80tq drag racing- Intercooler reevaluation [long]

[Jim Green]

--- JShadzi at aol.com wrote:
> Well, I drag raced on Sunday at Buttonwillow, had
> fun, but learned something 
> about the car, here are the specs:
> 
> Time: 10am to Noon
> 
> Temp: 90-105F(by 11:00)
> 
> Conditions: Sunny
> 
> Track condition: quattro, need I say more?
> 
> Clutch: Slipping, so I was easy on it-but not so bad
> that it could not do 15 
> consecutive runs, and still feel fine afterwards
> (stock 240 mm 7A BTW)
> 
> Detonation: Little to none, but I am sure the 105
> Oct. helped...
> 
> Boost: 17.5psi
> 
> ET: 15.8  (I know, I know, let me explain...)
> 
> Trap speed: 96 mph (I will talk more about this too)
> 
> 60': 2.2 sec.
> 
> # runs: 15 in 1.75 hr. (basically a run every 6 min
> or so)
> 
> Ok, so my ET sucked, and was way off my "street
> estimates".  I really figured 
> I would be in the low 14's, or mid 13's.  Despite my
> best efforts at tuning 
> the fuel curve, I remained consistent within 2/10th 
> of a second on all 
> completed runs, so at least I was consistent!
> 
> Here is what was happening-I was getting a great
> launch, I was never 
> "outlaunched" all morning, acceleration thru 1-2 was
> strong, what I expected, 
> 0-60 felt in the 5 second range.  But, the top of
> 2nd would get real soft, 
> and by 3rd gear, the car would essentially NOT
> accelerate.  By the 4th gear 
> shift I was crossing the 1/4mile mark, usually in
> the mid 90's.  To give you 
> an idea, I put myself up against a chipped S4tt for
> a few runs-typically, I 
> was 2-3 carlengths in front of him by 2nd gear, but
> once into 3rd he would 
> accelerate past me to finish about 4-5 carlengths
> ahead, very frustrating!  
> So, after my session, I was perplexed and
> dissapointed-cars are either fast 
> or slow for a reason, and my car is not slow, so I
> needed to find the reason.
> 
> Obviously, heat was a factor, I have done all the
> driving and tuning on my 
> car in the SF region, where temps. have rarely
> cracked 75F all summer, so the 
> car is a rocket, but in the 100F+ temps, I
> definitely felt it.  I began 
> wondering how much my (what I originally though)
> huge IC was really cooling 
> my intake charge?  A few test runs revealed a huge
> problem...in a run from 
> 40-80mph, my intake charge went from 41C to 91C! 
> Over a doubling in temp, 
> and imagine what it was doing in a full 0-95mph run.
>  One indication of this 
> was that I was noticing my boost falling from a max
> of 17.5 in 2nd, to below 
> 14psi in 4th.  A few hours of data logging on the
> way home revealed 
> incredible rates of heat soak whenever boost was
> present, and the rate was 
> the same, whether ambient was 15C or 50C
> (obviously).
> 
> One mistake I likely made before the race was
> turning boost up.  Looking 
> back, I bet my ET would have been much faster with
> only 10psi, leaving the IC 
> in a heat range that it could more easily manage. 
> Sitting in 100F in the 
> staging lane did not help either, an IC mister would
> have gone a long way to 
> help this (or one of those computer dusters in a
> can).  An interesting thing 
> to note, a trap speed of 96mph is more indicative of
> a car in the mid-14's, 
> for example a WRX (also all wheel drive) does a 14.4
> @95mph
> 
> SO, I will be upgrading the IC here real soon, my
> plan is to keep the IC I 
> currently have, but add a second identical core to
> the bottom of it and 
> modify the endtanks accordingly.  Thus, my new IC
> will be 18Lx14Hx3"Thick (up 
> from 7" high), and will flow over 800cfm.  Much
> "modification" will have to 
> be done to the front core support, I will be sure
> the post pictures and info 
> when it is all done.  
> 
> Another consideration- I believe I am running the
> stock k26 close to its 
> surge limit, where efficiency is poor and thus temps
> are high (the reason the 
> air-cooled Porches used a massive K27 was to keep
> the turbo in a high 
> efficiency range, thus reducing heat).  I am looking
> at possible T3/T4 combos 
> and a tube header in the future.
> 
> Any thoughts are welcome, gotta love these
> "experiments".
> 
> Javad Shadzi
> 80tq.com

Preach it brother!  I feel your pain, my next upgrade
is going to be an RS2 cover and either an RS2
intercooler or a ridiculous Spearco.  Anyone have
opinions on one over the other?  Piping is not an
issue.  I have to say the same thing about my car, 1st
and 2nd are great, but by the end of third, it seems
like its out of juice.  Cruising on the highway then
down shifting is always fun because the intercooler is
cool, but that doesn't last long because I often hit
18 psi in 4th and 5th which heats up the IC quickly. 
I also would like to do a turbo upgrade, but I didn't
win Powerball so I'll let Javad be the guinea pig as
usual ;-).

=====
Jim Green
'89 90tq 
http://www.geocities.com/jeg1976/

__________________________________________________
Do You Yahoo!?
Make international calls for as low as $.04/minute with Yahoo! Messenger
http://phonecard.yahoo.com/