Changing the pulley to get more horsepower
#1
05-04-2016, 12:57 AM
Changing the pulley to get more horsepower
I've been hearing that I could change the pulley on my 05 MC supercharger to add horsepower. Is that true? If so, what size pulley should I get? How much do they cost? What are the cons of installing one, if any?
#2
05-04-2016, 11:09 AM
While that is true to an extent, you can't just change pulley sizes and gain power. You have to do things to support the extra boost. Read the below for more info.
https://montecarloforum.com/forum/fwd-tech-guides-95-07-62/general-mod-plan-3800s-10942/#post101949 <-- link
https://montecarloforum.com/forum/fwd-tech-guides-95-07-62/general-mod-plan-3800s-10942/#post101949 <-- link
#3
05-04-2016, 04:42 PM
First off, more horsepower isn't as easy as just changing pullies. If it was, the car would've come with a smaller pulley from the factory.
The theory is that the factory supercharger is positive displacement in nature and is directly driven in proportion to the crankshaft via the belt. Given a fixed diameter crankshaft pulley, if you install a smaller supercharger pulley, more air will come out in a given amount of time. This is only part of the picture. As you speed the supercharger up, more pressure will build in the intake that the engine can't consume (ie higher boost), this makes it harder to put the additional air in. So as you speed the supercharger up, flow does go up but not linearly. Also, as a result, heat goes up as well, but goes up more and more quickly the more you speed the blower up.
The limiting factor here is octane. Given pump gas 91 that the engine is designed to run on, you can only have so much ignition timing and so much boost before you get knock. Luckily, the engine has sensors to pick up knock and will automatically reduce timing to stop it from happening (since it doesn't really have the ability to finely control boost). The first problem you run into is that if you start having too much timing pulled to accommodate the extra boost, the power starts to drop off rapidly and you end up shooting yourself in the foot in trying to make more power.
Beyond that, the computer takes time to react to a knock condition, and if the knock condition is very bad (ie lots of timing needs to be pulled to stop it), it may not be quick enough. When knock actually occurs, the resulting pressure wave is very hard on the piston. For emissions reasons, the factory wants to move the top piston ring land up as high as possible - the air/fuel trapped between the cylinder and piston doesn't burn well. The downside to this thin ring "land" is that it can be broken off with enough knock. It isn't typically instantly catastrophic to the engine, but having a chunk of piston bouncing around a chamber really tears stuff up. The fix is a rebuild or a replacement short block.
So what can you do to get more air out of thr supercharger without causing increased knock? The easy route is to increase the octane. Run unleaded race gas or convert to e85 (with proper injectors and tuning).
The harder way is to make the engine more efficient by doing mods. How many engine mods you need to do depends on how much knock you have stock and how much power you want to make. Keep in mind that over time, the intake gets plugged up with gunk from PCV and EGR, and that the pistons and chambers will develop a layer of carbon which effectively increases compression. So a good first step is to get your car scanned for KR to see if you have any knock now.
Once you have that bit of data, you need to figure out how deep you want to get into it. The factory pulley is 3.8". Going to a 3.5" or a 3.4" takes relatively few mods - simple bolt ons are usually sufficient (examples are rockers, headers, PLOG, downpipe, colder copper plugs, etc).
Going lower than that (3.25, 3.0, 2.8") depends which route you want to go. A cam, ported heads, and an intercooler are the big players here. You can get different levels of each that support a smaller pulley, or you can get them all to run the smallest possible pulley.
Beyond that, they sell down to a 2.55" from what I've seen, but anything under 2.8" requires you to machine down the snout of the blower for clearance. Keep in mind, at this stage, you're way out if the desirable efficiency levels of the blower. Outlet temps are very hot, and it may be better to consider switching to a turbo.
Now that you've decided what level you want to go to, you have to select the type of pulley. There are really two types - the 'press on' is just like the stock pulley, only smaller. It requires a special tool to safely remove and install it. These are cheap ($50 or 60), but are really only good if you don't intend to continue modding.
