Compression question
Well, it looks like we will have the 318 rebuilt. I don't have the space or ability to do it our selves. This is a going to be a driver but I was going to put the 340 cam in it. We are running the LD4B intake with a 600 edelbrock. They are going to rebuild my heads. I've read a ton of threads and I think this what we are going to do. Unless, there is something I should be doing while at the machine shop?
Thank you all
In my experience, for a streeter, with street gears and stock stall, both times; the factory340 cam into the stock-compression LA318, was a mistake. The bottom end goes soft and the power doesn't start 'til 4000. With 2.94s this is is ~42mph. The 268/276/110 aftermarket cam can be a good choice...... if Hi-Compression is achieved. However, for a DD I personally wouldn't recommend it, the fuel mileage is atrocious no matter what rear gears you run.
The factory 340 cam in a LA318 will need a hi-stall Convertor no matter what, and 3.23s minimum with an automatic.
The aftermarket 268cam will want about 9.8Scr. The factory Chrysler cam will want a bit more.
The reason for the compression difference is that the Chrysler cam is advertised at .008 lift whereas some/most aftermarkets are at .006. This means the Chrysler cam is actually bigger than 268 comparatively speaking, from intake valve closed seat to seat, which bleeds cylinder pressure back into the intake. Because of this, with a stock 1800TC, the bottom is soft, cuz it is stuck below 2200 until ~23mph with 2.94s; ~25mph with 2.76s..... and a DD spends a lot of time down there.
After about ~2000 this reversion begins to go away,and by 2200 power production can begin. The power starts at ~4000/42mph with 2.94s, and peaks around 5500/58mph; both in first gear.
Is that what you are after?
The stock LA318 compression ratio, if you value take-off power, limits you to a pretty small cam window. And the higher your operating elevation, the smaller the window.
