The Lotus Cars Community banner

1 - 12 of 12 Posts

·
Saffron Yellow is Lighter
Joined
·
1,291 Posts
Discussion Starter #1
I just purchased 2) MWR under-drive pulleys for the alternator and water pump. While I had everything apart and was looking around I noticed the Belt Idler Pulley on the rear of the engine. Looks like this is where the power steering pump was for other cars. See image below.



Has anyone looked at doing anything to completely remove this useless pulley? I know it would probably require reworking the belt tensioner design completely. Looking at the post below, when they changed out the alternator and water pump pulleys with light weight aluminum they saw a nice little power gain. (I realize there was some resizing/under/over-driving involved too) but I would assume 1 less pulley would give some back.

http://www.lotustalk.com/forums/f25/nst-pulleys-tested-33226/

If no one has a solution to completely remove the idler pulley, what about getting a nice light-weight equivalently sized pulley? Based on NST's light weight hardened aluminum pulleys they are cutting out at least 1/2 the weight.

NonStopTuning Lightweight Pulley Kits - Lotus - NonStopTuning

I contacted NST and they would just need a sample pulley to create the new one from and told me that it would probably cost in the $140 range for just one. I am not sure if they would have a Group Buy price, but if folks are interested we could ask. Might also want to get MWR in on this thread to see if it would be something they would be interested in adding to their pulley lineup.

:nanner:

So who is up for a group buy or for deleting the idler pulley?
 

·
Saffron Yellow is Lighter
Joined
·
1,291 Posts
Discussion Starter #2
Does anyone have a new idler pulley they could ship out for about 2 weeks to NST? That is all they would need to create a new aluminum version of it.
 

·
Registered
Joined
·
2,524 Posts
The idler is already very light. My guess is you're looking at saving an ounce or two. Would that net any real gain? Is there a way to calculate an estimate in advance?

I'd try to answer those questions before expending any effort or dollars. But good luck with your project!

Now that I think of it, I might have a spare pulley on hand. I can check tomorrow...
 

·
Saffron Yellow is Lighter
Joined
·
1,291 Posts
Discussion Starter #4
The plan is to loose about 1/2 the weight of the idler pulley. Not a big gain in weight lose, but its rotating mass so the effects are much greater. Dont have numbers, but know it will be a +. Oh well, if no one is interested I guess i will be the only one with another great mod.
 

·
Registered
Joined
·
572 Posts
I happen to be upgrading my cylinder head right now and I just took this pulley off my engine. Here is my analysis. First, the MWR water pump and alternator pulleys show a horsepower improvement on the dyno because they underdrive those accessories. The visible power gain comes from spinning them slightly slower, not because the pulleys where lighter. If it was possible to completely remove this idle pulley without affecting the serpentine belt, there would be no visible gains on a before/after dyno.

That said, I still like saving weight and will upgrade any part which doesn't sacrifice the car's strength/reliability, or my wallet too much. The steel idle pulley weighs 412 g, 0.91 lbs. If it was made the exact same size, but out of aluminum, it would weight ~.35 lbs (the bearings would still be steel obviously). It appears there is enough clearance that the pulley could go down in size, but at the end of the day, redesigning this pulley will only save .50-.75 lbs.

The steel cylinder spacer weighs 82 g, .18 lbs. If this was made out of aluminum it would weigh .06 lbs. An easy and straight forward, if minuscule, improvement. The nut and bolt weigh 102 g, .22 lbs. But it has what appears to be a custom stepped diameter between the threads and bearing surface.

Here's a link to Itslotswrk who recently took a look at this pulley as well. He found a plastic pulley, but the hole diameter and offset wont work. A spacer and pressed fit sleeve could work. But I would be concerned about adding extra parts to a component which is constantly spinning, premature wear could be an issue.

http://www.lotustalk.com/forums/2973450-post959.html

FYI, the engine must be jacked up on the passenger side in order for the long bolt to clear the frame and be removed. This requires the removal of two engine mounts. So it is not simple to remove this pulley.

 

·
Addict
2007 Lotus Exige S
Joined
·
1,422 Posts
FYI, the engine must be jacked up on the passenger side in order for the long bolt to clear the frame and be removed. This requires the removal of two engine mounts. So it is not simple to remove this pulley.
To clear the frame? If it was just clam off I might think about it when doing other work. Not sure I want this much effort to save that little and on an item that will need replaced again anyway.
 

·
Registered
Joined
·
2,969 Posts
To clear the frame? If it was just clam off I might think about it when doing other work. Not sure I want this much effort to save that little and on an item that will need replaced again anyway.
Yes I can personally attest to making this mistake before while installing the engine. The engine needs to be raised slightly in order clear the chassis, which means you have to undue the passenger side mount. The issue is that the bolt that holds on the idler pulley is like 6" long!

Heres a pic stolen from Google stolen from LotusTalk.

Honestly it would be a wiser solution to make sure the engine has small pulley on the opposite end of the serpentine and just make it a little bit smaller....if you know what I'm saying ;) :evil:
 

Attachments

·
Saffron Yellow is Lighter
Joined
·
1,291 Posts
Discussion Starter #8
FYI, the engine must be jacked up on the passenger side in order for the long bolt to clear the frame and be removed. This requires the removal of two engine mounts. So it is not simple to remove this pulley.
I have an earlier 05 car, but my nut was facing the passenger side so it fell right off. Sounds like they must have started assembling the cars with the bolt the other way around for you guys. Probably a better idea so the bearing is not sitting on the threads, but would suck to remove the pulley.
 

·
Saffron Yellow is Lighter
Joined
·
1,291 Posts
Discussion Starter #9
Honestly it would be a wiser solution to make sure the engine has small pulley on the opposite end of the serpentine and just make it a little bit smaller....if you know what I'm saying ;) :evil:
Are you saying it would be better if the idler pulley was a little bit smaller? Does anyone have any idea if we could get away with a slightly smaller pulley diameter for the idler without causing any issues? That could certainly be done, knowing it might take a slightly smaller belt then.
 

·
Registered
Joined
·
2,524 Posts
No, he's saying supercharge it...

A smaller idler wouldn't do anything but spin faster. If anything it would add a tiny bit more drag.
 

·
Registered
Joined
·
2,524 Posts
I have an earlier 05 car, but my nut was facing the passenger side...
I like that!

What could one use to "fill in" the threaded portion of the bolt where the pulley bearing would sit? JB Weld?
 

·
Registered
Joined
·
572 Posts
Since it was easy, I went ahead and made the spacer out of aluminum, saved .12 lbs, :rolleyes:



 
1 - 12 of 12 Posts
Top