Understanding Cam Specs

[Charlie Brown]

I have the following Lunati cam in my 426 w in my 64 Dodge. The specs are as follows, as taken from their web site -
Hydraulic Flat Tappet. This high performance street cam likes 2400 RPM stall, 800 CFM carb, dual plane intake and headers. Makes un- equaled power to 6200 RPM with proper valve springs.; Advertised Duration (Int/Exh): 268/276; Duration @ .050 (Int/Exh): 226/234; Gross Valve Lift (Int/Exh): .494/.513; LSA/ICL: 110/106; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1800-6200
My question(s) is the correlation between the LSA and ICL combined with the advertised duration.
What kind of vacuum at 800 idle speed should I expect?
What is the significance of the split LSA?
What is the significance of the split ICL?
I'm having some minor idle in gear quality and before I get into other areas (carb, ignition, etc), I'd like to know if what I'm experiencing is cam spec. related.
Is this cam capable of getting 14 inches of vacuum at idle in gear?
Thanks in advance to all the cam gurus.

 

[pnora]

The LSA you can not change its the way the cam is ground. The ICL you can change when degreeing a cam. What as the recommended cam degree and what did you degree it at?

 

[Charlie Brown]

The LSA you can not change its the way the cam is ground. The ICL you can change when degreeing a cam. What as the recommended cam degree and what did you degree it at?

This was not my build, so I'm not sure how the cam was installed.

 

[Krooser]

That cam is pretty snotty for a street car. It will never produce 15" of vacuum...maybe 8".

The split lift and duration numbers help fine tune a head with a less than ideal exhaust port

 

[4mulas]

That’s a lot of cam questions. I suggest you research camshaft and how they’re made and what all the stuff means. David fryberger does a good explanation on engine masters I believe which takes several minutes of speaking. Way to much to try and type coherently…

ANYWAY;

What does ‘having minor idle in gear quality’ mean? Are you having an issue?

What issues are you having?

What torque converter did you use?

110lsa will make a slightly lopey idle and have Lower vacuum than a stock magnum 440 cam. Vacuum could be from 12-14 I don’t know.

 

[Charlie Brown]

That’s a lot of cam questions. I suggest you research camshaft and how they’re made and what all the stuff means. David fryberger does a good explanation on engine masters I believe which takes several minutes of speaking. Way to much to try and type coherently…

ANYWAY;

What does ‘having minor idle in gear quality’ mean? Are you having an issue?

What issues are you having?

What torque converter did you use?

110lsa will make a slightly lopey idle and have Lower vacuum than a stock magnum 440 cam. Vacuum could be from 12-14 I don’t know.

Thanks for the reply. You are correct in that I should have done more research before posting. I got a little ahead of myself. I'm normally a research type of guy (ask my wife). Some of my questions don't even make sense. I feel a bit embarrassed for even posting this. I was looking for quick answers when I know that often, that is not possible. I'll re-visit this when I'm better informed.

 

[Mopar Hunter]

I feel a bit embarrassed for even posting this.

Never feel embarrassed for asking a question. You’ll never know the answer unless you ask a question.

 

[Black_Sheep]

What is the idle quality issue? Does it die when you put it in gear? Exhaust smells rich and burns your eyes? Won’t idle at a reasonable RPM? What is the initial ignition timing? What converter?

With a little more information I’m sure we can steer you in the right direction…

 

[toolmanmike]

I have the following Lunati cam in my 426 w in my 64 Dodge. The specs are as follows, as taken from their web site -
Hydraulic Flat Tappet. This high performance street cam likes 2400 RPM stall, 800 CFM carb, dual plane intake and headers. Makes un- equaled power to 6200 RPM with proper valve springs.; Advertised Duration (Int/Exh): 268/276; Duration @ .050 (Int/Exh): 226/234; Gross Valve Lift (Int/Exh): .494/.513; LSA/ICL: 110/106; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1800-6200
My question(s) is the correlation between the LSA and ICL combined with the advertised duration.
What kind of vacuum at 800 idle speed should I expect?
What is the significance of the split LSA?
What is the significance of the split ICL?
I'm having some minor idle in gear quality and before I get into other areas (carb, ignition, etc), I'd like to know if what I'm experiencing is cam spec. related.
Is this cam capable of getting 14 inches of vacuum at idle in gear?
Thanks in advance to all the cam gurus.

Put a vacuum gauge on it (manifold vacuum) and see what you have. What initial timing are you running? That can effect vacuum. That's not a very wild cam for a Hemi.

