MsVetteMan

Any simple explanation or formula? For instance I have been discussing increasing ponies on my stock 81 Vette, which came with a mere 190 ponies from the factory. Now I have been told by adding various items such as headers, dual exhaust (no cats), changing heads, and a new cam can increase my HP up to 350. Now how does that relate to speed?

Let's break it down:

Adding dual exhaust (No cats)....adds how much HP which = how much speed?

Then let's add headers -

then new heads -

then new cam -

Now we can add up a total hp increase, then we would increase speed by what?

Now I know it all depends on what type of headers, mufflers, heads, and cam, but just play along in and use some general average numbers for me.

Thanks, and this post sounds stupid, it's because I am indeed stupid when it comes to horsepower. Teach me in simple terms. Thanks.

P.S. - Please don't talk about changing gear ratio's or anything else and complicate the question. Let's deal with the above, and my stock car.

81corvettevortec

Speed=RPM (with out RPM you can't go anywhere. the more RPM the faster top speed you will have), are you meaning top speed or 1/4 mile speed?
Ryan.

mandm1200

????

flood

Torque wins races. HP sells cars.

You may have only a mere 190hp but how much torque? Around 250lb ft or so.

I have beat a few imports with my 165hp 75. They had more HP but I still took em. Prelude comes to mind (195hp). Its because I have around 260lb of torque.

flood

your top speed would be the same because your gearing is what limits that. The time it takes you to get there would be decreased.

0-60 or 0-whatever mph would improve.

tshort

I don't have a quick answer for you but I think you need to clarify a little better.
What do you mean by speed? 1/4mi trap speed? Or max speed the car will go given an unlimited amount of space? If the latter, why do you care? Where can you ever go max speed?

Generally for calculating either one it is a combination of horsepower, drag coefficient, tire size, and gearing. For me, I run out of gears before my horsepower limits me.

Maco78

I beat a civic si with a 96 bronco. 210 hp but 300 lb ft of torque.

The civic was even modified with headers and exhaust. Its all about the torque

MsVetteMan

I guess there's no simple answer to the simple questions, which obviously isn't simple........

So lets just go with faster speed, or speed increase in the 1/4 for this example.

Maco78

i would think around 350 hp and maybe 390 to 400 ft lbs of torque could give you around a mid 13

Maco78

but alot of the really good times you see depends on how good the driver is. reaction times, and shifting at the most efficient rpm

81corvettevortec

you would run out of RPM before HP, the same thing tshort said. maybe i was a little unclear.

Maco78

i get the feeling you wana know how well your gonna pull people on the high way things like that right?

427V8

The top end on my 460 hp 434 is 130.
running 6500 rpm, Power just goes away...

but it does ~110 in 12.9 seconds...

MsVetteMan

okay....let me try again.....

Say I ran the 1/4 and my top speed was _____ mph. (fill in the blank for this 1981, L81, automatic, stock, typical motor.)

Now I have added dual exhaust (not cats) and just say dyno ceramic headers. My old speed in the 1/4 of _____ will be increase to _____ mph.

Now lets add some new heads and the increase will be.......

and the cam........


I know it all depends on what I could run the 1/4 in now (which I don't know), and the exact replacement parts used, so let's discuss in general terms.

75 Stingray!

I found an equation a while back:
8.702*(10^-6)*Drag Co*Frontal area of car in sq. feet*MPH^3 = HP required to go MPH you entered into formula.

mandm1200

" How does increasing horsepower translate to speed. "

As a general rule increasing horsepower will translate into higher speeds. There are equations that can be used to calculate the approximate mph in the 1/4 mile for a given weight and hp of a car. Low/Mid torque is what many people want for street driven cars. Why? Because cruising from stoplight to stoplight people do not generally wind the engine up to 7000rpm's. Horsepower is calculated from torque. Moving the torque higher in the rpm's will yeild more horsepower for the same giving torque.
To find out how much speed you'll pick up by adding 30hp, find one of the calculators on the web and punch in your numbers.
Perhaps Desktop Dyno has this built into the program?

djcwardog

Although 1/4 mile times are a great benchmark, it is easy to confuse the correlation between trap speeds and elapsed time (ET) for the run. Sometimes you can run a slower time (ET) yet achieve a higher trap speed. Therefore, I think the best benchmark for you is the first derivative of velocity (speed (a scalar quantity) measured going in a certain direction - a vector quantity) which is...acceleration! Now think 0-60 time in seconds. It boils down to "how quickly will my car gain speed - or accelerate?" The more power you add, the lower those times are, in general and up to a point where shifting time and gearing may afffect further increases. Since you don't want to complicate things by discussing new gear ratios, etc... then stick with 0-60. Chances are that your car right now will run high 7's or so 0-60. Go out and time it yourself, easy enough to do. Look in the back of any Motor Trend, Car and Driver, or Road & track magazine and see how all sorts of new cars perform 0-60. Power, weight and gearing tell the tale. I think that the follow-on to DeskTop Dyno 2000 has performance calculations built in so you can try your car out on the computer. It is set for 1/4 mile times but I think you can break out 0-60 as well, not sure as I only have DD2000. As you add the items you list, you'll see the 0-60 time decrease. You can likely get it in the low 5 second range with all your goodies added in... Your goal to increase torque as HP is merely a calculated product of torque at any given RPM. This is all called "bench racing" by the way and it gives many of us hours of fun and stimulating discussion as we plan out mods to our cars... Enjoy!

81corvettevortec

http://www.cartestsoftware.com/cartest4.5/index.html
This is a pretty good little program, it will be close to a real # if you plug everything in correctly, you can change tire pressures, most variables. and best of all its free! check it out see what you think.
Ryan.

captainmorgan

I think he is trying to find out how much HP gain he will get for each mod (headers into duals, heads, CAM...). Also what the HP gain equals in increased MHP in the 1/4.

MsVetteMan

EXACTLY!! Hey....we are getting their.....I'm not looking for exact numbers, just somethings that will give me an idea. I can associate speed, not HP.