Questions about David Vizard 128 Rule and Dyno Tests

[rpetrowsky]

I don't have answer for you on dyno tests /results. Use entering your numbers I do get a little different results.

Stan

TMC_rpetrowsky.gif

Thanks for running that! I wasn't expecting anyone to run numbers, but really appreciate it. I would love to see a major publication test the results for real world application.

[HQM383]

If you test with a fixed ivc you are simply testing how much overlap your motor likes.

I'd go further to say all that is being tested is the effects and flow-on effects on varying the EVO event. No cam event or spec operates in isolation.

[HQM383]

I'm a new member here and am trying to fill in my knowledge gap on something that seems overlooked when discussing David Vizard's "128 rule" and overlap. I apologize as I realize this topic has been discussed ad nauseum. Unfortunately, all of the dyno tests I find show simply tightening the LSA while maintaining the same duration. This results in an overall increase in torque, for some obvious reasons. However, in his, books, David Vizard talks about how those wider LSA cams have too long of a duration. To actually test his theory would require treating overlap and IVC as a fixed event and adjusting duration with the change in LSA. The tests treat duration as a fixed event and adjust overlap and IVC. Therefore, the LSA dyno tests aren't really showing anything about his theory.

Is there any test out there to show dyno tests of camshafts with identical overlap and IVC closing points that would validate David Vizard's theories? Doing this type of test would mean the narrower LSA was ground with less duration and advance that the wider LSA.

I'm in the process of planning an engine build and am greatly interested in the results of such a test before I order a cam. One cam designer has come said 285/289 on 113.5 LSA for a 408 Windsor with Trick Flow 11r 190 heads and about 10.5:1 compression. This gives 60 degrees overlap. Using the David Vizard formula gives me closer to 273/277 on 105 LSA and 65 degrees overlap. There is obviously a world of difference between these two cams. I would really like to see how a dyno test of his formula keeping overlap similar plays out before making up my mind.

Thanks!
Robert

Forget the 128 thing. Get yourself a good simulation program, know where you want the torque band to suit your vehicle and application and start playing around with profiles. When you have zeroed in on a few profiles talk to your cam grinder for final selection.

[F-BIRD'88]

The 128 number is not correct for the twisted wedge head. It will be a larger number.. DV can advise on that. Ask him. Its his formula.

[skinny z]

DV appears to have left the building.
HE contacted ME regarding some perceived misconceptions I had when discussing his 128 "formula".

viewtopic.php?t=65977&start=30

What I was trying to do was play nice with many of DV's detractors while still putting a positive spin on how he specs a cam and how I eventually had mine done (Thanks Jones Cams!).

[skinny z]

If you test with a fixed ivc you are simply testing how much overlap your motor likes.

Seems a seldom discussed topic as the overlap is considered by most as something that just "happens" when the cam is scienced out rather than formula or chart based.
FWIW, from a carbureted tuning standpoint, having the overlap of cam "A" and how it's been managed (tuning-wise) if nothing else gives me a jumping off point for cam "B" should that value be significantly different.
What I can say from the meager amount of test time I had before other car variables got in the way (such as a transmission) was that my newly spec'd Jones cam sounds and behaves remarkedly different from the off the shelf cams I had previously been running. But that evaluation is purely subjective as it's never ben race tested.
This is despite very similar compression ratios.
Previous 288/294, 236/292/ 110/104. 10.2 SCR / 8.07 DCR. 66° ABDC IVC. Cranking pressure 160 (185 theory). Wheezy worn out shortblock.
Current 284/280, 232/236, 108,104. 10.24 SCR / 8.23 DCR. 64° ABDC IVC. Cranking pressure (188 theory) Actual still untested.
Overlap went from 71°to 66°.

[F-BIRD'88]

I have a choice but I'd also like to steer you to Mike CAMKING Jones Cams. Let him spec a cam for your car.
Go to his web site and fill out his cam recomendation form, with all the needed info. It is free and his cams are good.

