Ive been hearing a lot of different things locally about how big of an exhaust i should run on my gsr and im just looking for some feedback on what i should do..

as far as i know 3" or greater is obviously for turbo, but ive also seen plenty of all motor cars run 3" exhausts too. Some have a 2.5 collector out to a 3" pipe.

What is the best size for maximum torque gain? If i keep my car, i would need to retune it and a get a less restrictive exhaust (im running just a high flow cat with oem pipes) and a more modern larger intake manifold (running skunk2 gen. 1 mani now)

im making decent power right now with the restrictive *** exhaust and the cheap chrome tune. 186whp 148tq.

plan to get a hondata before tune and maybe head to jeff evans down in PA.

what are ur guys suggestions?
Thanks.

 

Everything past the collector is a restriction. Power from exhaust comes from manifold pairing and lengths. The bigger the exhaust piping after the collector, the more of a power gain, at every RPM and load point.

Go as big as you can. Your restrictions are packaging and your comfort level (noise, tone, etc).

I chose a happy medium, 2.75" (70mm) with an extra resonator instead of a 'test pipe'. Skunk2 and T1R offer 70mm units. I gained ~4whp everywhere going from a T1R 65mm to T1R 70mm.

 

3" is HUGE, thats a cross-sectional area of 7.065"......2.5" has a cross-sectional of 4.9", and 2.75" has a cross-sectional of 5.93"...........just think about how much air can flow thru 3" piping........ALOT, which means that velocity(directly affects torque) would be low until you start to approach the point where its flowing max volume.

id say no bigger than 2.75"........i personally think 2.5" would be just fine.

 

If you gain more power by running long, skinny pipes after the final manifold collector, why don't you see full exhaust systems on race cars? If your theory is true, you would see tuned pipe lengths on Formula-1 cars, LMP cars, GP cars, they would all have tuned exhaust piping after the manifold system.

I'll repeat myself. Everything after the final merge collector is a restriction. If you are not convinced of this, go read SAE papers, or buy a manifold textbook. Find any point at which they discuss tuning pipe after the collector.

All scavenging and pairing (tuning) occurs in the manifold system. Once the exhaust gasses pass the final merge collector, they are just being routed for ideal evacuation (ie: no exhaust gasses in the cockpit) or allowing for emission control devices.

 

guess youve never heard of a H or X pipe huh, thats scavenging/tuning AFTER the manifold........

ALSO you are comparing racecars to street cars..........most racecars could care less about low RPMs which is where a street car needs smaller diameter to keep your torque up because most people dont drive around at turning high rpms all the time.

i dont care how many times you repeat yourself. in a street car you have to find the BALANCE, between high volume at high rpms so the engine doesnt choke and high velocity at low rpms which means lower volume at high rpm.

on any given engine at a given RPM there is a perfect exhaust size.

i have personally seen the results of exhaust tuning AFTER the collectors and THERE IS TUNING THAT CAN BE DONE.

NASCAR spec dodge engine, on a dynojet. 800hp at the crank, our baseline run was 687hp and after trying different jets and a different carb, and chassis tuning we were at about 700hp, so then we started trying different exhaust......always using the same header and collector.......ended up getting 709hp to the wheels.

 

H-Pipes and X-Pipes are after the collector. Therefore performance would be better without them. They are used for improving the sound of the exhaust, they do not improve performance.

Exhaust manifolds can be and are often designed to aid in low RPM torque, look at the difference between an OEM exhaust manifold and a high end performance exhaust manifold.

Like 92typer said, it's about manifold design. The pipe pairing, lengths, diameter, etc.

 

WRONG, look at dyno sheets of without x or h pipe and with x or h pipe.......they dont have much affect on peak power, but they move the power around.

a static exhaust manifold or header(static meaning it cant change its geometry...similar to variable intake manifolds) designed for a particular engine CANNOT provide both excellent low RPM velocity AND excellent high RPM volume beyond a certain point........aftermarket parts help because OEM parts can be VERY restrictive so there is alot of room for improvement in all areas.

the reason alot of high end race engines dont use a full exhaust system is 1 it adds weight, 2 theres no room in the engine bay, the highest levels of racing except for nascar pretty much all have mid engine cars.......the collectors pretty much exit out the back of the car, 3 their headers are designed specifically for THAT engine so they build the header to suit a particular track or type of track. they dont use a "B16" header........they do alot of R&D and build their own. and what they build has a very specific purpose(high rpm power for a race like LeMans where they spend alot of time accelerating flat out, or not quite as much power but a broader power band for a track like Infineon where there is a mix of fast and slow corners and ALOT of shifting)

FACT: nascar(while i hate it, they build some amazing engines) uses H and X pipe systems on their cars. you are talking about 358c.i. pushrod engines turning anywhere between 7500-9500rpm for 3-4 hours at a time. on a track like california they barely drop below 9000rpm while racing..........you saying they dont know what they are doing?

 

I'm trying to follow your thoughts here.

First you say this:

Then you say this:

That NASCAR info sounds like a very specific engine speed range, with a very specific power level in mind, for a specific track or track type. If you assume minimum engine speed (mechanically) for a NASCAR engine is 1,500 RPM, NASCAR only uses 25% of their operating range (9500-7500/9500-1500).

Formula-1 cars will typically exit a corner around 9,000 – 11,000 RPM, and peak engine speed is 19,000 RPM (FIA mandated limit). Since F1 engines idle around 5,000 RPM, they use 70% of their operating range (19000-9000/19000-5000).

