Any Formula 1 Engineers on here?

[Suggs.OR]

From an engineering standpoint with the downpipe at a fixed diameter and controlling the initial flow into the exhaust system, why is there any gain by splitting into 2 larger pipe diameters? Q=AV right, and continuity principles apply do they not?

I could take my garden hose and run it into 2 large culverts, but I don't think it gets me anywhere.

I can see reduction in friction losses, but can't believe that is a huge deal in such a short run such as this exhaust is. Isn't this a "well it looks cool thing"?

So, I am as guilty as the next guy of doing things for looks (and sound) - why not, its fun and otherwise we would still all be driving '65 Ford Falcons.

But curious what the pipe flow engineers have to say.....

Not an F1 engineer but am a mechanical engineer who deals with all types of air all day. Im clearly not an expert on engines so take it with a grain of salt...

Friction losses are 100% going to play into this. What people dont realize is that the flow of the pipe is not the same across the entire diameter of the pipe. Near the very edges of the pipe the fluid flow is moving slower than the fluid in the very center of the pipe. with this much exhaust flow and a 3" pipe there is significant pressure losses, its just not hugely noticeable because of the short length of the system and its designed to be a higher pressure system.

Lets first calculate the exhaust of the Supra. From a quick google search it says on average the car needs about 2 cfm per 1 engine HP. The 2021 Supra has 382 for a rough total of 744 CFM through the exhaust system as a point of reference, in an office building if you have 100 sq ft office you can guess it will have about 100 cfm.

As you can see the 3" downpipe is good for the 744 CFM coming off of the exhaust but the 382 HP is above the recommended max HP per pipe. Note once again this is all rough data from the first google link when i googled "how to calculate muffler sizes."

It is perfectly ok to have higher than recommended flows but in the downpipe you also have the CC which is going to increase the overall area the exhaust can flow. I imagine that the DP is also made of a stronger material than the rest of the exhaust system.

So now that we have made it through the CC at 3" why not just stay with the single 3"? It has to deal with the back pressure and there being more than optimal flow for the exhaust system past the downpipe. You would likely want to do the 3 1/4" or 3 1/2" exhaust assuming any mods were being done. splitting it into 2 is going to cause back pressure at the fittings where it splits but if you have the (2) 3 inch pipes you have more area, so slower fluid flow, less pressure drop, and less back pressure all causing better flow.

Another reason why you would have to split things into 2 is just for space concerns. I dont think the supra exhaust is 100% round the entire length. I thin it flattens to an oval a little bit so it can be more flat. People tend to tell me 1/2" makes a difference in size and it does here too. Its just easier to route two smaller pipes than one large pipe.

This is pure speculation but for the supra i imagine when you are in normal mode you dont have that high HP that needs the large exhaust and they are able to shut off one of the pipes (the sport mode exhaust flap) and one works perfectly fine. You couldnt do this with a single exhaust obviously.

Also, in my opinion its just better looking than a single exhaust.

Once again for good measure.. im not an engineer who works with engines but i deal with fluid flows every day. same principles different application. So if anything here is wrong i dont care enough to correct it.

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