Supercharging a S600 V12 coupe w140

[srupp1969]

Hi@all,

I just wanted to hear your comments about following idea that I have in mind for quite a time.
Playing around with the plan to supercharge my S600 coupe model 93 i plan to go following way:
As space in the engine bay of the V12 is very limited I want to replace the stock secondary air pump with a s38 Rotrex unit mounted on a custom made bracket + air/air intercooler (front mounted). The pump is larger than the rotrex so enough space should be available.
The Rotrex and the pump are using an 8 v rib with a PK-profile so this could work inline with the other stuff (A/C pump , pas pump, aso.).
I want to achieve a power gain of around 100 hp, stock comp.ratio (10:1) should be maintained. Therefore I am heading for a 5-7 psi setup.
Some questions that came up:
- Has anybody heard about such a conversion or has some experience in supercharging a v12/V8 Merc. engines.
- Is it possible to arrange the charger inline with the mentioned other units (a/c, pas) or is a direct driveline
to the crank required ? If possible do I need another rib tensioner directly positioned on the custom bracket or
is the stock tensioner doing the job.

I do not want to go the twin supercharger road because I want to hold the setup as simple as possible.
Setup: supercharger->intercooler->split hosesto the two throttle bodies
Associated hardware stuff: custom bracket, oil circuit supercharger (cooler, filter), air filter, pop off vent, (rib tensioner), custom hoses, plumbing, fasteners
As the V12 has a very advanced ignition and fueling system (Bosch LH-jetronic) a comp. ratio of 10:1 and unique knock sensor control for each single cylinder I think it could be a good basis for a light supercharge tuning.

I am curios to hear your comments and would be glad if we could start a fruitful discussion.

Regards

Stefan Rupp

[stevieturbo]

I havent heard of such a conversion. But as long as belt wrap is good...use a Gates belt. I dont see why it wont work.

Id also say use the biggest blower you can ( without going nuts )

[chuntington101]

how much can the S387 flow?? io heard the most the Rotex's can go is 600bhp. not sure on the lbs/min though.

Chris.

[Busa_Rush]

The belt sounds fine but don't forget that the sc will take 20 to 30 bhp to drive it at max power so you'll need to make sure the other ancilliaries and the belt run can cope with the necessary belt tension. The belt will need to be pretty tight ad as mentioned above, wrapped round the sc pully for at least 150 degrees, mine is 180 degrees.

Sounds an interestig project, have a chat with Richard at TTS about it, he probably hasn't done a V12 engine but he has done a lot of bike and cars over the past few years inc replacing the Merc sc on a car last year.

How are you going to add the extra fuel ?

[srupp1969]

Hi@all,

thanks for your comments.
The s38 is the biggest unit available and can support from 400 to 630 hp supercharged.
I want a gain of 100 HP over the stock 397 HP therefore around 6-8 PSI (0,3-04 bar) should be already enough and the stock fuel system should be still capable of supporting this relatively low boost level with a rolling road chip tuning.
Belt tension and slip might be the biggest problem. I am not quite sure if the rotrex centrifugal unit absorbs between 20 to 30 hp under full boost compared to a twin screw charger that has a lot more inner friction than the smaller rotrex unit. Would be interesting to know if there is a calc. formula where you are able to calculate the belt tensioner force related the charger moment to know if the stock tensioner can do the job or if there is another one necessary.
Thanks for the tip with 150 degree cover angle on the pulley. This would have been one of my next question. Is this the absolut minimum ? 180 degree might not possible given the location of the rotrex in this setup.

Cheers
Stefan

[tr7v8]

Umm. I think you may struggle. I've wriiten some Excel to calculate based on the formulas in Corky Bells book Supercharged. Assuming this is a 6,000cc engine then using the Excel I've written you're looking at 1.13 Pressure ratio (just under 2PSI) using an intercooler & 32.6Lb minute airflow & that is way off the efficiency map of the Vortech V5 & just on the V9.
Unfortunately I can't find maps for the Rotrex product range at all.
I think you'll be looking at a higher BHP increase

Edited by tr7v8 on Thursday 10th January 10:44

[srupp1969]

TR7V8,

thanks for the effort.
The max flow rate of the C38-81 Rotrex is 0,55 Kg/s @15 degree C and 0,1013 mPa, that equals to 72,753 lbs/min.
Here is the link to the tech. spec. of the rotrex I have in mind.
Hhttp://www.rotrex.com/pdfs/Rotrex_Technical_Datasheet_C38_Range_V4.0.pdfi
There is also a conversion formula from Kg/S to CFM (?).
May be this can tell you a bit more than me.
Just going to order this book :-).

Cheers
Stefan

Edited by srupp1969 on Thursday 10th January 11:29

Edited by srupp1969 on Thursday 10th January 11:33

[tr7v8]

Even further off the surge side on that map.
You're looking for 0.018Kg/S & 1.13 Pressure ratio (intercooled)
I've pinged you a mail, I'll send you the sheet.

[eliot]

tr7v8 said:

Umm. I think you may struggle. I've wriiten some Excel to calculate based on the formulas in Corky Bells book Supercharged. Assuming this is a 6,000cc engine then using the Excel I've written you're looking at 1.13 Pressure ratio (just under 2PSI) using an intercooler & 32.6Lb minute airflow & that is way off the efficiency map of the Vortech V5 & just on the V9.
Unfortunately I can't find maps for the Rotrex product range at all.
I think you'll be looking at a higher BHP increase

I think your'e right. Putting a 6L into my calcs gives about 35Kg/s - but not at the low pressure ratios you require.
Here's my rough estimates:


And I think you will need to address your'e fueling - as I maxed out my injectors within a few PSI of boosting my 5.7, dont think an OEM will have that much headroom in it.

