968 Supercharger Kit Development
03-03-2011, 03:52 AM
#1006
Three Wheelin'
We are improving our Stage 1 and Stage 2 kits.
Very few who are driving our 968 kit on the street as designed are experiencing any belt slip issues. However, those who DE Day or track the car have reported belt slip - we are adjusting our kit to eliminate belt slip for all.
Stage 1: the new Stage 1 pulley is in production now and is slightly larger, knurled across the entire face, and hard-coated for toughness. This improved supercharger pulley will be available as a free upgrade to all current kit owners.
I expect it to be ready to ship in about 3-4 weeks.
Stage 2: we are designing and manufacturing a billet alluminum crank pulley for the 968 now for the Stage 2 kits. This is similar to those we make for our other Porsche and Ferrari kits. This will speed up the blower without loosing tractive force normally associated with going to a smaller supercharger pulley.
The Stage 2 pulley will be available at cost to current Stage 2 kit owners, and retail pricing on the Stage 2 kit will go up as a result of the added part supplied.
Very few who are driving our 968 kit on the street as designed are experiencing any belt slip issues. However, those who DE Day or track the car have reported belt slip - we are adjusting our kit to eliminate belt slip for all.
Stage 1: the new Stage 1 pulley is in production now and is slightly larger, knurled across the entire face, and hard-coated for toughness. This improved supercharger pulley will be available as a free upgrade to all current kit owners.
I expect it to be ready to ship in about 3-4 weeks.
Stage 2: we are designing and manufacturing a billet alluminum crank pulley for the 968 now for the Stage 2 kits. This is similar to those we make for our other Porsche and Ferrari kits. This will speed up the blower without loosing tractive force normally associated with going to a smaller supercharger pulley.
The Stage 2 pulley will be available at cost to current Stage 2 kit owners, and retail pricing on the Stage 2 kit will go up as a result of the added part supplied.
Last edited by Eric_Oz_S2; 03-03-2011 at 04:54 AM.
03-03-2011, 04:34 AM
#1007
Instructor
Join Date: Dec 2008
Location: bahrain
Posts: 183
Likes: 0
Received 0 Likes
on
0 Posts
Just an observation Karl
Knurling the pully and toughening it ,wouldnt shorten the belt life by eating away the top layer of the belt covering the poly vee on the other side?
Going bigger of course offers more surface for grip.
GILMER belts also would avoid any problems from the begining ,similar to the
dry sump pump systems,or as per the cam belts.Positive grip all time.
Knurling the pully and toughening it ,wouldnt shorten the belt life by eating away the top layer of the belt covering the poly vee on the other side?
Going bigger of course offers more surface for grip.
GILMER belts also would avoid any problems from the begining ,similar to the
dry sump pump systems,or as per the cam belts.Positive grip all time.
03-03-2011, 09:56 AM
#1008
Nordschleife Master
The issue is finding the correct size, and believe me I have tried and am still working on it. With the larger crank pulley and SC pulley, we may be getting close to making a double-sided belt work.
03-03-2011, 04:13 PM
#1009
Addict
Rennlist Member
Rennlist Member
I have not been having a problem with belt slip on the street but I keep my belt very tight. A double sided belt would be an improvement, but the shortest double sided belt on the market is too long by about 5"
However I looked at my spare engine the other day and I think it might be possible to run a double sided belt if another idler is located above the AC compressor. Ideally it would add wrap to the crank pulley by routing the belt over this new idler between the AC pump and the crank, but it'd be easier to run the belt over this idler between the alternator and AC compressor.
When I looked at this problem before I only looked at fooling with the reversing idler size and location and came up dry. I wish at that time, when I had the double sided belt in hand, I thought of this other option.
In a perfect world there would be a way to put a chevy spring belt tensioner in that spot to make belt tension constant and easy to set.
-Joel.
However I looked at my spare engine the other day and I think it might be possible to run a double sided belt if another idler is located above the AC compressor. Ideally it would add wrap to the crank pulley by routing the belt over this new idler between the AC pump and the crank, but it'd be easier to run the belt over this idler between the alternator and AC compressor.
When I looked at this problem before I only looked at fooling with the reversing idler size and location and came up dry. I wish at that time, when I had the double sided belt in hand, I thought of this other option.
In a perfect world there would be a way to put a chevy spring belt tensioner in that spot to make belt tension constant and easy to set.
-Joel.
