Re: Ported Dart 215's with port energy discussion 3.0

[Carnut1]

exhaust bowl dart 215.jpg

An older exhaust bowl pic on junk head.
Question: When you design a exhaust do you like to keep the throat ratio tighter to reduce the pressure in the throat or do you think a larger throat ratio gives a better area to get the exhaust out? These darts I was able to actually get the mid lift flows better with a tighter bowl ratio than the larger throat ratio and similar high lift flows. Thanks, Charlie

[groberts101]

exhaust bowl dart 215.jpgAn older exhaust bowl pic on junk head.
Question: When you design a exhaust do you like to keep the throat ratio tighter to reduce the pressure in the throat or do you think a larger throat ratio gives a better area to get the exhaust out? These darts I was able to actually get the mid lift flows better with a tighter bowl ratio than the larger throat ratio and similar high lift flows. Thanks, Charlie

There is no set rule to use but usually that depends on the combo of parts and the intended application, Charlie. Compression ratio, intended rpm operating range, etc. Based on your first post in this new thread indicating a milder build(lower stall converter street gears tbi and such).. it seems you'd want to discourage reversional tendiencies of a blown out throat. Not all about absolute flow numbers and the street exhaust will have a large impact on final results.

My gut reaction would be to not exceed about 88% but I'm not sure what size valve you're using so it may need to be larger % wise to help make up for the smaller valve?

Also, yeah.. here I go again, LOL.. that throat is way too round on the short sides transition IMO. But I can't really tell how deep the bowls are and that impacts on how quickly you need to transition coming out of the throat and around the SSR. Just a quick observation based on the little I can see in that pic so I may be way off base there. In my early defense.. I usually prefer an asymmetrical throat shape leading into the SSR. Kinda like a baby intake ports squarish SSR transition to the choke if you catch my drift here.

[Carnut1]

Funny, I agree on the floor of that exhaust. Squaring the sides made for loss of flow. Now maybe I didn't take it far enough but I was able to get a good flow curve with a similar port.

[Carnut1]

1.6" valve with a .88 throat now.

[Carnut1]

I should add the exhaust bowl is quite deep.

[groberts101]

Ok sounds like the shape is good for that taller roof/angle then. Maybe test it at a higher depression to see what happens to the speed gradients at each corner/wall transition of the SSR?

[Carnut1]

Ok sounds like the shape is good for that taller roof/angle then. Maybe test it at a higher depression to see what happens to the speed gradients at each corner/wall transition of the SSR?

The ssr shape is quite round if you look at a port curve drawing. A lower floor or square ssr corners seems to cause more noise and lower flows. Thanks, Charlie

[groberts101]

Ok sounds like the shape is good for that taller roof/angle then. Maybe test it at a higher depression to see what happens to the speed gradients at each corner/wall transition of the SSR?

The ssr shape is quite round if you look at a port curve drawing. A lower floor or square ssr corners seems to cause more noise and lower flows. Thanks, Charlie

Sounds like you have a pretty good handle on then, Charlie.

Have a good one and good luck with it all,

Greg

[Carnut1]

Ok sounds like the shape is good for that taller roof/angle then. Maybe test it at a higher depression to see what happens to the speed gradients at each corner/wall transition of the SSR?

The ssr shape is quite round if you look at a port curve drawing. A lower floor or square ssr corners seems to cause more noise and lower flows. Thanks, Charlie

I can only go to about 36" without puking oil from my manometer. I will try at higher depression. Thanks, Charlie

[Carnut1]

20180403_183805.jpg

Hand drawn ssr apex airspeeds. Right side is the cylinder wall side. Input welcome. Taken at .7" lift. 304 ft/sec center pinch airspeed. Thanks, Charlie

[randy331]

I follow the push rod bulges shape in the divider and make it as thin as I dare opposite the bulge.

On curved runner single 4 intakes I disagree with this on the outside 4 runners.

On straight runner intakes maybe.

Randy

[GARY C]

I follow the push rod bulges shape in the divider and make it as thin as I dare opposite the bulge.

On curved runner single 4 intakes I disagree with this on the outside 4 runners.

On straight runner intakes maybe.

Randy

I have often wondered about that as it makes the air have to keep turning... I prefer to start with a smaller head, thin the center and prp as needed, fill in the floor some if possible and then use a trim to fit gasket so I don't have to flare the intake opening and can keep the runner as straight and consistent as possible.

[groberts101]

I follow the push rod bulges shape in the divider and make it as thin as I dare opposite the bulge.

On curved runner single 4 intakes I disagree with this on the outside 4 runners.

On straight runner intakes maybe.

Randy

If the pinch is very cross section limited.. as many of the older iron castings often were, it is usually far more important to gain the needed area for speed reduction and potential flow gains than worrying about the shape requirement.

IOW, if the pinch is just too damned small and creates speed related issues further downstream that cannot be fully mitigated, over the ssr, then shape often becomes a secondary consideration. This is why many of the older castings can gain flow despite using very sharp 1/8" corner radii through the pinch. Shape only gets you so far since the world is far from perfect when it comes to squeezing more flow through a limited space area. Shape trumps size unless it's still too damned small to hit the needed numbers and you do what is needed to make it all work.

Personally, rather than just digging opposite the pr bulge I'd just thin that common wall all the way to the gasket and leave the pinch side of the gasket opening alone. But I seem to be in the minority there as everyone seems to like to blow the entire entry size out just to match the gasket.

[groberts101]

I have often wondered about that as it makes the air have to keep turning... I prefer to start with a smaller head, thin the center and prp as needed, fill in the floor some if possible and then use a trim to fit gasket so I don't have to flare the intake opening and can keep the runner as straight and consistent as possible.

Copycat!.. I do that too! Lol

[groberts101]

20180403_183805.jpg Hand drawn ssr apex airspeeds. Right side is the cylinder wall side. Input welcome. Taken at .7" lift. 304 ft/sec center pinch airspeed. Thanks, Charlie

That looks like ass! No, really.. it does.

Sorry.. the juvenile just sneaks out uncontrollably sometimes.

What about the pinches floor speeds?

So I have another question. With such high apex speeds right at that vane.. why would you not gain flow by removing it altogether and reducing center apex speeds.. and potentially allowing more air to make it over the center of the short side.

IOW, it seems counterproductive to worry about fancy shapes when the port floor and apex speeds are still too fast. I'd imagine vanes would be best used when the available cross section was sufficient enough to not be affected by it(the vanes port volume displacement)and create those higher speeds. Just seems to me that finding flow in that area of the curtain is what we work so hard for in the first place, especially on a higher degree head like the sbc.

Dunno.. maybe the wet flow improvement trumps more flow in that area of the valve curtain?