supercharching options

it's not that my heart is set on a centrifugal charger, the charger lends itself to ease of instalation and the ability to retain the stock EFI. this will help signifigantly in keeping cost down.

i have looked at the whipple and thats also a choice. however as you know the EFI needs to be changed and a new plenum built. all doable but costly. i think a all-in-one charger/plenum would work nicely with a stand alone EFI. the only issue would be cooling the air charge. i could go the route of Jag/Mercedes and incorporate a water-air cooler in the plenum. but as one can see all that fab work would get costly.

 

i've been going over the calcs and here is where we stand.
base line of 205hp@6600rpm
desired HP 305hp@6600rpm
8psi
6600rpm ~ 30lb/min @ PR 1.55
8000rpm ~ 37lb/min @ PR 1.55
temp gain 94* = absolute of 554*
i calculated both ranges as peak HP is under redline and i wanted to see max psi.


heres the 10.2psi
base line 205hp@6600
desired 325hp@6600
6600rpm ~ 33lb/min @ PR 1.7
8000rpm ~ 40lb/min @ PR 1.7
temp gain 112* = absolute of 572*

thought i'd share the calcs, it's not hard but it tells you what to look for and if a specific unit will work or not.

 

it's all about sliding the desired power gain around. those numbers represent the maximum one could get without an intercooler. bringing the desired HP down to under 300 possibly in the 275~290 range will drop the PR and flow required. more maps to review. the thermal effeciancy of the centrifugal is also a benefit. the HP required to drive the charger at 8k rpm in the above calcs (305hp 8psi, 37lb/min) is 17hp and that number drops to near zero below boost levels due to the design of the charger. the twin screw requires more power due to its design, but the trade off there is boost accros the RPM range.

the blow off valve will still be needed due to the layout of the metered air and the throttle location, too small for a bypass. the valve would dump just behind the compressor keeping a column of charged air within the metered area behind the throtle to reduce lag.
calcs;
Basic engine airflow rate = CIDxRPMx0.5xEv/1728
Ev = engine effeciancy
with this CFM you can calculate your lb/min at your PR (pressure ratio) from other lengthy calcs.

i have the calcs from the Corky Bell supercharged book, oddly he mentions the centrifugal as being great for the street as it retains stock idle and low speed drivability. the twin screw although better at providing boost down low causes idle and drivability problems becouse it comes on sooner, not that it can't be engineerd to solve those issues. but that arangement is better suited for the track. the one reason manufacture don't use the centrifugal is noise not power reasons. the whine from the charger would be annoying to some if not most consumers concerned about the high fidelity of there latest CD.

personally i love to run my car to redline at every shift. for me having the power in the upper range is fine. as it is now i can cruise with traffic without much issue, it's the dump it and run passing power i'm looking for. i'm going to dig up the gear ratio's on the mondial as i have a feeling they are different from the 308.
i can cruise at 85mph @ 4k rpm
65mph @ 3k rpm
so my freeway crusing speeds are right where the boost is. on the street well....

 

i don't have anything against either design, if the centrifugal is so bad then we wouldn't see it in use. they both have +'s & -'s . the Bell book i have is from 2001 by Bently Pub, to me thats not old. it does cover the new generation of twin screw chargers. lets not forget Bell owns and designs twin screw charger systems. so for him to think that the centrifugal is good for a street car seems unbiased. the HP to drive a twin screw (not roots) developing the same peak power requires 27hp and a belt load of 127lbs vs the 17hp & 29lbs of the centrifugal, yes the twin screw gives more back at the bottom end but still requires more power to drive.

bottom line if cost wasn't the issues i would work out a positive twin screw charger system, but under the constraints of space and EFI the centrifugal is a better fit.

mark, i know the benifits of the twin screw it's just not possible to develop a bolt-on kit for 5k.

