Best exhaust under $1.5k

[monstar]

The discussions above are only for NA applications though correct?

So if I were to go supercharger in future, the gain is a relatively free flowing exhaust?

Free flowing across wide powerband, yes indeed. However I've made better headers which are ideally suited to forced induction, called 180° crossover headers. These organise the pulse per bank to be sequential like a flat plane crank.
Short of that, converting everything to a forced induction properly, the sensible thing before an exhaust swap would be efficient blower cam swap ie 5° wider lobe seperation and no ground in advance, and better valve springs at least for longevity performance and safety.
I am happy with the Pacemakers and collector setup per above posts and I get 640 HP on e85, but when you make same on 98 an exhaust swap will be least of your concerns. The friction and heat issue is the big Gorilla. HSV lads don't swap the cast iron stocko header logs much, and those are just poor by comparison.
Also imprtant to note that although supercharging with a blower cam does compensate for lack of decent scavenging and velocity, the torque and HP is not a plateau rather a dome, peters out before top RPM (CFM). In other words the fastest 9s Gen-F GTS runs 1 7/8" headers, the fastest NA G8 runs 1 3/4" headers. But the free spinning NA is flowing more with a matched pipe bore at 7200 rpm.
In sum no you don't need to swap headers for typical blow job. If seriously looking to race mods... if you intend race HP as the goal... maybe best get 1 7/8" straight pipes with a cone wrapped around into one straight pipe pointing to the rear. But don't hold back, bimodal cut-outs merging into one downpipe.
View media item 119

 

[duaned]

Keep us informed on the group buy Monstar.

 

[gavmen]

Free flowing across wide powerband, yes indeed. However I've made better headers which are ideally suited to forced induction, called 180° crossover headers....
View media item 119

Yeah might be the go later on when I've actually slapped the blower. I want to see at least 1-2 years of the car warranty before I void it with straight engine mods (opening the block). I voided my previous car's warranty (turbo) within 12 months lol.... it is good to know that the exhaust you're putting together will, as I suspected, would not hold it back in a supercharged application.

cheers

gav

 

[Not_An_Abba_Fan]

No, there is no reversion caused by this collector. Actually creates propulsion, ie can be measured as thrust...

You said it yourself, "expansion chamber diameter decreases causing part of the pressure wave to return to the cylinder" (Not a direct quote but close enough) That is back pressure.

The discussions above are only for NA applications though correct?

So if I were to go supercharger in future, the gain is a relatively free flowing exhaust?

Forced induction totally voids exhaust flow and velocity theory. When you force more air in, you get a bigger bang, this forces the exhaust out. You will never have any collector design aid in scavenging, the scavenging effect will be totally overcome by the exhaust pressure and velocity from the forced induction combustion process. In FI applications, the bigger exhaust the better. You just need to shift volume, if you restrict it in any way it will affect the efficiency of the blower/turbo. However, there is always a "but". Too big and you will create back pressure just by the exhaust cooling process as it slows down. You would need a pretty large exhaust pipe though, 5" or 6".

When you need to build an exhaust for race applications, what racing? 1/4 mile? Circuit? Rally cross? Each will have their own design criteria.

 

[monstar]

You said it yourself, "expansion chamber diameter decreases causing part of the pressure wave to return to the cylinder" (Not a direct quote but close enough) That is back pressure.

No, rarefaction is the opposite to back pressure.

 

[426Cuda]

No, rarefaction is the opposite to back pressure.

Interesting. So, if rarefaction is the opposite of compression, it's actually like "stretching" the gases, thus reducing pressure?

 

[monstar]

Interesting. So, if rarefaction is the opposite of compression, it's actually like "stretching" the gases, thus reducing pressure?

Yes exactly. 'Ripple' of stretched goodness goes right to the exhaust valve.

 

[blackve76]

VCM OTR
Ace. Except when you want to do the right thing and keep the air filter clean, have to basically disassemble and uninstall to remove element to clean. Orssom OTR is same performance different execution but piss easy to maintain.
Pacemaker headers
Those are basic 4-1 straight pipes into merge cone that by its nature has one rpm peak and that's out of reach 99% of the engine's operating range. Same with all 4-1, ok if you want to make noise and spruik about the hp screaming tits off at peak rpm, like most people do BTW. Other than that a stupid waste of money, but nowhere as ridiculous as buying Difilipo oversized POS which deliver worse performance 95% of time (like strapping fire hose to garden tap).
Also if you are going to the extent of proper aftermarket headers you need a custom tuned secondary / collector. Otherwise all these designs are next to useless. The ones you need are PH5387 with diffuser extension before the HFC.
High flow cat????
Yes, they are all made in China from spin steel with coated steel substrate, can pay too much for shiny ones with nice logo just get 200 CPI 4" barrel 2.5" in/out. Price ~$150-$350 each.
HSV VF Centre section
Excellent and simple, extreme value. The only negative is that the x-pipe is more a balancer hence acts like H-pipe, is in the correct location in that regard. However you will get better usable torque with a proper x-pipe device in the correct location (likely tuned further back just behind tunnel brace).
Standard VF muffler
Of course the rear muffler makes a massive impact to sound character and the latest stocko ones are good I think FWIW.

Had try Y's then cammed thought should change headers and the added 4>1's bout 10kw gain up top with no loss of owner down low, around 5kw at 2500. 4>1's losing power isnt a issue in 6l or 6.2. looking for my dyno sheet.

 

[monstar]

Had try Y's then cammed thought should change headers and the added 4>1's bout 10kw gain up top with no loss of owner down low, around 5kw at 2500. 4>1's losing power isnt a issue in 6l or 6.2. looking for my dyno sheet.

Goodo, cam has 10x greater influence than induction or exhaust tuning. Probably cam was better suited to one set than the other. Or are you saying that 4-1 is better overall for top end power because of that?
Some people think so, which is a furphy. The fastest NA drag racing Zeta runs tri-y at 10.3 seconds near 8000 RPM. I run tri-y carrying 500 kg daily in a 2100 kg car with 825 Nm. It's not the design but the spec.

 

[Not_An_Abba_Fan]

No, rarefaction is the opposite to back pressure.

Whether a wave is compressed or rarefied, if it is travelling in the opposite direct to the exhaust flow, it is back pressure. Pressure wave tuning is only effective in the primary pipes. Anything downstream of the collectors has no effect on cylinder scavenging. Any type of reversion or reflection in the exhaust stream after the collectors is back pressure.

What you need after the primary merge is velocity. Creating a low pressure area after the pressure wave of each exhaust pulse when it reaches the collector is what results in the velocity of the exhaust. Even then, it can only be optimal at a given rpm range that the headers are tuned for. ANYTHING after the end of the collectors is a restriction in terms of exhaust flow and velocity. The only reason the rest of the exhaust exists is to meet legal requirements. Having an expansion chamber in the exhaust on a 4 stroke can only result in back pressure. Pulse jets need a combustion event at the front of the chamber, just having pressure waves pulse in is not enough to create the propulsion at the rear. They need a sizable expansion of gas that only a combustion event can provide. That's my understanding of their principle from what I have read anyway.