Exhausting times....

[Stav]

Guys its funny how Stiddy caused a sensation for the 3 inch xorst. It works well but I have to ask the question....is this really the optimal setup? Is 3.5 inch better? Is 2/3/4 inch better?

[EvilChief]

all depends on cam, head porting, valve diameters, NA/boost and of course application (bottom rend or top end performance)

[StealthAu]

I really think you need to look at your headers before worrying about upgrading the size of the exhaust.

[Stav]

Originally Posted by StealthAu

I really think you need to look at your headers before worrying about upgrading the size of the exhaust.

I want to get these headers working to their max before changing them.

[V3RSAC3]

whoa whoa hang on .. i got a 2.5" .. and now their bringing out a 3.5"? oh dammit, im left behind already :( lol

[EvilChief]

Originally Posted by V3RSAC3

whoa whoa hang on .. i got a 2.5" .. and now their bringing out a 3.5"? oh dammit, im left behind already :( lol

actually 4" is the latest craze ...

[5.0 ED]

Considering a good 2.5inch mandrel bent system with straight thru mufflers flows 400cfm and a similar 3inch flows around 550cfm, and they say the general rule of thumb is your exhaust to intake flow ratio of 3/4's and being that the tb flows what about 600cfm, therefore needing an exhaust flow of 450cfm, then i think you'd need one extremely wild 4litre to justify anything over 3inch in a straigh thru mandrel bent system.

in saying that here i am with a twin 2.5 on a 5litre and a 680cfm throttle body and clogged air cleaner.

More what i have found is its not pipe size but more having a better flowing muffler/cat etc.

Being that some so called hi flow 2.5inch ceramic cats only flow 200cfm and a metal core 2.5inch cat is between 340-380cfm, and as for mufflers a good straight thru none perforated 2.5 inch around 450-500cfm, a straight thru perforated muffler is about 300cfm, and a baffled muffler flows about 200cfm, you get the idea. Also too note hotdog resonators with perforated dog legs, don't flow well, i read somewhere a 16inch 2.5inch redback perforated hotdog flows 280cfm. So if you want an extra resonator put on to make it quieter then a glass packed not perforated type is of little restriction and is actually quieter.

Now i have generalised these figures and recommend anyone wanting performance and changing their exhaust should do some searchs on the net to see what flows best.

[SIKSIX]

Hey, since we are on the topic. I am just wondering you guys with 3'' and over, how do you go about connecting to the extractors. Do you guys cut back the extractors to 3'' or go from 2.5'' outlet on the extractors to 3'' pipe.

Beacuse i was just wondering if there is any gains to be had/lost doing this (cutting) to the extractors.

[Stav]

Good info whiteghia.

SikSix..my 3 inch was done by simply having a 3 inch flange welded onto the headers.Bolted straight on.What have you been up to man? When are you running again? Help shuffle the top ten

[SIKSIX]

Originally Posted by Stav

SikSix..my 3 inch was done by simply having a 3 inch flange welded onto the headers.Bolted straight on.What have you been up to man? When are you running again? Help shuffle the top ten

School and work, I have raced again since the 14.4 but with no luck, 60 ft's were ok (2.1-2.0) but the bit the clutch cable hooks onto the fork slowly bent over the night left me granny, granny shifting (to save my g/box) but still managed 14.6@95-ish mph so theres more in it. At least i like to think so : . Then it gave up completely snapping off that night and so did i for a while but damn this forum is getting me back into it!!

On topic, how much gain is there to be had in upgrading the cat? cause i am still running my std. cat and what is the life on one of them things. How can i tell if it needs replaceing?

Just seen the post, i have pacie comps i think 4480's, std cat, red back 2.5" (recently no resonator)

[Mechan1k]

Stock is good if you don't want to wake up the neighbours. :P

[Sox]

5.0whiteaughia's info is good, and it's what I've been saying for years.
IMO, 2.5" is pretty much the optimal size for our trusty 4L I6's, BUT, you need very good mufflers.
3" is ok if you're into **** factor, but it has no advantage over a 2.5".
Anything greater than 3" and you're just being a tool.

[5.0 ED]

The problem is what are good mufflers, a lot of these so called good mufflers don't flow that well at all. Your generally pretty right with a glass packed straight thru design muffler without dog legs, flowmasters for example are suppost to be one of the best but if you look up their flow rates, their not very good at all.

I went for hooker aerochambers on my car basically because of their destrinct sound and in 2.5inch the flow 440cfm each, being im running twin thats ample, and they are full stainless steel and cost $100 each from vpw, if i was looking at maximum flow i would have gone the hooker maxflow, from what i have seen they seem to be one of the best available, not sure on price thou.