03-04-2011, 12:57 PM
#1012
Developer
Thread Starter
The double-sided belts were made very briefly for one year of Corvette. They do not come in different sizes. So far, I have never found the length we have needed.
03-05-2011, 09:00 AM
#1013
Addict
Rennlist Member
Rennlist Member
Maybe someone like this will make a shorter belt:
http://www.cptbelts.com/
If not these guys, I'm sure there is a supplier out there who can make them. The long belt can probably be cut, spliced and sewn or glued up to test a shorter length.
There appear to be a lot of companies in China making belts as well and some of these outfits will do small runs.
http://www.acron.com.cn/enproduct_show.asp?id=23
That's one example. I also found a place in Germany that has a minimum order of 100 that might also do it.
For testing, The long belt can probably be cut, spliced and sewn / glued up to test the shorter length. Just cut each layer off in steps over several inches of length and clamp it up with belt scraps for tooth alignment.
-Joel.
http://www.cptbelts.com/
If not these guys, I'm sure there is a supplier out there who can make them. The long belt can probably be cut, spliced and sewn or glued up to test a shorter length.
There appear to be a lot of companies in China making belts as well and some of these outfits will do small runs.
http://www.acron.com.cn/enproduct_show.asp?id=23
That's one example. I also found a place in Germany that has a minimum order of 100 that might also do it.
For testing, The long belt can probably be cut, spliced and sewn / glued up to test the shorter length. Just cut each layer off in steps over several inches of length and clamp it up with belt scraps for tooth alignment.
-Joel.
03-15-2011, 09:44 PM
#1014
Addict
Rennlist Member
Rennlist Member
Update - I am working on a solution using the Corvette double sided belt. I should be able to test the fit of the belt and a new lower idler.
Tim's idea of a larger pulley between the alternator and AC pump might also work to use up maybe 2" of the excess belt but does not add wrap to the crank pulley and you still have 3" more belt to contend with.
For racing you might be set with a bigger idler and a larger alternator pulley. It might not charge well at idle but for racing this is not a big concern. The lowered alternator drag might buy you a fraction of an HP also (whee.) I do not know if an uprated voltage regulator would help with that. I doubt that is a solution for the street. A larger alternator pulley might also interfere with the larger idler.
My favorite solution to this problem thus far is to put a pulley down between the crank and AC pump. My measurements suggest it might have to mount so low that the lower timing belt cover would need to be trimmed to clear it, but I still hope it might fit higher than that and present no significant technical challenges.
Does anyone know if the crank pulley on a 968 is the same size as the pulley on a 951? I have a 951 engine in my shop I have been using to figure some of this out.
-Joel.
Tim's idea of a larger pulley between the alternator and AC pump might also work to use up maybe 2" of the excess belt but does not add wrap to the crank pulley and you still have 3" more belt to contend with.
For racing you might be set with a bigger idler and a larger alternator pulley. It might not charge well at idle but for racing this is not a big concern. The lowered alternator drag might buy you a fraction of an HP also (whee.) I do not know if an uprated voltage regulator would help with that. I doubt that is a solution for the street. A larger alternator pulley might also interfere with the larger idler.
My favorite solution to this problem thus far is to put a pulley down between the crank and AC pump. My measurements suggest it might have to mount so low that the lower timing belt cover would need to be trimmed to clear it, but I still hope it might fit higher than that and present no significant technical challenges.
Does anyone know if the crank pulley on a 968 is the same size as the pulley on a 951? I have a 951 engine in my shop I have been using to figure some of this out.
-Joel.
03-15-2011, 10:02 PM
#1015
Nordschleife Master
Joel,
I'll be interested in your results. I believe that the crank pulleys are the same size for the 951 and 968 but do not have pet here to confirm. My extra 968 pulley is currently in Carl's hands. Carl mentioned earlier that we are working on a stage II racing solution. Hopefully more soon.
I'll be interested in your results. I believe that the crank pulleys are the same size for the 951 and 968 but do not have pet here to confirm. My extra 968 pulley is currently in Carl's hands. Carl mentioned earlier that we are working on a stage II racing solution. Hopefully more soon.
03-16-2011, 10:39 AM
#1016
Developer
Thread Starter
Joel's direction is a little different than mine, he's trying to get a double-sided 6-rib belt in there. I'm supplying him with a few bits while he experiments.
I picked up the new supercharger drive pulleys yesterday and they look fantastic. I have sent them off to be hard-coated now, turn-around is usually under a week. That will help those racers in Stage 1 who have had belt slip issues (again, street-driven kits have not).
