Quench certainly is important; getting the air in/out is one thing, combustion characteristics is another.

 

Toobroke is at it again. His comparison of a hemi head combustion chamber to a sbc head combustion chamber is apples to oranges.

 

Local speed shop sells in shop built engines for around the same price as crate engines with similar power levels.

Check with your local builder...you never know!

 

I agree with you. That looks like a 9:1-9.5:1 compression camshaft. That cam will fall in it's face at 5,000 rpm in a 383. Plus, those head flow numbers look like they want more lift. I cam with 282-288 advertised intake duration (230-240@.050) would do wonders for this combo.

 

Thanks for all the replies....The cam that is in the 383 block is said to be a custom grind cam....Do not know the specs of the cam....To be on the safe side I was just going to use the lunati cam in my 350 since I know the specs......

I purchased this small block around five years ago , covered it and left it in my garage for use one day in the Vette......A C4 ZR-1 later and about 10 grand in that motor to bring it up to over 500 horse, I'm thinking of doing the 73 now.....

As far as the cam I have no problem buying another but which one? Don't want to spend the money for a roller set up so I will stick w hydraulic flat tappet..

With the combo I have, what cam is good? Want torque over high end HP......Decent street manners since the car will be 2-4K RPM most of time...

Thanks for all the info...

 

It would be great if the guys giving out camshaft advice in this thread actually knew what they were looking at..... Since none of you actually do - now would be a good time learn.

Class is now in session:

The Lunati cam card lobe timing events are calculated from the duration @.050 not advertised duration.

The actual closing event for the Intake lobe is 60* ABDC...

BTW That's actually NOT the real degree that the valve will hit the seat because advertised duration's are based on .006 of tappet lift and none of this takes into account rocker arm ratio, valve train deflection, ect..... but why don't you actually breaking out a degree wheel and dial indicator on the valve spring retainer some time and see for yourself.

So how do you calculate those fancy cam lobe events? It's very easy grade school math.
We know the advertised duration is 268 degrees and we know the Intake Centerline is 106*.

To find the Opening Event you take the Duration (in this case the Advertised Duration) and divide it 2. 268/2=134. Then you take the remainder of 134 and subtract from it, the lobe centerline which is 106. 134-106=28* BTDC.

To find the Closing Event you take the Duration and subtract 180. 268-180=88. Then you take the sum of 88 and subtract the Opening Event which we just calculated as 28. 88-28=60* BBDC.

Somethings to ponder about Dynamic Compression Ratio (DCR).

First off - It's a very BIG waste of time to calculate it. It's a made up number that means almost nothing and has been perpetuated on the internet for years as something actually useful, when in reality it's nothing of the sort. It doesn't tell you anything useful and I guarantee you will never build a good engine compromising cam events so that you can fit them to some magical DCR number.

On top of that, Two thirds of the time I see someone spouting off about DCR this and that, they don't even use the right information to calculate it. But that doesn't even matter because even calculated correctly, DCR is nothing but useless information. Here's why:

Even the name "Dynamic Compression Ratio" is wrong because there is nothing "Dynamic" about it.... it attempts to calculate the mass/volume of Air and Fuel in the chamber based on a static number - The Intake Closing Point/Degree/Event (which I have already pointed out is very flawed because it is NOT the actual point which the valve closes)....

Also if there were anything Dynamic about DCR, it'd take into account engine RPM, Ram Effect and Volumetric Efficiency - All of which effect the mass/volume of Air and Fuel that enters the chamber before the valve closes.... It doesn't even take into account overlap which has a HUGE effect on the start of the Intake cycle.

People want so badly to understand camshafts and put them into little formulas they can explain simply..... unfortunately it's not that simple. Even the best engine builders learn something every time we change an event. Sometimes it's not even what we thought we'd learn and challenges things we think we know...

Class dismissed.
Will

 

at the crank or at the wheels?

 

I totally missed the 4 degree advance ground in and the 106 ICL.

When I use the seat-to-seat duration #'s in DDyno and set the advance to +4, it also spits out an IVC of 60; IVO of 28; EVO 72; EVC24 (so the only mistake seems to be missing the +4 advance ground in).


If class is still in session: why does the cam card say "In Closes: 39.5 ABDC" and "In Opens 7.5 BTDC"???!?



DDyno now says: 437ft lbs from 3,500-4,000 and HP 379 down at 5,000 RPM for a 383.

As a 350: 414 ft lbs @ 4,000; 378 HP @ 5,500.


Adam

 

Most of the DCR calculators ask for the advertised cam intake duration, LSA, and advance/retard and CALCULATE the IVC event from there. (I've used 3 different online calculators and 3 different stand-alone tools and they all ask for intake duration.

With the information I put into the JeepStrokers.com DCR calculator AND the +4 ground-in advance that I missed, it correctly calculates an IVC of 60 and if the static CR is 10.45, it calculates a DCR of 8.64.



I don't understand why the listed IVC on the cam card isn't the actual cam card; I'm hoping someone can shed some light on that part...


Adam

 

The cam card shows valve events @.050 lift (instead of the advertised duration @ .006 or .004 depending on the cam grinder).

 

is he really back?!?!?!!?




300hp rear wheels... low flow heads... mild cam... low compression.

 

The Cam card uses the @.050 duration (227*) to calculate the tappet/lobe closing points.