 

the book most people have issue with is the earlier one 'maximum boost'. yes a twin screw will develop more power and torque than the centrifugal. but i would not use that charger with the CIS. once we move into the newer EFI than it becomes the best choice. i do think a kit could be done for the 308 with a twinscrew for around 10k, but how many would go that route? my design constraints are to keep the stock EFI and add a nominal amount of power for as little cost as possible. quite alot of contradiction in there but it's the problem at hand.

once i'm done working out the centrifugal design i'll do one for the twin screw also as i had mentioned before. this would be for those willing to replace the EFI and go beyond 'stock'.

please don't infer that i'm ignoring your input, you have invaluable time and effort spent on this. time permitting i'd love to work on a twinscrew system for the 308 motor with you.

 

further updates: it's long,
i've been going over the BOsch info and found some interesting things. the CIS unit Ferrari used started with the basic K-jet and moved over to the KE-jet. most know this, however what is interesting is that Ferrari used a 'tweeked' version of the stock setup Bosch put out. it's not uncommen for a mfg. to work with Bosch and come up with a specific setup. what is frustrating though is that Bosch won't list the specifics of what Ferrari did, you ahve to go to Ferrari and we know how much fun that can be. not to worry though, see Ferrari still used off the shelf parts (advanced components) but combined them to 'create' a high performance variation. Bosch has plenty of information on the various controls and how they work with each other, it's just a matter of putting it together.

also i have come to find out that the CIS in K-basic & K-lambda is a very elegant and simple. the only down side is the air restriction vs. a hotwire element. sure it's older technology but still good technology. the CIS can handle up to a 70% increase in power and still function under it's stock components. the trick here is having the right stock components. thankfully Ferrari used just those parts. our fuel distribution blocks have individual adjustment screws at every injector port, very uncommen. the WUR is both vacumm and boost usable. from my research it looks that ferrari sourced parts that are used in FI applications, why? better performance? more adjustable? adaptability? not sure but it works in our favor. now please note according to bosch the CIS unit can only work with low boost pressures, they were not specific but do mention 8psi as being safe.

another tidbit, the funnel that the metering plate moves in on the K-basic is made to match the motor. what this means is a CIS metering unit from a Porsche for example will not work right with the ferrari. when they moved to Lambda the funnel become a generic conical shape. becouse the use of a specific shape per motor and its power characteristics when we boost the motor we need to increase airflow in the same manner in which the motor normally does. i'll try and explain, the cross section of the funnel is narrow-wide-narrow. it's narrow at idle to provide lift on the plate at low rpm, then it widens as the rpm increases and near WOT the narrow region allows it to properly meter air under very low vacumm. the plate being a fixed size restriction and the walls varying in size will require less/more air to based on where it is. i.e. a wide section with the same air flow of a narrow one would move the plate at different rates and hight, sense the plate is moving the metering rod the air fule ratio is affected based on that design.

by adding more air, we affect how the plate will move and meter air. if we jam in more air at idle the plate would move beyond it's design range per rpm and over fuel the motor and cause idle issues. same for across the range, so does this mean we can't add FI? nope, we need to add it in the same way. a turbo is a good example. it builds pressure as rpms increase and has little to no boost at idle and under 3k for example. same goes for the centrifugal charger. however the lyshom design adds to much pressure at low speeds and the CIS-basic would have a very hard time correctly metering it. the later versions of CIS would not as the funnel is no longer engine specific.

now some are thinking, well the plate moves the metering rod and that fuels the injectors, so how does the engine not go lean when adding more air at the same rpm. ahh bosch gave us the WUR, which is funny becouse it was named that for early use of warm up regulation. however we are once again lucky, ferrari used a boost/vacumm and altitude compensating WUR. what this means is it reads the boost or vacumm and restrics or increases the control pressure on the metering rod to compensate for the fuel requirements, same goes for altitude. neat'o huh! makes me wonder what it costs to replace one though $$$$$.

so it looks as though we have all the basics components to add boost with out needing to piggy back on any controls.

next up lambda....