Subject is the question; I'm trying to determine if the aftermarket pulley I got with my FD is an underdrive pulley or not. It looks like the pulley set that Banzai Racing sells, but there's no way to know for sure. The diameter on my pulley is a smidge larger than 4" diameter (measured at outside edge diameter), so if the OEM one is a larger diameter, mine must be an underdrive.

Thanks!

 

I can’t measure now but if the pulley is the same diameter as the back part that has the crank trigger wheel then it is under Drive. Stock and stock size pulleys are typically larger than the trigger wheel.

Dale

 

It's an underdrive then, as it's about the same diameter as the crank trigger part. Picture from when things were disassembled while I was doing A/C line plumbing shows it pretty clearly:

 

Pete, here is the measurements off the stock pulley and the one banzai sells. 98% sure you have an under drive on there.


~ GW

 

My car has the stock intercooler so it's hard to measure, but the OD of the pulley (including the lip) looks like about 4.5 inches diameter.

 

 

Thanks guys, I definitely have an underdrive pulley then.

Reason I asked is I just noticed that when I flip on the headlights with the car idling at 900RPMs, my voltage will drop from its normal 13.6 to 14.1V range to about 13.0 to 13.2V. At the time the engine fans were running. Switching off the head lights, OR bumping up my idle speed a little with the gas pedal to 1000RPMs and voltage goes back to normal 13.6~14.1 range with the headlights on. Weird thing is none of the other high current electrical loads (e.g., engine cooling fans, A/C clutch & blower fan at max speed, rear window defroster) cause a similar voltage drop at 900RPM idle when they initially kick in. So these symptoms have me thinking of the following scenarios:

1. Is the headlight circuit pulling a ridiculously higher than normal current draw due to a bad connection/component somewhere?
2. Alternator's voltage regulator may be going bad?
3. Maybe I just need to switch to a stock/OEM pulley to bring the alternator revs up at idle speed?

 

Yep you need proper pullies. I had an under drive main pulley for 5 minutes back in the day - I had this exact same thing, Car would actually dip to 12's with the brake lights on at a stop light.

This is one of those parts that's designed for track use only cars that people put on a street car Because Racecar BRO! Yeah it sucks on a street driven car.

There are aluminum stock-size main pullies out there. The sucky part is having to get new belts. Best way I've found to conquer that is about 3 trips to a parts store that has a large belt selection.

Dale

 

Pete, I had very similar output readings when the car was idling using the same under drive pulley, and it became worst when heat soaked. I spent some time logging when it happened and under what conditions ( tho mine was effected by cooling fans and rear defrost, etc) . I did return to the stock main pulley while retaining the others aftermarket ones and the large fluctuations are gone. Now I just get small normal ones. For what it’s worth, under drive pulleys work well for a car that sees extended times at high rpms, not so much at low speed and idle. I don’t believe the very minimal gains ( read a few hp ) outweigh the negatives. Just for reference I do run a full-size red top Optima that’s been relocated to the rear bin and at the time a stock alternator ( have since put in the IRP upgraded unit ) along with a power fc. If my memory serves, you are running a link ECU and a GM throttlebody. I would imagine the reason you don’t see much fluctuation on the other things maybe because that was adjusted properly in the ECU which has significantly more adjustability than a power fc. I’m not sure if your link was setup to see the eld signal or not. But since the other loads don’t seem to bother, it very well may be. I would try sticking the stock pulley back on for now and give it a try. If you are running a pineapple racing idler pulley I can give you the belt sizes for both. I did eventually upgrade my alternator to the IRP unit which shifted my output voltage while running from around 13.4 -13.8 ( after I put the stock pulley back on ) up to 13.8 - 14.2 depending on conditions. One thing I forgot, are you running stock headlights or an aftermarket set?


~ GW

 

I took a close look at some of my Link ECU logs, and the data confirms that the voltage drop at idle only occurs when the headlights are on, regardless of whatever other electrical loads are operating at the same time. The clue in the logs is that I'll have the same voltage drop with headlights lights on, whether or not the E-fans are running - so even with the E-fan loads off, I still have a voltage drop with the lights on. Also, the lights are on the dim side unless I rev the engine above idle. Stock OEM headlights, with OEM halogen bulbs that I haven't replaced yet.

This all has me thinking I've got a problem in the headlight circuit to track down - headlights by themselves should draw approximately 9.2 amps at steady state per Ohms law: (55Watts per bulb x 2 bulbs)/12V = 9.16A. The fans draw considerably more current than that, especially when running at max speed - and my logs show zero voltage drops at idle when the fans are running at max speed, which leads me to conclude that the headlight circuit is drawing much more current than it should, but not necessarily enough to blow the fuse. IIRC, the headlight circuit protected by a 30A fuse, so if the true current thru the headlight circuit is anywhere close to that, it could explain the voltage drop.

