Theoretical top speed

[thewrx]

Aero and rotational weight of drive train are going to be biggest blockers to a “theoretical top speed”. If the mph limit was removed 150 ish seems like a reasonable estimate. I would probably change the tire setup if i was going to try that regularly, and make sure they are perfectly balanced too.

 

[Durango]

Hmmm - interesting thread. I have had a couple Hellcats and never took one over maybe 125, even though they were rated to go 198 or 200, dependent on which one it was. So will I be disappointed to "only" go 118? Naw - as long as I can get to, say 100, before pretty much any other truck (and most non-Hellcat cars) I'll be happy.
Yes, some say I'm boring...

 

[nutgambler]

had 2018 Hellcat at 150mph for 10 miles ..had plenty of power left and felt solid..
2015 Viper different story felt like a freight train it just kept pulling and pulling ,rock solid at 160 mph

 

[Durango]

had 2018 Hellcat at 150mph for 10 miles ..had plenty of power left and felt solid..
2015 Viper different story felt like a freight train it just kept pulling and pulling ,rock solid at 160 mph

I see you're in NJ - they must have better roads than we do out in CA - there's few roads here I'd go 150 on without expecting to get airborne (or worse) because of some lift in the pavement...

 

[Bambi]

Hmmm - interesting thread. I have had a couple Hellcats and never took one over maybe 125, even though they were rated to go 198 or 200, dependent on which one it was. So will I be disappointed to "only" go 118? Naw - as long as I can get to, say 100, before pretty much any other truck (and most non-Hellcat cars) I'll be happy.
Yes, some say I'm boring...

You need more than 118 to rollrace....

so if it has the gearing. The only issue is how much drag it can overcome and how much lift it generates. I’m guessing 150-170 though 170 is probably serious pucker factor

 

[Durango]

I don't do much roll racing - probably last time was in a diesel 2500 before DEF - smoked anybody nearby.

Weren't the Trackhawks limited to just under 180 - a Ram has to have more drag etc than any other vehicle they make - oh wait, the Promaster is going to be worse.

 

[soulsea]

So all we have to do is basic math accounting for the laws of thermodynamics, factoring precise mass according to one's options and breakfast menu, drag coefficient, power, friction, downforce, ambient temps, relative humidity, wind force/direction, fuel amount and type, altitude, and a few other bits.

Seems like a lot of work given that Darwin will let us know for sure ... nothing theoretical about it.

 

[Bambi]

O

So all we have to do is basic math accounting for the laws of thermodynamics, factoring precise mass according to one's options and breakfast menu, drag coefficient, power, friction, downforce, ambient temps, relative humidity, wind force/direction, fuel amount and type, altitude, and a few other bits.

Seems like a lot of work given that Darwin will let us know for sure ... nothing theoretical about it.

Or pull the governor and let her rip. Same diff

 

[soulsea]

That's exactly what I said.

 

[Bambi]

That's exactly what I said.

I said it better

 

[soulsea]

I said it better

Listen, no one here would be more pleased than I if a cosmic event were to manifest that imparted you with the realization that there is no law requiring you to type everything you think.

With that said, I'd rather you didn't die testing the the theoretical top speed of a 6700lb brick in order for my desire to come true.

There are two reasons for this. 1. I don't want it on my karma. 2. You might haunt me and have some super afterlife weed to to do it with.

In short, and I can't believe I'm saying this, please be careful.

 

[Bambi]

Listen, no one here would be more pleased than I if a cosmic event were to manifest that imparted you with the realization that there is no law requiring you to type everything you think.

With that said, I'd rather you didn't die testing the the theoretical top speed of a 6700lb brick in order for my desire to come true.

There are two reasons for this. 1. I don't want it on my karma. 2. You might haunt me and have some super afterlife weed to to do it with.

In short, and I can't believe I'm saying this, please be careful.

Awe schucks. I knew you liked me. I’m still gonna type my thoughts but your concern warms my heart

 

[Bambi]

So all we have to do is basic math accounting for the laws of thermodynamics, factoring precise mass according to one's options and breakfast menu, drag coefficient, power, friction, downforce, ambient temps, relative humidity, wind force/direction, fuel amount and type, altitude, and a few other bits.

Seems like a lot of work given that Darwin will let us know for sure ... nothing theoretical about it.

Also this thread is about theoretical top speed based on gearing. I excluded aero/tires/etc so your post is off topic =)

 

[topdawg4ever]

Excited to put the spurs to her.

 

[thewrx]

Again, like I stated at first, don't hold me to any of this. It was a quick search for gear ratios, final drive, tire size (and actual diameter) and looking at a pic of the tach to get max RPM. it appears to show either 5600 or 5700 ?? Cant tell for sure.

With all else equal, its the tire size that is driving that speed through the roof. Cars are going to have much smaller tires so even with all the same gearing they will have a much lower top speed. The smaller tires will allow them to accelerate quicker, but at the cost of top speed. So technically, given enough power to overcome all other resistances a 37" tire would give you an even higher theoretical top speed.

The Hellcats have 275/40R20 which so an actual height of 28.1 so if the TRX had the same 28.1 tire size, top speed is only 197MPH.

Gear	Ratio	MPH
1	4.71​	34​
2	3.14​	52​
3	2.1​	77​
4	1.67​	97​
5	1.29​	126​
6	1​	162​
7	0.84​	193​
8	0.67​	242​

Also your max speed gear is almost never your OD gear(s). I would guess its 6th possibly 7th, but I come from the land of 6l80e, 4l80e, and 4l65e so it was 3rd or 4th-5th on dyno runs.

 

[tripleB]

Also your max speed gear is almost never your OD gear(s). I would guess its 6th possibly 7th, but I come from the land of 6l80e, 4l80e, and 4l65e so it was 3rd or 4th-5th on dyno runs.

You are correct, actual max speed is not going to be in 8th gear, but the theoretical RPM/gear limited top speed that was asked for is calculated assuming that you have enough power to overcome all other resistances.

 

[tripleB]

Just a follow up to confirm gearing. On my way home from the office today on a long straight flat section, I set the cruise at 60MPH and manually shifted from 3rd through 8th while capturing the RPM of each. This confirms the numbers I used above for the transmission gearing are correct, and the math used above was spot on. Each of these gave calculated speeds ranging 59.54 to 60.59

3rd - 4350
4th - 3450
5th - 2650
6th - 2050
7th - 1750
8th - 1400

 

[JRex]

Theoretical speed kinda means an area 51 vehicle with a TRX hellcat in it? Still fun.

Just guessing here, the way around a governed speed limit, would be a cracked/tuned PCM, which would void warranty?

Does anyone know or know how to calculate what speed the actual TRX, starts to become unstable or that loosing control feeling?

Sure there is a reason why they governed it.

 

[Caliche]

Theoretical speed kinda means an area 51 vehicle with a TRX hellcat in it? Still fun.

Just guessing here, the way around a governed speed limit, would be a cracked/tuned PCM, which would void warranty?

Does anyone know or know how to calculate what speed the actual TRX, starts to become unstable or that loosing control feeling?

Sure there is a reason why they governed it.

Supposedly it’s all about tire rating.

 

[EhhSea]

All seriousness aside, I was really expecting @Bambi to post this by now....