360 degree v8 headers pipe max

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Isaac91n
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360 degree v8 headers pipe max

Post by Isaac91n »

Hi all. I've just download pipemax. I've loaded all details into it for my methanol burning 406 sbc 23degree race car engine. It currently has a set of home built 180 degree cross over headers. I love the sound, I like the theory of them but the Primary lengths are too long for my engine spec at around 40 inch. Pipemax indicated that ideal length is 28 inch (from memory) for 2nd harmonic for what I want to achieve (peak power at 7000) However, I think it quoted about 82 inches for first harmonic but it just notes that the first harmonic is not usually used as its too long to fit most cars. Anyway, I want to throw the book at these headers which for me means stepping the primary pipes and making a true 4 2 1 by pairing cylinders which fire 360 degrees apart into 4 pipes and then pairing those which are 180 degrees apart together into two tail pipes. This would normally be impossible to do with the second harmonic lengths. But 1st harmonic lengths would give me plenty of room to make it work. So, all that to say, here is my question:

How do I work out what length my secondary pipes should be compared to my primary pipes.

And

How do I work out the spacing of each step in the primary pipes.

Thanks, I know this will be a huge amount of work but I love fabrication and this would be a very rewarding job.

Cheers.
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Re: 360 degree v8 headers pipe max

Post by juuhanaa »

What size exhaust valve you have? Do you want waves to help exhaust gases out, or are you planning 4-2-1 as a anti reversion device? When primary pipe is 40 inch long including the exhaust port, what is the 1st and 2nd harmonic lengths?



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Re: 360 degree v8 headers pipe max

Post by ptuomov »

I would buy Vannik’s software for playing with this kind of an unusual setup. https://vannik.co.za/EngMod4T.htm
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Re: 360 degree v8 headers pipe max

Post by Isaac91n »

juuhanaa wrote: Thu Aug 11, 2022 12:51 pm What size exhaust valve you have? Do you want waves to help exhaust gases out, or are you planning 4-2-1 as a anti reversion device? When primary pipe is 40 inch long including the exhaust port, what is the 1st and 2nd harmonic lengths?



-juhana
Exhaust valve is 1.600 diameter with 8mm stem

Sorry, with my question I made a mistake, I called it 2nd harmonic but what I meant was 3rd harmonic so I am planning to use this design so waves assist gasses out (and to get induction charge moving into the cylinder)

The 1st harmonic length is 82.919 to 85.434 inches
The 3rd harmonic length is 28.717 to 28.232 inches

Thanks for looking into my question.
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Re: 360 degree v8 headers pipe max

Post by Isaac91n »

ptuomov wrote: Thu Aug 11, 2022 2:08 pm I would buy Vannik’s software for playing with this kind of an unusual setup. https://vannik.co.za/EngMod4T.htm

Thank you very much, I'll take a look it.

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Re: 360 degree v8 headers pipe max

Post by naukkis79 »

You need different kind of calculations for 180 degree headers. It's not about reflecting harmonics but next firing cylinder exhaust pulse to suck vacuum to previous cylinders overlap period. And as exhaust flow took some time after EVO it is possible tune that scavenging to pretty wide rpm range. 40" or about one meter length of 4-1 header for 7000 rpm should be fine.
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Re: 360 degree v8 headers pipe max

Post by juuhanaa »

My question about "harmonic length" was an exercise in, what is the length that wave travels back and forth, and when it can help the exhaust gases out. I'm a fan off tuning the exhaust system into peak power rpm, but the engines i mainly work has a valve area to support the size i need for the given length, and the "restricted" cam timing events doesn't hurt bottom end power.. That said, i would start from 27,964in length to make the headers flow more @ 7000rpm and EVO 75degree BBTC, but now the size for the given length would be 2,255in :D Sorry i cant help you in tuning the headers with more complex exhaust system, but there is others in this forum who probably can :) Anyway i made a quicky calculus for your engine using the formulas below,

Here is a formula i used to find out the primary length:

Header pipe length (in inches) = ((850*(180+EVO))/RPM – 3

EVO is how many crank degrees BBTC exhaust valve opens.

Formula to calculate what size we need for a given length to maintain particle velocity:

Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1

cylinder. disp. = one cylinder cid and hdr len is in inches

This give us 1.61in diameter which matches the size of an exhaust valve, but it is calculated for a 50.75cid and 40,35in length, and the given length (based on the formulas) matches 5000rpm and EVO 75degree BBTC.



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Re: 360 degree v8 headers pipe max

Post by BLSTIC »

My computer is unavailable right now so I can't do a model. But is the implication here that a 80" header is roughly good for high rpm if chasing the first harmonic?

Because I also wish 180 degree headers would fit for the sexy noise they make, but can't make them short enough for the application. Perhaps a 8-4-2 grouping with 8-4 join 360 degrees apart doing the crossover is possible...

I like the 180 degree headers for the smaller choke as well. Without a 90 degree interference lump I imagine the choke doesn't need to be much bigger than the incoming primaries...

I want my computer back so I can test this. Unless anyone else can?
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Re: 360 degree v8 headers pipe max

Post by Isaac91n »

naukkis79 wrote: Thu Aug 11, 2022 3:42 pm You need different kind of calculations for 180 degree headers. It's not about reflecting harmonics but next firing cylinder exhaust pulse to suck vacuum to previous cylinders overlap period. And as exhaust flow took some time after EVO it is possible tune that scavenging to pretty wide rpm range. 40" or about one meter length of 4-1 header for 7000 rpm should be fine.
Thankyou for your reply, I'm kinda sad that this is the case, I was quite excited about the prospect of building these headers but looks like what I already have is actually fine. Am I leaving hp on the table with this setup, am I better off going the more conventional route of a standard 4 into one and an x pipe. My real goal is max torque per cubic inch. I am only an amateur when it comes to engine building but Id really like to see over 600 ft/lb from this engine. Of course cam selection is key to this as well and perhaps I need to back the truck up a bit and get advice on that first.
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Re: 360 degree v8 headers pipe max

Post by Isaac91n »

BLSTIC wrote: Mon Aug 15, 2022 2:55 am My computer is unavailable right now so I can't do a model. But is the implication here that a 80" header is roughly good for high rpm if chasing the first harmonic?

