HELP ! for a cam dumby

[haack52]

I don't know why, but I just can not understand the calculations that go into cams.
So I'm not going to try!
Can someone help me in predicting what this engine is going to run like with this cam ?
Duration @ .050 224 IN 233 EX
Duration @.006 270 IN 285 EX
Lobe lift .3180 IN .3065 EX
Separation 110
Gross lift .509 IN .490 EX
Degree IN lobe to 109
1970 Cutlass 455 9.5 compression stock exhaust edelbrock 750.
I need the smooth idle (I have a wife), but I don't want this to be a dog.
This is a new cam and it will replace a Mondello JM 20-22 that is terrible.
Can this cam give the smooth idle or do I need to buy ANOTHER one???

[J-(Chicago)]

Picture an engine as a Mcdonald's straw in your mouth.
Put your finger over the end to block the air. Now try to breathe in.

You can't because your finger (the intake valve) right now is closed.

Intake lift is how far off of the straw you can lift your finger to breathe, and intake duration is how long you can lift it for before you must cap it off.

Ok, so now you have some air in your lungs, but can't hold your breath forever.
Try breathing out.
You can't because your finger (the exhaust valve now) is closed.
Exhaust duration is how long your finger makes you hold your breath for before you can exhale and blow out of the straw.
And exhaust lift is how far you may lift your finger off of the straw to exhale.

The lobe separation angle is how far of a timespan you have to work with before you have to inhale again and start the cycle again. You might be thinking..." Oh crap. I'm still exhaling and here comes the intake lobe again."

Too bad. You have to stop where you are at with the exhale and start inhaling again. If you get the timing perfect you won't get dizzy and pass out.

You have to figure out how big your intake straw is on your motor, and how big your exhaust straw is. You could have a fast intake like with a toilet paper tube, but if you have to exhale through a McDonalds straw, and you have the same duration on both, it won't work out too well will it?

Every cam will be perfect at only one speed.

Here's a simple theory:
It's easy for me to breathe in a lung full of air through a toilet paper tube, so I won't need a lot of intake duration. Too much and my lungs will pop so we'll call it 2 seconds. Your stock exhaust is restrictive like a straw so it will take you 4 seconds to exhale through the straw instead of the 2 seconds it would have taken with the TP tube.
You don't want to have too much overlap time or your intake air will go right out your exhaust. You want to give your lungs enough time to get that oxygen out of that air and use it to power you.

Your compression ratio is very good on that motor, so you will have decent air velocity blasting through it. Think of compression as how powerful your lungs are when forcing the air out of the straw.

Your LSA is on a 110, so it shouldn't be too obnoxious. Generally, the 106 LSA cams are the really choppy ones. As far as "smooth idle" That is open to opinion. That cam seems like it will have too high of a powerband for a stock intake and exhaust motor.

So the new question is:
Watcha got?
Other than 9.5 compression and stock exhaust?

[cutlassefi]

Weird way to descibe it J but I guess it works.

A JM 20-22 is 226/233, .496/.512 on a 110. Why are you going thru the trouble of putting almost the same cam back in and expecting different results?

Someting in the 215-218 range on intake duration @ .050 will help. Or something on a 112 will help too. Install with a bit more advance and that will help virtually every cam drive better.

Lunati has some good grinds that keep a good amount of lift to retain some performance. Check em out.

[jslabotsky]

I think he may need some help understanding the different terms on the cam card. I'm trying to improve my understanding of this, so I'd like to take a stab at explaining it so I can see how close I get. Experts please correct my errors.

• The duration @.050 gives an indication how long, in degrees of crank rotation, the valve is open wide enough to flow a considerable amount of air/fuel charge or exhaust gas.
• The duration @.006 indicates how long the entire open/close event takes. This, combined with duration @.050 and gross lift gives you an idea how steep the ramp is - that is, how fast the valve opens/closes. The steeper the ramp, the harder on the valvetrain. I don't know what effect this has on performance other than I'm guessing a steeper ramp allows for longer duration @.050.
• Lobe separation angle indicates how far apart the centers of the instake and exhaust lobes are. This in conjunction with lift and duration tells you how much overlap there is (how many degrees of rotation both valves are open). Valve overlap can help increase the velocity of intake charge entering the cynlinder. IIRC a lot of overlap creates a lumpy idle and hurts low-RPM power but helps high-RPM power.
• Gross lift is the total amount of lift the cam provides at the center of each lobe. Actual lift at the valve may vary due to other factors, chief among them the rocker arm ratio. Gotta' watch this with big cams to be sure your rockers and springs can handle enough lift. IIRC the cam you named is fine with stock springs.

It sounds like cutlassefi is suggesting a little less duration or a little more lobe separation because it will reduce the overlap and smooth things out.

Well, how close did I get?

[cutlassefi]

Very. Except the @ .050 number is the time the valve is open between .050 on the up side and .050 on the down side, not "wide enough to flow a considerable amount of ..... It's just an industry standard of measurement.

