[the heckler]

I run a comp XS290S in my 496 that is very similar in build to yours. solid flat tappet with a sassy idle but strong throughout the range of steet motor. 252/260 @ .050 - 598/598 lift. It is right on the edge but a great fit. Sputs racing engines in minn. gets the credit for the selection. I have a remote vacuum canister for my brakes with zero issues....

 

[dreis454]

Joe,
Each lobe requiring mechanical clearance has clearance factor. This amount of clearance is then factored with stock ratio number to come up with the lash on the cam. The duration numbers take this into account. Now if you vary in your lash adjustment from this number you are correct it will change the duration numbers.

When I calculate lobe area I factor a ramp clearance into the equation. What I post is what the customer will see with my lash setting.

Rule of thumb for every .002" of lash change + or - you change the duration by 1 degree up or down.

This helps me understand how to compare duration @ .050" between the two.

 

[cstraub]

This helps me understand how to compare duration @ .050" between the two.

You've probably seen me give radical lash advice to several people on many boards. Lash adjustment is FREE and it will tell you a lot about the cam that is in the engine. If the engine picks up with a different lash adjustment then what the cam came with it tells you that you have the wrong camshaft.

John Reed taught me many moons ago that LASH is the most important tuning tool you have.

 

[Stokerboats]

The combination is the most important part.

I agree with this statement but that said the correct combination with the better head is going to make more power. I guess we agree then.

 

[427L88]

I was going to comment , before eyeing any cam recomendations that Chris made, but.... the same grind I use in my 427 is a wee-bit-o-nasty, but would be utterly tame in a 496. In fact, Harold said it would make a fine very torquey cam done by 6200 maybe, but not to feed it much more than 10:1, adn it ought idle at 15"Hg.

243/251 on a 112 LSA at .660 lift is what Lunati lists the roller version as. Would seem spot on.

Since that would be a custom grind (I beleive its an HR) you might just as well have Chris spec the lobes for you and have Bullet or whomever do it up.

Also, a 427 is a different animal than a 496, to be sure, but one of the best moves I made was to REPLACE the plenum divider I had milled out of the #163 back when I was a punk at age 17. Why? Because the L88 manis all had it milled out.

The engine never revved to 7500 as fast as it did with a Weiand plenum divider back in the mani. It left around .700" gap at the top. Perfect.

Chris' estimate of a 30hp loss may be conservative! But again, a 496 wnats a bigger plenum than an ol L88 motor does.

 

[cstraub]

I agree with this statement but that said the correct combination with the better head is going to make more power. I guess we agree then.

What makes a better head?

 

[Stokerboats]

What makes a better head?

Chris, exactly how much air can a cam flow? You gotta have a port. The more efficient the port, the better the flow
The one with the best port for a given displacement. You could take my cyl head and Johns (same casting), optimize a cam for either and mine will result in more power in the same engine given the induction system is optimized for both. And no I don't want to go find my respective flow figures.:noway:

 

[Stokerboats]

And by the way, since John is now domesticated with kids (they own him) and is trying to handcuff himself with a hydraulic governor he may as well get a 200r4 trans and a q-jet, maybe even A/C. Actually none of which would really be detrimental.

 

[cstraub]

Chris, exactly how much air can a cam flow? You gotta have a port. The more efficient the port, the better the flow
The one with the best port for a given displacement. You could take my cyl head and Johns (same casting), optimize a cam for either and mine will result in more power in the same engine given the induction system is optimized for both. And no I don't want to go find my respective flow figures.:noway:

How much air do you need to fill a given cylinder displacement?

 

[dreis454]

How much air do you need to fill a given cylinder displacement?

An equal amount of the cylinder displacement?

 

[692envy]

The heads are only efficient if they have the correct cam to optimize their potential.

 

[Stokerboats]

The heads are only efficient if they have the correct cam to optimize their potential.

Our goal is to make power.

 

[Stokerboats]

how much air do you need to fill a given cylinder displacement?

110%

 

[69 Ratt Vette]

And by the way, since John is now domesticated with kids (they own him) and is trying to handcuff himself with a hydraulic governor he may as well get a 200r4 trans and a q-jet, maybe even A/C. Actually none of which would really be detrimental.

Ouch !! LOL.

 

[540Hotrod]

Now there's a real world comparison. Pro Stock engines.:noway:

Sounds like real world to me. It's a N/A engine that makes insane power. The concept is that it's a lot tougher to fill a cylinder than it is to empty it. I'll take intake flow anyday and do what I have to do with the exhaust side. I can add duration to intake side and kill a lot of power...but adding to exhaust side don't hurt much. *Might* kill a little low end TQ...but it will extend the RPM range and make power at higher RPM if the ports can't do it on their own.

I do agree 100% that heads are the vital part of any combo. That's where the power is in all cases. Better heads are always a good investment and then match the cam to them. As Chris said.. assuming *X* rpm range.....better heads allow for smaller cams quite often and they pick up low/mid range as well as beng able to make more power as it climbs than a combo with weaker heads...and especially one you're having to *crutch* with a cam to try and make it do something it really shouldn't be trying...like Super Stockers.

Throw more cam in a combo with great heads and you can raise RPM and make more power in most cases until they just can't flow enough to keep climbing. But the big cam can start having the low end detrimental effects without raising HP too much after a point.

Your car is a perfect example of an excellent combo that has lots of track time sorting it out. It just flat works!

JIM

 

[Stokerboats]

jim, I'm thinking a pro stock at 17 to 1 comp with an rpm operating band of what, a thousand rpm's wouldn't be anywhere in the park as a comparison to the lesser levels of build that we actually do use . People poo poo excellent exhaust ports/flow but why? Where exactly is the downside. Seem's all work at the good port then accept mediocrity on the exhaust. My mentor has a very different view on it and is able to achieve values where others just stop.

 

[69 Ratt Vette]

jim, I'm thinking a pro stock at 17 to 1 comp with an rpm operating band of what, a thousand rpm's wouldn't be anywhere in the park as a comparison to the lesser levels of build that we actually do use . People poo poo excellent exhaust ports/flow but why? Where exactly is the downside. Seem's all work at the good port then accept mediocrity on the exhaust. My mentor has a very different view on it and is able to achieve values where others just stop.

And here we go again..........

I am no head expert, but maybe in a NA application too high of an exhaust flow # kills velocity. I do know (like Jim stated) high exhaust port numbers are not needed, and even though not an exact comparrison, a pro-stock engine provides some guidlines that we can probably learn from.

On another note; last I heard from someone in the know, pro-stock engines were in the 14 to 1 range due to VE numbers of around 130%

I got to take the 69 out for a half hour drive yesterday, damn I love driving that car.

 

[cstraub]

In some cases will kill the exhaust port flow to make more power.

 

[GRN69CHV]

So, maybe cylinder head design has progressed to the point where it's time to just do what Big Ed preaches and go back to single pattern cams?

 

[cstraub]

So, maybe cylinder head design has progressed to the point where it's time to just do what Big Ed preaches and go back to single pattern cams?

You have 2 port for every cylinder, one works on depression and the other works with high pressure. I won't say the valve path won't be the same for each but I will say 99.9% of time it won't be. And I am just talking about .050", the MARKETING NUMBER.