 

[Charlie Brown]

What is the idle quality issue? Does it die when you put it in gear? Exhaust smells rich and burns your eyes? Won’t idle at a reasonable RPM? What is the initial ignition timing? What converter?

With a little more information I’m sure we can steer you in the right direction…

What I am trying to do is eliminate one item at a time. I know that there are several possible areas that I can look at. I am starting with the cam and working from there. My initial post was not as well thought out as it should have been. I really should have started by asking what kind of vacuum reading should I expect from this cam. Thanks.

 

[beanhead]

That cam is pretty snotty for a street car. It will never produce 15" of vacuum...maybe 8".

The split lift and duration numbers help fine tune a head with a less than ideal exhaust port

Did you read that right....it's 226 on the intake @ .050....nowhere near snotty in a 426W.

I have the following Lunati cam in my 426 w in my 64 Dodge. The specs are as follows, as taken from their web site -
Hydraulic Flat Tappet. This high performance street cam likes 2400 RPM stall, 800 CFM carb, dual plane intake and headers. Makes un- equaled power to 6200 RPM with proper valve springs.; Advertised Duration (Int/Exh): 268/276; Duration @ .050 (Int/Exh): 226/234; Gross Valve Lift (Int/Exh): .494/.513; LSA/ICL: 110/106; Valve Lash (Int/Exh): Hyd/Hyd; RPM Range: 1800-6200
My question(s) is the correlation between the LSA and ICL combined with the advertised duration.
What kind of vacuum at 800 idle speed should I expect?
What is the significance of the split LSA?
What is the significance of the split ICL?
I'm having some minor idle in gear quality and before I get into other areas (carb, ignition, etc), I'd like to know if what I'm experiencing is cam spec. related.
Is this cam capable of getting 14 inches of vacuum at idle in gear?
Thanks in advance to all the cam gurus.

I've gotten to a nice 13-14 in/hg at an 800 rpm idle with a (slightly bigger) 231 degrees @ .050" in a (slightly bigger) 440, with tuning you should be able to get it where you want it.
The "split" ICL and LSA you mention are just a result of the math relationship between the intake and exhaust lobes, so don't sweat that stuff. A true "split" profile wedge engine cam typically has more exhaust lift than the intake. Most shelf cams are ground like that so don't sweat that either.
Get the idle timing up around 18 degrees or more, while being careful to limit total timing at 32-36ish (depending on the heads) before you dig into the carb. Pay attention to the converter recommendation; too low a stall can be tricky to tune in gear with an aftermarket cam.

 

[Geoff 2]

There is no way you will get 14" of vac, in gear, with that cam that has 108 LSA.

If you want more idle vacuum, change to a cam that is a single pattern with about 220* @ 050 such bas an Isky 270 Mega.
BB Chrys do NOT tolerate a lot of duration because of the high rod/stroke ratio, see below.

 

[Geoff 2]

Also, you will need a LOT of timing at idle, with either cam; if you keep the current cam, you may need as much as 35* at idle. Yes 35* !!!! Maybe more. Easiest way to do this is using vac adv connected to manifold vacuum. Choose, say 15* initial & add 20* with vac adv. See below

 

[Geoff 2]

And.....

 

[PRHeads]

There is no way you will get 14" of vac, in gear, with that cam that has 108 LSA.

The cam in post #1 has an LSA of 110, with a recommended ICL of 106.

I look at it as a Lunati version of a Comp XE268.

One thing I’ve found that can affect idle quality is the carbs ability to provide enough idle fuel mixture to the engine with a reduced vacuum signal(lower vacuum).
I generally prefer carbs that have 4 corner idle in engines where the idle vacuum(after tuning) still ends up at 12” or lower.

As mentioned previously, too tight of a converter can also create challenges when trying to obtain a strong idle in gear.

Ultimately though, it’s a matter of sorting out the carb, the ignition curve, and the stall speed as a “system” to get the driveability right.

The cam in question isn’t so big it should create any insurmountable tuning challenges.

 

[Charlie Brown]

The cam in post #1 has an LSA of 110, with a recommended ICL of 106.

I look at it as a Lunati version of a Comp XE268.

One thing I’ve found that can affect idle quality is the carbs ability to provide enough idle fuel mixture to the engine with a reduced vacuum signal(lower vacuum).
I generally prefer carbs that have 4 corner idle in engines where the idle vacuum(after tuning) still ends up at 12” or lower.

As mentioned previously, too tight of a converter can also create challenges when trying to obtain a strong idle in gear.

Ultimately though, it’s a matter of sorting out the carb, the ignition curve, and the stall speed as a “system” to get the driveability right.

