Lets talk dynamic compression ratios

[cb900f]

I've been searching around trying to find out about the dynamic compression of these motors with the use of VVTI. I ASS-umed we could use this to our advantage with boosted applications to lower DCR in the upper RPM's. Is this true?

I found this:
http://www.svtperformance.com/forums/2011-2014-mustangs-354/786520-cause-8-a.html

Which Shaun said the VVTI INCREASES DCR in these motors. Can the pro's out there help a little?

Lastly, the LiveLink software shows VVTI intake and exhaust degrees. Is this opening, closing, or ?

Thanks!
:beer:

 

[Shaun@AED]

Yes you can. For instance targeting 'Zero' degrees advance / retard at WOT on a supercharged setup will nearly double boost, yet power output will be significantly decreased. Essentially not allowing as much air into the engine via cam timing resulting in less power and higher back pressure (boost).

 

[CPRsm]

It shows degress in that it turns, but you have to figure it out as far as it's actual relation to crank. I did it a while ago somwe could try cam profiles that were turbo friendly. A bit of work lol.
The intake will help on DCR, but more for the mid range than, anything to prevent detonation. Piston speed it high enough at high rpm that DCR isn't such a role anymore. After 5200 or so you start retarding to chase intake wave pulses, than worrying about DCR.

 

[Voltwings]

My main experience working with DCR is from the mazdaspeed3. We only had access to the intake cam, and when tuning big turbos, i would increase the VVT in the spool region a few degrees to increase the dynamic compression and spool the turbo. For example, on a 35r car, floored at 3000 rpms, the car saw 21 psi at 4000 rpms. Advance the VVT 3* in the spool region (different for every car/application) and that same car now saw 31 psi at 4000 rpms. This was for E85 cars that could take the increase in pressure.

For pump gas cars, i would retard the timing, getting the flame front closer to the exhaust valve opening (essentually "creating" more exhaust gas energy), then up the VVT to basically make up some of the natural torque loss from retarding the ignition timing. Basically in this case, you'd have slightly less natural torque, but more exhaust gas. Its pretty neat stuff to play with, but for the cost involved, im not sure i feel like tuning the Coyote myself, Sean will probably be hearing from me before too long

As far as using it to help top, CPRsm pretty much nailed that on the head, most cars that are tuned are already tuned to maximize the DCR up top.

Heres a good article i came across that kind of explains cam timing (effects DCR) in relation to boosted applicataions: Cam Gear Tuning | Adjustable Gear Tuning | Cam Wheels

 

[cb900f]

Thanks for the reply's!

So... Boost being the amount of resistance air has while traveling through the engine, why would you want to increase this as seen here:

http://www.svtperformance.com/forums/2011-2014-mustangs-354/987563-just-blew-engine-up-3.html#post13801989

 

[Shaun@AED]

Boost is simply back pressure. Mass of airflow thru the engine is what produces power and therefore increases cylinder pressure.

The valve event vs boost reference was simply an example.

You can log lb/min of airflow and adjust cam timing for more/less airflow at a given RPM. Keep in mind the other effects cam timing will produce, like reversion, EGR, etc. This can lead to higher cylinder temps if exhaust gasses are re-entering the combustion chamber due to reversion along with other effects that are not desirable.

 

[cb900f]

So then what kind of DCR are people seeing on these motors?

 

[Voltwings]

So then what kind of DCR are people seeing on these motors?

Depending on your cam advance / retard, it changes, which is why its called the Dynamic ratio. I dont mean to insult your intellegance by saying that, but its not something so easily obtained. Typically though, i believe Dyanmic compression is always lower than static (11:1 on stock coyote).

Heres another good article i found helpful. Particuarly this excerpt explaining the intake cams impact on DCR:

"If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn."


Compression Ratio Explained (Static & Dynamic) - Team Integra Forums - Team Integra

 

[D.T.R]

Depending on your cam advance / retard, it changes, which is why its called the Dynamic ratio. I dont mean to insult your intellegance by saying that, but its not something so easily obtained. Typically though, i believe Dyanmic compression is always lower than static (11:1 on stock coyote).

