Audi S4 vs RS4 Tuning Comparison Question

[BlackShadow]

I was thinking about future tuning for my S4, and can't seem to understand the following:

It seems that if you remap an RS4 and stick a full Milltech on it, you get 460 bhp.

It you take an S4 and remap it with KO4 turbos, RS4 injectors, MAF a full Milltech etc, you don't get 460 bhp. In fact you seem to get a bit below or a bit above 400bhp, depending on which tuner you think is more credible.

In the second example haven't you basically converted an S4 to an RS4? Therefore, why the difference in tuned power?

[JonnyX]

RS4 has different heads, cams and internals.

[TarmacTerrorist]

Does anybody actaully know the full list of mods which was done to the 2.7 S4 engine by Cosworth for the RS4 ????

[KayGee]

re-worked heads, head gasket, turbos, airbox, MAF, Injectors, ECU, cams (inlet), fuel pump, fuel rail, intercooler, engine mounts, intake manifold, oil cooler and intake hoses.

[KayGee]

Forgot the clutch and flywheel.

[BlackShadow]

OK, thanks guys. I think that is a pretty comprehensive answer.

[Dippy]

I thought that the exhaust manifold was different too - it's one of the biggest restrictors on the S4 in regard to peak power.

The biggest factor by far is the RS4's cam profile. Clearly you can put a lot of RS4 parts on the S4, but until you put RS4 heads on, peak power will be limited.

However be warned, Cosworth also used different piston and crankshaft parts to handle the extra stress. If you want to go into serious engine mods, then check the price of a complete RS4 engine first.

[tombs]

Would'nt it be easier just to go and buy and RS4 !!

[BlackShadow]

I think it would also be cheaper to buy an RS4, than mess about making an S4 into an RS4. That's why I asked the question to some extent. I don't have the dosh at the moment to buy an RS4, and wondered whether it is worth messing about upgrading an S4 little by little. I think I've reached the conclusion that the answer is that it isn't worth messing about. After chipping an S4 with a full exhaust and sport cats (i.e. 340-350bhp), I think that might be were the value for money reaches its optimum peak, with a deterioration thereafter as regards bhp gained per (thousand) pound spent. I think I would only fit KO4s turbos if the original ones blew - something not unthinkable on a 75,000 mile S4.

Perhaps, 350 bhp is enought for road use anyway. It's not the size that counts it is how you use it.

[KayGee]

I also think the exhaust manifold is different but haven't found any proof it is. Equally unsure about the pistons and crank hence I didn't mention them.

The S4 engine produces monstrous amounts of torque when fully tweaked.....

[NortheastS4]

I suppose another cheaper option is fit Nitrous
at around £600-700 for an extra 100bhp, thats a lot of bang for the buck!!

[Dippy]

After chipping an S4 with a full exhaust and sport cats (i.e. 340-350bhp), I think that might be were the value for money reaches its optimum peak, with a deterioration thereafter as regards bhp gained per (thousand) pound spent. I think I would only fit KO4s turbos if the original ones blew - something not unthinkable on a 75,000 mile S4.

Yup - thats precisely my position right now - expect my car's only done 40,000 miles so I don't expect to replace the turbos yet...

Perhaps, 350 bhp is enought for road use anyway. It's not the size that counts it is how you use it.

I'd agree for about 95% of the time. But there are those occasions where I'm overtaking (especially another performance car) that I feel I could still do with more power!

[rharris]

I've not driven an RS4, but I hear the S4 has more torque. As someone said above, RS4 heads and Cams help it produce the HP. Stage 2+(chip, exhaust and downpipes), S4's make more torque than RS4s. There are some guys in the states with S4's making more lbs/HP than RS4s.

Stage II+ S4's are quicker than RS4's until you hit triple digits speeds. The K03's, which are very small, spool a little quicker. The RS4 is more than the engine. Overall is it's a better package...but, the S4 can be made to hold it's own.

There are a few 450+ HP S4 in the states, which have run fine without engine issues.


Check out some of the links below.



http://biturbo.com - This is a good reference site for S4 issues.

http://s4biturbo.com/timeslips.cgi - S4/RS4 1/4 Times

www.awe-tuning.com

www.achtuning.com

BTW, I am Stage II(Chip and Exhaust). The S4 intercoolers SUCK! They heatsoat very quickly, causing the engine to pull timing. Upgrading the to RS4, AWE-tuning, DUH Engineering FMIC, or $portec units make make a difference.

[Golich]

Yup different pistons, larger gudgeon pin, higher grade bolts for the big end caps, oil draining from cylinder heads is guided to the sump by partition walls and a baffle plate which prevents oil churning. cast iron crankcase strengthened. The depth of the threads for the the head bolts was increased.

But you are right a simple remap alone produces approx 380ftlbs from the S4 while the stock RS4 has only 320ftlbs and the lack of torque is noticeable. Having come from an AMD chipped S4 to a stock RS4. You really have to ring the RS4's neck to get the performance out of it. But the huge difference is that the RS4 pulls like a train all the way to the rev limiter while the chipped S4 is spent by about 5500rpm.

For months after getting my RS4 I kept on hitting the rev limiter while passing cars! The engine just keeps pulling you don't get the usual signing off feel when you know to instinctively reach for the next gear.

I toyed with the economies of spending £25K on top of my S4 for an RS4. Personally if you can live with plainer look of the S4 then value for money has got to be with the S4. As someone noted above if your turbos need replacing anyway at £5-6K the KKK04 upgrade including the RS4 injectors/MAF etc is very good value for money for over 420bhp and torque. This is seriously wicked power and would destroy a stock RS4.

And I read an article some time back in Audi driver about an American race team racing modified S4s with RS4 heads that they have yet to blow an S4 block running at 460bhp.

Clearly Audi/Cosworth have built in a healthy factor of safety into their engines. As MTM can extract 600bhp from the RS4 engine without any strengthening changes to the block/head.

I just had to have the RS4 for it's flared arches and sills, the alloys, the seats, revised interior over my 97S4. I realised it was the whole package. I calculated I would have to spend in excess of £12K-£15K. To make my S4 look and out perform an RS4 and it would still never be an RS4 with limited increase in resale for what would be a considerable expense. So my dream car came home.

[Golich]

If someone knows how to post a PDF file, I can post the Sept 2002 Audi driver article.