Top Speed?

[SF-CHSE]

What is the top speed for a 383 '68 Charger with 3.23 gears.  My car was chassis dyno tuned in STL at 140 MPH. I've had the car up to 135 or 140, hard to tell with the spedo needle fluctuating, before loosing my nerve. The car will go faster but I begin to worry about the Firestone 500's. I figure at some point the car hits an aerodynamic wall due to the recessed grill design an will go no faster. 160?
SF

[XS29J8]

What is the top speed for a 383 '68 Charger with 3.23 gears.  My car was chassis dyno tuned in STL at 140 MPH. I've had the car up to 135 or 140, hard to tell with the spedo needle fluctuating, before loosing my nerve. The car will go faster but I begin to worry about the Firestone 500's. I figure at some point the car hits an aerodynamic wall due to the recessed grill design an will go no faster. 160?
SF

Without an Aero spoiler of some sort a stock 68 Charger generally becomes airborne @ about 145 mph, so 160 would be unobtainable. Yes I know from experience............. ............


Steve

[70charginglizard]

on an off note I believe someone had a daytona doin about 237 on the salt flats not too long ago. That must have been cool to watch.

[SF-CHSE]

XS,
I'm no engineer nor do I have the practical experience you posses over 140 MPH, but how did the '68's run NASCAR without a Daytona wing and aero nose?  What am I missing?
SF

[68X426]

What is the top speed for a 383 '68 Charger with 3.23 gears.  My car was chassis dyno tuned in STL at 140 MPH. I've had the car up to 135 or 140, hard to tell with the spedo needle fluctuating, before loosing my nerve. The car will go faster but I begin to worry about the Firestone 500's. I figure at some point the car hits an aerodynamic wall due to the recessed grill design an will go no faster. 160?
SF

Alex, the answer is: What is infinite speed.

BUT ONLY IF you can eliminate all the factors that slow it down. Those factors are all about stability, as you stated. Ironically you can go well over 200 mph but it's returning safely to zero mph that we all want to acheive.

Here's some math: assuming a 25 inch tire, the 3.23 gear, and a standard TQF 727, speeds at rpms are:
5000 rpm yields 115 mph
6000 rpm yields 138 mph
7000 rpm yields 161 mph
and if you could only get to 10000 rpm, you got yourself 230 mph.

So the most accurate answer is likely 138 mph.

If you could use a 1.00 final ratio gear, and get 10k rpm, top speed is 744 mph. And with a 33 inch tire you get 982 mph. As long as nothing slows you down.

All of this is what Bonneville speed records are about. Find the right combo of factors to go fast and return safely. Set records. Get the girl.

There are all sorts of calulators on line that will work up HYPOTHETICAL speeds. In the real world it's about the limiting factors of safety, stability, tires, aero features, rpms, gearing, suspension, road conditions, etc, etc.

If you saw a 135-140 speedo, safely, well then you've been to the twilight zone and returned. It would cost a lot of dough to get past that. More than just tires. And leave some dough for the funeral.

[68X426]

XS,
I'm no engineer nor do I have the practical experience you posses over 140 MPH, but how did the '68's run NASCAR without a Daytona wing and aero nose?  What am I missing?
SF

Gear ratios, rpms, tire height, suspension, tires, size of driver's stones. See previous post.

[70charginglizard]

Ludicrous speed.....NOW!

[Road Dog]

I've been to 140-145 indicated on the Goose and the car had lots more left. Felt great too! Car and driver said 156 mph for a 68 hemi charger with 3:23 gears.
The 1969 440 Polara Police Pursuit car was clocked at 149 mph+.

[SF-CHSE]

Great response 68X.  You got me on the RPM's as I do not have a tach.  However I've had the car up to 130+ a dozen times.  I'm not buying the math. At 130+ i've got plenty left of pedal before I hit the floorboard and no the engine does not sound like it is straining.  Hmm, what are the guys in Europe hitting on the Autobahn in their Chargers?  138 max no way...

[68X426]

So you are saying that at 130+ mph you are not at the cars limits? Then the physics of the matter are that you have a taller tire than 25 inches, a taller final gear ratio than 3.23, or a 383 that is still delivering useable power to the ground beyond 6000 rpm, or a combination of all three.

Here is a great calculator to work with. http://users.erols.com/dmapes/GEARCLC.HTM

My Hemi Road Runner top speed (HYPOTHETICAL) is 172 when my particulars are inputed. But it will only go 130 in the real world. So it is 75% efficient. It loses 25% to all the limiting factors already discussed. Your Charger may have a hypothetical max of 185 mph and real world max of 150. So it may be 81% efficient.

Sounds like you want to go more than 140. Here's the test: what would a tire blow out at 150 do to you and the little 2-point NOS seat belt? Do you have a roll cage, reinforcements, helmet, nomex suit, ambulance trailing behind, and lots of insurance? Speed is awesome, but you are right at the cars limit. Why test 1968 equipment on today's pavement?

[LeadfootBob]

XS,
I'm no engineer nor do I have the practical experience you posses over 140 MPH, but how did the '68's run NASCAR without a Daytona wing and aero nose?  What am I missing?
SF

Dig around a bit on allpar, somewhere there's an account of the first all-out run with the then-new Gen 2 charger on the track... Let's just say it sounded like an "interesting" experience.

