i have a 98 gt mustang 5spd (4.6 of course) and i have 4:10 rear gears in it.. the car is pretty quick and is completely stock besides the gear.. some ppl tell me that if i want to build it for red light racing then i should build it for bottom end power and not top end.. im kinda confused about what they mean.. i know bottom end is low rpms and top end is high rpms (i think thats what it means).. So even if i was racing red light to red light and i had to my pedal floored the whole time wouldnt my rpms be high? so wouldnt that be considered top end? what good is bottom end if your racing and you are flooring it the whole time and your rpms are high.. i notice most of my power between 2500 and 4500 rpms and my redline is 6000.. so is my power considered top end or bottom end? im really confused.. if i made the car bottom end and someone w/ a top end car was next to me at a light couldnt he just keeps his rpms up at take off and stay w/ me? can someone help clarify this for me?.. i plan on switching the heads out for the PI heads and intake and cam, installing a K&N CAI, maf sensor bigger throttle body and injectors, and hurst shifter..
confused about bottom end vs top end
- Thread starter confusion4you
- Start date
Bottomend is meant to mean to have 'lots of torque' downlow that comes on fast, and topend is lots of horsepower (typically made in higher rpm).
Even stoplight to stoplight racing, I think you need to have midrange-higher rpm horsepower...It only takes a second to be above 3500 rpm and so you typically will race between 3500-5500 rpm...
So shoot for midrange to higher rpm, like you are setup from the factory. A PI headswap will help that out...
Even stoplight to stoplight racing, I think you need to have midrange-higher rpm horsepower...It only takes a second to be above 3500 rpm and so you typically will race between 3500-5500 rpm...
So shoot for midrange to higher rpm, like you are setup from the factory. A PI headswap will help that out...
so whats the big deal about ppl having lots of bottom end then if most of racing revolves around high rpms .. if i had good top end wouldnt i be able to still accelerate off the line fast if i held my rpms up before take off.. how come cars like 350z's can accelerate faster at top speeds than my mustang (just and example i havent tried it yet). i hear ppl say that ricers are made for top end but they pull off the line slow.. couldnt they keep their rpms up and pull off the line just as fast as someone w/ lots of bottom end?
Tim2002GT
Founding Member
You can try to "leave a light" at higher rpm's, but the sudden impact of that power range to the tires may cause unwanted tirespin.
Stan Weiss
Member
+1
Unless you are riding around with slicks or DR with the 4.1:1 rear I do not believe you can start above 2500 RPM.i mean i love the torque i have when i take off , its really quick.. but whats the diff between low end and top end power once you've already shot off the line and your going thru the gears. i mean i usually take it up to about 4500 5000 rpm and shift and in each gear i usually drop back down to 3000 or more . so wouldnt that mean i have top end power? or does bottom end mean that each time i shift and the rpms drop down to 3000 it will pick up faster to 4500 5000 vs waiting for the rpms to hit 4000 4500 before the accel. kicks in?
Stan Weiss
Member
What is the distance of the race? Remember the low end power will only be used in first gear. But the shorter the race the more important this is.
wouldnt a 1/4 mile race be good for bottom end power? even if it was , dont you get up to over a 100 in a 1/4 mile ,so while your shifting thru the gears your rpms are gonna be high so once again wouldnt you be in top end range? what kinda power would be good say, if i was goin down the rd around 45mph and i wanted to take off and race someone.. usually if i could i would downshift and get the rpms up. but wouldnt that be mid-high end power?
larrendeuce
Member
I can offer a few examples of cars using engines with different powerbands.
Drag racing would be high rpm, you can launch high, with gearing it will remain high through the 1/4.
Road racing would be mid to high, gotta have torque to pull out of a corner, too narrow and high a powerband you might not be competitive.
Street would be mid to low mostly. Most people don't drive at 6000 rpm going to work. Having an engine with a high rpm powerband would mean it feels slow and sluggish at low rpm cruise. You still can downshift and turn rpm to pass and get on the highway though.
I'd say a good comparison would be a stock 5 liter vs stock 4.6.(manual trans for sake of this) If your turning 1500 rpm (or 25-30 mph) driving along in 3rd and punch the gas in the 5 liter the engine won't lug, you'll feel a smooth powerful(matter of opinion) acceleration, car seems lighter and easier to drive. However the same with a 4.6 the engine will lug, and seem sluggish until 2000-2500 rpm, after which power will come on fast (again opinion) and feel faster then the 5 liter.
Drag racing would be high rpm, you can launch high, with gearing it will remain high through the 1/4.
Road racing would be mid to high, gotta have torque to pull out of a corner, too narrow and high a powerband you might not be competitive.
