picking a cam for your combo

[grumpyvette]

picking a cam for your combo, lets say your building a hot street/strip 383 with a auto trans, alto the process will remain the same with any engine combo, the rpm ranges,etc. will change with the engine combo you chose to build

 

ok lets go thru the basics

first the reasonable rpm range

with a 383 youll want to stay to a max rpm thats not much more than 4000fpm, thats about 6500rpm with the 3.75 stroke

next youll want to find a cam that allows both a reasonable dynamic compression ratio and good volumetric efficiency up to that approximate 6500 rpm red line

 

next youll need to know your true static compression ratio

http://www.newcovenant.com/speedcrafter/calculators/compressionratio.htm

 

and then dynamic compression ratio

http://cochise.uia.net/pkelley2/DynamicCR.html

 

next youll want to find a cam with a reasonable overlap / LSA and lift for your application

 

http://members.uia.net/pkelley2/Overlap.html

 

http://www.chevyhiperformance.com/techarticles/95298/

 

these are the valve timeing overlap ranges that are most likely to work correctly

trucks/good mileage towing 10-35 degs overlap

daily driven low rpm performance 30-55degs overlap

hot street performance 50-75 degs overlap

oval track racing 70-95degs overlap

dragster/comp eliminator engines 90-115 degs overlap

The LSA, or lobe separation angle, is ground into the cam and cannot be changed. It is the angle that separates the intake and exhaust lobe for a particular cylinder, and is measured in camshaft degrees.

The intake lobe centerline is measured in crankshaft degrees. The #1 intake lobe centerline is usually between 100° to 110° ATDC and is what you use to degree the cam. The cam manufacturer will publish the specs for the cam based on a given intake lobe centerline. Comp Cams, for instance, produces a large number of cams with 110_° LSA ground 4° advanced, so they list the specs for the cam with a 106° intake lobe centerline. You can calculate the ILC by adding the intake opening angle in °BTDC, the intake closing angle in °ABDC, plus 180° for the distance from TDC to BDC. Divide by 2 and subtract the intake opening angle and you will have the ILC. For example a 12-430-8 Comp Cam lists IO at 34°BTDC, IC at 66° ATDC, so 34 + 66 + 180 = 280. 280/2 = 140. 140 - 34 = 106° ILC.

 

this is some of the best basic cam info youll find so read this first http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm (lessons 1-8)

 

then youll want to match the valve lift to the port flow charicteristics

http://www.chevyhiperformance.com/techarticles/41598/

 

now since your not giving all the info, Ill need to guess at some info.

I can tell you right now youll be looking at a cam with close to 230 deg@.o50 lift, wheither it should be slightly larger or smaller in duration, its LSA and wheither the cam needs a longer duration exhaust lobe will be determined by the other parts in your combo and if your going to run nitrous

without knowing your true compression ratio,your true cylinder head flow, and your rear gearing and trans stall speed you can,t get a true picture, your cars weight and tire height will also have a noticable effect on the results, so you need to factor in your probable shift points and rpm drop between gears

http://www.prestage.com/carmath/dynochart.asp

 

http://www.wallaceracing.com/reargear.htm

 

heres how to find the port size that close to ideal

http://www.newcovenant.com/speedcrafter/calculators/runnerarea.htm]http://www.newcovenant.com/speedcrafter/calculators/runnerarea.htm]http://www.newcovenant.com/speedcrafter/calculators/runnerarea.htm

heres how to find the port length thats close to ideal

 

http://www.bgsoflex.com/intakeln.html

 

heres how to get some idea on the header config

 

http://victorylibrary.com/mopar/header-tech-c.htm

 

keep in mind that you don,t want to build an engine that makes 500hp at a narrow peak at 6500rpm if your stall speed and gearing and trans shift points limmit your engine to the 2000rpm-5500rpm range.

 

WELL YOU ASKED WHY!!! AND HOW TO FIGURE IT OUT!!

