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Exhaust blown diffuser options

Exhaust blown diffuser options

Exhaust blown diffuser options

A question for my Eng-Tips automotive brethren!

Background: Hill climb/time trials car. Car has a front air dam and splitter, radiator ducted through the hood, flat undertray extending back to approximately the firewall. Rear wing with large end plates. Less than ideal exhaust piping presently, which is a side exit exhaust, all of which sits below the floor pans. No flat undertray on mid-section of the car presently. Ample room for a rear diffuser starting behind or below the rear differential and rear control arms. Car currently has side skirts which run to the rear tires, and curve inwards behind the front tires.

Limitations: Flat undertray may or may not be permitted due to a series rule that prohibits additional underbody bracing. For purpose of this discussion, assume we are dealing with a factory floor pan without sheeting. Diffuser width/length is unrestricted. Exhaust limitation is past the centerline of the vehicle only - may exit out the side, or the back. Underbody vanes/skirting would also be permitted.

Goals: Any added mid to rear downforce or drag reduction that is not negated by the added weight of the diffuser, which would be aluminum or alumalite sheet.

Given these conditions, the question is primarily a two parter. The first being whether or not there is any benefit to having a diffuser of any size be functional/worth the effort without a flat floor. The latter part - if I were to re-route the exhaust to the rear of the vehicle, where would the exhaust outlet be most beneficial in an attempt to optimize the function of the diffuser? At the mouth? Mid-way? At the diffuser exit?

Any feedback or thoughts on the subject would be greatly appreciated.

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