LTH primary size

[Redfuzzbutt]

Wanting to go with LTH in the next year for the potential performance gain and easy of breathing. Most primary's are 1 7/8" but there are options for 2" as well.

If I'm just staying conservative with boost and hp, is there a real world difference between the two primary sizes? Car has a Whipple.

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[S550AC11]

I have 1 3/4 primary, 11 psi and just over 800rwhp. I'm sure as power goes up a bigger header would help but I'm not sure at what point that would be

 

[Jackson1320]

1 7/8 is what you want on a boosted coyote unless you are looking at 1400+ Hp/tq and big boy boost

 

[Redfuzzbutt]

I have 1 3/4 primary, 11 psi and just over 800rwhp. I'm sure as power goes up a bigger header would help but I'm not sure at what point that would be

1 7/8 is what you want on a boosted coyote unless you are looking at 1400+ Hp/tq and big boy boost

Perfect, the answers I was hoping for. Thx gents.

 

[LethalPerformance]

1-7/8" will work the best for many. NA as well as most boosted applications. Our 2018 GT with the Gen 5 3.0L Whipple @ 19psi ran the 1-7/8" headers from Kooks and had no issues turning a number at the track with the car going 8.60's@157 consistently.

If you are looking to build an all out race car and are looking for every possible bit of power then the 2" would be what I suggest. But even an 1100rwhp car will love some 1-7/8" headers.

Let us know if there's anything we can help you with.

 

[Angrey]

There's some pretty good videos about this topic if you research. The executive summary is that primary size has a directly positive relationship to peak torque rpm. Generally speaking, bigger primaries, peak torque moves higher in the rpm range. Smaller primaries moves the peak torque lower in the rpm range.

Generally speaking, you can make good power/torque with various sizes, it's just where you want it to be in terms of use. Naturally aspirated obviously favors smaller primaries for things like off roading and low end torque preferred use.

You could make more power than the chassis will handle with either 1-7/8 or 2" it's just how you want it to rev out.

 

[K4fxd]

Actually you size the tube diameter for gas flow, or HP. The primary tube length rocks the torque peak.
Surprisingly the 4 valve heads work well NA with 2 inch.

 

[Angrey]

Actually you size the tube diameter for gas flow, or HP. The primary tube length rocks the torque peak.
Surprisingly the 4 valve heads work well NA with 2 inch.

The rule of thumb for selection is usually based off HP, but the raw calc for the size is based upon peak torque rpm and engine size.

What size headers should I buy? (summitracing.com)

You set what you want your peak torque to be at (RPM) and then from there it gives you the area (and you can then determine radius and/or diameter).

Interesting note. Headers are tubes (not pipes) and therefore the sizes are listed as outside diameter (O.D.) vs pipe listings which are generally inside diameter (I.D.). This can be problematic because the actual size of the flow channel can change upon material type/thickness and still have the same O.D.

Meaning 2 different headers of different materials (but otherwise identical layout/arrangement) can both be listed as 1-7/8" primary tubes but have different flow characteristics based off slightly different inside dimensions.

 

[K4fxd]

Any decent engine sim program will show you I am correct.

You size the tube diameter for the HP level of the cylinder regardless of engine size, and you tune the torque peak with length.

It translates to the real world also.
I will agree with you that if you go too big you will kill torque, but the peak RPM will remain the same.

I have personally tested this on all out race engines, and have made the mistake on the street when I was young and dumb.

 

[bankyf]

1-7/8" will work the best for many. NA as well as most boosted applications. Our 2018 GT with the Gen 5 3.0L Whipple @ 19psi ran the 1-7/8" headers from Kooks and had no issues turning a number at the track with the car going 8.60's@157 consistently.

If you are looking to build an all out race car and are looking for every possible bit of power then the 2" would be what I suggest. But even an 1100rwhp car will love some 1-7/8" headers.

Let us know if there's anything we can help you with.

Any thoughts on the special stepped set of Kooks that you have listed (but I can't find on Kooks website). I inadvertently ordered a set of 1 3/4" from you and didn't realize my mistake until they were installed, so I will likely be doing it all over again soon

 

[LethalPerformance]

Any thoughts on the special stepped set of Kooks that you have listed (but I can't find on Kooks website). I inadvertently ordered a set of 1 3/4" from you and didn't realize my mistake until they were installed, so I will likely be doing it all over again soon

Stepped headers work great. I run them on my Whipple powered 2003 Cobra and they support the power without any issues.

Thanks a bunch for your business! I personally wouldn't be too concerned with the 1-3/4" as they work very well too. I would only swap them out if you plan on doing a high hp build with lots of boost. Otherwise on an NA setup or even mildly boosted setup the 1-3/4" won't be an issue.

Let us know if there's anything else we can help you with in the meantime.

Thanks!

 

[gimmie11s]

The rule of thumb for selection is usually based off HP, but the raw calc for the size is based upon peak torque rpm and engine size.

What size headers should I buy? (summitracing.com)

You set what you want your peak torque to be at (RPM) and then from there it gives you the area (and you can then determine radius and/or diameter).

Interesting note. Headers are tubes (not pipes) and therefore the sizes are listed as outside diameter (O.D.) vs pipe listings which are generally inside diameter (I.D.). This can be problematic because the actual size of the flow channel can change upon material type/thickness and still have the same O.D.

Meaning 2 different headers of different materials (but otherwise identical layout/arrangement) can both be listed as 1-7/8" primary tubes but have different flow characteristics based off slightly different inside dimensions.

Any decent engine sim program will show you I am correct.

You size the tube diameter for the HP level of the cylinder regardless of engine size, and you tune the torque peak with length.

It translates to the real world also.
I will agree with you that if you go too big you will kill torque, but the peak RPM will remain the same.

I have personally tested this on all out race engines, and have made the mistake on the street when I was young and dumb.

Horsepower does not exist. Only torque exists--- horsepower is a calculated number based off of a raw torque value across an RPM range.

It sounds like you both are trying to illustrate the same point, just in a different way.

 

[Slow306stang]

This was my results with increasing exhaust flow on a built coyote.

I had,
1 7/8" long tubes, 3" x-pipe, and a 3" MBRP cat back.

I installed,
2" long tubes, 3.5" x-pipe, 3.5" bullet mufflers dumped.

I did swap intake manifolds from the Boss to the Holley Race manifold but I highly doubt there was any gains. The gains above 150mph on the graph are from having the proper fueling.

 

[K4fxd]

It sounds like you both are trying to illustrate the same point,

The difference is you want to size the tube for total airflow and velocity at peak HP not peak torque.

 

[bankyf]

This was my results with increasing exhaust flow on a built coyote.

I had,
1 7/8" long tubes, 3" x-pipe, and a 3" MBRP cat back.

I installed,
2" long tubes, 3.5" x-pipe, 3.5" bullet mufflers dumped.

I did swap intake manifolds from the Boss to the Holley Race manifold but I highly doubt there was any gains. The gains above 150mph on the graph are from having the proper fueling.

I'm intrigued..... would you care to share a little bit about the build (clearly non turbo) that made that kind of power?

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