Flat Plane V8 Race Engine - Single Exit Exhaust Question

[exhausted]

Primaries short works upstairs and you keep adding secondary till you don't make any more on the bottom.

[oneaves2005]

Hi All,

So I have managed to find time to run this as an inline 4 cylinder (as no flat plane option in pipemax). I have pasted the results below, manifold lengths seem ok and match well with the exhaust port areas, lengths seem reasonable. The collector diameter still seems a bit big though. I am tempted to run with a 2.25" collector, and increase to a 2.5" where they join into one single tailpipe. There is so much conflicting information online about exhaust systems and i guess the answer is to go with what seems sensible and then try different things if it doesn't work out. I am trying my best to get as close as possible as I don't have the budget to test different systems.

Will go for the above unless anyone thinks it's way off?

Engine Application = Race Engine • Mid-Range Peak TQ • Hi RPM Peak HP

--- Primary Tube Specs : Tri-Y Race Header • Single Tube diameter size ---
Primary Y Segment Single Tube Diameter = 1.583 Best Length = 13.444 -to- 14.633 inches
Secondary Y Segment Single Tube Diameter = 1.583 Best Length = 13.444 -to- 14.633 inches
Primary + Secondary Segment's Total Best Length = 26.888 -to- 29.265 inches

--- Primary Tube Harmonics --- ( One-End-Closed Tube = Odd Numbered Harmonics )
1st Harmonic = 86.264 to 88.642 inches long ... typically never used ( too long to fit any Vehicle )
3rd Harmonic = 26.888 to 29.265 inches long ... highly recommended , best Torque and HP Curve
5th Harmonic = 15.013 to 17.390 inches long ... shortest recommended ( Shorty or very Hi-RPM Header )
7th Harmonic = 9.923 to 12.301 inches long ... shortest recommended ( Shorty, Hugger, or Log Style )
9th Harmonic = 7.096 to 9.473 inches long ... shortest recommended ( Log Style or Cast-Manifold )
11th Harmonic = 5.297 to 7.674 inches long ... shortest recommended ( Log Style or Cast-Manifold )
------------------------------------------------------------------------------------------------------
--- Collector Specs : Straight Tube Collector • or Straight with a more Merge shape ---
Peak TQ Diameter Range = 2.653 -to- 2.778 Best Length= 19.509 -or- 39.019 inches
Best Mid-Range Diameter = 2.778 Best Length= 19.509 -or- 39.019 inches
Peak HP Diameter Range = 2.778 -to- 2.903 Best Length= 19.509 -or- 9.755 inches

H-Pipe Location= 19.509 or 9.755 inches X-Pipe Location= 78.038 or 39.019 inches
( both H-Pipe and X-Pipe locations are measured from Primary Tube ends inside the Collector )

Dual-Exhaust System Diameter = 2.653 to 2.903 inches Dual-Exhaust's each Muffler CFM = 231
Single-Exhaust System Diameter = 2.576 to 2.701 inches Single-Exhaust's one Muffler CFM = 461

--- Collector's Harmonics --- ( Both-Ends-Open Tube = Odd and Even Numbered Harmonics )
1st Harmonic = 156.075 inches long ... longest recommended with Mufflers and TailPipes
2nd Harmonic = 78.038 inches long ... longest recommended with Mufflers and TailPipes
3rd Harmonic = 39.019 inches long ... greater Low RPM Torque -to- Peak Torque RPM
4th Harmonic = 19.509 inches long ... highly recommended , best Torque and HP Curve combination
5th Harmonic = 9.755 inches long ... reduced Peak Torque , higher RPM HP gains possible
6th Harmonic = 4.877 inches long ... reduced Low RPM Torque , even though Tuned Length

Best TQ + HP Tuned Collector Lengths= 4.877, 9.755, 19.509, 39.019, 78.038, 156.075 inches long
Worst TQ + HP Loss Collector Lengths= 7.316, 14.632, 29.264, 58.528, 117.056, 234.113 inches long

[cjperformance]

For some reason it was in my mind that your were restricted to runnint 2.5 collector and tailpipe! I read back and realise that is not so. In that case then yes, 2.25 collectors are fine, then into the 2.5 tailpipe.
The headers must be right though, you can not run a tight exhaust system with oversized headers, gas velocity has to be right ideally from the valve, but at least from the header plate/primary pipe and right thru the whole system or you will never see the systems potential.
You can likely go a little smaller on choke size than i first suggested but I am not a flat plane specialist so im working from 90 deg experience, so dont take me for gospel there!

[exhausted]

I am sorry you all, I thought I was posting to the 6 banger thread...

[oneaves2005]

I am sorry you all, I thought I was posting to the 6 banger thread...

I did wonder!

[midnightbluS10]

Self GM ecotech 6 banger. Didn't go to final collector, didn't need the bottom end...
1.75@6", big step to 2.12and then to 2.25 @ 20"?
2.5" chokes
Self Racing 6 CYL 07-2008 007.jpg
Self Racing 6 CYL 07-2008 006.jpg
Self Racing 6 CYL 07-2008 002.jpg

Is that a 4.2L?

[exhausted]

Self GM ecotech 6 banger. Didn't go to final collector, didn't need the bottom end...
1.75@6", big step to 2.12and then to 2.25 @ 20"?
2.5" chokes
Self Racing 6 CYL 07-2008 007.jpg
Self Racing 6 CYL 07-2008 006.jpg
Self Racing 6 CYL 07-2008 002.jpg

Is that a 4.2L?

