As a few people have mentioned all comparisons should be made on the SAME CAR, SAME DYNO and the SAME DAY

 

hmmm.....bag me if you will as I'm a relative newbie to all this stuff - but I do know fans and pumps in process industries.....

I had a look at the CAI results and would like to pose some challenges to the notion.

From Robs data I've looked at it from another point of view.

Forgive me if I talk in kPa - that's what I know best (Australia).
1 atmosphere is 14.7psi, or 101.3kPa or roughly 400in WG
Your manifold pressure supplied by the SC is around 12-18 psi or lets round that to 15psi for this arguement - or 105kPa

When you have a restriction on the suction side of your blower this will detract from the discharge side. This is more the case with fans etc. with plenty of "bypass" around the vanes - but for SC's they are almost a positive displacement device with very little slip past the vanes and ill therefore simply demand more power for the same rpm with little effect on the output.

Lets put that aside....

I have rejigged the numbers Rob presented into a flow base instead of pressure based.
see attached.
I have allocated 2 nominal levels - 400cfm and 650 cfm and recalculated the drop backwards based on the square rule..."double the flow rate and you quadrouple the pressure drop".

Form this you can see the presure drops are small in comparision to the SC output mentioned above and what we are all chasing. You might get a 2kPa benefit from best to worst...and in the scheme of an SC (based on the 105kPa I've presented above) that's about a 2% improvement in performance.
And that's not withstanding the comment around it being a positive displacement pump and not greatly affected by suction restrictions.
Also of note - pressure and density wise....2kPa is roughly (again I use that word) equal to about 2deg in AIT...I think you'd be much better off chasing AIT's than intake pressure.

Shoot me down - I'm happy to open up the discussion. as I say - I'm a noob and could be missing something here.

 

Did you see my dyno results of the single versus the dual setup? Also there are two intake pipes doing the air flow so the pressure drop is not 4x. The flow is not increased 2x either, maybe 1.5x. Woody

 

2x, 1.5x?...Not sure what you mean.
the 650cfm is through the suction or the discharge of a MAF or equivalent?
I assume the cfm is measured at suction side where you meaure your 15"?

oem intake system (stock filters) - infers the standard 2 x pipes....so 325cfm each - yeh?

if that gives you 15inWG - you can still square rule it down to 650 or 450.

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couldn't quite find an easy comparison of "same car same day" stock v others - sorry.

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I did pickup a previous comment that there is more "slip" past the vanes at low revs. and less intake restriction helps minimise this, still small fry unless it all adds up to a bag of chips...;>)
ie: 2% + 1% + 2% + 1% + 2% + 1% = 9% improvement overall.

 

Wow, this 3 year old thread is back from the dead...

 

Need someone to do a sanity check on this calc below.....

 

is it possible to get 874 cfm thru a 74mm t/b?

 

interesting...I like my 1/4 mile times myself...that is the only reality check I need....stock CAI, 13.1, single CAI, 12.9, dual CAI, 12.7, add a code 3 pulley, 12.5, add a tune from LET, now Eurocharged, 12.2... and that was just the roadster... The coupe has even more mods.....lol

 

Sure - and those times are great.
I'm just a frustrated engineer with too much time on his hands.
Mind you I do most of the calcs between 4 and 6AM after I wake up - early riser.
The morning is for thinking of crap, the evening is for doing crap.

If I can tie it back to the original post for this thread...
>>>one point is that these figures are much higher than Robs original figures where he used at 15"WG with the OEM air being at 445cfm.
Seems just for 6200rpm the car as OEM should be able to take the 760cfm, (it may however be at 30"WG vacuum).

>>>another interesting *** bit I got from investigating this, is that the E37 version of the M112 Motor....
"Wikipedia.....The E37 is a 3.7 L (3724 cc) version. It retains the 84 mm stroke of the E320 but is bored to 97 mm....."
This version of the M112 is used in the ML350, S350 and SL350
Comparing 97mm to our 90mm = 3.5mm extra bore in the radius. I was suprised by this, since unless its a totally different casting, the block has some upside for some possible honing - or droping the E37 in and swaping the SC etc. over.

Air velocity through the TB is coming in at 85m/s which I thought was a tad high until I saw this page....
Throttle Body Calculator
it indicates 86m/s at 1psi drop across the plate...
I'm also picking up from parts locators that it may be the same throttle body used inthe S430, S500 AND S55...unconfirmed.
So I'm guessing okay

 

Thinking about it - one reduction in this number may be made when reviewing the actuall cylinder pressure just before Inlet Valve closing. I'm not sure how much of an effect it would have, since at valve closing, I've assumed the prs in the cylinder is equal to the inlet plenum pressure (say 14.5psi). It may be marginally less than this 'cause the inlet valve inlet velocity may behigh and hence there may be some losses here.
Having said that if you look at the attached figure - the cylinder may well be on its way back up by the tme the inlet valve is closed.
See attach.
Total Inlet stroke (84mm) at 6200rpm is only 4.8 milliseconds, so that means the cylinder is travelling at an average (sinusoidal) rate of 17.8m/s (100miles/hr!).

 

Rob,
Any chance you can update some of these numbers for your C32 DCAI and other evolutions?
eg: I think you mentioned here....
C32 for the DCAI 659cfm
E55 for the DCAI 684cfm
E55 stock .........515cfm
(I'm assuming at your std 15"WG )

Note - From my calcs I'm getting about +1psi boost at 6000rpm (on a 61/155mm pulley arrangement) when going from ....
a SLK32 stock arrangement(446) to the DCAI(748)
which is equivalent to a about a -2mm reduction in pulley diameter - ie: not too shabby....

 

yes, we also flow tested a stock e55 upper plenum versus one we ported and coated a couple months ago, we made 9% increase in cfm on them, ill have to find where I wrote the actual cfm numbers down though


I have a few more goodies here to flow test in the next month or so, id like to get a big pile or stuff to bring though to offset the cost of firing the machine up.