I'll keep my spec to my self..

[F-BIRD'88]

DV has his own forum section. on Speed-Talk. You can go there, create a thread and ask DV about your engine.
Or you can DM him privately also.
Don't be afraid to ask.

[Tom68]

Overlap went from 71°to 66°.

6 thou overlap I take it. We could also call that idle overlap since even 6 thou opening will see some exhaust flowing into the manifold at idle.

50 thou overlap we could call power overlap since at WOT we want the exhaust pulling on the intake at that sort of opening.

Cynical me says overlap is a result of valvetrains needing ramps to get valves to an amount of opening that has some flow.

There may well be an ideal overlap for power for a given combination but the more power you can make with the least overlap makes most everything else better.

[HQM383]

DV appears to have left the building.
HE contacted ME regarding some perceived misconceptions I had when discussing his 128 "formula".

Did he set you straight with the misconceptions?

[skinny z]

Overlap went from 71°to 66°.

6 thou overlap I take it. We could also call that idle overlap since even 6 thou opening will see some exhaust flowing into the manifold at idle.

50 thou overlap we could call power overlap since at WOT we want the exhaust pulling on the intake at that sort of opening.

Cynical me says overlap is a result of valvetrains needing ramps to get valves to an amount of opening that has some flow.

There may well be an ideal overlap for power for a given combination but the more power you can make with the least overlap makes most everything else better.

Something to consider too is the increased lift during overlap. I trust the lobe profile I now have is superior to the one I did have. Although less seat to seat timing, the window is not as small as first perceived.

[skinny z]

DV appears to have left the building.
HE contacted ME regarding some perceived misconceptions I had when discussing his 128 "formula".

Did he set you straight with the misconceptions?

No sir.
My PM reply is still in the outbox.
Interestingly though, I have no misconceptions at all. My grasp of his approach and that of say a Mike Jones is all very clear. I'm just trying to be diplomatic.

[Tom68]

Overlap went from 71°to 66°.

6 thou overlap I take it. We could also call that idle overlap since even 6 thou opening will see some exhaust flowing into the manifold at idle.

50 thou overlap we could call power overlap since at WOT we want the exhaust pulling on the intake at that sort of opening.

Cynical me says overlap is a result of valvetrains needing ramps to get valves to an amount of opening that has some flow.

There may well be an ideal overlap for power for a given combination but the more power you can make with the least overlap makes most everything else better.

Something to consider too is the increased lift during overlap. I trust the lobe profile I now have is superior to the one I did have. Although less seat to seat timing, the window is not as small as first perceived.

Opening of each valve on each Cam at TDC would be a good comparison.

[Geoff2]

The 128 rule was for SBC, but works well for parallel valve heads. CR of 9.0-10:1. It depicts the best LSA for those parameters. There are correction factors when the factors fall outside of those mentioned. Eg, BBC, I believe 132 is used, not 128.

All the DV haters/detractors carry on about DV & his 128 rule, but as yet I have not seen ONE test that has disproven 128. Lots of noise & fluff. Nor have I heard of anybody who tested 19,000+ cam profiles, which is where the 128 rule originated.

One thing I see mentioned a lot by the detractors is....LSA is just 'a number'. Yes it is; it tells you where the max valve opening occurs. taking a 106 LSA as an example, that would be the exh valve fully open 106* BTDC & the intake fully open 106* ATDC. Couple with piston speed, I would think those would be important numbers for airflow into & out of the cyls.

A guy who calls himself the 'Cattle Dog Garage' tested the 128 rule to see how good it was. It is a You Tube video, goes for 34 min [ not the 1hr + video ]. Sorry, do not know how how to link.

[digger]

All the DV haters/detractors carry on about DV & his 128 rule, but as yet I have not seen ONE test that has disproven 128.

what is the specific claim to be disproved exactly? i'm pretty sure ill be able to find a dyno result from the public domain