Sorry I do not have a clue...

[ptuomov]

My European friends tell me that four bangers like pipes (that I can't deny).

[midnightbluS10]

Self GM ecotech 6 banger. Didn't go to final collector, didn't need the bottom end...
1.75@6", big step to 2.12and then to 2.25 @ 20"?
2.5" chokes
Self Racing 6 CYL 07-2008 007.jpg
Self Racing 6 CYL 07-2008 006.jpg
Self Racing 6 CYL 07-2008 002.jpg

Is that a 4.2L?

Sorry I do not have a clue...

It does appear to be. A little bit of Googling led me to pics from Bohn Racing and their Trailblazer-based 242ci I6 which looks just like this one externally.




From.

https://www.enginelabs.com/news/homegro ... rns-heads/

Wait. Is that the same engine? Lol That exhaust looks awful familiar. And that engine is a beast. Wow!

[englertracing]

I am sorry you all, I thought I was posting to the 6 banger thread...

Are all of those exhausts welded with silicon bronze?

[exhausted]

Now that comp engine is impressive. Also the mention of using a inertia dyno!
The only way to dyno a engine, IMO.

[oneaves2005]

Hi All,

Sorry to drag this up again. I just have a couple more questions that I am sure you can help me with.

I’m fairly comfortable with using a 4-2-1 system with the pipe diameters:

Primary 1.625”
Secondary 1.75”
Collector 2.25”
Two collectors join to a single tailpipe of 2.5”

I have been reading further on the 4-2-1 systems and seem to have got even more confused. I have two questions:

Question 1 – In my application, would there be a benefit to sequential pairing of the primaries? Or would 1-4 and 2-3 be best (remembering this is a flat plane V8, essentially two 4 inline cylinders)?

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.

Weirdly, about 10 years ago I used to race a car (very successfully) with a Twin Cam 1800cc 4 cylinder engine, it produced 200bhp at 7,800rpm and max torque around 5,600rpm and was a very smooth yet responsive engine, it had mild cams but was a 4 valve head that breathed well. I found the header from it in the workshop, it had a 4-2-1 with 1.625” primaries @ 27” long with 1.75” secondaries at 12” long into a 2.25” pipe……..

I have added a picture of the engine as it stands, just for fun.

Thanks in advance!

[cjperformance]

What is the firing pattern you run?
Or , firing order and cylinder numbering sequence?

[oneaves2005]

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

[exhausted]

Greetings, I have been working with 421 headers since about 1995 when I built the first "modern" 421 headers for Winston Cup Plate motors. They suffered severe reversion issues because of the high intake depression as a result of the restrictors. The 421 headers made a big difference in reversion and ran much better than any 4into1 header on those engines. Then it turned out that they ran better on even the open motors. While they did not necessarily make more power at the top of the power curve, they made a lot more power at the bottom of the curve and raced better,faster.
Since then I have worked with all types of race engines from many types of racing.
I have never made a set of 421 headers that utilized a close pairing of the primaries. I see this as a effort to help 4 of the cylinders scavange by inertia/velocity at the pairing while leaving the other 4 cylinders behind. The function of a 421 design is to disrupt and reduce reversion waves in a given assembly. I define reversion waves as pressure waves going the wrong way in our system, and there are many and the slower the engine turns the more reversion hurts power. So while any 421 design is going to do that all by itself if you are going to give up the further separation of waves from individual cylinders by close pairing, you might as well just go ahead and build a 4into1 header. Now this is all my opinion...
The only time I have ever seen headers like that were on BMW road race engines, (as that is all they are ever used for.) The rpm range will also come into play in this discussion as the higher rpm you can keep an engine, the less reversion is an issue. So it is only honest for me to say that I have never done a back to back development project to compare the two phasing options in 421 headers for 4 or V8 engines. I am not aware of any other outfit that would be willing or did spend the time and money on answering that exhaust question...
How a header is designed and fabricated is a player here also as a poor flowing 4into1 made by one fellow compared to a good flowing 421,even closely paired, will lead many into thinking a 421 header is a better header. That is a road I avoid taking as it will lead to wrong conclusions.
Please understand my viewpoint. Maximum horsepower is about flow and is usually accompanied by higher rpms. A 421 header is not designed or needed and a 4into1 design is able to do different things in those cases where we are trying to use the exhaust system to pull hard on the engine at the maximum rpm. A different discussion.
Over the years I have come to see 8000 rpm (maximum rpm ) as the dividing point between 421 and 4into1 header. The number of gears is the other main player in that range also as the more gears the lower the threshold. Back in the late 90's I started doing some 421's for the NHRA PS cars. At that time they were chipping at about 4500rpm and shifting say 8200 or so? The 421 afforded so much bottom end power they would see a big gain on the track. The rpm band they were running was being hurt (overall) by reversion. As rpm bands increased over the years, they no longer find any advantage in the 421. Anyway, the 8000rpm number is my breaking point for my customers. I have done 421's for higher rpm bands for certain applications but those are outliers with unusual gearing.

So i guess in the end, IMO, I see a close pairing 421 header as a compromise as it probably/might/not necessarily will show a bit more top end power over a full separation 421 all else being equal, (ie, the same fabricator and header skills). While that would not be a bad thing, ok? the question is what about a properly built 4into1 for that given engine. I would not and do not waste my customers money building a close coupled 421.