those with underdrive pullies...
Melting Slicks
Joined: May 2001
Posts: 2,700
Likes: 3
From: Lebanon KY
Re: those with underdrive pullies... (JJ 86)
the previous owner of my 86 said he put underdrive pullies on it. how can i tell if i have them? and yeah a tenth for a $150 sounds like a good deal to me too :D
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: those with underdrive pullies... (corvettemaster)
Go with the March Power & Amp series pulleys (Summit) and install the underdrive crank and the overdrive alt pulleys.
The only "difficulty" involved is in getting the correct Gates serpentine belt length. It took me like 3 trips to AutoZone to get it right.
If you have an underdrive crank pulley it will be only about 5-6" dia, whereas the stock pulley is around 8-9" dia. If you have the overdrive alt pulley it is so small that you need to grind a socket to get it onto the nut; if not, you will be seeing low charge at idle.
[Modified by 65Z01, 4:56 PM 3/19/2004]
The only "difficulty" involved is in getting the correct Gates serpentine belt length. It took me like 3 trips to AutoZone to get it right.
If you have an underdrive crank pulley it will be only about 5-6" dia, whereas the stock pulley is around 8-9" dia. If you have the overdrive alt pulley it is so small that you need to grind a socket to get it onto the nut; if not, you will be seeing low charge at idle.
[Modified by 65Z01, 4:56 PM 3/19/2004]
Pro
Joined: Jan 2003
Posts: 515
Likes: 3
From: newark DE
Re: those with underdrive pullies... (Spankyellow)
i put just the crank pulley on my L98. i dont have any charging or overheating issues with it. the car also gained a solid 1mph through the traps... previous best was 103.79, after the pulley i was trapping 104.73
Racer
Joined: Feb 2004
Posts: 445
Likes: 1
From: Atlanta GA
Re: those with underdrive pullies... (JJ 86)
on an L98 is this a worth while mod? Also how difficult is the install? What kinds of gains should i expect? :smash:
The only "difficulty" involved is in getting the correct Gates serpentine belt length. It took me like 3 trips to AutoZone to get it right.
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Le Mans Master
Joined: May 2000
Posts: 7,033
Likes: 12
Re: those with underdrive pullies... (Spankyellow)
It's been a few years since I put my march set on but I thought with that set you kept your same belt. Correct? I didn't notice on my last vette with 2.59 gears I could squeal the tires after the pulley change and b4 I couldn't.
Race Director
Joined: Sep 2003
Posts: 16,838
Likes: 341
From: Database Error Indiana
Re: those with underdrive pullies... (Spankyellow)
Ok the rain stopped. I have the March Power and Amp pulleys. Gates belt
Ko60860. This is pretty faded. Also says 58.0. Pretty sure its 58 inches. This was used on my 86 and 87. Not the same belt as stock. Dont know what other years are the same. Luck. :thumbs: Edit: 58" seems short for a belt.. The part # should get you what you need.
[Modified by Spankyellow, 4:26 PM 3/20/2004]
Ko60860. This is pretty faded. Also says 58.0. Pretty sure its 58 inches. This was used on my 86 and 87. Not the same belt as stock. Dont know what other years are the same. Luck. :thumbs: Edit: 58" seems short for a belt.. The part # should get you what you need.
[Modified by Spankyellow, 4:26 PM 3/20/2004]
Racer
Joined: Feb 2004
Posts: 445
Likes: 1
From: Atlanta GA
Re: those with underdrive pullies... (Spankyellow)
I have the March Power and Amp pulleys. Gates belt
Ko60860. This is pretty faded. Also says 58.0. Pretty sure its 58 inches. This was used on my 86 and 87. The part # should get you what you need.
Ko60860. This is pretty faded. Also says 58.0. Pretty sure its 58 inches. This was used on my 86 and 87. The part # should get you what you need.
http://www.marchperf.com/pg10.html
Safety Car
Joined: Jun 2000
Posts: 4,870
Likes: 25
From: Long Island, NY
Re: those with underdrive pullies... (Midnight89)
There is a solid 1 tenth gain in ET with this mod.
I have a slight charging issue when idling with the headlights on, otherwise it is ok.
Vic
I have a slight charging issue when idling with the headlights on, otherwise it is ok.
Vic
Le Mans Master
Joined: Mar 2001
Posts: 9,464
Likes: 1
From: Modesto CA
Re: those with underdrive pullies... (Vic'89)
I recently put this pulley BACK on. (had it off due to charging issues.) I'll report back with any gains I get when I go back to the track. (ran the same times with it and without it, but made some other changes...)
Racer
Joined: Jul 2002
Posts: 447
Likes: 0
From: Malta Europe
Re: those with underdrive pullies... (Vic'89)
I did the underdrive pulley + the alternator pulley and bealive me with only the crank pulley you`ll have charging problems !!! there is an other thing , my before and after MPH at the traps remained the same @ 99MPH :banghead:
Racer
Joined: Sep 2002
Posts: 407
Likes: 0
From: Alma AR
Re: those with underdrive pullies... (JJ 86)
I have a 1990 auto L98 and I was considering under drive pulleys. Then I happened to read a book at Barnes and Nobles, I think it was called 101 projects for your Corvette. In there the author says that it's not a good idea to change the pulleys. He says that GM engineers spent a lot of time considering the size of the pulleys and the conditions they were going to encounter, and sized them acordingly. Any change will have a negative effect to the car somewhere at some time. Get the book and read it, then decide if a tenth is worth it.
Intermediate
Joined: Feb 2004
Posts: 41
Likes: 0
From: Tualatin OR
Re: those with underdrive pullies... (PBnf)
I've read through that same book and I think the author is rather pessimistic about aftermarket parts. The book is geared more toward regular maintenance and not speed parts. But that's just my .02. Anyway, I'd do it and definately go with March stuff
Racer
Joined: Sep 2002
Posts: 407
Likes: 0
From: Alma AR
Re: those with underdrive pullies... (X-SDime)
I kind of had that feeling too, but I thought it was worth mentioning. Also I thought of something others in this forum might know something about. It's stated that there might or will be charging problems with underdrive altenator pulleys. Well, what if you added an aftermarket altenator that rated at a higher amperage than the staock unit. Would that make up for the pulleys? :confused:
