Rocker setup, 7500 RPM SBF

General engine tech -- Drag Racing to Circle Track

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xr4x4ti
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Re: Rocker setup, 7500 RPM SBF

Post by xr4x4ti » Fri Oct 12, 2018 2:41 pm

cjperformance wrote:
Fri Oct 12, 2018 5:50 am
gruntguru wrote:
Fri Oct 12, 2018 3:04 am
If the shift to 5th puts the engine at a higher BHP, the engine torque will be MUCH HIGHER and the final drive and tyres will see higher torque (in the same proportion as the power). Rule of thumb - always have your engine as close to peak power as possible.

Not suggesting you should shift to 5th - the shift time may be a bigger loss - just saying.
So what is faster, forgetting a gear shift, just reaching peak hp at the stripe or reaching peak at say 1000' and running the last 320 above peak but still increasing rpm?
That is the question. If I had a details HP curve, one could try to be a bit scientific about it. But, my gut suggests I am better off not shifting. If 5th gear was more like .8 if might make more sense.

Of course this ignores the fact that 5th gear in a T56 is really not meant to be a "power gear" and is not designed for the loads.

My next tire purchase with get me closer to a 25+ inch rolling diameter which will help the situation.

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Re: Rocker setup, 7500 RPM SBF

Post by cjperformance » Fri Oct 12, 2018 3:17 pm

Well if you have just hit peak hp in top gear at the stripe , your gearing is too high and you wont see the best potential ET. You need to be hitting peak hp rpm as early as possible within the realms if your combos over peak rpm capabilitly.
Look from another angle. If your car can just hit say 120mph at the stripe, what happens to your et if you set it up to hit 120mph at 1000' (arbitrary number) and travel the rest of the track at 120mph let alone using some past peak rpm to carry it out to say 123mph ? - The ET drops, you have travelled more of the track at a higher speed , even if you did not increase rpm/mph after peak hp.
Craig.

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Re: Rocker setup, 7500 RPM SBF

Post by xr4x4ti » Fri Oct 12, 2018 3:44 pm

cjperformance wrote:
Fri Oct 12, 2018 3:17 pm
Well if you have just hit peak hp in top gear at the stripe , your gearing is too high and you wont see the best potential ET. You need to be hitting peak hp rpm as early as possible within the realms if your combos over peak rpm capabilitly.
Look from another angle. If your car can just hit say 120mph at the stripe, what happens to your et if you set it up to hit 120mph at 1000' (arbitrary number) and travel the rest of the track at 120mph let alone using some past peak rpm to carry it out to say 123mph ? - The ET drops, you have travelled more of the track at a higher speed , even if you did not increase rpm/mph after peak hp.
There were way to many variables for it to be a very scientific comparison. But, on the surface, going from 4:1 gears and shifting into 5, to 3.73 gears and running it to redline dropped my ET by .2 and increased my MPH from 129-132. That suggests it was a move in the right direction.

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Re: Rocker setup, 7500 RPM SBF

Post by cjperformance » Fri Oct 12, 2018 4:34 pm

xr4x4ti wrote:
Fri Oct 12, 2018 3:44 pm
cjperformance wrote:
Fri Oct 12, 2018 3:17 pm
Well if you have just hit peak hp in top gear at the stripe , your gearing is too high and you wont see the best potential ET. You need to be hitting peak hp rpm as early as possible within the realms if your combos over peak rpm capabilitly.
Look from another angle. If your car can just hit say 120mph at the stripe, what happens to your et if you set it up to hit 120mph at 1000' (arbitrary number) and travel the rest of the track at 120mph let alone using some past peak rpm to carry it out to say 123mph ? - The ET drops, you have travelled more of the track at a higher speed , even if you did not increase rpm/mph after peak hp.
There were way to many variables for it to be a very scientific comparison. But, on the surface, going from 4:1 gears and shifting into 5, to 3.73 gears and running it to redline dropped my ET by .2 and increased my MPH from 129-132. That suggests it was a move in the right direction.
Yes, so if you can run some more rpm now by upping the rpm usage limit and not make that shift you will get another small improvement.
Craig.

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Re: Rocker setup, 7500 RPM SBF

Post by gruntguru » Fri Oct 12, 2018 5:56 pm

cjperformance wrote:
Fri Oct 12, 2018 5:50 am
gruntguru wrote:
Fri Oct 12, 2018 3:04 am
If the shift to 5th puts the engine at a higher BHP, the engine torque will be MUCH HIGHER and the final drive and tyres will see higher torque (in the same proportion as the power). Rule of thumb - always have your engine as close to peak power as possible.

Not suggesting you should shift to 5th - the shift time may be a bigger loss - just saying.
So what is faster, forgetting a gear shift, just reaching peak hp at the stripe or reaching peak at say 1000' and running the last 320 above peak but still increasing rpm?
Agree. 99 times out of 100 it will be the third option.

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