4-cyl header design

[howieschoon]

Hello,
I posted this several months ago but have been getting rather eager to build it so I am going to post it again. It was originally in the "Say what you want" section, so if someone wants to remove that would be quite alright with me. Cammer said that I should get a copy of pipemax, but this is currently the only header or intake manifold that I plan on making anytime in the near future and I don't have much money to spend on this project, so it is somewhat out of my budget (even though it is quite reasonably priced and sounds like it works very well!). Here is m original post:

Hello all,
It’s my first post anywhere on the internet so hopefully I don’t do too terribly. I found this website about a month ago while I was looking for information on 4-cyl exhaust headers and was quite thrilled that David Vizard was the “director of technical writing.” The car/engine this is for is a 1991 Pontiac Sunbird with a 2.0L 4cyl. While this is not a common car to modify, I have had it for about 10 years and am quite attached to it. I would like the header to mainly improve torque and gas mileage as this is my daily driver and doesn’t need high RPM horsepower, most of the time. I would like it to be tuned for about 4000RPM. For this reason and for packaging constraints I would like to use a tri-y design with the first sections about 20”-24” long and the overall primary lengths to be between about 72”-76” (unequal lengths). I used 1400FPS for the speed of sound and a cam with 214deg duration at 0.050” lift (yes, it is a rather small cam). Hopefully my lengths are right, if not please correct me. I wasn’t sure if I should use 180deg or 214deg. or whatever the cam timing is at 0.006” lift to get the time. What I wasn’t sure about was the pipe diameter and if I should have it step up in size or not. I read somewhere that on an even fire 4cyl that the collector should only be about 20% larger (not sure if this was diameter or area) than the primary since the pulses are evenly spaced. Has anyone here heard this before, or even better tested it? Also, should I have the tube size increase by 10% or so at the first “Y” and then another 10% at the collector? I was thinking about using 15ga stainless steel pipe which would give me about a 1.35” ID (I got this size recommendation somewhere, a while ago) with 1.5” OD pipe for the primaries and I think the rest of my exhaust is 1.75”, which I could make larger if it would be worthwhile. I am going to coat the pipes inside and out with Tech Line’s Black Satin (baked in an oven @ 750deg). I want to keep as much heat in the pipes as possible and to have it last a long time. Sorry this is so long and thanks for any and all help.
Howard

Also, if it helps, it has an 86.5mm bore and an 86mm stroke. Any questions please ask.
Thanks again for any help,
Howard

[Devious]

Post the valve diameters, rod length, and port flow (if possible), and I will run it through PipeMax and Dynomation5 to see what comes out.

[howieschoon]

Hello Devious,
Unfortunately, I have no idea what the port flow is.
The intake valve is 1.646" (41.808mm) and the exhaust is 1.437" (36.5mm). Stems are both 7mm (.276").
Max lift should be around .393" (.262 at cam).
The rod length is 5.594" (142.088mm).
Bore is 3.406" (86.5mm) and stroke is 3.386" (86mm).
Compression ratio is about 9.5:1.
Lobe seperation angle is 120deg.
I have an AERA printout of the specs for it, that is where I got most of this.
It should make 110-120HP at the flywheel (this is mostly just an educated guess).
I really do appreciate it. Let me know if there is anything else that would be helpful to know, I might be able to find it. Also, I think Pipemax uses the 2nd wave, is this because it is easier or better or there just usually isn't room for the first one? I should have something like 80" that I could use for it, so if the first is better, I think I would have room.
Thanks again,
Howard

[Devious]

Do you have exhaust cam specs?

You mentioned wanting it tuned for 4000 rpm, by this do you mean power or torque peaking at this rpm? I would assume you mean peak torque developed at this rpm, but I want to be sure. PipeMax generally uses a split of 1500 rpm between peak power and peak torque.

[howieschoon]

Hello Devious,
It is a SOHC with only 8 valves, the exhaust is the same 214deg at .050" lift with .262" lift at the cam. Sorry, yes I would like peak torque at 4000RPM, well, how about 3500RPM for peak torque and 5000RPM for peak HP then, that would be more in the range that I use. This is definately not a fast car, it never will be, I just want it to be more fun driving around town on the highway and hopefully get a bit better gas milage.
Thanks again,
Howard

[Devious]

Here are the numbers from PipeMax for peak power at 5000 rpm using a street Tri-Y:

--- Tri-Y Header Design Specs --- for 123.403 CID from 3000 to 5500 RPM

1st Y-Segment Dia.= 1.347 Length= 16.4 to 18.1 inches long
2nd Y-Segment Dia.= 1.472 Length= 16.4 to 18.1 inches long

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 1.943 to 2.193 Tuned Lengths= 20.6 best and 10.3 or 41.1

H-Pipe= 20.6 X-Pipe= 82.2 distance behind end of Primary Tube ends

-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 20.6 , 41.1 , 82.2 , 164.5 inches long

Worst HP/TQ Loss Collector Lengths= 30.8 , 61.7 , 123.4 , 246.7 inches long

Note=> measured from where the Primary Pipes end inside the Collector to
the point the tailpipe exits into the atmosphere.

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
3rd Harmonic = 32.8 inches long, both Y-Segments combined Length, best TQ + HP

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 164.5 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 82.2 inches long ... longest recommended with Mufflers
3rd Harmonic = 41.1 inches long ... more bottom-end Torque
4th Harmonic = 20.6 inches long ... highly recommended , best Torque Curve
5th Harmonic = 10.3 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 5.1 inches long ... reduced Torque , not recommended


************** Metric Units ******************


--- Tri-Y Header Design Specs --- for 2.022 Liters from 3000 to 5500 RPM

1st Y-Segment Dia. MM= 34.219 Length= 416.9 to 459.5 MM long
2nd Y-Segment Dia. MM= 37.394 Length= 416.9 to 459.5 MM long

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter MM= 49.342 to 55.692 Tuned Lengths= 522.3 best and 261.1 or 1044.5

H-Pipe= 522.3 X-Pipe= 2089.1 distance behind end of Primary Tube ends

-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 522.3 , 1044.5 , 2089.1 , 4178.2 MM long

Worst HP/TQ Loss Collector Lengths= 783.4 , 1566.8 , 3133.6 , 6267.2 MM long

Note=> measured from where the Primary Pipes end inside the Collector to
the point the tailpipe exits into the atmosphere.

Note-> all Pipe Diameters are OD and based-off 1.588 MM Pipe thickness

---- Primary Pipe's Harmonics ----
3rd Harmonic = 833.8 MM long, both Y-Segments combined Length, best TQ + HP

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 4178.2 MM long ... longest with Mufflers and TailPipes
2nd Harmonic = 2089.1 MM long ... longest recommended with Mufflers
3rd Harmonic = 1044.5 MM long ... more bottom-end Torque
4th Harmonic = 522.3 MM long ... highly recommended , best Torque Curve
5th Harmonic = 261.1 MM long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 130.6 MM long ... reduced Torque , not recommended

[seattle smitty]

When you guys are talking about a "Tri-Y" on an inline four, do you mean that in the primary section you are pairing #1 with #2, and #3 with #4? Because I thought I understood that the preferred primary combination was 1+4 and 2+3 . . . .

[howieschoon]

The firing order is 1-3-4-2, so I will pair 1 with 4 and 2 with 3 so that they are 180deg apart.

[seattle smitty]

Thanks, Howie, that's how I remembered it, but I seem to have more senior moments now that I am one. I like your project car because of its unusualness.

[Stan Weiss]

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