Rotrex C38-61 supercharger

pitsnow · Post by **pitsnow** » Sun Mar 18, 2007 7:20 pm

Warning! This will be a long post.

I have too much time on my hand, so I once more consider how I could supercharge my 4.6 engine.
The solution is the Rotrex charger C38-61. See link below
http://www.rotrex.com/pdfs/Rotrex_Techn ... e_V1.7.pdf

I should be able to squeeze this under the bonnet. But without an air to air charge cooler as there is no space. But my thinking is, if I keep the boost low, say 8 pis max @ 6000 rpm, I might get away without a charge cooler.

My calculation is the following:
The 4.6 will be revved to a max. of 6000 rpm. Compression ratio is 9.5:1

It will need air every second cycle, hence will need 4456cc x 6000 rpm / 2 = 13668000 cc per min or 482.6 cfm maximum.

The C38-61 has a ref limit of 90’000 and a 1:7.5 ratio. The max cfm at 90’000 is 865.9 cfm (0.5kg/s x 1731.8 )
So the max pressure the unit would provide @ 6000 rpm engine speed (if I drive it to max 12’000 rpm @ 6000 rpm engine = 2:1) would be:

865.9 cfm / 482.6 cfm = 1.794 factor
1.794 x 14.5 PSI = 26.013 PSI absolute
Boost pressure = 26.013 PSI – 14.5 PSI (ambient) = 11.5 PSI

Are my calculations correct so far?

Obviously 11.5 PSI is more than I can reasonable expect to boost the engine without detonation.

Hence I would have to drive the supercharger below it’s maximum.

If I go to 80’000 rpm (10’666 on shaft) the unit provides a maximum of 0.47 kg/s or 814cfm. This would bring me to 9.95 PSI boost. Still high!

70’000 will give 0.4kg/s or 692.7cfm = 6.31PSI boost. A bid low now. So my desired speed would be somewhere between 70’000 and 80’000 rpm for the supercharger.
Maybe a ratio of 1.7:1 = 6000 rpm x 1.7 x 7.5 = 76’500 rpm on the turbine.

Now the question is, how much of the boost created by the turbine will end in the cylinder? There must be some looses on the way.
So I might be better off planning for the 9.95PSI boost and see how much of it will remain after all the induction looses?

And the next question is, what would the engine be likely to produce power wise on say 8 PSI boost? My LT77 gearbox is not known for liking high torques.

I would also have to change the current high overlap / high lift camshaft to a low overlap / high lift one.

Any thoughts or corrections to my calculations are welcome.

bill shurvinton · Post by **bill shurvinton** » Sun Mar 18, 2007 11:35 pm

not2fast.wryday.com

Click on turbo calculator and play. At 8 PSI your isothermal gain is 8/14.5, or 55%. Obviously adiabatic gain is less, as the air gets heated during compression.

pitsnow · Post by **pitsnow** » Mon Mar 19, 2007 7:01 am

Hi Bill

The link was this one, was it not:
http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

The calculations give low power figures for the boost.
With 8 psi and all the numbers it comes up with 316 HP / 277 ft-lb.
That is a bid on the low side, especially the torque.
Anyway, it will be what it will be. The good thing is that the injectors size should be OK with 260cc / 24lb.

bill shurvinton · Post by **bill shurvinton** » Mon Mar 19, 2007 8:47 am

Yup, they must have changed the URL slightly (or my memory has failed me).

remember that the calculator is sensitive to a number of parameters. You need to work a bit to get the NA power to the level you know you have before messing with boost. It is also fun to play with Water injection to see how that changes the numbers, but set the methanol to 10%

FWIW 316HP in a 750-800kg car is fsck fast.

Paul B · Post by **Paul B** » Tue Mar 20, 2007 5:57 pm

Fit some Derailleur gears to the drive system so you can change blower overdrive speed on the fly?
:racing

Boosted LS1 · Post by **Boosted LS1** » Wed Mar 21, 2007 8:52 pm

I fitted a rotrex to a marcos lm500 with a 4.8 engine which I built, low compression, just under 9:1 iirc. I don't know what the figures were afterwards but at 6 psi boost it would blow your hand away from the outlet whilst on tickover

Boosted.