The cam in question isn’t so big it should create any insurmountable tuning challenges.

Converter is approx. 2400, carb is a 670 avenger and ignition curve has yet to be determined. I plan to check the distributor curve and then move on to the carb. Your comment about reduced vacuum to the idle fuel mixture circuit makes sense. Thanks for your input.

 

[Ray70Chrg]

I have that exact cam in a 383, not a 426. It's a vodoo 703. My best idle is at 900 rpm and I get 14 in. of vacuum. I have 16 degrees of advance with the distributor vacuum disconnected. 14 in. of vacuum is enough to run the p/b booster and a/c controls on my car. The cam has 4 degrees advance built into it, so that's why you have the 110/106 numbers. It's a good cam on the street, I wouldn't call it snotty even though I don't know what that means. Good luck with your car.

 

[PRHeads]

Converter is approx. 2400, carb is a 670 avenger and ignition curve has yet to be determined.

As I said, those three items need to all be looked at together as a “system”.

At this point, I’d start with getting the ignition curve sorted out.
I think you’re going to want at least 15* of initial timing, idling in gear.
More initial timing = more idle vacuum……..and more vacuum helps pull more fuel thru the circuit.
Limit max mechanical timing to 38*.
Hopefully you have a distributor that allows for some adjustment of the amount of advance available(although that isn’t mandatory if you’re just experimenting with the affects of initial timing on idle characteristics).

If you check the current initial timing and find it’s already well into the teens……..then theres a good possibility the carb is having trouble supplying enough fuel with lower than ideal vacuum(which is how much idling in gear?)
Also, there’s no law on how many turns out the mixture screws need to be.
I often see two corner idle carbs that are marginally working in a low(er) idle vacuum situation that end up needing the mixture screws out way more than 1.5 turns.
3-4 turns out is not uncommon to get a decent idle out of them.

One more thought……
If the advance springs are weak enough to allow for any appreciable amount of advance in neutral…….and some of that advance is lost when putting the trans in gear……..the lower advance in gear lowers the vacuum signal, which often diminishes the idle quality…….which lowers the idle speed, which lowers the vacuum, etc, etc.
Having the timing change kept to minimum going from idling in neutral to idling in gear can often make a noticeable difference.
This can often be a challenge to get sorted out, and is a good argument for a programmable distributor.

 

[Charlie Brown]

I have that exact cam in a 383, not a 426. It's a vodoo 703. My best idle is at 900 rpm and I get 14 in. of vacuum. I have 16 degrees of advance with the distributor vacuum disconnected. 14 in. of vacuum is enough to run the p/b booster and a/c controls on my car. The cam has 4 degrees advance built into it, so that's why you have the 110/106 numbers. It's a good cam on the street, I wouldn't call it snotty even though I don't know what that means. Good luck with your car.

I'd be happy to have those numbers - I'll be digging into the tuning process further.

 

[Charlie Brown]

As I said, those three items need to all be looked at together as a “system”.

At this point, I’d start with getting the ignition curve sorted out.
I think you’re going to want at least 15* of initial timing, idling in gear.
More initial timing = more idle vacuum……..and more vacuum helps pull more fuel thru the circuit.
Limit max mechanical timing to 38*.
Hopefully you have a distributor that allows for some adjustment of the amount of advance available(although that isn’t mandatory if you’re just experimenting with the affects of initial timing on idle characteristics).

If you check the current initial timing and find it’s already well into the teens……..then theres a good possibility the carb is having trouble supplying enough fuel with lower than ideal vacuum(which is how much idling in gear?)
Also, there’s no law on how many turns out the mixture screws need to be.
I often see two corner idle carbs that are marginally working in a low(er) idle vacuum situation that end up needing the mixture screws out way more than 1.5 turns.
3-4 turns out is not uncommon to get a decent idle out of them.

One more thought……
If the advance springs are weak enough to allow for any appreciable amount of advance in neutral…….and some of that advance is lost when putting the trans in gear……..the lower advance in gear lowers the vacuum signal, which often diminishes the idle quality…….which lowers the idle speed, which lowers the vacuum, etc, etc.
Having the timing change kept to minimum going from idling in neutral to idling in gear can often make a noticeable difference.
This can often be a challenge to get sorted out, and is a good argument for a programmable distributor.

This is great information, Thanks for this. I do know that the engine has a Pertronix Igniter 2 conversion as well as a FBO Advance limiter plate installed. I'll have to sort out the timing and advance specs that I currently have. Unfortunately, I do not have the additional springs that came with this kit to tune further - I'll see if I can pick some up somewhere.