[Guest Jason]

I'm confused about LSA for fuel injection. Looking at various cam offerings, I've noticed that LSA is always wider for computer controlled vehicles such as my LT1. I generally find them with 112° vs. 110° or less for a carb'd vehicle. WHat are the reasons for this wide separation? Is it generally to help pass emissions?

Even long duration/high overlap cams have the same LSA as short duration cams, so I wouldn't think overlap is a problem with FI.

 

Playing with Desktop Dyno, I've found 112° a bit wide for an otherwise stock LT1.

 

-Jason

[grumpyvette]

basically it has to do with the fact that the sensors in an EFI system with the stock software tend to function more relieably if the vacume reading don,t fluxuate as greatly and the air collums in the runners don,t have strong reversion pulse strength, spreading the LSA tends to allow the same total duration but less overlap (the period both valves remain open at the same time) overlap is used effectively for cylinder scavaging at the tuned RPM levels where the exhaust headers help draw in the fresh intake charge but at lower rpms overlap can cause reversion, carbs are slightly less sensitive at low rpms. wider LSA also tend to widden the torque curve slightly allowing a widder operating range and a smoother idle at the cost of a slight drop in the peak torque while tighter LSAs tend to drop rpm where peak low rpm torque occures but raise the peak slightly earlier in the curve

here things to read

 

 

The LSA, or lobe separation angle, is ground into the cam and cannot be changed. It is the angle that separates the intake and exhaust lobe for a particular cylinder, and is measured in camshaft degrees.

The intake lobe centerline is measured in crankshaft degrees. The #1 intake lobe centerline is usually between 100° to 110° ATDC and is what you use to degree the cam. The cam manufacturer will publish the specs for the cam based on a given intake lobe centerline. Comp Cams, for instance, produces a large number of cams with 110­° LSA ground 4° advanced, so they list the specs for the cam with a 106° intake lobe centerline. You can calculate the ILC by adding the intake opening angle in °BTDC, the intake closing angle in °ABDC, plus 180° for the distance from TDC to BDC. Divide by 2 and subtract the intake opening angle and you will have the ILC. For example a 12-430-8 Comp Cam lists IO at 34°BTDC, IC at 66° ATDC, so 34 + 66 + 180 = 280. 280/2 = 140. 140 - 34 = 106° ILC.

 

these are the valve timeing overlap ranges that are most likely to work correctly

 

trucks/good mileage towing 10-35 degs overlap

daily driven low rpm performance 30-55degs overlap

hot street performance 50-75 degs overlap

oval track racing 70-95degs overlap

dragster/comp eliminator engines 90-115 degs overlap

 

 

this is some of the best basic cam info youll find so read this first,

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm (lessons 1-8)

 

http://ctfba.tripod.com/main/technical/cams/cambasics/cambasics.htm

 

http://ctfba.tripod.com/main/technical/cams/cambasics/GraphAttack.htm

 

http://www.iskycams.com/techtips.html#2002

[Kevin Shasteen]

Excellant compilation GrumpyV.

 

This needs to be a sticky(!), so grumpy doesnt have to compile this the next time the issue comes up in another thread.

 

The only thing I could add to the vast amount of knowledge in the above listed liks is that everyoe of us needs to learn to recongnize patterns. It isnt that difficult w/a little perseverance.

 

When you, myself or anyone, finds themselves reading an article on an engine build and this engine build then gives a dyno, we need to learn to recognize patterns. We need to understand what effects airflow velocity: a) Volume, Temperature, c) Pressure. With each item listed below we need to ask the question, "How do we as tuners effect the airflow velocity w/said modifications?" So when you are reading that article: make a mental note as to what components they used and what was the outcome.

 

1) Intake Manifold (Fuel Delivery): how is low rpm vacuum effected by cam specs, what was the peak rpm

2) Cam Spec's utilized, LSA, LCA, Duration, Lift: how did this cam spec alter the inital dyno characteristics w/Cyl.Head airflow: as wherein the rpm range does the peak tq/hp surface.

3) Cyl.Heads...port sizing, incremental valve lift/valve size w/airflow numbers

4) Dynamic Compression Ratio = Optimum Static Compression Ratio

5) How does all this change w/metalurgy...cast iron -vs- alum?

