I've been trying to get my head around this for quite some time now but something logically just doesn't make sense with some people's performance claims with pulleys. What I am talking about is the "no significant power versus quicker revs" theory surrounding the AP pulley.

I know the gains from a pulley come in two forms. First, the pulley may be lighter, thus reducing the parasitic loss on the engine and allowing more power to reach the wheels. That one is simple. Secondly, the pulley may be underdriven which brings the rotational mass closer to the crankshaft (or whatever shaft it's on) and, if I'm not mistaken, the smaller circumference disc has to be rotated a shorter distance than the stock (in the same amount of time) and through the magic of physics (I am over stepping my knowledge boundary at this point) once again more power is reaching the wheels that was previously lost on the stock pulley.

This brings me to my point. How can some people say "a pulley doesn't get any noticeable power to the wheels" but then come back with "but your engine will rev noticeably faster." What in the hell is the difference? This claim is so contradicting in my opinion. If your engine is able to rev faster then it is undeniably producing more horsepower (compared to the SAE stock trim numbers). After all what moves drivetrain components faster? More torque right? This argument is driving me nuts as I research pullies, and sometimes I get the idea that a couple of ill-informed people are just parroting misinterpretted information.

Again, I want to reiterate that I know no additional power is being produced by the engine, but rather being freed up compared to stock form. I would be incredibly grateful if someone trained in the ways of science could help me solve this conundrum.

 

I think when people say "it revs faster" they are meaning that when you rev the engine in neutral it is more responsive .
I agree with what you are saying though . If there is no power gain but it " revs faster " while in motion that is a complete contradition .

Throttle response is another much misunderstood measurement . When I think of throttle response - it is the time lag between pressing down on the accelerator & feeling the surge of power from the engine .
I lot of people are saying the pullies help with this . When I first got mine I thought it did . Now I'm not so sure - would like to hop in a stock 8 for a comparison.
In theory pullies do help for all these three things but by how much seems to depend on what mind altering substances you are on at the time .

 

Z, the argument that you are citing isn't really the one you think it is. You are correct in that getting an engine to rev quicker involves getting it to make more torque. The thing to note is that people say pulleys don't get any "noticeable" power to the wheels. It is conceivable that an engine CAN rev quicker and still have no noticeable power gains to the wheels. That's because most people cannot notice a 4-5 h.p. gain at the rear wheels. In our cars, a 5 h.p. gain equates roughly .1 second gain in the 1/4 mile. The argument is really one of whether or not a pulley is a good value, especially when compared to other mods that typically cost the same amount of money. Most people who spend hundreds of dollars on mods for their cars usually want to see more dramatic power gains but with the RX-8 that is not the case. Because Mazda did a pretty decent job of tuning the car, and the fact that people with imported vehicles still seem willing to spend far more for mods than the domestic owners will, getting more power from the RX-8 will cost hundreds of dollars per attempt/part.

Here's a shorter explanation; 5 h.p. will make an engine rev quicker because it doesn't take much h.p. to move the parts around as it is running but that same 5 h.p. will be almost imperceptible while you are driving the car.

 

Z I know exactly what you are saying, a while ago when I was researching the likes I got into that circular confusion as well.

The engine will rev more freely however the greater the load/stress, the less significantly fast it will allow the enging to rev. There's an inverse correlation between engine load and how fast the engine will rev. The lighter the load the more gain of responsiveness you will feel with the pulleys. This is my best undestanding of pulleys/flywheel/mods that let the engine rev more freely.

Take that for what its worth, could be wrong, just my best concept of the idea. Of course like charles said the amount free'd may be so minimal it borderlines unoticable at all.

 

The underdrive part changes the gearing ratio of the crankshaft pulley to the accessories.

So for example (this is just an example) for one turn of the crankshaft pulley the alternator pulley will be turned 5 times with the normal pulley. With a smaller diameter crankshaft pulley one turn of the pulley will only turn the alternator 4 times. Lets say it takes 5 Newtons of force to turn the alternator pulley once. Then before pulley replacement the alternator is taking 25 newtons of the engine's total output. After pulley replacement the alternator will only take 20 newtons of force per one turn of the crankshaft pulley. That is 5 Newtons of power that is freed up to drive the wheels or whatever else.

Anyone that says a pulley replace will not incease rwhp is an idiot.

That being said, there are two ways to decrease accesory load. One is to make the crankshaft pulley with a smaller diameter, such as with the AP pulley. The second way is to make the accesory pullies such as alternator, water pump and A/C physically bigger, such as with the greddy pulley kit which increases the size of the water pump pulley and lightens it.

 

Having used underdrive pullies on rotaries in the past, I can tell you from personal experience that I could tell no difference in any way at all. I didn't notice a faster revving engine and I didn't feel more power. There may have been more, but not enough for me to feel. I still have an underdrive pulley but it's in a box in storage where it's been for 5 years. I'm too lazy to take the 30 minutes to install it on the current car. That tells you something right there.

