Any need to retune after installing an underdrive pulley? Car has a tune for the heads and cam that were installed in feb 2011. Thanks for your help.

 

NO - it's not a bolt that it will effect the tune! It's more like an unleashing of hidden power being robbed by turning mass -

Lighten turning mass and you increase the power!

Thanks,Matt

 

Thanks. That was my thought too. Just wanted to confirm from people that have more knowledge about this than me. Thanks for your help.

 

Maybe a stupid question, anyone put on a underdrive pulley in a stock vetted with no issues? Is it worth it?

 

Many have put it on-waste of time and money.

 

Yes there are plenty of people who have done it and not to increase performance rather to replace a defective OEM under drive pulley. I am one such person who went with a Powerbond over re-installing another GM pulley that is known to separate and wobble.

 

Not really worth it if the OE pulley is fine. It's a fair amount of work to swap it out. Most go to an underdrive pulley when installing a cam since it's got to be removed anyway to swap the cam out.

 

Don't know what scuttlebutt you've read, but I could immediately tell how much more the car wanted to rev when I had mine installed. My stocker was coming apart, so it was well worth the time and money.

 

Not trying to hijack thread, but how do you know what size serpentine belt to get for the smaller pulley?

 

All you have to do is ask here on this forum..or ask the undrive pulley vendor, they should have the correct swapout belt chart when using their HB. As far as putting an under drive pulley on your C5... ! As theses cars become older, the OEM Crank pulley is looking for a reason to delaminate or wobble due to a backed out bolt.. In either case the potential is there.. with an underdrive pulley You remove any threat of a delamination, and you pick up about 10 ponies.. the job is fairly straight forward.. Shop time is 4 hours.. pulleys are around 200 dollars. the big thing is proper torque procedure. If you can do the job yourself ,,, the 200 dollars for the pulley and new bolt is worth it. Shop time @ 90 an hour is 360 dollars.. two new belts are about 40 dollars. Also , with a new pulley you will want to use either a Gaytorback or a Gates...the reason is the design of the ribs in relation to the overall width.. many cheap belts do not afford the clearance that gates and Gaytorback do...this clearance is what helps to make the pulley system quiet.. there are only a few thousandths clearance in some cases.. the AC Belt which runs behind the balancer first stage ( drive belt ribs ) can easily come in contact with the belt if the belt is designed poorly.. the run out ( grooves to width ) is a critical dimension on a C5. AS the cars get older , the pulley bearings allow the pulleys to wobble slightly, thus creating a wider run out.. so you need additional clearance which is afforded by either Goodyear Gatorback or Gates.. Many people have talked about Goodyear Gatorbacks as curing their problem but no one has actually offered the reason why.. So Now you got it... Gates is just as good as Gaytorback, and you can get them at NAPA.. its their belt brand but they are made by Gates...
Bill aka ET

 

What do you think underdrive pulleys actually do?

 

Thanks E.T.

This exactly the information I was looking for. New pulley and 10 extra h.p. is great.

Thanks again for helping us guys who do not have the knowledge we need.... and realize it.

 

Well, new tuner said we needed to adjust the tune. He said after the new underdrive it was knocking. Said he could fix everything up for me. I guess my old tuner/builder that put on used parts, which is the reason I had to do the underdrive pulley really is not that good. Looking forward to getting the car back. It has been a couple of months since I got to go for a spin.

 

Mine washes and waxes the car, keeps it vacuumed and automatically moves it out of the way of falling bird poop when it's parked in a parking lot. When it's not doing all that it's slowing down the speed of the accessories and reducing the load and parasitic drag on the engine.

 

No tuner around here is going to do that job for 4 hours. I did it on mine and if you do it right and pin the pulley you are looking at 8 at least. I would not have done it if I wasn't swapping cams, the price/performance is just not there. As for tune, no need for a tune with a simple underdrive swap, if you are knocking after you have some other tuning issues but its pretty unlikely its because of the pully itself.

-Ken

 

The money/hp makes the ud pully not worth it. I also did mine, had issues with over heating, and when I took it off I saw a 2 hp difference. Money and time wasted.

 

Hahahaha NICE!

 

Dang, parasites in your engine, gonna get Orkin to look at mine.