Common Sbc Myth's

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Originally Posted by erik erikson

I think what Bob is refering to is called lobe lift here in the US anyway.
Lobe lift X rocker arm ratio = max. lift.
An example would be .350 lobe lift X rocker arm ratio 1.5 =.525 net valve lift.

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No the dwell is the # of degrees that the lifter is at the top of the lobe (degrees at .525 net lift).

Camshaft lobes have the opening ramp, then the dwell, then the closing ramp .

Hi Perf Cams are ground with more dwell to hold the valve at max lift longer.

Look at this link and read it all

http://www.pipercams.co.uk/NewPiperW...echAdvice.html

So, the valve "Dwells" at wide open postition longer.

There is also dwell for pistons in your engine , like how long the piston dwells at TDC or BDC. Things have to stop and dwell for a few dgrees then start to move the other direction.

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Originally Posted by shawnlee28

You know that is talking about the cam on the distributor?right?Not the actuall cam shaft of the engine that moves the valves.

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No, I assumed it was the horizontal one. Shows what I know about old ignition systems :LOL:

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Originally Posted by Bob W

No the dwell is the # of degrees that the lifter is at the top of the lobe.

Camshaft lobes have the opening ramp, then the dwell, then the closing ramp .

Hi Perf Cams are ground with more dwell to hold the valve at max lift longer.

Look at this link and read it all

http://www.pipercams.co.uk/NewPiperW...echAdvice.html

So, the valve "Dwells" at wide open postition longer.

There is also dwell for pistons in your engine , like how long the piston dwells at TDC or BDC. Things have to stop and dwell for a few dgrees then start to move the other direction.

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Yes,rods will stay longer at TDC with a longer rod.
There are no cam companies in the US the recognize this "dwell" term.

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Originally Posted by Bob W

... If you go way back to post #16 I said that I ran a cam with more dwell and that's all I said. Then all of a sudden we are here.

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:LOL: It seems like chaos, but the whole conversation would take about ten minutes with ten guys with 16oz cups in their hands standing around a stainless steel drum with manual siphon device affixed to the top to dispense liquid contained therein. Just seems crazy with everyone posting and quoting and replying to such...

So we have Canadian Dwell :D associated with the valvetrain and dealing with valve dwell due to cam lobe. Full roller cams understood to have a high degree (no pun intended) of dwell. (i.e. opens quicker, stays there longer)

And we have outdated American Dwell associated with ignition/distributor and the amount of spark (or rather, length of time a spark is) delivered at a precise time in any given combustion stroke.

The former being non-adjustable (in terms of degrees) and the latter being adjustable.

As far as the original post goes. It's fun to get off topic sometimes but let me say this: I think SBC's are bad to the bone and probably the best motor out there for hotrodders, but whatever you can do with a small block, you can do it bigger (hence, better) with a big block (oldest discussion out there, I know :rolleyes: )...that's why I have a big block under my hood.:D

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Originally Posted by poncho62

I think the person that started this thread is just jealous of the best engine ever built............The SB Chevy. Just because some kids say they can do this or that, doesn't make the engine a slug....It just makes those kids FOS

BTW, I turn mine up to 5400 rpm.....thats all I need it to.

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I wouldn't call it the best engine ever built. it's a good engine with a lot of aftermarket parts made for it, which it makes it a good candadait for cheap power, the reason it's so popular

Why do you think there are a lot of aftermarket parts made for it????

There ya go..............

I have heard of the term dwell in regard to time at tdc on a cam, but not for years... Schneider and Lunati used to play with it some on their roller cams. Now cam science has gone so far beyond dwell and do more engineering in the cam opening and closing ramp rates. When time at TDC was the rage, lots of the chebbie guys were boring their lifter bores out to use the Ford lifters so they could have the point of the lobe, thereby the dwell, longer. Nobody is wrong here, just some of us are a lot older then others......:LOL: :LOL: :LOL:

If Tech comes along, I'm sure he could explain all the differences in cam engineering over the years if he were inclined to write a book. I still do it the easy way, call one of the engineers at Comp Cams and get one ground. Got to remember, years ago we didn't have all the long rods to keep the piston at the top longer, and the emphasis was all on the cam designers to make the engine work. This was also when flow benches were rare, and everyone thought bigger was better on port and runner size.....

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Originally Posted by DennyW

Actually, the cam lobe dwell should be longer than the piston dwell, as to get the flow going to fill, or empty the cylinder quicker. :LOL: Along with a modified lobe ramp to speed up the sealing of the valve.

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Denny, this goes back to an old discussion we used to have to kill time running countless miles towing the sprinter around from track to track...... Does scavenging the cylinder make the engine think it has a blower on top, or does scavenging increase the velocity of the intake charge so much that it doen't atomize the mixture properly and give the cylinder a false rich condition and kill a good burn across the piston top....????? The tow from Rapid City, SD back to the shop was 380 miles, we did it every Friday night (aka Sat. AM) for a couple years. This was the topic on a number of those trips!!!!! Not sure we ever resolved the issue, or if anybody ever managed to convince the others that his viewpoint was right!!!! And no, I'm not even going to say which side of the argument I was on!!!:LOL: :LOL: :LOL: You don't even want to know what some of the other topics were!!!!:eek:

Oh yeah, we were running methonol, too. And sometimes somebody would sneak by and toss about a 4% load of nitromethane in the tank.... Made the discussion even more lively on the way home.....:LOL: :LOL: :LOL: :LOL:

PS---at 10% in a 40 lap main on a 1/2 mile dry slick track, the piston tops resemble crispy critters!!!!!

Dwell means to stay in a place for a certan amount of time. Bob is right. When refering to points dwell is the amount of time the points stay open, same as with piston staying at TDC or BDC for x amount of time, same with lifters.

I stand corrected, the amount of time points closed.:)