Non-vanos "hot cam" setup

[digger]

I used Desktop Dyno to figure it out. It actually has a preset for BMW 6 cylinder motors. I just went in and put in the numbers for my motor (bore, stroke, deck height, combustion chamber cc's, etc) and then put in my cam numbers (240/240, lift, and lsa). Then changed my numbers to stock cams and it spit out the dynamic. I think it was closer to 11.4x:1 than 11.5:1.

All the DCR effectively tells you is how much of the stroke is actually used for compression (conversely how much stroke is lost before intake valve closes) this is because compression only starts when the intake valve closes. Therefore the Swept volume is adjusted to account for this. A DCR of 11.4-11.5 with a ststic CR of 11.7 means the intake valve is closing almost at BDC.

What is the intake valve closing timing After BDC in degrees?
This is a seat-seat (or close to it advertised duration equivalent). Most factory cams close intake valve around 50-60* After BDC aftermarket can get to 70-90*.
So for 86mm crank, 84mm bore, 135mm rod 50* ABDC intake closing you only be using 74.7mm of the stroke which is 74.7/86 = 0.86 x swpt volume so if static CR is 11.7 .

Swept Vol = 476cc
CR = 10.7
chamber vol 44.5cc

DCR
Swept vol = 476.6 * 0.86 = 409.9cc
chamber vol = 44.5cc
DCR = 10.21

The DCR goes a long way to determining low end torque characteristics of cammed engines with fixed valve timing and one reason big cam lose lowend is because of a low DCR.

http://www.empirenet.com/pkelley2/DynamicCR.html

[PiercedE30]

But that doesn't take into account the opening and closing of the exhaust valve. That is the only thing that I change in DD when comparing dynamic cr. That's it. I made sure the LSA was 110* and that the lift was correct. If my computers power supply hadn't of taken a shit on me I would post a screen shot of it for you.

[digger]

But that doesn't take into account the opening and closing of the exhaust valve. That is the only thing that I change in DD when comparing dynamic cr. That's it. I made sure the LSA was 110* and that the lift was correct. If my computers power supply hadn't of taken a shit on me I would post a screen shot of it for you.

exhaust opening and closing is irrelevant for the calulation of the dynamic compression ratio, its only the intake valve closing thats important for the calulation that is how its defined. All you need is

Swept Volume
Combustion Chamber Volume
Stroke
Rod Length
Inlet Cam Timing

[PiercedE30]

Yea, I saw that in the one of the calculators that you linked to, after I posted. I dunno why it changed then. I'll have to try and get my other computer running again and post what I did. Maybe I was playing around with advancing the intake some.....

[static]

exhaust opening and closing is irrelevant for the calulation of the dynamic compression ratio...

eeehm, i disagree. if your premise was true, change in cam overlap wouldn't change anything in the power characteristics of the engine.

change in exh open/close timing is very much relevant to dynamic CP as it controls the supercharging effect of scavenged exh gases, and thus controls the amount of a/f mixture entering the chamber.
hell, why is there a dual-vanos?

[digger]

eeehm, i disagree. if your premise was true, change in cam overlap wouldn't change anything in the power characteristics of the engine.

change in exh open/close timing is very much relevant to dynamic CP as it controls the supercharging effect of scavenged exh gases, and thus controls the amount of a/f mixture entering the chamber.
hell, why is there a dual-vanos?

The dynamic compression ratio is as i defined. It is rpm independant unless you have variable valve timing.

Your talking about something different i.e. the volumetric efficiency (or what is effectively the running compression which varies with rpm) this is different to DCR.

[static]

The dynamic compression ratio is as i defined. It is rpm independant unless you have variable valve timing.

Your talking about something different i.e. the volumetric efficiency (or what is effectively the running compression which varies with rpm) this is different to DCR.

you're right! i was confusing it with running compression.

[So Live]

Wow, this turned into quite the converstaion :)

Theres a whole thread on bimmerforums about FI cam set ups. It was suggested that rattier cams may have a serious affect on horsepower. For me, this mod would be free cause i have a spare set of cams. So why not try it out? Im not up to spec with all the cam terms and exactly what they do or might affect so bear with me!

[PiercedE30]

Chris,
I picked up the 256/244 cams that Cameron on BFc FI got from Brew. Should be here on Wednesday.

[So Live]

Drooooooooollll. You need to DYNO your car!!!!!!