1 5/8 or 1 7/8?

[wanna_b_03]

I did a search and come up empty. right now my car makes 550 to the rear wheels, my goal is to have 700-750. I only want to buy one set of headers. Will 1 5/8 flow good enough for 700+ HP or do I need 1 7/8 for that kind of power. If it is 1 7/8 do I need to step up to a 3 inch collector with that power goal in mind?

 

[Termilvr]

Iam running 1 3/4 w/3in to 2.5 in midpipe I should making low 700s

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[Emwun Garand]

I have Kooks 1 7/8 to a 3.5 collector and I'm making 740 on 20lbs boost.

 

[shurur]

I posted this question in the new edge section and got ZERO responses...I'm sharing this with you..and watching responses...some have been claiming NA engines will respond to larger headers...but I'm not convinced...SC may be a different story..but I'm not convinced...

And as far as 1-5/8 vs 1-7/8??..still not convinced..there is a real lack of dyno data out there...before and after Dynos header swaps...as opposed to anecdotal "evidence".....and a huge $ difference for different size headers...huge $$ especially if a lucky rabbit's foot would have done the same thing...not lucky for the rabbit of course..

My Thread Here:
http://www.svtperformance.com/forums/new-edge-cobras-51/862324-1-5-8-vs-1-3-4-headers.html

And my small unanswered post/response/question here!!
http://www.svtperformance.com/forums/new-edge-cobras-51/779628-broke-400rwhp-d-2.html

 

[Blown10thCobra]

Not going to get into the ins and outs and dynamics of it because its too damn early for me lol, but I would go with the 1-5/8. Although our cars are FI, with it being supercharged it's going to act more like an NA car on the exhaust side of things as opposed to a turbo setup.

 

[shurur]

Not going to get into the ins and outs and dynamics of it because its too damn early for me lol, but I would go with the 1-5/8. Although our cars are FI, with it being supercharged it's going to act more like an NA car on the exhaust side of things as opposed to a turbo setup.

Thank YOU for this response!!!.....please do get into the ins and outs when you do have the time...I want to know and listen and understand..

 

[TNTLightning]

An engine is basically an air pump. The more air you can get in and out, the more power you make. 1 3/4" will be sufficient for up to 700ish, for 750+rwhp, go for 1 7/8". Below 600, 1 5/8" will give you the best torque.

 

[Blown10thCobra]

Long story short, it all has to do with back pressure. On an NA car you can stick a 6" exhaust on it and it'll flow gasses like the world is about to end but you won't have power from shit. A supercharged application is going to respond exhaust-wise like an NA car will. You're only forcing air INTO the engine. It's not dependent on exhaust gasses at all. On a turbo application, the turbo takes care of all that. It's forcing air into the manifold, and it's forcing the exhaust gas out. That's why turbo diesel trucks can run these massive exhaust systems and we can't.

 

[04SolidSnake]

Long story short, it all has to do with back pressure. On an NA car you can stick a 6" exhaust on it and it'll flow gasses like the world is about to end but you won't have power from shit. A supercharged application is going to respond exhaust-wise like an NA car will. You're only forcing air INTO the engine. It's not dependent on exhaust gasses at all. On a turbo application, the turbo takes care of all that. It's forcing air into the manifold, and it's forcing the exhaust gas out. That's why turbo diesel trucks can run these massive exhaust systems and we can't.

I'll disagree with "forcing" the exhaust gases out on a turbo car. The reason a supercharged car behaves more like an NA car, is that the exhaust side looks exactly like an NA car, so the scavenging effect, and back pressure all are directly affected by the size and shape of the exhaust. On a turbo charged car, the back pressure and scavenging is already taken car of because you are putting a big ole restriction in the exhaust flow, which the the turbo charger itself which is using the exhaust to drive the compressor wheel. The bigger the better on a turbo car, because unlike your car's engine, backpressure does nothing but hinder the turbo's efficiency. That's why turbo guys run stupid huge exhaust systems diesel, or gas it doesn't matter.

 

[Blown10thCobra]

Maybe forcing was the wrong word, but basically said the same thing.

