472/500 Intake MIA

[Shoehorn]

I followed the link blueyes, and that's not a dyno sheet. He even fully admits to pulling the last set of numbers directly from his ass.

[BluEyes]

Yeah, it's called a flowchart. Airflow translates to HP - that's why carburetors and cylinder heads are rated by how much air they flow.

He guessed at the 0.6" flow numbers. So what? Since the intake itself doesn't change at different valve lifts, an extrapolation from the data can be pretty accurate. Besides, if you're running a cam with 0.6" lift you really should be looking at dropping the dual plane altogether and going to a single plane anyways, so I don't see how that one data point is relevant to this discussion.

Look, the point is the stock manifold is NOT a "piece of crap". Yeah, it's heavy - so is the car. Considering 99.999% of us got one with our car when we bought it, the 'bang for the buck' factor of a modified stock intake blows away the Edelbrock.
No one ever said that the Edelbrock manifold wouldn't outpreform the stock intake. But, on a street-driven vehicle, is the $250 worth it? Will there be THAT much of a difference? There IS probably enough difference to notice but I'd rather put a few buck into the gaskets and a few grinding bits to re-work the stock manifold, then put the remainder towards headers and dual exhust. For the cost of your Edelbrock manifold and carb, I could re-work the stock intake, rebuild the stock carb, AND put on headers.
PLUS, you have to drop the AC? C'mon, this is a Cadillac after all. Removing AC is something I do on my Camaro, not my Cadillac. If you're looking for maximum performance at the expense of all else, I think you really need to re-evaluate your choice of chassis. If you want performance with class, then why would you drop the AC?

I really don't understand how you can say that a 750 or 800cfm Q-jet is restrictive compared to a "800ish" cfm edelbrock. 800cfm is 800cfm, period.


Notyet - why this mod increases performance has to do with the manifold design itself. When GM cas the manifold, it was a true dual-plane design. Only half the cylinders pull on each side of the carb. The inner pair from one bank, and the outer pair on the other bank are teamed together in each plane of the manifold (you can see this if you follow the runner paths on the manifold). Each plane in the manifold is completley seperate from the other with no crossover between the two.
So, what does this mean? Well, first off this design cures the problem inherent in all domestic V8 firing orders. Because of the shape of the crank, there will always be two neighboring cylinders on one side that fire right after each other. Without this manifold design, these cylinders tend to run lean because one will steal some of the charge from the other. The dual plane's seperated runners prevents this.
But, further, since there are two divided parts of the manifold, there is less air for each cylinder to get moving when it draws in on the intake stroke. This results in better manifold vacuum, and better throttle response.
The downside to this is that it limits upper RPM power. When one cylinder pulls in, it can only pull on half the carb. So, instead of seeing a 800cfm carb, the cylinder only sees 400cfm.
Part of the improvement in power from this mod is that removing the divider lets each cylinder pull on the full 800cfm at high RPM. The rest of the gain is just in cleaning up the entry from the carb to the manifold by removing all that metal. Fully removing the divider like that will likely reduce part throttle and low RPM torque and response somewhat though.

Another thing to do when you're in there is to use a grinding bit and smooth out the harsh right angle edge where the air transitions from going down to flowing along the runners. These are pretty common mods for most GM intakes (grinding out the center divider, and smoothing the runner transition) and have long been proven to produce results just about what you'll get from your average aftermarket performance type.

[davesdeville]

Originally Posted by BluEyes

Have you read the Cad Company catalog? On a 10:1 500ci motor with the edelbrock intake, headers, ported heads, and a pretty hefty cam the Holley DID make more power. By a whopping 3hp and 6lb-ft.
Q-jet made 477hp, 575lb-ft. Holley made 480hp, 581lb-ft. This is with an 850cfm model 4871, and I'll guarantee you that the q-jet gets better throttle response and mileage.
Around the bottom of page 9 in the Cad Company catalog, they give their take on the carbs, and basically say that for a street car to stick with the q-jet. Now, why would a retailer say to stick with the stock carb when they could sell people Holleys for hundereds apiece?

All that's true but keep in mind the Holley only started making more power at 477hp. Under that power level the QJet wasn't sacrificing any power.

Originally Posted by Shoehorn

I followed the link blueyes, and that's not a dyno sheet. He even fully admits to pulling the last set of numbers directly from his ass.

That is what's called a flow chart. Where they put the intake on a flow bench and see how much air gets through. And you have the nerve to call ME an idiot. :rolleyes2

Originally Posted by Shoehorn

I'm done, I can't argue with this kind of stupidity. I think I'll go build a honda out of all stock honda parts because they are the best and I'll smoke all those ricers with aftermarket crap. Has to be true, some guy said so.

You know what, do that. Find a ricer with the same car as you but with 18" wheels, a body kit, heavy wing, cone filter hot air intake. You'd beat him. It's funny that pretty much the only time you've been right in this thread is when you're trying to be sarcastic.