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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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oneaves2005
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by oneaves2005 » Tue Jan 07, 2020 8:04 am

Hi Calvin,

Many thanks for your reply, all makes sense. I think the 4-2-1 will work better for me than a 4-1. We have limited traction, and fairly wide gear ratios, max RPM will be less than 8,000, likely around 7,500. Wet weather racing is a consideration here in the uk and the ability to use a low gear for corner exit stability is a major benefit and something that is quite tricky with the 4-1 systems currently being used.

I would welcome thoughts on calculating the primary length of a long 4-2-1 system and what the benefits of that might be?

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

Post by exhausted » Tue Jan 07, 2020 8:06 am

Your second question,
"Question 2 – I have been looking at several 4-2-1 systems made and used in the UK by very successful race teams that have very long primaries (around what you would expect for a 4-1 system) with a short 8-12” secondary. What is the benefit of this and should I do it also, if so where on earth would the lengths be calculated from as pipemax uses 50/50 split for the primary and secondary pipes."

Still not knowing how big this engine is or the power band, I have always found shorter primaries and longer secondaries as a much more powerful 421 design. I will not go the other way. A long primary header with some 421 collectors stuck on is 1960's, a little bit of torque and a loss in power, sorry. :(

I would want to build you a 8into4into1 header, sizing would be based on power level :D
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 » Tue Jan 07, 2020 8:20 am

From earlier in the thread, it’s about 400hp 250ci/4.1L flat plane V8 with 4000-7500 power band. Correct me if I’m wrong.

I would personally start with a known high performing 2L four banger header design for about 200hp power level and then ask the question whether a Y and a tail pipe can be used to further improve the power curve.

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

Post by exhausted » Tue Jan 07, 2020 8:28 am

At that power and rpm band, I would want to be around 1.5" and 18" primaries, stepping to 1.62 if the 1.5 was more than 5% smaller than the port area. 1.75" secondaries for at least 12" after the primary collector, and a choke in final collectors of 2.0". If that 2" has to be longer than 12" I would step to 2.12 and again to 2.25 if they had to be that long to get to the final merge collector into the tailpipe of 2.5"OD. :D
Sticking a AR chamber somewhere in the tailpipe would be a good idea. One near the final merge and one about halfway down the tailpipe.
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by oneaves2005 » Tue Jan 07, 2020 8:44 am

This is great info.

The exhaust port area at the flange suits a 1.625" pipe to match, perhaps the exhaust port is too big but that's what i'm stuck with :(

As kindly said by ptuomov, 400hp 250ci/4.1L flat plane V8 with 4000-7500 power band

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

Post by oneaves2005 » Tue Jan 07, 2020 8:45 am

Also, system has to exit at the rear of the car, via a single silencer. so a fairly long tailpipe from the collectors

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

Post by ptuomov » Tue Jan 07, 2020 9:18 am

oneaves2005 wrote:
Tue Jan 07, 2020 8:45 am
Also, system has to exit at the rear of the car, via a single silencer. so a fairly long tailpipe from the collectors
You might want to look at the BMW M3 S14/E30 headers as well. The displacement is slightly larger but rpms are similar (or higher). Those from the factory come with 4-2-1 that has pretty much the shortest primaries that fit without sharp bends or merge angles and very long secondaries. I don't know the diameters, but secondaries appear slightly larger than primaries. I think some road racing cars used stepped 4-1 headers instead.

Is there a noise limit or is the muffler just for show?
Last edited by ptuomov on Tue Jan 07, 2020 9:20 am, edited 1 time in total.

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

Post by oneaves2005 » Tue Jan 07, 2020 9:20 am

Will take a look.

The muffler is for noise limits, we have a 105db limit for circuit racing.

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

Post by ptuomov » Tue Jan 07, 2020 9:30 am

oneaves2005 wrote:
Tue Jan 07, 2020 9:20 am
The muffler is for noise limits, we have a 105db limit for circuit racing.
Are you below the minimum weight or does the muffler have to be light as well?

