headers for small overlap cams

[dynoflo]

will an engine with only 13 degrees overlap respond to tuned headers as well as a high overlap cam does?

[panic]

That's the OL @ .050" Yes? Need the nominal, lash, or .006" duration.
No, the overlap "window" (degrees with both valves open) area is roughly proportionate to the square of the nominal OL duration, divided by 100 to get a useful number (HT: Vizard). Increased OL or narrow LSA opens the window very quickly.
Example: IVO 40° BTDC, EVC 40° ATDC = 80° OL, square is 6,400, area factor is 64.
Extending each position by 10°: IVO 50° BTDC, EVC 50° ATDC = 100° OL, square is 10,000, area factor is 100: 56% larger.

I don't know the minimum effective size, I suspect a small window with a very strong signal (small primary, high static CR, early exhaust opening) will work as well as a larger window with a big primary, etc.
90 years ago, low CR engines with very small OL used huge exhaust valves and ports: reduces pumping loss.

[maxracesoftware]

will an engine with only 13 degrees overlap respond to tuned headers as well as a high overlap cam does?

from another Thread ,

even if an Engine has negative Overlap Period Cam specs ,
it will still benefit from Header Tuned Lengths/Diameters because negative wave pressure helps decrease exhaust pumping losses
as Piston rises towards TDC-Overlap Period

i've seen this effect on my Dyno tests many times

[ptuomov]

Negative overlap at 0.050” or actually negative overlap at the seat events?

With literal negative overlap, I guess pulling a vacuum in the combustion chamber at the time when EVC still helps.

[nitro2]

The exhaust can be designed to increase HP/TQ for ANY cam, even negative overlap cams as mentioned. Three main benefits: 1) reducing pumping losses, 2) reducing intake charge contamination, 3) reducing/eliminating reversion. 2) and 3) are related but not exactly the same thing.

Intake length tuning can also be made to work well with ANY cam not just big overlap/long duration cams.

[pdq67]

Two questions!

1. Will small headers help a 283 with a generic, "Performer", cam in it? (204/214 cam)...

Just would like a bit more out of it is all.

2. And does anybody make 1.5" diameter, 4-tube, long tube headers to complement this cam in a small engine?

Just dreaming is all..... Say, a small boat engine..

pdq67

[CamKing]

will an engine with only 13 degrees overlap respond to tuned headers as well as a high overlap cam does?

What would tuned header length have to do with overlap ?
You tune the header length, so the pulse is moving away from the exhaust valve, as the exhaust valve opens, so it will evacuate the cylinder sooner. You want the pressure in the cylinder as low as possible, when the intake valve opens, so the intake charge will fill quicker. The purpose for tuning the headers, has nothing to do with overlap.

[skinny z]

What would tuned header length have to do with overlap ?
You tune the header length, so the pulse is moving away from the exhaust valve, as the exhaust valve opens, so it will evacuate the cylinder sooner. You want the pressure in the cylinder as low as possible, when the intake valve opens, so the intake charge will fill quicker. The purpose for tuning the headers, has nothing to do with overlap.

Isn't there an advantage to exposing the intake tract to this low pressure so as to start the filling process with greater energy? That is to say, with the exhaust and intake in overlap, the suction created by the receding exhaust pulse draws on the intake with greater effect?

[CamKing]

Isn't there an advantage to exposing the intake tract to this low pressure so as to start the filling process with greater energy? That is to say, with the exhaust and intake in overlap, the suction created by the receding exhaust pulse draws on the intake with greater effect?

To get the intake tract moving, you just need the pressure below the intake valve, to be lower then the pressure above the intake valve.
That's what the tuned length exhaust helps with. It causes a wave that heads down the exhaust port, from the exhaust valve, when the exh valve starts to open, and helps evacuate the cylinder more efficiently, reducing the pressure underneath the intake valve. That's the goal, no matter if there's a lot of overlap, a little overlap, or no overlap.

[GARY C]

Isn't there an advantage to exposing the intake tract to this low pressure so as to start the filling process with greater energy? That is to say, with the exhaust and intake in overlap, the suction created by the receding exhaust pulse draws on the intake with greater effect?

To get the intake tract moving, you just need the pressure below the intake valve, to be lower then the pressure above the intake valve.
That's what the tuned length exhaust helps with. It causes a wave that heads down the exhaust port, from the exhaust valve, when the exh valve starts to open, and helps evacuate the cylinder more efficiently, reducing the pressure underneath the intake valve. That's the goal, no matter if there's a lot of overlap, a little overlap, or no overlap.

So technically changing either the cam or the header alone may not show a power gain where changing both if matched correctly could or should?