test&tune:Tpis airfoil,52mm TB, adj. fuel reg.,flowmaster mufflers
I went to the local track here (Capital) again Friday and
I wanted to post more results for those of you considering
some of the above performance modifications.
I ran twice and turned 13.38 the first time(best). This
was at 85 deg. F outside temp., launch at about 180deg
oil temp. Launched car at about 2000 rpm, w/GY GSC's,
2.11 sec to 60 foot.
This compares well with 13.29, 13.31 bests I ran at another
MD track, Cecil county. Outside temp was cooler though, maybe
Only difference in the car between these 2 runs was the installation
of the Tpis airfoil AFTER Cecil County runs.
So, I ran .09 sec slower even with the airfoil installed. The 13.29 and
13.38 times are good comparisions as I had 2.11 sec to 60 feet on both
I must conclude that the air foil does very little if anything; it's effect
is more than eclipsed by weather changes.
I also conclude (see previous post) that the coolant bypass along with
a new fuel filter provides an excellent combo.
My previous best at Capital raceway was 13.6 s, this before the coolant
bypass (and new fuel filter ) and air foil. So for sure, the bypass/fuel filter and airfoil
are good for .22 sec, at the same track.
I'll offer some 1 data point on the other (52mm TB, vortex rammer, adj. reg,
and flowmaster mufflers):
I met a fellow with a Black '93 like mine at Capitol the same night I did the 13.6 run.
His '93 ran a best 13.8 with drag tires (Nitto); these gave him 1.9-2 sec 60 foot times.
Well, I met him again last Friday. He had extensively changed the car, adding the vortex
rammer, a 52mm BBK TB, adj fuel reg., and flowmaster mufflers (not the cat back system).
To my great surprise, he ran a best 13.58s right before my eyes. This with a the 1.9 s
60 foot time.
So with all that gear, he gained about .22 s. I have to conclude that the 52 mm TB
and adj. fuel reg. did nothing; maybe the rammer subtracted .05? (like my claw did)
and the mufflers .15 s?
Realize that temperature really makes a big difference in times... also realize that an adjustable fuel pressure regulator only helps if it is necessary... The way the engine is tuned is what makes the car go fast... if this guy put the regulator on, and cranked up the pressure, the computer will actually shorten the pulse of the injector, this may cause the injector to not spray properly, which kills horsepower... The really good tuners actually do not care about the 'number' that the fuel pressure is set to... they actually test the exhaust and from there they adjust the fuel pressure to make sure the mix is proper... if the mix is good, the computer won't cut down the the pulse time on the injector... this gives you optimum spray patterns, air/fuel ratio, and max horsepower... I have seen many people put adjustable fuel pressure regulators on their car, and get slower times.... Like any modification, it is only going to work well if the car is tuned properly.... Another factor you need to look at is the speed the cars ran, you only posted times... Time doesn't give an accurate measure on horsepower... speed on the other hand is much more accurate.. post the time and speed and I can calculate the RWHP for you
I'd really like to know how you can calculate that. My best time was a 13.526 @ 102.68 MPH. I think I can run a 13.4, but I seem to spin the tires too much. I've just been trying to launch at different RPM's, and haven't gotten it down good yet. Thanks for the info. -JimS
Gone but not forgotten
it's all about seat time and yes weather plays a good part in it matter of fact weather is everything. andy i think your over calculating bolt on factors and forgetting about seat time. seat time in the car is everything! something stupid as staging is very critical when running the #'s 6 inches isn't much in distance from staged to deep staged but that 6 inches would throw your ET off an easy tenth and very easily with all the other equations thrown in there also. shallow stage as much as you can and you will get your BEST ET's and a more consistent ET.