I'd consider necking down the tailpipe just before it ends to 2.5" if you are allowed to use larger pipe upstream. When thinking about my exhaust, I assumed (without much evidence) that once the pulses have been combined the exhaust gas cools by about 25% of the difference between exhaust gas and ambient temperature per meter of pipe length: viewtopic.php?f=1&t=49628&start=45#p662407 . If this assumption is ball-park correct, you could reduce your flow losses by tapering the exhaust to a larger diameter with a cone after the last Y and before the muffler but then coming down to the specified minimum 2.5" at the end when the exhaust gas has cooled.

I agree with others that you want the tertiary (?) collector pipes to be equal length before the Y-merge and as straight as possible upstream of the Y before the pulses have been combined. If you have an expansion cone after the last Y, my logic says that this larger pipe diameter is where one can make some turns.

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

Post by exhausted » Tue Jan 07, 2020 9:47 am

oneaves2005 wrote:
Tue Jan 07, 2020 8:44 am
This is great info.

The exhaust port area at the flange suits a 1.625" pipe to match, perhaps the exhaust port is too big but that's what i'm stuck with :(

As kindly said by ptuomov, 400hp 250ci/4.1L flat plane V8 with 4000-7500 power band
It is not your fault the manufacturer made the ports larger than you need...
Well then, 1.625" OD for 16-18" for Primary. Drop the 1.5 tubing, you do not need to step. :)
Also I need to say the length of tubing between the final collctors on each bank to the final 2into1 tailpipe collector need to be the same length, pretty close, like within 1" if shorter than 12" and 2-3" unequal if longer. Exactly is usually possible in those situations. :)
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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 » Tue Jan 07, 2020 9:56 am

ptuomov wrote:
Tue Jan 07, 2020 9:18 am
oneaves2005 wrote:
Tue Jan 07, 2020 8:45 am
Also, system has to exit at the rear of the car, via a single silencer. so a fairly long tailpipe from the collectors
You might want to look at the BMW M3 S14/E30 headers as well. The displacement is slightly larger but rpms are similar (or higher). Those from the factory come with 4-2-1 that has pretty much the shortest primaries that fit without sharp bends or merge angles and very long secondaries. I don't know the diameters, but secondaries appear slightly larger than primaries. I think some road racing cars used stepped 4-1 headers instead.

Is there a noise limit or is the muffler just for show?
While I would agree that really short primaries and long secondaries are the way to go, the factory has done a lot of testing on that stuff but in the case of this application he would be safer at 16-18" primaries and 12" secondaries not having any software that could even come close on the system past the headers.

That ought to get some folks going...
Look, when I was doing a lot of stuff for the Cup teams, every once and a while some factory engineers would stick in their two cents from the computer mountains. They were so far off it was usually a touchy subject, eh? Seriously, how many efforts/teams are going to actually build three different headers based on computer sims and actually test the results. Usually does not happen and so you see what the computer spits out on the cars. There still is no solution to the best system besides building and testing. Time and money and if there really was a big difference, you would not be able to see them... :)
Calvin Elston
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704-443-8088
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by exhausted » Tue Jan 07, 2020 10:03 am

I could stay on this rant a bit for your entertainment...

Was way back in the mid 90's, I was tapped to make the headers and system for the Mazda GTP 4 rotor car as they were local here in Charlotte. The factory boys had designed the headers sizing and lengths, I didn't argue too much but the original headers they sent to America with the engine that did actually fit the car were built like a plumber built them. Really tight radius bends and long straight sections. The sets I build had no straight tube in them, (ie, smooth) and made over 75 more horsepower. Same tube size... Horsepower is flow. :)
Calvin Elston
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Web: www.elstonheaders.com
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Re: Flat Plane V8 Race Engine - Single Exit Exhaust Question

Post by oneaves2005 » 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

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

Post by ptuomov » Tue Jan 07, 2020 10:11 am

exhausted wrote:
Tue Jan 07, 2020 10:03 am
The sets I build had no straight tube in them, (ie, smooth) and made over 75 more horsepower. Same tube size... Horsepower is flow. :)
If you have to make tight bends, do you still recommend the small pipe sizes such as 2.25" OD for 200hp 4-cylinder bank?

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

Post by exhausted » 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...
Calvin Elston
Elston Exhaust Inc.
Matthews, NC 28104
704-443-8088
Web: www.elstonheaders.com
Blog: www.exhausting101.com

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