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UD pully discussion
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Posted by: kissajew86

I made a seperate thread for the UD pully Disccussion

Posted by: 1969Vette

"UD pullies have been proven in the past to add 7 hp"

Is this absolutely the truth? Can anyone else verify this? I was recently researching alot of performance mods and was ready to spent over a grand on underdrive pulleys, BBK cold air, 70mm TB, 73mm mass air, superchip, and posi-trac....

http://www.rpmoutlet.com/newv6m.htm

that site claims 14.2+ RWHP and 8.1+ RWTQ from underdrive pullies.... and others say they do work good, so Im still thinking of buying those...

but...

they also claim a ton of power from the intake, TB, TB spacer, Mass air, etc. and while I researched more there are alot of people saying that it doesnt give you much at all because the upper intake or plenum, whatever, is what mainly restricts the flow...

so has anyone noticed or can anyone prove a noticeable increase in performance from either an intake, TB, TB spacer, or mass air? because I dont want to go and spent over $600 on an intake system that claims a ton of power but does nothing...

$430 BBK intake w/ 70mm Throttle Body and TB spacer.. claims 28RWHP
$190 C&L 73mm Mass air... claims an easy 12+ RWHP

=$620 for 40+RWHP claimed, which is like 50HP flywheel from an intake, which does not sound real at all.... I know that is 'up to' that ammount of power, but still even if it was 25HP, that is about a 13% increase over stock HP. That seems like a big increase when others are saying the upper intake is too restrctive.

I only have 1 mod on my car right now, since I've been trying to pay it off ASAP.... and that is a GT takeoff cat-back exhaust w/ H-pipe.... This I can confirm that it makes my car feel super smooth in the way it runs and revs, I also have noticed I'd say about 5-10HP gain, but that could be more, Im no measuring machine. It also sounds sort-of like a stock GT, just alittle quiter, and I like it because it doesn't open up the exhaust too much to make it sound ricey.... I had a MAC dual exhaust on my 95 v6 and it would sound great at startup, but then would making some bad raspy farting-type sounds every once in a while after it warmed up.

Sorry about the big post...

Summary....
GT takeoff exhaust = good, 5-10+HP gain, runs smoother, good sound
want more info on intakes, TB, TB spacers, mass airs, UD Pulleys, 1.8RRs, etc.

what did each individual mod do? ("felt like 5-10hp" for example) that helps alot more than, 'I have blah blah blah done and have over 400HP'....

Posted by: 1969Vette

The more I search, Underdrive Pulleys are looking like more and more BS...

http://www.teamscr.com/pulleys.html

that site claims that they did a dyno run without a serpentine belt and only got 3HP! and that underdrive pulleys would only give you about 0.6HP! and that underdrive pulleys can destroy your crankshaft.

http://www.dcr.net/~hensley/page7.html

that site, which sells lightweight aluminum underdrive pulleys, explains that you may only save about 0.85HP!

http://www.marchperf.com/underdrive2.html

here is another seller of underdrive pulleys which claims performance gains up to 12.5HP+ (which must be for like an 800HP car)... because they then go on to say, "Your HP gain with an electric pump may not be as much as you think" and, "..our pulleys only made 1 HP less then a electric water pump set-up.
so if an electric water pump doesnt give you as much as you think, and UD pulleys give you less, then Im guessing they are saying UD pulleys don't give you much at all.

http://www.uucmotorwerks.com/udp/udp...escription.htm

in this site, which sells the "Ultimate Under Drive Pulley Set", read the right-hand side in the grey box... there are a ton of possible drawbacks for only 1, 2, or 3HP....

pros... large claimed HP/TQ gains
claimed longer accessory life (alt, water pump, etc.)

cons... actual very low HP/TQ gains?
possible crankshaft issues if it is not balanced/weighted correctly
possible cooling issues with an underdriven water pump
possible electric/charging issues with underdriven alternator
possible power steering pump issues

and on other message boards there are people claiming no change, and people that claim they do notice a differance....

so right now I am considering aggainst paying $200 for less than 1hp and possible problems with all accessories.

