A good start!!

 

LT4POWR
Here is a visual for you to look at....
Might help you figure out what you’re looking for.

I roughed in a typical LT4 power curve (to equal your 416 rwhp), your trans gears and rear axle, 285-40-17 rears, etc.
The dots go from 2500 to 6500 rpm (500 rpm increments).

Every car manufacturer has to give the EPA something called "Target Road Load Coefficients, A, B, and C", that are loaded into a polynomial equation to give required RWHP per MPH.
The EPA uses these to simulate the road load on a dyno.
They are suppose to be derived from coast down tests, but I've looked at them over the years and I think GM just uses theoretical values, here's why.
The Dark Blue line is the GM numbers for the Corvette (from the A-B-C coef).
The Light Blue line is my calculations of theoretical RWHP for our C4's.
The Red Line is an average of all the other sports cars from the EPA list, and BTW they cluster together pretty close.

When your RWHP intersects these line (you pick which one) your at your theoretical top speed (however long it might take to get to it).

If we use the red line (not your engine redline the graph one), at 6500 rpm in 5th (168 mph), you have about 100 hp left to accelerate, in 6th at 168mph, you only have about 20 hp.
To "Feel" the same to you in 6th, as it does in 5th at 168 mph, you could guess that you would have to add about 80 hp ?

 

I see you used to be a fighter pilot. I am a licensed Private Pilot myself.
So, I'll leave you alone. But I do have some good advice for you........don't forget to slow down and hold your nose up in your turns.......

 

Keep your Mach up and pull a few more G's. I am still a fighter pilot. Just don't fly them anymore.

 

To SuperL98

Nice job of showing what goes on.....

 

Great Graph! and I think that your calculation would work out perfectly on the dyno, however, respectfully - I believe that it should take much more than 80 hp to make 6th gear feel like 5th while in motion. My reason for this is because of the increased wind resitance at those speeds. I have a lot of material on transport trucks and engine spec'ing for certain requirements (I sell/lease commercial trucks) however at this point, I can refer you to this website that spells it out better than I can. http://www.corvettebuyers.com/c4vettes/performance.htm

"It would seem that Mr. Lingenfelter is a pretty smart guy! His 200 MPH C5 produced 500 HP (and a whopping 500 ft-lbs of torque; gotta love turbocharging)!"

If ultimate top speed is what you're looking to achieve, you may need to look at changing your rear drive ratio (if that's allowed in the rules) in conjunction with your engine.

 

I went 60 to 135 all in 6th gear once.

 

You could calculate what woud be your speed range in 6th and then find the increase in wind resistance which goes up as the 3rd power of speed.
Then do the math on torque increase needed to achieve current 5th gear torque values in 6th gear with your now motor.
Finally combine the two needed increases in power (torque) to estimate the total needed increase.

That might give you a good idea of the min. power increase to pull (i.e. accelerate) in 6th as well as you now do in 5th.

 

Nothing really to get excited about, I do this about once a week. I start at about 70 mph because of my cam and then to >160 mph. Doesn't do any harm to 6th gear as I see it.

 

[QUOTE=SuperL98;1567027570]LT4POWR
When your RWHP intersects these line (you pick which one) your at your theoretical top speed (however long it might take to get to it).
QUOTE]

What is interesting is that with his existing gearing he is not able to obtain the top speed theoretically possible with 416 RWHP...

So more important than how much horsepower do I need is what gearing do I need to get the most out of the horsepower I already have!!!

The ideal setup would be when the curves intersect at the maximum engine horsepower point

 

Well, I'm still not clear on what the question, we are trying to answer, really is

But, In my old spreadsheet here, I can multiply the HP curve by any percent.
I had to increase it a little under 22 percent, to get 6-th gear to match what it was in 5-th @ 168 mph

 

If I understand your question correctly I believe he is asking "how much power will he need to achieve the cars calculated maximum top speed? 'X MPH' "

Maximum RPM x 0.5 x 3.92 x the rolling circumference of your wheel & tire = Z Inches/minute or Feet/min. F/m to MPH = 'X MPH'
Now that we know our estimated top speed we only need to figure out how much HP will you require to overcome the rolling and aero resistance to achieve that estimate of 'X MPH' ?????

 

Well, the OP probably doesn't care anymore, but I'm between projects and a little bored
So if that's the question, how's this look?
He'll need about 850 to 900 RWHP to run around 250 mph.

 

Holy S#it!

so what compromise in hp can he get away with if he increases his gearing to 4.10's or 4.56's ? (4.56's might be a bit too tall ???)

 

If you are out of hp in 5th, then 6th will never pull, as you will be at less horsepower.

If you run out of RPM in 5th, well I guess it depends on how fast you are going as to how much power you will need in order to keep pulling.

I believe the B2K cars reach top speed in 6th, as I believe with a 4,500 rpm shift and 3:54:1 rear gears, a ZF car would run out of 5th at around 130mph. That is slow enough and they have their peak power low enough that 6th should keep pulling.

But if you are at like 6,000 rpm, an 5-6 shift will drop you to 4,000 RPM. Considering with 3:45:1 gears that you would be at about 170mph or so, you'd need a stout motor, I'd guess around 350-400hp at 4,000 rpm to keep pulling. But that's totally a guess (about the power required, not the rpms and speed).

Edit: Wow, just ignore my post. I didn't realize there was a page 2 chock full of graphs and answers. Cool stuff!

 

Yea, that's kinda what I was wondering too...4.10-4.56 gears would probably increase the chances of accelerating (instead of bogging) in 6th, but another take could be to go backwards and do a 3.73 and get more out of 5th.

 

No

Yes

I guess next time (hopefully in a couple of weeks) I'll shift into 6th and see what happens.

 

Awesome graphs! Thanks
At that power and mph. I was really more wanting to know, not what power was needed to get max seed out of my gearing, but more along the lines of what power is need to get "some" acceleration in 6th, instead of bogging the motor, and being gear/rpm limited in 5th.

 

What actually accelerates a car is rear wheel torque......rear wheel torque is motor torque multiplied by the overall gear ratio. In your case the gear ratios in 5th & 6th are 3.92*0.75=2.94 and 3.92*0.50=1.96, so in 6th gear you need 2.94/1.96=1.50 or 1.5 times as much motor torque to have the same acclerating force in 6th as in 5th...

So you need 50% more horsepower in 6th to have the same accelerating force as in 5th......spraying it would work

Look at SuperL98's curves...lots of information there..