Sports Cars someone?

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Dave Saxton
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Re: Sports Cars someone?

Post by Dave Saxton »

Hypers are fine with a safe tune. The nice thing about hypers is that while being stronger than regular cast they have a slower rate of expansion than forged. This allows tighter tolerances and smoother running engine with less blow by. They also weigh in about the same as cast, so unless the shop has the equipment for precise balancing it makes it easier on them. However, be careful with the tune as any too lean condition or detonation can destroy them quickly.

Here's the math for injector size:

(HP x BSFC)/ number of cylinders = injector size in lb per hour ( x % duty cycle desired)

For naturally asperated engines using a modern combustion chamber, the Brake Specific Fuel Consumption is about 0.50. For forced induction it could go up to 0.55 or 0.60 depending on how much boost. You usually want the injectors meet the max fuel delivery needs at less than 100% duty cycle. 85% duty cycle is a good figure so divide by .85. Cheating by greatly increasing fuel pressure when using inadequate injector size can cause a problem of insufficient fuel volume. As the pressure goes up the volume goes down. Most fuel management systems increase fuel pressure with boost but this needs to be within reason. For example, if the normal rail pressure is 40 psi then with 150 hp added by boost the fuel pressure should only increase to about 44 psi.

The fuel pump capacity is also HP related:

HP x bsfc x .6094 x 1.3 = liters per hour required.
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Re: Sports Cars someone?

Post by steffen19k »

Unfortunately it all comes back to the CFM rate of the engine, and while I can make some educated guesses and follow up on lots of theory, in the end, the only way I feel I'm getting this engine done right is with a trip to a flow bench, and talking with people who live and breathe ECM tuning.

But its still a fun project.
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Karl Heidenreich
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Re: Sports Cars someone?

Post by Karl Heidenreich »

Got my Porsche all in pieces now... :kaput: Need to do some engine work that could take some months. :? What a disgrace.
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