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Discussion Starter #1
I want to start a dialogue on camshafts, how they function and what effects or results the many specifications have.

First of all I have an 2122 Edelbrock cam for my 66 289 coming out of the engine is what I assume to be a stock 2V cam.

I'm asking what effect will the valve overlap have on my compression ratio and compression pressure, how to determine or calculate? The compression pressure was 165 PSI I would like to back calc. the old ration as well to compare.

FYI the stock overlap I calculated at 36 deg,
the new 2122 cam calculated at 51 deg and
Specs from a "K" 271 HP calculated out at 82 deg

The formula used was
add intake and exhast advertised durations and divide result by four
subtract the LSA (lobe separation angle) and
multiply the result by two


So this particular exercise is to also help me determine if my compression will be low enough to enable me to bolt on a blower. :)

fire away...
 

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I want to start a dialogue on camshafts, how they function and what effects or results the many specifications have.

First of all I have an 2122 Edelbrock cam for my 66 289 coming out of the engine is what I assume to be a stock 2V cam.

I'm asking what effect will the valve overlap have on my compression ratio and compression pressure, how to determine or calculate? The compression pressure was 165 PSI I would like to back calc. the old ration as well to compare.

FYI the stock overlap I calculated at 36 deg,
the new 2122 cam calculated at 51 deg and
Specs from a "K" 271 HP calculated out at 82 deg

The formula used was
add intake and exhast advertised durations and divide result by four
subtract the LSA (lobe separation angle) and
multiply the result by two


So this particular exercise is to also help me determine if my compression will be low enough to enable me to bolt on a blower. :)

fire away...
valve overlap has nothing to do with compression ratio .
 

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I'm going to jink sideways a bit to add a bit of focus to your thoughtful build process. You sound like the type that can make use of it. Knowing all the factors that affect your build and results is difficult, and most guys spend their lives learning all the things that play into it. But there's a way to analyze all that without knowing it all. Heat.

Heat is the source of our power and our problems in our engines. If you can maximize the heat in the right places, and minimize it in the wrong ones, the whole package will perform better. The way to get a handle on applying it is to view how it affects your greatest limiter - your fuel. This is why engines are built around the chosen fuel, and why a different fuel would require a different engine design. This is true whether building for max economy or max power - it's all focused on max efficiency with the chosen fuel.

As you screw your brain around to view it this way, you'll see how it affects (and how and why you would want to modify) every component from your intake, to your cam timing, to head design, to your exhaust design and even spark plug design (or lack of one ;)). Altering parameters to make more heat where it helps and less where it doesn't will give you more options from more components. I'm expanding the picture while trying to bring more focus. Hope that helps.

David
 

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What are your goal with this cam-shift? This Edelbrock-cam is wery far from beeing a good choice if you want some more driveable power out of your enegine.
 

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Discussion Starter #5 (Edited)
valve overlap has nothing to do with compression ratio .

my understanding so far is that youre correct regarding static compression ratios but what about dynamic? aren't they affected by cam events?

such as if valve overlap is robbing compression and vacuum in a poorly planned build. like a huge overlap and single plane manifold bolted onto a street engine with a choked exhaust and small ports etc. just sayin'
 

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Discussion Starter #6
What are your goal with this cam-shift? This Edelbrock-cam is wery far from beeing a good choice if you want some more driveable power out of your enegine.
Can you expand on this a bit?

fyi
Looking for 275-300 HP in a street run old school SBF.
My engine was a 2V 289 and I'm adding headers, a dual plane manifold with a 600 holley, port matched heads, tri Y headers, 2 1/2" SS custom exhaust, it's 0.060 over and this 2122 cam.
The cam was recommended for this build by a Mustang nut I have known for 35 years. I would love to bet him a box of beer he screwed this one up. So let me know why the Edelbrock is a bad fit?
 

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my understanding so far is that youre correct regarding static compression ratios but what about dynamic? aren't they affected by cam events?

such as if valve overlap is robbing compression and vacuum in a poorly planned build. like a huge overlap and single plane manifold bolted onto a street engine with a choked exhaust and small ports etc. just sayin'
dynamic isnt affected by overlap

poorly planned build is just that ..
what blower do you have ? boost pressure goal ?
 

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Intake valve closing event has a pretty big impact on low-speed cylinder filling (showing as a low vacuum, since you have no flow momentum.

I wouldn't worry too much about using cranking pressure as a measure of cam specs. That's, at best, a diagnostic tool for comparison between cylinders. It's a lot easier to use a degree wheel and a couple dial indicators, and a lot more reliable.

Overlap will have some correlation with fuel efficiency (more overlap, more fuel out the back) but even that depends on your whole combo, like Dan was saying.

Looking at cam basics (like timing of valve events, the impact of overlap and lobe separation, etc) is a good exercise (and there are a many books on the subject!) but when it comes to building an engine the cam you choose is no more or less important than any other part of the build.

Forced induction completely changes the ballgame when you're talking about cam timing, and a cam designed for power in a NA configuration will not be an ideal cam for forced induction.

Instead of starting from specific and working to general, lets start general and work to specifics. What are you trying to achieve and what do you have to start with?
 

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Can you expand on this a bit?

fyi
Looking for 275-300 HP in a street run old school SBF.
My engine was a 2V 289 and I'm adding headers, a dual plane manifold with a 600 holley, port matched heads, tri Y headers, 2 1/2" SS custom exhaust, it's 0.060 over and this 2122 cam.
The cam was recommended for this build by a Mustang nut I have known for 35 years. I would love to bet him a box of beer he screwed this one up. So let me know why the Edelbrock is a bad fit?
To get the best out of your combo you should look for a moderate cam with 108 degree lobe-separation. I`ve picked me a classic Isky Mega 264* for my 302, runs strong from 2-6k and with its 0.48 lioft it will match the stock heads:

Grind No./Type 264-MEGA HYDRAULICTremendous torque and good mid [CL-381264] - $240.00 : ISKY Racing Cams, Do It Right. Race with the Legend.

