Top Speed & Fuel Economy

[ljbprrfmof]

Quote:

Originally Posted by The Pope Lastly other than the cars being old and wore out how long of a distance are you going? A mile? 30 second blast? My old Charger needed 10 miles to milk its way up the last 20 MPH. Out west there are highways where you can run 100 miles at a time and not see one house or human, a little easier to reach top speed when you can run flat out for many miles.

That's what I need, a road to milk my car on.

[william]

Quote:

Originally Posted by Reaper1 OK...my run in my Daytona was done down a 1.5 mile bridge...I started at 80mph at the top...by the bottom that's all she had. I've had it on flat ground and it took around 2 miles to get to 120mph from around 60. Rob, I KNOW you're smarter than this. Come on. I do understand that air acts as a weight(aka drag), but I also know that it take 4-times the amount of power to double your speed. Also, look at the power band...the torque DROPS like a rock in the upper rpms...there WILL be a power limit to the top end of these cars before you run out of gear in stock form. Figure out the needed power for our cars to run the speed you're saying, then look at the power band and see if it matches. I can pretty much predict that the power isn't there. The simple physics is against these cars going much over 135mph with 150hp. For refference other cars with similar power numbers and shapes top out right around the same range. I'm simply not buying it.

Yeah, 150 hp in a stock shadow or daytona body... 150mph isn't going to happen. If we had the .cd and frontal area of one of these, we could put this to rest pretty quick mathematically.

[Reaper1]

IIRC the 1986 Daytona Turbo Z with aero package had a CD of around .32. What's weird is I actually remember reading one time that the figure was .26, but without a full body pan I'm not sure that's right.

Frontal area is easy...just measure the overall height and width of the car, then multiply them(make sure the untis are correct). Of course the figure is lower, so you can account for that by subtracting probably around 2ft^2. This is becuase the car angles in towards the center after the mid body-line. I know that's not very accurate, but it'll be kinda close. You could always actually measure it section by section and add them up...it'd just take a bit mroe time. Car&Driver may also have those figures....

The rest is just math!

[The Pope]

Quote:

Originally Posted by william Yeah, 150 hp in a stock shadow or daytona body... 150mph isn't going to happen. If we had the .cd and frontal area of one of these, we could put this to rest pretty quick mathematically.

consider the 150 HP shadow in question, the 88 CSX. This car did not have the same computer as the rest, it did have a version of an MP computer in it. Shelby wanted more power without paying to intercool the cars. I don't believe that the 88 CSX had 150 HP, the one I drove that was near new had a low more power over 120 than my stock near new 87 SC had. Around 130 the log car just doesn't want to run, the CSX is another story. My log car later of course with an MP computer flashed 14.5 PSI and held 13.5. Top speed changed a ton. We also base our HP figures off factory figures. The log cars are pretty close. The intercooled cars including the SRT 4 and the Mopar powered Mini Cooper all make about as much at the tires as rated at the crank. Is 175 HP enough to push a Daytona to 150? The math doesn't add up, but they were all rated that fast with an intercooler. Yet WHP for a great running stock T2 is also over 170.

Is all HP created equal? Ratings vary when you talk performance. I've seen 160 HP Honda Civics that can't get over 110 MPH, 170 GSR Acuras not going over 120 and the type R Acura not getting over 130. Can a 150 HP CSX do 140? I have done over 140 in one with few miles on it, didn't reach 150 where I was. Daytona's? Yes been past 150 and have had them tail gating me past 150. Torque? HP? On a tire dyno the TDs do run flat at 4,500 RPM, but they do maintain most of there power to 6,500. TDs don't have that sharp peak of power, looks more like a tilted table top than a spike.

[Reaper1]

I would REALLY like to see a chassis dyno chart of a STOCK TI or TII car. I bet this will be kind of hard to come by since we all mod them before we dyno them. Maybe one of the vendors can come through?

Published literature states that the top speed of the more powerful '87 AND '89 CSX/CSX-VNT(respectively..the VNT having more torque even!) at 132mph. The one that ran to 148mph was later PROVEN to be a ringer that had a dual-cal computer in it.