6) Exhaust Manifold/Pipes

 

*NOTE: the above 6 items will be effected by changes in Displacement.

**NOTE: Reference to #4...anyone wanting to understand Dynamic Comp.Ratio should check out Ed Staffel's book, ISBN# 1-884089-20-8

"How to Build Max Performance Chevy Rat Motors: Modify Big Block Chevys: hotrodding Big Block Chevys" page 108, 112-113

 

Excellant compilation GrumpyV

 

Kevin,

(Yea,Still an Inliner)

[grumpyvette]

thanks, I keep trying to answer the questions in ways that are easy to grasp for those with little previous info, I could get into far more detail but most guys would either not follow the info or not know the theory behind some concepts, those that already do know the basics ,don,t normally need much help

[Guest Nic-Rebel450CA]

I keep trying to answer the questions in ways that are easy to grasp for those with little previous info

 

You did a great job of that!

I am just starting to learn about cams, and that information was just inside the graspable range. It's great that you can take the benefit of your knowledge and present it in a way to help others who normally would have no idea what anyone was talking about.

 

This seems like a ton of information, I was actually thinking of leaving my cam selecting to a professional. I read in my How To Build a Chevy Small Block book about a company that will calculate the perfect cam for your engine, and then help you find a cam that is the closest match. I wonder if they go into all of this detail or not.

[grumpyvette]

Nic-Rebel450CA

 

read these first

http://www.oregoncamshaft.com/cam-basics.html

 

http://www.chevytalk.com/tech/101/Cam_Theory.html

 

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

 

 

 

 

I would HIGHLY recommend that YOU DO NOT USE THAT COMPANYs services

I know several people who have that reported less than satisfactory results

if you don,t want to pick your own cam to match your combo the information is readily available for FREE if your willing to follow these instructions below EXACTLY

(1) determine exactly what your true engine combo, static compression,parts list, vehical weight,rear gear ratio, tire height,,trans stall speed , ETC.acctually is, decide on what type of cam you want and can afford,( flat tappet or roller whether its to be /solid/hydrolic,)

 

write it down so you can read it to them word for word, exactly the same info, do not purchase a cam untill all the data from all the companys is averaged

(2) call a minimum of FIVE cam companys TECH help lines and give EXACTLY the same info to each,(REPEAT..give EXACTLY the same info to each, write down the suggested cams LSA.LIFT, durration @.050

(3) average the results and buy the cam that matches that result the best, if you must choose a cam that matches the AVERAGE thats not an exact match , choose the cam that is the closest to that average but has a WIDER LSA and LOWER duration

 

(4) this method will keep you from taking bad advice and get you a good combo

 

I would highly suggest these cam companys

CRANE 1-386-258-6174 Tech Line

CROWER 1-619-661-6477

LUNATI 1-901-365-0950

ISKY 1-323-770-0930

ERSON 1-775.882.1622

engle cams 1-(310) 450-0806

 

PS theres a well known cam company thats NOT listed that has CONSTANTLY given me BAD advise, THATS WHY THEY ARE NOT LISTED!

 

NO IM NOT GOING TO NAME THEM

[Guest Nic-Rebel450CA]

Hey, but you didnt mention .....

 

I will be sure to study the material. I have plenty of time, and much to gain from learning. I am already studying engine design much more than I ever planned regarding my engine build up, and I think I have increased my engine knowledge about 10-fold so far. All I use to know about cams was where they go and what they look like and that they change the performance somehow.

 

I have a couple questions, if I may, as I have not seen them addressed anywhere as of yet.

 

Regarding LSA: I think I grasp the LSA... It would seem that the LSA is a factor of the middle of the intake duration, and the middle of the exhaust duration. Is that correct? Or can two cams have exact same IO, IC, EO, and EC but have different LSAs? (If they can, I am completely lost)

 

Regarding slope of the lobe. Is the parabolic curve of the lobe always the same in relation to the peak, or do different manufacturers have different parabolic forms? (Specifically, for my engine, I am planning on a low lift, but wondering if anyone makes a cam that has a steep slope so it will have more dwell time towards the top of the peak)

 

If both of these questions are covered in the sources you mentioned, just send a :malebitchslap: and a Keep Reading!

