Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

SP2P Intake

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Cliff Ruggles:
Installing an intake with smaller runners does nothing to improve engine efficiency anyplace, hence why the SP2P intakes are not popular.  Matter of fact you can experience issues running an intake that doesn't have enough plenum volume for the engine, so I'd recommend obtaining a factory intake instead.  Plus an iron intake (preferred) improves thermal efficiency if you are looking for improved MPG's.  The added heat allows you to effectively burn a leaner mixture.  Keep in mind that it is a wet-flow system and we are trying to induce a cool/cold intake charge to the carburetor, mix fuel with it, then very quickly raise the temperature by compressing/heating it up so that it will burn effectively. 

Nothing has change in that arena since the very first internal combustion engines were introduced.  A heated intake is a LOT more effective than a cold one in a wet-flow system, despite what you hear on various Forums from "guru's" and other resident experts who really know little if nothing about this topic.

The manufactures even took steps to heat the carburetor to make things even better, hence the "hot-slot" intakes used thru the late 1960's.  Excellent idea in theory, and effective at improving economy and reducing pollutants, but fuel boils at a relatively low temperature so those systems often cause issues in the hot summer months, or if you get stuck in traffic idling for long periods of time, etc......

Cliff Ruggles:
"Well, I guess we will just change jets until we don't see any carbon on the plugs."

That is NOT how we tune a Q-jet for improvements at light engine load and for fuel economy.  Get a set of my full taper primary metering rods so you will have full control of part throttle A/F from rich to lean via the APT system.

Teamed with the correct jet size there will be no need to remove plugs to look at them, you can tune for best results instead.......

novadude:

--- Quote from: Cliff Ruggles on April 05, 2022, 02:56:31 AM ---

Nothing has change in that arena since the very first internal combustion engines were introduced.  A heated intake is a LOT more effective than a cold one in a wet-flow system, despite what you hear on various Forums from "guru's" and other resident experts who really know little if nothing about this topic.



--- End quote ---

THIS!!!!  I have no idea why you see so many basic 300hp 350 chevy engines at car cruises, etc with "air-gap" intakes.

old cars:
Although the factory Small Block Chevy intake design was good at the time, port runner shape has evolved since then so much that you could spend 30 ( experienced )  hours porting to gain 20 hp on a motor starting with some 300 HP.
You can look at 20-30 hp gain on a 350 / 325hp range engine swapping out to a current dual plane Weiand , Professional Products, Holley, or Edelbrock. On a 383 SBC the increase will be better.
These performance increases are well documented independently.
I am not saying a 305 sbc will see this.

Cliff Ruggles:
"I have no idea why you see so many basic 300hp 350 chevy engines at car cruises, etc with "air-gap" intakes."

IF you are going to market a part, carb, intake, distributor, camshaft, etc you MUST tell the target audience that it works better everyplace than what you are currently using.  In most cases, at the power levels of the engines these high rise aluminum intakes are installed on, about the only true statement is that you took 27 pounds of the front of the vehicle swapping out your iron intake for an aluminum aftermarket intake.

I for one do NOT buy into the BS that all of these intake make more power than what you just removed.

What Old Cars says may be true in some cases as some of these intakes are very well designed with larger runners, so they can show more top end power with some engine builds.  So I'm not telling anyone reading this to toss theirs in the trash and put the stock one back in place. 

I will say however, that with a lot of engine builds you aren't making more power (torque), giving up some throttle response, low speed power and often average power in the loaded RPM range.

A few years back we were on the dyno with a 428 Pontiac engine.  It was bore to 440CID, aftermarket 260cfm aluminum heads, 10.6 to 1 compression, and custom ground 236/242 @ .050 hydraulic roller camshaft. 

We dyno'd it at 497hp/540tq with a factory cast iron intake.  The intake was slightly "modified" so for sure it gave naysayers a reason to cry foul.  Even so, we were asked to test an Edelbrock Performer RPM intake against it, so I did.  With no other changes the very next pull netted 491hp/535tq.

Yes, to everyone's surprise it made LESS power at every RPM.  With that in mind and thinking about the engine combo, how many folks have you seen install Edelbrock Performer RPM intakes on 350 Chevy builds with 882 heads, 8 to 1 compression, a Comp XE262 cam, and think they are making more power anyplace?  To make matters worse, more times than not the taller intake requires a drop base air cleaner moving the air cleaner lid closer to the carb.  I've dyno tested those drop base air cleaners and found that they can know upwards of 30hp right out of the engine if/when you move the lid too close to the carburetor.......some food for thought on this topic.......

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