The TIII IROC R/T's topped out at around 150mph...this is a known quantity. Please tell me how a car that has LESS power(torque and hp) with similar drag characteristics can MATCH that performance? It simply is physically impossible.

Also, how do you know how fast you were going? The speedo's stop reading at 125 in P-bodies, so did you actually take the rpm number and figure it out?

What Daytona was matching your speed at 150mph? It wasn't stock if it was(unless it was a TIII car). The top speed of stock TII and TIV cars is around 135mph....

I'll tell you what...when I get some time(finals are coming up, so it's limited for me right now), I'll sit down and I'll do the calculations based on the formulas in my fluid dynamics book(there are several problems in there dealing with drag and power). I'll post my findings, and I'll even post my paper if you'd like. I'll figure out how much power is required to attain a top speed of 150mph.

I can do estimates of the CD and frontal area(for a P-body), but if somebody knows these figures, or knows where I may be able to get them, it would sure be helpful to produce accurate results.

Then lets compare that figure to a chassis dyno chart of a STOCK TI or even a TII car! It is a known fact that Shelby was requested to detune the power of the '87 CSX for Thrifty as the company determined the '87 to be too fast! #1, it's not intercooled, #2 it doesn't produce as much boost, #3 it used a smaller turbo(IIRC)...they are NOT making 174hp...

[janus]

hi guys,
i'm following this thread eagerly, very interesting!
on my 150mph story, i'm gonna tell you something. i dont show off normally, i know TDers are not like that but i dont see any sense in it, i only tell people these things if they ask for it or wanna know. i really saw 150mph in my 92 TI. the european tach goes up to 260kph. as said, i dont know whether it was the high torque T1, other gearing or my 225 rubber. i just know that me and my buddy both saw the speedo needle at 250kph. it took some time to get there, but i was not running down a hill or something - it was just a straight 3 lane highway, i was going like left lane right pedal again, it took some time to reach these speeds.
comments welcome, i understand you guys are cynical about this! i was really astonished by this vmax as well as to my knowledge the engine was completely stock, and not even well maintained! the oil filter was so old it was even rusty when i got it
too bad i had to swap the headgasket, i'm just in the process of getting it back on the road so i might be able to do another run

[Reaper1]

The gearing for a A568 is 3.85. IIRC the gearing top speed based on rpm of the engine is around 168-172mph(for an 8V engine).

As stated before...the KNOWN top speed of a TIII IROC R/T completely stock is right at 150ph.

The car is aerodynamicaly EXACTLY the same. Power from that engine is 217lb-ft@2800rpm/224hp@6000rpm.

The Hi-torque TI compares at: 210lb-ft@2000rpm/152hp@4800rpm

BOTH rated at the crank. The power bands are VERY different, and given the same rpm the TI is NOT going to be producing the same amount of power as the TIII for top speed, no matter if it's measured at the wheels or the crank.

I'm not being cynical...I'm being realistic. Tire size CAN effect speedo readings, but unless you are running some really off size, it should only be reading a few % off(this will vary with manufacturer and wear of the tire)...this of course is not a linear relationship, so the faster you go, the more the actual difference. Also, most speedos read slightly fast to begin with. The more wear on the tires, the worse this gets.

[janus]

ok well, i just looked up the formula for the force of aerodynamic drag.

from Drag equation - Wikipedia, the free encyclopedia
density is 1.2 kg/m³ for air at ca. 21°C, or 70°F
velocity is about 65 m/s which is 145mph or 234kph, squared is 4 225
Cd is .32 if i remember correctly? anybody has more precise info on that?
i'm pretty much confused about the A ... imho this should be the cross-sectional area perpendicular to the motion direction, but dunno how to exactely measure or calculate that. anyone?

next step would be to see how much force we can really put down with the car.
what's the A568's gear ration in 5th gear? i guess 3.85 is the final drive ratio right?

i think that rolling friction can be left out over 100mph, as it is not relevant any longer.



p.s.: sorry i think i got the wrong word "cynical" -> i meant more like distrustful or suspicious. anyways, i still think that if it really wasn't real 250kph it was the tires influence. riding on 225/50 16 or 55 16? dont really know. tread was about 6mm back then xD

[gkcooper]

My '95 common block TBI Dakota will go slightly over 100 mph. It also gets 24-26 mpg commuting so I say listen to the Pope's advice and do some basic tuning first. I bought a brand new '88 Daytona 2.5 TBI and it would bury the 125 speedometer.

