intake to flow like a single plane intake. you might consider a 7.25" or a 5.5" multi plate mini clutch with a reverse drive starter but expect to spend a couple of thousand, the difference going into and coming out of the corner on a road race track is like night and day and worth every penny.

 

[69427]

Edelbrock doesn`t do sloppy work like that, your notch looks home made. cutting one full inch out of the plenum ala the #198 ZL-1 GM intake might help but to be honest it will take a whole lot more than $500 to get a dual plane intake to flow like a single plane intake. you might consider a 7.25" or a 5.5" multi plate mini clutch with a reverse drive starter but expect to spend a couple of thousand, the difference going into and coming out of the corner on a road race track is like night and day and worth every penny.

I don't want a single plane intake. I used to have one on the old engine. IMHO they look out of place on a street Corvette, and my philosophy is (for a street vehicle) that if it looks like a race car it damn well better be the fastest car at any event one enters (or you end up looking like a poser). With this current engine configuration I rarely get outpulled when running against other street machines (including Z06s and the single GT3RS I shared the track with). I'm just looking for a few more visually unnoticeable free horsepower with this mod.
I understand the physics of the clutch and starter upgrades. But again, this is a street Corvette and I occasionally have to take off from a traffic light without attracting the attention of the local gendarme.

Edit 10/20: I just happened to see an intake manifold identical to this on ebay. It has the identical notch in the plenum. I looked at mine with a magnifying glass and the "texture" in the notch shows that it is a cast notch, not a "home made" modification.