Exhaust Porting Help

[Rick360]

Does the 90% rule for valve throat size apply to exhaust ports also?

According to Darin Morgan's interview the flow bench can't tell you how to design or port the exhaust. Does anybody have any tips for the exhaust that show on a dyno or racetrack?

Does the exit velocity target that Darin speaks of, apply to average velocity or maximum velcoity?

On an exhaust port that has a sharp turn, is it normal to read negative velocity at the floor?

Thanks,

Rick

[cboggs]

Rick,

If you have some combo specific info that would help.
Every engine likes something different.

One thing that always shows on the track or dyno is turbulence.
If the exhaust port is turbulent I've almost always seen it on the dyno.

If I remember right the target air speed number Darin talked about
was specific to a 500" pro stock, .. although I do try to keep air speed
around the same number.

As for the negative number along the floor, .. yes I've seen that
on a few heads as well. I do a bunch of Pinto 2.L heads for road
racing that will do that. Doesn't hurt power in that combo.

Curtis

[Rick360]

The heads in particular are a set of 034 bowties w/2.05/1.60 on a 355sbc. Roller cam 268/276 .650" lift. 14:1 comp. Ported Victor Jr, 750holley, 1.875 headers.

This is the same heads I got some help on the intake side, on this forum, a while back. Now I am looking over the exhaust for any HP I can find there. But its hard to see it if you don't know what you're looking for.

Rick

[maxracesoftware]

Rick be very careful porting or opening up the
exhaust port on a #034 Bowtie head...
that particular Head was cast smaller in the exhaust port than most
other Heads you'll come across.

its a lot safer to "widen" that exhaust port,
than to raise the roof or increase the vertical height of that port.
there's water everywhere,
even widening the port has to be done very carefully !!!

On an exhaust port that has a sharp turn, is it normal to read negative velocity at the floor?

did you try that same Flow Test / Pitot Probing with a short Pipe attached to the exhaust port ?

[Rick360]

did you try that same Flow Test / Pitot Probing with a short Pipe attached to the exhaust port ?

No, my pipe I use to flow with is curved and is too long to reach the port with my pitot tube with it on the head. How long a pipe is needed to simulate a header pipe properly?

Rick

[cboggs]

Larry to the rescue !!!

Thanks larry, .. as I can offer NO advice on a head I'm not familliar with.

BTW, .. did you get the e-mail I sent???

Curtis

[bill jones]

-cut a short piece of curved exhaust tube, hold it up to the port and then rotate it up down left and right and see what happens.
-I found that when the pipe comes out and down that it makes the air flow across the floor much better than if the pipe goes straight out or upward.
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-In real life there is always a pipe attached so if you are measuring with a pitot tube you need to make the exhaust pipe with an access hole so that you can fish the pitot tube in thru there to see what happens with the exhaust tube in place and facing the exact direction it will be in real life.

[joe]

Jones you come up with summa the coolest stuff I've ever heard ! that deal about checking byrotating the x tubing is one of the best I've heard , have you ever used a mandrel too bend the tube as you flow too see what makes the x port work best ?
That tip about flowing flathead valves was very instructive also !
Been hot rodding for a while have you ?[/quote]

[maxracesoftware]

No, my pipe I use to flow with is curved and is too long to reach the port with my pitot tube with it on the head. ---Rick

did that curved pipe .. increase the Exhaust Flow when you attached it ??

How long a pipe is needed to simulate a header pipe properly?

the purpose of using a Pipe is to ;

1-most Exhaust Port's short turns/Floors are "still in the process of turning"....and a Pipe helps to straighten out and transition flow out of the
Exhaust Port.....that's why, almost 100 % PerCent of the time, an Exhaust Port will flow more with a Pipe -VS- without a Pipe.

2-to see how much an Exhaust Port is ultimately capable of flowing in CFM

i use various diameter short 4" inch long Pipes , most all have the exit lip of the Pipe rolled/formed to a small radius exit ledge.
by using that small radius at the end of the Pipe's exit,
it lets the air transition into the atmosphere smoother with higher velocity and less turbulence, increasing the Exhaust Flow CFM.

this radiused-exit short Pipe makes the Exhaust Port flow as much as it can....so when i do bolt on and tryout the real Headers on the exhaust ports , i have a baseline CFM number to compare against.

same as Flow Testing on the Intake side.....
using a radius entry almost always makes a Cyl Head flow more
than not using a radius entry or bare head Flow Test .

you're trying to see what a Cylinder Head is "ultimately" capable of Flowing in CFM on both the Intake and Exhaust sides....in that way,
you have a Flow Number to compare against when you tryout
or bolt on an Intake Manifold + Carb to see how much restriction,
or if you bolt on a Header to see how much flow restriction that causes.

Thanks larry, .. as I can offer NO advice on a head I'm not familliar with.
BTW, .. did you get the e-mail I sent??? ------Curtis

No ... i just checked my Email . just send me a PM on this Forum .

