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Any1 ever though of going down this route.

That way you would keep the excellent low down grunt of the S4 but would get better top end like the RS4.

Not sure if it can be done or what sort of max power they would produce.

I remember driving Harry's MTM'd RS4 it had loads and loads of power but took a wee bit to get going, where as my MRC'd S4 was instant but had no where near as much top end power. If we could have both it would make for a very fast car.

It has been done, Paul, but the outcome wasn't very positive, too high back pressure from the wee K03 hot sides and not enough top end power could be achieved. This along with some reliability issues from what I've heard too...

IMHO not a great idea. straight K04s on an S4 aren't that laggy and low RPM grunt is better than an RS4 due to the different head port design on the S4.

HTH,

Mihnea

however, if you want a pair of K03s for experimental purposes your more then welcome to them. You still got them Minhea

Cheers Mihnea that does help. So I will scrap that idea. Good to know the S4 will build boost a wee bit quicker than the RS4.

Thanks for your offer Andy but I have no idea what I would do with them apart from prob take them to bits just to play

K04's are hardly any different to K03's low down in my experience

so its all in the head port design as Minhea said. Ok but what does that mean in laymans terms?

It means you better watch out Harry

Not sure but prob the RS4 head will have bigger more free flowing ports to aid the amount of flow higher up the rev range, but the bigger the ports the slower the gasses will travel so will hurt spool up slightly. This is only a small prob low down the rev range.

I think Volume and Velocity both have a bearing on turbo spool time and it seems to be a bit of a compromise.

Smaller ports = fast flowing air but restrictive @ high revs

Larger ports = slower air but more of it for making bigger power.

Once the turbos spool up bigger ports all the way.

Well thats my understanding anyway

so does that mean having 2.4 cylinder heads gives you even better flow through the valves making more power or is it just beacuse they have bigger valves being from a N.A engine...

It means you better watch out Harry

Ok maybe not

Good to know Dave.

Sorry Woody I have no idea re the 2.4 heads

Take a look at the torque curve of a K04'd S4 and compare to a remapped K03 S4 and you'll see that the extra lag is almost negligible.

unfortunately the torque curve doesnt really tell you anything about lag - only lack of boost at lower revs

the dyno run is done with the throttle wide open all the time and allows the revs to build up - real lag shows up when you press the throttle and it takes time for the torque/boost to arrive - this doesnt show at all on the torque curve, but a larger turbo will have less low down torque and probably more lag so the 2 are often associated together with larger turbos

unfortunately the torque curve doesnt really tell you anything about lag - only lack of boost at lower revs

the dyno run is done with the throttle wide open all the time and allows the revs to build up - real lag shows up when you press the throttle and it takes time for the torque/boost to arrive - this doesnt show at all on the torque curve, but a larger turbo will have less low down torque and probably more lag so the 2 are often associated together with larger turbos

How about an IHI turbo kit??

More power and torque with a good remap. Jabbasport are doing quite well with that set up. K04's are quite a small turbo to be dealing with a lot of exhaust gases.

Just a thought as I am having a 1.9 rebuild to my S3 but power/torque will be severely limited till I can afford to put the IHI kit on (like 100bhp). Also the IHI turbo tends to be quite reliable.

@black s3 this is for the 2.7t, ihi don't offer a solution afaik

@s4woody, i think valves are same size but ports are larger on 2.4 , no?