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This has been killin me. I cant find any information on it, I hope someone out there knows. I have a Eaton supercharger on my car in a custom installation. Its currently driven by my factory style 5 rib serp belt. I am at the point where i suspect it is slipping on the belt drive system after a certain RPM. What I cannot find is any way to calculate what a Gates 5 rib serp belt can handle as far as power transmission and traction on the pulleys. I dont like to "throw parts" at problems until they are fixed, I think its far cheaper to calculate and troubleshoot, then fix it right the first time... but im coming up short on any specifics about belt drives. I was also looking at changing over to a cogged belt and pulley system to guarantee no slippage, but again, only if i can prove that my current belt is a liability. where can i find info? thanks
 

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The serpentine system you have has a tension designed for the OEM application. If you increase the tension you may get more boost but possibly to the detriment of other acceories bearings. On Procharged smaller centrifugal systems six rib belts rarely produce much over 650hp. There are some 8 rib non serpentine (dedicated systems) that produce 900hp -1000hp.....At around or below that level most make the switch to cogged...then reverse drive(short cogged) and ultimately gear driven.....

You could tighten it a little and see where you go from there ....The cost of changing all the accessries to cogged is prohibitive/not possible with idlers on both sides etc. What car, engine, rpm range , power goal, compression etc have you got?....

Oh, and welcome to the site. You're lucky you weren't flamed!!!!!!!
 

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I am running a built GM Quad 4 DOHC 2.3L 4 Cyl Engine with lowered compression to 8.5:1 pistons. I have installed a Eaton M90 Roots supercharger onto the motor, but first discharge thru a very large front mount intercooler to bring the temps down, and top it off with Alky injection. Im running a 1.91 belt drive ratio, my max motor RPM is 7500, bring the max supercharger speed to 14,000-15,000 RPMs. At these speeds, my charger's flow map indicates I should be ingesting 600 CFM's. My current boost pressure is 12-14 PSI, (or 180kpa).

The problem is, right around 4800 RPMS, my HP flatlines, and just holds its current level. So, lets say I make 210WHP @ 4800 RPMs, well, I make pretty much that exact same power all the way to redline (7500). This is the reason I believe my belt is slipping...

At 4800 Engine RPMs, with a 1.91:1 drive ratio, my charger is going 9,170 RPM's. My chargers flow map indicates it should be ingesting 380 CFMs. If you take the simple quick formula to figure out CFM to HP by mulitpling by .7, you get... 380 x .7 = 266 at the crank. So, with a supercharger pulling on that and the drive train loss, I'd say its pretty consistant with 210 WHP. But since my HP stops building there, I can only assume my airflow stalls at this speed. Since its a positive displacement pump, The only way to do that is to slip on the belt right?

If i am capable of 600 CFM's, then 600 x .7 = 420, So I think I should be seeing probably 375'ish at the wheels, but Im only seeing half that! Im sure there is a major problem somewhere, and Ive tried just about everything, it MUST be belt slip.

Im running a Regular Gates 5 Rib Micro-v Serp belt, with a factory spingloaded automatic tensioner. I did change the way my belt routes, and added an extra idler pulley to increase belt wrap on both the crank and SC'r pulley, and did pick up some power, but like i said, Im still down by half, and there is still a major problem.

Also, my chargers data maps indicate that at 9000 RPMs, it will be consuming around 30 HP from the crank... and at 15000 it will be demanding 50HP! So, am willing to bet 30HP is the limit of a 5 rib micro-v belt, what do you think?



 

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Both the above comments are correct check that first.....

Do you know what happens to the boost from 4800 till 7500 engine rpm. If it drops as you consume more cfm then investigate the belt slip and blower efficiency/size.

What's the N/A power curve? Did it make power past 4800 rpm when it was N/A if not, take a look at your head, manifold and cam....If it did make power up top when N/A then have a look at your ignition and timing...
 

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I dont have much experience with blowers myself, but I know quite a few people that do. About all of them have had the slippage problem. Im going to take a guess that you do as well. Especially if you added an extra idler for more "wrap" and it helped the problem. From what Ive seen most everyone switches to cogs. The sticky belt dressing that mrtbolt64 mentioned would be a good idea I think. If that helps even more, then you probably have a slippage problem.
 

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Great questions. Yes, the N/A form of this motor STOCK will produce 180 HP at the crank and continues building HP thru the entire RPM band, here is a FLYWHEEL dyno of a stock motor similar to mine in most every aspect except i have lower compression ratio, custom race header, and strenth mods....



The boost does appear to suffer a slight loss as RPM increases from 4800 to 7500. I would expect it to "creap" up higher during this time as the engine moved farther away from its VE efficency range, but just the opposite is happening. Again, this leads me to believe the engines demand is outrunning the superchargers output. N/A this engine consumes 280 CFM's at peak power, which occurs at 6300 RPM's. So, I believe the SC'r is outputting all it can, then it begins to slip around the 380CFM mark, but the engine is continually "catching up", so im losing boost pressure as RPM increases. sound logical?
Here is a screenshot of my datalog from a 1/4mi pass last friday night. The HP curve is only accurate for 3rd gear, becuase i have to input my FDR, gear ratio, tire OD, vehicle wieght so it can calculate HP from RPM rate of change. This will only be accurate for the one gear of my choosing when i input the numbers, and the gear i chose was 3rd gear. Have a look at the WHITE trend line in the bottom window, this represents actual WHP. Notice its losing as RPM increases. Also notice the RED trend line in the same window.. this trend represents what WHP "Should" be based on mainly on theoretical airflow, basically, IF i have the air coming in that i think i do, This is what my WHP should be at each RPM point. you can see the redline moves up with RPM, the WHITE line is always falling from the "projected" line, never gaining.
Also, look at the TEAL colored line at the very top. this trend line represents my boost pressure. notice it also falls slightly at RPM increases.