Unless I saw a dyno of a stock 3.8L mustang (i have 3.9) and stock w/ underdrive pullies and saw a 5HP+ differance (both properly warmed up, etc), I am not taking the risk. I'll keep putting it toward my payments.

Posted by: ExBamaGal

Wish I could help on your questions about underdrive pulleys but I don't have them nor do I know anyone personally that does. Well, hubby has some for his truck but they're not installed. I'm a little curious about this myself.

Posted by: 1969Vette

ok, more research...

I now found out that what I qouted from the sites claiming under 1HP was just the parasitic loss of the accessories, the main power gain are from reduced rotational mass, as in this qoute....

"each pound of mass taken off the crankshaft is worth approximately 2.7hp at the flywheel"

so if you are going from a 5lb pulley to a 1lb pulley (which is usually the case) that is a 4lb savings X 2.7HP/lb = 10.8HP + the parasitic loss which we'll use the example of 3HP... 3HP * .25 (25% underdrive pulley) = .75HP

10.8 + .75 = 11.55HP which * .8 (automatic trans friction losses) = 9.24HP

so I, having an automatic should expect around 9HP gain, people with manual should expect around 10.

This all now makes pretty good sense to me and now I have to find a lightweight pulley with a harmonic balancer and through my research, 25% shouldn't give you any problems or very minimal... just make sure they are installed perfectly (even and torqued correctly) or then you could have crankshaft problems.

Other than that, the ones at rpmoutlet may be too small and have negitive effects on your accesories by overstressing them and not be able to cool your engine very well... I believe these are more for constant high RPM situations such as racing or crazy aggresive drivers. This is what the one site was talking about with taking a big chance for a possible 1, 2, or 3HP extra gain.

I'd say stick with 25% (to avoid stress on accesories and inadiquete cooling/charging), preferably aluminum (for lighter weight and best power gains), with a harmonic balancer/dampener (to avoid crankshaft failure).... also I've heard stay away from 'piggyback' system which somehow utilize your stock setup and just add a smaller aluminum pulley in front, or reuse the stock balancer, or whatever, i forget, but stay away from them.

I'll continue researching this subject and try to find the best set and share it with you all.

I also found dynos!!!!!!!!!! although they are for Saturns...

They show about 10HP and 6TQ peak gain, but possibly 12HP and 15TQ at other RPMs if you study the dyno charts.

dyno info can be found here....

http://www.geocities.com/conemower/pulleyinfo.htm

(UD Pulleys)

bow down to, and get you some lightweight underdrive pulleys

Posted by: 1969Vette

also, you could just get a lightweight crank pulley and gets most of the power gain (7-9HP), lose all of your parasitic loss (a whopping .75HP for 25%) and not have any worries about cooling, charging, power steering, a/c, etc.

I personally as of right now would still go with 25%, but just go lightweight if you're worried about those issues. I will try to find out they sell them, or else you may have to get one custom made, like stock size, but aluminum instead of steel.

Posted by: 1969Vette

Damn this ish is confussing, sorry, the dynos are for Saturns and they show 2-4HPandTQ increase (the top graph after link is baseline runs and the bottom is actual gains), so we should still see at least 5HPandTQ....

Posted by: 1969Vette

I found this site which is very helpful...

http://www.miracerros.com/mustang/pulley_tech.htm

It shows all pulley sizes, related stock accessory RPM, 25% UD pulley RPM, 25% w/ 10% UD alt. pulleys and more.

with this info, Im now back to wanting the 42% UD crank pulley for alittle more power than 25%, as long as I can find a 4.5" water pump pulley (25% underdriven) and 2" alternator pulley (20% underdriven).

