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

Post by exhausted » Tue Jan 07, 2020 10:54 am

exhausted wrote:
Tue Jan 07, 2020 10:18 am
oneaves2005 wrote:
Tue Jan 07, 2020 10:06 am
Excellent info, that's my mind sorted.

1.625" primary 16-18" long
1.625" secondary 12" long
2.25" collectors equal length (these are realistically going to be about 40"+ long before they join to a single pipe (this is the diameter suggested if I have followed correctly) - Do I need a choke or just a straight 2.25" pipe off the merge collector?
2.5" tailpipe

I can now stop losing sleep over this!

I will post dyno results when the system is complete in about 6 weeks time.

Thanks all.

Ollie
1.88" OD secondary at least 12" of tubing, you do not need to step unless they are full of 2" radius bends...
Primary collectors would be MC2-163-188
Final bank collector would be MC2-188-200
Step the 2" every 12" of length until reaching the final merge
Final merge would be exit at 2.25 and step the tail pipe from there every 24"? or whatever you want but I do not believe it ever needs to be bigger than 2.5" OD. I would try and fit a AR chamber at each step of the tailpipe. Placement would be where space is available.
If space allows I would think about running 2.25 for say 18-20" and step all the way to 2.5" using a AR chamber...
Sorry, Secondary of 1.88" OD should be at least 12" maybe 14". Do not need to step.
Final bank collectors would go from 1.88" in to 2.12" out. MC2 188-212
So we are at 2.12 from bank final to final tailpipe merge. I would start wanting to step that 2.12 to 2.25" if they get longer than say 14-15" to reach the final tailpipe merge. So depending on how long that is, I would probably suggest a final merge of MC2-225-2.5. Step the 2.12 to 2.25 even if it right at the final merge, eh? And just go to the 2.5 right off the bat and run it all the way to the back. Doesn't bother me at that point.
Probably safer staying big all the way.
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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

Post by oneaves2005 » Tue Jan 07, 2020 11:31 am

Thanks.

What's the benefit in such a big step between primaries and secondaries (1.625-1.88)? Most I have seen increase by 0.125" from primary to secondary.......

AND

If you had to chose a single pipe diameter from the collectors to the Y merge to one pipe and the final tailpipe, what would they be? This is just in case the price goes up too much when I tell the fabricators what I want!

Kind Regards

Ollie

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

Post by exhausted » Tue Jan 07, 2020 11:46 am

oneaves2005 wrote:
Tue Jan 07, 2020 11:31 am
Thanks.

What's the benefit in such a big step between primaries and secondaries (1.625-1.88)? Most I have seen increase by 0.125" from primary to secondary.......

AND

If you had to chose a single pipe diameter from the collectors to the Y merge to one pipe and the final tailpipe, what would they be? This is just in case the price goes up too much when I tell the fabricators what I want!

Kind Regards

Ollie
Most merge 2 way collectors I use are .250 across the collector.
Just figure 2.25" for that.
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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

Post by oneaves2005 » Tue Jan 07, 2020 12:18 pm

Great, Thanks.

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

Post by cjperformance » Tue Jan 07, 2020 6:18 pm

oneaves2005 wrote:
Tue Jan 07, 2020 5:57 am
Hi, with one bank number odd and the other even (1-3-5-7 front to back N/S and 2-4-6-8 front to back O/S) the firing order is 1-4-5-2-7-6-3-8

So essentially if it were a 4 cylinder it would fire 1-3-4-2 on both sides
Given that firing sequence you would pair cyls 1&3 , 5&7 ,,, then 2&8 , 4&6.
So you are seperating each primary branch by 1 exhaust stroke.
Craig.

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

Post by exhausted » Tue Jan 07, 2020 7:07 pm

cjperformance wrote:
Tue Jan 07, 2020 6:18 pm
oneaves2005 wrote:
Tue Jan 07, 2020 5:57 am
Hi, with one bank number odd and the other even (1-3-5-7 front to back N/S and 2-4-6-8 front to back O/S) the firing order is 1-4-5-2-7-6-3-8

So essentially if it were a 4 cylinder it would fire 1-3-4-2 on both sides
Given that firing sequence you would pair cyls 1&3 , 5&7 ,,, then 2&8 , 4&6.
So you are seperating each primary branch by 1 exhaust stroke.
I would pair 1&7 and 3&5, 2&8 and 4&6. :D
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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

Post by ptuomov » Tue Jan 07, 2020 7:11 pm

Yes, I'd go for 360 degree blowdown pulse separation at the first merge, such that 180 interference only happens at the second merge and is too far in time and space to actually interfere with the overlap.

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

Post by cjperformance » Tue Jan 07, 2020 7:33 pm

exhausted wrote:
Tue Jan 07, 2020 7:07 pm
cjperformance wrote:
Tue Jan 07, 2020 6:18 pm
oneaves2005 wrote:
Tue Jan 07, 2020 5:57 am
Hi, with one bank number odd and the other even (1-3-5-7 front to back N/S and 2-4-6-8 front to back O/S) the firing order is 1-4-5-2-7-6-3-8

So essentially if it were a 4 cylinder it would fire 1-3-4-2 on both sides
Given that firing sequence you would pair cyls 1&3 , 5&7 ,,, then 2&8 , 4&6.
So you are seperating each primary branch by 1 exhaust stroke.
I would pair 1&7 and 3&5, 2&8 and 4&6. :D
=D> YES Thankyou Calvin! 1&7 , 3&5
(NOT 1&3 , 5&7as i had stupidy said !!)
Then ,, 2&8 ,4&6 ,, as I had said and as you can see im not a flat planer! #-o
(Not a flat earther either :lol: )
Craig.