Lewis · Post by **Lewis** » Wed Mar 21, 2007 11:18 pm

Fit some Derailleur gears to the drive system so you can change blower overdrive speed on the fly?

This appeals to me.

I'm now visioning my Dolomite with a blower jammed out of the hood, with a dangerous looking chain assembly and gearbox on the front, along with a big ratchet shift alongside the transmission, with a "military power" marking at the top end

Must.....Not........Succumb......

pitsnow · Post by **pitsnow** » Thu Mar 22, 2007 7:13 am

Boosted LS1 wrote:I fitted a rotrex to a marcos lm500 with a 4.8 engine which I built, low compression, just under 9:1 iirc. I don't know what the figures were afterwards but at 6 psi boost it would blow your hand away from the outlet whilst on tickover

Boosted.

Where did you get the Rotex from?
The only company replaying to me inquiry was a HITECH in Germany.
Rotrex lists 2 UK distributors (GMC Motorsports in Scotland and TTS Performance in England) but I am waiting on a reply from both of them.
HITECH wants Euro 1900 plus 19% VAT = Euro 2261 = £1’500.-
GMC Motorsport lists the C38-61 (bigger but similar output) for £ 1’350 plus VAT = £1’586
I was hoping for a bid less than this but don’t we always.

Boosted LS1 · Post by **Boosted LS1** » Thu Mar 22, 2007 9:19 am

My customer bought the biggest one they do and it came from GMC in Scotland. The oils pretty expensive as well.

Boosted.

SC500 · Post by **SC500** » Fri Nov 16, 2007 9:46 am

Hi Pitsnow

I work for SC-Power and we specialise in supercharging TVR's using the Rotrex system.
Lots of information on the website and please feel free to give us a call.
www.sc-power.co.uk

Post by **Coops** » Fri Nov 16, 2007 10:15 am

pitsnow wrote:
Boosted LS1 wrote:I fitted a rotrex to a marcos lm500 with a 4.8 engine which I built, low compression, just under 9:1 iirc. I don't know what the figures were afterwards but at 6 psi boost it would blow your hand away from the outlet whilst on tickover

Boosted.
Where did you get the Rotex from?
The only company replaying to me inquiry was a HITECH in Germany.
Rotrex lists 2 UK distributors (GMC Motorsports in Scotland and TTS Performance in England) but I am waiting on a reply from both of them.
HITECH wants Euro 1900 plus 19% VAT = Euro 2261 = £1’500.-
GMC Motorsport lists the C38-61 (bigger but similar output) for £ 1’350 plus VAT = £1’586
I was hoping for a bid less than this but don’t we always.

I was looking at going this route pits,
but only one company got back to me which was sc power, as above,
the price was out of my range at the time, thus was looking at chargers with nigel at uk blowers the vortech and paxton, worked out not a bad price shipping it in, but due to family commitments early on this year it even put that on hold

SC500 · Post by **SC500** » Fri Nov 16, 2007 11:08 am

FYI we are going to have on the website soon prices for just the charger and our brackets.
We understand the need to keep costs down and the fact that our system which utilises a second plenum will not fit in 7 type cars or Morgan's.
Also I think allot of people on here would rather make their own induction pipe work just for the challenge.

Post by **Coops** » Fri Nov 16, 2007 11:59 am

some of us will have to make our own brackets too

as space is limited to where we can fit the charger.
will you do just the charger????

SC500 · Post by **SC500** » Fri Nov 16, 2007 1:30 pm

No, sorry, currently we are only going to sell the Rotrex charger and our bracket.
It's a compact package though and I'd be suprised if it didn't fit.

Post by **Coops** » Mon Jan 21, 2013 12:07 am

Old post i know,
but just an update after many mails and phone calls with David from SC Power they are supplying me with a rotrex C38-91 charger and bracket kit
will keep you all updated etc how it goes.