[Hotrocks]

I apologize if I was impatient in my previous question on this, and for it being a bit convoluted.

Always heard the Sportsman II's were lacking in the exhaust department. The guy who did the valve job back cut the valves 30° (intake also), and did a good job on tbe bowl blending and short turn.

Knowing to stay off the floors, I opened one exhaust port just a little on the sides, mostly on the roof. *Port is now about .055" taller, just outside of a 1404 gasket on the roof, (with gasket lifted to header bolt contact. I'm gonna use 1405's). Blended it in. Port heights average 1.355" tall, this one is now 1.410". 《Did I remove too much?

*The port isn't quite square, about .030" narrower near the top. 《Should it be more square?
I don't want to go any further or start on the other ports before getting some input. I wasn't near this doubtful porting smog era factory heads, lol.

 

[BogiesAnnex1]

The Sportsman II is something of a half step between the old Chevy Camel Hump dual quench head and the L31 Vortec in chamber and port configurations. If you’re not racing in a class that requires it I wouldn’t necessarily recommend it for a street of non-this class build. It really is heavy with pretty thick cross sections to withstand the rigors of racing, this really doesn’t bring much except more weight on a street engine.

The intake kind of follows along the L31 scheme where the floor is a bit wider than the roof of the intake port, this is done to slow the floor flow which also causes that layer to gain pressure this helps ease the flow around the short turn into the pocket.

On the exhaust side the major effort is usually on the roof as this is where the major flow concentrates. I find that you need to be conservative with the short side as putting too much flow here acts like a valve reducing total port flow.

These heads just ask to be ported and have plenty of meat in the casting, it’s really hard to do something that messes them up. I rather think the Chevy D port they love so much is a mistake. But really in the end even with Corvette heads they were dinking around with pumping up mid range torque more than top end power.

A really important aspect to exhaust flow is a good blend at the header. The exhaust is a very fast, hot, high pressure flow, you don’t want miss matches at the header flange.

In the end without a flow bench test it’s hard to say where the flows went, but in general it’s hard to do things that reduce flow, you simply make suboptimal improvements at worst.

Porting smog heads are what worry me as it’s easy to cut them into the cooing jackets.

Bogie

Bogie

 

[Hotrocks]

I'm aware that these heads aren't the most efficient, they don't flow so great for the intake runner size, and they're meant to be ported. But it's what I have, don't have the money now for a more efficient head.

I didn't think I went too far, but wasn't 100% sure. Didn't know if these wanted a specific shape and size to be optimal, and how tall is too tall. I guess if the port still fits within a 1405, it isn't too big. (It's close to the gasket on the roof and sides, plenty of meat on the rest.) So I'll at least make the other exhaust ports match the one. Gonna somewhat taper the guide bosses too.

As for the headers, I have 1 3/4 primary headers. The tubes are swedged into a square shape a couple of inches before the flange.
And the openings are small, only in the 1.300" tall x 1.26" wide range! Must've been made for stock ports. So I'll grind the openings to a 1405, especially the tops, (while the ports will be smaller). When I break through anywhere, just weld where that happens, which will probably be halfway around every tube, lol. Thanks.

 

[BogiesAnnex1]

The worst alignment is when the downstream component overlaps into the up stream. For intake to head port the worse is the head port puts a wall into the stream coming from the intake manifold. For the exhaust it is where the manifold or the header flange hangs into the head‘s port, just to be sure I’m clear about this. The opposite situation isn’t optimal as there is a condition called vena-contractra that occurs where a smaller passage abruptly dumps into a larger. In this case there is a natural occurring necking by the flow field, but this is nowhere as obstructive to the flow as when it hits a wall. So where you can try to make transitions smooth as possible.

Typically in porting probably 80% of the gains are in streamlining the valve guide projection in the pocket and next biggest offender being the pocket wall to the seat. The back cut behind the valve’s seat to streamline the seat into the backside of the valve this is very beneficial to the low through mid lift zone which the valve sees twice in its cycle so it is important. This applies to intake and exhaust valves.

You can jiggle different rocker ratios as well. The end cylinders of the SBC are more welcoming of higher ratio rockers than the inboards on the intake side. That is to say that using 1.6 to 1.7 rockers on the intakes of 1, 2, 7, 8 are more productive than long ratio rockers on the 3, 4, 5, 6 cylinders. This kind of balances up cylinder to cylinder power. Exhausts are happy with the same ratio all around except except cylinders 5 and 7 which are only 90 degrees apart and look a lot in flow terms as one large cylinder so using a higher ratio rocker on these two when using manifolds or short headers can pick up the flow, for long tubes dumping to a collector or to atmosphere this is less rocker combination is important.

Bogie