Top speed

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

Both cars would need equal power/aero/gearing and different redlines for redline to be the limitation.

Post by **Onizuka** » Thu Jan 23, 2003 2:58 pm

Dori Dori wrote:J-Spec Tuner, Top speed is not, I repeat, IS NOT only determined by gearing. You are wrong, wrong, WRONG; and I hope nobody buys into that load of B S. There are 3 main factors that determine a cars top speed. Gearing, drag, and POWER (hp that is). Why do you think that top speed cars have insane power? To overcome drag. In your scenario of every other factor remaining constant, the more powerful car will have the higher top speed. Period.

top speed cars have "insanly high power" because they have insanely high gears. that doesn't even matter compared to the cars we are talking about that come no where near teminal velocity. Drag only really becomes a major factor as you start to approch terminal velocity. what you say about power and and top speed still has little effect on the to speed of these two cars because like i said: Ka has taller gears but less revs, and th SR is the other way around, regardless of power they are about the same. Period.

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

You didn't say that last time, you said this:Quote »What you say is all true but top speed is determind by gears and only gears[/quote]...and that is misinformation. Gearing is just as important as drag and hp. By your theory, a 50hp car shaped like a bus could reach 1000mph with proper gearing. Poopoo on that. Think before you type.

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

I found the KA gear ratios:1st.... 3.322nd... 1.903rd.... 1.314th..... 1.05th..... .76

From R&T for DOHC...but I have a feeling those are rounded off. If they are, then those are the exact gear ratios as the S13 Silvia K's transmission.

I Did a little math...if both cars had 205/60/15 tires, a 4.08 rear end, and enough power to pull itself to its redline, the top speeds would be as follows:

For KA, at:6500rpm...153.94mph

For SR at 7000rpm...166mph

Post by **T_love** » Thu Jan 23, 2003 2:58 pm

I knew this forum would become educational one day. Keep it going guys ( and gals?)

P.S. What's the highest speed(MPH) anybody has hit on the SR without changes in gearing and reasonable horsepower (not over 350-400)?

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

Assuming that the KA guys on here really did redline their cars in 5th, the SR should have the HP stock to take it to it's RPM limited top speed of 166mph

Post by **sultan** » Thu Jan 23, 2003 2:58 pm

i think some people are confusing theoretical top speed with top speed. theoretical top speed is determined by gearing and tire size only, and doesn't tell you how much more power you need to reach it. my car's theoretical top speed is 226 calculating in the JWT ecu to remove limiter which also raises redline to 7200 or 7300 rpm. actual top speed with ecu would be around 170 with stock gearing for my car.

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

What are you trying to say sultan?

Post by **sultan** » Thu Jan 23, 2003 2:58 pm

i believe the original question was how fast is a stock sr20 with no limiter. so, has anyone with an sr20 hit top speed and what is it? i don't really care what the car can theoretically do, i care what it can do.

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

Well, you should care for a couple of reasons. 1. Speedometors suck after 90-100mph. 2. People lie out their teeth on the internet. So unless someone out there has a GPS, SR20DET, the urge to test thier car's top speed abilities, record it on video, and then post it on the internet; my 'theories' are the best thing you have to go by.

Post by **Onizuka** » Thu Jan 23, 2003 2:58 pm

Dori Dori wrote:
...and that is misinformation. Gearing is just as important as drag and hp. By your theory, a 50hp car shaped like a bus could reach 1000mph with proper gearing. Poopoo on that. Think before you type.

did you hear me say terminal velocity??? well i did and i also said that does have an effect. and also like i said, cars built for top speed has nothing to do with 240's, neither does a 50 hp bus.

EDIT: also imagin that bus going strait down a hill at 80 degree below horizontal. the bus's top speed would still be determined by gearing, not horse power.

EDIT: a 240 will NEVER reach terminal velocity on the ground, you would have to drop it out of an airplane

sorry but on emore EDIT: yes, hp can be a factor, but after you pass a certain hp to overcome the aerodynamic drag at redline, it doesnt matter. its probably requirs less hp than you think to reach top speed in a 240.

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

Why do you keep bringing up terminal velocity? Do you even know what that means? Of course a Silvia won't reach terminal velocity on the ground. Nothing will. Terminal velocity is a state of no acceleration on a falling object. FALLING OBJECT...not a rolling object. Why on earth did you even bring it up?

