So I am talking to a friend of mine about my last day at the track I ran about 15.10 and a 92.50. I said it was 92 degrees F and I figured on a cooler day, say 68-70F, I would probably get into high 14s and maybe 93-94mph.

He says no, I would run the same speed but get there faster. My ET would imrpove but MPH would not.

????

I thought I knew ETs and MPH but I guess I really don't after all. I always figured ET was how fast you got there (torque) and MPH was how fast you went (HP). I figured that when the ambient temp dropped both torque and HP would improve because one is a co-efficient of the other. So if I dropped into the 14s with an improved ET my MPH would have to increase as well ?

Can somebody please enlighten me on ETs and MPH and what factors determine either ?
Can ET decrease/increase but MPH stays the same ?
What about vice versa, MPH decrease/increase but ET stays the same ?
What effect does ambient temp really have ?

thx in advance,
RP.

 

cooler temps make denser air then better mph(horsepower) better ET's up to a point,to cold of a temp makes traction more difficult..

warmer temps makes the air less dense then less horspower,but warm temps make rubber all soft and sticky..up to a point..Too high temps burns rubber to the point of leaving tire gunk at the track...

IMO I would take the ET's as it is..For every action theres a reaction..lol


would've,could've should've
Daz've

 

Palric, what 60' time did you have on the 15.1 run?

 

i see that all the time with my car. i have seen up to 1 second difference in et but still run the same MPH. i have no idea why. but i think it has to do with 60' times. looking at all my slips they seem to be the key.

 

yup.. and gearing(I think)

Da

 

It depends on what rpm your max hp is at palric. Here me out on this for a second.

Say your car makes max hp at 4500 RPM. For 3.73 gearing that's 90 mph at 1:1 ratio. Whether it's automatic or stick you should always end the 1/4 mile in a 1:1 ratio gear.

No matter what conditions your car runs in, your max hp due to engine combo is effectively locked with a max speed of 90 mph. You physically can't get any faster than 90 mph unless you shift into an overdrive gear.

What comes into play is how quickly you can make it to that speed. Here's how the torque curve is greatly affected by weather conditions and cannot ever truly be measure except on a dyno.

So break it down to 2 different scenarios. Slow acceleration due to humid hot air, less O2 and higher acceleration cold dense high O2 air. Cold air has the flatter torque curve thus higher acceleration, the hot air has the steeper torque curve thus less acceleration. Remember torque curves down as RPM goes up, flatter is better.

In the low acceleration scenario, due to lower acceleration, more distance is covered at lower speeds taking longer to complete the 1/4 mile.

Take the simple idea of two cars on the highway one at 120 kmph and the other at 140 kmph. The one at 120 kmph will cover less distance than the 140 kmph car in the same amount of time. Rearranged the car at 140 will travel the same amount of distance as the 120 kmph car but in less time.

In the high acceleration scenario, we have more distance is covered at higher speed completing the same amount of distance with less time in the 1/4 mile.

The key to weather is not max hp, its the torque curve.

The effect is cold air more time is spent at higher speeds giving a lower ET. Since your combo is effectivly locked at an MPH due to car setup you will still end the 1/4 mile at that mph. What matters is how long it takes to get to that mph and how long is spent at that mph which will produce the faster times.

If your 92 mph is achieved at roughly the max hp then you will not get a faster trap speed than that. To see if this is true just gun it in 1:1 gear till the tach comes to a halt and basically struggles to move up. That mph is the maximum you'll ever see in a 1/4 mile due to complete car setup.

If you want quicker times, you'll have to focus on mods that will flatten the torque curve. Ie mods that allow the rpm to keep climbing at the same rate.

Unfortunately, power is not the problem I see with your car, traction is. Those 60 ft times you had were really long. A car that can finish at 92 mph despite 2.5 60 ft times shows a car with a lot of power. Dense cold air would just confound you as you would make more power and even slower times and same mph...

For the 1/4 mile keep this in mind...

HP is for bragging, Torque wins races...

Power is nothing if it can't get to the ground...

 

lol again

traction has an effect on MPH

why?

If your spinning off the line what would you do.?.let go of the gas..so the first 50 feet or more.. youre not using your maximum horsepowerage..lol..And if youre late on the shift you will cross the line at less RPM..before your max power..Assuming thats where you shift anyway..so..


Daz

 

slade 1 i think you took a left turn back there. we are not talking about gears or even air temps. in one afternoon or even one run right after the last one i can see a BIG time difference and run the same MPH the only thing that is not the same is the 60'

 

I did several runs all in the 15.1xx and all 92.xx mph (except for one 15.4 @ 89mph I blew a shift). Sure was consistent.