[turbokid]

I hit 125mph going in an 89 lebaron w/ a 2.5 inch exhaust and thats it. I know forsure the 87 glhs was rated at 134 for topspeed. Haven't tried and dont want to (its not my car).

[ljbprrfmof]

Update on my CSX-T

We installed the new stock fuel injectors, and while doing so, found a pile of vacuum leaks, Both hoses and connectors. We put in simple Tee's that look like crap, but work.

Does anyone know where to get the factory vacuum hose connectors? I think they may be NS1.

We also did an oil change with MOBIL 1 0/40 (It was what we had on hand from doing Crossfire oil changes).

The car now runs very smoothly. When I would put the clutch in, it would idle around 1800 RPM and slowly come down to 12-1300. Now it just idles down to 1100 RPM.

I filled the tank and began measuring the fuel economy. I thought it would be better to get a reading on that since gas has hit a new historic high today, locally. $3.599 per gallon. I am thinking about building one of those hydrogen conversions and running it on water. LOL

I also learned over the weekend, a guy up the road from me has a dyno. I think I need to go chat with him.

I couldn't be happier with the driveability today. It almost has me thinking of leaving this one stock and finding another car to modify.

This thread has been very interesting & educational. Thanks for all the great posts.

[envyyourethics]

I passed a Civic hatch in my 2.5 NA aries wagon to see what it had in it since the speedo ended at 85. He said his speedo was hovering at 120mph. I imagine I was doing 125-130 when I passed him.

Sure I put alot into building it, but im sure it didnt break 130hp.

[turbokid]

Thats nice for an Aries wagon non turbo. I need to do some more mods on my lebaron

[Reaper1]

Janus, that formula is correct according to my fluid dynamics book. The negative is simply for sign convention idicating that the drag force is acting in the opposite direction of the force pushing the object forward.

"A" in the formula is the frontal area of the car. This is what I was trying to see if anybody knew. You can estimate it by doing a basic base times height calculation for the car...or you can split it in to separate sections and add up the totals to get a more accurate indication of what it really is. Basically take a sillouhette of the car as you look at it from the front, put it against a grid backdrop where each square is some known measurement and figure out what total area that sillouhette takes up. That is frontal area.

I found a site that lists the frontal area for an '89 CSX-VNT at 1.98m^2.

With your above posted numbers(which seem correct) the drag force is 1606N(newtons).

The overall gear ratio of a 1992 A568 in 5th gear is 2.73:1. Stock tire size is 195/60/15 which equals a radius of 12.1in=1.01ft. 145mph=12760ft/sec. Revolutions=Velocity/Radius: 12634rpm. Divide by the overall drive ratio....4628rpm at the engine.

So, now we need a dyno chart of a 100% STOCK TI engine(of blow-through design).

Out of curiosity I used the same method to determin the engine speed of an IROC R/T at 150mph. I came up with 4765rpm. Note that I did use the stock 205/55/16 tire size for the calculation. According to a factory literature graph of the TIII engine, at this point in the power band the engine would be making around just under 200hp and just over 200lbft of torque. Note that right at this area is where the torque curve falls off...right at 5000rpm.


According to the chassis dyno of MY car(which is posted here on TD) at that same rpm I'm making around 200hp/225lb-ft torque from my 2.2 which was pushing 20#'s of boost among other things(all also listed here on TD) on a STOCK long-block/head/turbo/manifolds/cam 1988 2.2.

Somebody PLEASE find a dyno chart!!!

[Reaper1]

Oh...I forgot, rolling resistance will be a factor in the forces acting against the car moving. Of course it depends on a LOT of factors as to what this really is.

I'm tired...I have class in 3 hours...I don't feel like messing with it any more right now...