Camshaft lsa and low end torque

[hoffman900]

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

Necessary evil, flow though is only bad for economy and emissions, good for chamber purging and flame shows.

Are we building burger cruisers or is this Speedtalk?

You only have so much time to fill a cylinder, and any wasted fuel is wasted power. They're internal combustion engines at the end of the day (not air pumps like people wrongly attribute them). You can literally can convert that fuel to power potential lost.

The events and mechanical limitations of the valvetrain (and the derivatives it can handle) dictate the overlap area, and it is always more than enough, and most likely more than an engine needs. It’s almost that simple.

Like the I4 examples people asked about. I’ve been involved in a few of those. They all have small bores with heads with no included angles, so they are absolutely starving for air. Furthermore, valvetrain geometry, lifter diameter, and rocker placement means valve lift is limited. Add in they are relatively low revving, and now you have a lot of duration to make up for lift limitations, your EVO and IVC events means with all that duration, you have way more overlap than you’d ever want.

I do know of an example where Mike spec’ed a cam for one of those engines types and his centerlines and events meant for a wider LSA. The engine made more power and used less fuel than just about every other design over 40 years of racing history. How about that…

[Tom68]

any wasted fuel is wasted power.

Evil desirable necessity.

To have the valve open enough to fill the cylinder at high speed you have to get it underway well before the piston reaches TDC.

We don't have instantaneous valve opening yet.

[ClassAct]

I stopped looking at it that way -

Initiates the beginning of your intake stoke. It's a tool. Figuring out how to use it effectively is the issue, at least for me anyway.

Necessary evil in production cars, a power producing necessity in race cars.

I think Warp knows some things.

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

You need just enough to “talk” to the intake port. Anymore just sucks fuel out the exhaust. Fuel in the exhaust pipe just makes things glow, it makes no power as it’s now not in the cylinder. George Bryce even talks about how little overlap he runs on his Pro Stock Bike engines.

I read Godbolds book (more than once) and he said no such thing as you infer it. Not even close.

[Tom68]

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.



Are we building burger cruisers or is this Speedtalk?

We're building lawn mowers, snow mobiles, burger cruisers, Flat Heads and anything else you can think of. We're not building F1 motors, we just look to them for inspiration, well at least we used to.

I read Godbolds book (more than once) and he said no such thing as you infer it. Not even close.

Think he got confused with LSA.

Harold did seem to hate overlap, but I'm sure none of the others did.

[Tom68]

OK, so I got Billy's book out. I don't always agree with the way he sees engine operation but he has way way more experience than me.
Since this is an LSA thread he did point out something that we all should remember, and I quote.

"Because every four-stroke engine is sensitive to low-lift timing points and numb to exactly where peak lift occurs, pay close attention to how lobe offset shifts timing points to properly compare various camshafts."
For the numpty's LSA is calculated from peak lift of intake and exhaust. With symmetrical lobes we accept peak lift measured from 50 thou points, but is your lobe symmetrical.

So we're back to valve timing events, EVO, IVO, EVC, IVC, pick your lift point, in regard to idling, 10 odd thou, in regard to power production 200 odd thou. MEASURED AT THE VALVE.
We measure at the lobe because it's simple, simple isn't good.

[hoffman900]

Necessary evil in production cars, a power producing necessity in race cars.

I think Warp knows some things.

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

You need just enough to “talk” to the intake port. Anymore just sucks fuel out the exhaust. Fuel in the exhaust pipe just makes things glow, it makes no power as it’s now not in the cylinder. George Bryce even talks about how little overlap he runs on his Pro Stock Bike engines.

I read Godbolds book (more than once) and he said no such thing as you infer it. Not even close.

He has said it in podcast interviews

[hoffman900]

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.



Are we building burger cruisers or is this Speedtalk?

We're building lawn mowers, snow mobiles, burger cruisers, Flat Heads and anything else you can think of. We're not building F1 motors, we just look to them for inspiration, well at least we used to.

I read Godbolds book (more than once) and he said no such thing as you infer it. Not even close.

Think he got confused with LSA.

Harold did seem to hate overlap, but I'm sure none of the others did.

There is only one person who harps on overlap as something you need to “choose” and everyone got so tired arguing against his fans on here, that it’s now a ghost town these days.

You need overlap, but my argument is that it is not the tuning tool that one person has argued, and the results of the events means you have plenty.

George Bryce:

I have a different view...our overlap, in all of the cams we race are result of the opening required to have the intake valve, far enough open when the piston is going the fastest, on it's way down the bore...so the inlet port can let the most atmosphere enter into the void left by the fast moving piston.
We do not design our over lap...we move the intake valve the fastest we can. So it is the most open....on the intake stroke...when the demand is the most. Between 75 and 78 ATDC.

If we wait till TDC to start the opening ...then it will never be open enough ,lift wise, to do us any good....as the piston is speeding away..75 or 78 ATDC is the fastest it goes.
The way earley valve opening is a means to an end..NOT an advantage, sorry. If your cam designer could move your intake valve fast enough to match the piston speed, he would...He cant. Several reasons he cant...1 if he does..he cant stop it at full lift.....so he has to design the lobe to help the parts follow the lobe...
"Things at rest tend to stay at rest"...so he needs to gently start the valve moving, then accelerate as quickly as possible. When it gets near the peak lift...he has to slow it down.."things in motion tend to remain in motion"....so all of this starting, moving, hauling ass, slowing down and stopping...just from IVO, to peak lift, 100 times a second.
This stuff take a lot of degrees crankshaft rotation.