With your reasoning, F1 would benefit from having X and H pipes. Since:
Also,

Most race cars are purposely built under-weight.

F1 cars are built under weight so that they can ballast the car for appropriate weight distribution for the particular tire compound and track layout. With that in mind, if there was any performance benefit to post-collector piping, they could easily add 2 lbs of piping with X's and H's all over the place, and remove 2lbs from their 300 pound ballasts. (Average F1 ballast weight is roughly 140kg). Same weight + more power = faster...right?

Ricardo Wave, the software program used for wave propagation and harmonics for Ferrari's F1 team (and most OEM's), lists X and H pipes ('Geometry Piping') under the 'Acoustic Options' list. Acoustics = Noise. So why would the world's best manifold tuning software package list X and H pipes as 'Acoustic Options'... unless:

I'll let this post end with one question for you:

Is it possible that NASCAR uses full length exhausts and piping because they aren't allowed to run open collector and have sound limits?

Let us imagine that is remotely possible for sake of argument. Now we have to route piping out the back of the chassis. Those mufflers are going to be your greatest restriction in the system, so if you can merge two pipes together to make the X pipe, which is acoustically tuned to reduce your db output, your mufflers can be smaller and less restrictive, thus more power from your routed piping and muffler system!

We'll never know because NASCAR rules are not posted publicly, but from another US spec series:

 

/thread

 

92typeR is right

 

I personally think the best would be a 3'' mid pipe with 2 resonators and a 2.5'' axle back with a straight through muffler. As gases move away from the engine they cool down and loose pressure/velocity, that's why I like smaller axle-backs. Lots of people do the opposite though, 2.5'' into 3''.

 

great info!

thanks for your quick response guys!

 

i moved from a 2.25 exhaust to 3 inch on my 94 gsr. car still feels the same down low but midrange and top end from 5500 on up on the butt dyno feels alot better. of course i added a blox intake manifold and street tuned on a lc1 wide band and crome. had to add alot of fuel up top, took some out mid range but i'd recommend 3 inch exhaust.

 

no there is no rule stating that nascar has to have an h or x pipe, they do have to have an exhaust system that exits behind the driver and in front of the rear tire/s.....which side depends on the track.

so they dont have to use h or x........then why would they use it? my point is and has been that there is tuning that can be done AFTER the collector. you say they are listed under acoustic........well we are flowing air thru a tube, which reverberates and bounces around.............so what if we can get it to bounce around in an orderly and uniform fashion? just a thought.

you do however bring up some good points, the best one being about F1 using more of their rpm range. definitely something to consider. id like to compare some nascar(only using nascar as an example cuz its a bit more available in the US) dyno pulls from a road course car(2 a year is pathetic) and a high-speed oval like charlotte(you cant use daytona or talledega cuz they are restrictor plate tracks). and then look at the specs for the engine and see exactly what is different.........particularly the intake and exhaust tuning.

 

A bigger exhaust will always have a point of diminishing returns given the total amout of flow needed. When exhaust pressure & speed drops drops you get areas of unstable pressure in your exhaust ie. around bends, muffler inlet/outlet, & exhaust tip. This is where exhaust revertion occurs. That will cause a pipe that is oversized to actualy cause bottlenecks in an exhaust system, because the systems flow requirement has not been met. A 2L motor can benifit from 3" exhaust but it would need to be in the 300+hp range to trully utilize the volume of 3" pipe. 2.5" is all that is needed for -300hp The flow will actualy improve given the higher pressure.

 

The reason Nascar uses an X/H pipe is because of the two separate cylinder banks. This is a moot point. After all, this is Honda-Tech. A 3" exhaust will make more power than a 2.5" exhaust on any tuned Honda engine, you don't need to be making more than 300 hp. :scoffs:

 

i think to much thought is bein put into this alot of ppl look at v8's and compare them to 4 banger even if the fire order is the same " up to 4 cylenders ". velocity and scavaging wont be. there has been close to stock test where 3 inch has been an improvement everywhere , of course sound is a big lost with this, there is no such thing as quit 3 inch
"depending on taste of sound".. look at a honda head. a simple way to think about making power is to get as much air as you can to flow threw that head as fast as you can efficently lets say your looking for a top end car .. so you got your intake set up as big plenum fat short runners do you think a 2.5 or a 3 inch header back is your best option .... now you say there is tuning to be made after the collector.. i personaly think the only thing to be made or switched around after the collector is where you want your power band . and that is only because exh. affects the load on the motor

 

As was mentioned above, the tuning after the collector when using an X/H pipe is to control sound. Once sound is controlled, it can allow for higher flowing muflers to be used which is where the largest restriction in most exhausts is located and then more power is freed up. An "H" pipe was often referred to as a "balance tube" to help balance the sound using the exhaust pulses from the opposing cylinder banks in a typical V8.

 

Once you get past the collector, you want the absolute least amount of back pressure. Period. That's why the drag cars all use megaphones on the collectors and nothing else (unless the rules require an exhaust).

X and Y pipes are mostly irrelevant to this thread - they really only do anything on cars with two banks of cylinders or at least two true merge collectors (unless you are just trying to change the sound). And even V8s make more power with just headers dumping into separate megaphones. NASCAR rules require an exhaust that exits at the rear of the car, so they use an X or Y pipe tuned to work with the entire exhaust system (including the header). It makes sense for them because they spend so much time in a narrow rpm range.

So, for the OP - yes, bigger is better, but as the area of a circle (and therefore the volume of the pipe) increase geometrically, the benefits (amount of increase) rapidly diminish as you get past a certain point.

Best of luck with your project.