Empire performance exhausts

[_R_J_K_]

Common trait of china exhausts is that they hang reeaally low too.

 

[PIR4TE]

Add to that thermal expansion and you get a much higher CFM requirement of the exhaust than you would ever see in a bench flow test.

Ah OK, now that makes sense:

GenIV 6.0 stock

Exhaust Gas Temperature at end of 4 second 600 RPM/sec Dyno accel test is 743.3ºC or 1829.61 Rankine

Intake Air Temperature (average) is 32ºC or 529.27 Rankine

Volume Increase is 1829.61 / 529.27 = 3.46x

Factor of the Combustion Products = 1.0756x

Therefore

Exhaust Gas Volume of GenIV 6.0 stock at 0.480" (max valve lift) is (130 CFM x 3.46) x 1.0756 = 483.37 CFM total

Given 115 CFM per in^2 capacity of straight pipe, the max ID of exhaust pipe cat back is 4.2" or 2.1" per side

For a stock engine the stock catback appears well suited. Whereas a tuned engine with bolt-ons dyno'd at 250rkw requires 4.72" or 2.36" ID per side hence the stock 2.25" OD catback possibly becomes a minor restriction at high rpm. Some of us knew that with empirical results, granted, above is the scientific basis behind catback size.

It's worth noting that EGT reduces exponentially down the exhaust, such that 30% is typically dissipated in the headers before cat, and end (tailpipe) temps are 25% of cat temp in a VE / VF. So smaller diameter silencers at rear are not an issue, apart from noise.

 

[Big-Al]

Just get your cocks out and compare sizes already. Enuff of this ****.

 

[Not_An_Abba_Fan]

Also, the thing with fluid dynamics is gas flows best when hot. So the walls of the pipe create drag on the flow because of heat loss to the atmospere. It's only the inside 60-70% of the diameter that actually flows well, that is taken into account when designing optimal pipe sizing for exhausts. A computer program and maths doesn't really work in the real world.

 

[Immortality]

Just get your cocks out and compare sizes already. Enuff of this ****.

I've always been of the opinion that IF I have to get my cock out, somebody is going to have to suck it!

 

[Not_An_Abba_Fan]

I've always been of the opinion that IF I have to get my cock out, somebody is going to have to suck it!

You either get it sucked a lot, or you don't take a piss very often.....

 

[PIR4TE]

You either get it sucked a lot, or you don't take a piss very often.....

Nah it's different in NZ, there are a lot of sheep around...

 

[Immortality]

BAhhhhhhhhh

 

[Tsunamix]

Your numbers seem off...

According to the Engineering toolbox....Air - Density and Specific Weight

500 Deg C equates to a density 0.4565, (to convert to a change in density, 1.184/.4565 = 2.59 x), at 1000 Degrees C, 1.184 /.2772 = 4.27 x. 750 being exactly half way in between is 3.43 so your conversion is close enough.

130cfm x 3.43 = 445.9 cfm at the merge, but decreasing as air temp decreases along it's length

I have a table that suggests that a 2 1/2" twin system flows about 509CFM, and a twin 2 1/4" about 408 CFM total. How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

I used this conversion for my new design, but it's based on Engine Horsepower, rather than doing a FI flow calculation. I'm using the old rule of thumb that rear wheel HP (308 on my 6) = Engine kW. That means an estimated 400HP at the engine, and a twin 2.5" need on my six.

It also means that my current exhaust (Single 2.5") is really restrictive

On your system I'm thinking of Headers with 3" collectors, 3" ballistic cats, then a twin 2.5" from the cats back.

 

[PIR4TE]

Your numbers seem off...

130cfm x 3.43 = 445.9 cfm at the merge, but decreasing as air temp decreases along it's length

I have a table that suggests that a 2 1/2" twin system flows about 509CFM, and a twin 2 1/4" about 408 CFM total. How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

I used this conversion for my new design, but it's based on Engine Horsepower, rather than doing a FI flow calculation. I'm using the old rule of thumb that rear wheel HP (308 on my 6) = Engine kW. That means an estimated 400HP at the engine, and a twin 2.5" need on my six.

It also means that my current exhaust (Single 2.5") is really restrictive

On your system I'm thinking of Headers with 3" collectors, 3" ballistic cats, then a twin 2.5" from the cats back.

Thanks for checking those calcs mate. Yes I've seen that table which as the author says is just meant as a rough and quick approximation, just like the rwhp = kW at fly rule of thumb, somewhat inaccurate versus factors used in the PipeMax software. In addition to catback dia the key points I wanted to establish were Primary and Secondary dia and length, point of merge and dia, collector dia and length, H or X pipe where to locate it and why.

Having said that my 'collectors' are indeed 3" expanding to 4" then twin 2.5" catback, very similar to your thinking. Seeing I have the program on my mac laying dormant I would be glad to calculate exact exhaust dimensions specific to your car for shits and giggles if you like.

Basically I need engine type and changed specification of any modifications, type of headers planned i.e. custom race, tri-y (4-2-1), street (4-1s), shorty (std cats), zoomie (haha).