Over scavenging creates a situation where too much of the incoming fuel mixture goes out the exhaust in lieu of going into the cylinder which hurts fuel efficiency, overall performance, and can permit the exhaust to run much hotter than normal.

 

Increasing the exhaust duration forces the exhaust valve to close later after TDC and in turn increases the valve overlap for the exhaust valve closing and intake valve opening.  By using a dual pattern camshaft that has more exhaust duration than the intake, the exhaust is open (at overlap) for more degrees past TDC than the intake is open before TDC which makes it ideal for exhaust head flows or exhaust systems that are inefficient.  Increased overlap can be beneficial for high rpm performance applications but causes some inefficiencies at the lower rpms usually in the form of fuel dilution and/or excess fuel mixture going out the exhaust by lieu of the intake and exhaust valves both being open simultaneously.  With this then is a power band that has been shifted to a higher rpm and in turn leaves the engine with less low end torque or being more sluggish on the bottom end.  As the exhaust duration is increased, a reduction in manifold vacuum is created as the open exhaust valve ultimately becomes a vacuum leak for the cylinder for as long as the exhaust valve is open after TDC.  There is a point for a given combination up to where overlap is beneficial but anything beyond this threshold has the power band shifting radically and becoming exponentially more negative in regards to low end performance.

 

Because of the myriad of engine combinations and resultant exhaust systems to go with these, there are a multitude of camshaft grinds to cover all the different options.  The key here is to pick the camshaft that fits your driving style along with the engine/chassis combination.  I’m all too familiar with instances where dead stock camshafts would easily outperform a performance grind only because the performance grind was not suited for the combination in which it was installed.

 

Anyone else can jump in at any time to add to this.  This is a grey area and open to interpolation from different points of view.

Lorena, Texas (South of Waco)

Ted, thanks for the input.  It does help. I agree completely about apllication & components.

I guess my dumb logic is:

Camshaft "A"     Intake:  230 duration @.050, .500 lift @ valve

                     Exhaust: 230 duration @.050, .500 lift @ valve

107 degree lobe centers, installed straight up. 

Camshaft "B":     Intake:  220 duration @.050, .500 lift @ valve

                     Exhaust: 220 duration @.050, .500 lift @ valve

107 degree lobe centers, installed straight up.

Shouldn't camshaft "A" have more of a midrange powerband, with strong torque?

Shouldn't camshaft "B" have more of a flat torque curve, with a later, or higher rpm powerband.

If I was a person who had a powerband in mind that was in between these, instead of picking the cams that propotiionatly are in between, wouldn't a combination of these two lobes in one cam have a mixture of both attributes, a midrange cam with a flatter torque curve?

Kevin

I used to hang out at the corral.net, mostly talking about tuning 5.0L engines, and there was a tuner there who could tune a 5.0 and increase torque and horsepower and still use the stock cam. I think his name was Buddy Rawls. He would explain that a good valve job and good ports (better heads) would make a stock cam look 'bigger'.



Between good heads, improved intakes, better headers and better tuning, he would get something like 50 horsepower with the stock cam. But most of the guys there were into swapping parts so the talk was mostly about E303 cams and such.

Best regards,



Paul Menten

Meridian, Idaho

As Paul mentioned, it's the total combination that must be taken into consideration when selecting a camshaft.  At best, any given camshaft is a compromise as for those areas in the rpm range where something is gained, there are other areas where something is lost.  This is where degreeing in the camshafts becomes a valuable tool as camshafts that are not an exact fit for a combination can be 'dialed' in for increased performance in the desired operating range.

Increasing the lobe centerline would create a flatter torque curve.  Increasing the duration raises the powerband.  Where both camshafts have the same lobe centerline, camshaft B would have an rpm opertating range that is lower than that of camshaft A with camshaft B having increased manifold vacuum at idle and better idling characteristics.

Lorena, Texas (South of Waco)

Ok, so I think I need to go with a smaller cam then.  This is a truck after all.  I only hope that it will still have a bumpy idle, & work will with my 4.10's & .068 od 5 speed combo.

I talked to my guy @ Erson last night & he ran a bunch of numbers, including my "wanna be" cam that comp proposed. 

I gave him the flow specs from Mummert's street port 1.94/1.60 ecz-g chart.  He actually proposed a grind that is a dual pattern, but with slightly more duration & valve lift on the intake side.  He said it should build real strong torque, & with the lobe separation should have the idle I am looking for. 

