Another "How much will it make?" Project "Special Needs"

[CGT]

but it's also a very good indicator of the overlap window requirement as well

By measuring reverse flow? How do you determine overlap requirements from flow at 28 inches? Even if comparing to other or previous combinations, how do you know the previous combination's overlap requirement was right, wrong, close, etc?

EVO is mostly the size of the cylinder at that crank angle vs rpm. On special needs the piston is 2.84" down the bore at 60* BBDC. That leaves .66" of piston travel BBDC. How much pressure could there still be at that point, and how much possible force could it still apply at that rod/crank angle??

Very interesting point. The power stroke would have to be all but done at that point, and that's assuming that the EVO isn't delayed by deflection in the system against pressure at that point. The EVO may not be quite as early as the numbers suggest in a dynamic state. Of course EVO at .006 (seat duration) is another 30 deg or so earlier yet.

[F1Fever]

I've read 80% of the power is transferred by 90* crank rotation with the majority being way earlier in the rotation.
There is a thread in the advanced section that deals with bore centerline being offset from the crank centerline

[GARY C]

You have all the good stuff I should be asking you.

I have the good stuff???

You have cos cam and ci, I have to pick camz the old way, by looking at previous results.

Randy

How do you think Cos Cams came about? I think my posts about CI are clear.

[groberts101]

but it's also a very good indicator of the overlap window requirement as well

By measuring reverse flow? How do you determine overlap requirements from flow at 28 inches? Even if comparing to other or previous combinations, how do you know the previous combination's overlap requirement was right, wrong, close, etc?

Sorry.. written too quickly and used one entirely wrong word in that reply. Should have been.. "it's also a very good indicator of the overlap window AVAILABILITY as well".

Although I fudged it up a bit, I was simply trying to convey that flow data can be and is often used to more accurately and optimally spec the camshafts timing events based on the castings/port designs available overlap flow window. Without more comprehensive data being given to the cam designer in relation to the actual capability of the cylinder heads tested flow rates and more specific E/I bias, he'll simply need to base his recommendations on previous experience with cylinder heads of similar design and flow capability. Running blindly on "expected average's" simply creates less resolution for the cam designer to better spec final timing and overlap requirements. Hopefully I didn't fudge it up as badly this time around.

[randy331]

Sorry.. written too quickly and used one entirely wrong word in that reply. Should have been.. "it's also a very good indicator of the overlap window AVAILABILITY as well".

Although I fudged it up a bit, I was simply trying to convey that flow data can be and is often used to more accurately and optimally spec the camshafts timing events based on the castings/port designs available overlap flow window.

Any chance you'd tell me what you'd do for cam for the engine in this thread with the flowZ I posted for it on page 5, vs what you'd do differently VS the flowZ zums posted on his valve job test at the top of page 6 ? And, more importantly, why.

The heads I posted about on page 5 are the ones going on this engine, the ones zums posted aren't, but I'd like to see what you'd change cam wise IF they were?

Well,...maybe zums will send his heads for testing too?????

Part of the charity parts program discussed earlier!! LOL

We'll call it, " The no racer left behind " program.

Randy

[zums]

We'll call it, " The no racer left behind " program.

Randy[/quote]

I thought it was the "all Heads Matter" program, :
I think rpm should be top on the list for cam choice, for a quick dirty look at flow being part of cam choice just look at a typical 462 gm casting , that thing peaks at 221 cfm maybe @ .55 and 158 cc, and you are in super stock ,you gonna run a 223* @ .05 .55 lift because of the sheet, or 281* @ .05 .69 lift

[randy331]

The engine this thread is about has 2.08 intake valves, but 50* seats. So I figured up the actual window area this set up has vs a common 45* seat at the low lifts. ( .050" - .200" ). If one were to spec LSA with 128 for this engine, would it be fair to use the valve size that, with a 45* seat, gives equivalent window area at these lifts?

Below is the valve size that gives the equivalent window area with a 45* seat as the 2.08" valve has with a 50* seat.

Lift----valve diameter
.050"----1.890"
.100"----1.875"
.150"----1.921"
.200"----1.928"

So, about equal to a 1.90" valve on average at those lifts.

359 / 8 = 44.875
44.875 / 1.90 = 23.69
23.69 x .91 = 21.49
128 - 21.49 = 106.51

Is my math right?
Should special needs have a 106.5 LSA ?
And rounding down is better so 106 ?
Or would 105 be even better cause it's still short on flowZ at .250 lift vs a conventional 45* 2.08" valve?

Randy

[RevTheory]

That's an interesting way to go about it, Randy and you're probably right in doing so. If that's the case, then yes. Add in +0.6* for a 1.6 rocker and an aggressive lobe and you could justify a 107 LSA.

As for going tighter, I'm not sure if I'd go that way or advance the cam beyond the standard +4*. I suppose that depends on how well the exhaust is doing during overlap. Having said all of that, I have ZERO experience optimizing cams with those seat angles so take it for whatever it's worth.

[CGT]

Well the exhaust side has a 50 deg seat as well. So its going to show a very small window for valve size through those lift ranges as well.

[randy331]

Well the exhaust side has a 50 deg seat as well. So its going to show a very small window for valve size through those lift ranges as well.

Just wondering if you ever got the right cam ordered for this engine?

Randy

[steve316]

What would be the right cam?

[sjre]

DEFINETLY waiting for results!!!!!

[CGT]

Loaded up and ready to go! Will be trying the previously mentioned cam first, then going from there.

[CGT]

What would be the right cam?

Got a couple ideas for a potential cam test, I know Randy does as well. Cam selection is a very controversial subject around here, so I am trying not to impart valvetrain drama upon this thread.

I'd like to have one ordered to test on dyno day, but on the other hand I'd really like to see what I can learn from cam positioning with the current cam first.

Who knows, I do plan on having fun and learning regardless.

[RevTheory]

It's all about the flowz!