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Underdrive Pulley

This is a discussion on Underdrive Pulley within the GTO forums, part of the Vehicle Specific category; ...folks who have the smaller pulley ( more power less parasitic drag) we all know the Alt/A/C etc turn "slower"...one ...

  1. #1
    Grand Imperial Wizard Sarge's Avatar
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    Underdrive Pulley

    ...folks who have the smaller pulley ( more power less parasitic drag) we all know the Alt/A/C etc turn "slower"...one side effect that hit me in the face recently was the fuel pump voltage.
    Doing some testing/playing around I checked the Walbro 255 switched 12V to the pump...at idle it was 11.8....at wot it was 13.4....Wired up a Kenne Bell BaP at now have 17.2 volts at WOT. This makes the pump much more efficient and works much less providing fuel to the rails versus having to struggle at lower voltages. I am of the mind this will increase pump life expectancy much longer versus making a pump work at lower voltages.
    Just food for thought....

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    Grand Imperial Wizard Sarge's Avatar
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    Yup...I found a very good article with back up documentation.....what I thought...makes sense....pump works harder with low voltage.....
    Quote Originally Posted by Kenne Bell
    Never overlook voltage variations. 1 Volt is 10% fuel capacity. The Boost-A-Pump is also a voltage regulator and therefore compensates for voltage fluctuations in your electrical system. And, contrary to the opinions of some, the BAP will actually INCREASE the life of the pumps because they do not have to work as hard with the increased voltage and amperage supplied by the BAP (see our post at http://www.corral.net/forums/showthr...hreadid=418287 - LOOK AT THE CHARTS). Note how much LESS duty cycle is imposed on the pump when the BAP is used? LESS DUTY CYCLE = LONGER PUMP LIFE.

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    Veteran 0rion's Avatar
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    this is one area I really need to read and learn more about...... I just have a very basic understanding of how voltage effects fuel flow.
    I would assume a pump is rated at 12 volts so mine is 255lph @12 v. What I don't know is how you convert fuel flow at wot to see how much fuel you're flowing? I would assume it would be a really pretty algebra problem. It would have to factor in fuel pressure at wot and injector pulse width along with voltage at wot. I could see on people that are running big set ups this would be an important issue but for me I've never seen it as something I should look into simply because I'm just a heads/cam car. I did do the racetronix hotwire kit so that the pump draws straight from the alternator which should offer a little help with voltage drop but I also run an underdrive pulley and see where you're coming from with the BAP.
    Last edited by 0rion; 09-06-2008 at 05:18 PM.

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    Grand Imperial Wizard Sarge's Avatar
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    No all pumps are rated to 18V. All of them. At under say 15V at WOT they are struggling like a bitch.

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    Senior Member Hurley711's Avatar
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    soooo......is an aftermarket UD pulley good or bad for the cars performance?

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    Quote Originally Posted by Hurley711 View Post
    soooo......is an aftermarket UD pulley good or bad for the cars performance?
    good.....anytime you decrease parasitic loss it's a good thing. Sarge's point is that if you do that it's a good idea to add that bap so your fuel pump doesn't struggle.

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    Knight of Chaos xzaero0's Avatar
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    I've got a camaros performer magizine march issue that addresses this with the LT1. They claim that the stock wiring harness drops at WOT and they lost around 25% drop on pump volume. They run the feed directly from the altenator where the voltage is the highest. They also replaced the stock pump and wire with a racetronix pump and wire, the wire is also a 10 gauge wire not a 7 like the factory. Racetronix uses a walbro fuel pump rated at 255lb/hr @ 43.5psi @ 13.5V.

    I had the pump and wiring harness upgraded on my 00 TA when I had the 9" installed. I figured that it would be a good idea since I was planning on running N20 later on, and hell the rear end was already out. I couldnt really tell a difference with the fuel system since I had alot done while it was in the shop, but its a good upgrade to go with. I have a underdrive pulley also, I need to get the overdrive pulley for the altenator too.

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    Member The Silver Goat's Avatar
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    Does this beg the question about the water pump as well?
    Don't convert to an electric pump if you go with an under drive pulley?
    Stay belt driven.

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    Knight of Chaos xzaero0's Avatar
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    Quote Originally Posted by The Silver Goat View Post
    Does this beg the question about the water pump as well?
    Don't convert to an electric pump if you go with an under drive pulley?
    Stay belt driven.
    Ive got a Mizierre EWP with my underdrive pulley and havent had any problems with cooling or with any of my other electricals. Shouldnt the overdrive pulley for the alternator remedy any problem with a lower charge?

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    Grand Imperial Wizard Sarge's Avatar
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    Quote Originally Posted by xzaero0 View Post
    Ive got a Mizierre EWP with my underdrive pulley and havent had any problems with cooling or with any of my other electricals. Shouldnt the overdrive pulley for the alternator remedy any problem with a lower charge?
    Yes...from a voltage perspective. But the f/p voltage even on a stock setup should be boosted even with mild mods.

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    Grand Imperial Wizard Sarge's Avatar
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    Quote Originally Posted by The Silver Goat View Post
    Does this beg the question about the water pump as well?
    Don't convert to an electric pump if you go with an under drive pulley?
    Stay belt driven.
    I think the coolant flow is above adequate to begin with frankly....when we slow it down it remains above the adequate mark.

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    Member The Silver Goat's Avatar
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    Qucik Silver Metalic
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    Quote Originally Posted by Sarge View Post
    I think the coolant flow is above adequate to begin with frankly....when we slow it down it remains above the adequate mark.
    That's good to know... The shop that did my dyno tune made a couple of cams... I'm considering installing one, new heads, an under pulley and I'll add a fual pump to the list...

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    Grand Imperial Wizard Sarge's Avatar
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    Head and cam car I would just utilize the KB BaP on the stock pump.

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    Member The Silver Goat's Avatar
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    Qucik Silver Metalic
    2004 GTO - M6

    KB BaP stands for?

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    Grand Imperial Wizard Sarge's Avatar
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    Kenne Bell Boost a Pump
    http://www.kennebell.net/accessories...ories-home.htm
    Forget all the vacuum bullshit and just wire the vacuum sensor wires together so it is on all the time.....set it at 50%...your pump will last longer and you'll get more fuel to the rails.

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    Quick Silver Metalic
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    Quote Originally Posted by xzaero0 View Post
    I've got a camaros performer magizine march issue that addresses this with the LT1. They claim that the stock wiring harness drops at WOT and they lost around 25% drop on pump volume. They run the feed directly from the altenator where the voltage is the highest. They also replaced the stock pump and wire with a racetronix pump and wire, the wire is also a 10 gauge wire not a 7 like the factory. Racetronix uses a walbro fuel pump rated at 255lb/hr @ 43.5psi @ 13.5V.

    I had the pump and wiring harness upgraded on my 00 TA when I had the 9" installed. I figured that it would be a good idea since I was planning on running N20 later on, and hell the rear end was already out. I couldnt really tell a difference with the fuel system since I had alot done while it was in the shop, but its a good upgrade to go with. I have a underdrive pulley also, I need to get the overdrive pulley for the altenator too.
    A 10 guage wire is quite a bit smaller then a 7 guage, though 7 guage isn't a standard size.

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