How does one determine the correct Intake Valve Closing point based on cubic inches and desired peak RPM?

Or is this camshaft guru secret stuff?

 

Have you seen the Overlap-Valve-Events-Editorial thread? It has lots of excellent discussion.

Hopefully some of the guru's will comment.

 

Yes sir, I have read it many times. Very good info in there. I figured out from some very respectable posters there that when dealing with a 5.7 LS, 43 IVC gives you about a 6300 RPM peak. I just don�t know how they got there( other than dyno runs) or how you figure it for larger/smaller cubic inches and higher/lower intentions.

 

The 63-6400 rpm peak has to do more factory plastic intakes peaking at that range.

 

I think it's by experiment. I'm not the kind of person that's ever going to unlock the secrets of cam theory LOL!, so what I did was benchmark some highly successful builds that were similar to what I was doing. I noticed all those builds had intake valve closing within 1� of each other regardless of the duration they chose. And then I compared to the tons of average builds and noticed their valve closing was earlier. That kind of clued me in to what works for my engine.

I made spreadsheets, did a bunch of comparisons, did some reading to try to understand things and eventually lost confidence in myself to get it right. It's a complex topic matter. But it's dirt cheap to pay a professional for help so that's what I did. And I hired the guy that had a hand in most the highly successful builds I found....

 

"Experiment" is a good word, however "example" might fit this context a bit better, as there have been so many successful variations by now, that one could copy it and do well. This does apply to where to close the intake valve. Find a good build that closest emulates where you are going and go that way. We can't all grind a bunch of cams and see what works. Follow what has worked for others. That way you eliminate the "guinea pig" stage.

 

Fascinating comments in here. Makes me think about my combo. I have an off the shelf TSP 216/220 .600 / .600 112+2 has an IVO of 2* and IVC of 38, ICL of 110.

It basically peaks around 6350 but runs flat to just below 7000 rpm where it starts to drop. So, it feels strong all the way to close to 7000 rpm. Standard LS6 manifold unfortunately, I wondered if this is a limitation to moving the peak higher and posts here indicate it may be. I would love a TPiS 90 mm to offer a little more but not possible as I am outside the USA.

Instead, Im actually considering changing to +4 advance, to bring the power in a little earlier. Brings the IVO to 0* and importantly for me, IVC of 36 and ICL of 108. TSP indicated it may cost me top end but I think I'm limited by

If I had my time again, I probably would have chosen the TSP 214/220 .600 / .600 112 and ran it at +4 advance. IVO of -1*, IVC of 35 and ICL of 108. I think with my ported heads / 11:1 compression, it would be great for down low power. Not worth swapping though.

 

I have read that somewhere before.

There was a quote in that write up that said 43 (@.050) IVC for 6300 and 40 for 6000 RPM peak for a 5.7 LS1.

According to Pulse Red, his 5.7 peaks at 6300 with a 38 IVC.

I don�t know. Like someone said, experimentation will get you there.

Perhaps there is no secret mathematical formula.

 

For me, it's a little hard to tell on my dyno sheet, as due to it starting at 1900, the increments at the point in question are 6250, 6500, 6800. It looks like it's peak between 6300 and 6350 to me but unless I'm being stupid, it's certainly higher than 6250.

 

Is there a particular goal in mind or just wanting to understand how it works in general?

FWIW

Probably engine dyno software helps with simulation to get in the ballpark and then test on actual dyno. There maybe a formula, no idea.

Using the summit-cam-timing-calculator can also help with ballparking if you know all the cam specs and where the cam peaks etc. Of course off specs are given and degrees of advance are omitted.

Ultimately, unless checking the cam with a cam doctor or similar and degreeing in the cam as many times the published specs for cams are off slightly.

We cam doctored my 224/224 XER on a 113 LSA back in 2002 that was custom ordered from COMP Cams via a NASCAR shop. The cam specs were with in ~1 degree but it was actually something like ~224.8/224.9 on 112.4 etc.

The point being an adjustable timing set & degreeing in cam was required to get the exact valve events my installer selected. Otherwise a cam that looks like it's IVC is 40 might be a degree or so off in some cases.

 

I've done a close comparison with IVC in my recent tinkering.

204/222-112+2 (32ivc) vs. 212/218 - 115+0 (41ivc)
These cams have very close valve events besides the IVC.

My engine is an LQ4 with LS3 Pistons and stock 706 heads stock LS6 intake and throttle body and stock exhaust manifolds.
The car is a 2002 f body stock converter and 2.73 gears
The 32 IVC cam has slightly more exhaust overlap than the 41 IVC cam so it's not an exactly perfect comparison however I feel it's close enough.

Even with my very high static compression ratio The 32 Ivc feels stronger and more responsive everywhere in the RPM range I see in my restricted combination, though It does idle slightly rougher and the gas mileage is not as good as the 41 IVC cam I would attribute that more to the exhaust overlap than the IVC

The earlier IVC cam uses less timing advance at lower RPMs however up top it wants about the same 21 to 22 degrees all in as the 41 Ivc did. Both combinations work fine on decent mid-grade fuel so I switch back and forth with premium to be safe. The earlier IVC cam gets slightly worse mileage but I attribute that to the added exhausteration more so than the IVC but I could be wrong.

Due to the restrictions in my combination peak power is going to happen below 6,000 no matter what however because of the compression it's still carries the power flat all the way to 7, 000 if you wanted to.

I think IVC is most closely influenced by converter stall speed and rear gear ratio and you want to get it as early as possible If you were worried about power below peak torque, otherwise with a high stall and low gear you would rather want it as late as possible based on your compression to keep the curve climbing as it carries out so you can maximize your high RPM shift point.

 

Lots of good info in this thread. The factory intake runner length doesn�t seem to like much more than 51 degrees. Our truck cams range from 27 to 41 degrees. Our automotive cams range from 43 to 55 in general.

It�s important to think about the head/intake flow potential being used up by the bottom end in direct relation to piston speed. Bigger shortblocks peaking earlier and small ones later, but in direct relation to piston speed. This is affected by bore of course which dictates intake valve size and flow, but you get the idea.

Here�s a video we did on valve events. It�s fairly simple but there are some good nuggets in there.

 

Care to disclose just who "the guy" is?