But today sometimes an even better way of predicting how fast the ramps may be is by comparing the @ .050 number to the @ .200 number. Most cam companies give that now. The bigger the difference the faster the ramp. But don't confuse them with roller grinds. They'll seem slow at first then progressively get faster. That's because the lifters are so much heavier, you need to get them started before you start to try to yank them open.

Also having a faster ramp doesn't always mean t's harder on the valve train. Sometimes a faster ramp will just make it a.bit noisier. I do alot of roller stuff with Erson. They'll be the first one to tell you that their stuff won't make that last bit of hp like maybe Comp will but theirs is much easier on the valvetrain. However if you look at their profiles, they're not exactly slow but work very well.

As far as flat tappet stuff goes, I'd still take a peek at the Lunati profiles, and not just the VooDoo ones. They'll grind you whatever you want for just a few bux more and they have some designs available that will smooth out your low speed but retain throttle response and some lift so your hp loss won't be so noticeable. Check for yourself.

[jslabotsky]

Originally Posted by cutlassefi

Very. Except the @ .050 number is the time the valve is open between .050 on the up side and .050 on the down side, not "wide enough to flow a considerable amount of ..... It's just an industry standard of measurement.

Actually I do understand what it is, but I was trying to think of a way to explain in layman's terms why you would care about the @.050 measurement. Maybe I just don't really understand what that measurement is useful for.

haack52, I have been looking at cams similar to your existing Mondello for my first Olds build. I know you said the idle is rough, but I'm curious just how rough. It wouldn't bother me if the car shakes a little, but I'm looking to run power brakes and A/C. Is it really that unbearable?

[cutlassefi]

Originally Posted by jslabotsky

Actually I do understand what it is, but I was trying to think of a way to explain in layman's terms why you would care about the @.050 measurement. Maybe I just don't really understand what that measurement is useful for.

haack52, I have been looking at cams similar to your existing Mondello for my first Olds build. I know you said the idle is rough, but I'm curious just how rough. It wouldn't bother me if the car shakes a little, but I'm looking to run power brakes and A/C. Is it really that unbearable?

I question that too. A 9.5/1 455 with that cam should idle fairly well. I have a 350 with a 222/230 on a 112 that idles fine. You can hear it but it's fairly smooth. The EFI helps but I'm still wondering why this one doesn't idle well. Mild vacuum leak maybe?

[Mongoose]

I've run the JM 20-22 in my 455 before and thought it was very smooth. I've also run the JM 3-4 on 114 lobe centers and it was also a good idler, and plenty of vacuum for the brake booster.

Problem with classifying "a smooth idle" is that everyone has different perceptions of what is smooth to them. I'm a "hotrodder", so...

Maybe hack52 is just not running enough advance at idle, and/or he's trying to keep his in-gear idle below 800 rpm.

[haack52]

Thank guys for all the super help and advise!!!
In answer to some questions.
Watcha got?
1) Turbo 400 with stock converter, power brakes, roller lifters, stock Ga heads, Edelbrock 750 with a Torker manifold (I need to change this), 2.5" duel exhaust.
2) The reason I have the new cam that ends up being almost the same as what is in it now, is I ordered the cam before I bought this engine and was going to put it in another 455 I had. When I bought this engine (with 1000 miles on it), I wanted to run it before changing the cam. That's why I was asking if the little difference I see in the two cams was going to make any difference in the idle or vacuum. The vacuum is at 9" H2O at 800 rpm. I have checked for vacuum leaks over and over again, I even pressurized it and checked with soapy water, then"canned smoke".
3) The idle is a lopy idle at 700 rpm. but want to pull hard even then.
I don't want to change the converter, and I need more vacuum.
Jslabotsky..... If this is a cam you want you can have it when I pull it.
It has 1000 miles on it.
The thing is This isn't just my toy...the wife wants to be able to drive it and my son (18 years old) and we all know what he would do. The same thing we would do when we were 18.

[haack52]

Also.........Jslabotsky.......If you want this cam I'll mark the lifters as to their location and you can have those as well.

[J-(Chicago)]

If they don't take the cam, I will. Very generous of you.

[haack52]

Thats fine...I couldn't get anything for it even if I tried to sell it.
BUT I will need to find a buyer for the other new cam with the specs I listed earlier!!
So if you know of anyone interested, send them my way.

[jslabotsky]

Wow! Heck yes I'll take it the cam and lifters! Thanks man. If I can come up with anything interesting to offer in trade I will let you know. At the very least I'll be sure to credit you when I write up my build. (Which probably won't start until spring because we're expecting a new leadfoot to join the family around Feb. 1)

Fortunately I'm the only one who'll be driving my car, at least for a good long while. So I can afford to experiment a little and decide how radical a cam I can tolerate.

[haack52]

jslabosky...

[haack52]

Sorry.....hit the button too soon.........I will be getting to this engine in about 3 or 4 weeks.
So I'll let you know when I'm ready to send it.
Keep an eye out for a few things for me, a duel plane intake, (new) water pump, and an HEI dist.
I have the other new cam to swap also. The specs are what I listed earlier, about the same as the Mondello.