Horsepower is a unit of power measurement in a car. I’m sure everyone is clear about this term, but what about the double hump heads horsepower?
Suppose you are confused about this question; lucky for you because this post will solve all mysteries surrounding this automotive field.
I also introduce further information about the Chevy double-hump cylinder head that you should notice closely. Let’s get started!
What Is The Double Hump Heads Horsepower?
The double hump Chevy heads first appeared between the 1960s and 1970s; they were manufactured with large intakes, exhaust valves, and port volumes and recorded output ratings of around 350 horsepower.
Throughout its history, many modifications and types have upgraded new features from the previous ones. This post will only focus on four common categories for you to consider.
Tall Double-Hump Casting Marks
Horsepower heads with taller casting marks have a total of 4 castings whose numbers are related to seven digits.
Normally, people only use three last digits to differentiate several tall double hump heads.
Heads with the casting numbers, such as 291-, 461X, 461- or 462 don’t need to be equipped with bolt holes.
The exhaust or intake port’s volumes can reach 64cc or 170cc, depending on each model.
The valve diameters range from 1.5 to 2.02 inches, and the combustion chambers record between 62cc and 64cc volumes.
Greater volumes mean more power, so the compression ratios increase.
Short Double-Hump Casting Marks
Heads with short double-hump casting marks have been widely used in SBC vehicles.
Unlike ones of taller marks, all of them have accessory bolt holes regardless of the casting numbers, which end in 186 or 492.
In the past, they were mostly applied on some CI Z-28 engines or LT-1 350 CI Corvette engines.
However, the modern market does not favor this kind of engine due to its limited applications and functions.
In 1971, the combustion chambers were re-manufactured to heighten their compression ratios up to 72cc, while other parts did not change and bore a resemblance to tall double-hump horsepower heads.
Current Applications
Updated versions of Chevy double hump heads have witnessed a surging demand in various racing applications with the requirement of iron heads.
Compared to the previous versions, these are added with more utilities to enhance your car’s overall performance.
So if you are a collector fond of gathering those car parts, tall and short double-head horsepower is difficult to find.
For performance applications, there are other General Motors castings that are similar in specs.
The General Motors L-31 5.7L Vortec automobiles still favor the use of “041” stock heads because of their better flow.
Aftermarket Heads
The availability of factory GM performance castings has been on the decrease over time, so aftermarket manufacturers started to supply replacement heads in the 1980s.
The reason is that the OEM heads’ reconditioning costs are very high, so they decided to release replacement products to the public with a view to increasing the customers’ demand for better-performing and cost-effective alternatives.
What To Know About The Chevrolet Double-Hump Cylinder Head?
Given the old-school stock car racers and cylinder heads, Chevrolet double-hump cylinder heads stand out and make their names for great performance and minimal needs for machine maintenance.
To get you to know more about this Chevy head, or even a series of Chevy’s heads, I will present essential information about seven aspects as follows that you should pay close attention to.
Circle Track’s University Partnership
The University of North Carolina at Charlotte (UNCC) has the Motorsports and Automotive Research Center, which has succeeded in figuring out the variations between different part numbers of a double-hump family.
UNCC places a strong emphasis on automotive analysis and research by offering numerous engineering programs and other motorsports-related topics for its students.
In terms of infrastructure, the university is also famous for its state-of-the-art motorsports laboratory.
It provides optimal conditions for student-led racing teams by bringing real-world experience so students can handle sudden hurdles in real life more easily.
The Tests
A long time ago, Dallman tried to measure the dimensions of a 3917291- and 3890462-double-hump series by taking several tests to obtain exact information about their strengths and weaknesses.
All the testing has been thoroughly prepared with the help of tools, devices, and many precautions to secure performers’ safety.
One famous test that Dallman has performed is placing two horsepower heads on a flow bench with some undercut and standard valves.
The core factor that could affect the test’s outcome lies in two sets of valves. They must use both that are similar in terms of physical features and durability.
If not, it could result in a false and unreliable analysis.
Physical Measurements
Not every double-hump horsepower head is the same.
