After seeing the decent gains achieved through an extrude hone to the stock B5 S4 intake manifold I started to think about what I might do with my own Intake manifold. I had recently acquired an RS4 throttle body, RS4 metal throttle body boot, and RS4 up-pipes, but my purchase came at the same time as the RS4 intake manifold jumped from approximately $500 to over $800.
The prospect of paying in excess of $800 for an RS4 intake manifold got me thinking about lower cost alternatives that might get close to RS4 performance levels at less of a cost. A readily available option was the Silly Rabbit Motorsport modified Intake Manifold. The catch was, as is the case with most aftermarket components, there wasn’t enough evidence to convince me that the product was worth the cost.
SRM offers to enlarge the stock B5 S4 intake manifold plenum and to do some porting of the internal surfaces for a cost of $300. That seems reasonable if the product can deliver. For an additional charge of $300 they will fit an adapter flange to the stock IM so that it can accept an RS4 throttle body and provide an RS4 throttle body to go on the intake manifold, now this is getting interesting. How would a ported, enlarged plenum stock S4 intake manifold with an RS4 TB adapter flange fare against a full blown, $800+, RS4 intake manifold?
To answer the question I contacted SRM about doing a two stage test of their product. First I would baseline an untouched stock B5 S4 intake manifold that I had on hand. Then I would send it out to SRM for the plenum and porting work, but retain the stock throttle body size. The intake manifold would be returned for flow testing, to assess the gains from the work a person could expect to get if they wanted to keep a stock throttle body.
Then the intake manifold would be sent to SRM again, this time to have the RS4 throttle body adapter flange mounted to it. With that modification done the intake manifold would be sent to me again for final testing and comparison to the RS4 intake manifold that I’ve previously flow tested.
I wouldn’t be writing all of this if Silly Rabbit Motorsport had not been willing to participate in the testing, so as soon as I baseline this stock S4 intake manifold it will be off to SRM for some modifications.
Here are some pictures of the test article prior to undergoing the modifications.