The other type of pulley is the modular type (about $125). You still need a special tool to remove the stock pulley and to press on a "hub", but future pulley changes only require you to remove the belt and undo a handful of screws.
Any way you go, it is important to try and keep knock / KR at or near 0. Certainly, many people have stuck on a 3.4" pulley on an otherwise stock engine and haven't chipped pistons, but your engine mods should work together. Your car will be more reliable and will make more power if you do supporting mods together with a pulley change.
The theory is that the factory supercharger is positive displacement in nature and is directly driven in proportion to the crankshaft via the belt. Given a fixed diameter crankshaft pulley, if you install a smaller supercharger pulley, more air will come out in a given amount of time. This is only part of the picture. As you speed the supercharger up, more pressure will build in the intake that the engine can't consume (ie higher boost), this makes it harder to put the additional air in. So as you speed the supercharger up, flow does go up but not linearly. Also, as a result, heat goes up as well, but goes up more and more quickly the more you speed the blower up.
The limiting factor here is octane. Given pump gas 91 that the engine is designed to run on, you can only have so much ignition timing and so much boost before you get knock. Luckily, the engine has sensors to pick up knock and will automatically reduce timing to stop it from happening (since it doesn't really have the ability to finely control boost). The first problem you run into is that if you start having too much timing pulled to accommodate the extra boost, the power starts to drop off rapidly and you end up shooting yourself in the foot in trying to make more power.
Beyond that, the computer takes time to react to a knock condition, and if the knock condition is very bad (ie lots of timing needs to be pulled to stop it), it may not be quick enough. When knock actually occurs, the resulting pressure wave is very hard on the piston. For emissions reasons, the factory wants to move the top piston ring land up as high as possible - the air/fuel trapped between the cylinder and piston doesn't burn well. The downside to this thin ring "land" is that it can be broken off with enough knock. It isn't typically instantly catastrophic to the engine, but having a chunk of piston bouncing around a chamber really tears stuff up. The fix is a rebuild or a replacement short block.
So what can you do to get more air out of thr supercharger without causing increased knock? The easy route is to increase the octane. Run unleaded race gas or convert to e85 (with proper injectors and tuning).
The harder way is to make the engine more efficient by doing mods. How many engine mods you need to do depends on how much knock you have stock and how much power you want to make. Keep in mind that over time, the intake gets plugged up with gunk from PCV and EGR, and that the pistons and chambers will develop a layer of carbon which effectively increases compression. So a good first step is to get your car scanned for KR to see if you have any knock now.
Once you have that bit of data, you need to figure out how deep you want to get into it. The factory pulley is 3.8". Going to a 3.5" or a 3.4" takes relatively few mods - simple bolt ons are usually sufficient (examples are rockers, headers, PLOG, downpipe, colder copper plugs, etc).
Going lower than that (3.25, 3.0, 2.8") depends which route you want to go. A cam, ported heads, and an intercooler are the big players here. You can get different levels of each that support a smaller pulley, or you can get them all to run the smallest possible pulley.
Beyond that, they sell down to a 2.55" from what I've seen, but anything under 2.8" requires you to machine down the snout of the blower for clearance. Keep in mind, at this stage, you're way out if the desirable efficiency levels of the blower. Outlet temps are very hot, and it may be better to consider switching to a turbo.
Now that you've decided what level you want to go to, you have to select the type of pulley. There are really two types - the 'press on' is just like the stock pulley, only smaller. It requires a special tool to safely remove and install it. These are cheap ($50 or 60), but are really only good if you don't intend to continue modding.
The other type of pulley is the modular type (about $125). You still need a special tool to remove the stock pulley and to press on a "hub", but future pulley changes only require you to remove the belt and undo a handful of screws.
Any way you go, it is important to try and keep knock / KR at or near 0. Certainly, many people have stuck on a 3.4" pulley on an otherwise stock engine and haven't chipped pistons, but your engine mods should work together. Your car will be more reliable and will make more power if you do supporting mods together with a pulley change.
