I'm using an excel spreadsheet to calculate valve events, etc.

I am using the .006 lift event to calculate DCR. However, I see people on the forum reporting DCR as though they are calculating off the .050 lift event.

Please, which is correct? 25 degrees of rotation makes a huge difference in the number.

 

Never heard of anyone using .050 duration to calculate those, it would give wild numbers.

You can calculate anyway you want it, but to be able to compare it to what most others are talking about (eg. with numbers between high 7s and high 8s) it's the .006 duration.

 

Ok, so I've been doing it right. Thank you!

 

Do yourself a favor forget about DCR. I don't know who came up with that but it is basically an useless number. There are to many variables to be worried about that number. There are time when it can be used but for these types of application on here it's not needed.

 

Even for predicting detonation? That's really all I use it for

 

You can make a low compression engine detonate if you load it low enough. You can run 14 to one on the street with no detonation if you never load the engine. We ran 18 to one on Pro Stock Motor cycles but you could not load it or open the throttle until you were past 9500 rpms if you did it would blow the head gasket out. So the DCR is kind of useless. You could have a engine that detonates at 3500 loaded, and changed to a 4500 stall you would never see it.

 

I've read Martin Smallwood say the same thing. Cylinder pressure matters more than SCR or DCR. If cylinder filling at a given RPM were accomplished equally by a small/fast lobe or a larger/soft lobe would power at that rpm be the same ? Would detonation (at the same load) ? If Darth or I could pick up a few HP with a $100.00 head mill, why not ? Also Mr. Fabre, who's valve job do you like ? Maybe an off-topic question but I value your opinion.

Darth_V8r, which calculator do you use ? I use the Piano Prodigy VE and the 4th tab wants events @ .006
I recently read something by Larry Widner saying swirl and quality of mix/burn had a larger effect on detonation. The Soft Head
I'm curious your take on his ideas.

 

Kip, thank you for that explanation. I have seen what you describe in my own engine - I can make it detonate at 1500-2000 by lugging it in fourth and hitting the gas, but once I get past 2k, it's rarely knocks at full throttle. Now I get that has to do with tune, and I've already booked NicD to tune the car, but I see what you're saying.

I guess another easy example is tightening quench to reduce detonation, which I also did successfully. DCR increases, but less detonation compared to before.

 

I'm using an excel spreadsheet posted by JRP some time ago. It was an older thread I found in the stickies.

I read the article you linked. I need to digest it some, but he does make one comment I'm certain I disagree with. He recommends reducing velocity in the intake ports, and Tony does everything he can to protect port velocities. I'm siding with Tony on this. But I need to re-read it to fully understand it.

He seems to be highly in favor of inducing swirl, and almost every ported head I see has a good bit of the swirl ramp removed. Definitely a different take

 

It may be a different article but he also says his valve jobs sacrifice low lift flow to improve anti-reversion. Old Stroker once asked why flow at .050" is important. "What is happening at .050" valve lift" ? and I thought ... overlap.
But this EnDyn guy Widner says because of the swirl, he can run incredible compressions without detonation. Less fuel consumption per HP and a engine that while down a bit on power, can recover rpm after a shift and accelerate faster. You mention Tony, AFR had a keen interest in his work and their chambers seem to direct the flame front to the hot exhaust valve as he suggests. New MMS heads retain the swirl ramp. FRH heads do also. He also talks about the intake valve as part of the quench area and a multi-lobed cam that opens bTDC, then closes at TDC to open again after. He says CFM and valve events do not make power, combustion does.
I'm still "digesting it" myself.

 

Not my Wegner Automotive Research 799s; Karl left it in there and only modified it ever so slightly.
Anxious to see how a head that only flows 297 cfm past the stock valve will do having a bit more swirl and turbulance.
The 100 through 400 lift numbers are comparable with the TEA and AI stuff but the upper lift numbers taper off which could be the ramp or perhaps something else like the valvejob angles ???

