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Flat Plane V8 Race Engine - Single Exit Exhaust Question

General engine tech -- Drag Racing to Circle Track

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RevTheory
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by RevTheory » Fri Dec 06, 2019 9:02 am

I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by Rick! » Fri Dec 06, 2019 9:15 am

What are the dimensions of the exhaust port? The torque hole with the 1.75 primaries is a huge ‘tell’ on what the engine wants. Like englert mentioned, a set of stepped headers should help considerably. Pipemax can help estimate diameters and positions. You may not be able to connect the brown down low to the blue up top but there’s room for improvement between the two.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by oneaves2005 » Fri Dec 06, 2019 9:51 am

Rick! wrote:
Fri Dec 06, 2019 9:15 am
What are the dimensions of the exhaust port? The torque hole with the 1.75 primaries is a huge ‘tell’ on what the engine wants. Like englert mentioned, a set of stepped headers should help considerably. Pipemax can help estimate diameters and positions. You may not be able to connect the brown down low to the blue up top but there’s room for improvement between the two.
The exhaust port is about 10.5 square centimeters I think. The area works well with a 40mm O.D or 1.625" O.D pipe... Perhaps a 1.625 off the head with a step to 1.75". Will by pipemax and see what that spits out.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by oneaves2005 » Fri Dec 06, 2019 9:52 am

RevTheory wrote:
Fri Dec 06, 2019 9:02 am
I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?
There is potential to join a little sooner, where the bellhousing meets the gearbox maybe.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by RevTheory » Fri Dec 06, 2019 11:08 am

oneaves2005 wrote:
Fri Dec 06, 2019 9:52 am
RevTheory wrote:
Fri Dec 06, 2019 9:02 am
I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?
There is potential to join a little sooner, where the bellhousing meets the gearbox maybe.
Maybe explore that option. That would be a good spot for an a/r device as well.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by cjperformance » Fri Dec 06, 2019 3:08 pm

You need to get the 2 collector pipes as close to equal length as possible.
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by cjperformance » Fri Dec 06, 2019 3:15 pm

RevTheory wrote:
Fri Dec 06, 2019 9:02 am
I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?
The 1st problem with joining that far forward is the unequal collector pipe lengths, 2nd problem is the gas is still quite hot and the predetermined tailpipe diameter of 2.5" is on the small side.
Craig.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by RevTheory » Fri Dec 06, 2019 3:29 pm

cjperformance wrote:
Fri Dec 06, 2019 3:15 pm
RevTheory wrote:
Fri Dec 06, 2019 9:02 am
I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?
The 1st problem with joining that far forward is the unequal collector pipe lengths, 2nd problem is the gas is still quite hot and the predetermined tailpipe diameter of 2.5" is on the small side.
I was thinking along the lines of the short side being the shorter Pipemax recommended length and then the longer side hopefully fitting with one of the longer recommended lengths or at the very least, not one of the worst recommended lengths.

Dual 2.5 in x 3 inch, a/r out.

Maybe?

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by cjperformance » Fri Dec 06, 2019 4:33 pm

RevTheory wrote:
Fri Dec 06, 2019 3:29 pm
cjperformance wrote:
Fri Dec 06, 2019 3:15 pm
RevTheory wrote:
Fri Dec 06, 2019 9:02 am
I'm not sure how much usable energy you'll have joining them that far back. Is there no way to hop over or go under the bell housing?
The 1st problem with joining that far forward is the unequal collector pipe lengths, 2nd problem is the gas is still quite hot and the predetermined tailpipe diameter of 2.5" is on the small side.
I was thinking along the lines of the short side being the shorter Pipemax recommended length and then the longer side hopefully fitting with one of the longer recommended lengths or at the very least, not one of the worst recommended lengths.

Dual 2.5 in x 3 inch, a/r out.