#4
05-04-2016, 05:01 PM
First off, more horsepower isn't as easy as just changing pullies. If it was, the car would've come with a smaller pulley from the factory.
The theory is that the factory supercharger is positive displacement in nature and is directly driven in proportion to the crankshaft via the belt. Given a fixed diameter crankshaft pulley, if you install a smaller supercharger pulley, more air will come out in a given amount of time. This is only part of the picture. As you speed the supercharger up, more pressure will build in the intake that the engine can't consume (ie higher boost), this makes it harder to put the additional air in. So as you speed the supercharger up, flow does go up but not linearly. Also, as a result, heat goes up as well, but goes up more and more quickly the more you speed the blower up.
The limiting factor here is octane. Given pump gas 91 that the engine is designed to run on, you can only have so much ignition timing and so much boost before you get knock. Luckily, the engine has sensors to pick up knock and will automatically reduce timing to stop it from happening (since it doesn't really have the ability to finely control boost). The first problem you run into is that if you start having too much timing pulled to accommodate the extra boost, the power starts to drop off rapidly and you end up shooting yourself in the foot in trying to make more power.
Beyond that, the computer takes time to react to a knock condition, and if the knock condition is very bad (ie lots of timing needs to be pulled to stop it), it may not be quick enough. When knock actually occurs, the resulting pressure wave is very hard on the piston. For emissions reasons, the factory wants to move the top piston ring land up as high as possible - the air/fuel trapped between the cylinder and piston doesn't burn well. The downside to this thin ring "land" is that it can be broken off with enough knock. It isn't typically instantly catastrophic to the engine, but having a chunk of piston bouncing around a chamber really tears stuff up. The fix is a rebuild or a replacement short block.
So what can you do to get more air out of thr supercharger without causing increased knock? The easy route is to increase the octane. Run unleaded race gas or convert to e85 (with proper injectors and tuning).
The harder way is to make the engine more efficient by doing mods. How many engine mods you need to do depends on how much knock you have stock and how much power you want to make. Keep in mind that over time, the intake gets plugged up with gunk from PCV and EGR, and that the pistons and chambers will develop a layer of carbon which effectively increases compression. So a good first step is to get your car scanned for KR to see if you have any knock now.
Once you have that bit of data, you need to figure out how deep you want to get into it. The factory pulley is 3.8". Going to a 3.5" or a 3.4" takes relatively few mods - simple bolt ons are usually sufficient (examples are rockers, headers, PLOG, downpipe, colder copper plugs, etc).
Going lower than that (3.25, 3.0, 2.8") depends which route you want to go. A cam, ported heads, and an intercooler are the big players here. You can get different levels of each that support a smaller pulley, or you can get them all to run the smallest possible pulley.
Beyond that, they sell down to a 2.55" from what I've seen, but anything under 2.8" requires you to machine down the snout of the blower for clearance. Keep in mind, at this stage, you're way out if the desirable efficiency levels of the blower. Outlet temps are very hot, and it may be better to consider switching to a turbo.
Now that you've decided what level you want to go to, you have to select the type of pulley. There are really two types - the 'press on' is just like the stock pulley, only smaller. It requires a special tool to safely remove and install it. These are cheap ($50 or 60), but are really only good if you don't intend to continue modding.
The other type of pulley is the modular type (about $125). You still need a special tool to remove the stock pulley and to press on a "hub", but future pulley changes only require you to remove the belt and undo a handful of screws.
Any way you go, it is important to try and keep knock / KR at or near 0. Certainly, many people have stuck on a 3.4" pulley on an otherwise stock engine and haven't chipped pistons, but your engine mods should work together. Your car will be more reliable and will make more power if you do supporting mods together with a pulley change.
The theory is that the factory supercharger is positive displacement in nature and is directly driven in proportion to the crankshaft via the belt. Given a fixed diameter crankshaft pulley, if you install a smaller supercharger pulley, more air will come out in a given amount of time. This is only part of the picture. As you speed the supercharger up, more pressure will build in the intake that the engine can't consume (ie higher boost), this makes it harder to put the additional air in. So as you speed the supercharger up, flow does go up but not linearly. Also, as a result, heat goes up as well, but goes up more and more quickly the more you speed the blower up.
