Dcr

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Well DCR is like SCR: it never changes wiht engine running conditions. It is a CR number based upon SCR and intake closing; VE is not ever an input to computing DCR. (Look at any DCR calculator and see if you can find VE as an input.... you won't find one.)

As such, DCR is like SCR: it is a reference number for evaluation and planning.

What I think you are really meaning is perhaps best called 'effective' CR, i.e., the CR that would result in the actually experienced cylinder pressure, which does indeed change with VE....

Agreed on the time factor at high RPM, BTW.
 
Well that's the question, isn't it??.... If your basing your engine on a DCR calculation of 100% VE and your engine is only ever seeing 88% VE then should you take this into account? Could you actually use a higher DCR number than what you think you could run?
Are the recommended DCR numbers you see floating around on the net based on dyno testing of engines that see higher VE's than a normal engine? therefor would these numbers be conservative when compared with a lower performance engine?

Let's take the OP's original 8.0 DCR in the 367Ci SB assuming the 100% VE
Now let's just say it only ever sees 88% VE. This gives us a new DCR of only 7.04.
Should he be actually aiming for 9.1 DCR?? to compensate??
I'm just pointing out that assuming a DCR Calculator is going to give you magic numbers for the best cam event's for a chosen CR is not necessarily correct.
 
Bakerlite said:
Well that's the question, isn't it??.... If your basing your engine on a DCR calculation of 100% VE and your engine is only ever seeing 88% VE then should you take this into account? Could you actually use a higher DCR number than what you think you could run?
Are the recommended DCR numbers you see floating around on the net based on dyno testing of engines that see higher VE's than a normal engine? therefor would these numbers be conservative when compared with a lower performance engine?

Let's take the OP's original 8.0 DCR in the 367Ci SB assuming the 100% VE
Now let's just say it only ever sees 88% VE. This gives us a new DCR of only 7.04.
Should he be actually aiming for 9.1 DCR?? to compensate??
I'm just pointing out that assuming a DCR Calculator is going to give you magic numbers for the best cam event's for a chosen CR is not necessarily correct.
Click to expand...
Yes it is the question. I have always just assumed that the DCR and SCR recommendations are general guides based on typical experience, which includes the general effects of VE. The DCR is a step beyond simple SCR numbers to allow for the cam timing effects, and no more. And I would expect that the recommended maximums are conservative so that the folks putting them out (especially manufacturers and builders) don't end up with being blamed for putting out info that blows up engines right and left.

Interesting on the other DCR link and thanks; I will have to look at that one. Maybe I need to plug in my Starion 2.6L parameters and see how long ago it should have blown up!
 
Just for grins here is the result from my Starion 2.6L turbo rally motor in the rbracing calculator:
- SCR 8.2:1
- 264 cam intake advertised duration (estimating 33 degrees ABDC intake closing at .050" lift to use in this calculator)
- 1000' altitude
- Rod length is just going off of memory

The rbracing output message is:

Your engine summary is as follows: Bore 3.596 inches, stroke 3.858 inches, rod c-c length 8 inches, with a static compression ratio of 8.2 :1. Your camshaft specifications call for an inlet valve closing of 32 degrees ABDC (after bottom dead center).

Your chamber volume is 89.18 cc's. With this camshaft your dynamic, or effective stroke is 3.63 inches. Your dynamic compression ratio is 7.57 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 147.95 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 14 PSI is 14.78 :1.
 
Shazzam!!

8 inch rod?..................14.78/1..........................Why are we worrying about 11/1? Oh wait,SERIOUSLY retarded ignition timing. Yeah that would be a disaster when NA.

32*ABDC, I would assume is on the seat? Wowsers that is early! The Wallace Racing calculator spits out the same numbers.

Makes you wonder what the cylinder pressure goes to when the candle gets lit....
Boy I bet that's a ride. I make that out as about 157 cubes?
 
Like I said, the rod length is a guess...too lazy to go and measure. They are a bit on the long side. But 7" did not change the output significantly. The rbracing calculator uses closing timing at .050" lift, not at advertised duration. So that is why the closing looks so early. Real intake closing is a more common 49 degrees.

The ignition timing is just stock... as far as I know, We found a lot of odd things in this car... which was purported to be the fastest Showroom Stock Station in the country at one time.... a lot of tricky mods here and there keep popping up! LOL

ECU is the stock '88/'89 version. The detonation management tactic is to cut the fuel....you DON'T want to do that ever again after the first time....it is like a cinder block materializes in the crankcase and the crank smashes into it....repeatedly!

Yes, I figure we are in the 275 HP range now on 14-15 psi boost. It has been a 100% reliable engine, but that is a credit to the design. The Starion/Conquest engines came with a lot of performance features designed in at the factory, like piston oilers and a very good oiling system built-in. Plus a better crank than came in the more pedestrian 2.6L's. We have used both hypers and now have Mahle forged VW flat tops in it.

The real challenge is putting the power to the ground. Only on a well packed, low gravel coverage stage road can you really use the power with RWD only. But, it is a hoot when it hooks up.

But it is good to be back in V8-land for a change....
 
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