Rotrex Superchargers
Discussion
I have recently been looking into Rotrex'ing my GTM Libra B18C Type R engine kit car. I have figured out how to mount it, what belts to use, etc.. as no off the shelf kit designed for a civic or integra will fit in this car, installation wise I'm happy.
The kits use a C30-94 and that's what I've been looking for, but not had much luck. I've found quite a few C38 chargers which is the larger unit, and I was just wondering if it's possible to run a bigger unit but spin it slower. I'd ask the likes of TTS or someone but I doubt they'd give much information away without me actually buying it from them.
What I'm unsure of in a nutshell is, is oversizing a supercharger just as bad as lets say fitting too large a turbo to an engine? Will it be laggy or will I end up having to constantly bleed off pressure. I'm only looking to make around 9 psi but would be good to have some capacity for the future. I appreciate the B18 is only 1.8 but the C38 is commonly used on the K20A which is still a "small" engine.
Anyone with experience able to chime in? No guesswork please.
The kits use a C30-94 and that's what I've been looking for, but not had much luck. I've found quite a few C38 chargers which is the larger unit, and I was just wondering if it's possible to run a bigger unit but spin it slower. I'd ask the likes of TTS or someone but I doubt they'd give much information away without me actually buying it from them.
What I'm unsure of in a nutshell is, is oversizing a supercharger just as bad as lets say fitting too large a turbo to an engine? Will it be laggy or will I end up having to constantly bleed off pressure. I'm only looking to make around 9 psi but would be good to have some capacity for the future. I appreciate the B18 is only 1.8 but the C38 is commonly used on the K20A which is still a "small" engine.
Anyone with experience able to chime in? No guesswork please.
HappyMidget said:
Superchargers are fairly easy to change speed, just change the pulley size. Larger crank pulley makes it spin faster, so just get an underdrive pulley when you install it
I get that, but what I'm unsure of is will this be less responsive than the smaller C30-94 spinning faster? Forgot they were centri so can't really comment on the boost characteristics and for some reason the tech sheets available here do not seem to be opening for me http://www.rotrex.com/Home/Products/Fixed-Ratio-Su... The page does have approximate power ranges, so if the 38 is in the power band you are looking for it should be fine. I don't think you will have boost lag like a turbo, as a turbo has to accelerate the impeller and turbine weight with gas so impeller speed is not directly related to RPM unlike the centri which is a direct correlation.
I have the C30 on my Type R and it does suit the engine perfectly IMO.
A friend has a C38 on his for more outright power. I believe as above that the size of the pulley affects your boost level etc.
I would call TTS, I found them to be helpful (although I have spent some money with them!)
A friend has a C38 on his for more outright power. I believe as above that the size of the pulley affects your boost level etc.
I would call TTS, I found them to be helpful (although I have spent some money with them!)
There's some details here with compressor maps etc, but I'm not really versed in how to read them
http://www.google.co.uk/url?sa=t&rct=j&q=&...
https://www.verboom.net/images/speedster/20140419/...
http://www.google.co.uk/url?sa=t&rct=j&q=&...
https://www.verboom.net/images/speedster/20140419/...
If you strap a Rotrex C30-94 to a Honda K20 and charge cool is properly, get north of 400HP.
The power band charts are not sufficient to properly select a Rotrex supercharger. you need to know the boost you get the desired power level.
Often folks spec a C30-74 for a 230HP engine with 1.8l at only 0.5-0.6bar. The runs the SC close to the choke line at high rpm as boost is too low for the air flow.
A c30-94 at lower rpm would be a much better and more efficient choice.
The C38 units get you even further power wise. Their only issue is that they do not like hard rev limiters like K20 and F20/22c Honda engine have. These engine also tend to hit the litter often. The sudden rom changes cause the turbine shafts to break. you also have to consider drivability. I am rather unsure if you car is much fund to drive (on the road at least) with more than 300HP, let alone 400.
