Blower question

cronin49 · Jun 16, 2010

Hey guys, I am wondering, with my Novi 2000 setup, when will the rpm's stop climbing if I am trying to max out in 5th gear. Obviously I can't really try it on the street, the most I've done is 120-125 mph in 4th at redline. Look at my sig. for what I've done to my car. Thanks

trinity_gt · Jun 16, 2010

Probably when you spin a bearing and/or throw a rod.

If the motor holds together for such a run, the RPM will stop climbing when the power required to maintain a certain speed (against wind and rolling resistance) matches the power produced by the engine, or the rev limiter, whichever occurs first.

cronin49 · Jun 16, 2010

trinity_gt said:
Probably when you spin a bearing and/or throw a rod.

If the motor holds together for such a run, the RPM will stop climbing when the power required to maintain a certain speed (against wind and rolling resistance) matches the power produced by the engine, or the rev limiter, whichever occurs first.

Thanks for the answer... My engine should hold together because it's got a Cobra short block with forged pistons, rods, etc. your answer really doesn't give me what I want, I know I won't hit the rev limiter because I would be doing 200 or so mph with my 373 gears.
At 2500 rpm in 5th I am doing close to 85 mph, just did that yesterday. That means that if I were able to get her up to 5000 rpm I would be doing about 170 mph.
Does anyone think that our blown Mustangs can do 170???

Rickyll7 · Jun 16, 2010

Maybe, but it doesn't sound like a good idea.

trinity_gt · Jun 16, 2010

I've read of stock 03 Cobras approaching ~170MPH with the speed limiter disabled.

Rickyll7 · Jun 16, 2010

Yeah, but they don't usualy make out so well when they do that. They tend to get their pistons expanding faster than the cylinder walls once they hold those high loads for too long. Then bad things happen.

Midnight2V · Jun 16, 2010

Keep in mind that at speeds north of 140, sn95 bodied cars tend to develop a lot of lift. Unless you are running a functional spoiler and a Cobra R style chin or similar panels to support sufficient downforce, you could quickly lose control of your vehicle. At those speeds, let's just say the results would be unwelcome.

Rickyll7 · Jun 16, 2010

Midnight, how in the world do you run 17psi and 10:1 CR? Are you using race fuel all the time?

cronin49 · Jun 17, 2010

I played the fool and took her out this morning for a cruise on a long straight section of RT 17 here in SC. I took her up to 100 mph and was at 3000rpm in 5th.
Damn I wish someone knew when the revs would stop climbing due to drag, etc.
4500-5000rpm? At 4000 rpm I calculate I'd be doing 130-135. I know that's do-able.
Now at 5000 rpm I'd hit 165-170.
I wonder if our blown cars are capable of pushing it to 5000 rpm.
I guess I'll never know unless I could run her on a nice long airport landing strip.

Midnight2V · Jun 17, 2010

I'm still only making 12 psi at 6000 RPM, I don't hit 17# until a little over 7000 RPM using 94 octane ethanol-free gas. That's going off of my boost guage on a dyno. In all honesty, my guage could be inaccurate and I am making less boost than what it tells me...or I could be making more. I've never actually had race gas in my car, although I would certainly be interested to see what it could do on C-16.

The fact that I'm running a centrifugal and not making a lot of boost until well over 4000RPM helps out a lot since detonation associated with high compression is usually a low RPM, high boost concern. Not making a lot of boost until high up usually helps to prevent that. Its contrary to the logic for positive displacement blowers. The chamber work on my heads is supposed to help as well.

As far as the aerodynamic drag question is concerned, I remember reading an article in motortrend many, many moons ago, that in order to hit 200mph in a car with a 0.28 total drag coefficient (aerodynamic and rolling) you need just over 475 hp to the wheels.

Anyone have an idea what the aerodynamic or rolling coefficients are for our cars?

trinity_gt · Jun 17, 2010

As I noted earlier, I've read of un-limited Cobras approaching 170. You're making Cobra-like power and have Cobra-like aero so expect a similar top speed...

N8Dogg98 · Jun 17, 2010

Be careful doing those high speed runs man. There was a guy on here a couple years ago with a TT silver 2002 GT (I think it was an '02 anyways) pushing around 550 RWHP on the stock block. Needless to say he got his car up to about 155 mph on an empty stretch of hwy and lost control. The car suffered some rear end damage and he walked away unscathed, however at that speed he was incredibly lucky to say the least. IIRC the tail end of his car hit the guard rail and messed up his rear end, 1/4 panel, and rear bumper.

Dark04GT · Jun 17, 2010

A rough estimate:
Aero Horsepower (wheel horsepower) = 0.000007 x Frontal Area x Cd x Speed^3

Take in mind this is the minimum amount of power to maintain the speed you are looking for and doesn't account for rolling resistance which will consume an additional ~5-6% more HP.

I found the Cd for a new edge is roughly 0.36, frontal area is roughly 22.5 sqft. So in optimal conditions you should be able to hit 170.

This calculator is more realistic:
RSR Aero-horsepower Calculator

P.s. Don't do this on the street, find a nice long track or take it to the salt flats. :Track:

cronin49 · Jun 17, 2010

Dark04GT said:
A rough estimate:
Aero Horsepower (wheel horsepower) = 0.000007 x Frontal Area x Cd x Speed^3

Take in mind this is the minimum amount of power to maintain the speed you are looking for and doesn't account for rolling resistance which will consume an additional ~5-6% more HP.

I found the Cd for a new edge is roughly 0.36, frontal area is roughly 22.5 sqft. So in optimal conditions you should be able to hit 170.

This calculator is more realistic:
RSR Aero-horsepower Calculator

P.s. Don't do this on the street, find a nice long track or take it to the salt flats. :Track:

Thanks bro... I would never try this on the street.

Barnaby · Jun 18, 2010

Here's another one to try. http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est.html

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