Isky Timing Chart

* Big Joe Sherman used exactly these two cams as an example of a bad and good cam; both advertising 214 at 0.50 but the Isky made +40hp over the Edelbrock

http://www.fordmuscleforums.com/all-ford-techboard/457289-1-7-rockers-good-idea-bad-idea-ones-2.html


Some stuff about lobeseparation:

Engine Camshaft Basics - Popular Hot Rodding Magazine

Good luck with your build!
 

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Don't lose sight of the fact that HP is a calculated number...We don't race dynos.. Tork is what makes a car fun to drive. You didn't mention whether you were running an auto or standard tranny, that makes a big difference also in cam selection. Everyone here has made some good points, but all the cam co's have tech lines and people just waiting to call and help pick the best can for every application. Having siad all that...My thinking is that combo will make a pretty nice running motor, and should put you in the range you want to be. But Id still look around and see what else is out there.
 

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Don't lose sight of the fact that HP is a calculated number...We don't race dynos.. Tork is what makes a car fun to drive.
For the love of God let's not go there again! Slowly back away from the keyboard and hope nobody notices . . .
;)
David
 

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Don't lose sight of the fact that HP is a calculated number...We don't race dynos.. Tork is what makes a car fun to drive. You didn't mention whether you were running an auto or standard tranny, that makes a big difference also in cam selection. Everyone here has made some good points, but all the cam co's have tech lines and people just waiting to call and help pick the best can for every application. Having siad all that...My thinking is that combo will make a pretty nice running motor, and should put you in the range you want to be. But Id still look around and see what else is out there.
call cam co's , most tech's just read a program like the parts house look up a w/p or ......
 

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I ran that Edelbrock cam for several years, 25 years ago. It's an RV grind used to pump up low rpm torque in small motors and get reasonable gas mileage in the mean time. It's not a performance cam, and in my motors it would stop pulling hard at around 4700 rpm. BTW, Edelbrock doesn't grind or even design their own cams, they are generic off-the-shelf items that you can buy everywhere for half the price that Edelbrock charges.

Summit Racing SUM-3600 - Summit Racing® Camshafts - Overview - SummitRacing.com

It's an old, obsolete design. Get a modern roller cam and don't look back.
 

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think Eldbrock would step up the cams to current tech .

would make his product test perform at a higher level .

most buy for the numbers and price . better bang for the buck equal better sales
 

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I want to start a dialogue on camshafts, how they function and what effects or results the many specifications have. . . .
So this particular exercise is to also help me determine if my compression will be low enough to enable me to bolt on a blower. :)
Back to your earlier question, you can boost any engine, but how much and when its limited by all the other factors. Your cam example is generically pretty good for a street blower cam. A 112° LSA to push torque to higher rpms (relieving heat and pressure at lower rpms) and limiting raw fuel transfer out the exhaust. Longer exhaust duration for stock-ish heads with limited exhaust flow. Enough asymmetric duration and lift to get the good stuff in and out on limited boost.

Offhand, that cam should be good for around 500 FWHP at pump gas boost levels - but all your other components and tuning must match-up to let it do that and also remain reliable. It's short enough (greater low-rpm dynamic compression) you'd have to stay low on static compression, but I'd say 8 to 8.5:1 should be tunable on 92 octane pumpcrap to hit that HP with a 65% blower efficiency at peak and maybe 75% inter/aftercooler efficiency (shooting low here) - again depending on your other parts matching. Stretching the LSA a bit further with a dose of equally applied duration would increase your static compression capability a bit. HTH

David
 

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Discussion Starter #19
dynamic isnt affected by overlap

poorly planned build is just that ..
what blower do you have ? boost pressure goal ?
I don't have a blower... yet.

If I do it will probably be something that will tuck under the hood.

Just concentrating on getting the damn car done. I don't seem to have the time to finish anything.
 

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Discussion Starter #20
Definitely not looking for 500 HP in this build. I don't think I have the rods or crank to start pounding that level of power, neither do I have the heads. My rocker posts are pressed in. But that's not to say there isn't a build in the future going that way. I'm tooled up to pull and assemble engines and the plan is to have a daily driver set up and a more aggressive track set up. I'm not even ruling out a second third member. second third member because my first isn't enough... did I just say that?

haven't looked at torque curves on that cam either yet the request when asking my connection to select something was for a lengthy and flat curve at the 2500-4500 range. Looking for about a 5-5500 RPM redline with those stock heads.

Back to your earlier question, you can boost any engine, but how much and when its limited by all the other factors. Your cam example is generically pretty good for a street blower cam. A 112° LSA to push torque to higher rpms (relieving heat and pressure at lower rpms) and limiting raw fuel transfer out the exhaust. Longer exhaust duration for stock-ish heads with limited exhaust flow. Enough asymmetric duration and lift to get the good stuff in and out on limited boost.

Offhand, that cam should be good for around 500 FWHP at pump gas boost levels - but all your other components and tuning must match-up to let it do that and also remain reliable. It's short enough (greater low-rpm dynamic compression) you'd have to stay low on static compression, but I'd say 8 to 8.5:1 should be tunable on 92 octane pumpcrap to hit that HP with a 65% blower efficiency at peak and maybe 75% inter/aftercooler efficiency (shooting low here) - again depending on your other parts matching. Stretching the LSA a bit further with a dose of equally applied duration would increase your static compression capability a bit. HTH

David
 
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