 

yeah that your lazy ....... i kid

 

Well thanks for your responses. I know from reading these forums often that the ones that replied are the most knowledgeable of the bunch here so I trust your information. I've ordered the AP pulley and will install it sometime between classes and work this week. If anything its another few hp and something else that will look cool under the hood. Thanks again for the clarifications and have a nice holiday weekend.

 

I was debating going FI or NA, so held off on the AP pulley. I decided to go totally NA for now, so I've ordered the pulley and will test it with the g-timer.

I think the confusion could possible come from the pulley debate being mixed with the flywheel debate.

A lighter and underdriven pulley should result in HP gains. I think the point that some people were making was that the HP gains were not significant enough to really mean much. If the pulley gives you only 5 HP or even 10 HP than some people don't care. Such people would only be impressed by FI numbers like 50 HP to 100 HP increase.

Also, a good pulley would cause a difference in "feel" of the car (somewhat like the flywheel), in terms of responsiveness. For some people, they could care less if their 0-60 to 1/4 mile numbers did not improve by a 1/2 to 1 second. Other people, may like or be impressed by the greater feel of responsiveness.

 

Many arguments/debates such as these are far less about the physics and engineeering than they are human interpretations and perceptions. We know, mathematically, that certain mods will leave more power to motivate the car but it is just a matter of whether or not that power is perceptible or worth the pursuit and money. Then again, some of us just like to swap parts all day long.

 

Amen

 

agreed.. for a 150 bucks it wasnt a bad thing, with a collection of mods the pullies may inturn actually do just that little bit more, or it may not.

 

They'll definitely help. That's why when I was pondering modifying my own car a few years ago I decided that every bit of power I could wring out of the engine was my main objective and the cost was a secondary consideration. I then prioritized my list with the mods that I KNEW would deliver more power at the top of the list, based on scientific principles, and the more questionable mods at the bottom. Nitrous, having not been sorted out yet, was in a different category altogether.

 

30 minutes to install? Thats decent time for install.. All you need I imagine is patience & pulley puller? (had to think about that wording for a sec..)

 

It's 30 minutes for someone who has had their factory intake removed a few times and is fairly quick at it. The pulley isn't pressed in place, but there are a few challenging angles that need to be dealt with. When I did my pulleys, all three, it took about an hour with hand tools and ingenuity. The crank pulley, alone, would take about 30 minutes.

 

The only reason that I bought the AP pulley was to underdrive the water pump to prevent cavatation of the pump and help keep the car cool on hot track days. Any improvments beyond that are gravy, but I doubt I'll be able to notice a difference. Placebo effect is worth at least 30bhp though .

 

Try this?

Better, try this.

 

Check out the So Cal Dyno thread. 2 or more people had pullies.

They also had mid pip and flywheel. One was 15 hp less and one had 2 hp more than mine.

I don't see any effect from the pullies. However if they can keep the car cooler at 8k and above on track days, then its worth it.

 

That is the one benefit that I do agree with. On the RX-7, the water pump would cavitate at 6500 rpm. By changing to the underdrive pulley it would now cavitate much higher.

I have a first generation RX-7. It is very easy to get to the main pulley which is why I can do it so fast. 30 minutes might be a little longer than it would actually take on that car.

 

Are you serious? I've probably read every useful thread on this forum. If you read my initial post that's why I needed clarification.

 

I bought the AP underdrive pullies... for a little more then 100 bucks, it doenst matter to me if i can FEEL anything or not. I agree that it will "free up" some power, but not enough to notice in daily life.

I will say though that my ACT Prolite flywheel + AP Pullies + SuperCAT + Exhaust + MS Suspension = more fun then a Stock RX8

 

Absolutely, I am completely serious. I mean no disrespect, but when I read your post, my first thought was that you hadn't done enough thinking yourself. The concepts are pretty simple. It shouldn't be difficult to get your brain wrapped around them, once you actually start thinking. Reading more threads is a good place to start.

 

Reading threads that contained different points-of-view was what confused him and asking for clarification was exactly what we tell people to do. One thing I wonder is why it is so easy for people to forget that there was a point in their own lives where they didn't know everything and had to ask for help, themselves. His question was not near as ill-informed nor ill-contrived as most of the posts I see on this forum.

 

It's always good to ask questions. I for one don't always advocate searching rather than asking as you still get different answers and some views may change over time. The only thing you can do is get all the information that you can, make your own decision based on that info and then see if it's something you may want to try for yourself. There is no better way to learn than to do. Different people have different perceptions and some people like certain mods that others don't. My personal favorite mod is an aluminum flywheel but others don't necessarily agree and opinions differ on the topic.

 

The flywheel example is a good one because that issue had loads of controversy, early on, as to the driveability and benefit of light wheels but look how that particular mod is much more widely accepted and encouraged these days.