Different size Header

[Daryl333]

I've just bought a Whipple Gen 3 for my 17 GT.
I have 1 3/4" ARH Catted longtubes. I never thought I would be going FI and found these at a very good price.
Horsepower is very expensive here in Canada.
Since I am going to boost my car i've been trying to find if my 1 3/4" Headers are going to be a detriment or not. Since getting new ones would be a considerable amount up here.(3500+)
I found this article it was the only one I could find that was comparing two sizes in a boosted application.
And I know it's two totally different setups but just wanted to see what people opinions about this and my situation.
Thx.

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[K4fxd]

You will be better off with larger tubes but it will still run good with the 1 and 3/4's

If you do decide to replace the headers go with 2 inch since you are FI. The coyote likes larger tubes than push rod motors.

 

[Grimreaper]

Agreed more is better on this topic. Lots of high power supercharged setups running around on stock catted setups though. I don't think I'd go lt over cat delete pipes much less swapping 1 3/4 primaries for 2. At least for a sub 800whp setup. And even then end goals matter. Diminishing returns etc..

Run what you brung. It's enough. But I would have back up cats ready to go or test pipes made.

 

[Angrey]

Sigh, header myths online are about as bad as motor oil myths.

Above a certain minimum header diameter, increasing or decreasing the header tube diameter simply shifts the peak torque left or right on the rpm scale. Tube LENGTH rocks the curve around the peak point (either flattening/lifting the curve on the low side and lowering it on the high side or the opposite).

From Summit's page:


Primary size is the most important part of selecting headers for your engine.

• Longer primaries reduce the possibility of Exhaust Reversion.
• Equal length primaries time the pulses of exhaust into The Collector to maintain even flow.
• The diameter of the tube directly affects the speed of the exhaust gases traveling through it.

Exhaust travels faster through a small tube than a large one. When you change the size of the tube, you change the flow velocity of the exhaust. Changing the flow velocity changes The Scavenging Effect in the cylinder. The engine will react to different size primary tubes by changing the torque curve.

Primary Length affects the shape of the Torque curve.

• Longer primary tubes produce more torque before the peak. Torque will then fall off after the peak.
• Shorter primary tubes produce more torque after the peak. However, this means less torque before the peak.

**This is why full-length headers provide more low-end power than a set of shorty headers.**​

Primary Diameter affects the torque peak, in relation to rpm.

• Larger diameter primaries will shift the torque peak higher in the rpm range.
• Smaller diameter primaries will shift the torque peak lower in the rpm range.

If your primary tubes are too small, they restrict airflow and rob the engine of power. If your primary tubes are too big, they will shift the torque peak too high in the rpm range to take full advantage of.

 

[wish i was fast]

Sigh, header myths online are about as bad as motor oil myths.

Above a certain minimum header diameter, increasing or decreasing the header tube diameter simply shifts the peak torque left or right on the rpm scale. Tube LENGTH rocks the curve around the peak point (either flattening/lifting the curve on the low side and lowering it on the high side or the opposite).

From Summit's page:


Primary size is the most important part of selecting headers for your engine.

• Longer primaries reduce the possibility of Exhaust Reversion.
• Equal length primaries time the pulses of exhaust into The Collector to maintain even flow.
• The diameter of the tube directly affects the speed of the exhaust gases traveling through it.

Exhaust travels faster through a small tube than a large one. When you change the size of the tube, you change the flow velocity of the exhaust. Changing the flow velocity changes The Scavenging Effect in the cylinder. The engine will react to different size primary tubes by changing the torque curve.

Primary Length affects the shape of the Torque curve.

• Longer primary tubes produce more torque before the peak. Torque will then fall off after the peak.
• Shorter primary tubes produce more torque after the peak. However, this means less torque before the peak.

**This is why full-length headers provide more low-end power than a set of shorty headers.**​

Primary Diameter affects the torque peak, in relation to rpm.

• Larger diameter primaries will shift the torque peak higher in the rpm range.
• Smaller diameter primaries will shift the torque peak lower in the rpm range.

If your primary tubes are too small, they restrict airflow and rob the engine of power. If your primary tubes are too big, they will shift the torque peak too high in the rpm range to take full advantage of.

good accurate information.
it's not just bigger is better.

 

[GregO]

good accurate information.
it's not just bigger is better.

No header myths here.
Accurate when applied to 2 valve heads, not so much with 4 valve.