[Sox]

Originally Posted by 5.0whiteaughia

The problem is what are good mufflers, a lot of these so called good mufflers don't flow that well at all. Your generally pretty right with a glass packed straight thru design muffler without dog legs, flowmasters for example are suppost to be one of the best but if you look up their flow rates, their not very good at all.

Absolutely, many brand name items don't meet their supposed claims.
It isn't that difficult to determine whether your muffles are restrictive though, just plonk it on a dyno and run it back to back with the exhaust unbolted at the header flange. Or of course do the same test on the drag strip.

I went for hooker aerochambers on my car basically because of their destrinct sound and in 2.5inch the flow 440cfm each, being im running twin thats ample, and they are full stainless steel and cost $100 each from vpw, if i was looking at maximum flow i would have gone the hooker maxflow, from what i have seen they seem to be one of the best available, not sure on price thou.

I've been visiting a local exhaust guru for the last 20 years, he's tucked away in a little unit in Blacktown and knows his stuff. All I need to do is tell him exactly what I want, and he provides. I don't even question the brand, and he has yet to give me a bump steer.

[Stav]

Originally Posted by Sox

Absolutely, many brand name items don't meet their supposed claims.
It isn't that difficult to determine whether your muffles are restrictive though, just plonk it on a dyno and run it back to back with the exhaust unbolted at the header flange. Or of course do the same test on the drag strip.

.

I have to disagree here. Firstly if there is a legal cat as part of the dropped exhaust it will always gain power .To do it properly you would need the catalytic convertor removed (for track or dyno only) and then check if the rest of the exhaust is restrictive. Of course you would have to rebolt the cat back on for street usage.
A cat can not flow as well as a straight through pipe of the same size(off road pipe)

[Sox]

Originally Posted by Stav

I have to disagree here. Firstly if there is a legal cat as part of the dropped exhaust it will always gain power .To do it properly you would need the catalytic convertor removed (for track or dyno only) and then check if the rest of the exhaust is restrictive. Of course you would have to rebolt the cat back on for street usage.

What ever are you on about Stav? Why would the test not work? We're measuring differences between full exhaust and no exhaust. With or without cat, that's up to you. If you have a restrictive cat, it will show that up too.

A cat can not flow as well as a straight through pipe of the same size(off road pipe)

Can you explain what you're actually meaning here? A cat can flow whatever the design intends it to flow, the inlet/outlet diameter is not the only parameter which determines the flow, it's the size and design of the innards too.

[Stav]

Originally Posted by Sox

What ever are you on about Stav? Why would the test not work? We're measuring differences between full exhaust and no exhaust. With or without cat, that's up to you. If you have a restrictive cat, it will show that up too.
Can you explain what you're actually meaning here? A cat can flow whatever the design intends it to flow, the inlet/outlet diameter is not the only parameter which determines the flow, it's the size and design of the innards too.

Firstly, if you drop the exhaust and gain power then how do you know that the 2.5 inch is the ultimate size? The dropped exhaust is unrestricted.Doesnt this mean the exhaust is better with huge pipes and even larger than 2.5 inch? If you have used this method for your system then did you actually achieve the same power as the dropped system with your upgraded system? Or did the car not match the power?

What I was saying about a cat is that if there was no cat but a straight through pipe then the obstruction/resistance of the honeycomb structure is eliminated .You wouldn't dream of having such a structure in your exhaust port despite the flow figures.

[5.0 ED]

Well the dyno test isn't really conclusive unless you spend the time to tune each one up properly, theres many dyno tests on the net of mufflers being trial, but as i said its not conclusive, if you tune your car up for one and change it to another it will effect the outcome.

And besides that, who as a normal working person wants to spend the money to buy 10 mufflers and dyno their car with each one, technically making each muffler s/h.

[Sox]

Originally Posted by 5.0whiteaughia

Well the dyno test isn't really conclusive unless you spend the time to tune each one up properly, theres many dyno tests on the net of mufflers being trial, but as i said its not conclusive, if you tune your car up for one and change it to another it will effect the outcome.

And besides that, who as a normal working person wants to spend the money to buy 10 mufflers and dyno their car with each one, technically making each muffler s/h.

Eh?
I never mentioned anything about buying 10 mufflers.
What I said was it's easy to determine how much of a restriction your current exhaust is. Plonk it on a dyno and unbolt at the header flange with a few back to back runs

Tuning ain't neccesary in this instance because we're just monitoring any change.

[5.0 ED]

First of all any exhaust is restrictive compared to open headers, you can't put a piece of pipe on 2metres long and expect it to not decrease flow to some point. If you want to work out whats best than you would need to try different things like different mufflers for example.

