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so when you say “under drive” it reads like that is what you are calling the lower crank pulley. If so, stock means it’s stock diameter. When we all say under drive we mean that it’s xx% under driven to slow down accessories driven from crank pulley to typically free up a few horsepower or make rev a bit snappier. I don’t know many cases where someone would under drive a crank pulley with a blower attached. I know folks will over drive them so the upper pulley doesn’t have to be as small to help with better belt wrap.
just trying to help with terminology used here, that’s all.
My mistake, I wrote that late one evening and wasn't thinking in the moment. Yes, you are correct, I was referring to the crank pulley. Thank you.
Originally Posted by old motorhead
I had a really hard time eliminating belt slip on my Heartbeat setup. I had a bigger pulley than you and a blower cam. Both of which will lower boost compared to how your setup. My boost peaked at 9.9psi at about 2500rpm and stayed right at 9.5psi through the run. Short of a worn out blower or other mechanical issues, you should be north of 11psi. Assuming low altitude.
The first thing I'd do is to make sure your serp belt isn't too long. Your belt stretches as boost and rpm go up. The belt also stretches with age. Your belt may seem nice and tight now. That's may not be the case once you go WOT. If you can compress the tensioner much at all, your belt is too long. You need to use the shortest belt you can get on there....with two people. That way the tensioner has a long stroke before losing the ability to keep the belt tight. This video is probably worth a thousand of my words: Video: Watch a Supercharger Belt Tensioner at Work| Videos | Grassroots Motorsports
Very interesting. I'll say that I can move the tension relatively easily.. So it very well could be slipping. Side by side on both of my corvettes I'll say maybe the LS2 car is 10% tighter than the Heartbeat car as far as ease of moving the tensioner. Based on what you said, I'll assume that that should not be the case and that it should be much, much tighter being a blower car.
Did you ever upgrade the 6 rib to an 8 or with that belt were you able to control it?
What all is needed to go from a 6 rib setup to an 8 or 10? Aftermarket tensioner and wider alternator pulley? I'll do some research but figured I'd ask while i'm posting.
My mistake, I wrote that late one evening and wasn't thinking in the moment. Yes, you are correct, I was referring to the crank pulley. Thank you.
Very interesting. I'll say that I can move the tension relatively easily.. So it very well could be slipping. Side by side on both of my corvettes I'll say maybe the LS2 car is 10% tighter than the Heartbeat car as far as ease of moving the tensioner. Based on what you said, I'll assume that that should not be the case and that it should be much, much tighter being a blower car.
Did you ever upgrade the 6 rib to an 8 or with that belt were you able to control it?
What all is needed to go from a 6 rib setup to an 8 or 10? Aftermarket tensioner and wider alternator pulley? I'll do some research but figured I'd ask while i'm posting.
Pretty much sea level ~600ft
Flat midwest.
Innovators west sells full kits like this. One thing to keep in mind is when you go 10% OD on the crank, it would be prudent to get a larger diameter alternator pulley to underdrive the alternator. If stock alternator IW makes one, if Mechman alternator then Mechman offers one (from a Ford application if I remember correctly) Any loss of idle charging output should be negated by higher idle rpm when running an aftermarket camshaft. If you run a camshaft, often you will stretch the RPMs a little further up the tach so again you'd want to underdrive that alternator. More so on a stock alternator versus a higher end built unit like a Mechman for example. I run a 170a mechman with the above mentioned Ford pulley. (8rib) Kinda wishing I'd have 10 rib but 8 rib will get you quite far, a variable to that is specific belt routing/configuration which varies from engine/blower combo to engine/blower combo. It's not only about belt slip, but overall belt control. Wider belt will stretch less and flutter/waver less, and thus require less tensioner travel. Again, specific combinations required varying amounts of addressing with extra idlers to increase crank wrap etc. The fact you're coming from a 6 rib.....everything can only improve from there for you by going 8 rib.
Before you add ribs (and expense), try what worked for me. I don't remember the belt exact belt length. The way to find out the shortest one you can get on there is to grab a couple shorter than the one you have now from your local auto parts store. The one that's sized right will be tough to get on with the tensioner compressed. If it goes on easily, it's too long. Find the correct length and then order the Gatorback belt in that length.
It doesn't matter how tight you think the belt is with the engine stopped. The belt stretches under load. If the tensioner is out of travel after the belt stretches, your belt will slip. So, you need to have the tensioner all the way compressed when your engine isn't running. If the belt is too long, it gives up some of the travel it needs to keep the belt tight. Not sure I'm painting a clear enough picture.
I need to replace the belt anyways as its getting old. I'll buy a size or two down and give it a shot. I will say, however, that there are no signs of belt material anywhere on the pulleys or engine bay so I find it hard to believe that is the primary issue. The current belt that was on it is a 98" so i'll try some 97" sizes and see.
I guess if I can get away with using this 6 rib setup I will try to do so, based on the price of that IW pulley kit.
