[s-cars] Re: RS2 definitive answers

[QSHIPQ at aol.com]

In a message dated 10/18/2004 6:03:37 AM Eastern Daylight Time, Mihnea Cotet <mihnea.cotet at easynet.be> writes:

>Hmmm, if you put it that way (VE thing) it's ok for me, but I am absolutely 
>positive the ECU doesn't use knock correction on short-term boost control. 
>I could post the real formulas/block diagrams for boost control to you so 
>you can see for yourself, but if this is to happen, it's gonna be off-list.

Hey, what's 'short term' v 'long term' Minhea?  Since I presented audi documentation of some trim in boost pressure with knock, what would one need to look at as time increases?  You have given me a definitive 'no' challenge, and I just quoted Audi documentation directly that there is documentation to support my claim that CAT and KNOCK affect boost control function.  Now what?  After selective knock control 'doesn't' do the job, audi claims Fuel increases (to cool things down) and boost decreases.  What's in the "long term" vs "short term" that you might be able to look at? 

>Scott, the RS2 hot side is great, but assuming a totally free-flowing 
>exhaust, it IS going to be the restriction in terms of exhaust backpressure 

To what? I presume with "a totally free-flowing exhaust" you are including the RS2 EM?  Then less EM backpressure isn't necessarily going to make the RS2 turbo perform better.  That statement is a bit misleading Minhea.  With a freeflow exhaust (or with a better EM), the RS2 will hit an optimum output for a given exhaust energy.  As do all turbos.  The question is really, is that optimum output going to supply the needs of the engine.  Then, short term (peak) or long term (continuous).  

>from the hot side itself. Believe me or not, it makes no difference to me, 
>I think I know how to tune a Motronic ECU (and I've long moved on to more 
>challenging things like 1.8Ts, RS4s and such) and I know how to recognize 
>it when boost is too high at the top end and the engine can't evacuate the 
>exhaust gasses fast enough, and pinging/retarding starts to occur. I've 
>discussed these theories with various people and we all agree except for 
>you, sorry but I don't care if you don't, I can't spend my life arguing 
>with you, I have an international business to run and a family to feed too...

Hunh?!!?  Please don't "spend your life arguing with me".  Who am I to have such honor?;)  Minhea, I've read several of your posts over the years as you have "learned" about the inner workings of 4 cycle engines, turbo theory, and EFI theory and application.  Several of them (even recently) conflict with accepted theory and practice.  HAVING the software decoding for Motronic is an enviable position.  I dare say, if a few folks here in the states also had them, you'd be up for some tough 'international' competition.  My unsolicited advice?  Never stop learning Minhea.  I don't run an international business (well I did sell a 7200 overseas, does that count;), and I do have a family to feed.  I'm also well acquainted and versed with turbocharger and turbocharger theory.  I was one of the very first to acquire an RS2 unit in '95 and promptly dismantled it to find 'better', I built and sold RS2 comps before KKK. I've swapped and evaluated more turbos on I5's than I care to count. Still looking for turbos with less compromises...  Certainly the RS2 qualifies as having few (dare I say the fewest?).  

As such, I've ventured opinions on the RS2/7200 turbocharger units.  Are there 'better' turbos out there?  Depending on your definition, I'm sure there are.  Is a RS2/7200 a great turbo for most folks?  I'm sure it is, cuz it can hit some impressive numbers for it's size.  As I look to the S car crowd specifically, 300-400pHP is where 90% are playing.  Then, is the RS2 a good turbo choice? 

>Example of what I'm saying: if the hot side wasn't that big a restriction, 
>why on earth did the Audi 90 IMSA run a K27 #13 hot side on its 750-840HP 
>engine???? I guess a K26#8 could have been enough, or even a K27#7 from a 
>SQ, but wouldn't it be because of the otherwise relatively high exhaust 
>backpressure generated by a smaller hot side at these sort of power levels????

Minhea, even Hap isn't there yet!  I'm happy to discuss some of the wilder turbos that Audisport used, but let's not ever forget that the problem Audisport always had with the I5 was displacement restrictions.  k27 bolted up to 2.1 or 2.226 liters makes for a slug, then rabid dog.  BTDT.  Even Audisports drivers have documented complaints of lack of torque.  Audisports own Anti-Lag system is proof that it was a problem.  If displacement wasn't an issue, A-L wouldn't have been hanging onto the engines at all.

>> >>Hehe, yup, totally agreed, but a better manifold will also free up a 
>> couple
>> >>more HP from the same turbo.

That's not an automatic IMO.  Depends on the manifold, depends on the turbo.  


>Don't get me wrong, it is a GREAT turbo, however if your goals are above 
>370 crank HP, look elsewhere people, there's nothing for you here.

A RS2/7200 turbo is capable of 400pHP.  I might suggest that cold side mods to the 7200 could deliver more.  But then again, as has been my point, for where *most* folks are playing now with S cars, the RS2 is sufficient.

 Same 
>applies to hot sides/turbines. If you're looking for 400+ crank HP, there's 
>no way a K26#6 hot side can handle it without seriously compromising power 
>at the top end. 


No way?  

It's all about trade-offs anyway. But we've seen this on 
>various high-HP 20vt engines in the UK mainly, where people would upgrade 
>their exhausts/hot sides because I was thinking that we were having a 
>backpressure issue, and we've seen gains as high as 30 to 40 HP just going 
>up one size in the hot side and keeping the same boost curve/timing 
>advance/fuel mixture at WOT. Free a couple more degrees of timing at the 
>top end (up to 10 more in some cases), lean the mixture out some more 
>because of the drop in EGTs (because of the increased timing) and voila, 
>you have 50 more HP from the same cold side with no internal mods to the 
>engine itself.

I'm happy to speak to fuel curves vs exhaust backpressure.  High heat = high velocity.  High velocity = more turbo output for a given rpm.  I believe a better comparative test would be to just leave the hot side alone, and tweek fuel.  Too much fuel is a common problem I see on these dyno vs fuel sheets.

I might also propose that actual turbo heat can be controlled more effectively as well, and I am currently testing this on an I5 turbo car.

Minhea, happy to discuss in detail concepts and practices with regard to turbo engines.  I urge you to consider me and others with differing opinions as possible opportunities to learn.  I still am, and I hope my customer cars are better for it.

Best Regards

Scott Justusson
www.qshipq.com