Drive a S/C off the cam pulley instead of the crank nose.

[Rabbit on Roids]

ok, so, is the cam strong enough to have say, a 7 or 8 inch serp pulley mounted to the cam sprocket to drive a supercharger? or is that just asking to break the cam or timing belt or something? you would still be driving the s/c by the crank pulley, but you would be using the timing belt as an intermediate belt. and then the load from the charger would be taken by the cam shaft instead of directly on the crank nose.

the more im thinking about this, the more im not sure if the timing belt would be up to the additional task of a large s/c. volvo penta diesels have a supercharger drive system somewhat similar to this also, as the supercharger is not driven directly from the crank. it has a LARGE pulley directly above the harmonic balancer, and that one drives the s/c.

anyone else have any input as to why it would or would not work?

[RabbitJockey]

i think it'd be fine, i guess you've never seen a magna charger

[Rabbit on Roids]

wow... thats... friggen gorgeous.

yes, thats exactly what i want to do. i kinda half expected it to be impossible or something..

[Rabbit on Roids]

no, im going to mount the serp pulley to the cam sprocket. not the cam. there is going to be no additional load on the cam. and besides, my cam does have a key in it. 

every time ive had to time it, i left the key out, timed it, set the key back in, and the sprocket slid back on every time just right. i see no reason not to run with a key as long as it times out right.

[Rabbit on Roids]

i think it'd be fine, i guess you've never seen a magna charger

the more i look at this car, the more i doubt im going to be able to use a 8" pulley like i want to.  only problem is, im gonna run a charger with a 3" or so pulley on it and i dunno if you can get anything much smaller. right now im thinking that the s/c rpm will be right around 9-10k with engine RPM at 6k and a 8" or so pulley driving the s/c. is that going to be enough? cause i know that an M90 is rated for 12,500 rpm, and 15 psi boost. how fast is an ideal s/c speed?

[G60ING]

no, im going to mount the serp pulley to the cam sprocket. not the cam. there is going to be no additional load on the cam. and besides, my cam does have a key in it. 

every time ive had to time it, i left the key out, timed it, set the key back in, and the sprocket slid back on every time just right. i see no reason not to run with a key as long as it times out right.

I wouldn't put any additional stress on the cam sprocket. The Crank sprockets have a keyway or a flat spot with a lot stronger bolt setup and they still give way. If the Cam/sprocket was Keyed then I'd say give it a shot but not on a diesel unkeyed setup.

When I saw the topic's title I envisioned one of the mk1 gasser autotech charger combos.

[lovinthedeez]

isn't that otti's car (or his friends)? its all over the vortex

[gldgti]

decide how much boost you want, then you can figure out hte sproket size you need. roughly speaking, (and i mean roughly) all you do is take the supercharger volume (roots blowers sweep a certain volume per revolution) and relate that to your engine volume. a 1.5 needs 750cc of air per revolution, and if the superchager displaces 2 litres per rev, then running it at 1:1 might get you more than 15psi... i dunno what SC you want to use though.... although, 1:1 o nthe crank has gotta be 2:1 form the cam i guess :-)

[OM617]

I get what you're saying.  Right on.  I can't see why it wouldn't work.

Except you'll snap the belt in a very short time. It already has to transmit 20+hp to drive the cam and injection pump. Adding another 20hp to drive a supercharger wouldn't be good for durability. You'll also need a MUCH larger pulley on the cam. The one in the picture is only 1.25-1.5x crank rpm, thats why its unusually large for that engine.

[Rabbit on Roids]

no, im going to mount the serp pulley to the cam sprocket. not the cam. there is going to be no additional load on the cam. and besides, my cam does have a key in it. 

every time ive had to time it, i left the key out, timed it, set the key back in, and the sprocket slid back on every time just right. i see no reason not to run with a key as long as it times out right.

I wouldn't put any additional stress on the cam sprocket. The Crank sprockets have a keyway or a flat spot with a lot stronger bolt setup and they still give way. If the Cam/sprocket was Keyed then I'd say give it a shot but not on a diesel unkeyed setup.

When I saw the topic's title I envisioned one of the mk1 gasser autotech charger combos.

again, im not going to be stressing the cam. and it has a key in the keyway. the charger pulley is going to be bolted to the cam sprocket. and im using an M90 on a 90 cubic inch engine. so are you guys saying that im gonna want it drivven at a fairly low RPM?

the little flat spot that holds the crank sprocket from spinning, i dont dig it..

and OM617, i knew you would have some reason as to why it wouldnt work. but there again, why does the gasser magna charger work? it uses a EVEN SMALLER belt than a diesel engine. and it has no problem driving the s/c, im shaft, and cam. i doubt they snap belts very often. if you look at a diesel timing belt, its heavy duty.. way more than a gasser belt. its half again wider, and alot thicker too. even if i do snap a timing belt, oh well. i had a supercharged diesel for a little while and you didnt... lol

[Rabbit on Roids]

ROR is right, if the two sprockets are bolted together then the interface of cam and sprocket will not be stressed more than is stock form other than perhaps a bit of added imbalance from the added sprocket.  The stress on the timing belt would be increased.  If I were running like that I'd shorten the timing belt interval.  Maybe make it 30K instead of 60K miles.  If it failed you'd know you should have changed it sooner...

PFFFFT... if im gonna be building something like this, its gonna get new belts twice a year. im thinking 10 or 15k mile intervals.  its gonna be 100% trial and error, but hey, its not like i will be out anything if the setup doesnt work.

another thing, i know VW cams are TOUGH. if you take a small block chev cam and drop it on the concrete, it goes *BOOM*
if you drop a VW cam on the concrete, you pick it up, dust it off, and install it back in the engine you are working on.

crap, i really feel like i accomplished a DECENT idea. if andrew is agreeing, then i must be going in somewhat the right direction...

and its kinda nice knowing that im not going to need a super HUGE pulley to drive the M90 (i know, its rather large, but it was free)

[RabbitJockey]

m90 are huge aren't they?

[Rabbit on Roids]

m90 are huge aren't they?

yea, they are rather big for a 1.5, they came stock on 3.8's and could be used pretty easy on a V8 with a little over drive for the s/c. but, being that its so big, i shouldnt have to work it hard at all to do what i want with it. i should be able to keep it under driven (slower than crank speed) and still make decent boost.

[truckinwagen]

the problem with under-driving an eaton is that they are so inefficient at low rotational speeds, that you may not see any boost at all.

they really need to be spun fast to overcome thier leakback.

[Rabbit on Roids]

well, i can get anything from a 3.8 inch pulley, clear down to a 2.6" pulley. so i will have lots of room to play around. i just need to swap to the GTP pulley, because the ford pulley is too wide, its like 6 or 8 ribs.