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Chevy valves in a small block Ford head



Chevy valves in a small block Ford head


Yes. Before all of these aftermarket heads were available, this was a pretty common swap for early 289 - 302 and even some of the 351W heads. Both Ford and Chevy heads use 11/32" valve stems and are very close in length. The 1.94" and 1.50" Chevy valves fit nicely into the asthmatic early Ford heads. A little pocket porting and gasket matching goes a long way with this swap. The trick though is; you MUST un-shroud the valves in the combustion chambers! Bigger valves do NOT mean you'll get more flow. In fact, you can actually LOSE flow by having valves that are too big and they become shrouded by the walls of the combustion chamber.

This is true for ANY head of any make or brand, from Chevy to Dodge, and beyond. In fact, this is a common mistake Chevy guys make when fitting older cast iron 1.94" valve heads with bigger 2.02" / 1.60" valves. If you don't unshroud the chambers, you'll actually LOSE flow. I prove this on a SuperFlow 901 flow bench in my DVD titled "Heads, Porting & Valve Trains", and it isn't by just a little bit. It can be by a LOT depending on the circumstances, such as valve lift, combustion chamber size and shape, etc, but for an overall picture, bigger is absolutely NOT better if the valves aren't unshrouded.

The bigger the valve, the closer it gets to the wall of the combustion chamber. The area between the valve and that chamber wall MUST be machined to give more clearance around that side of the valve so the incoming fuel and air charge can get around and past that chamber wall and into the cylinder. 

Chevy valves in a Ford head

This is true for ANY head of any make or brand, from Chevy to Dodge, and beyond. In fact, this is a common mistake Chevy guys make when fitting older cast iron 1.94" valve heads with bigger 2.02" / 1.60" valves. If you don't unshroud the chambers, you'll actually LOSE flow. I prove this on a SuperFlow 901 flow bench in my DVD titled "Heads, Porting & Valve Trains", and it isn't by just a little bit. It can be by a LOT depending on the circumstances, such as valve lift, combustion chamber size and shape, etc, but for an overall picture, bigger is absolutely NOT better if the valves aren't unshrouded.

The bigger the valve, the closer it gets to the wall of the combustion chamber. Look at the image to the right. You can enlarge it by clicking on it. Notice the area between the arrows I drew on it and how close that huge valve is to the side of the cylinder wall. Mind you, this is an early 2,000's Winston Cup head off of a car we did the engine for back then, so even though the valve appears to be shrouded (for illustration purposes) the fact is; this is actually an illusion with these particular heads because the chamber depth is really shallow right there, but you can't see the depth in the image so it looks exactly like a valve would look that needs to be unshrouded.

The area I'm pointing to between the valve and that chamber wall MUST be machined to give more clearance around that side of the valve so the incoming fuel and air charge can get around and past that chamber wall and into the cylinder. Look at the exhaust valve below it and see how much room there is between the chamber wall and the valve. That's how an unshrouded valve should look. Keep in mind, these are BIG breathing Yates High Port NASCAR heads so that intake valve is a whopping 2 1/4" inches in diameter!!! There simply isn't enough diameter of that chamber TO open it up anymore or the valve would be into the cylinder wall. Again, the way they get around this is to make the chamber really shallow in that area so when the valve lifts off the seat, it gets far away from that chamber wall. Well, you can't do that with most heads, especially stock heads, because those chambers are much deeper and most of the time the valves (even with high lift cams) don't come "out" of the chamber, so even at full lift, the valve is still up against that narrow area of the chamber wall which prevents that side of the valve from flowing fuel and air, or exhaust.

I show this pretty extensively and clearly in my "Heads, Porting & Valve Trains" DVD set.

Chevy valves in ford heads

This is the exhaust side of that same chamber and look how the area I'm pointing to is much wider so exhaust gas can flow past that valve from all sides. This is ideally how valve should look inside a chamber, but anytime you stuff bigger valves into a chamber of a given size, a portion of that valve is going to get closer to the chamber wall and will prevent flow on that side of the valve if you don't machine that chamber wall back. This was a common problem for stuffing big Chevy valves into early Ford heads and why guys that didn't really know what they were doing didn't see the benefits or gains in power that they could have if they had done this extra step of unshrouding the valves. It's also a common problem for the Chevy guys when they converted their 1.94" heads to 2.02" heads. Most of the time they didn't unshroud those valves and they didn't gain much benefit from those larger valves.

unshrouding the valves

I go into this is MUCH greater detail in our "Heads, Porting & Valve Trains" DVD which is a multi disk set with over 5 hours of info just on the valve train, and again, I show this exact scenario with shrouded and unshrouded valves on a flow bench so you can see if first hand. We also have many other titles in our Auto Shop Videos series covering all kinds of tips, tricks and full-on engine builds in extreme detail that you should check out. Top industry professionals such as Vic Edelbrock, Mike Thermos (founder of NOS) and even the great Jay Leno love these videos! They also make great Christmas, Birthday and Father's Day gifts. Check them out by clicking HERE.

unshouding the valves

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