The limiting factor here is octane. Given pump gas 91 that the engine is designed to run on, you can only have so much ignition timing and so much boost before you get knock. Luckily, the engine has sensors to pick up knock and will automatically reduce timing to stop it from happening (since it doesn't really have the ability to finely control boost). The first problem you run into is that if you start having too much timing pulled to accommodate the extra boost, the power starts to drop off rapidly and you end up shooting yourself in the foot in trying to make more power.
Beyond that, the computer takes time to react to a knock condition, and if the knock condition is very bad (ie lots of timing needs to be pulled to stop it), it may not be quick enough. When knock actually occurs, the resulting pressure wave is very hard on the piston. For emissions reasons, the factory wants to move the top piston ring land up as high as possible - the air/fuel trapped between the cylinder and piston doesn't burn well. The downside to this thin ring "land" is that it can be broken off with enough knock. It isn't typically instantly catastrophic to the engine, but having a chunk of piston bouncing around a chamber really tears stuff up. The fix is a rebuild or a replacement short block.
So what can you do to get more air out of thr supercharger without causing increased knock? The easy route is to increase the octane. Run unleaded race gas or convert to e85 (with proper injectors and tuning).
The harder way is to make the engine more efficient by doing mods. How many engine mods you need to do depends on how much knock you have stock and how much power you want to make. Keep in mind that over time, the intake gets plugged up with gunk from PCV and EGR, and that the pistons and chambers will develop a layer of carbon which effectively increases compression. So a good first step is to get your car scanned for KR to see if you have any knock now.
Once you have that bit of data, you need to figure out how deep you want to get into it. The factory pulley is 3.8". Going to a 3.5" or a 3.4" takes relatively few mods - simple bolt ons are usually sufficient (examples are rockers, headers, PLOG, downpipe, colder copper plugs, etc).
Going lower than that (3.25, 3.0, 2.8") depends which route you want to go. A cam, ported heads, and an intercooler are the big players here. You can get different levels of each that support a smaller pulley, or you can get them all to run the smallest possible pulley.
Beyond that, they sell down to a 2.55" from what I've seen, but anything under 2.8" requires you to machine down the snout of the blower for clearance. Keep in mind, at this stage, you're way out if the desirable efficiency levels of the blower. Outlet temps are very hot, and it may be better to consider switching to a turbo.
Now that you've decided what level you want to go to, you have to select the type of pulley. There are really two types - the 'press on' is just like the stock pulley, only smaller. It requires a special tool to safely remove and install it. These are cheap ($50 or 60), but are really only good if you don't intend to continue modding.
The other type of pulley is the modular type (about $125). You still need a special tool to remove the stock pulley and to press on a "hub", but future pulley changes only require you to remove the belt and undo a handful of screws.
Any way you go, it is important to try and keep knock / KR at or near 0. Certainly, many people have stuck on a 3.4" pulley on an otherwise stock engine and haven't chipped pistons, but your engine mods should work together. Your car will be more reliable and will make more power if you do supporting mods together with a pulley change.
#5
05-04-2016, 05:02 PM
And side note, i've gone from a 3.8" to a 3.4" pulley and i've gained a whole 14 hp, and 39 torque at the wheels. This is with a cold air intake, plog, ceramic crossover, 3" downpipe, 1 step colder plugs and a dyno tune. Not easy to get power lol
#6
05-04-2016, 07:24 PM
Certainly you can pick up power on almost any car with a tune, the gains just aren't huge on a 3800.
As far as making your car faster, how much faster are you wanting to make it and what is your budget? We can help guide you to the best bang for your buck with that info.
#7
05-06-2016, 09:35 AM
@ bumpin96monte, very interesting, I learned a lot.How many times did I hear "Just change the pulley for a smaller one, your car will be much faster !".
I always answer, "Yeah I'm sure it's that simple...".
Now I know what to answer them
