More boost versus higher RPM?

[TooSoonJunior]

Looking at some blower speed calcs for my whipple, and dawned on me...

Wouldn't it be safer to run 15psi to 7,000rpms versus 12psi to 8,000rpms?

The math....

A 3.25" upper pulley + Stock Lower = 14,603 blower rpms at 7,000rpms

A 3.625 upper pulley + Stock Lower = 14,495 blower rpms at 7,750rpms

I would think the higher boost setup would actually be faster as it will make more torque in the midrange, and wouldn't it be less strain on the motor in general to not be wound out so far?

Thoughts??

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[RockStang]

Looking at some blower speed calcs for my whipple, and dawned on me...

Wouldn't it be safer to run 15psi to 7,000rpms versus 12psi to 8,000rpms?

The math....

A 3.25" upper pulley + Stock Lower = 14,603 blower rpms at 7,000rpms

A 3.625 upper pulley + Stock Lower = 14,495 blower rpms at 7,750rpms

I would think the higher boost setup would actually be faster as it will make more torque in the midrange, and wouldn't it be less strain on the motor in general to not be wound out so far?

Thoughts??

Good question. Will be interesting to hear some feedback. I'm actually planning on having PBD turn down my RPMs now that I'm pushing the motor harder. Going to try the 3.25 pulley on MS109 and I'm nervous about running to 8k rpm. I would think the increased torque even at lower rpms would still increase stress though.

 

[kcc0521]

It might be safer but you have to make sure your rev limit is set to prevent it going too high and over boosting the car.

 

[jhatley7]

I would stay under 7500 and 15psi on stock block. Just my opinion from reading and breaking.

To answer you question, it would probably be the same stress or worse on the lower rpm higher bost. So when u punch it down low, you will lug the motor. So the pistons and rods are seeing more pressure for a longer period of time, less rpm. Whereas low boost higher rpm, will see less boost and less cycle time up high.

 

[Stuntman]

7500 is already alot for a blower. Not sure I'd go 8k on a stock motor.

 

[dubster99]

7500 is already alot for a blower. Not sure I'd go 8k on a stock motor.

I agree. Rpm is hard enough, let alone with boost.

 

[turbosc297]

Same theory as lugging a motor. I'd prefer to make the same power with more rpm as its less stress and less time spent under load per revolution. This assuming it's within the rpm limits of the rotating assembly.
I also never ever plan on a motor lasting more than 50k miles, or even 10-20k in extreme conditions. Desired mileage out of a motor will influence your decision the most I'd guess

 

[Stuntman]

Same theory as lugging a motor. I'd prefer to make the same power with more rpm as its less stress and less time spent under load per revolution. This assuming it's within the rpm limits of the rotating assembly.

 

[TooSoonJunior]

Not sure I agree about less stress with 8k rpms, the speed that piston is flying around, stopping and starting, at 8k rpms I would think is much more severe than peak torque at 4500-5000 rpms. But I am no engineer. I don't intend on running higher boost and doing roll races from 2500 rpms, THAT is lugging this motor.

 

[Stuntman]

Force increases with the square of speed.

 

[Slamdcoop0428]

High cylinder pressure with low rpm is hell on a motor

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