does anyone know ow to get a 1/4 mile et from 1/8??

[lowsseries]

i have a question regarding how fast my truck is.after i recently got it running without checking the timing or doing anything other than putting my new carb and intake on it and just getting it started. i went down my road to an area i knew to be 1/8 mile. i ran 78 mph in this 1/8 mile stretch i didnt have it running right i just fixed the wirirng after changing to carb from fuel injection and it ran so i wanted to drive it.its got a tpi305 from a camaro and 700/r4 i dont expect it to be anything wild but im curious as to what this relates to in the 1/4 mile.im assuming since the tires i have are 185/60/14 that the speedo is about 10 mph off so im just curious if anyone can guestimate or have an idea of what that can roughly vorrealte to in the quartermile.im assuming its a 305 cuz i was sitting on the motor trying to read the casting numbers upside down with no real light since its a tight fit and had a rough idea of what some numbers were i called the napa machinshop in my area and they told me based on the numbers i have its prolly a 305 since i guessed on some numbers.so any help on a 1/4 et would be cool thanks

[adam]

go to a track and find out

[lowsseries]

well im still not done with it or i would take it to the track

[Injected]

I'm pretty good at this and have built and programed several calculators that do just what you are asking.

What you need to know is F=M*A (once you take in to consideration all of the other variables like drag coefficient and coefficient of friction from the road, blah, blah, blah). You know your instantaneous speed at the end of a known distance, which is only one of the variables (acceleration, sort of). You want to know what would happen if you extended that distance. We still need to find the mass of the object being accelerated (that is the total weight of the vehicle with you in it). If you can reach 78 mph in a truck that weighs X, then we know the force and can predict the force applied over any distance.

What is the net weight of the vehicle?

Also, are you saying you don't know what engine is in your truck?!?

[lowsseries]

its an 85 single cab s10 im not sure what it weigs with me in it i guess say 2900lbs

[Injected]

According to this site (http://www.edgesz28.com/edgesZ28/et.htm) (found by doing a simple google search for "1/8", "horsepower", and "calculator),

Estimated RWHP for 1/8 mile = (MPH*1.27/234)^3*Weight.

Now, to do the work for you:

Estimated RWHP for 1/8 mile = (78*1.27/234)^3*2900

Estimated RWHP for 1/8 mile = 220 RWHP

Now, take that and plug it into the 1/4 mile formula from the same exact site:

Estimated 1/4 Mile ET = ((2900/220)^0.333)*5.825

Estimated 1/4 Mile ET = 13.75 seconds.

There you go. 220 * 1.15 is 253 flywheel hp, so you're looking at an engine with about 260-275 hp stock.

[kevint]

well, considering you said your speedo is "off" by 10mph, without specifying which direction, your speed can vary between 68 and 88mph. when you say you have 185/60/14 tires...i would assume that maybe your speed would be on the lower end of the spectrum, as I can imagine a carbed 305 can light those up pretty easily.

Anyway, you can most certainly use the math presented by Injected, but youll never really know until you take it to a track. first and foremost, instantaneous speed isnt how a 1/4, or 1/8mile speed is measured....its taken over the last 55 feet before the finish line or half-track marker (or 65' i dont remember which)

Vehicles vary so much that I really find it hard to believe that you can 'calculate' the et and speed of a 1/4mile run by simply using your speed....if anybody has ever seen an NHRA XPLOD sport compact event...some turboed cars can run 8.30 at 175mph.....on our super comp dragster, we can run 175mph with an et of 7.65 and a lame setup.

But, going by your speed...78mph +/-10...i can say that your going roughly 100-120mph in the 1/4....so, i dunno....like i, and one other have said, take it to the track.