227/2=113.5

113.5-106=7.5* BTDC

227-180=47

47-7.5=39.5* ABDC

Will

 

It's a good conversation to have. But this part on DCR is more like a school of indoctrination of a particular view / opinion.

DCR is the WORST indicator of whether an engine will have a detonation risk or what grade fuel it will need to run, except for the static compression ratio that doesn't account for the IVC event... (Which is where many people will run to when you tell them that DCR is garbage and now they're worse off in terms of accurately predicting detonation risk.)

Yes DCR needs to be used with caveats and people need to understand that it's only a rough indicator; professional engine builders use far more factors to far more accurately calculate detonation risk, and yes, it is just a more accurate "Static CR" estimate that happens to account for the IVC event, but it accounts for the 1st and 2nd most important influencers of detonation. (Static CR and IVC.)


Even if you take into account engine RPM, wave tuning RPM, ram effect, VE by RPM, overlap, you're still missing cooling temp, air temp (huge impact), quench, and AFR and timing at each of those RPM points.

If we let perfect be the enemy of "good" or "better" (than just traditional static CR guidelines not accounting for IVC), then we're screwed because we're just not going to get to perfect.

DCR's better than what came before it, when used as an INDICATOR and a RANGE and useful to determine relative safety and whether your cam meets a minimum "safe" bar. PipeMax's actual dynamic calculation is also more useful but doesn't look at any temperatures, AFR, or ignition timing.

All we need is "Good enough" and we can adjust the cam's advance/retard, ignition timing, and AFR from there to ensure safety; DCR, IMHO, is "good enough" until you push things and then you want to look at a few more factors.


An "is X "good enough"?" conversation is, by definition subjective, and opinions will vary.

Adam

 

Why do they do that if it's so far from the actual closing points?


One more question (a real question; not rhetorical): Does the rocker ratio actually matter in terms of the actual valve close timing? (if the cam lobe is at 0 lift, 1.5*0=0, 1.6*0=0, 1.7*0=0)

I can see rocker ratio mattering in the mid and max valve lift some, but at 0 valve lift / close & open events it shouldn't be a factor because anything times 0 = 0. --Right?


Adam

 

I haven't been around very long but I've certainly never heard anyone say anything akin to less quench making more power or having any relationship to power; simply that keeping the quench tight helps keep detonation at bay, both by increasing turbulence as the pressure/temp in the chamber approaches it's peak, and by getting the air-fuel mixture away from the walls/rings where detonation seems to set in.

You're not arguing the relationship between quench and detonation resistance, are you?


Adam

 

You'll want to use the .050 events on the cam card when you degree the cam. You can degree the cam using just the ICL, but it's fun to check duration @.050 too. Rocker ratio will minimally affect valve events at the valve. Additional rocker ratio will add a small amount of duration.

 

As I pointed out, where they calculate the advertised duration, the tappet is not actually at 0 lift.... it's at .006 lift. So yes rocker ratio will matter. The reason they do this is because finding the actual closing point of the valve may be very difficult and not repeatable for most people. Honestly repeating .006 of tappet lift to the same degree of cam rotation is kinda difficult. Even solid rollers which use .020 tappet lift are tough to judge because the jerk the tappet off 0 lift so abruptly in the lash ramp.

The reason cam companies use .050 tappet numbers is because it's an easily repeatable tappet height measurement for engine builders to check the camshaft for proper timing events.
Will

 

But only in the middle of the lobe, right?

Here's the typical diagram showing the impact on duration from different rocker ratios that I'm thinking of:




Adam

 

Awesome! It finally "clicked" for me. I'm slow sometimes, but with enough precision questioning, I finally get it.

The duration even down at the "advertised" lift of 0.006" or 0.004" will also increase (a teeny tiny bit) because the advertised lift isn't the ACTUAL open/close point- that is to say it's not the point of 0 lobe lift on the cam; the ACTUAL, physical open/close point and duration at 0.000", won't change, though (and we don't even measure / look at it).



Adam

 

Quench is a tricky thing to manage in some combo's.

And I want to point out that piston to head distance is just one thing that affects "quench". Quench is actually an area where 2 surfaces (usually flat) oppose each other in close relationship. However Toyota did some very interesting research back in the 90's that studied the effect of angled quench areas.....

Anyway yes, the goal is to create turbulence in the AF mixture and direct it to the center of the bore (or near the plug) as the piston approaches TDC... then it helps to speed up the flame front after the plug fires and the piston reaches and goes past TDC .

In 23* SBC's and 24* BBC's the chamber design is horrid.... the plug is in the wrong place, there is very little swirl built into the port designs and there is lots of "dead area" in the chamber.... one of the ways to help them out was to decrease the piston to head distance to make the quench areas closer together. This is why people refer to it as "tight quench".

This typically resulted in a "more efficient engine" because the engines will require less timing advance to make power.

Closing up the piston to head distance can be a problem in high powered forced induction engines.

To give wedge chamber power adder engines a "bigger tuning window" we often increase piston to head distance or taking things we learned from the Toyota SAE papers we physically change the design of the quench areas on the cyl head chamber/piston to be less efficient.

This is why Hemi's rule in Top Fuel...... little to no flat quench area.

On pump gas street engines espc stock valve angle BBC and SBC's I have run the piston to head distance as close as .034 with good results.

I ran a few limited class oval track engines at .025 one season as an experiment but the pistons showed evidence of slightly bumping the head and I set it back to .036 with no loss of power.
Will