On the Exhaust side...We run overlap because there is not enough time to get all of the ex out when we should have. Several reasons...the ex valve is too small, the pipe is too small, the port is too small...the EVO is at the wrong time...Because us N/A engine builders want the biggest intake valve we can fit..." bigger intake please",,...."exhaust valve?" Nah,...just put 320 degrees on that lobe, at .050 ...."it is not that big of a deal"....How do we fit 320 degrees on there? Start way too soon...close it way too late...that way we can have "a cool thing called overlap...let the pipe do some more work"....because of all the gently starting, moving, accelerating, ass hauling required...then slowing down and coming to a close and not bouncing..when we land on the seat...all to get the exhaust valve at full lift near the BDC so all the ex can get out of a teeny weeny little valve and port....

This leaves us with "clipping" clearance problems on overlap...intake valve is opening and it bumps into a closing exhaust valve...this is overlap to me...
Last horrible result of overlap is dang deep piston pockets...Intake pockets are so big and deep..99% of piston failures are right in the space the top ring and the valve pocket try to share. Why are the intake pockets so deep....because we need the intake valve open about .250 lift at TDC!....Why? Go back and read the 1st part of my rant.. Sorry for the very incomplete ramble...oh BTW...I dont like much overlap...

Hey, I am just talking about what I think. I think that through history, we have opened the valve faster and faster and quicker.
It needs to close where it needs to close to suit the rpm we run in...to trap the most mixture.
It needs to open as late as it can and still be going fast as it can to match depression in cylinder.
We get many gains in power, thinking of it this way....
If you are convinced that overlap is planned, needed and you configure your engine/cam design to suit overlap...GOOD!
All I am trying to say it is a by-product of "left overs" in event planning....
Intake closing
Exhaust opening
Intake opening
Exhaust closing
-
-
-
-
overlap

THAT is the order of importance to us. US!!! at this time...just us

You can go back through threads here since 2007 on this stuff. This is a thread that pops up every 6 months.

[gregsdart]

But it is a great read. LSA and low speed torque to me mean how much torque can i generate at 6200 rpm, because that is where my converter flashes to.
The compexity of cams and race valvetrain parts bogles my mind . Finding out i lose .040 max lift with the springs i run, then getting a bit better spring and now i only see .030 loss of lift, but know that also coresponds to the valve opening when it is accelerating. Also, jusst how much duration do i lose on the opening sides of the valve motion? Cam twist? A lot to think about when you go beyond stock parts!

[Warp Speed]

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

Necessary evil, flow though is only bad for economy and emissions, good for chamber purging and flame shows.

What I mean by necessary evil, is that you need it to cleans the chamber, and to help initiate positive intake flow while opening the valve prior to TDC, but like many other things, it can inhibit proper valve events. The old compromise thing again! Lol

[JC565Ford]

What I mean by necessary evil, is that you need it to cleans the chamber, and to help initiate positive intake flow while opening the valve prior to TDC, but like many other things, it can inhibit proper valve events. The old compromise thing again! Lol

Well stated.

[JC565Ford]

I think Warp knows some things.

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

You need just enough to “talk” to the intake port. Anymore just sucks fuel out the exhaust. Fuel in the exhaust pipe just makes things glow, it makes no power as it’s now not in the cylinder. George Bryce even talks about how little overlap he runs on his Pro Stock Bike engines.

You actually just agreed with me -

[hoffman900]

I think Warp knows some things.

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

You need just enough to “talk” to the intake port. Anymore just sucks fuel out the exhaust. Fuel in the exhaust pipe just makes things glow, it makes no power as it’s now not in the cylinder. George Bryce even talks about how little overlap he runs on his Pro Stock Bike engines.

You actually just agreed with me -

I agree with you more than you think.

[JC565Ford]

There is only one person who harps on overlap as something you need to “choose” and everyone got so tired arguing against his fans on here, that it’s now a ghost town these days.

You need overlap, but my argument is that it is not the tuning tool that one person has argued, and the results of the events means you have plenty.

You can use it to your advantage if you understand what's going on. It very much depends on what you're trying to build
RPM Range. Related parts Tri-Y headers, merged collectors, ex rocker ratio, they can all work together.

[Stan Weiss]

Unless I misunderstand Prof. Blair's work. He talks about overlap areas needed.

Stan

[hoffman900]

Unless I misunderstand Prof. Blair's work. He talks about overlap areas needed.

Stan

Is anyone purposely adding on a slow opening for explicit purposes of adding overlap volume and not for dynamic reasons?

Harold went the other way, where Comp’s “low shock” is about dynamics and was “found” because they flipped a Brookshire style lobe backwards and was better on the Spintron. As Mike has pointed out, it’s really just an inverse radius lobe.

Look at all the dams in chambers between the intake valve and exhaust valve, or “twisted” hemi’s for explicit reason to HURT overlap flow.