Because I also wish 180 degree headers would fit for the sexy noise they make, but can't make them short enough for the application. Perhaps a 8-4-2 grouping with 8-4 join 360 degrees apart doing the crossover is possible...

I like the 180 degree headers for the smaller choke as well. Without a 90 degree interference lump I imagine the choke doesn't need to be much bigger than the incoming primaries...

I want my computer back so I can test this. Unless anyone else can?
Yes this was the theory I was working on. My plan was that if chasing that 1st harmonic was a bad idea for power then what could be possible would be to pair the two cylinders that are 180 degrees apart on each bank and cross them over with the corresponding two on the other side giving me a 4 2 1 header just not paired quite correctly, it would be comparable to how a subaru flat 4 is paired with the factory 4 2 1 headers. The reason I am chasing a 4 2 1 header so hard is that every bit of literature I've read regarding 4 cylinder engine headers is that a 4 2 1 is the best for anything running peak power up to 7000 rpm. The engine is in a speedway car so a broad torque curve, without sacrificing any top end power would be amazing.
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Re: 360 degree v8 headers pipe max

Post by BLSTIC »

180 degree grouping isn't ideal, especially with the almost zero runner length Subarus have, but it's a ton better than 90 degree grouping.

Most flat plane 4 cylinders (ie not Yamaha) have 360 degree primary pairing so the 180 interference isn't a thing until nearly a metre from the head, so you almost never get a high pressure pulse during overlap.

I wonder if enough steps would counter the "pipe too long" problem but I wouldn't know until I got my sim going again
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Re: 360 degree v8 headers pipe max

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Re: 360 degree v8 headers pipe max

Post by SchmidtMotorWorks »

juuhanaa wrote: Fri Aug 12, 2022 8:11 am My question about "harmonic length" was an exercise in, what is the length that wave travels back and forth, and when it can help the exhaust gases out. I'm a fan off tuning the exhaust system into peak power rpm, but the engines i mainly work has a valve area to support the size i need for the given length, and the "restricted" cam timing events doesn't hurt bottom end power.. That said, i would start from 27,964in length to make the headers flow more @ 7000rpm and EVO 75degree BBTC, but now the size for the given length would be 2,255in :D Sorry i cant help you in tuning the headers with more complex exhaust system, but there is others in this forum who probably can :) Anyway i made a quicky calculus for your engine using the formulas below,

Here is a formula i used to find out the primary length:

Header pipe length (in inches) = ((850*(180+EVO))/RPM – 3

EVO is how many crank degrees BBTC exhaust valve opens.

Formula to calculate what size we need for a given length to maintain particle velocity:

Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1

cylinder. disp. = one cylinder cid and hdr len is in inches

This give us 1.61in diameter which matches the size of an exhaust valve, but it is calculated for a 50.75cid and 40,35in length, and the given length (based on the formulas) matches 5000rpm and EVO 75degree BBTC.



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How did you arrive at those formula?
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Re: 360 degree v8 headers pipe max

Post by juuhanaa »

SchmidtMotorWorks wrote: Tue Aug 16, 2022 12:18 am
juuhanaa wrote: Fri Aug 12, 2022 8:11 am My question about "harmonic length" was an exercise in, what is the length that wave travels back and forth, and when it can help the exhaust gases out. I'm a fan off tuning the exhaust system into peak power rpm, but the engines i mainly work has a valve area to support the size i need for the given length, and the "restricted" cam timing events doesn't hurt bottom end power.. That said, i would start from 27,964in length to make the headers flow more @ 7000rpm and EVO 75degree BBTC, but now the size for the given length would be 2,255in :D Sorry i cant help you in tuning the headers with more complex exhaust system, but there is others in this forum who probably can :) Anyway i made a quicky calculus for your engine using the formulas below,

Here is a formula i used to find out the primary length:

Header pipe length (in inches) = ((850*(180+EVO))/RPM – 3

EVO is how many crank degrees BBTC exhaust valve opens.

Formula to calculate what size we need for a given length to maintain particle velocity:

Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1

cylinder. disp. = one cylinder cid and hdr len is in inches

This give us 1.61in diameter which matches the size of an exhaust valve, but it is calculated for a 50.75cid and 40,35in length, and the given length (based on the formulas) matches 5000rpm and EVO 75degree BBTC.



-juhana
How did you arrive at those formula?
I'm not sure if you're asking what the variables are in those formulas, but it comes to how we want build the engine and what becomes a restriction.. a valve for example.. If we know more about the intake, why can't we give more area for exhaust? I dont yet see why 1.46ft lbs/cid and 7000rpm for 406, couldn't be doable using a smaller than 2.15 intake valve?
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Re: 360 degree v8 headers pipe max

Post by SchmidtMotorWorks »

juuhanaa wrote: Tue Aug 16, 2022 12:39 pm I'm not sure if you're asking what the variables are in those formulas, but it comes to how we want build the engine and what becomes a restriction.. a valve for example.. If we know more about the intake, why can't we give more area for exhaust? I dont yet see why 1.46ft lbs/cid and 7000rpm for 406, couldn't be doable using a smaller than 2.15 intake valve?
I'm wondering how you came up with the formula.
Is it based on physics or empirical data or something else?
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