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Old 02-19-2020, 12:52 PM   #1
61Klassic
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Default Centre exhaust port baffle or fourth port?

Looking for the opinions of the knowledgeable chaps on here that may have done either.
I know you obviously can’t do both, but which would you choose to help squeeze the last few ponies out of your flathead.
Either make your own baffle, or enlarge the exhaust crossover port to the intake manifold and add a fourth exhaust port.
The engine is used for racing, 293ci, potvin 425, lightweight non adjustable lifters, lightweight custom made titanium valves and heavily ported.

Thanks for any advice given.
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Old 02-19-2020, 01:01 PM   #2
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Default Re: Centre exhaust port baffle or fourth port?

Given the firing order, I don’t think it’s an issue. I also think trying to make a fourth port, by dividing the center into two, would end up being more restrictive. JMO
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Old 02-19-2020, 01:11 PM   #3
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Default Re: Centre exhaust port baffle or fourth port?

JWL did a lot of dyno work on this subject. He made a pretty neat divider that the results can be found in his book Flathead Facts.

Kong Jackson and others have fooled around with adding extra exhaust ports, but I don't know if dyno results were ever compiled with this modification.

The recent 59 block I did had those cast iron dividers in the ports. I can tell you they certainly looked more like a plug than a help. We took them out.

Last edited by Tim Ayers; 02-19-2020 at 01:25 PM.
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Old 02-19-2020, 01:13 PM   #4
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Default Re: Centre exhaust port baffle or fourth port?

Hi Ralph. If I was to do a fourth port I wouldn’t be dividing the centre into two. I’ll either fit a port divider/baffle OR a fourth port.
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Old 02-19-2020, 01:15 PM   #5
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Default Re: Centre exhaust port baffle or fourth port?

Hi Tim.
I’ve got JWL’s book and like his divider. I’m just wondering which would be more beneficial, that or a fourth port.
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Old 02-19-2020, 01:32 PM   #6
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Default Re: Centre exhaust port baffle or fourth port?

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Originally Posted by 61Klassic View Post
Hi Tim.
Iíve got JWLís book and like his divider. Iím just wondering which would be more beneficial, that or a fourth port.
Got it. I think you'll need to talk some of the heavy hitters have done the adding extra port work.

What type of racing are we taking about? Will the block be dry or wet? Wet adds another layer of consideration if adding an extra port. I've seen them added to the upper ends of each side of block where the exhaust wraps around into the end port bends.
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Old 02-19-2020, 02:33 PM   #7
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Default Re: Centre exhaust port baffle or fourth port?

The block will have full cooling system. Racing is everything from drag racing, to hill climbs and sprints to high speed time trials at Pendine.
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Old 02-19-2020, 02:34 PM   #8
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Default Re: Centre exhaust port baffle or fourth port?

I think the majority of power is found on the intake side. Some flow bench testing would be helpful to see how your intake and exhaust match up. I ran a dragster with a similar sized motor and the 425 eliminator, three exhaust ports, made power to at least 7000 rpm. I did a lot of port and head work. John Bradley ran multiple exhaust ports with great success back in the day. Opinions will likely be all over the place on this. Disclaimer: I do not compare myself to the legendary Mr Bradley.
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Old 02-19-2020, 02:46 PM   #9
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Default Re: Centre exhaust port baffle or fourth port?

Quote:
Originally Posted by Flathead View Post
I think the majority of power is found on the intake side. Some flow bench testing would be helpful to see how your intake and exhaust match up. I ran a dragster with a similar sized motor and the 425 eliminator, three exhaust ports, made power to at least 7000 rpm. I did a lot of port and head work. John Bradley ran multiple exhaust ports with great success back in the day. Opinions will likely be all over the place on this. Disclaimer: I do not compare myself to the legendary Mr Bradley.
John Bradley's name was the one that escaped me.

Our own Ronnie Roadster has done extensive block work, testing and racing as well. I'm hoping he'll chime in.

Last edited by Tim Ayers; 02-19-2020 at 02:56 PM.
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Old 02-19-2020, 02:58 PM   #10
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Default Re: Centre exhaust port baffle or fourth port?

Excellent read with some pictures...> http://www.midstateantiquestockcarcl...at_heads9.html


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Old 02-19-2020, 03:10 PM   #11
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Default Re: Centre exhaust port baffle or fourth port?

I've done some flowbench testing of the ports and found that the stock center port flows better than any of the others. I opened up th end poets (on the cover of my book) and that was only a 4% increase. The center port in used onece per revolution, where as the end ports are used once every 2 relovitions, so inevect you don't have to make another port. From a tuning stand point the center port has more exhausr velosith whiv\ch in a header can creal a vacuum to improve flow at hi Rpm's. I think this is the reasonthe flathead has a unique sound. However with all this said:: " One never knows" After 67 years after they quit building them, we still find ways to make them better. Imagin what a new block wit better ports could do???
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Old 02-19-2020, 03:18 PM   #12
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Default Re: Centre exhaust port baffle or fourth port?

