MPH drop

[Tim Hensley]

I made five passes last Sunday
My mph first pass was 118.5
Next was 117.9
All the way down to 117.2 last pass each pass got slower.
It’s the intercooler getting hot right

[earlbrown]

Or the air going to crap.

[Tim Hensley]

I’m probably over thinking it.  For 1 mph. Should I take my leaf blower?

[Steve Wood]

how long between passes? what was the ambient temp doing? Are you spraying alky?

[Tim Hensley]

30 minutes on one set 45 minutes to a hour the rest
85 degrees and spraying Alky

[wmsonta]

If your 60 ft and the 1/8th times are going the same direction, in the same proportion, it probably isn't the car.
In the quarter, you are talking maybe 5 hp average for the run. The difference in rollout can be .15 sec at full throttle. Bracket racers could name a dozen things.

Head/tail wind, coolant temp consistent, etc. Most bracket racers never stop practicing their leave and their times will vary 1mph in an eighth.
You are making enough steam to go 118/quarter. Get some seat time/enjoyment. There will plenty of time to worry.
JMO.
 

[Steve Wood]

You are not what I call hot lapping and I suspect that is not what caused you to slow down.  I am not a fan of hot lapping.  Not because of the I.C. temp, but, because you can cook the oil pretty quick if you don't let it drop back down.  That's hard on parts.


Particularly when spraying alky, I notice that some of the guys that actually measure temps and such stuff are beginning to go back to stock location intercoolers and are still knocking on the door to the 8's.  I'm sure those guys are blowing air across the core after the run to remove some of the heat faster but I have not asked that question.  I have seen a couple with fans added to them which are run after the run.


The hardest concept for many is to understand that when you make an 8-11 second run, the intercooler does not do significant cooling from air flow.  It might do some cooling if you are road racing or such under continuous throttle, but, in a drag race, it's not worth worrying about.


Basically, an intercooler is a heat sink.  It may look like a radiator, but the tubes are not made like a radiator tube.  Lack of pressure drop is far more important than cooling from airflow.  Alky more than makes up for any supposed lack of temp drop.  The trick is to cool the core back down before the next run so one is always running on the same baseline.


I saw someone's ic on FB the other day and it was positioned parallel to the ground with a fan on it that activated after the run.


Heat Sink-it absorbs and carries heat to the fins and in 8-11 seconds, that needs no real time air flow.

[daveismissing]

Quaker City- FWIW We did note some guys running generators to power fans blowing into the grill. And because Steve had already explained it to me I could sound smart to the Mrs

[Steve Wood]

Ricers used to spray CO2 on them to get them really chilly, really quickly...sure stresses the structure in a hurry.


Dave, did you see that discussion on FB where Ortofski, or however he spells it, stated he ran the same temps and same times when he stuffed a blanket in the air intake to block air flow as he did without it?  LOL, The crowd went wild calling him an idiot.  I did not recognize any names in the mob and I suspect most of them still believe what their favorite internet vendor tells them.

[earlbrown]

Kinda goes back to this....

http://www.autospeed.com/cms/article.html?&A=110772

[Tim Hensley]

I was working on my 60 time,each pass I added timing 129-130-131 to the TT chip, nice and slow looking for KR and WB 1/8 mile mph stayed at 93.1-.5
60 and 1/8 ET and 1/4 ET improved from
1st pass. 11.612 @118.33 60ft 1.799
Last pass 11.556 @117.13 60ft 1.687
Not great improvement but improvement
Trying to get data on converter it could be loosened up on the bottom and tighten on top just a little ,but it’s street manners are so good I don’t want to mess that up.

[wmsonta]

I was working on my 60 time,each pass I added timing 129-130-131 to the TT chip, nice and slow looking for KR and WB 1/8 mile mph stayed at 93.1-.5
60 and 1/8 ET and 1/4 ET improved from
1st pass. 11.612 @118.33 60ft 1.799
Last pass 11.556 @117.13 60ft 1.687

Yup.
You should expect the mph to drop further tenths as the ET drops. The only way to improve both is to make more power. You are using the same power more efficiently. At that size car, I would consider 1.6x shorts to be pretty good.

Congrats on a mid 11 sec street car.

[Steve Wood]

Earl, I don't think I have seen that particular article before.  It sums it up nicely altho' I am sure that 90% will want to argue about what color to paint the intercooler to make it cool better.


I think I will save the candles after my next seance.

[Steve Wood]

Tim, For 93 octane plus alky spray, my experience is that in low gear, one wants to run more timing to spool the turbo and get the alky to make some heat which translates to power.  This can really help when the converter might be a hair tight for optimum performance on the bottom end.


Short times are everything.  On a moderate cars like yours, we see that one tenth on the short time often translates to 1.5 tenths at the other end in the quarter.  If we get more serious and start running into the tens, then that tenth may become two tenths on the top end.


To improve on short times, it takes more power and the ability to stick it to the ground.  In other words, you spin, you lose.  Experience tells us that a 1.6 short time is usually not too hard to achieve on a turbo Buick if the engine is healthy and the converter matches the turbo with sticky tires and a rear suspension that is fairly healthy in factory form.


If that is so, then the limiting factor is how much boost we can hit the rear tires with before they spin.  I recall guys that were putting fiberglass on the front end and bags of cement in the trunk to be able to leave harder without spinning.


The basic problem with G-Bodies is poor geometry in the rear.  Often the instant center is located up near the front wheels and the car does not want to load the rear tires on launch.  Add a little too much boost and the car does not want to leave the line because the back tires are blown away. To go a lot faster/quicker, one must do something about that.


Anyway, again with alky and 93, use timing in low gear to fine tune or improve the short times.  In the remaining gears, use as little timing as possible and rely on additional boost to make the mph.

I have seldom seen more than 18 degs of timing in third gear make the car go any faster, but, I have seen cars slow down on more timing because they could not make the boost.

Coincidentally, the larger the turbo, the less timing one can usually run.  And also, the more alky one sprays, the faster the car will go assuming one does not put the fire out in low gear with too much.

[1 RARE T]

Trying to make a car run it's best time in 85* weather is bound to frustrate anyone.