I was having one of my boost junkie sessions today in my car (wait, that's everyday ), and I realized something rather obvious. With my particular turbo (Greddy 15G), it spools at 2800rpm and pulls pretty well until about 6k, where it starts to drop off. By the time I hit redline, the power has really dipped off.

Now what I decided to try today was shifting at 6k instead of 7k like I usually do when I'm racing (ricer's instinct I guess ). I noticed that the car pulled a lot harder in my opinion and when I'd shift, I'd go into the next gear a lot harder than when I used to shift from redline of the previous gear.

What I'm asking is: if my powerband starts to drop off at 6k, should I shift into the next gear at 6k instead of redline? I know the question is pretty retarded at first glance, but think about car's like the SRT-4. Doesn't it make it's peak power at lik 2500 or 3500rpm? I know that it would be stupid to shift at 3k in a car that revs to 6-7k, but I'm just stirring the pot.

What do you guys think about this? I know that the "shift at redline" mentality is pretty common here on H-T, considering that most of you guys in this forum have larger turbos that are very efficient up to redline, as opposed to my dinky greddy turbo, which is very efficient in the mid-range but falls off before redline.

When I ran at the track in late August, I was shifting at redline, but I could feel the car's power drop off after 6k; I ran a 14.8 @ 94mph, 7.5 psi, EX coupe, greddy kit, blue box, all-season tires, blah blah.

Now if I would have shifted at 6k in every gear would I have ran a faster time?

Am I making any sense here? Or just rambling?

 

it sounds right to me, you dont want to shift where there is no power so shifting when in the power band or right befor power drops off would definitly make the car faster.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18C1CYA &raquo;</TD></TR><TR><TD CLASS="quote">it sounds right to me, you dont want to shift where there is no power so shifting when in the power band or right befor power drops off would definitly make the car faster. </TD></TR></TABLE>

So for my particular setup, I should be shifting at 6k instead of redline?

 

agreed. i would go put it on the dyno to see where it maxs out at and shift at that point.

 

driving an underturboed honda sucks. Of all motors to NOT rev out... sheesh

 

if your just gonna guesstimate, id go for the healthy medium of 6500. you want to shift after your power has dropped so you can be at a higher rpm in the next gear.

but if you want to really know when to shift you'll need your gear ratios + dyno chart + some math = which will tell you where you should shift

oh, and thats not to mention the really long gear ratios of the d16's

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bailhatch &raquo;</TD></TR><TR><TD CLASS="quote">driving an underturboed honda sucks. Of all motors to NOT rev out... sheesh </TD></TR></TABLE>

*shrug*

Sorry I'm a broke college student, this is the best I can do for now. Gotta start somewhere right?

 

i wasn't ragging on you. I'm in the same boat I have put a few different turbos on different honda motors and the undersized turbos really took the fun out of a motor that loves to rev. My first setup was like this so i know how lame it is. The t3 I have now is pretty good but I would really prefer a power curve that pretty much mimics the stock one but with a abit more low-mid and obviously a shitload more top end right to redline. It's a real balancing act because too large of a turbo is not that fun on the street either.

 

You should calculate your torque times your gear ratio's and figure out when in each gear you have more torque available in the next gear. Once you find those point's you should be close. And the rest you just have to figure out on the track. Sometimes you may have to trade some acceleration for better transient response.

 

All you have to do to figure out where to shift is look at your dyno chart and detirmine the point at which the rpm you are shifting at is making less horsepower than the RPM that shift would put you at. For example, if you have a 200whp car, and the power dips starting at 6k down to like 180 by 7k but you were making 185 by lets say 4.9k then the shift will put you in a fatter part of the powerband than you were in and you want to make the shift. Ideally what you want is to be in a part of the band that makes the most power at all times.


Hope my logic is sound and this makes sense.
Matt

 

just take it to the track and 1 run shift at 7 and another at 6 and see which ones faster

 

At the track, yu still need to carry your gears to the end of 4th. Shifting at 6k might put yu into 5th...which is going to kill you

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suprdave &raquo;</TD></TR><TR><TD CLASS="quote">At the track, yu still need to carry your gears to the end of 4th. Shifting at 6k might put yu into 5th...which is going to kill you</TD></TR></TABLE> yeah that probly will kill you but just shift sooner for 1-3 and see what happens, just go to the track and play with it

 

i would say shifting at 6k is way too early. With the crappy d series gearing that would kill you. Plus just because your torque peak dips off at a certain point it doesn't mean you aren't still making more hp up top.

 

the main downfall i see to shifting at 6 is the long geared d16 tranny. i liked the compromise idea of shifting at like 6500. try that one and see how it does.

 

You guys are all bringing up really good points, I'm learning a lot. Keep it coming

 

I dont know if shifting at 6 is a good idea, because of what's mentioned.

Where do you land when you shift at 6 compared to 7? It'll probably take you longer to get back up to 6 when you shift at 6. Did that make sense?

Example, even though the b18b's max power is at ~6500, you're supposed to redline 1st and 2nd just to land higher in the powerband for third... That's what I do at least.

 

ok, i'm going to try to explain this to the best of my knowledge. i might be wrong on some things, but hey i'm just stating my theory in my head.
your shift point and powerband are directly related in which to make faster et's on the strip. i'm gonna leave torque aside since horsepower is torque*rpm/5252. Now being the variable for your setup, your powerband will be in different locations. once your powerband starts to fall isn't necessarily optimum shift point. <U>the goal is to line the shift rpm's up to where your making more power in the next gear that youre making now, and/or redline, whichever comes first </U> so optimum shift point will be when you can make more power in the next gear than you're making in the gear now. on very small turbo cars or heads that can't breathe, this might be earlier in the powerband than redline, it all depends on the volumetric efficiency of your motor, and the setup you've got. Also it depends on your gearing, cause you can accelerate faster in 1st and 2nd than you can in 4th or 5th. so this comes into play as well with the setup, so you have to take this into play as well. so unless youre motor setup and gearing is whack, take it to redline. again, i'm no professional, i'm just a kid with what i call common sense...


Modified by nskforlife at 11:08 PM 5/1/2007

 

sorry to be harsh but.....wtf is the point bring this back from the dead? Way to beat a dead horse dude

 

go here i found it lat nite its a good site http://www.fatboyraceworks.com/gears/index.php?