[Kevin Shasteen]

Nic,

 

I dont want to answer for Grumpy since you addressed him-but allow me if you will to throw this out at you.

 

The best aid I found when attempting to understand the cam and cam vernacular was in a book:

 

"The Best of Hotrod: High Performance Camshafts" Vol.11

Published by CarTech, w/a Copywrite date of 2000

ISBN# 1-884089-50-X

 

I read this book at least a dozen times or so: somewhere around the 5th or 6th time the underlying dynamics began to actually stick in my brain.

 

As far as LSA, it is merely the mathematical average of your Lobe Center Angles. This means that your Exhaust Lobe Center when added to your Intake Center Line and divided by 2 will equal your LSA.

 

Your 4 major cam spec's/timing events are:

1) Exhaust Valve Open...EVO

2) Exhaust Valve Close...EVC

3) Intake Valve Open......IVO

4) Intake Valve Close......IVC

 

*NOTE: there are subtle nuances that occur within these four cam specs but are not as important if all we are doing is trying to understand LSA.

 

Because of the fact that our cam timing events are timed to the crankshaft when you read of a cam event such as 35* IVO your mind should immediately recognize that this degree point is a measurment of Crankshaft rotation within the Intake Stroke. Our car engines are 4 stroke engines, the four strokes are:

 

1) Intake............180*'s

2) Compression...180*'s

3) Combustion....180*'s

4) Exhaust..........180*'s

 

Each stroke of our engine consumes 180*'s of Crank Rotation and each cam event will be slated specifically for one of those 4 strokes. Yet the Cam Timing Event listed will actually begin on the preceding stroke. Such as, if you read of an 35* IVO then you should realize that the IVO actually begins just prior to the Intake Stroke. The stroke that precedes the Intake Stroke is the Exhaust Stroke: hence-the IVO will actually begin on the end of the Exhaust Stroke....this is where TDC Overlap occurs. W/out going into detail on the other strokes you get the picture, each cam timing event, which is slated specifically for one particular stroke of the engine and not any other, actually begins at the end of the previous stroke.

 

Now, back to LSA. LSA is the measurment of how much Crank Rotation takes place from the point your camshaft reaches your Exhaust Lobe Center (peak lift), where the LSA measurement begins, up to the cam position of Intake Lobe Center (peak lift).

 

How you install your cam:

1) Advanced

2) Straight Up

3) Retarded

 

.., will determine if your peak tq/hp will occur sooner, on time, or late based on how you install said cam.

 

You have heard or read where a cam mfg will grind their cam 4* advanced to aid in negating timing chain stretch: yes/no? What this means is that they have ground their Intake Lobe Center 4* advanced.

 

So if that cam mfg lists their cam with an 110* LSA and it was ground 4* advanced-then our Lobe Centers will be:

 

110* - 4* = 106*

 

.., and their Exhaust Lobe Center will be:

 

110* + 4* = 114*

 

Add the two and then divide by 2 and you will have your mathematical average...which represents your LSA:

 

(106* + 114*) / 2 = LSA

220* / 2 = 110* LSA

 

A wider LSA w/a shorter duration will offer a broader power band where just the opposite, a narrower LSA w/a longer duration will make for a peakier power band whose peak rpm is more rpm specific.

 

The issues of LSA, Lift and Duration determine the idle-ability/intensity/revability of your engine.

 

Get the Best of Hotrod book and read it over and over until you grasp the issues. As you read that book AND the sites Grumpy offered-you need to constantly ask yourself, "How does what I am reading effect airflow velocity?"

 

Most of this info can be found in the sites that Grumpy listed...but you should also take a look at the book as IMHO I found it to be invaluable.

 

Kevin,

(Yea,Still an Inliner)

[A. G. Olphart]

GrumpyV- Neat plan of attack: Thanks!