Under drive pulley
- Thread starter utahviper
- Start date
Snakester
Enthusiast
I'll add to the question. For those who have added underdrive pulleys, how well does the charging system/battery handle it.
I had underdrive pulleys on my Mustang and the battery died in two years, and the lights would dim at idle, and surge when you hit the gas (as if you were flashing your high beams).
It would be nice to know if the same problems exist for underdrive pulleys and Vipers, and how much RWHP gain is actually realized.
-Dean.
I had underdrive pulleys on my Mustang and the battery died in two years, and the lights would dim at idle, and surge when you hit the gas (as if you were flashing your high beams).
It would be nice to know if the same problems exist for underdrive pulleys and Vipers, and how much RWHP gain is actually realized.
-Dean.
Jerry Scott[CO]
Viper Owner
I have had Dave's 25% pulley on the car for 2 years and have had no charging problems. Don't know what power it makes, since I have never dynoed it.
Jerry Scott
Jerry Scott
Summit Racing sells an Auto Specialties 25% under drive pulley (Part Number 504500) for $50.69. It is advertised for the Dodge Truck, but I called Auto Specialties and they said it fits perfectly. You will have to buy a shorter belt which retails for less than $20 bucks. The Kelly Springfield part number for the belt is 785K6. The NAPA part number is NBH25060785. It is a 6 rib belt (the pulley is a 7 rib just like the stock pulley) vice the 7 rib belt that comes stock on the Viper (no one seems to make a shorter 7 rib belt) but I was assured by Auto Specialties that would not cause any problems.
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Greg D on 01-31-2002 at 07:45 AM</font>
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Greg D on 01-31-2002 at 07:45 AM</font>
BlackACR
Enthusiast
GregD, are you going to try this set up??? If, so let us know how well it works.
I will be ordering the pulley from Summit very soon. (I have a few more items on my Summit "wish list" I need to order also) I don't think I'll be doing a before/after dyno pull, but I can let you know how the charging, cooling and power steering systems respond. (I don't think there will be a noticeable SOTP feeling to report though)
Tom F&L GoR
Enthusiast
My '94 came with the 6 rib/underdrive combination Greg D describes. Purchased in '98, recently changed the battery not due to any problems, but because I never looked to know for sure how old it was. Only at idle, lights, fogs, AC, and brakes on would the voltage head towards 12, otherwise normal. The only downside is that the smooth pulleys will grow rust where the new belt doesn't cover them.
True.... Auto Specialties does not manufacture a 50% under drive pulley, but they do offer a 42% under drive pulley (P/N 994000 retailing at $83.99) for the same Dodge truck application as the 25% under drive pulley mentioned above.
The Auto Specialties pulleys are black nitrided for corrosion resistance. (They are steel)
Considering the PMOI (Polar Moment of Inertia) of a crank pulley is relatively small, (it is only 4-5 inches larger in diameter than the crank shaft centerline) I wonder what 1-pound is worth at that small of a PMOI.
I do respectfully disagree with
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The 25% Truck Pulley weighs as much or MORE than the Stock one!
<HR></BLOCKQUOTE>and <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
no reciprication Mass Saved
<HR></BLOCKQUOTE>
The truck pulley does weigh less than the stocker, albeit less than a pound but, due to it's reduced PMOI (it is 25% smaller in diameter than the stocker) the engine "sees" less rotating mass. (Via the dumbbell effect) This probably isn't much but it is a reduction in reciprocating mass as seen by the engine.
I must say the pulleys Dave has for sale look to be a work of art.
The Auto Specialties pulleys are black nitrided for corrosion resistance. (They are steel)
Considering the PMOI (Polar Moment of Inertia) of a crank pulley is relatively small, (it is only 4-5 inches larger in diameter than the crank shaft centerline) I wonder what 1-pound is worth at that small of a PMOI.
I do respectfully disagree with
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The 25% Truck Pulley weighs as much or MORE than the Stock one!
<HR></BLOCKQUOTE>and <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
no reciprication Mass Saved
<HR></BLOCKQUOTE>
The truck pulley does weigh less than the stocker, albeit less than a pound but, due to it's reduced PMOI (it is 25% smaller in diameter than the stocker) the engine "sees" less rotating mass. (Via the dumbbell effect) This probably isn't much but it is a reduction in reciprocating mass as seen by the engine.
I must say the pulleys Dave has for sale look to be a work of art.
Miles B
Enthusiast
I think the point is also to underdrive the alternator etc too.. smaller wheel, same revs, hopefully less work done on the alternator.. well that's the theory, but there are a hell of a lot of factors at play..
So that's where the saving is as well as in the reduction of rotational inertia spinning the wheel up (which I agree, would not be a hell of a lot at all). Bike racers often pull the generator out and charge their battery up real good before short lap sessions. Again, not sure how much of a difference it would make on a V10.. the dyno could tell us these things and many more!
I'd certainly hate to see the volume on my system drop for no good reason
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Miles B on 02-01-2002 at 03:55 PM</font>
So that's where the saving is as well as in the reduction of rotational inertia spinning the wheel up (which I agree, would not be a hell of a lot at all). Bike racers often pull the generator out and charge their battery up real good before short lap sessions. Again, not sure how much of a difference it would make on a V10.. the dyno could tell us these things and many more!
I'd certainly hate to see the volume on my system drop for no good reason
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Miles B on 02-01-2002 at 03:55 PM</font>
PhilC
Enthusiast
Hey 2001 Z-06, do you still have one of those 50% pulleys left. I'll buy it if you do. Please E-mail me at your earliest convenience. Thanks
Phil
Phil
ruckdr
Enthusiast
I just received and installed the 25% smaller/lighter aluminum drive pulley, offered from Dave.
Here are the specs:
Stock Pulley (with Air Cond.) 2 lbs. 7 oz.;
7 in. Dia;
77.6 in. belt (7 rib)
25% under Aluminum Pulley: 1 lb. 0 oz.;
5 1/2 in Dia.;
74.7 in. belt (6 rib)
(Requires purchase of shorter belt - any auto parts store; price $20-$35)
Runs good and charges at 14 + amps with AC and Radio, a slight dim when lights added at idle, but recovers instantly.
Pulley cost is $157.00 shipping included.
A very nice piece.
Here are the specs:
Stock Pulley (with Air Cond.) 2 lbs. 7 oz.;
7 in. Dia;
77.6 in. belt (7 rib)
25% under Aluminum Pulley: 1 lb. 0 oz.;
5 1/2 in Dia.;
74.7 in. belt (6 rib)
(Requires purchase of shorter belt - any auto parts store; price $20-$35)
Runs good and charges at 14 + amps with AC and Radio, a slight dim when lights added at idle, but recovers instantly.
Pulley cost is $157.00 shipping included.
A very nice piece.