[bill jones]

-JOE,,,
-it was real hard to get some headers onto my SF 300 bench with the exhaust ports facing towards me.
-I had to notch the steel plate top of my flowbench so I could get certain headers to fit.
-That was in the early 1980's so I've forgot a lot of what happened when I was "going to school" on air flow.
-I do NOT normally use a tube an any exhaust.
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-I normally always flowtest at 25", because I had access to more believable flownumnbers and I have well over 200 pages worth of 25" flow data and that's about 6 months worth of work to convert everything to 28", so I do the 6% math to get there.
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-When I was actively building headers as part of my engine building & tuning & racing efforts I would work with the curve angles off the exhaust ports to try to stay where it always helped flow.
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-The heads that I have done the most work on mostly are all production based low port 23 degree SBC's so they pretty well all like the pipe to come out and down somewhat.
-Two things that I did find about headers is perfectly round tubing is not necessarily the best contour for the crossection of the bends, and where the tubes enter the collector the pipes all need to be basically straight for about 4 pipe diameters before they get collected.
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-One other thing is when testing headers is you drill a "Smokey" pyrometer hole in each tube so that you can test the suck power of the other 3 headers tubes while you are flowtesting one cylinder.
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-I forgot what the flathead chat was about.

[Rick360]

did that curved pipe .. increase the Exhaust Flow when you attached it ??

Yes, in every test I have ever done the pipe helped the exhaust flow. Usually 5% or more.

Thanks for the info. I might try radiusing the exit on my pipe to see how it works. I also may try to put a small hole in it for my pitot probe to measure inside the pipe up close to the head exit.

One of my original questions that nobody has addressed yet is the 90% rule and whether it applies to eshaust ports also or is it a smaller number?

Rick

[maxracesoftware]

One of my original questions that nobody has addressed yet is the 90% rule and whether it applies to eshaust ports also or is it a smaller number? ----Rick

i use .89% to .90% PerCent of the Exhaust valve OD
to set the Cutter to bore the seat insert area
then just Radius Cut the seat , then blend radius into the .89-.90 bore cut

you can push this seat insert bore area more to .91-.92 % PerCent
but you will loose most of the radius transition into the seat-bore
and almost always reduces Low to Mid-Lift Flow , with a little better
High Lift Flow , but can greatly increase port noise and turbulence

you can use a "Tulip-Shape" exhaust valve to help out Mid-Lift Flow
especially if made out of lighter Titanium, also you can keep Exhaust Valve margins thick ( .080-to-.120" thick) to help out.

the Tulip-Shape will pickup the Exh Port velocity up and usually Flow better overall.

[bill jones]

-Personally I have never been able to get a flow number curve I like with the exhaust ports that big so I tend to make all my exhaust ports too small particularly at the venturi or choke.
-On a 1.600" valve I like to stay at about 1.360" (.85 of the valve diameter) or smaller thru the venturi but I move the venturi towards the short turn side slightly.
-I would rather have the bowl smaller to start with so I can shape it to my liking.
-I do NOT want the bowl cut with a cutter that centers off the valve guide centerline as I never can make'm flow, it's just something about how I port heads and the equipment I have to work with.
-The throat is not usually round but more of a slightly tri-oval or tri-oblong shape.

[Darin Morgan]

-Personally I have never been able to get a flow number curve I like with the exhaust ports that big so I tend to make all my exhaust ports too small particularly at the venturi or choke.
-On a 1.600" valve I like to stay at about 1.360" (.85 of the valve diameter) or smaller thru the venturi but I move the venturi towards the short turn side slightly.
-I would rather have the bowl smaller to start with so I can shape it to my liking.
-I do NOT want the bowl cut with a cutter that centers off the valve guide centerline as I never can make'm flow, it's just something about how I port heads and the equipment I have to work with.
-The throat is not usually round but more of a slightly tri-oval or tri-oblong shape.

I do it EXACTLY like bill just stated except for one small thing. I use a 91-92% throat because in the engines we crowd the valve over the chamber wall and the exposed area to the chamber seems to be more important than the amount of flow on the bench. In most engines the ex throat does not need to be pushed out like we do in the Pro Stock engines. I also know that the SOUND of the port is extremely important! If I had two identical ex ports and one flowed 300 and was smooth as glass and the other flowed 310 and was turbulent and the monometer jumps a half inch, the one that is smooth will make more power every single time. My ex ports are also biased to the SSR and are oval in shape. I make them almost striate on the chamber wall side. If you think in terms of how much the gasses have to turn and bias the throat ( intake and exhaust) to the air flow, it will move more air every time. My intake throats are biased .050 to the SSR! That is trade secret not many people want us to talk about isn't it Bill.

[bill jones]

-When I first started flowtesting I found that particularly on SBC's where they have left and right hand ports, that I had to flow at least a pair of ports to get anywhere.
-Then a while later it got to where I found I needed to flow every hole with every small porting change.
-To do that you have to be able to flow test quick and that means getting "tooled" up.
-It takes me about 50 minutes to assemble and flow a set of heads in .100" increments to .700" lift.
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-Once I started doing every port I found the lefts vs rights are always distinct challenge, but I also found that my better flowing port throats were rarely centered.
-So I hand contour some valves to fit my best ports (down inside the throat), make an alignment mark towards the short turn, and dial indicate them to see the ovalness of the shape.
-Problem here is that you may need 4 examples just to do SBC exhaust ports as the center pair are backwards to each other and the end ports don't even resemble the center ports.
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-Hmmm,,,I don't think I'm supposed to be talking about this.