Streetmaster to Airgap
Good observation. So its safe to say that the engine wasn't really handicapped by the tiny manifold runner that's way smaller than the 360 head port?
Mostly Correct. But correct.
Your assertion. These 2 intakes are at opposites ends of the spectrum. Doesn't look like that engine needed all that much air flow to make 230 Hp at the wheels.
Correct
The Edelbrock head had a totally different thought process behind it when it was designed.
What was 318WR's honest question?
Has anyone used that Edelbrock intake at the track into the 11’s? (Paraphrased)
So the engines not using all the airflow the heads are giving to it?
The heads do not give the cfm. The heads cfm ratings are based on a machine with a 28” depression, which is what is getting the air to move. What is your vacuum reading @ WOT?
The heads ability to flow is a combination of the days air pressure (millibars) the vacuum generated by the engine, the size of the carb, the intake manifold & how well it flows all going past the head, which “Allows” only so much through it.
Just means the sum of all parts combined equates to the amount of air that can be moved.
Bam!!!!
So the heads flow 200 cfm but it only uses 175?
Even less once you understand that an engine doesn’t suck in the air and fuel at 28”’s of depression.
Doesn't look like the manifold was the restriction.
Not really, but as fishmen said, it is the some of parts.
Is the demand for air greater at 3000 or 5600 rpm?
That's a difference of 6%
The demand is higher because there is more rpm. Each revolution will have the engine digest a certain amount of air. Lets use 1oz. for each revolution. Now the engine idles at 740 rpm’s, that’s 740 oz’s. Cruising the Hwy @ 3200 rpm’s, that’s 3200 oz’s. Etc….
But now we have to look at the intakes. Let’s say the head will flow 200. The intakes once bolted to the head almost always hinder the heads ability to breath in the Air and fuel. The cfm drops because the head is now trying to move air and fuel, not just air like on the test bench.
The small port intake may flow 200 or even 250, but that was with dry air. Now add in fuel which requires more energy and since it is very heavy vs air, the fuel flows slower and also slows down the air.
Now the engine can only digest 175 cfm worth of air and fuel. By swapping to the rpm with its larger and better shaped ports for moving air, even though the lower ports have a harder time keeping up, there still moving more air and fuel due to the volume contained within the larger runner. Even if the RPM still slowed down the A&F to 175, there is just simply more available to squeeze in past the valve.
While 15 HP isn’t huge on its own, IMO, 15 hp is a huge amount on the swap of intakes on this low powered engine. Make the same swap on a well built street strip ride and it’ll be 50 or better.
Notice how the other parts only added a few hp? But in total, it all added up to nice package. They also help each other out. The whole engine gets better.
IMO, I actually think it was a good write up showing how an average guys without a lot of bucks can make a nice street ride. If someone had this type of a starter platform, and then paid the piper for the articles parts, there would only be 3 things to a hotter package.
Converter, gears and a better camshaft. Ok, maybe wheels and tires to. This is a good reason 5.9’s are popular? Even better with a forced induction. Look around FABO because there’s several that have done this.