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

Post by Rick! » Wed Jan 08, 2020 7:03 am

exhausted wrote:
Tue Jan 07, 2020 7:07 pm
cjperformance wrote:
Tue Jan 07, 2020 6:18 pm
oneaves2005 wrote:
Tue Jan 07, 2020 5:57 am
Hi, with one bank number odd and the other even (1-3-5-7 front to back N/S and 2-4-6-8 front to back O/S) the firing order is 1-4-5-2-7-6-3-8

So essentially if it were a 4 cylinder it would fire 1-3-4-2 on both sides
Given that firing sequence you would pair cyls 1&3 , 5&7 ,,, then 2&8 , 4&6.
So you are seperating each primary branch by 1 exhaust stroke.
I would pair 1&7 and 3&5, 2&8 and 4&6. :D
kinda like this?
Image

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

Post by exhausted » Wed Jan 08, 2020 7:33 am

cjperformance wrote:
Tue Jan 07, 2020 7:33 pm
exhausted wrote:
Tue Jan 07, 2020 7:07 pm
cjperformance wrote:
Tue Jan 07, 2020 6:18 pm


Given that firing sequence you would pair cyls 1&3 , 5&7 ,,, then 2&8 , 4&6.
So you are seperating each primary branch by 1 exhaust stroke.
I would pair 1&7 and 3&5, 2&8 and 4&6. :D
=D> YES Thankyou Calvin! 1&7 , 3&5
(NOT 1&3 , 5&7as i had stupidy said !!)
Then ,, 2&8 ,4&6 ,, as I had said and as you can see im not a flat planer! #-o
(Not a flat earther either :lol: )
Hey, I thought you were just showing how to do the close timing as opposed to the most separated timing. I was not trying to say that is wrong. It gets different results and is not the most effective 421 layout for minimizing reversion and I would never build like that. IMO :)
Calvin Elston
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704-443-8088
Web: www.elstonheaders.com
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by ptuomov » Wed Jan 08, 2020 7:50 am

Although some may think that factory engineers are idiots and their computer models are snake oil, I think that this Mazda skyactiv logic for 4-2-1 four banger header is sensible. The primary plus secondary length has to be long enough such that there is no exhaust blowdown interference at the lowest used rpm of the powerband:
81B8E434-7474-4156-A520-26C4D8093847.png
240C2559-EC44-43A7-8D38-AD1CF6CAC909.png
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Wed Jan 08, 2020 8:02 am

ptuomov wrote:
Wed Jan 08, 2020 7:50 am
Although some may think that factory engineers are idiots and their computer models are snake oil, I think that this Mazda skyactiv logic for 4-2-1 four banger header is sensible. The primary plus secondary length has to be long enough such that there is no exhaust blowdown interference at the lowest used rpm of the powerband:

81B8E434-7474-4156-A520-26C4D8093847.png

240C2559-EC44-43A7-8D38-AD1CF6CAC909.png
HaHa! I don't think that software is snakeoil, it is the people using it and the way they see engines and where the power is to be found. they have come a long way and I applaud the work. (but back in the 90's they were way off on racing stuff)
Your response here proposes both the primary and secondary length to be long enough, didn't you mean the primary length? And the "power" or energy in the "blowdown" is different for a lot of situations. At least in racing, most only worry about maximum horsepower at WOT. I always found it interesting that I could run a 421 at least 2-4" longer overall length than a 4into1 without losing top end power. Not sure why that is yet and probably never will.
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704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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

Post by exhausted » Wed Jan 08, 2020 8:08 am

ptuomov wrote:
Wed Jan 08, 2020 7:50 am
Although some may think that factory engineers are idiots and their computer models are snake oil, I think that this Mazda skyactiv logic for 4-2-1 four banger header is sensible. The primary plus secondary length has to be long enough such that there is no exhaust blowdown interference at the lowest used rpm of the powerband:

81B8E434-7474-4156-A520-26C4D8093847.png

240C2559-EC44-43A7-8D38-AD1CF6CAC909.png
This is true. An example when I suggest a primary of say 16", combining that with the other leg of 16" is 32" and that is enough length to cover a bottom rpm of usually 5000 rpm. So there you go. Combine that with the overall length and it is not too hard to see how a 421 layout can disperse pressure waves.

In my world. "blowdown" is particle flow and a different animal than pressure waves. A Top Fuel motor "blowdown" will fill the entire pipe but a NA motor much less... :)
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Wed Jan 08, 2020 8:17 am

I have a bit more time so I want to throw this out. If we look at the combined lengths of 421 paired cylinder exhaust tube lengths and are shooting for say 16" each or 32" total, I am willing to shorten one and lengthen the other while still maintaining that 32" number for both of them.
A important reality when trying to snake tubes into a given chassis. Unequal length primary lengths for 421 headers are not that big a player but combined lengths are. :)

(When I refer here to "primary" I mean the length of tubing from the cylinder head to the first merge collector or "y". The "Secondaries" are from the primary "y"'s to the final "Y". "y" = "merge")
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by ptuomov » Wed Jan 08, 2020 9:29 am

exhausted wrote:
Wed Jan 08, 2020 8:17 am
I have a bit more time so I want to throw this out. If we look at the combined lengths of 421 paired cylinder exhaust tube lengths and are shooting for say 16" each or 32" total, I am willing to shorten one and lengthen the other while still maintaining that 32" number for both of them.
A important reality when trying to snake tubes into a given chassis. Unequal length primary lengths for 421 headers are not that big a player but combined lengths are. :)

(When I refer here to "primary" I mean the length of tubing from the cylinder head to the first merge collector or "y". The "Secondaries" are from the primary "y"'s to the final "Y". "y" = "merge")
I would say that this is consistent with various high-quality factory designs from, say, BMW.

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