Throwing my belt at 7050rpms. Why?

[slalombuggy]

Power pulley, slow your fan down. I can almost touch the belt together on my race engine and hit 8000rpm at the shift with a power pulley (well a dry sump pulley that is even smaller). Never thrown a belt. Also check to make sure the pulleys are aligned which I'm sure you have, the faster they turn the more critical alignment is. I had a serpentine bellt on my first big engine and ran it over 7000 rpm a few times, but I also set it to slip at that speed. At around 6800 you could start to hear the belt squeal, which leads me to believe that's when the fan started to stall. Just a theory I guess.

brad

[ralf]

[67rustavenger]

Ok. I'll bite.
What's the correlation between the W110 camshaft and tossing fan belts at 7050RPM with stock pulley's?

[Type 5 Joe]

Probably because that RPM exceeded the 110's powerband.

Once the torque drops off its time to shift.
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[Dale M.]

I have had two different engines (2180 and 2084) over the last 15 years and they have seen over 7000 RPM many times and only once in all those years I threw one belt off autocross car engine....

Both engines have power pulleys to slow fan speeds and belt/pulley alignment is best possible and used best quality belts one can get....

Not sure what cam shaft has to do with belt problems other than engine stop developing torque as cam tops out..... Most of the time on auto-x car we ran in second gear and engine has to work from 1500 to 7000 RPM because on short courses there is not really time or need to shift....

Dale
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[richierich]

[vwracerdave]

Yes you can turn over 7000 RPM with a power pulley because the fan turns slower. The problem is turning over 7000 RPM with a stock sized pulley. The fan can not turn that fast and throws the belt.

Don't forget with a stock sized pulley the fan/alt turns about 1.8 times the crankshaft speed so at 7000 RPM X 1.8 = 12,600 RPM fan speed.
and a power pulley turns about 1.5 times. 7000 RPM X 1.5 = 11,200 RPM fan speed.

There is going to be a point when you will throw the belt on a power pulley too because the fan can not turn any faster, but I don't know what RPM that is because I have never gotten there. Using the math above it would be around 8400 RPM.

On a side note I have had far better luck with the cheapest $3 Taiwan belt than the real high dollar good quality belts. The cheap belts are thinner and fit deeper into the pulley grooves and they also slip more.
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[Volks Wagen]

[VW_Jimbo]

[Clatter]

Ya,
If you run a power pulley on the street for some miles,
It would be good to have a CHT and keep an eye on it.


Some have gotten away with a loose belt.
When it gets the RPM up there it slips easily,
And since there’s lower tension,
It can live.

Maybe a Gates belt, run a bit loose?
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[modok]

It would be interesting to see which belts work better.
I don't know, but wonder.
I never intentionally bought a special imported belt...but, If that's anything like "continental" fuel line, (imported fire hazard)..... maybe the belts are the same way? or not? LETS SEE

Sorry you didn't know that this would happen? well, maybe that's for the best, it would not be an adventure if you already knew everything.
Even among the OE parts there are slightly different sizes of crank pulleys, and different possibilities with the belt size and washer stack, as well as different fan widths. The belt whip is partly due to the speed variation of the engine which is made worse by longer strokes and lighter flywheels. So, maybe if you had a heavy flywheel and a 78 stroke it would not do it.....or, who knows! I don't.
Not a lot of people turning 7k rpm with a long stroke "street motor"
A fan clutch, possibly viscous coupling.... would be a great way to have it all but it is a very difficult thing to design and build on a "one off" basis.

[Bruce]

Do you guys really think a cheap belt is the answer?

When I had this problem, I tried several brands of belts. Gates is the one that survived 7500+ with stock pulleys.

I looks like you have early "generator" type pulleys. If so, you need to upgrade to later "alternator" type then use the wider alternator belt.

Your thin generator belt is stretching, then it flips over in the groove
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[jbbugs]

Bruce is correct. The Gates belt usually fixes this issue., as long as you don't have a pulley issue.
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[jpaull]

[tattooed_pariah]

I keep thinking of something along the lines of, "I keep sitting on these empty cardboard boxes, and they hold up for a little bit, but then crumple.. why?"

Some things just aren't designed to be used they way we use them.. I doubt many V-belts are meant to be run at 7k rpms... especially using stock pulleys that were designed with 3500-4k rpms in mind..
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[VW_Jimbo]

Again, thank you all! The amount of knowledge on here is humbling!

I will try the Gates belt first. Then I will move on to an alternator pulley and a Gates belt. If the problem is still present, well then I will need to curb my enthusiasm, a bit.

Yes, I do understand the cam has a power limit, and I am exceeding it. The first time it happened was a shock and had not been really paying attention to anything except the rpm gauge. Just wanted to know if my calculations were correct and that I could hit 8 grand. Got to 7400.

Second time I was not paying attention, just having fun. The remainder of the times it is me pushing things, because that is where I find life to be. All in or nothing! That’s why I love rock climbing. I am an extremist.

Regardless of the rpm limitation, in general, I try and live life with no limits. I like being able to push things just a little bit further. I have found that place right beyond safe to be the sweet spot.

I went with the 110, for two reasons. I knew of the 110 from past engines I had played with, and two I wanted the influence from the cam to arrive at a lower rpm, since most of this cars driving is between street lights or stop signs. There are way too many around here!
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[slalombuggy]

A few of the guys running at Bonneville have made a belt guide to keep the belts on their engines at 7000rpm sustained speeds. It is simply an "L" shaped bracket that bolts to the top front case bolt and holds a 1" bearing that rides on top of the belt with little tension but I guess just keeps it from bouncing. I haven't tossed a belt so I've never used one, as I said before, I can almost pinch my belt together it runs so slack and I use a Scat drysump pulley.

brad

[mikedjames]

[Bill Schwimmer]

Ditto on the Gates belt. Used them many times past 7500 with stock size pulley, however once the belt stays on you might be finding your next weak link.

[slalombuggy]