And I never disputed the fact that gearing can limit top speed. I disputed your 'theory' that "top speed is determind by gears and only gears"...those were your words and they are wrong, wrong, wrong.

Post by **Onizuka** » Thu Jan 23, 2003 2:58 pm

Dori Dori wrote: They can have different top speeds though, only because they have different power/torque levels.

i was just frustrated at this statement you said, which is also very not true.

I know, i know, i said the whole thing about gears and gears bla bla bla.

yes there are several factor is top speed but you only need that extra hp if you are going really really fast, that is my point. a 300 pound car with 1000 hp and a 300 pound car with 5 hp will have a same top speed if they have the same gearing that limits them, say, to 10mph.

Edit: sorry about the terminal velocity thing (yes i know what terminal velocity is), reading back, i have no idea why i even brough it up, i was thinking of air drag and how fast you would really need to be going in order for it to be a engine power problem...

Post by **Onizuka** » Thu Jan 23, 2003 2:58 pm

Dori Dori wrote:From R&T for DOHC...but I have a feeling those are rounded off. If they are, then those are the exact gear ratios as the S13 Silvia K's transmission.

I think those numbers you found are off, because we have already determined that with an sr and a ka both going at 70mph: the KA is at ~3050 and the SR is at ~3300-3500

Post by **pampadori** » Thu Jan 23, 2003 2:58 pm

at leat my crazy *** sr! maybe i have a different trans then most redtops. i don't know.. i'd say that a stock sr with 205hp could do about 140mph. with about 300hp or more, you could take it to 165mph or whatever the gearing stops you at. for over 170mph, you need to have a lot of power. about 350rwhp i would think.shaun

Post by **Dori Dori** » Thu Jan 23, 2003 2:58 pm

J-Spec Tuner wrote:i was just frustrated at this statement you said, which is also very not true.

Yes, it can be true...I guess I should have specified that given enough gearing, the car with more hp will have the higher top speed. I thought it was common sense.

Post by **James** » Thu Jan 23, 2003 2:58 pm

Well I'll have to try and find out this summer where we can get with this new car....The Civic hit a indicated H on the mph on a Si speedo (ends at 145) with the LS transmission, the APR Stage 3 jetta said he was reading 160 and I was pulling on him still he said, about 5 car lengths in front of him. My friend has talked about getting his father in-laws GPS and figure out how fast we are really going someday so I guess my S14 will have to find out.-James

Post by **slide** » Thu Jan 23, 2003 2:58 pm

most of you guys cars are pretty old an you know that old cars tachs an speedometers are kind of in accurate.......well even new cars ahahhhahh

Post by **C-Kwik** » Thu Jan 23, 2003 2:58 pm

I noticed there has been almost two different debates on this. With no aerodynamic drag, a car is limited to overall gearing including tires and redline.

But to truly understand drag limited top speed, you should all look into some of the things top speed race cars do. Of course the aerodynamic drag has a large part to do with it. As does HP. As long as gearing allows it, than HP should get you there, right? Wrong! Of course having enough gearing is an issue, but more importantly, how much torque is being transmitted to the ground at what speed. Keep in mind that in each gear, the torque peak is where you have the most acceleration. It is quite possible to shift into the next gear and max out before you hit your torque peak. And perhaps the motor has enough torque at it's peak to overcome the drag at the corresponding speed. But if it can't get to the torque peak, it's moot. You'll find the most serious top speed record breakers will hit their top speeds right about at the torque peak, and it would not be uncommon to find the last few gears to be very close in ratio with the lower gears being quite tall and spaced apart quite a bit. Especially given the peaky nature of a high HP motor's torque curve.

In general though, the HP vs drag is a very good indication of what the drag limited top speed is. But does not mean it will actually hit the calculated top speed. Gearing can play an important role in this case.

Post by **themadscientist** » Thu Jan 23, 2003 2:58 pm

as an example, While I have had Big Evil up to 209kph it took for-ev-er to do it, my RPMs stopped climbing at full throttle and I lost momentum as soon as the road even thought about sloping up. That tells me that while I had the gears to make a higher speed possible I lacked the horsepower to reach it. It takes gearing and enough horsepower to close the deal.

Top speed

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