[craigawoodman]

In my reading on superchargers it strongly recommended against using a toothed belt to drive the supercharger. It does not give reasons for this. Given the debate over belt slip at high rpm's, why can you not use a toothed belt to drive the supercharger to eliminate slip totally?



Top fuellers use a toothed belt to drive the supercharger (and these a massive units), most modern cars and bikes use toothed rubber belts to drive the cam shafts. So if you can drive the cam shafts with a toothed belt - why would you not drive the supercharger with a toothed belt?



Can anyone provide some wisdom on the logic or otherwise of using a toothed rubber belt to drive the supercharger.



Thanks,

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[flash]

i never really thought about it, since everybody i know uses a grooved belt, but likely because of the chance of ripping a tooth due to the sudden drag a supercharger can add - do that a few times and you have a smooth belt, and we already know how well that works

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[RS Barn]

Craig,

I had a 968 with Speed Force SC and a 951 intercooler. I found the intercooler killed the power and actually raised charge pipe temps dramatically. I took off intercooler and raised charge pressure to get power I expected at lower intake temps. I've always believed in testing,testing,testing rather than believing what someone else has said is true. It's worked out so far for me.

Pete

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[Dubai944]

Thats an interesting comment regarding the 951 intercooler. I have long suspected it isn't doing much on my setup, and my intake temps are very high....



Back to the topic, I have done a lot of research on belt setups. The pros for cog belt setups are no slip, but there is a lot of anecdotal evidence of supercharger cog belts breaking with constant acceleration and deceleration loads. The rib belt design does slip to some extent and this is seen as a safety feature on a car which has to be driven at constantly varying load conditons, unlike the top fuel dragsters. Also some regard the louder noise from a cog belt to be a negative on a road car.



I have even seen some drag racer setups where they have bolted the supercharger directly on the end of the crankshaft with a drive gear box! A bit impractical in our cars though....!



The best solution I can see is to use a cog belt with a sprag drive pulley on the charger which freewheels when not under load. ATI are making them now and I am already looking at that option.

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[RS Barn]

I didn't mean to change direction on Belt issue but needed to chime in on Intercooler issue. I spent three days and lots of money disproving what was thought to be common knowledge. We picked up 20+HP and cooler intake temps bucking the system.

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[Dubai944]

No it was a great comment. Based on that I think I will run a test bypassing my intercooler this week.

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[flash]

yeah - not sure where the intercooler came into the discussion of the belt, but it is an excellent topic, and we should start a new thread for that



but intercoolers are tricky things - you can't just bolt one on - as a very general statement, low boost centrifugal units (below 7lbs) do not benefit from them, and in fact can easily become complicated by them - a lot of things play into this, like flow pattern, cooler placement, overall size, connecting plumbing size, shape and material, yada yada - they don't act like turbos or roots blowers, and need very different things



back on belts, a toothed belt, while a better idea, as it is less subject to friction, has less contact area per inch than a polyribbed belt, largely because it is only really contacting on the drive side of the tooth, and so it makes sense that it would be more likely to slip a tooth, which would lead to failure - tension would be a much bigger issue too - i'm sure it could be made to work, but the cost of the pulleys would be much higher, and the engineering to get all of the pulleys lined up in exactly the right places so that the teeth on one were spaced out exactly to match where the teeth on the other needed to be, and factor in belt stretch, would be rather intensive - it took me quite a bit just to get the grooved pulleys all lined up at the right distances - you'd probably need multiple automatic tensioners to do it and have it handle the drag load of the supercharger, which is many times that of an air conditioning compressor - it would be easier to line the pulleys up in a single plane though

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[craigawoodman]

Thanks for the replies - it is all helping. I saw the car at the mechanic's today and spent two hours looking for solutions to some of the problems - to say the installation has not been straight forward would be an understatement.



The major issue that Flash alluded to would be the costs of the additional drive sprockets and idlers.



We will look at running a double sided belt, but even this will need a new pulley machined up.



I will have to post some of the issues we have found so far trying to get this to work. Some of these are of my own making by running a separate engine control unit - but I believe I need this to protect the engine.



So running a toothed belt, whilst eliminating slip may in fact cause other issues and would be fairly cost prohibitive. THe pulley's and idlers would have to be sized correctly to ensure constant engagement of the teeth as well.

On the intercooler issue, we are also struggling to get one to fit. The room at the front of the car is limited, along with the intake causing issues. Any suggestions or work done on placing an intercooler at the front of the car (excluding a 968 RS style intercooler) would be of use. Also, we are possibly going to go back to a air/water intercooler to assist in packaging.



Thanks,



Craig

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[flash]

let's start an intercooler thread for that - it will make for a great discussion, but definitely a very involved one

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