That way the water pump and alternator would be moving alittle bit better than just putting on a 25% crankshaft pulley, but the a/c and powersteering would be robbing less power. That is what I'm looking for because I'm not too worried about very slow tight turns or super cold a/c in Jersey. It does get hot, but not hot enough to waste a few HP on extra a/c. I'm mainly worried about cooling the engine and charging so I dont get a dead battery or fading.

here's an example of some kits and what I'm looking for personally.

*these are all as the link shows, the speed the accesories would run at given the engine is running at 1000RPM. 42% of 7" stock crank = 4.06" (we'll assume its really a 4" crank pulley, so #s for 42% may accually be a bit more)

stock 25%crank 25%w/10%alt 25%w/10%altwat 42%RPMoutlet mine
a/c - 1400 1050 1050 1050 812 812
wat - 1167 875 875 972 677 889
alt - 2800 2100 2333 2333 1624 2000
p/s - 1077 808 808 808 625 625

RPM Outlet also offers an underdriven water pump pulley, but I don't know the size.

my way (42% UD crank, 25% UD wat, 20% UD alt) may be the ultimate streetable UD Pulley system...

*crank is giving you most possible power before going to a race UD pulley.
*water pump gives you 2% less worry than a 25% crank alone
*alternator is exactly on with this qoute from the linked site, "Generally, on street cars the alternator can be safely run at about 2 times the speed of the crankshaft."
*a/c is robbing the least before going to a race UD pulley
*p/s is robbing the least before going to a race pulley

or you could use that site to figure out how to mix and match your own pulleys for what you are looking for... he also has alot of other tech and how-to's if you click on the bottom pink MENU button. It's a good read, check it out.

Posted by: 1969Vette

ok, so after probably about 20hrs of total research the past few day, reading through forums, dealer sites, tech sites, etc. I have come to this conclusion.

42% UD Pulleys - It seems as though it is only people who have never had UD pulleys, have 25% UD Pulleys, or dealers of 25% UD Pulleys that are saying negative things about 42% (which is only actually ~35% from one post I read from someone who measured stock and RPMoutlet).

People who actually have the 42% Pulleys have said things like, 'had for 2 months, no problems', 'had for 2 weeks, no problems yet', etc. They like the performance gains, have no problems with charging or cooling, etc.

A dealer of 25% pulleys states that voltage should be between 13v-15v and if it dips below it takes from the battery which could lead to a dead battery over time due to stress. But, in a thread there was someone with 42% who took the actual voltage numbers and at idle was well over 14v, engine running, everything off.... a/c was the biggest drain. stock stereo, defrost, etc. did not take much power at all, you could run practically all electrical equipment and no a/c and still be over 13v with 42%. Also, his cooling was like normal in 90* weather. So just dont run a/c at idle and you should have absolutely 0 problems.

The dealer tested 25% and 50% and recomended to not go over 25%.... they never tested RPM outlet's 42% (which was supposedly measures at only 35% actual). 50% (or 52%) is the race version from like Summit and such, and not intended for street use anyway. So they basically tested a street version and race version and said, don't use the race version on the street.... DUH!!!!

Go with 42% if you are looking for max performance with minor worry about charging and cooling, but both should be fine, just remember, no a/c at idle. Not recommended if you have over a 1000w+ system or are in extreme weather (you may need that water pump)

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25% UD Pulleys - This set takes away any worries, so if you don't want to risk getting too close to extremes with charging, cooling, crank worries, etc. stick with these. This set is more for anybody, still a great power adder 8HP/8TQ across all RPM. The same comments have come from owners of these pulleys... no problems, easy install (like all other sizes), good power, etc.

Go with 25% if you want good power gains across all RPM, but don't want to worry about any problems that could happen. If you still have worries you could also get an overdrive (yes smaller, but overdrive as in it spins faster) alt. or water pump pulley. Not recommended if you have a show quality system 2500w+ or so. (or at least also get the alt pulley)

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overall, my reasearch has proven to me that underdrive pulleys are an extremely great 'bang for buck' performance mod. I recommend them highly and will be getting 42% soon, it's just up to you what size to get for your needs and worries.

