The 426 race Hemi came before the 426 street versions. To make the race engine more streetable, changes had to be made. Many people ask me how they differ. Let’s examine the differences between the two engines.
The differences between a 426 Street and race Hemi are the street version’s lower compression ratio of 10.25:1 compared to 12.5:1, and a lower lift camshaft. The street Hemi had two four barrel Carter carburetors while the race Hemi had one or two four barrel Holley carburetors. The street version had regular exhaust manifolds instead of headers.
- The street Hemi carburetors were mounted inline while the dual four barrel carburetors on the race Hemi were mounted across from each other.
- The street Hemi had a heat riser from the exhaust manifold to the intake manifold to allow heat during engine warmup.
- The most visual difference was the black wrinkle painted valve covers on the street engine compared to the race version’s chrome finish.
- The 1965 NHRA race Hemi switched to aluminum cylinder heads, while the street version always had cast iron.
- The front left street cylinder head had a slight inward curve to make room for the power steering pump. This curve was absent on the race head.
- The front right race cylinder head had an inward curve on the intake side for distributor clearance. This curve was absent on the street head.
- The street engine had bigger spark plug tube covers to repel water experienced during inclement weather.
- Due to the lower compression ratio, lower lift camshaft and exhaust manifolds, the street Hemi had less horsepower than the race Hemi.
This article will take a closer look at these differences including side-by-side photos. In addition, a few less obvious differences which didn’t affect performance but were necessary for the street engine.
The following specifications I learned from my personal experience and research. For the past 37 years, I’ve read Mopar engine manuals, books and articles covering information on Hemi engines.
The Differences Between the 426 Race Hemi Engines
To examine the differences between the street and race versions, first a clarification needs to be made about the race Hemi.
There were two Race Hemis developed, one for Nascar and one for the NHRA. The Nascar one, aka Track Hemi, had one four barrel carburetor. This was to satisfy the Nascar regulations for carburetors.
The NHRA version, aka Drag Hemi, had two four barrel carburetors mounted across from each other. They were mounted on a cross ram intake manifold.
Another difference between the two was the cylinder heads. In 1965 the NHRA version switched from cast iron to aluminum heads with 2.23″ intakes instead of 2.25.”
Since Chrysler didn’t run in Nascar during the start of 1965, there was no Track version of the race engine in the beginning of the year.
Other than those two differences, the Race Hemis were basically the same with slightly different camshaft lifts and durations. The track Hemi cam was a little more aggressive.
Find out why the Hemi was banned twice in my article, Why the 426 Hemi was Banned From Nascar.
The Differences Between the Street and Race Engines
|426 Race Hemi||426 Street Hemi|
|Block||Cast iron||Cast iron|
|Cylinder heads||Steel (1964)|
|Cylinder head design||Hemispherical||Hemispherical|
|Valves||2.25 Intake/2.23″ In(Alum)|
|Carburetors||(1) 4 barrel (Nascar)|
(2) 4 barrels (NHRA)
|(2) 4 barrels|
|Intake manifold||Cross ram||Inline|
|Exhaust manifolds||Headers||Regular manifolds|
|Valve covers||Chrome finish||Black finish|
The main reason for the differences was to allow the following:
- The street version to require less maintenance.
- Use gasoline from any gas station.
- To run efficiently during any traffic conditions and cold weather.
Of course each of the two engines had a different sound and idle. The street version has a much smoother idle due to its less aggressive camshaft. Both Race Hemis have a choppy idle.
The first time I heard a street Hemi I was in awe. It was in a ’67 GTX next to us at a stoplight. We tried to stay at the same pace of that car for as long as possible. Hearing the engine at idle and revving up through the gears was a special sound. It’s a moment I’ll never forget.
The following is a detailed explanation of all the differences.
The race Hemi had a compression ratio of 12.5″1. This is too high for an engine on pump gasoline.
Therefore, the street version received lower compression pistons lowering the ratio down to 10.25:1.
The lift and duration were lowered for the street Hemi to make it more streetable. The milder camshaft allowed for better low-end response for most driving conditions.
For this reason different valve springs were used between the two engines.