 

[ShadowGT]

I did a search and come up empty. right now my car makes 550 to the rear wheels, my goal is to have 700-750. I only want to buy one set of headers. Will 1 5/8 flow good enough for 700+ HP or do I need 1 7/8 for that kind of power. If it is 1 7/8 do I need to step up to a 3 inch collector with that power goal in mind?

I went through the same 1 5/8 vs 1 3/4 about 2 years ago, I also did a ton of research on the forums and reading on the subject. I had already used the Kooks 1 5/8 headers from my n/a Mach 1, and to be honest didnt feel the $1200 for the 1 3/4 was worth it for the new Boss 302 F1-D Procharger build.

To make a long story short I made 710whp@ 17psi with the 1 5/8 headers, with a race tune these #'s only increased. To be honest if your worried about the power $1200 for a 1 3/4 or 1 7/8 header could definately be money spent torward custom cams or ported heads IMO. If you have any questions let me know.

 

[Termilvr]

Stock motor, 2.2-2.6 ts, 18psi or so go with 1 5/8
stock motor,2.2-2.6 ts, 20+ go with 1 5/8 or 1 3/4
stock motor, 2.8-3.4 ts, any boost range go with 1 3/4
built motor, 2.2-2.6 ts, any boost range go with 1 3/4
built motor 2.8-3.4 ts, go with 1 7/8
just my opinion

 

[wanna_b_03]

To make a long story short I made 710whp@ 17psi with the 1 5/8 headers, with a race tune these #'s only increased. To be honest if your worried about the power $1200 for a 1 3/4 or 1 7/8 header could definately be money spent torward custom cams or ported heads IMO. If you have any questions let me know.[/QUOTE]

I planned on getting stage 2 or 3 blower cams down the road. So if your saying 1 5/8 into 2 1/2 exhaust is sufficient enough for 700HP then that will allow me to get those cams faster.

Thanks for the help guys

 

[GodStang]

1-5/8" should not even be made for these cars. There is so so so much info on this unfortunetly most is not on this site. The tech side of this bored went years ago. One thing to think about if you do not hook up the correct catback size then headers dont matter that much. I have seen the correct complete exhaust setup gain 100+rwhp on a twin screw car.

One huge gain about adding the correct LTs on a twin screw is the boost drop that the free flowing exhaust provides. Add it back and that is more power.

 

[GodStang]

I planned on getting stage 2 or 3 blower cams down the road. So if your saying 1 5/8 into 2 1/2 exhaust is sufficient enough for 700HP then that will allow me to get those cams faster.

Good god no it is not sufficient..

 

[wanna_b_03]

Good god no it is not sufficient..

Then 1 3/4 with a 3inch collector?

 

[GodStang]

Then 1 3/4 with a 3inch collector?

If you do not go anymore than 700 1-3/4" and 2.5" will do as the gains for 3" are not there for the headache of a 3" exhaust. You start to go anything over that then 1-7/8" and 3". One guy with a 2.4L put special 2" primaries into a 3.5" collector and back gained big power. The only thing is he had special Kmember. I ran 1-3/4" x 2.5" for years at low 700s and it was great great power and response. Once I went to upper 700s I swapped to the 1-7/8" and 3" and but had to swap kmembers.

 

[wanna_b_03]

If you do not go anymore than 700 1-3/4" and 2.5" will do as the gains for 3" are not there for the headache of a 3" exhaust. You start to go anything over that then 1-7/8" and 3". One guy with a 2.4L put special 2" primaries into a 3.5" collector and back gained big power. The only thing is he had special Kmember. I ran 1-3/4" x 2.5" for years at low 700s and it was great great power and response. Once I went to upper 700s I swapped to the 1-7/8" and 3" and but had to swap kmembers.

I thought 1 5/8 sounded small, but that was the common response I got on here so I figured it was sufficient for 700 horse. I feel more comfortable spending money on 1 3/4 with my power goal in mind. thanks for your help and all your good info

 

[MICLO50]

are larger diameter headers needed for 7-8xx whp or would this setup suffice? 1 5/8 stepped to 1 3/4 LT's w/ 3 inch collector, 3 inch OR/X, 3 inch catback?

 

[Termilvr]

I think people say 1 5/8 are fine because then they can get Mac headers for a lot cheaper because if your going to spend the big bucks on headers might as well make it worth it and get bigger primary's.