Randy my friend you bring some good points and observations to the table, so lets talk.
Randy:
For cam over lap,or reversion of exhaust air can be somewhat takin care of
with proper built headers.
Mike:
You are correct Randy thats why designing and building tuned headers is more of an art form than a production process. The big header mfg'ers are more into production and sales than they are about producing a product with real world benefits, its all about the money baby!
Randy since you were a pro racer at one time I'm sure there was times that you were at the track with cars racing as well so you may know about a practice that I'm going to expose to everyone here that does not know about it.
The big header co's give contigincy(spelling) money to racers that advertise that they run there brand of headers, depending upon how they place in the race. A well known fact to all racers and the header mfg'ers is that the racers sporting the header mfg'ers stickers or metal name plates welded to there headers are NOT infact using there headers at all.
Truth is you could buy the metal name plates from Hooker headers from Summit or Jegs to mention a few places and weld them to your headers, if you placed well in those races where cont. money was given the header rep at the track would OK a check be cut to you as long as you have there sticker or nameplate.....am I the only one that this practice smells bad to?
All of that is done for the mfg'ers marketing boys and girls because they then inturn create an advertising blitz to promote sales by claiming so many good finish's at the race with there product. More like false advertising, but hey..they are displaying the co's decals on there car or the metal tag on the headers themselves so who knows otherwise.....right?
Randy:
As black as SC combustion chambers are ,I would say this may be a problem.
Mike:
You're onto something there Randy and all your experiance building and racing high perf motors has made you very observant, so consider this.
During my reply to Dave I talked about effectively scavenging the cylinders of burnt exhaust gases. Does it make sense to you that what you are observing with the blackened combustion chambers could also be caused by not effectively scavenging the cylinder of burnt gases as well?
Randy:
If you look at the floor of the exhaust port on a STEG head.
he does weld build up for the exhaust floors.To raise the radius for better flow.And he leaves the mouth floor of the exhaust header flange straight across the bottom.this is for reversion.
Mike:
You are correct Randy but there's more going on there than realized.
Stieg did not invent that port configuration, but let me be very clear about this. I am in no way trying to say or infer that Stieg is claiming to have invented that port, so please no flames.
That port was invented back in the early 80's by an a fella that I met and talk to from time to time named Larry Widmere. Those of you that do not know who Larry is he is the guy that built the heads for Bill Elliot when he set the speed record at Talladaga and pretty much dominated NASCAR. Another racer he helped was Bob Gliden when he owened NHRA Pro Stock. When Larry's support of these racers was pulled they withered away, he also built engines for Penske racing in the late 70's.
Anyway he designed that port as you mentioned Randy to seriously rework the short turn radius on Ford heads that proved to be a big holdback of power. One of the things that Larry accidentaly discovered by doing this was that the exhaust port now flowed at a supersonic speed. That inturn allowed the exhaust blowdown in the cylinder to happen very fast and much more efficently. The fact that the flat port floor caused a mismatch between the cylinder port and the exhaust header flange thus preventing reversion of the exhaust gases back into the cylinder was just a good side effect and not the intended reason for doing it.
By the way.....not to toot my own horn but I did that to my cylinder heads in late 99, I just never talked about it....speed secrets ya know! LOL!!!
Randy:
To make a header that works best all across the RPM range (daily driver).You will have to compromise.
Mike:
True dat is! But thats what makes designing headers fun, trying to come up with the best set of compromises for the big payoff.
Randy:
The best header is purpose built.One header for each job.
Mike:
True, but that applies to engines as well. Do we agree on that?
Randy:
If you build headers,I would want them to be coated with a heat barrier
and shiny.
Mike:
Well of course! LOL!!!!
I just noticed that I missed a few of Daves qeustions so the remainder of this post concerns those qeustions.
Dave:
Is that 1 5/8" primary pipe ID or OD?
Mike:
That would be OD Dave. All tubing is sized by OD where pipe on the other hand is sized by ID, that is the industry std.
Dave:
And where exactly do you find 2 3/8" pipe anyhow?
Mike:
Tubing Dave not pipe, that little slip of just 1 word when calling suppliers will get you the reply"Theres no such thing".
To be completely honest with you 2 3/8" tubing is not common but any big tubing supplier can get it for you if they do not stock it.