Even the two Race Hemis had slightly different camshaft lifts and durations.
|426 Race Hemi|
|426 Race Hemi|
|Camshaft Lift||1964-65: .540″|
|1966-67: .467″ Int/.473″ Ex|
1968-71: .490″ Int/.481″ Ex
|Camshaft Duration||1964-65: 312 degrees|
1966: 328 degrees
|1964: 300 degrees|
1965: 312 degrees
|1966-67: 276 degrees|
1968-71: 284 degrees
The cams were either made by Isky or Racer Brown.
Find out the camshaft’s actual lift and duration for all the years in my article, 426 Hemi Specifications – Complete Engine Specs.
Carburetors and Intake Manifold
The race Hemi for Nascar (Track Hemi) had one four barrel Holley carburetor. This was to satisfy the Nascar regulations for carburetors.
The engine for NHRA (Drag Hemi) had two four barrel carburetors mounted across from each other on a cross ram intake manifold. The cross ram was aluminum in 1964 and switched to magnesium in 1965.
The street Hemi had two four barrel Carter carburetors mounted inline (tandem) with each other. They were mounted on a dual plane aluminum intake manifold.
Learn more about the carburetors in my article, The Carburetors on a 426 Hemi.
The Race Hemis used a higher performance header design.
The street Hemi has regular exhaust manifolds but was designed with less restrictive air flow than a traditional exhaust manifold found on other cars.
The right side (passenger) exhaust manifold had two heat riser tubes leading from a coiled bi-metallic heat valve up to the intake manifold.
The tubes entered the rear of the intake manifold to a chamber underneath the rear (primary) carburetor. Once the engine reached operating temperature, the valve would close blocking the heat from rising up the tube.
The heat riser was absent from the racing version.
Find out if both Hemi versions were big or small blocks. Check out my article, Is a 426 Hemi a Big Block?
The race Hemi had cast iron cylinder heads in 1964 but switched to aluminum cylinder heads in 1965. The street Hemi always had cast iron heads.
The 1965 aluminum race head used on the drag engine (NHRA) had 2.23″ intake valves to provide space for the valve seat inserts. The street head all had 2.25″ intake valves.
The cylinder heads for both had a slightly different shape.
The left front street head had a small inward curve to allow extra clearance for the power steering pump upper housing and fill cap.
The Race Hemi head has no inward curve, it’s straight shown in the picture below.
For a complete breakdown of all 426 Hemi head casting numbers, check out my article, 426 Hemi Head Casting Numbers.
The right front racing head had an inward curve on the intake side to allow for more distributor clearance.
The street head is straight with no curve shown in the picture below.
Everyone knows about Hemi cylinder heads but what does it really mean? Find out in my article, What Hemi Means in an Engine: Generation 1, 2 and 3 Hemis.
Valve Covers (Rocker arm covers)
Since the cylinder heads had different shapes as described above, the valve covers and the gaskets used for sealing, also have different shapes.
The shapes are subtle but do exist, and the parts and gaskets cannot interchange with each other.
Another difference is the color and finish. The race covers are chrome and the street versions are painted with a black wrinkle finish.
For me, the first thing I ever noticed while seeing a Hemi for the first time was the valve covers. While other Mopar big blocks had the same color valve covers as the block, the black Hemi ones were a sharp contrast to the orange colored heads and blocks.
The color difference drew more attention to the huge Hemi head, like it didn’t need it already.
Spark Plug Tube Cover
The spark plug tube covers that meet with the valve covers are different. The street covers are wider and seal more of an area against the valve cover to repel water.
Therefore, if you dare drive your million dollar street Hemi in the rain or snow, you can be assured your spark plug tubes will probably remain dry.
Any questions or if you have more information you’d like to contribute, send us an email found on our contact page.
Interested in More 426 Hemi Tidbits? Check out these related articles
- Wikipedia: Chrysler Hemi engine
- Google Books: How to Rebuild and Modify Chrysler 426 Hemi Engines
- Google Books: Muscle Car Confidential
- Google Books: Hemi: A History of Chrysler’s Iconic V-8 In Competition
- Google Books: Complete Chrysler Hemi Engine Manual
- Book: Hemi
- Google Books: Chrysler Engines 1922-1998