The Gen 1's are supposed to be even worse, look at the body shape. What does it resemble? An aircraft wing. Vacuum-inducing on the top, flat underneath = lift built into the body. Brilliant 

[SF-CHSE]

68X,
I'm sending up the white flag on this topic.
Sometimes its just nice to know that when I see a new Corvette or Porsche in my rear view that I can give them a run.
I'm not condoning 140+ speeds on the highway nor will I attempt to max out my 41 year old classic.
Gotta be more like 150 than 130 MPH.
But at those speeds who's watching the meter anyway!
SF

[RD]

I was racing a 68 383 charger in my 73 charger back in high school (more like follow the leader to be truthful).  My speedometer was pegged at the six o clock position (was a 120mph) and her's was showing 148 (she had a 150mph).

So my guess.. 148mph

she did have a 3.23 geared charger.. sorry should have mentioned it.. mine was 2.76

[68X426]

Sometimes its just nice to know that when I see a new Corvette or Porsche in my rear view that I can give them a run.

It's not always the car, it's the driver! You can blow their doors off, just got to surprise them.

Here's a great site that provides the reminder of what happens to those "hot" cars and the things their drivers accomplish with speed.

http://www.wreckedexotics.com/newphotos/exotics/

[NYCMille]

Well to give you some idea... my '68 with a mild 440 and final OD of 2.96 ratio in OD has been up to about 153 mph... I know this because I got radar'd... long story..

Anyway, at those speeds the front end was actually quite planted... it's the rear that gets a bit funky. That rear window just circulates air in that trough of a rear window and you get some pretty wicked buffeting.

[Brass]

Here is one of those calculators 68X was talking about.  I'm wondering if a member created this but it is kind of fun to play with:

http://vexer.com/68rt/speed.html

[RECHRGD]

Back in the day (1968) I had my new R/T's speedo pegged at the 150mph mark on a lonely, long, straight road going toward Palmdale ca..  The car was bone stock with a 727, 323's, 440, and F70/14 polyglass tires.  I never got the feeling of it being too light in front or back, but I certainly didn't stay at that speed very long and there were no crosswinds to deal with.  I'm sure the speedo would have been a bit off at that speed, but I think the car was probably doing close to 140mph.  I think the front end getting light has a lot to do with the stance of the car.  A slighly nose down attitude would fare better at speed than nose up!  Bob

[Mike DC]

   
The stock speedos aren't worth much at these kinds of speeds.  Give it any incorrectness and it will multiply the error as the speed gets higher.  A speedo that's only a couple mph off the correct speed at 50 mph, will be WAY OFF at 130 mph.    




The effect of aerodynamics doesn't show up on the speed/RPM/tire/HP type calculators.  Those only work if you assume that the motor can overpower any & all conceivable aero resistance from the body.  


If you look at stuff like a droplet of water or a fish or a Bonneville streamliner, you notice that the back end is at least as relevant as the front end for aero reasons.  IMHO it's a viable question whether a 2nd-gen Charger would go faster with only the 500/Daytona rear window plug (and the stock front end) or only the Daytona nosecone (and the stock rear window).  

   

[68X426]

Here is one of those calculators 68X was talking about.  I'm wondering if a member created this but it is kind of fun to play with:

http://vexer.com/68rt/speed.html

That is a really cool tool, hadn't seen it before. It helps to demonstrate the interconnection of tire size, ratios, and rpms. Can't change the physics of TALL. Tall tire, tall gear, and tall rpm yields the most top speed. Then it becomes a matter of what compromises are acceptable to get the top speed.

Back to the original post. If the goal is to increase top speed only (to the disregard of all other driving performance) then the cheapest way to do it is to add the tallest tire possible.

[Arthu®]

If you look at stuff like a droplet of water or a fish or a Bonneville streamliner, you notice that the back end is at least as relevant as the front end for aero reasons.  IMHO it's a viable question whether a 2nd-gen Charger would go faster with only the 500/Daytona rear window plug (and the stock front end) or only the Daytona nosecone (and the stock rear window).  
   

Either improves the drag coefficient so my guess would be that yeah it would make a difference. I don't know by how much and if it would even be noticeable but theoretically both help lower the drag coefficient (which on a standard 1/2nd gen Charger is about as bad as they get for normal cars).

Arthur 

[westcoastdodge]

would a rolling road(dyno)not give you some idea of top speed

[Road Dog]

With these old cars (lack of aero) 170mph is attainable with the hp not getting too crazy. Above that number every additional mph calls for big increases in hp. Air is such a major factor above that speed. It is much cheaper at that point to make your vehicle more aerodynamic.

[FJMG]

The summer's bros. (of goldenrod fame) set a "B" production car speed record at 156 mph at bonneville with a '66 hemi plymouth. 170 would require a combination of more hp and less weight. As stated above the hp required to overcome aerodynamic drag goes EXPONENTIALLY with speed. When comparing, the daytona package only gave dodge about a 5-7 mph (which is obviously alot at 200mph) advantage over previous yrs. In the 90's Car & Driver had a stock firebird built with almost 700 hp and they maxed out at 204 mph. The firebirds smaller frontal area and better drag coefficient is the reason why when these cars (firebird) hit the salts the Daytona/superbird needed ALOT more hp just to keep up. I seem to remember an interview with one of the builders of a daytona land speed record car where he mentioned that once these firebirds came out the it become VERY costly to compete. These cars (firebirds) are now knocking on the 300 mph barrier, he stated that the only way his daytona would hit 300 is if dropped it out of an airplane.

[Mike DC]

               
Yeah, those 1980s Firebirds are about the best bang-for-the-buck aero body you can get.  Yank off the rear spoiler, add on a front air dam, and hit the salt. 


We love to hear the mighty deeds of the Daytona Charger program, but the truth is that car's body was basically a highly-polished turd.  It was an aerodynamically terrible factory shape that was given a few well-researched mods for the track. 

[70charginglizard]

http://www.youtube.com/watch?v=mk7VWcuVOf0

you just gotta laugh.