hope this helps,
The curb weight of a 93 coupe is 3,317 pounds.. I'll add 200 for the driver and gear and round up a bit to 3520 pounds (if you want me to change it let me know) your trap speed is 102.68 MPH... Since you have a 6-speed, I will factor a 15% drivetrain loss (this is a widely accepted number)... The horsepower numbers are: 258.7 RWHP, 304.4 HP at the crank... (I use a program I while back to calculate it, I would send it to you but I don't have the capability (due to being cheap) of making an .exe file, i run it within Visual studio)... I am sure someone here has the formula to calculate this.... You can take the formula and plug in numbers from any major auto magazine and get very close to the correct horsepower, so I feel it is accurate (assuming you have a good estimate of the car's weight)
I used to have a 93 6 speed that was set up very similar to your car... I used to run 105 mph in the quarter... that comes out to 325 HP at the crank, using the same weight... as you can see, speed takes a lot of HP... you should be above 325 HP at the crank, here is why: My '93 had the following mods: 1.6 roller rockers on the intake, 1.5 on the exhaust; open airbox with stock paper filter, throttle body airfoil, and straight pipe from the resonator back... Getting a good launch was always a problem for 2 reasons... I didn't want to blow the clutch (i had over 100k miles on the original by the way) and the car was just plain hard to hook up, so I would roll off the line, then nail the throttle... this causes a huge loss in time because in order to get a good trap speed, you need to feather the clutch... basically it comes down to the HP curve of your car... if you let the clutch slip by 50%, which should effectively double your RPM, and the HP of the engine is more than double, then you go faster... this is how some people get great times... it is all a matter of math... this is also why the trap speed indicates HP much better than time.... another reason to use speed is the gearing on stock corvettes is just not set up for the quarter mile... if it was you would be at the redline just as you go through the finish line, and in reality, you should have just shifted into 4th gear, which is not effective for good times...
when you go back to the track try a couple of things out:
everyone thinks that the best way to drive the car is to rev it out in every gear or 'power shift'... this is incorrect... you can 'sport shift' through first and second (meaning shift at lower RPM's, lets say 3,800 to 4,200 in both gears) this puts you in 3rd gear sooner, and lets you stay in 3rd longer... what this does is gives your car the chance to really use its horsepower because it takes alot of horsepower to make a car go fast in 3rd gear... rev it right up the red line in 3rd, then you should have to finish out the quarter mile in 4th... You may be surprised at your speed, and time... I have seen cars do this and get faster times and faster speeds, some get slower times with faster speeds, and a very rare few will do slower on both... My guess is your time will be very close, but your speed will be 105 MPH or higher... it will take some trial and error to see what RPM to shift at... maybe just sport shift in 1st, or maybe power shift in 1st, sport in 2nd, power in third..... see what happens, I think you will be surprised at the results
I just realized the reply poster was different than the thread starter, I am assuming southpaw has a higher trap speed
Gone but not forgotten
i met both these guys at the track about a month or so ago they both got 93 black LT-1's so i think they are at war to see which one can go faster! when i first met them down there (sothpaw thru rubbel), the other guy was just down there. both thier cars where close to stock giving the advantage to soth.
i gotta get my arse back to see them guys and get some more seat time for sept 9th for their corvette shootout also met few other guys that run their vettes up there. always a good time!
I'm here in Chicago, so I don't think I met you in MD, I'd race ya if I did. We do have offices there, but I've never gotten to take the Vette. My car is a 95' 6-Speed w/ Vortex Ram Air, TB Bypass, and running all Synthetic fluids. I will take your advise the next time I'm at the track and try shifting at lower RPM's. I've been shifting at 5500 RPM's in all gears. I finish the 1/4 mile shifting into 4th. You are about dead-on with your calculations! Thanks alot for your response. -JimS
Gone but not forgotten
I think I concur completely with what you wrote.
With respect to temperature, I was just pointing
out that the airfoil's effect is so slight that I can't
tell the difference because I don't know precisely
how the temperature effects the car and what the
exact temp. was the first day.
--As for the regulator, they claim (falsely) that it'll
help any car. I think (and it sounds like you agree)
that it'll only help if the pressure is under what it
should be to begin with. Yes, I bet the pulse width
will alter any gain by too much fuel pressure.
--I think my 13.38/13.29 runs were at 106.7 mph,
I think the 13.31 was actually 108mph (but that
time the tires didn't stick as well, hence the total
time is almost same but actually slower).
--I think nailing the shift from 2-3 really helps your time,
this requires some athleticism. Perhaps a late (5800) 3-4 would
also be good.
--I can't see shifting early (3800) for 1-2 or 2-3. I'm concerned with
the time not the mph--I have whatever hp I have even if I don't punch
it and run 14.5!
--I bet your CE would be fun at the strip!
?feather the clutch
What do you mean here? Do you mean
launching with the clutch 75% out so that
it's grabbing but not all the way out? I guess
that would increase your rpm... but I'm like
you in that I don't want to screw up the clutch.
I don't do burn outs for that reason.
The "sothpaw" isn't miss-spelled for southpaw--
I never explained it in my intro. though.