But then im going to say what you really need to think about is that your exhaust comes out in pulses, and optimally the pulses wave will flow thru to the end of the exhaust and on the rear of the pulse it'll create a vacuum pulling out the next pulse and so on. if you go to small in exhaust it'll blend into a constant pressure out the pipe, if you go to big the first pulse won't have left before the second pulse hits creating no vacuum to pull the next pulse out.

Just dropping the pipes and cats off a 6 with 4480's isn't really optimal for max power either, you should then place a extension on the pipe which helps create this vacuum pulling the next pulse. and the lengh of this extension depends on a lot of other things like displacement, cam, comp, heads etc. Generally speaking thou it should have at least a 10inch collector on them.

Then we have the problem with cat converters, that they are place to close to the collector and should be placed further back after the optimum collector lengh is used.

There was a group/company doing tests on mufflers etc. on a 5litre that i was reading the results of the other day, it had 4 into 1 extractors, now with a full twin 2.5inch exhaust it lost 4ft/lb of touque over open headers, then they put in a x pipe on the headers and it gained 30ft/lb of touque, then couple up the exhaust again and it lost 4ft/lb of touque again but was still up 26ft/lb over what it had with open headers. The touque measurements where an adverage of 3000-6000rpm. Now this gained power with the x pipe on it because it creates this vacuum.

What i am suggesting is to not go bigger in exhaust but to take a good hard look at it and work out how you can make your exhaust work better. And that if you are going to run a 3inch or bigger you should do it by changing the collector to be 3inch on the extractors where the last set of pipes meet and then give it enough lenght for the collector to work, and it is still a collector on tri y's.

[5.0 ED]

What i am saying is that it is the lenght of the pieces that matter. And need to be taken into example when designing a system. I will also say that different cams and heads need different systems.

[Stav]

Originally Posted by 5.0whiteaughia

What i am saying is that it is the lenght of the pieces that matter. And need to be taken into example when designing a system. I will also say that different cams and heads need different systems.

Absolutely!! So what are the best mufflers/cats etc?

[Sox]

Originally Posted by Stav

Absolutely!! So what are the best mufflers/cats etc?

I'll PM you the exhaust dude in Blacktown if you like, he has made all my systems for the last 20 years.
Remember my XH had 175rwkw and ran 14.4 with no traction. It had JMM race headers, with a press bent 2.5" system made by the guy in Blacktown. I believe the main muffler was custom made and it also had a resonator and a hot dog because I wanted it very quiet.
My current AU has a Mercury muffler fitted by him I think.

[Stav]

Originally Posted by Sox

I'll PM you the exhaust dude in Blacktown if you like, he has made all my systems for the last 20 years.
Remember my XH had 175rwkw and ran 14.4 with no traction. It had JMM race headers, with a press bent 2.5" system made by the guy in Blacktown. I believe the main muffler was custom made and it also had a resonator and a hot dog because I wanted it very quiet.
My current AU has a Mercury muffler fitted by him I think.

I have known yor exhaust bloke since was 7 mate. He is a very nice bloke. Used to be a customer at my dads corner store..


I also 100% agree with you that that the primary/secondary lengths and diameters have a huge effect on power delivery.

[Sox]

Originally Posted by Stav

I have known yor exhaust bloke since was 7 mate. He is a very nice bloke. Used to be a customer at my dads corner store..

I hope we're both on the same page here... Bruce, right.

[Sox]

Originally Posted by 5.0whiteaughia

What i am saying is that it is the lenght of the pieces that matter. And need to be taken into example when designing a system. I will also say that different cams and heads need different systems.

The length of pipes are only a concern at the ports, that is, primary and secondary lengths (and diameter) are important at the headers. Beyond the collector things are far less important, assuming diameter is great enough to not allow any significant restriction.

[Stav]

I think I am off to buy some test equipment to analyse my exhaust. I want to find what restriction I have at 6000rpm and where..

[The Monty]

So if 2.5 inch is ideal, why do the Saloon cars run a three inch straight from the extractors, to a side exit? These are the people that do the most R&D on these engines, maybe they are the ones we should be listening to.

[Stav]

Originally Posted by The Monty

So if 2.5 inch is ideal, why do the Saloon cars run a three inch straight from the extractors, to a side exit? These are the people that do the most R&D on these engines, maybe they are the ones we should be listening to.

Saloon cars are great but what works on different cars may not work as well on another. I think it gets to a point where we have to find what works on our combinations by our own testing.

[Sox]

Originally Posted by The Monty

So if 2.5 inch is ideal, why do the Saloon cars run a three inch straight from the extractors, to a side exit? These are the people that do the most R&D on these engines, maybe they are the ones we should be listening to.

Because they are race engines which are constantly revving high, likely always between 4000-6000rpm.
Road cars need to work off a different set of rules, such as low rpm power, noise control, etc.