Intake runner length

[Hib Halverson]

Originally Posted by tpepmeie

Quite the opposite, actually Hib. Since there is but one intake option for LT5's, I was trying to determine how best to utilize it with the rest of the engine combination. In fact, the Lotus guys got it quite right for their intended purpose. (snip)

I get it.

The other thing that intrigued me was why there was such a small difference observed between peak torque (6000), and peak hp rpm (7000) on my engine. That is not normal, you'd expect 1500 rpm minimum. Sure enough, there is a higher tuned length (7500), but I just didn't have the valve area to access it. And I have very large camshafts.

To get a bit off topic here, my belief, admittedly based pm old information from road racing in the late 90s, is that the cam drive mechanism in the LT5 is not very reliable above 7200 or so when using high-lift cams and appropriate greater pressure. Your thoughts?

Conclusions (mine, yours may vary)--unless you are going to fit very large valves and camshafts (to fully access the 2nd harmonic @ 7500), the factory intake lends itself to designing the engine and camshafts for maximum breathing efficiency at 6000 rpm.

No. I agree. What I was told way back when I began covering the engine's development is they were looking for an engine which would run best at 5800-6200 rpm with a rev limit at 6800-7000.

Second conclusion-- the shorter tuned lengths of a fabricated manifold will never match the specific output of the factory length at any speed below 8000. I think real-world testing backs that conclusion up.

Indeed it does but, also, that's gotta be true of any V8 of similar displacement and with runner length, port volume and valve events similar to that of the LT5.