[Injected]

*Disclaimer: I am grumpy this morning (dang commuters!). I don't want to offend anyone by this post. It is a challenge to the logic of the post quoted here, but in no way is a personal attack on kevint, whom I find to be a good-standing and valued member of this forum.Anyway, you can most certainly use the math presented by Injected, but youll never really know until you take it to a track. first and foremost, instantaneous speed isnt how a 1/4, or 1/8mile speed is measured....its taken over the last 55 feet before the finish line or half-track marker (or 65' i dont remember which)I guess you didn't read my post close enough. Of course the calculations are just estimates, but they are good ones. ET is directly related to trapspeed by the weight of the car (simple physics). You may post a given trap speed, but you still will have a run-specific insentaneous trapspeed. Calculating it is basic calculus. Taking into accounts all of the variables is insane amounts of basic mechanical physics.Vehicles vary so much that I really find it hard to believe that you can 'calculate' the et and speed of a 1/4mile run by simply using your speed....if anybody has ever seen an NHRA XPLOD sport compact event...some turboed cars can run 8.30 at 175mph.....on our super comp dragster, we can run 175mph with an et of 7.65 and a lame setup.Don't try to compare your self-proclaimed 'lame' setup with highly modified turbocharged cars in an attempt to say that one is superior because on the same trapspeed you are faster. You only further prove the point that there is a relationship between ET and trapspeed. Ever heard of John Sheppard (http://shepracing.com/)? Damn near street leagal four cylinder running 7.976@179.06MPH! That is right there with your super comp dragster. It's all about power to weight ratio and vehicle dynamics. There is no difference between your super comp dragster and a Toyota Yaris when it comes to what affects the outcome of a quarter-mile drag. The setups (yours and John's) are very different, the results are nearly the same because the variables that affect the outcome are the same. You cannot have a setup that ignores weight, power, drag, etc, etc. Period.But, going by your speed...78mph +/-10...i can say that your going roughly 100-120mph in the 1/4....so, i dunno....like i, and one other have said, take it to the track.
*sigh*

I can't stand it when people get all in a fit about 'calculations aren't like the real world'. They are fine representations, but to take into account every single variable wouldn't be feasable. The only way to take into account every single little thing that would occur, would be to go out and do it, but that doesn't mean crap either by the same accounts. You can never duplicate the same exact run again. You may get close, or be extremely consistent, but you will pretty much never see the same exact run twice. The wind might change a little, the conditions will vary slightly and all of those statistical anomolies will creep into the real world equation. You might run a few hundreths or tenths faster or slower, or have the same exact ET with a different 60'. Calculations represent what we know about what is affecting the equation (read: outcome). We know that two cars with different weights, one much lighter than the other, will run very different quarter mile times and trap very differently. Why do we know that? Because we understand the correlation between the variables. Those who say, "well that is just an estimate," I challenge them to build a better model (equation) to take into account more variables. How about coefficient of friction between the exact tire model and wear percentage of that model with the track, in the various conditions you may find it? That would help you calculate an accurate 60' time. How about including coefficient of drag for that vehicle based on cross-sectional area and air density, based on altitude, saturation and temperature, wind speed and direction. You see, calculations that take more into affect will be more accurate. If you are going to complain that these calculations aren't good, please, by all means introduce your own equation and logic. Don't say, "traps and ET are unrelated because I've seen two different cars with the same traps and different ET's" without a single clue as to how the two are in-fact related. To even insinuate that they are not is an utter disregard for how the real world (which you are so avid about) works.

I'll give you an example of how calculations can represent something real in a simple example with very few variables to affect it, and help him out in the process. His tire size is 185/60/14. That gives him a tire diameter of:

2*(185mm*.6) + 14"(2.54cm/in)=577.99(pretty accurate going to the hundreths of a mm). So 22.74" is his tire diameter. If he can find the stock tire size, then we can calculate the percentage increase or decrease in the setup and will know the exact speed he is off at any given speed. We could take into account deflection and tire wear, but at nominal speeds, it wouldn't make much, if any noticable difference.

[lowsseries]

injected well said no offense to kevint but i posted that i havent finished it yet and thats why i was askin based on what little info i have what i can expect roughly.since i might be waiting till next spring to ttake it to the track i was just curious what it ran. thanks for the info injected the trans should be from a 3rd gen f-body which had 235/55/16 or 245/50/16 depending on the model according to discounttire.

