Pulley swap numbers

Cobra Command

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Hey everyone. I'm wondering if anyone has any power increase numbers. I have a Whipple 2.3 (no idea what gen) running a 3.0 upper, wondering what the increase in hp/tq swapping to a 2.75.

Cheers.
 

olympic

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It should add about 1.5psi and 30-40hp. I can just about guarantee though that a 2.75" upper will belt slip like crazy.
 

MG0h3

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I run a 2.9 RR with zero slip on my 2.9.

Lethal has some new pullies that offer extra grip.


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Cobra Command

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It should add about 1.5psi and 30-40hp. I can just about guarantee though that a 2.75" upper will belt slip like crazy.


Ok thank you muchly. I will keep it as is.

Pretty impressive build you have going there, where in Canada are you? I'm on Vancouver Island. How are those stage 4 cams working out? I'd love to hear them.

Thanks again for the reply
 

olympic

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Ok thank you muchly. I will keep it as is.

Pretty impressive build you have going there, where in Canada are you? I'm on Vancouver Island. How are those stage 4 cams working out? I'd love to hear them.

Thanks again for the reply

The stage 4's sound awesome but they have too much duration for my setup which causes all sorts of driveability issues. I'm currently swapping them out for a set of Crower Stage 2's. Here's a clip of the Stage 4's


I'll be starting a build thread on the car very soon.
 

Cobra Command

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The stage 4's sound awesome but they have too much duration for my setup which causes all sorts of driveability issues. I'm currently swapping them out for a set of Crower Stage 2's. Here's a clip of the Stage 4's


I'll be starting a build thread on the car very soon.

IMG_3128.JPG
 

JCDriller

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The stage 4's sound awesome but they have too much duration for my setup which causes all sorts of driveability issues. I'm currently swapping them out for a set of Crower Stage 2's. Here's a clip of the Stage 4's


I'll be starting a build thread on the car very soon.


Man that sounds awesome!

What kind of issues does it cause? Can you give a few examples?
 

olympic

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There's 2 main problems big cams cause due to their excessive valve overlap:

1) low manifold vacuum. This causes the blower bypass valve to either stay closed or act erratically at low RPM, causing the car to buck, jerk and surge during low speed driving. I have to slip my clutch like crazy when taking off from a stop because if I let the RPM's drop too far the car will stumble and buck, sometimes even stall or backfire. Basically any driving below 2000 RPM is pain in the ass. A low vacuum bypass actuator DOES NOT solve the issue. A twin screw blower needs a strong intake vacuum signal to function properly.

2) intake reversion. During valve overlap hot exhaust gasses get sucked back into the intake manifold causing high IAT2's and heat soak. I can't drive my car in city traffic for more than about 20-30 minutes on a hot day. IAT2's will hit 170F even though the Killer Chiller has the IC fluid at 40F and the engine will heat soak so bad that it doesn't want to run.

I love the sound of the cams and will miss it but I built this car to drive and enjoy and the Stage 4 cams just made me hate driving it. If you're dead set on cams get some custom grinds from someone like Todd Warren who can spec the cams for your particular build. A local tuning shop is also a must because tuning driveability issues over the internet is very difficult.
 

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