Cranksahft Pulley Diameter

General Engine Discussion

Moderator: John_Heard

Post Reply
Message
Author
User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Cranksahft Pulley Diameter

#1 Post by Bruce69Camaro » Tue Oct 08, 2013 9:41 am

I need a new crankshaft pulley to work my alternator. It appears the place I got mine from listed it as a big block, but in fact it is a small block pulley and there is no returning it.

So here is my question, it looks like a factory big block crank pulley diameter is around 7" and maybe some change, if I was to use a pulley that had a 5.4" diameter, would that hurt my charging system?

I found this place that makes machined aluminum pulleys and the one I want is this 5.4" diameter and sells for $54.00.

I just can see paying $100 for a factory pulley :scratch:

Thanks
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

Re: Cranksahft Pulley Diameter

#2 Post by Craig W. » Tue Oct 08, 2013 3:26 pm

What size pulley do you have on it now?

Large diameter crank pulleys can yield excessive belt speed and lead to thrown belts. So a 7" may not actually be the hot ticket anyway.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#3 Post by Bruce69Camaro » Wed Oct 09, 2013 5:27 am

I had some confusion going on. I was thinking I needed to go bigger, but as it is, my pulley should work.
I think the pulley size is 3-1/2" or 4".

I was told the pulley was for a big block and it's for a small block. I found a site that said for a big block with a long water pump, from the face of the block to the middle of the pulley it should be 5-11/16". I took a mesurement and it was 5-11/16", so now I'm really confused, because this same chart said a small block with a long water pump should be 5-3/8".

Anyhow, I then took a measurment at the alternator pulley and it was more like 5-13/16" to the face of the block, so now I found it was misaligned and probably the reason is blew off. So I cut down the bracket 1/8" and now it lines up just right.

I just need to go get a belt and then I can check to see what kind of voltage I have.
Last edited by Bruce69Camaro on Wed Oct 09, 2013 8:43 am, edited 1 time in total.
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

Re: Cranksahft Pulley Diameter

#4 Post by Craig W. » Wed Oct 09, 2013 8:30 am

Wow, that's a big alternator pulley. Its better to slow the belt down with a smaller crank pulley than to slow the alternator with a bigger pulley. The real issue with tossing belts (provided there is good alignment and sufficient bracket strength) is the acceleration of the belt itself.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#5 Post by Bruce69Camaro » Wed Oct 09, 2013 8:46 am

Sorry Craig, I had to edit the posting, the alternator pulley size isn't 5-13/16", it's a stock size pulley. What I was referring to was the distance from the center of the pulley to the face of the block. I found out there was an alignment problem.

Right now, as it is, the alternator pulley is stock size and the crankshaft pulley is either 3-1/2" or 4".

This should be ok, correct?
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

Re: Cranksahft Pulley Diameter

#6 Post by Craig W. » Wed Oct 09, 2013 10:38 am

Yeah, I've run a very similar pulley ratio on my car for years. Never had a problem until I went too low with the alternator output. 40 amps wasn't enough to keep up so I'm going up to a 70 amp mini.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

User avatar
wikd69
Posts: 2067
Joined: Sat Feb 23, 2008 12:42 pm
Location: Rocklin, CA
Contact:

Re: Cranksahft Pulley Diameter

#7 Post by wikd69 » Thu Oct 10, 2013 1:27 am

If this is an issue with charging you might want to test your alternator. As I understand it, most 3 wire alternators will normally start charging at around 2500 RPM (give or take). At a lower RPM, it takes power to the exciter wire to make it generate a charge. That's what your voltage regulator does, as I understand it. Myself, I'm running a 7" pulley on the crank with a standard 4" (?) pulley on the alternator. I ended up swapping over to a single wire 140 amp unit I picked up through Summit.

You can also convert your old style alternator to a single wire unit by simply connecting the exciter wire to the power lead coming out of the alternator. You can google it to find the correct instructions. That way it's always charging at any RPM.