Unfortunately I don't have an OEM pulley to drop in there, and even if I did, the larger diameter might put the belt path a little too close to those custom A/C hoses I had to run to restore the A/C.

Game plan is to first replace the ancient headlight bulbs that came with the car with a new pair of halogens, which if it solves the problem, I'm done. If not, crack out the ammeter and see what kind of current the headlight circuit is pulling, and if it's above where it should be, start looking for poor contacts in the various connections, ground points & switches of the headlight circuit.

 

One thing to remember is the headlights being on it’s more than just the two headlight bulbs, there’s all the running lights, dash lights and I’m sure some aftermarket gauge lighting. It’s been a bit I’m not sure if the headlight bulbs and running lights / dash Lights are on separate circuits or not. Either way it’s kind of a irrelevant because when you turn the headlights on the total connected load increases. I would investigate to see if the link has a signal for when running lights/headlights are turned on and that it offsets for the extra load.


I think the stock pulley would fit with your ac lines, even if you had to slightly bend your mounting supports. I have a couple spare sets of stock main pulleys boxed away. I’d be happy to send you one to try out or you can take the hike to Annapolis one day and grab it. Shoot me a PM if you’re interested.

~ GW

 

^That's a good point that I forgot about GW. Those 1157 bulbs will consume about 27W each if you have your foot on the brake, and the headlights are on - which will add up to roughly double the current for just the headlights. But after reviewing the FSM schematics, I found that the headlights/fog lights circuit (ref. page Z56), parking/side marker & license plate lights (ref. Z60), turn signal/hazard lights (ref. Z62), horns/brake lights/reverse lights (ref. Z66) are each on individually fused circuits. There are a few common components between these circuits, such as the headlight switch, some ground points and common +12V power paths before each individual circuit's fuse (e.g., 60A BTN fuse, 120A main fuse,etc.).

The Link ECU doesn't detect electrical current loads directly, but it does provide various means to compensate idle speed for higher electrical & mechanical loading. For example, when the ECU is about to kick on the fans, it can bump up idle; it can also take switch inputs (e.g.., PS switch) to detect the extra mechanical load. Same deal for A/C, where the Link is integrated with the factory A/C wiring and manages the compressor.


Thanks GW, I might take you up on that offer to test fit. As it is now, the PS/AC belt along the bottom runs with about 1/4"~3/8" clearance to the A/C suction line, right where it attaches to its beadlock fitting, so there's really no easy way to relocate the line slightly.

This headlight project will have to wait a bit, as my FD is on the lift as I'm wrapping my down pipe now. Recently had a local shop do some fabrication work to recirculate my 2x external waste gates into the DP, probably should update my build thread again.

 

I figured they were on separate fuses. The switched input on the link would work. You could have it tied to the running lights as a trigger to bump up the idle speed a bit ( which is how the stock and power fc do it ).


No worries on the pulleys, they’re not new but can be cleaned up and painted. I’m sure you could figure out a way to make them work but you would be the best judge on that. It’s only 1/2” more in diameter and 1/4” in radius. Just let me know.

Also, I bet it’s going to be much quieter now with the reroute, save the ears a bit.

~ GW

 

It is worth replacing brake and running lights with LED, that reduces the current draw from lighting big time. Especially brake lights - we basically have 7 bulbs in the back for the brakes, 2 on each side and 3 in the middle brake light.

The small wedge bulb running lights and brake lights can be easily changed to LED. Turn signals require modding CPU#2 so you don't get hyper flash.

This solves the "interior light dimming at idle with brakes applied" that even bone stock cars have.

Dale

 

That is definite on my FD's "To Do" list Dale; I did that drill on my FC, replacing all external running/brake/signal lights with LED equivalents (including the fogs), and retrofitted HIDs for the headlights. Also did the CPU mod to eliminate the hyper-flash issue with the LED turn signals.

Since I have one of those Hall effect current sensors/ammeters (resolution +/- 0.5A), I tested the total system current draw on the FC before & after the lighting changes. Just swapping out the LED running lights dropped the total current draw for lighting (w/brakes applied) from 10s of amps down to 1's of amps. As for the headlights, the HIDs pull 35W each, so they reduced current draw roughly 30~40% compared to the 55W halogen sealed beams they replaced.

 

If anybody reading is looking for an OEM diameter aluminum main pulley, Super Now makes them. There was another place in England but Covid put them out of business last year.

Jack