193 Swirl Port Porting Question

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68maliblue
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193 Swirl Port Porting Question

Post by 68maliblue »

I’m doing a low $$$ 307 Chevy build with leftover parts and I have a low mile set of 193 swirl port heads that are the best heads I can come up with without spending any $$$. Engine is going into a rat rod 46 Chevy so it’s just something to have fun with. Cam is a small solid cam 224/224 @ .050” on a 108 LSA that I used to run in a 327. Compression ratio is going to be somewhere around 9:1. Question I have is should I open the throat up to the edge of the 90 deg step or remove this 90 deg step completely and open up the to the diameter leading in to the 45 deg seat. I’m leaning toward keeping the step and clean up everything below it But I am open to suggestions on what would be best.
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Re: 193 Swirl Port Porting Question

Post by mag2555 »

My question is how wide is that step?
Here’s why, with no bottom cut below the 45 there needs to be something there like that lip to somewhat act as a bottom cut.

In keeping with this line of thinking I would then open up the throat until that 90 degree lip had only .045”or .050” left to it.

The bigger throat will then help high lift flow, the low lift flow from .200” on up should stay the same and the reason for that lip in the first place which is to act as a wet flow fuel sheer point will still take place, albeit a little reduced.

Also if no other porting work is to be done to these intake ports then the guide needs to be Boat tailed greatly since it eats up a bunch of needed flow area on the roof!
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Re: 193 Swirl Port Porting Question

Post by 68maliblue »

I'll take some measurements and post later. Thanks.
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Re: 193 Swirl Port Porting Question

Post by 68maliblue »

Best I can measure it’s .055” wide. If I open the throat right to the edge of the 90 degree step that would give a diameter of 1.690” which is 87% of the intake valve diameter.
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Re: 193 Swirl Port Porting Question

Post by steve cowan »

68maliblue wrote: Fri Jun 04, 2021 4:05 pm I’m doing a low $$$ 307 Chevy build with leftover parts and I have a low mile set of 193 swirl port heads that are the best heads I can come up with without spending any $$$. Engine is going into a rat rod 46 Chevy so it’s just something to have fun with. Cam is a small solid cam 224/224 @ .050” on a 108 LSA that I used to run in a 327. Compression ratio is going to be somewhere around 9:1. Question I have is should I open the throat up to the edge of the 90 deg step or remove this 90 deg step completely and open up the to the diameter leading in to the 45 deg seat. I’m leaning toward keeping the step and clean up everything below it But I am open to suggestions on what would be best.
I don't think it is worth the time and effort opening throat,I doubt you would notice any difference, if you are using those heads as is I would just lap the valves and pat it on the head.
The minimum I would do personally is a valve job,set throat and bowl size,shape guide,blend top cut of valve job into chamber.
But not on those heads.
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Re: 193 Swirl Port Porting Question

Post by mag2555 »

So what size is the throat now( stock) ?

With that narrow of a lip I would not reduce it by more then .015” to gain a bigger throat diameter if your keeping that lip there.

If you where inclined to spend some money then the way to go would be to put intake seats in the heads and get that lip out of there completely.

Also another way to go would be to maximize the stock seat OD since they ate always undersized and then that would allow you to get some small amount of a bottom cut under that 45.

Along these same lines stepping up to a bigger valve would allow a far bigger bottom cut and attain even fatter flow numbers in the .200” lift range which is quite important to having the peak HP not nose over as fast as stock,

If you look up pictures of the latest Corvette head Intake bowls you can see what the factory came up with after a bunch more wet flow testing to generate swirl, combustion efficiency and high levels of air flow.
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Re: 193 Swirl Port Porting Question

Post by 68maliblue »

The edge of the casting (green arrow) measures 1.51 to 1.52” which makes a wall which appears to be there to keep the flow swirling. Plan is to remove this as it seems very restrictive. Seems like low hanging fruit for getting some extra flow without too much time invested.
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Re: 193 Swirl Port Porting Question

Post by mag2555 »

Just keep in mind one thing, that being that flow exiting the port does not swirl all the time!

