317 or 243 heads with Whipple and 408?
 

I know this question has been presented, but wanted to ask for my specific application to get some ideas. I currently have the LQ4 which I am going to be going through to stroke to 408. I wanted to know what you guys thought about keeping the 317 heads that are currently on there if I am going to be running a whipple with about 10psi. I have read the 317s will work better with boost and give me the lower CR. If that is the case, I would just have them cleaned up and reuse with all stock parts. Would this be advisable, or should I get new rockers, etc.?

The 317's have a 71cc chamber IIRC, the 243's have a 64cc chamber. So the 317's will have lower compression.

I'll leave the other questions to the FI experts.

How many miles are on the valve train components?

I have about 20-30k on the current valvetrain. My idea was just to go through the heads and clean them up and replace springs, etc. with stock parts.

Your going to want better springs.

And since you havent built the engine yet its up to you as far as the compression ratio, the heads dont really matter much.

So you think I will need to upgrade from the stock springs? I have been reading that the heads do play a role in CR also. I was thinking with about 10psi of boost, I wanted to be in the 9.5:1 ratio. That sound right?

While in your case figuring your goals and target ratio, I feel the 317’s cleaned up with a good valve job and better springs will do just fine, compression is not just compression and generally speaking you would be better with the tighter quench a head like the 243’s and “D” shaped pistons offer over a head designed with less quench and a regular bathtub dished piston. Of course there is more to it than that, even different piston designs than “D” shaped, but yes head design plays a big part in the ultimate potential of the engine. With the 317’s and 243’s the basic port design is comparable, yet due to the slightly better combustion chamber design the short turn radius is slightly improved in the 243/799 heads and results in an marginal edge in flow. Again though, I feel in your case a properly prepared set of 317’s will be more than adequate, especially since you already own them.

1Bear, thats what I was hoping. I will need to find out how much it would be for the valve job and cleaning. Hopefully not as much as buying a ready to go set of 243s. So I was looking at the TSP rotating assembly for the build. Do you think the K445X3 Wiseco's will work well? It is saying 9.7:1 at -15cc and 70cc of flow, so I should be pretty close to that with the 317s being at 71cc. The other option is the -20cc pistons, which would be 9.3:1.

fi go for 317 heads!