"sothpaw" was the prop. license tag for Stallone's
Black Lamborgini in Rocky IV. I really liked that film
when I was young and that scene in particular-- the
roar of the engine and the sleakness of the black
car at night!
He neglects to mention that he, too, had that plate - though on a black Trans Am...
oops, I just read it as southpaw, not sothpaw... anyway, the 108 MPH number equals 354 Crankshaft HP, the 106.7 equals 341 crankshaft HP... this is using the 3520 weight from before... you have got the power! In my opinion, a professional could get your car to run low 13's to 13 flat... Professionals don't care about your clutch of course... And the reason they can run that fast is the technique of feathering the clutch... basically, like you said in the reply, don't let it all the way out, which increases RPM... since the Engine's horsepower curve is a curve, and not flat, you can really increase your time by letting the clutch slip and getting the car into higher RPMs (and higher horsepower)... basically when you feather, you try to get the engine right up to its peak horsepower, but not higher... then you would slowly let out the clutch to keep it at the same rpm... by letting out the clutch you are making the car go faster, because it is slipping less. (ok, it is different in real life because it happens so fast, but that is as close of an explaination i can give)
As for the fuel pressure regulator... it can definitely help a modified engine, such as yours... it just needs to be set up properly... if it isn't the computer automatically reduces the pulse of the injector, and this can (and usually does) decrease your horsepower...
Also, the shifting thing... The horsepower of your engine is somewhat a bell shape... meaning, after a certain RPM, your car starts to lose HP.... on a stock LT1, the rating is 300 HP at 5000 RPM... this means above 5000 you are running with less than 300 HP.... you have modified your LT1 a bit, and the mods you have done should increase your max HP RPM meaning your peak HP will probably come up at around 5200 RPM... You may try shifting just a bit sooner, say 5500 instead of 5800, to take more advantage of the curve... all engines are different though, and you need to figure out what is best for yours....
Oh, and the LT4 is lots of fun... Nothing beats the stupid look every C5 owner gives me after I blow their doors off (except Z06 of course)
PS. thanks for reading yet another of my long long posts
Thanks for the long posts!
I think 342-354 might be too high,
I think I weigh maybe 170lb, maybe
175 with helmet, clothes,etc. There
was little junk in the car--just a few
Is a full tank of gas in the 3317lb?
Mine was full.
--I know that even I could get 13.2 out
of the car 'cause that would be the time if
I combined a good take off (2.1 sec to 60')
with the shift time from the 13.31 run (took
11.1 sec to go from 60' to 108 mph at 1/4mi that time).
--You are good, my dynoed peak hp does occur
at around 5200rpm and I do shift at 5500 to
take advantage! If you keep going you can
feel it run out of breath. When I said 5800,
I was just thinking about
what you said about staying longer in 3rd gear.
...yes... the Southpa tag was because sothpaw
was already taken in MD!
What kind of mods did you have when you did the dyno?, and what is your complete list now?... I really think the LT1 has big gains from a better intake with air-foil, TB coolant bypass, 1.6 roller rockers, chip, and exhaust (you didn't mention anything about that) Picking up 50 HP over stock wouldn't be uncommon... All of these mods work together, and if tuned properly should make big gains... (i especially like the rockers, because they reduce friction and mimic a mild camshaft change)
If I cut the weight down to 3500, and use the 106.7 speed, I get to 340 HP at the crank... this is just an estimate, it could be high or low, but a vette that can run that fast in the quarter mile should have that kind of HP...
It looks like you have a good handle on your HP curve too, that is always good... I constantly see people at the track revving the heck out of their cars and going slow, many actually have raised the red-line because they think more RPM = more power... they don't understand the horsepower curve concept...
Glad to hear I am on target with your car... makes me feel good all the time I have spent modifying, learning, modifying, helping to modify etc. to L98, LT1, and LT4 cars hasn't gone to waste!...
About that 3rd gear thing.... In my 93, I always got almost to the end of the track in 3rd, and thought I could make it... never seemed to work though... it just seemed soooo close! I hit the rev limiter a bunch of times... It took me a while to just get used to shifting!... a friend of mine with a z28 had the same problem.. he put in 4.10 gears and he was going through at redline in 4th... the gears shaved a few tenths off too... definitely an excellent mod. if you like drag racing... let me know about that dyno.. you got me curious now, thanks!
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