 

You plan on running a lot of compression also, please remind us how much. Your cam events are close to what Darth_V8r runs too. I know removing the swirl ramp can increase CFM but at what cost. It will be interesting to see how much timing your engine is happy with.

 

DCR is a useful calculation for ballparking compression and comparing between cams. It's really just looking at IVC for a given combo and coming up with optimal combos.

For example, a 240/248 112+0 camshaft and 10:1 is going to be a giant turd in a 346. Raise the compression to 11.8:1 and add 4 degrees of advance and you've basically just lowered the IVC while adding compression - thus bumping up the DCR calculation (which is all that calculation is giving you - it's not truly dynamic, it's just an IVC's affect on SCR calculation).

Once you realize this, you try to optimize the best you can. Most heads/cam packages would be fine in the 11:1 to 11.5:1 range. Really efficient heads and very large cams could make do with 11.8:1. But at some point, 93 is only going to burn so well.

So, the point is, on a 346, keep the IVC in the 42-45 range for good overall power, pushing to 46-48 for more top end, and size the compression accordingly. Keep is low 11s for everything but the big cams that push the IVC very late. Optimize quench, overlap, and valve events. They mean more. Going from 10.8:1 to 11.8:1 may make the car drive better, but it might only pick up 5-10HP at most. But it could cause a lot more KR as Kip was talking about.

I ended up keeping my compression around 11.2:1, and I rarely ever log KR with 26 degrees of timing at WOT on the street. Other things, like the coolant system efficiency, exhaust efficiency, etc help with this as well.

 

With GM bore matching 4.020"(.051" thick) gaskets I'd be 11.45, with Cometic 4.060"(.040" thick) gaskets it climbs to 11.7 and according to this : http://www.corvetteforum.com/forums/...tio-chart.html
The DCR would change from 8.67 to 8.9 as I'm at seventy degrees IVC
My pistons are @ zero deck so either way it may only want 22-23 degrees lead

 

There are time when it can be used but for these types of application on here it's not needed.

 

Sorry to belabor the point, but I'm checking to make sure it's sinking in...

Before I started all the mod work, I would occasionally get detonation in stock form in the 1500-2500 rpm range, but it went away at higher rpms.

I added an intake and headers and ported the throttle body, and the detonation was reduced - which I attributed to the improved scavenging of the exhaust cooling the heads better

I ported and milled the heads and installed a 041" gasket to tighten quench based on searches and posts by guys like Pat G and stopped having detonation altogether, so I firmly believe in using tighter quench to address detonation.

So, when I got the cam I got, I was aiming for 8.3 DCR, and I missed it by a little bit. But I was aiming for a mid 40's IVC, to that point. Now, compared to the stock cam, the duration at 050 is up by almost 30 degrees AND the IVC event is far earlier at 006.

So, what I'm hearing is that the improved cylinder filling and pressure, NOT THE DRC INCREASE, is what caused the detonation to return in the 1500-2000 range. And to be clear, all on a stock tune, but soon to be rectified - like in a week. Point is, the ignition and fuel events were constant.

 

Just a few points here. First The guy Larry Widmer At Endyne is VERY SMART. I and many other have learned a lot from him. DRC can be 8.3 on two engines one with a bad combustion chamber and one with a good combustion chamber now that number must be changed for one of the heads. Quinch is good and bad. You can have to much which will cause detonation of not enough which can hurt power. Swirl can be good or bad you can have to much. Port velocity is not everything the higher the air speed the less dense air becomes. Flow matters but port volume is critical. If you really want to hit the DCR correctly you need to add the rod length to the bore and stroke if not you can be 3 to 4 degrees off. The way you must cam and engine is first 1 Cubic Inches 2 Compression 3 rpms or application. A cam for a 4.8 will not be correct for a 7.0 So is DCR important? On special applications yes on most applications on here no but that is just my opinion. I see no rules that apply 100% of the time all combinations are different.