mph vs et??

**Stav** · 20-01-2007, 03:05 PM

Just looking at my last night out in August I have to ask if mph is really that big a deal to make a quick car? I am seing a bit of inconsistency here.With virtually a full tank of fuel I ran a best on the night of 14.857 at 92.45mph 14.858 at 92.20mph and my mate on the noght ran a 14.585 at 91.95mph. What does it all mean? It doesnt seem consistent with au i6 cars in the data base?

Doogstar · 20-01-2007, 03:38 PM

What were your 60 ft times, I think you'll find the difference lies there. The quicker you get off the line the quicker you get to the end but not nessacarily going faster.

My previous best was 14.7308 @ 97.02mph with a 2.2686 60ft.
My new PB is 14.577 @ 95.67mph with a 2.186 60ft.

ratter · 20-01-2007, 04:19 PM

your mph shows your power to weight ratio and your et shows how well the car gets it power down, which includes gearing, driving etc .

Lots of things can easily affect et, where mph is normally consistant unless changes are made to power or weight of the car

xdclevo · 20-01-2007, 04:25 PM

I bet your mates 60 foot time was .15 sec quicker than yours.

all4ford · 20-01-2007, 04:37 PM

Quote:

Originally Posted by ratter

your mph shows your power to weight ratio and your et shows how well the car gets it power down, which includes gearing, driving etc .

Lots of things can easily affect et, where mph is normally consistant unless changes are made to power or weight of the car

So by that logic, wouldn't a 600HP car in a 1700kg body, whether it had 4.11's or 2.9s as a diff ratio run the same MPH? I dont get how that could be at all possible.

ratter · 20-01-2007, 07:31 PM

Quote:

Originally Posted by all4ford

So by that logic, wouldn't a 600HP car in a 1700kg body, whether it had 4.11's or 2.9s as a diff ratio run the same MPH? I dont get how that could be at all possible.

There will be some slight variance in mph but not a great deal

**ebxr8240** · 21-01-2007, 01:38 AM

Quote:

Originally Posted by ratter

There will be some slight variance in mph but not a great deal

Yep .. But if you had wild cam etc a lower diff and higher converter helps...
Esp if it has 3.08 ratio...

all4ford · 22-01-2007, 07:43 AM

Quote:

Originally Posted by ratter

There will be some slight variance in mph but not a great deal

Thanks for that.

22-01-2007, 04:05 PM

Quote:

Originally Posted by all4ford

So by that logic, wouldn't a 600HP car in a 1700kg body, whether it had 4.11's or 2.9s as a diff ratio run the same MPH? I dont get how that could be at all possible.

Changing diff ratios will likely have more effect on your 60 foot thus giving you a better ET but a similiar MPH.The MPH will be the same because the engine in most cases will most likely find it's peak power at the end of the 400m.

eed-250 · 21-01-2007, 08:36 PM

i ran a 14.805 @ 91.2 mph
2.108 60'

my friends ef ran a 15.2@92mph so yeah i guess its all in the 60'

**ebxr8240** · 21-01-2007, 10:16 PM

12.2 @ 125 mph
2.3 or so 60 Ft..
Manual...

Kenaz · 22-01-2007, 01:24 PM

Quote:

Originally Posted by useless

What does it all mean? It doesnt seem consistent with au i6 cars in the data base?

Useless, my brother has a EF XR6 with DEV 4 cam, manual and 3.73 diff and he runs similar ET and MPH to you. I think 14.8 @ 92mph. Should be a little quicker than that next time out.

**Stav** · 22-01-2007, 04:45 PM

Quote:

Originally Posted by Kenaz

Useless, my brother has a EF XR6 with DEV 4 cam, manual and 3.73 diff and he runs similar ET and MPH to you. I think 14.8 @ 92mph. Should be a little quicker than that next time out.

I think these cams are generally fetching 92 mph at the end but theyve got some good mumbo from low to midrange when tuned right.I am very intersted to see how much difference my head will make when I finally get it back and in.

Kenaz · 22-01-2007, 04:50 PM

Quote:

Originally Posted by useless

but theyve got some good mumbo from low to midrange when tuned right.

Yeah, the low to mid range in his car is incredible. It sort of dies off a bit high in the rev range though.

**Stav** · 22-01-2007, 04:56 PM

Quote:

Originally Posted by Kenaz

Yeah, the low to mid range in his car is incredible. It sort of dies off a bit high in the rev range though.

Mine too.So seriously.what is the best time to shift gear changes at? Some say peak power some say peak torque? I am swaying towards a little above peak power to get into the meat of the power.

Scott · 22-01-2007, 05:20 PM

Quote:

Originally Posted by useless

Mine too.So seriously.what is the best time to shift gear changes at? Some say peak power some say peak torque? I am swaying towards a little above peak power to get into the meat of the power.

This is how I think:

Peak torque moves considerably dependant on which gear you are in. In reality, if you are at the top of the rev range in a any gear, you will have more torque than any where in the next gear up even if you have exceeded the peak torque for that gear. This means that whilst you are approaching red line in 1st, there is no other gear (above) that will give you the same or better acceleration or torque.... same goes for every gear as you go through the list.

If you shifted at max torque for the gear you are in, you would probably be shifting about 1000 revs (or there abouts) before your redline. This "missing" 1000 revs will deliver you into the next gear even lower in the torque curve which will equal slower acceleration.

