Thread: Common Sbc Myth's

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Set the valve lash at zero and they will pull a little more.

My 65 used a Cam Dynamics 431-2 stocker cam to pass tech. Those cams only measured 399 with 300 duration but the dwell was big.

Some of that old stock eliminator stuff from NHRA will really help with street cars.

Bob

Originally Posted by Bob W

Set the valve lash at zero and they will pull a little more.

My 65 used a Cam Dynamics 431-2 stocker cam to pass tech. Those cams only measured 399 with 300 duration but the dwell was big.

Some of that old stock eliminator stuff from NHRA will really help with street cars.

Bob

What are you talking about?
Is the 399 a lift value??
Is the 300 duration a advertised number??
If think you might be confusing "dwell" that is an electrical term often used when setting points with cam terms.

Originally Posted by erik erikson

What are you talking about?
Is the 399 a lift value??
Is the 300 duration a advertised number??
If think you might be confusing "dwell" that is an electrical term often used when setting points with cam terms.

Dwell is the amount of time the valve is fully open. NHRA stocker cams had a bigger dwell to load the cyl with fuel. They measured when the valve started to open and when it closed , the cam profile in the centre was fair game to play with. So the cam opens the valve real quick and holds it open as long as it can then closes real fast so that will still pass tech.

NHRA lists the 431 283 cam at .399 lift and 300 degrees of duration.

http://members.kos.net/willisb/racecars.html

Originally Posted by Bob W

Dwell is the amount of time the valve is fully open. NHRA stocker cams had a bigger dwell to load the cyl with fuel. They measured when the valve started to open and when it closed , the cam profile in the centre was fair game to play with. So the cam opens the valve real quick and holds it open as long as it can then closes real fast so that will still pass tech.

NHRA lists the 431 283 cam at .399 lift and 300 degrees of duration.

http://members.kos.net/willisb/racecars.html

Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe.
Duration at .050 is the industy standard and is a good value to compare cams from different manufactures.

Originally Posted by erik erikson

Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe.
Duration at .050 is the industy standard and is a good value to compare cams from different manufactures.

.050 is industry standard not NHRA. dwell is the amount of time the valve stays in the wide open postion.

I'm confused.

If dwell is a unit of time that the valve stays open in the max position then it varies with speed, and it also is a single point in time at the peak of valve opening? No makey sense ............

Kitz

Originally Posted by kitz

I'm confused.

If dwell is a unit of time that the valve stays open in the max position then it varies with speed, and it also is a single point in time at the peak of valve opening? No makey sense ............

Kitz

Your not the only one who is confused.

Dwell can also be measured in degrees. It's the degrees or time, the valve "Dwells" at it's highest opening.
I guess you have never saw a cam with a flat top on the lobe. The old stocker race cams were like that so it measured stock when turning the engine over with a dial indicator measuring the valve travel, but when it fired up the lift was even greater because the lifter would use the cam as a ramp and actualy be thrown higher creating more valve lift.

I am far from an expert, but isnt that similar to the definition of "valve float" and isnt that highly destructive to the valve train assembly and thus the rest of the motor? Especially at a zillion rpm's ?

Try this link http://www.pipercams.co.uk/NewPiperW...echAdvice.html


Bob

Originally Posted by 65cayne

I am far from an expert, but isnt that similar to the definition of "valve float" and isnt that highly destructive to the valve train assembly and thus the rest of the motor? Especially at a zillion rpm's ?

The "D" cams were only used in race car engines and were not meant for street applications. The D series cams only went to about 5500 to 6000 rpms while the newer cams could attain higher rpm with out valve float.

Originally Posted by Bob W

...the lifter would use the cam as a ramp and actualy be thrown higher creating more valve lift.

I didn't see anything about this on your link. I understand the concept perfectly, just dont understand how these suckers could stay together. Must make a heck of a racket.

I just had a conversation with some guys last night about english getting broke down into incomprhensible bits.I said thats cool and 1 peson yeah its neat,the other guy felt it and said no its warm ,the other two went for jackets! !When speaking with others it usually works best to use common terminology that everyone understands as standard terms.I say thats bad to the bone and granny looks for a switch to spank with ,the 2 kids down the street say yeah that is cool and the preacher wants him to repent and 2 people overheard the kids say it was cool and went for jackets.
I have never heard dwell used as cam terminology before and you may loose some people along the way using terminology that no one else uses,kinda makes it hard to know what you are exsplaining.While working in the garage and asking for that doodad on the shelf may work in person ,it leaves alot to question over the internet as to what doodad or deallybob was he talking about.

I thought all car guys used those terms. If you click on the link I sent and scroll down it will show the dwell. Maybe street cars and bracket racers don't use these terms ?

"Dwell: As the valve reaches full lift it will stop moving for a few degrees before starting to drop back towards the seat, this period is known as the dwell. When checking the cam timing using the full lift figure method the mid-point of the dwell should be taken as exact full lift. "


The above quote is from the link I posted earlier. Happy reading.

Bob

Question: if “dwell” it the time that your valve “dwells” at TDC (max lift) then how do you set “dwell” with a dwell meter?.....isn’t “dwell” supposed to refer to something along the lines of a points ignition system? The more I type that word….the odder it looks to me….I must be losing my mind…dwell


btw: someone that works with me just stated that "you dont set dwell time on a cam, especially since all "D" cams were either "3/4 race" or "full race" grinds. There is nothing to adjust..."

Is he full of bologna?