raverx3m

iTrader: (1)

im trying to wrap my head around this but cant connect the dots


say i have 200whp motor with 2500lb car and gsr tranny my peak torque is at 7400rpm
peak power is at 8100rpm

between 8000 and 8500rpm the whp drops by 10 si its at 190
my reasoning is that i rather have 500rpm of 190 whp than shift at 8000 and drop to below vtec and spend that 500rpm in 120-140 range

correct me if im wrong please.

im just trying to understand where is the best shift point right after the peak whp or where the power starts dropping significantly?



ive also seen some cars where the whp graph just flatlines at higher rpm do you ride it out until it starts dropping or shift when you hit peak whp?

h2.4

if you had access to a Mustang Dyno, you could do a simulated 1/4mile run and start overlaying data...

Black R

Typically on vtec motors, shift right before rev limit.

raverx3m

iTrader: (1)

Yea thats advice i only saw it in every other thread i searched. Were not talking about stock engine here.

raverx3m

iTrader: (1)

Im talking about in relation to your power curve. Not rev limiter

Black R

Ok, another way to put it is to shift so that when the rpm drops, it's closest to peak whp as possible.

raverx3m

iTrader: (1)

my peak power is at 8100

you re not understanding the question

my power drops right after 8100 at 8500 it drops by about 10whp
which is still ok
how far should i go past the peak power once the power starts dropping at higher rpm

onefstek

Gear ratio has a lot to do with when you want to shift.

Stefan

raverx3m

iTrader: (1)

im asking more specific about powerband

i know the shift points for the tranny at different rpms

it falls out of vtec regardless from first to second
not asking about gear ratio here

Almtrhb

iTrader: (3)

Ok if your dropping below vtec on your 1-2nd shift. Either your shifting too early, your spinning but with 200hp I doubt that is the prob. The tire is too big, your shifting slow, or you need more power. Shift at a higher rpm so when the rpm comes down it stays in the sweet spot, maybe go to a 4.7 FD, Switch to a B16/ITR tranny instead of the gsr..... Just a few thoughts

Black R

Peak power at 8100? Shift at rev limiter. Or 9200. Whichever is higher.

PhilStubbs

Ummmmm....... Why not go to the track, make a run shifting at 8500, make a run shifting at 9k then compare? You can look at Dyno sheets and do math all day, but in the real world is where the variables you can't think of happen. Just try

raverx3m

iTrader: (1)

i was just asking to see if anyone can advise from experience.

i got my answer already thanks to those who actually answered

IN VTEC

iTrader: (3)

Calculate the RPM window for each gear and then calculate the area under the curve for a variety of shift points and RPM drops until you get the greatest area under the curve for each different window. That'll theoretically optimize the power band you have.

Gunmetal_B20_Hatch

iTrader: (9)

^ perfect answer

wreckeddc4

If you are shifting at 8500 on the factory tach the real engine rpm is most likely way off. I noticed on all my data logs that my tach was 5-700 rpms off up top.
If you use the check engine light as a shift light with like an s300 or something, set it to where you want and see what the tach says when it comes on.

Also with that gearing, you want a really small tire like 22". If your on a 205 50 15 that's closer to a 24" tire which will drop you outta vtec in between 1-2. Similar tire ratios with 16" street rims are even worse.

I ran a 215hp GSR with 17s on it down the track once and it went like 14.5. Swapped to a 15" street tire and went 13.80s.

The guys that are going quick with 200hp na setups run b16 gears with the low final drives as well. To keep the motor in peak hp/tq in every gear.

Divers

FD does NOT change anything. He would have the same issues.


Staying up in the power is worth more than running it past peak power IMO. With that said, feel free to take 1st (and maybe even 2nd) past 8500rpm. The loss in power really doesn't matter down there as you already have more power than traction. The 2-3 shift and 3-4 shift are closer together so you shouldn't all too low even shift at 8100-8500. If you find yourself going through the traps with lots of 4th left (which is most likely the cast with 200hp and a gsr tranny) I would get a shorter final drive. You will have more mechanical torque at the onset of your gears.

raverx3m

iTrader: (1)

so in other words try to make it so i pass the finish line right at the end of 3rd gear?


right now i dont have the best setup for drag racing tho

the 200whp was with a gsr tranny and 205-50-16 tires (tires were on sale so i got them) its not too bad
i can still keep up with 13.5 second stock cars

Divers

No, cross the finish line right at the redline of 4th.

soloDC

Look, I had a 205 Whp GSR that weighed in at 2170 pounds w/ no driver. My power peak (205 whp) was from 8100-8500 Rpms, after this my power drops to around 190 ish by 9,000 rpms. I set my rev limiter to 9200 Rpms. On 22 in slicks and a GSR trans with a 4.9 final drive I went out on the first run and shifted at 8500 Rpms, the car trapped 103 mph. Next run I went out and shifted at 9,100 Rpms just before my rev limiter and the car trapped 104.8 mph.... So I repeated the process and found revving the car out as high as possible in each gear gave me a slightly better ET and more MPH. My power curve was similar to the example you are giving. Also like some other ppl have said, do NOT shift gears based off of your stock rpm tach, it's more than likely to be off by 500 Rpm or so. Next thing is, is that your gearing is to big for 200 whp and the tires are to big as well. Get a 22 or 22.5 inch tire. Next it's wishful thinking that you will be able to finish the 1/4 mile at the top of 4th gear with a GSR trans, that won't happen unless you do a 4.9 final with a 22 in tire. So try to finish the 1/4 mile at the top of 3rd gear ( I used to do this) on a 22 in tire I would finish in 3rd gear at 9,100 Rpms trapping 102 mph, this was on the stock 4.4 final drive. By doing this yup will Not have to shift into 4 th gear and you should save yourself maybe .1-.2 tenths. I hope this helped lol.

EpHatchy

Good info.didnt know tires played that big of a roll at the drag strip.
I have less power and have a 23.5" tire.

raverx3m

iTrader: (1)

205 50 16 tires put my first and secong gear ratio longer than ls tranny

Zeal has tranny calculator you can play around with it.

soloDC

Yep, tires can either help you or hurt you... You should run a tire that gives you the best gearing, but can still grip on. There are some 22 in drag radial that fit on a 14 inch wheel. That's a great tire for a 200 HP and under car.

MugenSpeclNY

Can you list some
Of these options? Also 14inchx?inch wheel would you recommend?

EpHatchy

Please do. Also what 14" wheels would clear Integra brakes?