42% - should show gains of 10-12RWHP/8-12RWTQ
25% - should show gains of 6-8RWHP/5-8RWTQ

this gain is across the RPM range and at peak,.... bigger gains can be found throughout the RPM range, for example....

peak could go from 156 RWHP to 165 RWHP @~5000RPM - 5.8% peak gain
but also from 107 to 118 RWHP @~2800 - 10.3% gain

this is just an example, this what also happens with TQ from certain CAIs.

Posted by: Aussie XAXB

Underdrive pulleys came into being for racers that typically run their engines at high RPM constantly. With underdrive pulleys they can run their alternator and water pump at "regular" speeds so as not to overspin these components.

It was also noticed that an ancillary benefit of this would be the slight reduction of parasitic losses that are in direct relation to the amount of energy it took from the engine to turn the alternator and water pump. In racing where every engine makes about the same amount of power every 5 HP after that is a bonus.

In my opinon this trait was then marketed to the street crowd. It is a good way to sell aluminum pulleys.

As far as a weight savings goes it will be minimal unless you have grossly large steel pulley's to begin with. The thinner steel pulleys have to be replaced with a thicker aluminum pulley to offer the same strength. Even though aluminum in lighter than steel there will be more of it.

PEAK parasitic power recovered from UD pulleys on a street engine is typically about 2-7 HP depending on how hot of an engine you have and how fast you rev it to. You will not feel a 5 HP difference in your 3,400 pound car. People that claim they feel a power gain from an UD pulley change only are experiencing the "placebo affect."

If you are going to spend $600, rather than spending it on 5, 10, or 18 HP gains spend the money on a cam kit or some really good head work or even a new set of aftermarket iron heads. Now you will get an honest 30 - 60 HP gain, provided the rest of your components don't choke the engine.

As an old timer here I see people today usually looking to stack up 5 and 12 HP gains at a great cost instead of making the hard hitting changes of the cam and heads. If you have a 4 cylinder engine in a car that you want to be a street bruiser you don't get a high tech air cleaner, rear gears, and intake manifold for it to gain 15 HP and another .01 off your 1/4 mile time, you pull that sucker and drop a V8 into it. Likewise, rather than spending money for a pittance of power gain in 4 different places change the cam or heads and make a serious jump in power.

Steve

Posted by: 1969Vette

i tried to reply last night but it said my account was suspended for some reason. my main points were...

*you're right
*many of us talking about just boltons are younger and/or broke, can't wait to save, or don't to take appart the entire engine.
*im personally just trying to stay ahead of my friend's black '04 coupe. my car is faster by alittle, because he beats on his. I just need those little 5-12hp gains and I may not feel them, but I will notice it when im side by side with him.
*i use my car for cruising around, because it looks damn good, and for mustang meets. I know its not meant for speed, so i dont want to put any crazy amount of money into it or take apart the engine to make power.
*i would have a gt or older cobra if I wanted speed that bad, but with insurance and gas, I would barely be able to afford it right now.

Posted by: Aussie XAXB

You're willing to do a lot of research and math and you have that going for you. Probably the best thing in your situation then would be to go with a steeper rear gear. You won't be making more power but you will accelerate faster. And don't get into street racing. We've had quite a few here bite it already because of that.

Steve

Posted by: 1969Vette

not really street racing, just like back and forth when your side by side... or just like from say 40-60 in a 55mph zone or something. or just 0-60 from a 55mph stoplight. you're right that the gears would be best for this, but im worried about overrevving on the highway. I usually do 65-75 on the highway, but I don't want to be like 1000RPM higher than stock at this speed.

I already saw my friend's z28 only be able to do 80-90 TOPS with 3.73s... and at 65mph he was over 3000RPM in his last gear haha and my other v6 flew past him. did he just program it wrong? because that seems like a huge drop for a z28. he is kind-of bumb so i wouldnt put it past him to screw things up.