DCR discussion

Here is my take on DCR, you probably wont like it too much LOL

I use it all the time, so dont get me wrong, its a good tool. However...

IF you precisely measure everything, it is a value to estimate mechanically possible compression based solely on the intake lobe design combined with piston movement. It does not estimate cylinder pressure of a running engine.

Intake port effectiveness, volume, exhaust design, especially primary pipe sizing, overlap, all determine what the actual cylinder fill will be, and it changes at different RPM. Nevermind that chamber design and intake charge swirl or tumble will also change octane tolerance and power.

Most importantly, two engines with VERY different cylinder pressures during operation could have the same exact DCR.

Even still, I like to use it in an evolving "window" which is really widening to about 7.5-8.5 without electronic engine management (I'd go higher if the gonk is managing timing and mixture, and lower without concern too for budget and/or parts availability)

The problem I see here is that you have a lot of estimates in your input measurements. So really, DCR in your case isnt a great tool due to variables stacking onto variables ultimately being used as an approximation.

Your combo doesnt look crazy to me, seems like it would work, but I think seeing as you have it together and cant go back and precisely measure, just look to see how it compares to other combos and their drivability.

Just FYI, I am a DCR supporter, just dont get caught too deep into it, because different DCR formulas give different results, and none of those ultimately determine exactly what an engine will do.



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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 4 speed