If you just picked the revs for the 1-1 geared peak torque, you would find that you were shifting quite early in the rev range and delivering yourself too low in the next gear.

black ute · 22-01-2007, 02:46 PM

Don't forget theres normaly a few mph variation between the lanes at WSID, or so everybody says

Quadcams · 22-01-2007, 03:25 PM

Quote:

Originally Posted by black ute

Don't forget theres normaly a few mph variation between the lanes at WSID, or so everybody says

Not always just every now and then it can be out a little

Scott · 22-01-2007, 04:16 PM

Try this link, it has calculators that seem to work out whatever you need.

http://www.tciauto.com/Products/Tech...culators.asp#0

FS5 · 22-01-2007, 04:55 PM

stav i have found personaly ,the better 60ty better ET.what rpm and how quick you change gears have more of an effect on your mph.last time i was at willowbank i was playing around with this theory and when i changed gears right on the limmiter or even when i hit it i consistantly ran better mph.
firmer quicker shifts will increase your ET though ,more so in a manual because theres a lot more room for error ,but in a shift kitted auto iy shouldn't be a problem.

**Stav** · 22-01-2007, 05:04 PM

Quote:

Originally Posted by FS5

stav i have found personaly ,the better 60ty better ET.what rpm and how quick you change gears have more of an effect on your mph.last time i was at willowbank i was playing around with this theory and when i changed gears right on the limmiter or even when i hit it i consistantly ran better mph.
firmer quicker shifts will increase your ET though ,more so in a manual because theres a lot more room for error ,but in a shift kitted auto iy shouldn't be a problem.

My gtech timer has shift lights inside.I think I will set it for change at 5900 rpm then slam it in.How does it work?Hold first gear to just before the limiter then change to second?Then third? The dam auto seems to have a split second delay sometimes..maybe I over rev it.I can take it to 6000 rpM.

xr8ute · 22-01-2007, 05:22 PM

Quote:

Originally Posted by useless

The dam auto seems to have a split second delay sometimes..maybe I over rev it.I can take it to 6000 rpM.

Yep, this is one area where auto's suck.

Its a time thing. I used to move the shifter from 1st to 2nd about 300rpm before I wanted to actually shift. And becuase the engine revs where increasing slower in 2nd gear, I would move the shifter from 2nd to 3rd about 100rpm before I wanted it to change.

I hit the limiter bunch of times (its at only 5500rpm), and its not good for ET :(

You'll need to experiment a bit with yours Stav, and see what the delay is in rpm in each gear (between moving the shifter, and the gear change completing)

xr8ute · 22-01-2007, 05:16 PM

Most likely higher than peak rpm, and definitely higher than peak torque. Ideal shiftpoint for 1-2 shift may be different for the 2-3 shift.

I have been thinking a bit about this, but haven't done the math yet to see how it might work out in real life....but it seems to make sense to me, so bare with me :P

First start off with a dyno sheet showing power curve vs rpm

Then look at your gear ratios to find the rpm drop between 1st and 2nd...not sure what it will be, but lets just say its 2500rpm (i.e. you shift at 5500rpm, the revs drop to 3000rpm when you change into 2nd)

Using your power vs rpm graph again, find the two points 2500rpm apart that give the highest average rpm. Use the higher of those two points as your shiftpoint/

Do the same for the 2-3rd gearchange.

...should get you in the ballpark at least

Scott · 22-01-2007, 05:29 PM

It doesn't really matter what the number is at the wheels as the next gear will never be as high. Run it out of revs (assuming your power doesn't just die in the bum near the redline) and you will always be maximising your torque.

It's as much about what you are shifting into as what you are shifting out of.

Quadcams · 22-01-2007, 06:01 PM

Quote:

Originally Posted by GTP006

It doesn't really matter what the number is at the wheels as the next gear will never be as high. Run it out of revs (assuming your power doesn't just die in the bum near the redline) and you will always be maximising your torque.

It's as much about what you are shifting into as what you are shifting out of.

And taking into account each gear chang your torque will roughly half due to taller gear, myself always shift at redline 1st and 2nd then short shift a litle bit into 3rd and 4th due to taking longer to go from peak power to redline therefore better off being in next gear. eg for myself- 1st=6000rpm, 2nd=6000rpm, 3rd=5800rpm, 4th=5700rpm. After many a pass seems to net the best results.
End of the day its alot of trial and error working it out for your oun configeration, myself now with new motor will have to work this out all again.

**Stav** · 22-01-2007, 06:26 PM

Hmm interesting info here. The only prob I may have shifting in auto is that lag between shifts when changing gears,even the 2 shift kits I have dont resolve the problem.Essenyially the box doesnt change the shift quick enough.

xr8ute · 22-01-2007, 06:38 PM

Quote:

Originally Posted by useless

The only prob I may have shifting in auto is that lag between shifts when changing gears,even the 2 shift kits I have dont resolve the problem.

The beauty of that problem, at least in my case, is that the lag is very consistent/repeatable.

You can factor that lag into your shift strategy, and with only a little bit of effort, it will be changing gears when you want.

Aaron_EF8 · 24-01-2007, 01:17 PM

Just to get slightly off the original topic here.

If you have a G-Tech Pro RR (or whatever they're called) that can be plugged into a PC, do an acceleration run from low RPM to the redline in each gear and graph the acceleration and speed for each gear. Then overlap the 3/4 lines on a single graph, and look where each gear accelerates less than the next gear (IE the lines cross over), that's where the perfect shift point is.

**Stav** · 24-01-2007, 02:06 PM

Funny you should say that because I ahve the ss model (same as rr but no download) and its telling me some interesting facts. My peak power rarely hits above 4800rpm.The peak rpm point of a car is dictated mostly by intake and exhaust manifolding.at 4800 rpm peaking power there seems to be something choking airflow and power above this.