[lowsseries]

26.2 would be original tire size

[lowsseries]

so speedo is at 67.7 mph when going 78 yea lol

[kevint]

perfectly understandable.....so i guess i was more on the 'wrong side' than the 'right side' of things....just throwing in my two cents...ive been more wrong before....

anyway, I dont doubt how accurate math can be....being an engineering student and all....but im also not a particular fan of bench racing as opposed to just making a pass down the track. Ive managed to figure that our 1900lb car at 175mph makes around 900hp...ive even tried to figure out what the instantaneous 1/4mile speed is...which, when throttle-stopping, is very difficult. Especially when your start point is 0mph on the starting line. So, balls out acceleration for .12 seconds...then going on 'cruise' in high gear between that and the 3 second mark, then accelerating in high gear from that point to the finishline...135mph at the 1/8th, 175 in the quarter...all in 8.90 seconds.

Ive tried calculating how much fuel the system flows at 120psi fuel pressure too, using methanol and a final injector orifice of .034" in diameter....One equation said we were using too much in one particular run, and another equation said there was too little...how much, i dont know. BUT, we did learn through actually leaning out the fuel system that we were passing too much fuel thru the motor....but we cant factor in the effects of the spark plug gap, ignition timing, and whether or not the coil is malfunctioning due to the same tireshake that destroyed 3 torque converters last season, two sets of motor mounts, a cooling fan, and two sets of trans limiters...

Anyway, like I said, I PERSONALLY have learned that theres no better way to test a theory than to actually test it. Ive done the math, and the results for me simply do not match what real-life testing has shown.

Its my opinion, but thanks for the criticism (seriously)...

~Kevin

[lowsseries]

thanks for your info to kevin once i do get it together to a satisfactory degree to drive it i will spend every opportunity at the trackto fine tune it and see what happens but since i cnat do that yet i just have to wonder lol but if i got some things taken care i can have it done by sept which will be a great time to run it in the cool fall air. where are you from and where do you guys run your dragster at?do you compete nationally at all?

[kevint]

Im located in northern New Jersey...Parsippany to be exact. Im pretty much right between NYC and the Delaware River if you were to look at the map. We run in NHRA's Division 1 and have raced at tracks in New York, PA, Maryland, Delaware, New Jersey, and Virginia. National events are a rarity, but we did run in the Englishtown event when it was here. We plan on doing it again next year....

My little bit of advice is to just take it slow and do it at your own pace. Small changes are ideal, and once going in a certain direction works, keep making the small changes until performance suffers and then back up one step. take good notes so you have something to reference in the future. Keeping records of the weather when you make your runs is also a good idea, as soon you'll begin to develop patterns as to when your truck runs its best. Cold weather always turns out the best performance, but after a while youll know how to tune to compensate for when it gets really hot. If you have any questions, feel free to ask.

~Kevin

[kevint]

Just an update...the coil wasnt the problem, but slightly fattening up the idle and leaning the hell outta the main jet helped pick things up a bit. EGT's are still around 1060*F, so we can still go leaner. The track basically sucked all day, we had a huge amount of rain dumped on it yesterday and it was weeping up thru the surface. It spun on the launch, it spun when it came off the throttle stop and spun all the way to the end. Still managed to pull 171.45mph though despite the lack of traction. Once we go as lean as possible on the main supply, we can lean out the top end too. Right now we have a high-speed bypass set to open up at 65psi of fuel pressure. We can pull pressure away, add pressure, and take more or less fuel today at basically whatever pressure we want. So were getting close, but are still so far...

~Kevin

[hamrickac]

get a performance chip/download with a reader thing that tells you the speed and it should tell you your 1/4 mile speed and time.

[Injected]

get a performance chip/download with a reader thing that tells you the speed and it should tell you your 1/4 mile speed and time.
Wouldn't do him any good with such an incorrect tire size.

[lowsseries]

yea now that i think about it my uncorrected speedo reading was 88 i just correected it without knowing exactly to 78. that and when i did the math i noticed if uncorrected it was 78 a rough 1/4 mile would be 15.79.so i just corrected my mph twice hahahaha