Underdrive pulley

[Dave M]

Information on this is scattered through the thread on my project and in the weight savings section, but thought it would be easier to find and reference in one location.

The theory is to replace the crank pulley with an aluminum piece to lighten the rotating mass and allow less parasitic loss of HP to the wheels. The pulley is also a smaller diameter to allow less drag, and again, free up more HP to the wheels. There is plenty of discussion around the internet on pros/cons, including this good link from Brian:

An interesting article on some of the potential hazards of saving weight in the 'wrong' areas...
http://www.spdusa.com/pulley_kit.htm

I have an Unorthodox Racing pulley. It appears they are still available. Per the following link, it appears the same pulley was used on a few Isuzus. You can use the part number from this link to shop around. FYI - I found the same exact price at another vendor via a quick search.

http://www.wholehyper.com/old_site/unortho-isuzu.html

Because of the smaller diameter, you will need new accessory belts. I found mine at NAPA.

Alternator: #040250 - Micro-V belt, 9/16" x 25 3/4" (14mm x 655mm)
Power Steering: #060355 - V-ribbed belt, 27/32" x 36" (21mm x 915mm)

NOTE - I have removed my AC compressor, so the second belt only goes to the PS pump. You will need a longer belt to use with the AC.

[F1 LOTUS]

Does the underdrive pulley slow the water pump also?

[Candles]

No. The WP runs off the cambelt.

[Nige]

Found said pulley here: http://wholehyper.com/shtml/category/FullPath/2;7;70;728;1025;1059/id/1059.html listed for an Elan, haven't done anything about it (yet) though as the website doesn't appear to accept shipping outside the USA.

[Monty]

It`s a shame we didn`t have a group buy on this as my cambelt is being done tomo`s and would of been an ideal time to put it on

[Dico]

You can fit it next year whilst your engines out when fitting the samco hoses

Group buy sounds good. We need different belts as well though dont we?

[Dave M]

Found said pulley here: http://wholehyper.com/shtml/category/FullPath/2;7;70;728;1025;1059/id/1059.html listed for an Elan, haven't done anything about it (yet) though as the website doesn't appear to accept shipping outside the USA.

If this is the best price we can find and a few of you across the pond would like them, I'd be more than happy to accept the shipment and then forward them on.

[Nige]

Dave, as ever you're a star and that sounds like a plan, I'd be in for a group buy to add the pulley to the slowly growing pile of bits that I will fit to the car one day. OK who else is in?

[Dico]

Not sure on this one. Think i need some convincing

[Nige]

I e mailed the supplier of the underdrive pulley and they have confirmed that they will ship to the UK. I also asked about a discount for a group buy (nothing ventured) they currently have the pulley listed at $177 (can't be exact as their website is down at the moment). They are willing to offer a discount for a group buy. I don't know how much, but the bigger the buy the better the discount would seem reasonable. If you are interested then post here. No committment as I'm only gauging interest, also remember that VAT at 17.5% and import duty at 4% would also be payable on these if imported, so they are not cheap items for what they are. However they are cheaper now than than were see here http://www.isuzuperformance.com/bills/engpul.html linked from the old site for details.

[Monty]

VAT at 17.5% and import duty at 4% would also be payable on these if imported, so they are not cheap items for what they are.

Thats what i`m worried about, i`ve been stung enough this year by those people
I`d be also worried about it being a smaller pulley, must effect the alternator and powersteering

Anyway to find out which other car it fits and see if there`s a uk supplyer

ps got to buy Stevo`s stiffy to

[Nige]

Me too! Part of my logic is that I have a lightweight flywheel to go on one end of the crank and an equivalent, in % terms, reduction on the crank nose might keep things in trim. This is a highly unscientific approach known as guessing but I just dont have the facts to make a more reasoned assessment. The only overiding factor is that weight is bad and removing it is good, very much a Lotus ethos. As and when I do get around to installing all the bits I'm slowly collecting (car is in daily use at the moment) I will be aiming to reduce weight wherever. I've even started reasonably serious running again to sort out the single heaviest component .

As far as what other car it fits, as expected it's for the Isuzu engine, I haven't been able to locate a UK supplier.

[Matt RI]

Hey Dave!

I am intrigued by this idea... I want to change my CAM belt anyway- so I had been thinking of this for a while.

Has anyone contacted the place listed? The website is not coming up when I click on it. I had done a search a few weeks back as I was finding the Unorthodox Pulley listed by some performance shops. When I called to order- low and behold- no more in stock, and UR is not making them anymore. I even checked UR directly and they do not have any to sell in their "discontinued" bin, and are not anticipating making them again.

So, failing in the open market I tried an Isuzu forum. No spares lying around there to purchase. My asking for one did elicit questions on whether or not the UR pulley would cause undue harm and stress on the engine via a change in harmonics, etc. Frankly- that was not something that I was considering- I was of the "less weight, good" mantra... Anyone have any insight as to whether or not this is a mod that, while freeing up a couple additional HP, might create problems?

If you can find a pulley for sale, I have an interest...

[lwalling]

What kind of gains can be expected from UDP's on an Elan ? Thats what I want to know :).

I should be running my moderately modded little car on a chassis dyno this week or next as well.

[Doug]

What kind of gains can be expected from UDP's on an Elan ? Thats what I want to know .

definite = less sprung weight of wallet in pocket

hopeful = a few HP

[Darren]

I may be interested but I still need convincing re the diameter question + the need to change belts, which in the UK are around £30 for the alternator & PAS belt.

Ideally I'd like a lighter version of the stock item.

Another one for your list Brian ?

Darren.

[Dave M]

What kind of gains can be expected from UDP's on an Elan ? Thats what I want to know .

definite = less sprung weight of wallet in pocket

hopeful = a few HP

Doug's right...I'd be surprised if there were more than 2-3 HP freed up by this. As far as damage to the engine due to a change in balance? FWIW, the aftermarket pulleys should be balanced from the factory. Whether this "balance" messes with the stock rotating assembly is debatable. My entire assembly was balanced along with the flywheel and UDP when the engine was apart, so I have no fears. Considering one of my rods was "a lot heavier" (per the engine guy) than the others, my $.02 is the stock assembly may not be in perfect balance anyway. I've not read that our stock pulley in any way compensates for balance issues, so I don't see much of an issue from this standpoint. Whether or not it affects the alternator and PS pump remains to be seen, but I've heard good reports from those that have used them. I'll hopefully verify this shortly.

And I got mine from an Isuzu guy "used" (but never used) for way cheap years ago.

[Monty]

+ the need to change belts, which in the UK are around £30 for the alternator & PAS belt.
Darren.

Darren,

Alternator belt is only about £5
PAS belt is about £10
from u`r local moror factors

[F1 LOTUS]

I may be interested but I still need convincing re the diameter question + the need to change belts, which in the UK are around £30 for the alternator & PAS belt.

Ideally I'd like a lighter version of the stock item.

Another one for your list Brian ?

Darren.

HEY!!! ....