Although you don’t notice any differences with the naked eye, there are minor dissimilarities given their port length and width.
When measuring a double-hump head, you must also carefully take notice of various parts, such as the valve diameter, valve stem diameter, and seat angle.
The port height is also important by creating a larger cross-sectional area and affecting the airflow through entrances.
An air intake is also functional at switching the air, and when it fails (mostly due to broken air intake hoses), the flow will be hindered.
That’s why a higher port seems better. So when you purchase a new head, asking the staff for its height is a prerequisite.
On The Flow Bench
Apart from the famous test I have presented above, there are more tests with horsepower heads on the flow bench.
Dallman once tested the durability of double-hump heads of different manufacturers by using a two-barrel carburetor, an aluminum intake, and a device responsible for cleaning the air.
He has also examined the effective operation of two horsepower heads, one with a straight and standard stem, along with one equipped with an undercut stem.
Wet Flow
A setup for wet flow relies on a specialized liquid that is able to flow through the head, and its operation is not relevant to the flow bench.
In this way, the wet-flow setup can help users know how fuel reacts after passing the valve’s faces.
Despite the tube’s inches length, the wet-flow testing still forms a comprehensive picture of how the liquid behaves in relation to the faces of a valve and the combustion chamber’s working.
Head Specs
This post only focuses on the head specs of two models: 462- and 291-double-hump horsepower types.
462 | 291 | |||
Intake | Exhaust | Intake | Exhaust | |
Valve Dia. | 1.94 | 1.5 | 1.94 | 1.5 |
Stem Dia. | 3.43 | 3.43 | 3.43 | 3.43 |
Throat Dia. | 1.59 | 1.305 | 1.59 | 1.305 |
Seat Angle | 45 | 45 | 45 | 45 |
Port Volume | 171 | 75 | 171 | 76 |
Avg. Port Width | 1.074 | 1.303 | 1.092 | 1.322 |
Avg. Port Height | 1.927 | 1.405 | 1.950 | 1.373 |
Port Length | 5.0445 | 2.506 | 4.899 | 2.546 |
Port Mapping
Port mapping has been researched and done on the flow bench, and it is widely used today by many modern manufacturers.
The mapping is placed in different areas of the port with a view to measuring the flow amount.
This device is connected to a specialized computer via a program that displays the flow rate via a color-coded map.
Thanks to it, you will know the areas of your double-hump port where the air circulates effectively.
If your port mapping gets damaged, you can have it and your vehicle checked by professional mechanics. Yet, sometimes he might refuse to release your car in a specific case.
Frequently Asked Questions
What Should You Know About The Chevy Fuelie Heads?
The term Chevy Fuelie heads has been around since the 1960s. Until now, they are still applicable in various walks of life.
This horsepower head has an intake flow of roughly 202 CFM and about 141 CFM on the exhaust.
When equipped with a stock-looking port, the figure for an intake flow rises to 230 CFM and approximately 165 CFM for the exhaust.
This improvement is very important by adding more horsepower of between 15 and 25 CFM to your automobile’s engine.
Looking at the cost, the complete Fuelie head with modern features, like an undercover porting, stainless steel valves, anti-corrosion spring locators or flat tappet springs, etc., is priced at 2795 dollars.
The cost for a normal Fuelie horsepower head with original castings and screw-in studs falls in the range of 1695 dollars.
This option might be more suited to middle-class households if their budgets are limited.
What Kind Of HP Can A Set Of Double Hump Heads Make?
The answer is from 355 to 400 horsepower. The figure is not fixed but varies, depending on several double-hump head models.
As mentioned earlier, a Chevy Fuelie head with state-of-the-art features will likely produce more horsepower than old models, so its price is pretty high on average.
The Bottom Line
This article has unfolded the mystery of the double hump heads horsepower, including four different categories.
Moreover, I also help you explore more knowledge about the Chevrolet double-hump cylinder head and market prices for Chevy Fuelie heads.
Though the price might be beyond some drivers’ means, the power it delivers is well worth it.