Maybe?
Yes using to different but 'correct' lengths is better than just plain unequal od ball, i still prefer equal if at all possible. I dont think OP can use 3", i think they are restricter to a single 2.5" tailpipe, it would be counterproductive to go too big upstream of that when 2x 2.5" from collectors back is plenty for the HP.
Craig.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Sat Dec 07, 2019 9:46 pm

So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by MadBill » Sat Dec 07, 2019 10:25 pm

exhausted wrote:
Sat Dec 07, 2019 9:46 pm
So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
I've seen a number of crossover headers on Trans Am race cars (~850 HP, 358") where to equalize lengths the right side collector has a 360° loop before merging into a single 5" muffler. I've also seen ones where the right collector appears to match the shortest recommended PipeMax length and the left the "second best''. :-k
Felix, qui potuit rerum cognscere causas.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Sat Dec 07, 2019 11:18 pm

MadBill wrote:
Sat Dec 07, 2019 10:25 pm
exhausted wrote:
Sat Dec 07, 2019 9:46 pm
So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
I've seen a number of crossover headers on Trans Am race cars (~850 HP, 358") where to equalize lengths the right side collector has a 360° loop before merging into a single 5" muffler. I've also seen ones where the right collector appears to match the shortest recommended PipeMax length and the left the "second best''. :-k
No doubt Bill. I would wager money that those engines were not tested on a dyno with the cars headers.... now if they got on a chassis dyno maybe someone might have found out hw that worked but I doubt anyone ever built two complete systems and dyno'd them back to back on any type of dyno.
Also. I have built some of those systems and they are so large I doubt any configuration showed much difference. :D
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by MadBill » Sun Dec 08, 2019 12:14 am

exhausted wrote:
Sat Dec 07, 2019 11:18 pm
MadBill wrote:
Sat Dec 07, 2019 10:25 pm
exhausted wrote:
Sat Dec 07, 2019 9:46 pm
So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
I've seen a number of crossover headers on Trans Am race cars (~850 HP, 358") where to equalize lengths the right side collector has a 360° loop before merging into a single 5" muffler. I've also seen ones where the right collector appears to match the shortest recommended PipeMax length and the left the "second best''. :-k
No doubt Bill. I would wager money that those engines were not tested on a dyno with the cars headers.... now if they got on a chassis dyno maybe someone might have found out hw that worked but I doubt anyone ever built two complete systems and dyno'd them back to back on any type of dyno.
Also. I have built some of those systems and they are so large I doubt any configuration showed much difference. :D
I did observe a TA Corvette with a collector 'loop' on a Mustang chassis dyno. After spark and jet optimization it was right on 700 HP @ 8300 RPM. They didn't try any collector alternatives but replacing the 5" Flowmaster (30" Hg. back pressure) with an equal length of pipe netted one HP, as did removing the aircleaner.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by englertracing » Sun Dec 08, 2019 6:28 am

exhausted wrote:
Sat Dec 07, 2019 9:46 pm
So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
So
1. Is 1.625 off the head too large if it matches the port?
1.1 Could necking down to 1.5 after the flange benefit this engine as its quite small.

2. What might be an appropriate choke size for the collector?
2.1 could probably be quite small on a flat plane right? Perhaps.
even as tight as 1.5x primary area?

For a 1.625" header that would be a 2" choke

3. What would be a good diameter for the secondaries? 2.250"?
3.1 Do you cone up to that? Or is it effective to use for example
a few inches of 2", then a few inches of 2.125, then the 2.250
3.2 would it be good to run some length of the choke diameter to an AR and out with the ideal secondary size

4. What size tailpipe?
4.1 any choke in the 2-1?

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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Sun Dec 08, 2019 8:30 am

englertracing wrote:
Sun Dec 08, 2019 6:28 am
exhausted wrote:
Sat Dec 07, 2019 9:46 pm
So this is a 250 inch V8, two banks and each bank header is using a 2.5" collector choke?
What is the port area? IMO you are way off somewhere. :shock:

If I read 400 hp than 2.5 OD is good enough for a tail pipe and you can always step up a bit with some AR valves.
There is no problem running any engine through a single tailpipe. You do have to get both banks exactly equal length into the final merge though, that is critical. Even two 2.5" tubes going into one 2.5" tailpipe would be fine as the 2.5 is way too big already... :D
So
1. Is 1.625 off the head too large if it matches the port?
1.1 Could necking down to 1.5 after the flange benefit this engine as its quite small.

2. What might be an appropriate choke size for the collector?
2.1 could probably be quite small on a flat plane right? Perhaps.
even as tight as 1.5x primary area?

For a 1.625" header that would be a 2" choke

3. What would be a good diameter for the secondaries? 2.250"?
3.1 Do you cone up to that? Or is it effective to use for example
a few inches of 2", then a few inches of 2.125, then the 2.250
3.2 would it be good to run some length of the choke diameter to an AR and out with the ideal secondary size

4. What size tailpipe?
4.1 any choke in the 2-1?
Well I've stuck my finger in a hornets nest... You should just call me. Please email or pm me and I would be happy to talk.
Calvin
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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