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Street Race Truck More... The Toolbox

Chevy 461 Double Hump Cylinder Head Comparison - Tech Talk

11/7/2019

Today in the shop we’re learning about our new aluminum double hump cylinder heads for the small block Chevy V8. Wyatt and Joe compare them with the original GM 461 casting or "fuelie heads" that debuted on the 1961 Corvette with Rochester fuel injection. Our new cylinder heads have a similar external look to the GM 3782461 heads, but are made out of aluminum and have many improved features over original castings. Instead of rebuilding an original set of heads, you can use these to gain a performance advantage while maintaining the vintage look you want.

These new cylinder heads not only have the classic appearance, but they also weigh 20 pounds less than the original. This shaves 40 pounds off of the nose of your car. Also, aluminum dissipates heat better than cast iron, so you can typically run more compression on pump gas compared to an iron head.

There’s a lot going on inside this head that makes it better than an original double hump head. It has improved port shapes and a larger 180CC intake runner volume (versus 160cc on GM 3782461 heads). A raised intake port floor improves the short side radius, resulting in more even flow distribution across the back of the intake valve. Plus, the "dorsal fin" cast into the intake valve guide increases air velocity by eliminating dead spots in the flow path. The net effect is more efficient cylinder filling, which translates into big torque gains.

The improved combustion chamber also offers huge performance gains. On the new heads, note how the shape of chamber is an extension of the valve seat angles (rather than looking like a bathtub), improving mid-lift flow. Plus, the ample quench area pushes the air/fuel mixture into the perfect spot for a faster combustion rate. Also note how the spark plug on the aluminum head is closer to the center of the chamber and nearer to the exhaust valve, which improves the flame front across the cylinder.

These heads have 2.02" intake and 1.60" exhaust valves, whereas most 461 heads came with a 1.94" intake and 1.50" exhaust valve. However, even with a 4" wide chamber and large valves, these heads will still fit on a .040" over 283 engine, as well as the larger 327 Chevy. They share the same port location as the original 461 heads, so both factory and aftermarket manifolds will work.

We offer a bare casting as well as an assembled version. The assembled version comes loaded with all modern valve train components: 3/8-inch screw-in rocker arm studs, pushrod guide plates, positive stop valve stem seals, .550" lift springs, and hardened valve seats so you can run unleaded gas. Plus, we offer all the accessories you need to fully dress a L76, L87 or L79 small block Chevy for your classic Nova, Chevelle or Corvette.

Video Transcript

Joe: “Hello everyone, welcome to Speedway Motors Tech Talk I'm Joe and today we're here with Wyatt and he's going to tell us about some new cylinder heads that are pretty darn cool. What are they?”

Wyatt: “What we have here is an original GM 461 casting. These are often referred to as the ‘fuelie head’. These debuted on the ‘61 Corvette with the Rochester fuel injection, so that's why they're called ‘fuelie heads’. This is the first iteration of GM's double hump cylinder heads. There are many different versions of those. What we've done is we've taken the external look of it and turned that into an aluminum casting. These new aluminum castings are visually similar to the GM 378 24 61 heads, but they have many improved features that are a great option instead of rebuilding an original set of heads. They're really perfect for your muscle car restoration or even your vintage race car or even a nostalgic hot rod build.”

Joe: “You know that's kind of been the thing for years, you look under the hood of a muscle car or you look at a hot rod and it's got double hump heads and it's like whoa you know that's a hotrod small-block, so that's cool, but these are better.”

Wyatt: “These original heads weigh 42 pounds apiece, bare. Our new aluminum versions weigh 20 pounds apiece, so right there that shaves 40 pounds off the nose of your car. Also, the nice thing about aluminum is they radiate heat better than cast-iron does, so you can typically run a little bit more compression on pump gas with an aluminum head versus a cast-iron one. Typically, half a point maybe even a full point in some instances.”

Inside our new Double Hump Cylinder Heads

Joe: “Other than just being made out of aluminum instead of cast-iron there's a lot going on inside this head that makes it better, right?”

