What max compression on 93 Octane?

[Tippy]

Sounds like a good read

[Slanski62]

Sal, since the 3.4 build is popular, are there off-the-shelf cam grinds that have the target LSA of 112?

[gliding_serpent]

My head just exploded.

[scarceller]

Originally Posted by Slanski62

Sal, since the 3.4 build is popular, are there off-the-shelf cam grinds that have the target LSA of 112?

Yes, plenty of good cams with 110 to 114 LSA and a bunch in the 112-113
DC Cams has a few as does Elgin and WebCam.
Plus some factory cams, like the 964 cam that does well in these 3.4L engines. If you think about moving a 3.2L to 3.4 or 3.5 and twin plugging it you are basically creating a 964 type motor so why not use the 964 cam? The 964 factory cam has the intake on about 115deg and the exh on 111deg centerlines. average of about 113.

[scarceller]

What you said here is correct but the real reason is simply because if you increase the LSA and don't touch the duration you simply caused the intake valve to close later and thus reduced dynamic compression. But you can easily fix the dynamic compression issue by increasing the static. The inverse is true if you shorten the LSA, here you increased overlap and close the intake sooner and the dyn comp goes up.

You can NOT and SHOULD NOT alter the intake valve close point without revisiting the dynamic compression calculations! This is why you can't just throw any cam into a motor. The very best engine designers start with the cam and the head design and flow numbers and build the motor around it not the other way around.

So while your statements below are correct they are not the entire story, hopefully my explanation helps.

Originally Posted by Tippy

Damn Sal, you've really thought LSA through!

I just remember the basic rules of LSA:

1. Wide LSA = broad torque, bleeds compression, good for boosted and nitrous oxide motors
2. Narrow LSA = narrow torque band, peaky, higher hp (like a 2-cycle), maintains compression good for race cars and generally best for naturally aspirated engines