At low flow rates , up to maybe .300” lift the flow is taking the path of least resistance or as much of a straight line as it can into the runner and out of the valve.

This action is kind of like a teeter totter when the end that’s up in the air is at the push rod end of the intake port and the other end is in the chamber passed the valve on the short turn side.

As the flow rate goes up above .300” lift and the port is filling up with more air mass, this mass is now fallowing the contours of the port and then there’s more air trying to make its way around all of that crap on the roof of the bowl with adds swirl at the expense of flow!
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Re: 193 Swirl Port Porting Question

Post by 68maliblue »

Doesn’t seem like too much work to remove this retriction so I’m going to go ahead and take the throat out to 1.69-1.70 even with the edge of the 90 degree step and blend into the bowl. I might trim the valve guides if I’m feeling adventurous. Will also work over the exhaust with the usual clean up. The cam is only .430” net lift so low lift flow will be important.
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Re: 193 Swirl Port Porting Question

Post by jcisworthy »

The right valve job would get take care of that abrupt step. 90% of 1.72 valve is about 1.55 probably about the ID of the step. My experience with iron Chevy heads is the factory was close on sizing the bowls.
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Re: 193 Swirl Port Porting Question

Post by 68maliblue »

Intake valve diameter is 1.94”. Is 90% a better ratio of throat diameter to valve diameter? I’ve seen numbers ranging from 86-89%. Cleaning up the throat to the 90 deg step gets it to 87%. I don’t want to invest much into these heads. Just some bowl/throat cleanup and lap the valves. Figured since I’ve got them apart might as well clean up the bowl/throat area since it looked like low hanging fruit that wouldn’t require much time invested. Just wanted to know how far to take the throat. Thanks for all the replies so far.
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Re: 193 Swirl Port Porting Question

Post by steve cowan »

68maliblue wrote: Sat Jun 05, 2021 3:12 pm Intake valve diameter is 1.94”. Is 90% a better ratio of throat diameter to valve diameter? I’ve seen numbers ranging from 86-89%. Cleaning up the throat to the 90 deg step gets it to 87%. I don’t want to invest much into these heads. Just some bowl/throat cleanup and lap the valves. Figured since I’ve got them apart might as well clean up the bowl/throat area since it looked like low hanging fruit that wouldn’t require much time invested. Just wanted to know how far to take the throat. Thanks for all the replies so far.
Throat is usually measured at bottom cut of valve job,basically you will be blending bowl up to bottom of valve seat looks like 45deg??
20201216_134740.jpg
Looking at this valve job from the top cut
40 tc
50 seat
60,70 and 85 deg bottom cut is where I measure the throat which is 89% of a 1.94" intake valve.
Hope this helps.
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Re: 193 Swirl Port Porting Question

Post by Tuner »

The most important thing when using these heads is use no more than 25 degrees total spark advance.

This is a post from one of the threads about these heads in the "similar topics" links at the bottom of the page.
Plaintoast wrote: Wed Jan 28, 2015 10:12 am I did a real low buck build with a set of these, left the ramp in place, pushed the pushrod pinch jump thing smooth. Using an old single plane (not the best choice) a small hydro cam, 87 octane pee water, it was making 360 ft lbs as low as we could pull the dyno down. HP was 263@ 4500, and fell off like a cliff after that. My notes also say it only wanted 22 degrees total, I think we were around 8:1. Its currently still in a magazine car with 40,000+ miles and gets 22 mpg cruising. They have a place, high rpms isn't it, but they certainly make a decent torque/low rpm head.
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Re: 193 Swirl Port Porting Question

Post by PRH »

I don't think it is worth the time and effort opening throat,I doubt you would notice any difference, if you are using those heads as is I would just lap the valves and pat it on the head.
The minimum I would do personally is a valve job,set throat and bowl size,shape guide,blend top cut of valve job into chamber.
But not on those heads.
Agree 100%
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Re: 193 Swirl Port Porting Question

Post by jcisworthy »

I would leave the throat alone also for what you are doing. I take street out to 90% others may differ.
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