A87 Peanut head on L20b

[Luc.Datto]

I have an L20b engine with flat top pistons and what i’m pretty sure is the stock head on it. But i have an A87 head sitting aside. is the A87 head better for performance/more power? I’ve also heard that the A87 head with flat top pistons can blow gaskets.

 

Should I put the A87 head on and port it a bit or should I keep it as it is? 

 

I also have twin 45 webers and a mild cam to go on this engine. 

 

I need some answers from the professionals, thanks 👍

[datzenmike]

The A87 was an L18 head also used on the early L20B in the '74 610. It's open chamber but slightly smaller valves or ports and was replaced by the U67 for '75 vehicles. It will work just fine on an L20B but no advantage. Some import engines had a closed chamber design A87 head with smaller combustion chambers so there are some of those out there. A closed chamber head will boost compression and generate beneficial swirl increasing efficiency for a few, and I mean a few, hp. It may ping so the timing may need to be retarded slightly.

 

1/ If you have the open chamber head A87 the compression would be the same as the later U67 or W58 head at 8.4 and if you have flattop pistons it's 8.9.

 

2/ If by chance you have a closed chamber head the compression would be much higher at 10.68. The head gasket can easily handle this compression. You will want to dial the ignition advance back some as the burn time will be much shorter and will ping otherwise with this.

 

So take a picture of the combustion chamber and post it. It's likely open chamber.

[Luc.Datto]

Thanks. Once I get the head off of the motor I’ll find out if it’s closed or open chamber 

[Stoffregen Motorsports]

Using a larger cam takes up some of that additional cylinder pressure, so adding compression along with a big cam is the best way to go.

 

10:1 CR for the street is fine, but you may need to adjust your timing curve to suit. It can be done easily, if you know what you're doing.