Don Terrill’s Speed-Talk

I was going to post this in the other thread about reversion but think this deserves its own thread as it has several applications outside the scope of that thread.

Many here will remember the A/R cone headers that David Vizard promoted. Those really worked well by broadening the power down in the rpm range well beyond what the engine could tolerate with conventional headers. I think they were a sensational idea for serious engines that will see street use or require broad power (incl. road racing). Yet nobody seems to bother making cones anymore.... so question:

Is the benefit of simply running a larger header flange hole compared to the exhaust port in the head just as great as a proper port extension A/R cone with a primary pipe flared over it?

I'd think not as it seems too easy - but would greatly respect the opinions of people much wiser than me on this.

I'm not talking about peak power - let's assume both designs are close enough at the top 2000rpm of the engine range. I'm asking which design will pull better off idle and up to the point when the cam kicks in?

I believe the D shaped exhaust port on the newer head design is to address reversion issues.

IIRC, Vizard's testing indicated that anti-reversion cones only work in the
presence of a crossover pipe at or near the header collectors. Apparently,
the length of the cross-over is less important than its location. One of
the pictures I recall showed the cross-over connected at the collectors but
routed over the top of the dyno. Must have been an 8 feet long length of
tube. Also, the effect was greatest with relatively narrow lobe center cams,
presumably due to the greater reversion. Cyclone had the patents on the AR
headers but were bought out by one of the other header manufacturers. I
forget who they were but I called them years ago and they said they dropped
the entire line of AR flanged headers, claiming they didn't perform as
advertised. My guess is, if they were tested at all, they were tested on an
engine without a crossover and/or with a wide lobe separation cam.

> Yet nobody seems to bother making cones anymore....

I'd heard the Japanese import guys are putting the cones in the primary pipes
so I did a quickie search and came across an interview with John Grudynski of
HyTech Exhaust. In the interview, he said he had seen an old ad in "Car Craft"
magazine for headers with the anti-reversion chamber. He then called Jim
Feuling who designed them, got a set and started adding them to his header
designs for Honda inline 4 cylinder engines. He claims to have the rights
to their use now.

Dan Jones

We favor a port mismatch and the style pictured.

> We favor a port mismatch and the style pictured.

So the chamber is just an area change without anything (like a cone) inside?
Is the placement along the primary length important?

Dan Jones

The primary steps to the next larger size in the anti-reversion chamber. Since the primary extends into the chamber with a "square" edge, reverse flow doesn't like to enter. We've found that the first step is the best place for the chambers. In our experiments on the dyno and in the real world, placement didn't really seem to matter, as long as the chambers were no further than a foot away from the flange.
In combination with a significant port/primary mis-match, the chambers allow us to open the intake valve earlier without diluting the mixture with inert contaminents.

While only somewhat related, on many of the engine programs where we're working within EPA regulations, we can induce EGR by opening the intake valve a little earlier, eliminating the necessity of the EGR valve and related plumbing.

I am wondering in this as in the other thread, what kind of reversion are we talking about.
A restricted inlet, high vacumn low or high rpm?
Overcamed engines that have to be yanked down in rpm?
4 valve-4cyl engines having much better low lift flow more prone to the problem as well as more time between pulses...?
2 valve engines, unlimited intake and such...?
Simple cylinder dilution...? Carbon on the throttle plates?

IMO, 4 valve heads, being more recent in design and manufacture, come from computer designs. Rarely do they get "opened up" or ported with any benefit
as they are already larger than they should be. The headers are already too large cause the port is and now your bottom end power benefits from anything that attenuates the pressure waves and kills backwards flow, ie your not using any of the energy in exhaust to try and increase efficiency.

The Honda heads we do for the quickest all-motor front wheel drive car in the world move over 400cfm at less than .600" valve lift. The heads begin life with ports that flow about 315cfm, so our porting makes what I consider to be a significant difference in airflow. We use chamber and piston crown shape to mask flow from the exhaust to the intake during overlap.

Isn't Jeremy Lookofsky the quickest?

Larry Widmer wrote:The Honda heads we do for the quickest all-motor front wheel drive car in the world move over 400cfm at less than .600" valve lift. The heads begin life with ports that flow about 315cfm, so our porting makes what I consider to be a significant difference in airflow. We use chamber and piston crown shape to mask flow from the exhaust to the intake during overlap.

I am assuming that is a all out drag motor? Low lift flow must be something.

Bazman is talking street motor headers I think and most stuff I have seen I think is larger than it needs to be. A 4-2-1 design would offer the largest power curve. Adding area step mismatch at port might offer a bit more help but I always try to keep tube diameters smaller for the first 8-12 inches.

BAracer wrote:Isn't Jeremy Lookofsky the quickest?

...we've done every Cartel Custom cylinder head, including Jeremy's personal race heads for the last two-three years. We do 4-5 heads per week for Jeremy, and these proprietary designs are only available through Cartel Customs.

I had an 86 mazda 4 cylinder that had anti reversion cones from the factory, I pulled them out to see what difference it would make without them. Low end power dropped very slightly using the butt dyno, the top end picked up noticably, everyone who drove it without the cones commented on how well it went for a stock 85 mazda 4 cylinder. I concluded that the cones were probably put there for emission purposes!

Thanks guys. I like Larry's idea best, it is functional, simpler from a fabrication point of view, and doesn't require a cross over pipe that looks like spider legs.

Larry - have you had a good play with the Chev LS esp. heads and roller wave type pistons yet? I'm keen as I have a project coming up and was look at building a new LS3 or 7

Interesting that you ask about the GM LS engines, as the powerplant I'm slowly building for my 63 Grand Sport replica is based on a RHS tall-deck LS race block: http://www.theoldone.com/grandsport/art ... dsport.htm
Right now, I'm waiting on a pair of Horace Mast's cylinder heads, which we'll be working over for the project. I will be developing some unique Roller-Wave pistons for the engine, and we will be making them for enthusiasts as soon as we've completed the R&D later this year.

I checked out that Grand Sport link - what a cool project!! GM's answer to the Cobra 427 with modern technology applied.

I like the Kinlser intake, not turbo friendly but awesome for NA.

Will be keen to know how the engine comes up, looks like it is going to be a monster.