More boost with less RPM question

RockStang

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This is a thought I've been noodlin around with. I'm currently pushing 16psi at 8K rpm on the Whipple 2.9 and I don't have the nuggets to go down another pulley on a stock bottom end and run the rpm that high. I'm curious what others think about backing the RPM down to say 7500, going up a pulley that might hit est. 16.5psi at 7500 and make slightly more power across the rpm band and push the car a little faster down the track. Would that really make much difference?

Thanks for any input,

Joe





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Jackson1320

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This is a thought I've been noodlin around with. I'm currently pushing 16psi at 8K rpm on the Whipple 2.9 and I don't have the nuggets to go down another pulley on a stock bottom end and run the rpm that high. I'm curious what others think about backing the RPM down to say 7500, going up a pulley that might hit est. 16.5psi at 7500 and make slightly more power across the rpm band and push the car a little faster down the track. Would that really make much difference?

Thanks for any input,

Joe
More average horsepower across the RPM band is going to be better than a little higher max horsepower number. Why are you running it all the way to 8000 RPM. Also your car will last a lot longer shift in at 7500-7600
 
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RockStang

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Thanks. That’s basically what I was thinking. I don’t have any data to support it but it makes sense to me. Especially for a street car as long as traction isn’t an issue. I’m not convinced 8000rpm is really an issue but I will turn it down if I go higher boost. Not time or reason for that either, just to make myself feel better.
 

ice445

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I personally wouldn't run 8k on these engines. They can do it, sure. But the timing chain set won't like it over the long haul.
 

engineermike

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What’s more of a risk, high rpm or high cylinder pressure?
 

yote41

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I thought about doing this on my procharger as well. Dropping a pulley to get more power across the board and keeping it at 7500
 

engineermike

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Sure. That’s why virtually all modern engines have cylinder pressure limits as well as rev limits. Both of them break parts. Hell I’ve broken way more parts due to cylinder pressure than rpm.
 

WildHorse

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Yes Sir, but if I had to pick and live with one. Higher cylinder pressure @ a lower rpm would be my choice.
 

80FoxCoupe

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This is a thought I've been noodlin around with. I'm currently pushing 16psi at 8K rpm on the Whipple 2.9 and I don't have the nuggets to go down another pulley on a stock bottom end and run the rpm that high. I'm curious what others think about backing the RPM down to say 7500, going up a pulley that might hit est. 16.5psi at 7500 and make slightly more power across the rpm band and push the car a little faster down the track. Would that really make much difference?

Thanks for any input,

Joe
Whats the car run now?
 

BlackandBlue

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Higher cylinder pressure at lower rpm = higher average torque.
Lower cylinder pressure at lower rpm is less likely to knock.

I wouldn’t turn the gen 2 up to 8k. Gen 3 has upgraded valve train and I still think 8k is somewhat risky.

You run 93 and boostane?
 
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RockStang

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Whats the car run now?
we have a track day coming soon. I haven’t run it since I went 9.55 on MS109. So much on the car has changed. Im on slightly more boost, full fuel system with E85, higher stall converter, 2-step for what that’s worth. I’m really expecting a low 9 pass. I’m going to pose this question to my tuner and see what they think. They do this all the time and should have some feedback
 

markmurfie

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If it blows, that stock motor doesnt owe you anything. Years of abuse and operating at far greater values than its originally designed specs. Take it out, sell it while you can, and put in parts more designed for what you are wanting to do.

IMO a slightly lower RPM limit to run more boost has no effect on the safety of doing it. More flow from less pressure is the only thing that makes operating an engine safer. What you are wanting to do does not fit that. If you put the smaller pulley on, leave the RPM limit as is, the risk to the engine will be the same. One could argue lowering the RPM will actually put it at greater risk if the post shift RPM falls more toward peak torque closer to 5K rpms. All the while getting less flow. optimal shift points are done around HP peak(maximum flow), which is very high on the Whipple's due to the relatively flat torque curves.
 
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RockStang

RockStang

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I’m really just trying to work out how to keep the motor together so I can be one those few car that can grab an 8 sec 1/4 on stock motor. I ultimately don’t care it it blows up.
If it blows, that stock motor doesnt owe you anything.
Oh I agree with you. I accept that the motor could go at any time. This is really about pushing the parts you have to the limit and seeing what you can get done. I went 10.01 on 93 octane, 9.55 on 72lb injectors and a slightly slipping 6-rib setup. I'm just trying to see how deep I can get in the 9s while keeping the motor together.

I appreciate everyone's feedback. It definitely added a few things I wasn't thinking about.
 

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