More boost with 20% overdrive?

[illtal]

its pretty much 20% of whaterver boost ur making at the moment....give or take... so 10 psi would net you 12.... and so on

it's not, it's 20% lower than what would NORMALLY be on the top,
for instance 4.0" pulley with a 20% lower is the same as a stock lower with a 3.2 pulley on it.

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[illtal]

if you ever mess around with motorcycles it's the same concept. Upsizing the rear, is the same as lowering the front. for instance a 15F:45R gives a final drive ratio of 3.0; similarly, a combination of a 14F:42R gives a 3.0 final drive, but if you did 14F:45R you get a 3.214 final drive. Just think of the Rear as the Lower, and the front as the upper.

 

[Jackson1320]

I can tell you 100% from experience that this is wrong. I started with a 8-9 psi setup on a 4.00 upper and a stock lower. I added the 20% od balancer/pulley and ended up with 11psi. It just gives you 20% more size on your balancer. A 4.00 upper and a 20% lower is not the same as a 3.20 upper and a stock lower. Here’s proof

 

[illtal]

I can tell you 100% from experience that this is wrong. I started with a 8-9 psi setup on a 4.00 upper and a stock lower. I added the 20% od balancer/pulley and ended up with 11-12psi. It just gives you 20% more size on your balancer. It does not change the ratio by 20%. So a balancer goes from 6.5 to 7.88

it's not wrong, when it comes to a PD. Also because the restriction is lessened with a bigger TB which most of PD guys have when we do these kinds of things, it's not always apples to apples.

in the case of whipple what I said above is true... per whipples own chart:
in the case of the edelbrock with a 15 % lower, it's not exact but they give you a range instead of an exact number. could be lower or higher due to being able to run a different TB or whatever.
EB 3.75 - 15% = 3.1875 which is pretty close to the 3.25

whipple 15 PSI with the 20 lower, 4"-20% = 3.2"
whipple 15.5 PSI with the stock lower 3.250" again not exact but pretty close.

 

[Proshop]

So an overdrive pulley effects a centri different then a PD is what you guys are saying?

 

[illtal]

So an overdrive pulley effects a centri different then a PD is what you guys are saying?

it's likely true because the boost is linear on a centri I suspect. But I don't know. I would assume that you would spin it faster, quicker getting to a certain number earlier in the rpm range, how much earlier is up for debate. I know there are lot of other factors in it with the centri but in a perfect world my guess it that it would still make a target number quicker than with a stock lower.

notice on both charts how you get 4-5 psi more boost with the same pulley but the bigger lower.

 

[Jackson1320]

It’s not true. No matter what supercharger you have more blower rpm is more blower rpm. Yes a PD is linear but that just means that you get to your boost all at once. The rpm of the blower determines how much boost you make.
if you have a 4.00 upper and a 20% lower you will not have the same rpm as a 3.20 upper and a stock lower. It’s basic math. So if you have less rpm then you have less boost. I can’t believe I even have to point this out. Come on just admit when you’re wrong. You will get more respect

 

[Jackson1320]

So an overdrive pulley effects a centri different then a PD is what you guys are saying?

No it does not. On a centrifugal or a PD a overdrive balancer just gives your blower more RPM. the blower RPM is what determines the maximum boost you can make. If you turn a centrifugal slower you make less boost. if you turn a PD blower slower you make less boost. Same thing.

 

[Jackson1320]

1900rpm is 1900rpm on a PD or on a centrifugal. Now how much boost 1900rpm cost you will depend on a few different things. But no matter what supercharger you have 1900rpm is 1900rpm. Nothing can change it

 

[Proshop]

No it does not. On a centrifugal or a PD a overdrive balancer just gives your blower more RPM. the blower RPM is what determines the maximum boost you can make. If you turn a centrifugal slower you make less boost. if you turn a PD blower slower you make less boost. Same thing.

Got it more rpm is equaling more boost. So I need to see what the Roush 2650 can be spun up to and make sure I’m not over spinning it with my current 72mm pulley if I added on an overdrive.

 

[Jackson1320]

Got it more rpm is equaling more boost. So I need to see what the Roush 2650 can be spun up to and make sure I’m not over spinning it with my current 72mm pulley if I added on an overdrive.

Correct

 

[Jackson1320]

Got it more rpm is equaling more boost. So I need to see what the Roush 2650 can be spun up to and make sure I’m not over spinning it with my current 72mm pulley if I added on an overdrive.

A 20% od balancer = 7.88”

 

[illtal]

It’s not true. No matter what supercharger you have more blower rpm is more blower rpm. Yes a PD is linear but that just means that you get to your boost all at once. The rpm of the blower determines how much boost you make.
if you have a 4.00 upper and a 20% lower you will not have the same rpm as a 3.20 upper and a stock lower. It’s basic math. So if you have less rpm then you have less boost. I can’t believe I even have to point this out. Come on just admit when you’re wrong. You will get more respect

I don't have a problem with being wrong, but H ow do you explain more boost then on both the Whipple and the 2650 boost charts with the same upper but overdrive lower that is more than 1.5 and 2 lbs of boost just because a PD is instant in terms of boost, doesn't take away the fact that you are overdriving all the accessories on the belt drive IF you leave them all the same size.

youre telling me both Whipple and Edelbrock has it wrong?

 

[illtal]

Even on a PD if you spin more engine RPM The boost will keep rising, just look at any dyno sheet with boost logged.

 

[Proshop]

A 20% od balancer = 7.88”

Strike that it’s actually a 68mm.

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