Street would be mid to low mostly. Most people don't drive at 6000 rpm going to work. Having an engine with a high rpm powerband would mean it feels slow and sluggish at low rpm cruise. You still can downshift and turn rpm to pass and get on the highway though.
I'd say a good comparison would be a stock 5 liter vs stock 4.6.(manual trans for sake of this) If your turning 1500 rpm (or 25-30 mph) driving along in 3rd and punch the gas in the 5 liter the engine won't lug, you'll feel a smooth powerful(matter of opinion) acceleration, car seems lighter and easier to drive. However the same with a 4.6 the engine will lug, and seem sluggish until 2000-2500 rpm, after which power will come on fast (again opinion) and feel faster then the 5 liter.
thanks, that kinda cleared things up for me.. so i guess bottom end power is gonna be good for just the begining of the first few (1-3) gears and launching? so does that mean once you start getting into higher rpms its power is going to lag and you would have to shift sooner? if it made good low power then what if i downshifted to get high rpms to take off faster would that work since most of the power is being made in the low rpms . like u said, i am feeling my power starting around 2200-2500 and ending around 4500-4700. so would i have mid-high power range?
lexluthr69
New Member
You absolutely have "mid" power range. When folks talk about low-end, they're talking about having gob loads of torque to play with. High end is in reference to having "gob loads" of horsepower above 5250rpm, the point at which horsepower becomes the prime number and torque falls off...
It's best to think of it in terms of gearing. Where is your power when you are in a certain tranny gear, while also taking into consideration rear axle gearing. If you're driving a "race" that will keep you in no more than 1st through 3rd gear, than I would, personally, consider that a car in need of "low end" power. If it's a race where you'll hit all 5 or 6 gears, then that's a car in need of "high end" power.
Gearing is everything... It's the reason why we're so easily able to feel the difference between stock 3.27 gears, and 3.73 or 4.10 gears...
It's best to think of it in terms of gearing. Where is your power when you are in a certain tranny gear, while also taking into consideration rear axle gearing. If you're driving a "race" that will keep you in no more than 1st through 3rd gear, than I would, personally, consider that a car in need of "low end" power. If it's a race where you'll hit all 5 or 6 gears, then that's a car in need of "high end" power.
Gearing is everything... It's the reason why we're so easily able to feel the difference between stock 3.27 gears, and 3.73 or 4.10 gears...
ok that makes sense to me.. so for example when im racing from a stop and im going thru all the gears i usually shift out of first between 3800-4200 rpm's and then i hit second and it bumps me down to about 3000 and i take that up to about 5000 and shift to third and it knocks me back to around 3200-3500 and thats how it is for the rest of the gears.. so if im taking it close to redline (6000) in everygear and i shift and i get down to 3000 would i have mid-top end power?. would i want to increase my bottom end to get me back up from 3000 again in each gear or would i be increasing top end to get me back up from 3000? i was driving beside my dad in his SONATA ( '06 ) one day and we were on the highway doing about 70mph and we both goosed it. i dropped it down to 4th and floored it and pulled away from him and i hit about 100mph and shifted to 5th and a cpl seconds later he caught up to me and passed me.. when i shifted to fith i was back down to about 4200 rpms.. what could i do to solve that problem? i know mustangs are notorious for losing power in 5th thats why i have the 4:10 gear. but i have a sohc and he had dohc i think..
confusion - Shift higher than that, try 5400 or so in 1st-4th gear.
That bottomend is just for a second or so until you get past 3-3.5k...then from there you are using 'topend' power for the entire race.
In other words, if racing 1-4 gear (a bit more than a quarter mile), you are in the 'topend' range for 95% of the time.
I believe 'bottomend' is an old school term, when in reality it helps very little! It is just 5% of the race...
Torque gets you moving (bottomend), but the horsepower (topend) keeps you moving, whether it be in 1st or 5th gear...
That bottomend is just for a second or so until you get past 3-3.5k...then from there you are using 'topend' power for the entire race.
In other words, if racing 1-4 gear (a bit more than a quarter mile), you are in the 'topend' range for 95% of the time.
I believe 'bottomend' is an old school term, when in reality it helps very little! It is just 5% of the race...
Torque gets you moving (bottomend), but the horsepower (topend) keeps you moving, whether it be in 1st or 5th gear...
ok i will give that a try and see how she porforms.. so when i do the modds i wanna keep the power in the mid-high range? also this might sounda kinda dumb but ive kept trying to load a picture next to my name like everyone else has but everytime i load one nothing happens, i never see my pic.. what did you guys do to get your car pic next to your name?
goshia
New Member
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