Final effective gear ratio.

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chad linkhart

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So just curious as to what you guys think. I switch my tires to a smaller tire with the stock gears to currently a 245/45/20 until I can buy new back again but they will have the same diameter so with the new size my effective ratio is a 3.72. I have the 4.10 gears to put in but with the tire set up I have the effective would be a 4.29. I'll be putting a blower on so is this to much gear? I don't want the truck to be be building boost just cruising down the road.
 
I'm not sure I understand the question but if the new tires are the same diameter as the old, even if the rim diameter is different, your effective gear ratio won't change.
 
my new tires are 1.4 smaller diameter which increased effective stock 3.55 gear to 3.72. my concern is if i put my 4.10 gears in the effective gear would be 4.29 and not sure how that would react with a blower. I dont want to be building boost while cruising.
 
Most effective gear ratio???? Depends on what you are wanting. Lower gear ratios like 4.10 are 4.29 better for acceleration but give less MPG. Higher gear ratios like 3.55 and 3.73 are better for higher speeds and better gas mileage.



In the end it boils down to what you are looking for...stop light to stop light acceleration or better MPG on the highway....For just raw power, you need to know what RPM your engine will give you the most HP and how that equates to MPH.



If the vehicle is only going to be used for racing (which I doubt), then the lowest gear ratio will always give better acceleration, but your speed will be limited by your engines maxiimum RPM.



If you want a daily driver that compromises some acceleration for better MPG's, then I would not go much over 3.73...which sounds like where you are at now.



...Rich
 
Not looking for most effective. I'm wondering if that big of a gear will cause the blower to build boost while cruising at a steady speed.
 
ITs actually going to depend on the pulley set up and what the manufacturer says the RPM of the blower is to start boost.



you can calculate the engine RPM at the speed your cruising at and see.



Maybe get a 3:73 v6 rear and just bolt it in and you may be good.



There are programs on line to do the math unless you can do manually.



Good luck !



Todd Z
 
A direct drive (pulley drive) blower will continue to build boost, and increase with engine RPM. Typically this is controlled by the crank/blower pulley size ratios.



You cannot prevent the blower from creating boost except with a blow-off valve that limits the maximum boost pressure. I would suggest looking for a WOT (wide open throttle) boost control that only allows boost pressure when you have the throttle wide open.



I am more familiar with Turbocharges but I would assume that there are similar options for blowers.



Like Todd Z said, you need to understand the math to get the boost to kick in at specific engine RPMs when you want it and not kick in when you don't need it.



...Rich
 
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