(As quoted from the Wizard builder of the highest HP headers on the planet)
"There is another factor you run into here is 4 valve engines and there are a lot more of them in 4cyl than 8cyl. They breath like crazy and do not need anywhere near the cam timing to run the same rpm as a 2 valve engine. As a result they do not run into reversion problems as soon. This allows the engine builders to build bigger headers and rely solely on wave tuning to tune upstairs or not even bother "tuning" at all and still make power...
Basically there is less need to develop a exhaust system that can reduce reversion, so they don't."

Calvin Elston
Elston Exhaust

 

[Angrey]

Accurate when applied to 2 valve heads, not so much with 4 valve.

(As quoted from the Wizard builder of the highest HP headers on the planet)
"There is another factor you run into here is 4 valve engines and there are a lot more of them in 4cyl than 8cyl. They breath like crazy and do not need anywhere near the cam timing to run the same rpm as a 2 valve engine. As a result they do not run into reversion problems as soon. This allows the engine builders to build bigger headers and rely solely on wave tuning to tune upstairs or not even bother "tuning" at all and still make power...
Basically there is less need to develop a exhaust system that can reduce reversion, so they don't."

Calvin Elston
Elston Exhaust

No one is worried about reversion on coyote motors. The point is, there's a pervasive myth that bigger primary diameter results in noticeably more power. The reality is above a certain minimum diameter, increasing the tube diameter simply means the car needs to rev higher to reach maximum torque. Depending on gearing and use, that may or may not be preferable.

 

[K4fxd]

In many years of building high performance street and dedicated race engines I have found it best to size the header for the HP the engine actually makes. If you size for tq peak you run out of tube at the top. You size for HP and let the Tq fall where it may, you then use tube length to fine tune things.

4 valve heads are strange in the fact they will take oversized tubes and not lose any torque.

 

[GregO]

In many years of building high performance street and dedicated race engines I have found it best to size the header for the HP the engine actually makes. If you size for tq peak you run out of tube at the top. You size for HP and let the Tq fall where it may, you then use tube length to fine tune things.

4 valve heads are strange in the fact they will take oversized tubes and not lose any torque.

Great points,
I’ll add a close friend & colleague of mine builds step tube 4:1 race headers and in nearly every case his headers dropped ET’s vs. off the shelf headers. There’s magic in sizing the primary at the header flange correctly based on the takeoff radius.
The S550 header flange radius is limited due to the strut towers, primary’s are upsized by default in tight radius elbow fitments.

 

[GregO]

@Daryl333
Take into consideration that the GT500 5.2 uses OEM 1.75” primary 4:2:1 headers when weighing the economics of going to larger header primary’s. Making sure your collector back system is full 3.00” is more important than bumping primary header size to 1.875”+ IMO.

 

[Daryl333]

Agreed more is better on this topic. Lots of high power supercharged setups running around on stock catted setups though. I don't think I'd go lt over cat delete pipes much less swapping 1 3/4 primaries for 2. At least for a sub 800whp setup. And even then end goals matter. Diminishing returns etc..

Run what you brung. It's enough. But I would have back up cats ready to go or test pipes made.

I have these waiting if things don't turn out well for my cats. Hopefully motor will be intact if they fail.

 

[GregO]

I have these waiting if things don't turn out well for my cats. Hopefully motor will be intact if they fail.

And right there is the choke point I was referring to, 3.00” swaged down to 2.25”.

 

[Daryl333]

@Daryl333
Take into consideration that the GT500 5.2 uses OEM 1.75” primary 4:2:1 headers when weighing the economics of going to larger header primary’s. Making sure your collector back system is full 3.00” is more important than bumping primary header size to 1.875”+ IMO.

Being in Canada and due to the differences in dollar. (Our dollar being 65 cents per US)
Add in shipping and duties I will NOT being changing out Headers after reading this.
Lol

And right there is the choke point I was referring to, 3.00” swaged down to 2.25”.

I cut that part cut off on my N/A set up but yes I see the choke and get you on that point.
But after recently buying a used Gen3 stage2 Whipple up here in Canada plus OPGs and CS any more mods like a catback will be on hold for the near future.
Thx much for the info.

 

[GregO]

I cut that part cut off on my N/A set up but yes I see the choke and get you on that point.

Nice job, good to see you used a H style crossover.

 

[Daryl333]

Nice job, good to see you used a H style crossover.

Yup always, not into the sound of an X.

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