Your mileage may vary of course, and I could be full of it :mrgreen:
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#8 Post by Bruce69Camaro » Thu Oct 10, 2013 6:00 am

Thanks Harry,

It's a single wire, 105 amp alternator.

Talking to some guys over on YB it looks like my 6 ga. wire from the alternator might need bumped up to either 2 or 1 ga.

Have you heard from Rob lately?

I hope the guy is still around?
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

Re: Cranksahft Pulley Diameter

#9 Post by Craig W. » Thu Oct 10, 2013 7:50 am

1 gage is overkill for the alternator if you look at an amps vs. wire gage chart. I run 1/0 gage for my starter.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#10 Post by Bruce69Camaro » Thu Oct 10, 2013 7:56 am

What would you suggest?

I currently have 6 ga. with 1 ga. starter and ground wire.

I'm running a 6AL, blue fuel pump, SPAL 16" fan, electric water pump.

That's it.

Here is a question I just thought of, when I take a reading at the alternator, it should be around 14, correct?

Back at the battery, it should be 14v?

If not, then does this prove I'm loosing voltage due to the cable size?

Again, the alternator is a 105 amp, single wire.
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
wikd69
Posts: 2067
Joined: Sat Feb 23, 2008 12:42 pm
Location: Rocklin, CA
Contact:

Re: Cranksahft Pulley Diameter

#11 Post by wikd69 » Fri Oct 11, 2013 4:44 am

My battery is in the back and if I recall I ran 4 ga wire all the way forward just for the alternator, in addition to the 1 ga main power. I had to do that as well to isolate the engine power for the main power emergency cutoff at the back - prior to that, the damn thing would continue running on alternator power alone when the battery was cut out of the circuit. I got caught on that during pre-tech at the track.

Count up all the amps you pull at full tilt: fuel pump + fan + MSD box + whatever. Is your 105 amp alternator big enough ? I adopted a big electric fan out of a 98 Lincoln - it moves huge amounts of air but it also pulls close to 40 amps all by itself. I pull power for the fan relay directly from the post on my 140 amp alternator, instead of pushing power all the way back to the battery and then forward again over the single 1 ga power feed. Maybe overkill doing it that way, but it wasn't a big deal to wire it up.

I understand as well that your MSD box may get erratic (timing drift and spark issues plus weird behavior) when the voltage going to it is low.

All of this may not apply for you, so take what you need an leave the rest :)
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#12 Post by Bruce69Camaro » Fri Oct 11, 2013 6:03 am

As of right now, my amp drawing is only 38 amps.
MSD 6 AL = 7 amps ( 1 amp per 1000 RPM)
Holley blue pump = 3 amps
Water pump = 6 amps
SPAL fan = 22 amps

What are lights?

But I think I'm safe to say my 105 amp alternator is large enough...I hope????
Those who think they know it all have no way of finding out they don't......... :scratch:

User avatar
wikd69
Posts: 2067
Joined: Sat Feb 23, 2008 12:42 pm
Location: Rocklin, CA
Contact:

Re: Cranksahft Pulley Diameter

#13 Post by wikd69 » Fri Oct 11, 2013 9:23 am

Bruce69Camaro wrote:As of right now, my amp drawing is only 38 amps.
MSD 6 AL = 7 amps ( 1 amp per 1000 RPM)
Holley blue pump = 3 amps
Water pump = 6 amps
SPAL fan = 22 amps

What are lights?

But I think I'm safe to say my 105 amp alternator is large enough...I hope????
Are you sure your water pump is only pulling 6 amps ? That seems light. However, your 105 amp alt sounds like it should be big enough. I went with the bigger alternator because, well, I do overkill on everything :mrgreen:
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

User avatar
Bruce69Camaro
Posts: 1779
Joined: Thu Jul 23, 2009 11:07 am
Location: PA

Re: Cranksahft Pulley Diameter

#14 Post by Bruce69Camaro » Fri Oct 11, 2013 10:11 am

Just looked again and it says 6 amp draw...
Those who think they know it all have no way of finding out they don't......... :scratch:

Post Reply

Who is online

Users browsing this forum: No registered users and 3 guests