I'd stick to the C30-94. I had it on my Rover K in the Elise. Running it at max SC rpm, it had actually too much power to enjoy the full rev range on the road.
The C30 are also smaller is size.
The power band charts are not sufficient to properly select a Rotrex supercharger. you need to know the boost you get the desired power level.
Often folks spec a C30-74 for a 230HP engine with 1.8l at only 0.5-0.6bar. The runs the SC close to the choke line at high rpm as boost is too low for the air flow.
A c30-94 at lower rpm would be a much better and more efficient choice.
The C38 units get you even further power wise. Their only issue is that they do not like hard rev limiters like K20 and F20/22c Honda engine have. These engine also tend to hit the litter often. The sudden rom changes cause the turbine shafts to break. you also have to consider drivability. I am rather unsure if you car is much fund to drive (on the road at least) with more than 300HP, let alone 400.
I'd stick to the C30-94. I had it on my Rover K in the Elise. Running it at max SC rpm, it had actually too much power to enjoy the full rev range on the road.
The C30 are also smaller is size.
Yazza54 said:
There's some details here with compressor maps etc, but I'm not really versed in how to read them
http://www.google.co.uk/url?sa=t&rct=j&q=&...
https://www.verboom.net/images/speedster/20140419/...
Good article here on how to read the compressor maps: http://www.enginelabs.com/engine-tech/mastering-tu...http://www.google.co.uk/url?sa=t&rct=j&q=&...
https://www.verboom.net/images/speedster/20140419/...
I’m after some Rotrex advice if anyone is able to help?
I’m running a C30-94 in my EP3. Standard crank pulley is 140mm (so I’m told) and I have a 110mm pulley on the Rotrex end. Car is running 275bhp (intercooled) and making around 0.6bar boost.
My question is that if I fitted a smaller crank pulley - 130mm, and a smaller Rotrex pulley - 100mm would I get more boost? The calculators I’ve found tell me I’m safe for the revs but don’t tell me about if I’ll get any more actual boost?
I’m running a C30-94 in my EP3. Standard crank pulley is 140mm (so I’m told) and I have a 110mm pulley on the Rotrex end. Car is running 275bhp (intercooled) and making around 0.6bar boost.
My question is that if I fitted a smaller crank pulley - 130mm, and a smaller Rotrex pulley - 100mm would I get more boost? The calculators I’ve found tell me I’m safe for the revs but don’t tell me about if I’ll get any more actual boost?
The effects of reducing both pulleys counteract each other. Those pulley ratios work out to a 2% increase in the gearing (blower will run 2% faster for a given crank speed) by my calculation. Other things being equal that would give more boost, but not by a significant amount. In other words the two changes have pretty well cancelled each other out. Is that your intention?
To increase boost, you would want to increase the size of the crank pulley and / or reduce the size of the blower pulley.
To increase boost, you would want to increase the size of the crank pulley and / or reduce the size of the blower pulley.
GreenV8S said:
Butter Face said:
I would have to dial back the revs to keep it from overspeeding the charger?
To know that you'd need to know the engine and charger rev limits.Charger is a C30-94, peak input is 10,500 and peak impeller speed is 100,000.
Butter Face said:
GreenV8S said:
Rev limit on the engine?
It can be set to anywhere needed as part of the mapping; currently at 8300 so is overspeeding the charger at that point.Edited by Yazza54 on Tuesday 4th September 08:18
I'll add that what I looked into a while ago, and found it has already been done with some success is the use of a wastegate in the system to bleed boost. Can be mechanical or electrically controlled. But this would only really work with a larger rotrex that was capable of much higher cfm than you need. If you want more boost and are already overspinning it sounds like you need a bigger unit.
Changing the pulleys to hit peak impeller RPM sooner and then capping the engine Rev limit will produce a more tractable engine but if you have the revs you may as well use them.
Changing the pulleys to hit peak impeller RPM sooner and then capping the engine Rev limit will produce a more tractable engine but if you have the revs you may as well use them.
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