fbekholden.com

In practice a small increase from 2 inch to 2.25 inch, but that small diameter change increases the flow (in theory) by about 26%. Combined with the better design of the pipe layout (particularly between the extractors and the muffler) and importantly, the uniform pipe size through the bends, the overall change makes a substantial difference. Where the bends were before cut the diameter and therefore the flow considerably. The difference is noticeable.

I put an order in with Rares on line on the weekend. They are usually quick to post and bits arrive in a few days. I sent an email to see how it was going and this is the reply:

"Thanks for reaching out.

I can confirm we have stock of your order and it will be sent out at our earliest convenience"

I'm thinking that customer service attitudes are not quite what they used to be

I deal with the public in my present role and I can tell you it's not just customer service that is going down hill.

It really shocks me that this modern world is full of selfish victims.

People dont wave if you let them in the traffic, they wont say please or thank you, and will give you an entitled gobfull at a drop of a hat.

I say relax the rules and let people give each other a fist overhaul when required !

Getting older worries me sometimes as a lot of the young punks have no morals.

Why is this happening ?

Greg

EK283 wrote: Wed Jul 22, 2026 11:26 am I deal with the public in my present role and I can tell you it's not just customer service that is going down hill.

It really shocks me that this modern world is full of selfish victims.



Getting older worries me sometimes as a lot of the young punks have no morals.

Why is this happening ?

Greg

It has happened because of the "everyone gets a trophy" and the "smacking is child abuse" mentality - younguns aren't learning that there are consequences for bad behaviour nor are they learning about only the top of the heap get the chocolate - therefore entitled little shits who have no respect for others are in abundant supply.

2.25sq/2sq=1.26 so yes. Simple geometry.


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It's a bit trickier than that. If the flow is turbulent (likely in an exhaust), then you don't square the numbers (2.25²/2² = 25%). The answer is somewhere between (2.25^2.5/2^2.5 = 34%) and (2.25^2.7/2^2.7 = 37%). If the exhaust is long, the flow low and the bore large, the flow becomes more laminar and you get (2.25⁴/2⁴ = 60%).

As the gases change flow rate, they also change the amount of heat they lose in the exhaust pipe. This changes viscosity and density of the gas, which also changes the flow. Those calculations get harder.

Seems a bit fancy, but when you see the amount of money a NASCAR or Top Fuel team will put in to get a few % increase in flow then it makes more sense.

Cheers,
Harv

Wow, thanks Harv. The exhaust fellow said that with better flow the muffler and pipe is less hot so that all makes sense too. I can attest that better flow means more ponies

Yes alright Harv. My rationale is inclined to be static…


FB ute fixer upper, EK van on rotisserie

Brett027 wrote: Wed Jul 22, 2026 9:55 am I put an order in with Rares on line on the weekend. They are usually quick to post and bits arrive in a few days. I sent an email to see how it was going and this is the reply:

"Thanks for reaching out.

I can confirm we have stock of your order and it will be sent out at our earliest convenience"

I'm thinking that customer service attitudes are not quite what they used to be

Last 'Rares' purchase I made for the 1/4 vent rubbers was through SpeedSpares - has Rares branding on the site. Paid an extra couple of dollars to have it mailed express post. Was fitting the rubbers to the car the next day.
No excuse - but that reply smacks of AI.

Yes Lawrence is amazing at Speeds. I think he is no longer a Rares franchise unfortunately.

Brett027 wrote: Wed Jul 22, 2026 8:38 pm Wow, thanks Harv. The exhaust fellow said that with better flow the muffler and pipe is less hot so that all makes sense too. I can attest that better flow means more ponies

Better flow absolutely can make more power, but the dyno tells the real story. On a chassis or engine dyno, you typically see horsepower increase when exhaust restriction is reduced because the engine spends less work pushing exhaust gases out (reduced pumping losses). The gains depend on how restrictive the original system was.

The important point is that bigger flow doesn't always equal more power. Dyno testing regularly shows that an exhaust that's too large can reduce exhaust gas velocity and scavenging, costing torque in the low and mid-range. That's why a properly sized system often outperforms the biggest one.

As for heat, the exhaust can actually feel cooler downstream because the gases are moving through the system faster and spending less time transferring heat into the pipes and mufflers. However, exhaust gas temperature at the engine itself doesn't necessarily decrease just because the exhaust flows better.

The dyno is the only way to measure and it's common to see a well-designed exhaust pick up anywhere from 5–20 hp on a naturally aspirated V8 depending on the engine combination, while poorly matched systems can lose power despite flowing more air.

Just saying.

Greg

Thanks Greg.
I understand that 2.25 inch diameter is the sweet spot for holden sixes, and matches to the extractor outlet size. My dyno is my butt, and my butt says its degrees quicker than it was driving it in for the work compared to driving it home.

Brett027 wrote: Thu Jul 23, 2026 9:05 am Thanks Greg.
I understand that 2.25 inch diameter is the sweet spot for holden sixes, and matches to the extractor outlet size. My dyno is my butt, and my butt says its degrees quicker than it was driving it in for the work compared to driving it home.

Ha Ha, ultimately thats all that matters !!!

Greg

When I got the exhaust made on the ute the guy said he wasn’t sure that 2” would not be too big for it. He was not dvperienced on older cars so he sought some advice that confirmed it would be okay. Since we got hold of the sedan from Trev, I am sold on the 2.25” system. It sounds so much better for a start. Okay, it is a 202 vs 186, and it has a hot dog resonator in addition to sports muffler. I would definitely go the 2.25” next time, even if just for the sound. Oh, and my seat of the pants-o meter tells me the car goes better when ever I do any work to or spend money on mechanicals.


FB ute fixer upper, EK van on rotisserie