Heres another good article i found helpful. Particuarly this excerpt explaining the intake cams impact on DCR:

"If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn."


Compression Ratio Explained (Static & Dynamic) - Team Integra Forums - Team Integra

Dem lil Hondurz schooling errrryboday

 

[cb900f]

Depending on your cam advance / retard, it changes, which is why its called the Dynamic ratio. I dont mean to insult your intellegance by saying that, but its not something so easily obtained. Typically though, i believe Dyanmic compression is always lower than static (11:1 on stock coyote).

Heres another good article i found helpful. Particuarly this excerpt explaining the intake cams impact on DCR:

"If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn."


Compression Ratio Explained (Static & Dynamic) - Team Integra Forums - Team Integra

LMAO, no insult. The idea is to know how ragged I'm running my car. I was hoping to borrow the brains from someone who has done the math like CPRsm on a 5.0L, not a 1.8L. :rollseyes

If they can adjust the cams to get down to 9-8 DCR it would make sense on how these motors are staying somewhat together with 10-15psi of boost.

 

[Voltwings]

lol i'll admit Hondas get a bad wrap, but in all actuality, they're some of the only other "streetable" NA cars making over 100 whp per liter like we are. Theres good information to be had from them for sure.

Granted i come from mazdaspeedforums and our slogan is "FYHN", the middle two are "your honda," I'll let yall get creative with the other 2

 

[cb900f]

Maybe no one is interested, but here ya go.

Ok, I found the specs on the stock cams:

Intake Cam:
Advertised: 263
.050": 211
Lobe Lift: .235"
Centerline (Park / Max): 139 / 89

Exhaust Cam:
Advertised: 263
.050": 211
Lobe lift: .216
Centerline (Park / Max): 123 / 73

Valve events @ Park (no adv/ret) @.050":
IVO: 33.5 ATDC
IVC: 64.5 ABDC
EVO: 48.5 BBDC
EVC: 17.5 BTDC

Valve events @ Max @.050:
IVO: 16.5 BTDC
IVC: 14.5 ABDC
EVO: 1.5 ABDC
EVC: 32.5 ATDC



At Park DCR is :
Effective stroke is 2.85 inches.
Your dynamic compression ratio is 8.80:1 .

At maximum is:
Effective stroke is 3.61 inches.
Your dynamic compression ratio is 10.88:1 .

So it can adjust from 10.88 -> 8.80

Knowing this, mine is 10.88 -> 9.92 at 7k.

That's what I needed!

 

[Voltwings]

Amazing info, whered you find that?

 

[cb900f]

Most info was found via Google and I put it into a DCR calculator on the web.

 

[Voltwings]

go figure haha

 

[CPRsm]

You're DCR shouldn't be that high at higher rpm unless your intakes are really far advanced. At higher rpm the intakes are actually pretty retarded.

 

[Shaun@AED]

Those cam specs are what I put up for SCT dealers a few years back.
Be advised the intake cam duration is off by 3 degrees advertised (actual 260 vs 263)
Everything else is accurate.

 

[Elwood617]

Thanks for all the information

 

[cb900f]

You're DCR shouldn't be that high at higher rpm unless your intakes are really far advanced. At higher rpm the intakes are actually pretty retarded.

Livelink says my intake is -19* @ 7k

Following this: IVC: 64.5 ABDC

64.5 - 19* = 45.5

Putting the info into here:
Wallace Racing: Dynamic Compression Ratio Calculator

Leaves me with 9.9. Is my math off?

Bore: 92.2mm = 3.62992in
Stroke: 92.8mm = 3.653543in
Rod: 150.7mm = 5.9330709in
CR: 11:1

I've got a Roush TVS w/ 82mm pulley and JLT

 

[Shaun@AED]

The online calc does not state whether to use .050 valve events or .004/.006 (actual valve opening / closing).