[chuntington101]

i think the larger Rotex might work. the guys at Wheel 2 Wheel in the states make a kit for the 6.0ltr LS2 (see here http://www.w2wpowertrain.com/pc-105-63-gm-gen-3-4-... ). might be worth giving them a call see if they can tell you anything. also ass said above TTS have work alot with Rotex.

as for fueling a cheap and chearfull fix might be a fuel presure regulator. this would increase fuel presure by 1 psi per 1 psi of boost. you would also swap out the sotck injectors for some larger ones

anyway its a great project and please keep us posted on how it gose!

Chris.

[srupp1969]

Thanks guys for all your efforts.

I go and talk with the mentioned people at TTS and the US-Company to gain some more information about the right setup and the limitations.
If you want I am always open to discuss a different solution (Vortech for example), but I suppose it will be a centrifugal charger setup due to space and boost characteristic (the stock engine has already got 570 NM of torque over a low rpm range).
Btw: Rotrex page (Rotrex.com)says that the C38-81 headunit is well suited for engines from 3-6 litres displacement and from 400 to 690 HP.
I will find out.

Cheers
Stefan

Edited by srupp1969 on Thursday 10th January 13:30

[eliot]

chuntington101 said:

i think the larger Rotex might work. the guys at Wheel 2 Wheel in the states make a kit for the 6.0ltr LS2 (see here http://www.w2wpowertrain.com/pc-105-63-gm-gen-3-4-... ). might be worth giving them a call see if they can tell you anything. also ass said above TTS have work alot with Rotex.

as for fueling a cheap and chearfull fix might be a fuel presure regulator. this would increase fuel presure by 1 psi per 1 psi of boost. you would also swap out the sotck injectors for some larger ones

anyway its a great project and please keep us posted on how it gose!

Chris.

The issue is that the O/P wants to run low boost [pressure ratio] - which is of the bottom of the maps, regardless of the flow rates.

[stevieturbo]

With a low boost build, an 8-rib belt with good wrap, I doubt slippage will be a concern.
You shouldnt need to run the accessories that tight. And a good auto tensioner is probably best too.

Ideally you want the blower to be the first item the crank pulls.

[Busa_Rush]

srupp1969 said:

Hi@all,

thanks for your comments.
The s38 is the biggest unit available and can support from 400 to 630 hp supercharged.
I want a gain of 100 HP over the stock 397 HP therefore around 6-8 PSI (0,3-04 bar) should be already enough and the stock fuel system should be still capable of supporting this relatively low boost level with a rolling road chip tuning.
Belt tension and slip might be the biggest problem. I am not quite sure if the rotrex centrifugal unit absorbs between 20 to 30 hp under full boost compared to a twin screw charger that has a lot more inner friction than the smaller rotrex unit. Would be interesting to know if there is a calc. formula where you are able to calculate the belt tensioner force related the charger moment to know if the stock tensioner can do the job or if there is another one necessary.
Thanks for the tip with 150 degree cover angle on the pulley. This would have been one of my next question. Is this the absolut minimum ? 180 degree might not possible given the location of the rotrex in this setup.

Cheers
Stefan

There's no fixed formula that I know of for power consumed or the belt tension or wrap circumfrence, just my experience.

I'm running 1.2 bar on a Hayabusa engine and TTS have had the belt slipping if it's not tight enough. The crank pully only drives the sc, nothing else, so the wrap is quite good and you can make it reasonably firm but even then it can slip.

Although it's a centrifugal sc it has a 10:1 step up gearbox on it and does take a fair bit of power, although nowhere near as much as a screw compressor etc.

With 8psi you should get more than 100bhp if you've got almost 400 bhp already.

[stevieturbo]

Busa_Rush said:

I'm running 1.2 bar on a Hayabusa engine and TTS have had the belt slipping if it's not tight enough. The crank pully only drives the sc, nothing else, so the wrap is quite good and you can make it reasonably firm but even then it can slip.

Although it's a centrifugal sc it has a 10:1 step up gearbox on it and does take a fair bit of power, although nowhere near as much as a screw compressor etc.

With 8psi you should get more than 100bhp if you've got almost 400 bhp already.

How many ribs ? What sort of tensioner ?

Im using a manual tensioner on mine, but I am 100% convinced I have to overtension the belt to prevent slip. I believe that if I had an automatic tensioner, it wouldnt need to be as tight.

Aim for as much wrap as possible, and as many ribs. Apparently a Paxton Novi 2000 at full chat can take as much as 200hp to drive it....
Id guess my Vortech YSi is about the same. Although stepup gearing is different. The Paxton is only rated to 55,000rpm, whereas mine is 65,000rpm....
A higher internal stepup would allow the use of much larger pulleys, and subsequently more wrap, and less chance of slippage.
My Vortech has a very low step up though at 3.45:1

[chuntington101]

eliot said:

chuntington101 said:

i think the larger Rotex might work. the guys at Wheel 2 Wheel in the states make a kit for the 6.0ltr LS2 (see here http://www.w2wpowertrain.com/pc-105-63-gm-gen-3-4-... ). might be worth giving them a call see if they can tell you anything. also ass said above TTS have work alot with Rotex.

as for fueling a cheap and chearfull fix might be a fuel presure regulator. this would increase fuel presure by 1 psi per 1 psi of boost. you would also swap out the sotck injectors for some larger ones

anyway its a great project and please keep us posted on how it gose!

Chris.

The issue is that the O/P wants to run low boost [pressure ratio] - which is of the bottom of the maps, regardless of the flow rates.

i was just posting an example of a smilar sized engine running a Rotex to show it can be done.

Chris.