htown81vette

Here are some handy calculators. The first one is to calculate the cam angle (that we are talking about) and the second one is to calculate the DCR:

http://www.wallaceracing.com/cam-deg-calc.php

http://www.wallaceracing.com/dynamic-cr.php

63mako

The first one gives the same results as my formula.

For figuring DCR I use The KB silvolite DCR calculator
http://www.kb-silvolite.com/calc.php?action=comp
but for the last entry I input the actual intake closing point I have calculated instead of Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees
That is not an accurate way to figure actual intake closing point due to the variation in ramp rates.

gkull

Mako, I found my cam card. -5 cc pistons .015 piston to deck. .021 cometic gasket 4.060 64 cc heads 4.030X3.750

.036 Quench and thermal ceramic coated piston tops and moly sides


CC billet non sleeved SR

.050 236/244 112
.006 286/294

Valve event numbers Intake 11, 45 Ex 59, 5

63mako

Figure 11.24 to 1 and DCR is 8.81 to 1. Using my formula to calculate your actual intake closing point.
Your DCR is too high to run pump fuel normally. BUT your .036 quench, the thermal coatings, 4.11 and manual trans save you. Likely have a good cooling system as well. You could very well see some ping with your gearing now you didn't see with the 4.11. Your on the edge! Always.

gkull

It had the death rattle at cruising RPM and I had to run high octane blended with my first solid roller with the same build and a 232/238 or 240 Crane cam. I did hours and hours of simulations deciding on a cam and I didn't want to make it non- streetable. I screwed myself with the first cam

I actually ran and still have a 192 T-stat high flow in it with some 1/8th inch holes drilled around it. Stewart pump, big BeKool aluminum rad. and dual spals

Matt Gruber

So what is the DCR at cruising rpm, say 18" vacuum?
.
what it the DCR at peak torque (WOT)?
.
use gkull's combo to calculate.

63mako

DCR is a constant. It is designed into the build and does not change. It is based on intake closing point, static compression and to a lesser degree rod length.

htown81vette

The actual cylinder pressure while the motor is running is nearly impossible to calculate. Maybe someone in here has a PhD in Thermodynamics can do it. But it is beyond my abilities that is for sure.

63mako

Just refreshing this to help out those trying to put together their winter builds. Happy New Year!!

63mako

Back to the top for those that need it.

Little Mouse

Starting to read way more then i have in the past on head porting never done it before will be buying vizards book on it. Will someone that has ported heads for yrs maybe even has his own business doing it learn anything from reading not even a chance, im sure i will.

I don';t know what its going to cost but will have the head flowed before i start and after i'm done.

Easy to see how afr is getting there flow numbers over as cast heads, along with the smaller dia. valve stem helping a tad bit to.

TheSkunkWorks

FWIW, I do happen to subscribe to the school of thought that theoretical DCR (or what I prefer to call tDCR), as based on the intake valve closing event, is a calculation worthy of consideration when designing many a pump gas, street performance build.

That said, IMCO it's also worth noting that actual DCR in an operating engine varies relative to volumetric efficiency (VE%), thus putting the dynamic in DCR. And, higher VE% engines necessarily produce higher cylinder pressures, which is the real concern here. Thus, I'd caution against making the blanket assumption that any possible combination which mathematically results in a "safe" tDCR will always turn out to be so in practice. It may not be a perfect rule of thumb, but in general I'd suggest that tDCR info be given less weight the larger is the difference between tDCR and SCR for the build in question. My $.02

63mako

DCR is a tool. A lot of factors can affect its usefulness. Thermal coatings, tight quench, cooling system, timing curve, volumetric efficiency, Flat top, dome or dish piston, chamber design, efficiency of the head, intake and exhaust, overlap, A/F ratio, gearing and a variety of other factors can reduce the chance of detonation or on the other end of the spectrum increase it in a specific combination. That said DCR is a valid tool. Some builds will run fine on premium at higher than recommended DCR. Some will have issues a little below. It is a valuable and useful tool when designing a build but not carved in stone as the end all. It is tough to build a 12 to 1 engine that will run on 93 octane. It is also very easy to overcam a 8.5 to 1 engine and kill power by ending up with low cylinder pressures. That is NOT what this thread is about. It is about obtaining an accurate intake closing point to use in the calculators.

TheSkunkWorks

Understood, and good info for those who need help accomplishing the maths correctly.

It was only after following along for a bit that I felt it probably a good idea to point out for those who might not know otherwise that, yes, there are certain known limitations to the data's applicability; as I imagine certain follow-on questions likely have some viewers scratching their heads.