The questionS I have for you guys is this: with the cam specs that I paste below, will my valve to piston clearance be ok?

Do you agree that this would be a nice small step up from my current e-4/cite combo?

I think I remember that it IS possible to change the lifters from the bottom.. Can anyone confirm?   I have no problem pulling & putting it on a stand to use gravity & pull the pan,just need comfirmation.

Thanks,

Kevn

Erson custom gind:

PART NUMBER	E200000		GROSS VALVE LIFT INT.	0.496
GRIND	SPECIAL		GROSS VALVE LIFT EXH.	0.464
ENGINE	Y BLOCK		INTAKE OPEN	29
ROCKER RATIO	1.60		INTAKE CLOSE	61
ROCKER RATIO	1.60		EXHAUST OPEN	63
CAM LIFT INTAKE	.310		EXHAUST CLOSE	23
CAM LIFT EXHAUST	.290		OVERLAP@ LASH	52
LOBE SEPARATION	108		INTAKE PHASE	106
ADV. OR RET. DEG.	2		ANGLE or CENTERLINE
INTAKE "LASH" DUR.	270
EXHAUST "LASH" DUR.	266	#	EXHAUST PHASE	110
INTAKE DUR @ .050"	220		ANGLE or CENTERLINE
EXHAUST DUR @ .050"	218
JOURNAL SIZE	1.950		INTAKE OPEN @ .050	4
	.		INTAKE CLOSE @ .050	51
TDC	45		EXHAUST OPEN @ .050	39
			EXHAUST CLOSE @ .050	-1
HEEL TO NOSE	1.530		OVERLAP @ .050	3
W / .010" CLEARENCE	1.430
			TIMING POINT INT.	98
HEEL TO NOSE	1.530		TIMING POINT EXH.	-16
W / .010" CLEARENCE	1.430		OR	344
HOT LASH INTAKE	0.022		BASE CIRCLE IN.	0.8500
HOT LASH EXHAUST	0.022		BASE CIRCLE EX.	0.8500
DEFLECTION INTAKE	0.005		NET VALVE LIFT INTAKE	0.469
DEFLECTION EXHAUST	0.005		NET VALVE LIFT EXHAUST	0.437

I don't really know enough about cams to advise on this. One thing to consider, however, is the few options for exhaust on our trucks. I believe there are 4 options for dual exhaust. I'm assuming you will go dual. Red's headers has long tube and stubbies. Sanderson has stubbies. And of course the rams horn manifolds. The ability of these to flow will be a factor. The headers are all 1 1/2" primaries. I have a set of Red's stubbies and they are excellent quality and they fit easily. Anyway, what I'm trying to get at is if these exhaust options do not flow at least as much as the heads the shorter duration on the exhaust may not work so well. Really consider what you want to do with the truck and the parts that are available to achieve that goal. The cam is probably the one thing you should take the time to get right. It's not as easy as a small block to swap out if you find it doesn't work.


Lawrenceville, GA

Thanks 61'. 

The headers I have are very close to the stubbies that red's sells.  Mine have initial primaries that are also 1 1/2, after about 6 to 8 inches, they become 1 3/4. 

I built them using a pipe bender, a set of flanges, & a used set of 4 into 1 headers from a full size wagoneer.

How big a cam did you use??

My cam is a reproduction blower cam. It is 274 advertised, 226@.050 and .295" lift on 112 separation. It's not an exact repro as I discovered on another post somewhere in the forum. It has .005" more lift and more exhaust duration. I have ported g's as well. I have the idle set at 750 and I have 15" hg at that speed. It has good power off idle and it seems to really come alive between 2000 and 2500. It has some lope. It doesn't sound like a dragster but it is a performance sound.


Lawrenceville, GA

hey guys. just curious. you guys are talking bout custom grind cams right?  how much does it actually cost to have a cam custom ground?  if you were to have a custom groun cam for the y-block, couod it be ground to be setup with solid roller lifters?

Red Stake:

You have talked to a cam grinder who has been in business for nearly half a century, gave him your parameters, and he computer designed a cam specifically for your application.  Then you ask if any of us have any experience with such a cam.  Well, he designed it for you, how could we have any experience with it.  I say go with what he says.  It's his business.  He wants you to be happy with it.  Just my opinion.

John

John - "The Hoosier Hurricane"