RS246.com Forum :: The World's #1 Audi R, S and RS Enthusiast Community

My B6 S4 is currently running about 370 BHP with catback, high-flow cats and remap.

I'm very happy with it but I've been wondering what it would take (or if it's even possible) to get it up to 400 BHP? I don't want to de-cat, go FI or sacrifice the reliability of the engine.

Wow that's a pretty good power figure, have you verified that on a rolling road?

You might want to read this thread:

http://www.rs246.com/index.php?name=PNp ... ic&t=85307

Could be a good next step. I think getting 400BHP reliably on a rolling road might be hard to achive without a supercharger, but I'm quite new around here so it might have been done.

Apart from fitting long tube headers and a modified intak manifold there is not much else you can do other than going FI. I suppose nitrious is another option. The next step IMO is to reduce weight. LW wheels, battery, brake discs and front engine pulley will reduce the cars weight. The wheels and battery will do more wrt unsprung weight. The battery are seriously heavy, appporx 25kg, There are relaible and powerful race batteries available weighing half as much.

Unsprung weight has a ratio of 1:6.
1kg unsprung weight saved is equal to 6kgs sprung weight.

The stock alloys each weigh approx 13kg. TD Pro Race 1.2 weight 9kg

Therefore 3kgs saving per alloy = 3 x 4 x 6 = 72kgs effective saving off the car's sprung weight.

Or put it another way:

1720kgs for a B6 S4 divided by 370bhp (your car) = 4.64 kgs/bhp

That is every 4.64kg of sprung weight saved = 1bhp extra

So 72kgs saved / 4.64 = 15bhp extra equivalent due to the weight loss

The weight saving + longtube headers will push you nearer to the 400bhp mark.

Thanks for the replies. Very helpful.

I don't want to go FI but it sounds like I might be reaching the upper limits of where I can get to without some serious money being thrown at it.

What about different profile cams? Does the RS4 use different ones to the S4?

You might be able to squeeze a little more out using some kind of induction kit, but I guess you'd be looking at single figure increases for £££'s.

Induction kits don't work on our cars. In some cases they can actually lose power. Their problem is the close proximity of the auxiliary radiator to the air intake.

If I was pushing for 400bhp NA I'd be buying alot of JHmotorsport gear.

Inlet manifold and spacers
Longtube headers and 2.5 exhaust with x-pipe
Lightweight pulley
Then a trip to MRC for mapping.

That will see you hit 400, but it's not cheap! The headers are awesome, but expensive and require a fair bit of labour to fit.

Cam wise I believe CAT and Schrick make some, but again they aren't cheap and all the hardware needs to be replaced as it's all one time use.

You could easily spend £10k, more than a supercharger kit and more time out of action whilst being put together

370 sounds like a very good result. I was just about getting 360 just under with no cats, full straight thru exhaust system, jhm intake spacers and amd map.

I got 356 with MRC filter, 99 octane fuel, full miltek non res system with racing downpipes (no cats at all)

dont think 400 is possible without almost as much spend as the car is worth

BlingBling wrote:Apart from fitting long tube headers and a modified intak manifold there is not much else you can do other than going FI. I suppose nitrious is another option. The next step IMO is to reduce weight. LW wheels, battery, brake discs and front engine pulley will reduce the cars weight. The wheels and battery will do more wrt unsprung weight. The battery are seriously heavy, appporx 25kg, There are relaible and powerful race batteries available weighing half as much.

Unsprung weight has a ratio of 1:6.
1kg unsprung weight saved is equal to 6kgs sprung weight.

The stock alloys each weigh approx 13kg. TD Pro Race 1.2 weight 9kg

Therefore 3kgs saving per alloy = 3 x 4 x 6 = 72kgs effective saving off the car's sprung weight.

Or put it another way:

1720kgs for a B6 S4 divided by 370bhp (your car) = 4.64 kgs/bhp

That is every 4.64kg of sprung weight saved = 1bhp extra

So 72kgs saved / 4.64 = 15bhp extra equivalent due to the weight loss

The weight saving + longtube headers will push you nearer to the 400bhp mark.

Is the battery sprung or unsprung weight? I thought unsprung was only the wheels, brakes, tyres, some of the suspension linkage etc or have I got this wrong?