For Stage II, I am developing a larger crank pulley to increase supercharger speed without making the supercharger drive pulley any smaller. That's why I have Tim's 968 crank pulley (Thank's Tim!)
I picked up the new supercharger drive pulleys yesterday and they look fantastic. I have sent them off to be hard-coated now, turn-around is usually under a week. That will help those racers in Stage 1 who have had belt slip issues (again, street-driven kits have not).
For Stage II, I am developing a larger crank pulley to increase supercharger speed without making the supercharger drive pulley any smaller. That's why I have Tim's 968 crank pulley (Thank's Tim!)
03-16-2011, 05:01 PM
#1017
That sound promising.
I`m currently running n/a and getting to drive the car, whilst the belt slip is being sorted through the pulley upgrade.
An idea I have looked at, is a tensioner located between the primary and secondary mounts, though not a lot of space, to push/run the belt lower down to the s/c pulley and get more wrap on it. It could`nt be achieved below the pulley, because of the profile of the belt covers and run of the belt to the crank.
If a bigger crank pulley was made the covers would have to be removed or cut away
I`m currently running n/a and getting to drive the car, whilst the belt slip is being sorted through the pulley upgrade.
An idea I have looked at, is a tensioner located between the primary and secondary mounts, though not a lot of space, to push/run the belt lower down to the s/c pulley and get more wrap on it. It could`nt be achieved below the pulley, because of the profile of the belt covers and run of the belt to the crank.
If a bigger crank pulley was made the covers would have to be removed or cut away
03-24-2011, 01:40 AM
#1019
Addict
Rennlist Member
Rennlist Member
Update: I got the belt and did some test fitting. As I suspected, I can't put the pulley where I'd like to without making some other changes. It's possible however and would probably work as a solution.
In the spot where I wanted to put an idler, a 37mm 944 timing belt idler will fit and would use up enough belt to make the double sided belt fit. this idler is a bit small IMO and lacks flanges, however the belt would be managed well by the grooves in the AC and crank pulleys.
It should be possible to move that idler higher and use a larger diameter idler if some belt is gained back by going with a smaller reversing idler. The downside here is that it would slightly reduce SC pulley wrap and this is not desired. I could also for testing use an eccentric idler here to move the belt down a bit and maintain the wrap. Lots of options.
What I will probably try first however is simpler and should be sufficient for my needs. If I make a bracket to move Carl's idler inboard a ways, that would use up some belt. If need be a larger idler could be used in it's place and there are several inexpensive choices. This fix does not increase crank wrap but it could be that there is enough traction at the crank to drive the SC at these HP levels.
A bracket should be quite simple, there is an alternator bolt and a hole in the accessory bracket that would locate both ends of a section of channel steel or whatever. It might take a couple fries to get it right, or I could put that eccentric down there for now which will give me some kentucky windage, and then I could get started on fitting a grooved pulley. This would be easier if I still had access to the machine shop at my old place of work. If anybody feels like buying me a Harbor Freight mini precision lathe I am totally OK with that and have a 20% off coupon.
Anyway fret ye not this will get done one way or another.
-Joel.
In the spot where I wanted to put an idler, a 37mm 944 timing belt idler will fit and would use up enough belt to make the double sided belt fit. this idler is a bit small IMO and lacks flanges, however the belt would be managed well by the grooves in the AC and crank pulleys.
It should be possible to move that idler higher and use a larger diameter idler if some belt is gained back by going with a smaller reversing idler. The downside here is that it would slightly reduce SC pulley wrap and this is not desired. I could also for testing use an eccentric idler here to move the belt down a bit and maintain the wrap. Lots of options.
What I will probably try first however is simpler and should be sufficient for my needs. If I make a bracket to move Carl's idler inboard a ways, that would use up some belt. If need be a larger idler could be used in it's place and there are several inexpensive choices. This fix does not increase crank wrap but it could be that there is enough traction at the crank to drive the SC at these HP levels.
A bracket should be quite simple, there is an alternator bolt and a hole in the accessory bracket that would locate both ends of a section of channel steel or whatever. It might take a couple fries to get it right, or I could put that eccentric down there for now which will give me some kentucky windage, and then I could get started on fitting a grooved pulley. This would be easier if I still had access to the machine shop at my old place of work. If anybody feels like buying me a Harbor Freight mini precision lathe I am totally OK with that and have a 20% off coupon.
Anyway fret ye not this will get done one way or another.
-Joel.