Technical Alternator speed

It's a thought but there's 2 reasons not to. I'm trying to keep it as old school as possible, ie: as a HAMBster. Secondly, to change to that setup would probably cost more than what it cost for the Ross racing harmonic balancer that's already on it which from memory was approximately $600 Australian dollars a couple of years ago.

 

If there is a fan behind the small alternator pulley, the blade's could be pulling forward enough at high RPM to kick the belt off, a larger diameter pulley will prevent this and still charge well, just like the high performance car's of the 60's did, with larger than normal alternator pulley's. As a plus the larger diameter pulley's are usually deep groove to also help retain the belt.
As far as the belt turning inside out, I've experienced the same issue with cog/groove style belt's. It seem's some are not stiff enough to withstand the harmonic's of high RPM and they flip or get tossed.(even in deep groove pulley's) Switched to a regular, solid type v-belt with plenty of cord's molded in (I like AC Delco), and that seem's to have cured the problem, and that's with shifting at 7,500 RPM.
If this problem just came up recently, I would lean heavily toward the belt being the weak link, so to speak. As always, some pic's of your set up could tell us alot.

 

I kicked the fan blades out on one at 8700 rpm , belt stayed on but got chewed on by the blades.

 

From what I've read 18,000 RPM is about it for a modern alternator

 

spanners, be sure you have a stabilizing strut coming off the back of your alternator. I was having problems cracking my East Coast alternator case (7000 max engine RPM) until a call to them informed me I needed a strut off the back of the case to stabilize the unit at hi RPMs. That could be a part of your solution.

 

Since you stated you have some non-HAMB gear on the car, you may be interested in a different alternator if you're gonna rev it alot. I've heard from more than one source that the AC Delco style of alts like the 10si and 12si models dont handle the bigger RPMs, so the hot ticket is a Nippondenso like what mopar currently runs, along with toyota and tons of others. They are powerful, just need to make sure to get a unit that doesn need a computer to regulate it.

There are plenty of them but i haven't found out which ones i can source from junkyard or O'really instead of triple cost at powermaster. But yeah those Denso's can really handle the RPMs. Also- the more powerful Delcos have bigger stators that are more affected by RPM.

I'm planning on a denso unit since my fan pulls alot of amps by itself, and it may end up with a stereo and A/C.

-rick

 

Older school than late '40s? Gilmer belts go back a while. A couple pulleys and a belt would might not be cheap, but I bet you could get it done for less than $600.

 

Too true. I've tried to buy old fashioned solid belts but the only ones available are agricultural type which are usually very stiff with Kevlar reinforcement.

 

I'll get some photos of the setup I have. I'm using dual adjustment brackets after a bloke told me they used to have a similar thing happen with speedway cars.

 

We used to just mount bracket, top and bottom of belt mid span about a 1/16 away to control whip/belt toss off the alt pulley. Worked about 99%.

 

I'm thinking that the alternator he is using is the same one that was on my 2K DTS and the same one that is on most LS 6/--- Corvettes, Not much issue with overspinning it. The frame is smaller than the 10/12 SI and a lot smaller than the stock big case alternator that you find on Cad 500's and that I have on the 500 in my 71 GMC.

 

If the belt is twisting around on its back, I think it has to be the bracket flexing or the belt stretching. A tensioner might stop that. Is there any any possibility that the V on one of the pulleys is not V'd the same as the belt? Is there any room to cut the V deeper ?

 

Have you had your eyesight checked lately..........

Just jokin

 

Yes and had new Coke bottle bottoms installed in my new spectacles.

 

Sorry for the **** photo. Racecar is stored in a shipping container without lighting. Distance between pulley centres is 9".

 

I would bet those brackets are flexing, the belt is walking, and away it goes. It doesn't take much...

 

Pic of the " strut" ?

 

Sorry 2old2fast, I'm not where I can get a pic up. Mine is a slotted flat strut attached to a lug on the rear of the alternator joined to another flat strut bolted to an engine block boss so that the two struts bolt together with no preloaded stresses into the alternator case. Probably overkill, but no failures so far.

 

Reason I ask is I don't believe I've ever seen an additional brace used on an adjustable OEM alternator mount ?

 

My mounts are hand fabbed and as you can see by the photo the alternator is cantilevered out in front of the engine a good bit (to clear the aftermarket fluid dampener) so I get that there could be a "diving board effect" that induces stress in the case unless the alternator mounting is triangulated.

Spanners, how many degrees of wrap does your alternator belt have?

 

We run a mini 60 amp in our 1/2 mile dirt car. The engine sees 7000 at least twice a lap. It runs off the nose of the water pump with the same size serpentine belt pulley that’s on the alternator. Same one for 14 years without a failure.

 

I honestly wouldn't know the exact amount but I'd say the it's close to half the pulley.