Quote:
Originally Posted by petehoovie View Post
Excellent read with some pictures...> http://www.midstateantiquestockcarcl...at_heads9.html


Looks like the Midstate site has Ol' Ron's end exhaust port mod pictured.
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Old 02-19-2020, 03:20 PM   #13
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Default Re: Centre exhaust port baffle or fourth port?

Quote:
Originally Posted by Flathead View Post
I think the majority of power is found on the intake side. Some flow bench testing would be helpful to see how your intake and exhaust match up. I ran a dragster with a similar sized motor and the 425 eliminator, three exhaust ports, made power to at least 7000 rpm. I did a lot of port and head work. John Bradley ran multiple exhaust ports with great success back in the day. Opinions will likely be all over the place on this. Disclaimer: I do not compare myself to the legendary Mr Bradley.
Quote:
Originally Posted by Tim Ayers View Post
Looks like the Midstate site has Ol' Ron's end exhaust port mod pictured.

Yup...Ol' Ron is mentioned in the article...
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Old 02-19-2020, 04:05 PM   #14
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Default Re: Centre exhaust port baffle or fourth port?

Quote:
Originally Posted by 61Klassic View Post
Looking for the opinions of the knowledgeable chaps on here that may have done either.
I know you obviously canít do both, but which would you choose to help squeeze the last few ponies out of your flathead.
Either make your own baffle, or enlarge the exhaust crossover port to the intake manifold and add a fourth exhaust port.
The engine is used for racing, 293ci, potvin 425, lightweight non adjustable lifters, lightweight custom made titanium valves and heavily ported.

Thanks for any advice given.
Port dividers work good if you make them yourself. Mine are only about 1 inch square, 1/8 inch thick and extend only to the centerline of the valves.

Adding only the center top port probably won't be noticed on an engine running on gas. Additionally adding the two top, end ports will bring a noticable improvement.
On a car other than a dragster it might become a problem dealing with an exhaust pipe system that meets the rules AND STILL WORKS.

If you can run race gas or alcohol you will find more improvement in upping the compression to 14 to 1 and running 2 ring flat top gas ported pistons with low tension narrow rings. Add 5 stage dry sump oiling and you have 40 more hp.
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Old 02-19-2020, 04:36 PM   #15
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Default Re: Centre exhaust port baffle or fourth port?

I have had good results with a center divider that was installed well. Years ago, tried some using the bottom of the studs that came with them and they got loose. I use a 7/16 allan screw under the stud and that holds them well. Engine seems to cool better with them. I am sure that will vary with an individual engine.
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Old 02-19-2020, 05:07 PM   #16
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Default Re: Centre exhaust port baffle or fourth port?

So the general consensus is to forget the fourth port out of the heat riser and go with some homemade we’ll fitting dividers/baffles.
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Old 02-20-2020, 11:29 AM   #17
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Default Re: Centre exhaust port baffle or fourth port?

Not to get too far off topic here, but didn't Mark Kirby of Motor City Flathead create a new flathead block with four ports? I know he isn't in business anymore but he was with Shadow Rods in Saginaw, Mich. the last time I saw him. I think they still have a website. Shadowrods.com
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Old 02-20-2020, 01:28 PM   #18
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Default Re: Centre exhaust port baffle or fourth port?

The price I saw was out of reach for most and it wouldn't be allowed in any type of competition, so went nowhere. Also, if I remember correctly, it didn't use any original type parts, everything (or almost everything) had to be custom just to that block.
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Old 02-20-2020, 01:55 PM   #19
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Default Re: Centre exhaust port baffle or fourth port?

I've always wondered about exhaust baffles. I have a set I never used, because I could never see how putting a substantial-sized lump of metal in an already restrictive exhaust system could be of benefit. Going through this thread, I came up with a really "off-the-wall" idea. As I understand it, the primary value of the exhaust baffles is to keep the intake charge to one of the center cylinders from being contaminated by the exhaust from the adjacent cylinder. How about grinding a cam that would have reduced overlap on the center four cylinders to reduce this contamination? Perhaps the lift on those four cylinders could be increased to make up for the decreased duration? I realize that this may require different springs for the center cylinders, but I don't see that as a game changer.

Before anyone goes nuts, this is just my "out of the box" thinking for today.
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Old 02-20-2020, 03:31 PM   #20
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Default Re: Centre exhaust port baffle or fourth port?

Here's Mark and his flathead.
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