1971 Heads- Open or closed chamber?

[Justin B.]

Are 1971 #487heads open or closed chamber?

[Joe L.]

Re: 1971 Heads- Open or closed chamber?

Are 1971 #487heads open or closed chamber?

Justin------


The term "open" and "closed" chamber is applied to big block cylinder heads. The GM #3973487 is a small block cylinder head, so neither term applies. The 3973487 heads are 75.5 cc combustion chamber size.

[Justin B.]

Re: 1971 Heads- Open or closed chamber?

I would like to build a carbureted small block engine for an old car of mine and was wondering if these would be good heads for the project. Hoping to get roughly 350 h.p.

[Leif A.]

Re: 1971 Heads- Open or closed chamber?

best large-chamber head; 1.94/1.50 & 2.02/1.60 valves available. do you know what size valves your 487 head has? screw in studs? these heads were used on the LT1.

[Duke W.]

Re: 1971 Heads- Open or closed chamber?

I would like to build a carbureted small block engine for an old car of mine and was wondering if these would be good heads for the project. Hoping to get roughly 350 h.p.

At what RPM do you want it to achieve 350 HP?

Duke

[Justin B.]

Re: 1971 Heads- Open or closed chamber?

Honestly, I haven't really thought about it, as goofy as that sounds

[Justin B.]

Re: 1971 Heads- Open or closed chamber?

The valves are 2.02, 1.6 with screw in studs

[Leif A.]

Re: 1971 Heads- Open or closed chamber?

The valves are 2.02, 1.6 with screw in studs

You've got a very nice set of heads there. I think you can do just about anything you want with them. IMHO, GM never made a better head. You can get as serious as you want with them. My only suggestion would be sure to put hardened valve seats in them when you rebuild them. I'm sure other members will have some great suggestions for the different combos you can put with those heads i.e. domed pistons, head gaskets, cams, rockers, etc but you've got a great foundation for whatever you do with those heads. Best of luck with your build and keep us posted as to what you ultimately build.

[Duke W.]

Re: 1971 Heads- Open or closed chamber?

Honestly, I haven't really thought about it, as goofy as that sounds

Many view engines as one-dimensional, but they are not. Most of our driving is below 4000 revs, so power is important from off idle to the mid range, and engineering an engine to make more top end power usually reduces power in the lower rev range.

You also did not say how this power is measured. There are several different ways.

A better way to specify engine performance is to specify torque bandwidth, and a good high performance road engine should have no less than 80 percent of peak at 2000 in order to feel responsive in normal road driving. For automatic transmissions I spec 90 percent 2000.

Four very important issues are compression ratio, head flow, valve timing, and the spark advance map.

High compression is needed for maximum across the range output and fuel economy. Top end power is primarily a function of head flow, so if you want maximum top end power, head massaging is necessary. Then you select valve timing to achieve the low end torque spec, and optimizing the spark advance map is critical to achieving maximum torque bandwidth for any configuration.

Given the above it's possible to create a Gen I 327 or 350 using all vintage OE parts (though not necessarily OE to your engine) that makes 325-350 SAE net HP in the 6000-6500 range while meeting the low end torque bogey. This would equate to about 270-290 SAE corrected RWHP and 360-390 SAE gross horsepower, but requires the owner to understand the issues, have a detailed plan, pay very close attention to detail, and carefully manage required machine shop work.

A more torquey configuration using a hydaulic lifer cam can make about 300 SAE net horsepower, and such a configuration would be more useful for the way most of us use our cars.

The above are subjects you should understand and think about. They have been discussed many times, so some archive searching might get you off to a good start. Also, dig out your Fall 2010 Corvette Restorer. It has an article about how you system engineer a vintage engine to provide substantially more output while maintaining original external appearance and idle behavior.

Unfortunately, many simply turn over their engine to some "engine builder", spend thousands of dollars, and end up with a gas guzzling (and in some cases oil guzzling, too) dud. (There are many such stories in the archives.) The more time you spend planning up front and carefully managing the process end to end, the better results you will obtain.

Duke

[Justin B.]

Re: 1971 Heads- Open or closed chamber?

Many view engines as one-dimensional, but they are not. Most of our driving is below 4000 revs, so power is important from off idle to the mid range, and engineering an engine to make more top end power usually reduces power in the lower rev range.

You also did not say how this power is measured. There are several different ways.

A better way to specify engine performance is to specify torque bandwidth, and a good high performance road engine should have no less than 80 percent of peak at 2000 in order to feel responsive in normal road driving. For automatic transmissions I spec 90 percent 2000.

Four very important issues are compression ratio, head flow, valve timing, and the spark advance map.

High compression is needed for maximum across the range output and fuel economy. Top end power is primarily a function of head flow, so if you want maximum top end power, head massaging is necessary. Then you select valve timing to achieve the low end torque spec, and optimizing the spark advance map is critical to achieving maximum torque bandwidth for any configuration.

Given the above it's possible to create a Gen I 327 or 350 using all vintage OE parts (though not necessarily OE to your engine) that makes 325-350 SAE net HP in the 6000-6500 range while meeting the low end torque bogey. This would equate to about 270-290 SAE corrected RWHP and 360-390 SAE gross horsepower, but requires the owner to understand the issues, have a detailed plan, pay very close attention to detail, and carefully manage required machine shop work.

A more torquey configuration using a hydaulic lifer cam can make about 300 SAE net horsepower, and such a configuration would be more useful for the way most of us use our cars.

The above are subjects you should understand and think about. They have been discussed many times, so some archive searching might get you off to a good start. Also, dig out your Fall 2010 Corvette Restorer. It has an article about how you system engineer a vintage engine to provide substantially more output while maintaining original external appearance and idle behavior.

Unfortunately, many simply turn over their engine to some "engine builder", spend thousands of dollars, and end up with a gas guzzling (and in some cases oil guzzling, too) dud. (There are many such stories in the archives.) The more time you spend planning up front and carefully managing the process end to end, the better results you will obtain.

Duke

Duke, you are so right. I would like to have the power and torque off of the bottom end through mid-range, not so much at high rpms. Can you make any recommendations on cam, pistons, etc? I really have no knowledge when it comes to building motors. I just have to depend on you basic engine builders to guide me. Plus, it needs to run on 93 octane pump gas