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.

[tpepmeie]

Originally Posted by Hib Halverson

I get it.

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?

The chain drive configuration is not a problem, many highly successful Cosworth F1 and Indy engines used chain drive. What I have gathered, probably from yourself, Graham, and others is that the cam sprockets were intentionally made small to keep the overall engine width small enough to fit between the frame rails from the bottom. The consequence is that there is less chain "wrap" than you'd like for a high rpm engine. This inevitably stresses the chains more.

Solution? Higher strength cam chains. Jerry and I worked with IWIS to get some HD chains made last year.

Of more concern for high rpm operation, to me, is the lubrication and windage control. Too much crankcase pressure and the oil won't evacuate the top end well enough. I've already seen more positive crankcase pressure than I'd like at 7000 rpm. Dry sump would be ideal, but plumbing is nightmarish.

as always, YMMV.

[Hib Halverson]

Originally Posted by tpepmeie

(snip)

Solution? Higher strength cam chains. Jerry and I worked with IWIS to get some HD chains made last year.

I didn't know you guys had done that.
Problem solved.

[A26B]

I know where their is a dry sump LT5, at least part of it��

[grahambehan]

Originally Posted by Hog

Could anything be done with the planned MY1996+ LT5 intake with its 8 intake runners vs. 16?

Power peak at 7200 on this one, as per design spec

Graham

[XfireZ51]

Originally Posted by grahambehan

Power peak at 7200 on this one, as per design spec

Graham

Looking forward to seeing that one in a ZR-1 Graham

[tpepmeie]

Originally Posted by grahambehan

Power peak at 7200 on this one, as per design spec

Graham

Thanks, Graham. Do you recall the total length of the intake tract for that one?

Any chance to get that thing duplicated with a new casting? You'd have to make modified injector housings to work with the production heads, but those could probably easily be machined from billet.

I'd love to see that thing re-made and available for retro-fit. Consider mine the first order!

[Hog]

Originally Posted by grahambehan

Power peak at 7200 on this one, as per design spec

Graham

And boy does it sound good up there Graham. Good work.

http://www.youtube.com/watch?v=X-Z5oOIgv2o