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underdrive and overdrive?

 
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Old 03-13-2012, 04:00 PM
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underdrive and overdrive?

hi what is the difference between underdrive and overdrive crank pulleys? which are the best ones to get?

i have been researching and there seems to be alot of mixed reviews on this topic...any opinions on which one is best for hp gains?

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Old 03-13-2012, 06:25 PM
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Re: underdrive and overdrive?

Underdrive will spin the accessories slower, causing less parasitic drag on the engine, but might not spin them fast enough for them to work properly. Examples are low voltage from alternator, less power steering assist, and warm A/C.

Overdrive will spin the accessories faster, casing more parasitic drag, and possible over spin the accessories, causing the bearing to fail, or too high of a alternator voltage.

Neither will give you more "Horsepower". But the accessories act like extra flywheel weight, removing that weight will allow the engine to spin up faster and be more efficient. But it will be harder for the engine to stay spun up, due to internal engine resistance, and load from the transmission.
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Old 03-13-2012, 06:56 PM
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Re: underdrive and overdrive?

ah rite cheers so its not true then that underdrive pulleys transfer the power from alternator and p/s to engine to increase power because of less drag?

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Old 03-13-2012, 08:40 PM
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Re: underdrive and overdrive?

It is not giving the engine any extra horsepower, it just allows that little bit that was used to turn the PS, AC, and ALT to be sent to the transmission, which is not that much. The valvetrain has more resistance/drag than any of the accessories.
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Old 03-13-2012, 09:33 PM
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Re: underdrive and overdrive?

pretty much what dwend said. to clear it up more, by removing the weight that usually absorbs power, you are experiencing more power. you're not making more, just seeig more of the power you already have. I have the unorthodox racing crank pulley. I didn't get any of the other because I just didn't want them. I don't have any complains about it
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Old 03-14-2012, 01:21 AM
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Re: underdrive and overdrive?

Best bet is to just get a lightened pulley like the Unorthodox one.
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Old 03-14-2012, 11:13 AM
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Re: underdrive and overdrive?

ah rite cheers but i have heard bad things about unorthodox crank pulley that it causes stress on engine because it sends all the engine vibration back into the crank causing premature bearing failure...is this true?

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Old 03-14-2012, 11:40 AM
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Re: underdrive and overdrive?

no it's not. that was actually a knockoff pulley that someone bought off eBay and thought was an UR pulley. they've been making pulleys for something like 30 years, they're legit
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Old 03-14-2012, 11:54 AM
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Re: underdrive and overdrive?

ah rite ok so unorthodox crank pulley it is then :)
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Old 03-14-2012, 12:15 PM
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Re: underdrive and overdrive?

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Originally Posted by prelude2 View Post
ah rite cheers but i have heard bad things about unorthodox crank pulley that it causes stress on engine because it sends all the engine vibration back into the crank causing premature bearing failure...is this true?

cheers
They're legit and a good company, but that doesn't matter in this respect because, in concept, that's true. The solid pulley doesn't act as a vibration dampener as the OEM pulley does because it doesn't have the rubber insert. To me, this would mean premature failure, but I've never messed with it.
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Old 03-14-2012, 03:55 PM
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Re: underdrive and overdrive?

aye thats what i heard mate im just makin sure. just weighing out pros and cons cos i dont want to spend 120 on crank pulley to then ruin the bearings and have to spend fixing it. do you think its worth the risk???
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Old 03-14-2012, 04:34 PM
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Re: underdrive and overdrive?

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Originally Posted by prelude2 View Post
aye thats what i heard mate im just makin sure. just weighing out pros and cons cos i dont want to spend 120 on crank pulley to then ruin the bearings and have to spend fixing it. do you think its worth the risk???
Well I don't exactly know how much risk it poses. I've never messed with it, I've just heard it happens and it makes sense to me. It could be extremely rare, or very common. Someone with more experience in that respect needs to give you advice.
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Old 03-14-2012, 04:37 PM
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Re: underdrive and overdrive?

I;ve been wondering if its really worth changing the crank pulley, can you actually feel the difference?
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Old 03-14-2012, 07:27 PM
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Re: underdrive and overdrive?

yeah mate im going to have to find out becauce if its a common thing to cause engine wear im not goin to bother

cheers
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Old 03-15-2012, 08:57 AM
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Re: underdrive and overdrive?

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Originally Posted by SoFlaKidd View Post
I;ve been wondering if its really worth changing the crank pulley, can you actually feel the difference?
I have an underdrive pulley on my 5G, only because the OEM crank pulley dampener bit failed and Honda UK charge over 300 for a new crank pulley. IMO you can feel a slight improvement when you are not in VTEC, the engine picks up that tiny bit faster. In VTEC I notice no difference. I have no vibrations or any indication that I have an underdrive pulley installed.

Would I say its worth it on a near to stock engine? No, especially if you have a perfectly good OEM crank pulley.
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Old 03-15-2012, 10:22 AM
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Re: underdrive and overdrive?

Quote:
Originally Posted by merlin View Post
I have an underdrive pulley on my 5G, only because the OEM crank pulley dampener bit failed and Honda UK charge over 300 for a new crank pulley. IMO you can feel a slight improvement when you are not in VTEC, the engine picks up that tiny bit faster. In VTEC I notice no difference. I have no vibrations or any indication that I have an underdrive pulley installed.

Would I say its worth it on a near to stock engine? No, especially if you have a perfectly good OEM crank pulley.


I agree 1000000% on absolutely everything he said.

Same EXACT thing happened on my STi; rubber dampener failed on the OEM piece, so I replaced it with a lighter 1 piece aluminum one. And the same exact argument has been goin on the STi forums as well; i.e. a 1 piece unit "can" lead to premature bearing failure, but no one has had concrete evidence to determine 100% that it was infact due to the lack of dampening from the pulley.
Also the difference in revving up/down..... was marginal. Despite the HUGE weight difference. OEM was prolly around 12lb's, Perrin is MAYBE 2lb's.

If your OEM crank pulley is fine, just leave it.
If its busted, you decide for yourself if you wanna "upgrade" to a lighter 1 piece.
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Old 03-15-2012, 10:27 AM
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Re: underdrive and overdrive?

^^^^^ that's exactly what I did. they key slot on my OEM
pulley somehow broke, so I just got the UR one
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Old 03-15-2012, 11:47 AM
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Re: underdrive and overdrive?

ah ok so il keep it in mind if my oem one busts. cheers for advice people :)
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Old 03-16-2012, 04:43 AM
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Re: underdrive and overdrive?

has anyone had or have OBX pulleys??? only i have found some online and they look cool. are they knock offs or are they good quality?

cheers
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Old 03-16-2012, 05:31 PM
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Re: underdrive and overdrive?

i just want to say that i thought it was DRAG that the accessories made, not WEIGHT. So if your downsizing the pulley, putting less drag on the system makes it spin up faster but WILL NOT make it harder to stay at speed. The actual weight reduction of the pulley isn't too big as far as I know, so the engine's rotational energy isn't helped by the accessories in any way. The reason a lighter flywheel makes it spin down faster is because you remove mass and take away from its rotational energy... Somebody correct me if i'm wrong, but do tell me why.
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