Ok so as far as belts this is what we are looking at:
Car came with an Autozone 975K6 which is a 98" serpentine belt. I purchased a 97 5/8" and a 97 1/16" belt for testing purposes. Both belts fit without a ton of work to get them on.
I am not sure where the tension should sit without the engine running or with off. I attached two pictures: one showing engine off with 3 pencil marks as far as where the tensioner sits with no engine running load on it on the 3 different size belts and one with the original 98" belt with the engine running to show tensioner position...
Just in case anyone has a similar setup, or has seen a similar setup and know where this thing needs to sit. I imagine the 3 tick marks cast into the part are a signifier of where it should sit but I am unsure.
Belt slip may not be an issue but belt stretch very well could be. TIA
Green is the tightest you want to run a belt, yellow is what GM will tell you a new belt should run at, and orange means you've stretched/worn a belt to it's Max length for effective tension.
The problem with using an undersized belt for the drive needs of a blower is belt stretch. Let's say you run it at yellow which is proper to allow for ample tensioner movement in both directions, one for accel, the other for decel/gear changes (moreso on manual transmissions.) With a 6 rib your operating window will be wider because of the percentage of belt growth. Go to 8 rib and the operating window will narrow, and 10 rib would be even narrower.
It's simple really. GM engineers know what they are doing so follow their lead. GM used a 6 rib belt on a naturally aspirated Corvette, when they decided to bolt a 2300 cubic centimeter compressor on the engine, they stepped it up to an 11 rib (83-ish" long). When they put a 1900 cubic centimeter compressor on an LSA they used an 8 rib (66-ish" long) (dedicated belt even) and when they did a 1,740 cc compressor on a LT4 they used an 8 rib (84-ish inch long). Check with Ford on their supercharged stuff, also check with Mopar on their supercharged stuff. You aren't going to find 6 rib belts. So a 98" long 6 rib is NOT ideal.
Last edited by streetking408ys; 05-27-2024 at 02:36 PM.
The green Gates belts are called Fleetrunner.
"According to tensioner marks you are still in wear range" is inaccurate." First off It's arguable (if the deep v groove is the point of reference) that a stock engine with stock 6 rib is slightly beyond it's loose side threshold but that's neither here nor there so I digress. This is a supercharged engine that has a supercharger that's going to take up around 143 horsepower to spin (this is on the high side of max effort but still important) so that belt is going to STRETCH. What IS important is the actual real world stretch that little PK6 belt stretches during a WOT pull throughout the entire rpm range. This is where systems/configurations that use longer belts show one of their biggest cons. Longer belts stretch more. X% of a larger number is more stretch. If statically the tensioner is at the current orange mark and let's say you're on the dyno rolling in 4th gear and you go WOT at 2500rpm.......let's assume rev limiter at 6500.......so at what RPM point will the belt stretch of a 98" long belt run out of tensioner swing? If the tensioner locks out at 5500 rpm....you've now lost your tension up to 6500. If you had a shorter belt.....in the proper yellow range to start the run......depending on how much stretch you have AND (we are throwing in a new variable here) how much spring tension is in said tensioner. It looks to me that's just a poopy stock tensioner. A tensioner engineered to apply enough tensioner on a belt that drives common automotive accessories like an alternator/water pump, power steering. So here we are back at the crossroads of what I mentioned in an earlier reply, you need more belt (width, ie contact surface) Many people recommend things they may very well get away with, and you may also....but it's not the proper way. Spinning a pulley that has a high power demand comes down to 2 variables. Contact surface of belt/pulley and tension. You'll need to mix/match these 2 variables to get a desired result (no belt slip) You want as much contact as possible which will require as little tension as possible. Tension causes it's own issues, hard on bearings of the blower, hard on bearings in alternators, can pull shafts out of power steering pumps, can damage main bearings, can pull the pressed pulley off a water pump, belt damage etc. A wider belt will have less stretch, thus effectively requiring a tensioner that doesn't need 40 degrees of travel. Of course some people will tell you to have someone yank that tensioner over with a 3 foot breaker bar while you use both hands and all your might to get the belt popped on over a smooth idler. That's band-aiding. Belt needs swing on the tight side too for engine decel. Anyway. now that's out of the way, here is what Gates offers for shorter belts in Fleetrunner near your size.
I've had three TVS2300's on a few LS engines. A front drive on my work truck for well in excess of 250K miles. A jackshaft 2300 on my first C6 for 40K miles, and a Heartbeat 2300 on my second C6 for probably another 40K miles. Blower pulleys on all of them were between 3.1 and 3.3". The jackshaft 2300 had 1:1 rear pulleys so it's essentially the same.
I used the shortest serp belt that would fit on all of them. Never had any problem with any front mounted accessories, idler pulleys, or tensioners. Lots of WOT runs and trips to the strip. My truck ran low 12's at 5000#'s and it embarrassed lots of "muscle cars" at the strip. My vettes ran 10's rowing gears. Maybe I don't know what I'm talking about though.
Lots of way to skin your cat. Some don't cost much and work fine. Some cost a lot and may work fine too.
05-22-2024, 06:40 AM
