Engine Questions

[Black1987]

I know for most cams there is a recommended compression ratio, for instances Ford's X-cam it's 9.0:1 to 10.5:1. What happens if your compression ratio is lower (8:7:1) than the recommended?

Also, separate question what happens if someone installs the piston with the reference point on the piston facing the opposite direction than front of the engine block. However, all pistons are facing the opposite direction.

 

[liljoe07]

1: Generally a longer duration cam will have a Closing point farther past Bottom Dead Center. Makes the engine tend to be a little soft on the bottom end. Having a higher compression ratio helps this soft feeling. So to keep from guys putting in a cam that will be a turd, they give reccomendations like Gears, Converter Stall(If applicable) and compression.

2: not real sure here. Main thing that comes to mind is if you are talking about stock rods and pistons, is that being the pistons are pressed on the rods, if you put them in the wrong way then the small chamfer on the rod will be against the cheek of the crank. It will bind the assembly. There is two chamfers, one large and one small. Small chamfer faces each other and the large faces the crank cheek.

 

[Black1987]

1: Generally a longer duration cam will have a Closing point farther past Bottom Dead Center. Makes the engine tend to be a little soft on the bottom end. Having a higher compression ratio helps this soft feeling. So to keep from guys putting in a cam that will be a turd, they give reccomendations like Gears, Converter Stall(If applicable) and compression.

2: not real sure here. Main thing that comes to mind is if you are talking about stock rods and pistons, is that being the pistons are pressed on the rods, if you put them in the wrong way then the small chamfer on the rod will be against the cheek of the crank. It will bind the assembly. There is two chamfers, one large and one small. Small chamfer faces each other and the large faces the crank cheek.

Thanks, on the recommended compression ratio. Moreover, on to the piston situation, they are Speed Pro hypers on stock rods. The reason I ask is after researching their site, Speed Pro puts a reference mark on there pistons. This is to give a reference to the builder that the pistons are put in the same direction towards the front of the engine block. So, the all marks point toward the front. However, after taking apart my sister's long block, those marks are in the opposite direction??? So, is this a problem or fine because they all are intially in the same direction.

 

[liljoe07]

Pretty sure the stock pistons are symmetrical. Meaning some pistons have an offset on the pin, but Im pretty sure the stock ones dont. Granted I have never found the need to try to put the dot facing backward, but it shouldnt be an issue. Just have to remember that if you are going to reassemble with the same parts. Putting them in with the dot facing forward without correcting the rod chamfer issue will cause major problems.