Basically after some info from those who have been there and done it.

I will either later this winter or next, be fitting a rotrex supercharger to the Duratec.... so I need to clarify a few points.

I am going to be running 0.9bar boost on std compression ratio (albeit forged) internals. This is a proven set up as used on the 320bhp Caterham X330.

What I would like to do, is run a slightly undersize pulley so I can get the boost on earlier and then vent the excess as the rpms increase, gving a smoother power curve and also more power lower down the revs. So basically I am looking for a wastegate type solution, only for a supercharger. Anyone know of anything suitable, or has done it?

Or would you not bother and just size the pulley correctly in the first place?

I know that I will need a bypass valve to vent the boost on overrun and at cruising for better economy. So I need to source one of those too.

Hopefully someone can help

Cheers,
David

I thought the whole point of a supercharger was that the boost was there all the time, right from idle? What makes you think you'll be getting a lower pressure at low rev's? Given that your cam will be the real limit to when the engine picks up and that's already several thousand rpm is it worth wasting so much energy dumping unused air at more usable engine speeds? I'd also imagine it would sound like a hissing steam train all the time, which might get a bit annoying

[Edited on 25/8/09 by Mr Whippy]

i dont know about tried and tested, did Caterham make many X330's ?

quote:

---

Originally posted by graememk
i dont know about tried and tested, did Caterham make many X330's ?

---

i was under the impression you could get the duracell engine up to 250 bhp with a few internal mods anyway how much bhp do you need ?

Rods, Pistons, Head, cams, uprated bearings to make it last, steel fly wheel etc etc

quote:

---

Originally posted by Mr Whippy
I thought the whole point of a supercharger was that the boost was there all the time, right from idle?

---

Hi David - surely traction will be a major problem for you - so is early boost such a good thing - in the corners your revs should be in the right place to benefit from boost anyway so the only place early boost is possibly beneficial is from a standing start - and then you will be traction limited anyway.

I would stick with the standard pulley - I think blow off valves are just something more to cause problems and are difficult to get working right without creep which will negate some of their effectiveness. If you set the start of the opening at the maximum pressure then you will get some overboost putting your motor at risk (also if they stick closed) and if you set them to be part open at max pressure then you have boost creep problems with it taking longer than it should to reach max boost and also have wasted energy causing increased charge temperatures..

Is having power lower down the rev range a good idea in such a light car? Is it not better to follow a more well trodden path, it's not like you fall over superchwrhed duratec engines every week.

Something I forgot in my reply above - in a vehicle you don't feel acceleration - you only feel a change in acceleration (just like you don't feel gravity - only a change in gravity as when a lift starts or stops).

So ever increasing boost will impress you and your passengers much more than early boost peak with a plateau for the last few thousand revs.

What type of blower are you going for? If you go centrifugal you won't have much boost at low pressure anyway. If you go Roots you probably equally don't want to spin it too fast otherwise you'll lose efficiency...

Cheers chaps, good advice, keep it coming.

I will be using a C30-95 Rotrex supercharger Its about the only one that will fit I think.

quote:

---

Originally posted by Mr Whippy
I thought the whole point of a supercharger was that the boost was there all the time, right from idle?

---

that is teh same supercharger, i am looking, at but for not this winter next winter, when i am 19, i think my insurance will be ok with it.lol

stuart

I'd keep the boost low at low revs, since the engine (with stock CR!) will be more prone to detonation at lower engine speeds.

Also, using a blow-off valve at high engine speeds seems a waste of compressed air and will significantly increase fuel consumption at that engine operating point (but that's probably of less concern to you ;-)) and will make the entire setup significantly more complex.

If you really want low end grunt, fit a positive displacement supercharger.

scootz has a rotrex kit for sale on here

turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more with a turbo,ie more boost

quote:

---

Originally posted by jpindy3
turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more with a turbo,ie more boost

---

turbo it

there is alot more to go wrong with a charger than a turbo,more macanical.

[Edited on 25/8/09 by jpindy3]

I am a big fan of turbo's but as always there are compromises, a small lowish pressure turbo is most likely lighter than a supercharger (a good thing) - will reach full boost quicker and earlier than a supercharger (a good thing) - is not very linear in boost (a bad thing) - boost is not rev proportional (a bad thing) - might be more efficient - a good thing.

I think that overall a supercharger might give better control of power delivery on the track at the cost of more mechanical complexity and maybe weight and maybe thermal efficiency.

I think that most of the so called negative aspects of both can largely be corrected by the proper selection of the right unit.

I know that most people (including many so called experts) fit the most readily available turbos that might not be ideally matched to the air flow requirements of the application. Care taken to ensure an ideally matched turbine and compressor housings with the right nozzle sizes and trim levels will provide a turbo that will minimise lag.

quote:

---

Originally posted by flak monkey

quote:

---

Originally posted by jpindy3
turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more with a turbo,ie more boost

---

Um, wrong, wrong, wrong and wrong.

Neither is more reliable than the other. If anything i would say turbos are a little less reliable.

Supercharged engines perform MUCH better lower in the rev range as there is no lag before they come on boost. Its all a smooth power delivery. If you reatin stock CR as well your low down driveability is totally unaffected.

Fuel consumption, probably not much in it.

And you can run just as much boost with a SC as you can with a turbo.

David

---

quote:

---

Originally posted by jpindy3

so what happens when you want more power,

---

quote:

---

Originally posted by Ivan
Something I forgot in my reply above - in a vehicle you don't feel acceleration - you only feel a change in acceleration (just like you don't feel gravity - only a change in gravity as when a lift starts or stops).

So ever increasing boost will impress you and your passengers much more than early boost peak with a plateau for the last few thousand revs.

---

quote:

---

Originally posted by flak monkey

quote:

---

Originally posted by jpindy3

so what happens when you want more power,

---

Same thing you do with a turboed engine, up the boost. Smaller SC pulley and remap and away you go. More or less, theres always a limit on how far you can go before detonation becomes an issue though.

TBH I dont think I will want more than 320bhp in a seven.... and I reckon I will have trouble putting that much down

---