Wyatt: “Right so there are two main areas where these will outperform an original double hump head. The first is in filling the cylinder, so getting the air down into the cylinder more efficiently and that creates torque. So the new heads have an improved port shape, so they have a 180 CC intake runner versus 160 intake on the original heads. Also, the new heads have an improved short side radius. If you look at an original set of 461 heads the floor of these heads is very flat and so what that does is it creates a very sharp turn for the air at the right angle bend down to the valve, that's not good for flow. These new heads have a raised floor and you'll see kind of a ramp in there and that actually directs the flow better at the back of the valve. You'll also see the texturing around the valve guide itself and that actually increases velocity by eliminating dead spots behind the valve guide. The second area where these are better, and the main power production area, is in the combustion chambers. You'll see on these new heads there's ample quench area, so what that means is it pushes all the mixture into the combustion chamber itself again for a faster burn."

Wyatt: "Also, note on the new heads the spark plug is closer to the center of the combustion chamber than on the original heads. What that does is the closer you get the spark plug to the center, the flame front is better throughout the cylinder. Also, the spark plug is closer to the exhaust valve, so what that does is again helps the flame front from the hot exhaust valve to ignite the mixture. Those are the main areas where these will outperform an original set of heads."

Valve Size on New Aluminum Cylinder Heads

Joe: “What's the valve size on the new aluminum ones?”

Wyatt: “So the valve size here is a 2.02” intake 1.60” exhaust, so most of your 461 original castings came with a 1.94” 1.50” exhaust valve. Some of them did come with the 2.02” 1.60”, but these do have a bigger valve. With these you'll get a 3 angle valve job and so what that does is it again helps the air transition around the valve so you'll get great flow at low to mid lifts especially.

Period Correct Appearance

Joe: “So, you know it's not hard to find a performance aluminum small block cylinder head. The problem is they all have billet looking milled on the front of them, high-tech looking stuff on them, that looks really out of place on a period specific car. These you can kind of sneak into an old hot rod or an old muscle car and it'll look right.”

Wyatt: “Exactly. So, they share the same port locations as an original set of heads, so your factory intakes, your aftermarket intakes, exhaust manifolds, etc. will all work. Just like the originals, there are no bolt holes on the end for your accessory drive. You'll also see the double hump castings are very similar. Also, they have a raised valve cover rail, so the assembled versions actually have a tenth of an inch longer valve and a bigger spring, so you have to use roller rockers on the assembled versions of these head. And when roller rockers come into the equation, you usually have to run a taller valve cover which is maybe not something you want on vintage-looking engine. So, we've raised the valve cover rail here, so that you can run roller rockers with an original set of Corvette valve covers on top of them keeping the theme of your vintage looking engine.”

Joe: “And like you said, we offer a bare casting as well as an assembled version.”

Wyatt: “Right, so the assembled version comes loaded with all modern valve train components. It's got 3/8 inch screw in rocker arm studs, push rod guide plates, positive stop valve stem seals for better oil control. Also, it has hardened valve seats so you can use it with unleaded gas. All of these things would need to be added and machined on an original set of heads, which really inflates the expense of these heads. So really when you look at it that way, there's a lot of value right in these new heads versus rebuilding an old set of heads that have questionable history.”

Joe: “That you probably had to overpay for at the swap meet.”

Other Engine Parts to Complete the Early 1960's Look

Joe: “And the cool thing is we've got a lot of other stuff too, to dress up the rest of the engine.”

Wyatt: “Right, so we've got everything you need to fully dress it in that early 1960’s look. Maybe you're building a L76 a 365 horse 327 or maybe you're building a 350 horsepower L79 327, we've got all the accessories to fully dress those engines. We've got the finned Corvette style valve covers that will work great on these heads. We've got the two and a half inch outlet exhaust manifolds, the Corvette style ones. We've also got the alternator brackets [slide and base] to bolt these up to the manifold and the head.”

Joe: “Right since there's no accessory hole.”

Wyatt: “Exactly. Also, we've got this really cool L79 style air cleaner with the dual snorkel.” Joe: “These are super cool I can't wait to put these on an engine. I'm already scheming on what we can put these on. Thank you, Wyatt for telling us about these. And thanks to everybody for watching.”

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