My best 60 foot time was a 2.3?? and best reaction was an .836. I can't find the slips.

I think some people were pulling 1.9 and 2.0s for 60 foot times. If I could shave off the launch I could probably save 4/10s -- wonder how much that would cost $$$ ???. Bet my rear end would break.

I went sideways just about everytime off the light too, ended up launching down at about 2500rpm and hope for the best. I figure I'd need more runs (than 5) to find the ideal launch strategy.

thx,
RP.

 

We're trying to figure if palric did make the end of the run at max hp in 1:1... doesn't mean that he ran at max hp in every other gear though.

If he did make the end of the run at max hp then his trap speed will be the same.

If he didn't get to use max hp in the other gears it means he wasted a lot of time during the run at lower speeds.

Take mine and James runs... I had 89 mph avg runs while he had 88 mph avg runs. He always had me at the end with 0.2 sec or more. Looking at our slips at the 60 ft and 330 ft MPH, he had me every time with slightly higher mph which means during those sections he was travelling faster and covering those distances in quicker time than me even though I eventually finished the 1/4 mile at my peak hp rpm giving me a higher trap speed.

I always smoked him on the 60 ft times though. 2.2 avg for me and 2.3 avg for him. While on the 330 ft he edged me by 0.05 sec everytime due to his being at a higher speed than me quicker than I was. His car would peak around 88 by the end of the 1/4 mile but he travelled more distance at 88 mph than I did.

Hope this is making some sense to you.

 

Very interesting stuff. I really appreciate the effort Rovic. I think I catch the gist of your post I'll have to read it a few times for it to sink into my thick skull.

But here is the part I have trouble with -- I was not in a 1:1 gear when I hit the trap (assuming 4th is my 1:1 gear). In fact I was in 3rd gear at about 5800rpm and was consistently shifting out of 3rd into 4th to slow down after the trap.

Does this matter ? If it does, if ending the 1/4 in 1:1 is important then maybe I should switch up to 3.73s (hey GIVE ME AN EXCUSE and I'll do it !!!) from my 3.42s ? That would put me in 4th gear at the trap which means I'll be back in the lower part of my torque curve and accelerating more quickly once I'm in 4th. Of course the penalty would be the shift trime (I ain't as fast as I used to be) from 3rd to 4th.

What about going the 'other way', making more power in my upper rpm range with 3rd ? I could do this by installing headers and doing head work. Just thinking out loud -- don't know if this is a good 1/4 strategy or not ?

Maybe I would be better off spending $$$ on traction oriented upgrades instead ? Stuff that would improve 60 foot times like LCAs, SFCs, panhard, etc.

Oh yeah -- how detrimental would it be to one's 1/4 times if one had the A/C on (by accident of course) doesn't it kick out over a certain rpm level ?

thx in advance for your comments,
RP.

 

Well from what I know of your setup, you should have a flatter curve than most of us. You've put in cold air, you have the dual cats, have higher flow headers and a good cam. Your Jacobs system should give you plenty of spark energy in the higher RPM ranges, you commented on noticing the improved feel when driving at higher rpm after you installed the system and increased the gap. The loss of low end torque due to gapping is a better deal for you since your 60 ft times need improvement and putting the torque down to the low rpm is not gonna help that when you need traction.

I'm impressed that you managed the 92 mph in 3rd gear which isn't 1:1. Fourth gear is almost always 1:1 and 5th and 6th are reserved to overdrive. (Autos make 3rd their 1:1 ratio) Your setup is definitly a lot more powerful than even I can figure. What I'd recommend is that you try a few runs where you don't push your engine to max output in gears, try shifting about 500-750 rpm below the peak rpm of each gear. Usually at the end of the hp curve about 500 rpm prior to it, it just flattens out a lot.

Give me a shout on my cell and I'll try to explain it to you a bit better. Basically you want to end your run in 1:1 ratio at the max hp of your engine. Having no idea where that occurs in your car, I can't tell you what speed you should finish the 1/4 mile in.

I can say this, if you have 3.73 gears you will actually spend a lot of time at higher mph per gear allowing you to finish the 1/4 mile in a better amount of time provided you improve your traction...

Fix the traction issue first. I saw your rear come out from you a lot when you did your run. The trick is to get the weight to shift to the back first THEN floor it. With your rear sliding out like that you still had the weight on the front of the car. Time for sfc's...