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Discussion Starter #1
Anyone else feel that revving the car past about 5k seems pointless?

I find if i'm in say 3rd and floor it at about 2k you get lovely acceleration till about 5k then just feels flat.
 

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Anyone else feel that revving the car past about 5k seems pointless?

I find if i'm in say 3rd and floor it at about 2k you get lovely acceleration till about 5k then just feels flat.
and that's why some of us use a COBB AP.
 

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Discussion Starter #4
So what is actually happening at this RPM, does the boost flatten off or something? and a Cobb remap continues to increase it?
 

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So what is actually happening at this RPM, does the boost flatten off or something? and a Cobb remap continues to increase it?
tbh,i think Nissan expected too much abuse from us europeans and just made the mapping far too safe...thats the reason the GTR doesn´t do 310km/h...:D
 

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Heres a question , when is the best time to shift to maximize acceleration ?

Peak power ?
Peak torque ?
Redline ?
Somewhere else ?

Now with that said if you look at a dyno chart of a stock car with boost overlaid you will see that boost peaks at around 3000 rpms and starts to drop down to about 10 psi after 5000 rpms.

This is why companys sell aftermarket wastegate actuators, and Cobbs new boost control vs RPM does what it does. Keeps boost higher though the higher rev range.

The stock turbos on the R35 are pretty small, and they will do what small turbos do, run out of capacity at high RPM, boost, and you will see that nose over. The trade off is good response vs high rpm power.
 

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Heres a question , when is the best time to shift to maximize acceleration ?

Peak power ?
Peak torque ?
Redline ?
Somewhere else ?
You'll want to shift so that your current gear and the next gear get the most area under the dyno.

So if you have a dyno print off and on each gearshift you 'lose' 2000 rpm of engine speed then you want to find the 2000rpm range on the dyno bhp graph that has the most area underneath it.

Of course it gets a little more complicated as the gears will not have exactly the same spacing between them so you'd need to calculate for each shift (but that error is probably not significant as they won't differ that greatly)

Torque has little to do with acceleration (except that its a component of power), its all down to how much power you have and for how much of the rev range you have it.
 

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Discussion Starter #8
So are we saying what I am experiencing on the standard map is the manufacturer limiting boost above this RPM ?
 

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without new turbo's and injectors........get a new map the latest greatest :smokin:and short shift 1st 2nd 3rd with Traction control OFF (you have to short shift at around 4800 to 5000 rpm or you will light them up in the dry) then for all other gears there is a balance between torque and BHP with stock turbo's and injectors the torque drops off dramatically after 5300rpm so would suggest based on what i have seen shifting at around 5600 rpm as peak BHP is still up around 6400rpm but torque drop dramatcally after 5300rpm. But it is a balance and depends who is tuning you motor. If stock for me what i remember of when i had stock map best to shift around 5400rpm for best you can get. I AM SURE OTHERS WILL DISAGREE:D:D
 

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Discussion Starter #10
Does a Cobb map remove the flattening of the power at 5k and give you acceleration upto the redline?
 

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peak BHP is still up around 6400rpm but torque drop dramatcally after 5300rpm.
But logically acceleration is generated as a result of power and not torque (if we need to get to 100mph then we need to generate the kinetic energy required from the engine, and power is energy per unit time), so for maximum acceleration one would need as much bhp as possible for as long a period in the rev range as possible, which would most likely be by staying in gear through peak bhp. If someone has a dyno sheet to dissect and some shift data then we could work it out exactly.
 

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Ah well not always as per the physics lab. Tracks are not perfect and it is not possible to lay down the powre wioth stock wheels and tyres. Check the attached dyno chart and sent me your thoughts but i still have the fastest terminal in the UK short shifting:smokin:
 

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From your graphs John you want to change quite high, especially in the lower gears (subject to traction as you mention). Usually you want to change after peak power so that when you drop back in your are just below peak power = highest average power.
 

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You'll want to shift so that your current gear and the next gear get the most area under the dyno....
I think this sums it up nicely imho (assuming dyno = power plot graph).
 

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From your graphs John you want to change quite high, especially in the lower gears (subject to traction as you mention). Usually you want to change after peak power so that when you drop back in your are just below peak power = highest average power.
Interesting this as best terminal was acheived short shifting??? Cant wait for dry track as suspect it was all due to lack of traction now
 

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Discussion Starter #17
Ok, so I'm confused, can't someone just explain what happens past 5k ? on the standard map and what can solve this.
 

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Volumetric efficiency peaks at peak torque and then declines. Less airflow, less torque. However, power increases as long as torque declines slower than RPM increases.

You can increase the boost whilst the turbo is still efficient to gain power at the top, but you tend not to change the shape of the curve much, just lift it higher.

Bigger turbos and cams would shift it higher at the expense of driveability.

Is this what you wanted to know? This is nothing special about the GTR, it is generic to all consumer turbocharged engines, and most NA engines except Honda, BMW M power.
 

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Discussion Starter #19
A little to tech but I think I understand, I came from a RS4 to a GTR and the power didn't kick in until 5k so I guess it's kinda weird for me.

Would a remap help with this sort of flat spot? long term I'll probably get an exhaust and Cobb.
 

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sorry for sounding like a complete noob, but what do you mean when you say "short shifting"?
 
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