The engine is controlled exclusively by Megasquirt. I have full control over Spark and Fueling via a laptop. my current ignition and Volumetric Efficiency settings also in the above picture on the right hand side. Top table is VE, bottom table is spark. Tuned with Innovate LC-1 wideband system.


Im sure someone is going to say "you cant trust that method for WHP". To you i say, i was also skeptical, and so purchased a GTech Pro RR Performance meter, and ran it in the car. That too also confirmed what my mathmatics AND what megasquirt said. So, thats three things all saying the same thing. No, I am not paying 125 dollars and draging this car to a inertia dyno to quadruple confirm what i already know. Megasquirt is an onboard inertial dyno on its own. If you know how an inertia dyno works, you will agree that the method Megasquirt is working on to calculate HP is the same way a dyno shop is going to tell me. my car wieghts 3000lbs with driver, and runs 97MPH in the quarter, theres another confirmation of 210-220 WHP. I dont want to argue this point anymore than this. Here is the Gtech screen...



now, on the Gtech screen, this graph was taken proir to me redesigning my pulley system and adding a pulley, and increasing belt wrap. After, I know make 210whp. If you follow the "ramp" it was on before it levled out, you will see that 210whp would have been somewhere in the neighborhood of 4800 to 5000 RPMs. After doing my belt upgrade, i have in fact made these exact numbers. but when it gets to the new 5000 RPM level, it plateau's again.
So, belt slip? I do not see any dusting in my engine bay. thats why I cant say for cetain. But everything else looks like its pointing that way.
 

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Discussion Starter #9
so, lets pretend none of the above happened...
Does any one know how to calculate how much power you can transmit thru a serptentine belt?
 

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I doubt you will find any hard and fast way to calculate the hp potential of a serp belt. There are just too many variables (durometer of rubber of the belt, exact contact area of belt to pulleys, turque load applied to the belt, coefficient of friction between teh belt and the pulleys, tension applied to the belt, etc....). If I were you I would experiment around with increased belt tension first. Then I would look into adapting a mass air flow sensor into the tubing coming out of the intercooler to see what the actual airflow into the engine is. You could also try it before the intercooler to compare the airflow loss through the intercooler. Using a built in or separate IAT sensor could tell the effectiveness of the intercooler too.
 

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Ive been on www.gates.com all day long. I've been specing out a PolyChain GT2 belt drive system, just to see what it would cost for the belt, sprockets, and bushings. WOW! looking like 500-600 bux! Then I would still be faced with rigging up a custom tensioner somehow. But the sizing guide was able to take into account my speed ratio and load HP to come up with a Tooth Pitch, Belt lenth, belt width, and ultimately a belt P/N. Then did the same for finding the correct pulleys and bushings to go with them. However, they could not do the same for a multi-v belt. I dont see what the diff is. I guess I should just email them and ask the source.
 

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so, lets pretend none of the above happened...
Does any one know how to calculate how much power you can transmit thru a serptentine belt?
if you have any doubt. its time to switch to a better drive system. just remember use as big of a top wheel as you can. they are the weak link when it comes to spinning a blower hard.
 

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I had an 88 Cutlass Calais with the Quad 4... Always wanted to put a turbo on it, but never got around to it.

Are you logging your A/F ratios and injector cycle duty time? If it's running out of air, then the cycle duty on the injector should slow down as the computer pulls fuel out to keep the A/F correct. Right?
 

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Are you logging your A/F ratios and injector cycle duty time? If it's running out of air, then the cycle duty on the injector should slow down as the computer pulls fuel out to keep the A/F correct. Right ?
You are correct, My boost does tapper down with increased RPMs, and Volumetic Efficiency does hold steady after a certain RPM, indicating that airflow is holding a particular level and going no further, even thought the engine is consuming all that is thrown at it. I guess the more I lay my thoughts out all together, the more it makes the case clearer for me, its belt slip, cant be anything else.

I had an 88 Cutlass Calais with the Quad 4... Always wanted to put a turbo on it, but never got around to it.
Well, another Quad 4 fan, excellent. Here's the first one I built...



but then I wanted to swap to a Beretta GTZ, and remote mount the charger so i could run an FMIC, so here that is...







And I have the charger mounted down the front of the engine where the A/C compressor used to go, like this...

 

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a vac. gauge on the inlet side should give a indication of this.:smt115
been there, done that. Not only do I have a LS1 75MM TB going to a 3" dia pipe feeding the inlet of this charger, I did put a vac port in the piping right infront of the charger inlet and measured at WOT for any differance from 98KPA (1 atmoshere where I live) , I dropped about 1.5KPA, meaning i dont have any restriction letting air in... but all that speaks nothing of what the charger is doing mechanically, if its slipping in the belts, well then it wouldnt be trying to take in but so much... and upto that point, I dont have any intake restrictions. But, thanks for the tip.
 

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You are correct, My boost does tapper down with increased RPMs, and Volumetic Efficiency does hold steady after a certain RPM, indicating that airflow is holding a particular level and going no further, even thought the engine is consuming all that is thrown at it. I guess the more I lay my thoughts out all together, the more it makes the case clearer for me, its belt slip, cant be anything else.
There ya have it and there ya are. No need to know how much power the belt will hold, just important to know that you are exceeding it.

Time for either a belt with more ribs, as previously mentioned, or a toothed timing belt.

The guys over at http://rcdengineering.com/ will make what you want, although probably not at a price you like.
 
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