Turbo performance regarding exhaust placement

Dear All,

I have an EVO 9 track car rated around 600HP. Engine is a 4G63 stroked to 2.3L. I would like to ask what are the pros and cons for installing a bumper exit exhaust pipe compared to a side exit exhaust pipe compared to ordinary tail exit exhaust pipe. Will these differences lead to increase/reduce turbo lag issue, or turbo fatigue? Will the bumper exit exhaust pipe create excessive back pressure due to high exhaust temperature leaving the pipe without enough time to cool down before exiting to the atmosphere? The track we race in is at the Macau Guia Track with average temperature at race around 28-30 degrees Celsius

Best Regards,

Ronnie

Hi,

When you say "bumper exit" are you meaning the front bumper? If it is the rear bumper, I do not see what the difference would be between this location and the tail pipe exit location, as it is the length and diameter of the pipework between the turbo and exit, as well as the design of the muffler that will have the biggest influence on the amount of back pressure post turbo. Pre turbo back pressure is influenced more by the design and size of the exhaust housing and wastegate.

Exiting the exhaust out of the side of the front bumper (if it is allowed in the category that you race in) through a short length of pipe will have minimal back pressure, as long as the pipe is of a suitable diameter.

The shorter exhaust pipe is the less back pressure it's going to cause. That's pretty much it. Actual location doesn't really matter (side or top) - it's already shorter than regular exhaust system. However on a race car top location can cause blurring because of hot air moving up in front of window.

You did not mention your car's aero package.

May I ask, what is your top speed on the main straight?

At high speed, assuming properly sized and fabricated exhaust, a significant portion of the resulting back pressure could come from the air pressure at the exhaust outlet. At the same time, a significant portion of the aero drag comes from the vacuum at the back of the car.

If you want to optimize exhaust outlet placement, one way to do it is to measure the air pressure at different locations on the car (modern instrumentation would be nice, but a simple manometer would work). The potential added bonus would be reduced level of aero drag. 600 HP worth of air can change your car's aero characteristic, depending on where you dump it.

I don't understand your logic - run a pipe of the same, or slightly larger, internal diameter as the housing outlet and run it where it best fits.

I'd be dis-inclined to make it a bonnet/hood outlet because of the chance of any engine/turbo' isue dumping oil mist or liquid on the windscreen.

That said, that's a circuit racetrack and you may need to run a short pipe under the vehicle with an exit between the front and rear axle, sometimes it needs to be behind the "B" pillar, depending on series rules.

You may also find there's a noise limit, especially for track/test days, which really means a front exit is rules out.

Make sure you check with ALL the folks that could veto your exhaust - series scruitineer (if applicable), track owner, race/trackday/test day organiser.

Hi guys, sorry if I'm a bit unclear. Im not trying to run the exhaust outlet to the top of the bonnet, instead the side of the bumper as one of the option. The reason I'm hesitant to choose either options is because for my racecar, we have fitted a custom made rear subframe and diffuser which had obscure the stock exhaust placement. It is possible to change the design to fit the exhaust but it would disrupt the aerodynamics in the rear. However as mentioned by Gord, having a side exhaust at the b pillar would mean i have to cut through the chassis and affect the rigidity. That is why I would like to know if there is a significant difference on the three different placement to the engine performance.

P. S: there is no noise restriction and exhaust location restriction in the class I am racing on in the Macau Grand Prix

Thank you all for your prompt response though

Maybe I'm still getting it wrong but this is how that's done on my car which is very similar to Evo

Ah, in that case, something similar to what Shota has will be fine - I'd direct the outlet towards the back of the vehicle and maybe aim it a little up - make that waste gas work for me.

Screamer pipe is not visible on the picture but located exactly how Gord just described...