One of the best mods one can do to a NA car is to get an aftermarket camshaft if you are looking for more power (but keep this as the last mod). But one has to be careful while selecting a camshaft. Without getting into the basics of camshafts, different types of camshafts etc I shall focus more on the general points one must remember while picking up an aftermarket camshaft.
1. Selecting a cam based on whether you engine is Naturally Aspirated or running Forced Induction. First be sure where your build is going to end up at. NA engined cams have different characteristics to the FI engined cams.
2. One of the most important points to know while selecting a cam is to know the "desired RPM range" for which you want your camshaft to work.
Your head design, headers, intake manifold, cubic capacity, gear ratios and camshaft mainly determine the RPM curve and the torque curve of an engine. So, its of utmost importance to know what would be the desired RPM band you want your cam to kick and select its duration and lift accordingly.
Based on duration and lift, camshafts are generally classified into the following categories:
Source: Tighecams.Stage 1:
250º - 264º - Advertised Duration.
195º - 210º @ 0.050" Duration.
This range is designed for bottom end, better economy and better throttle response designed for a standard engine, if a engine has been modified this range of camshaft will still perform well, but wider lobe centres may be required to achieve best results.
Suitable for towing and heavy-duty applications, smooth idle, high vacuum for both auto and manual use. Typical lobe separation of 110deg - 113deg.
Power Range: 1850 - 5200 R.P.M.
264º - 272º - Advertised Duration.
210º - 225º @ 0.050" Duration.
This range is designed more for the midrange, smooth cruise and slightly lopy idle. Still suitable for automatic transmission using standard stall converter. Modified Distributor and exhaust system recommended. Good for towing in larger capacity engines.
Higher compression ratio not required, Larger valves not recommended.
Typical lobe separation 108º - 112º.
Power Range: 2000 - 5800 R.P.M.
272º - 290º - Advertised Duration.
225º - 245º @ 0.050" Duration.
This range is designed for modified street, limited modification race or speedway. Twin carburetors recommended for 4 cylinder engines.For road application suggest, Ported Cylinder head, Bigger Valves, Balancing and higher compression ratio (9 or 10:1). Distributor also requires regraphing. Loopy idle, if automatic transmission is used a higher stall will be required. A wide area of camshaft selection, different durations and lobe centre lines used to give different power ranges.
Lower rear axle ratio may be required to achieve the best from the modifications. Typical lobe separation of 106º - 110º.
Power Range: 2600 - 6500 R.P.M
NOTE: Valve spring retainers must be checked for suitability, depending on piston choice, valve to piston clearance will also require attention.
300º + - Advertised Duration.
250º + @ 0.050" Duration.
This range of camshaft is more for engine design rather than for camshaft replacement The engine most be designed and built with the design of the camshaft in perspective.
* Multiple carburetors recommended for both 4 and 6 cylinder engines.
* Valve springs must be checked for suitability, Harmonic testing recommended if high R.P.M. is to be used.
* High compression recommended to achieve best performance (Above 10.5:1}
Typical lobe separation of 100º - 106º.
Power Range: 4200 - 10000 R.P.M.
So what we can infer from the above is, shorter duration camshafts produce more low rpm torque, while camshafts with larger duration will tend to increase upper rpm horsepower at the expense of low rpm torque. In general, for every 10° increase in duration, the torque peak of the engine moves up by 500 rpm.
It is also advisable to buy a adjustable cam gear for stage 3 and above camshafts.
3. Knowing the compression ratio and its effects on camshaft selection.
Source: Compcams.If you have a lower compression motor, say 9.5:1, and you use a camshaft that is fairly large (increased overlap between lobes –which allows both the intake and exhaust valves to be open at the same time) then you will bleed off cylinder pressure and in effect – horsepower and torque.
On the other hand, if you’re running a high compression race motor and your camshaft has a minimal amount of overlap, the cylinder pressures can go sky high. This is far less of a problem for race engines than it is for street-bound engines, but it should be considered and factored in at the time that you choose your cam. In addition, the type of cylinder heads that you’re using and the quality of available fuel should be taken into consideration. If you have to stick with pump gas, the rule of thumb is to limit compression to 10:1 with cast iron heads and 11:1 compression with aluminum heads.
To know more about the Camshaft terminology check the link below:
http://www.pipercams.co.uk/NewPiperWeb/ ... rames.html
Once you have bought a camshaft and installed it, kindly make sure you break in the camshaft the proper way. Here is a video to show how to break-in the cam THE RIGHT WAY.
Points to remember while choosing a FI cam.
Source: Compcams• Nitrous creates a lot of cylinder heat and requires more exhaust duration to help evacuate the cylinder.
• Superchargers also increase cylinder heat and tend to work more efficiently with a wider lobe separation.
• Turbocharger technology has come a long way. Again, many variables should be considered, but in general you don’t need a very large cam. Turbo cams in fact, should have less exhaust duration than a N/A cam.
Note of caution: I have often seen this trick being pulled off by many tuners all over the country. They promise you brand new billets and instead what happens is that they send used cams for re-grind. Re-ground cams cost a lot lesser than brand new billet cams from say Crower/Piper/Compcams/TigheCams etc. So be sure of what you haven been promised, rather than getting ripped off by a tuner out to make a quick buck.
Electra Performance in Chennai, re-grinds almost all Indian cams. They even supply a cam spec sheet, which most tuners keep it to themselves and never give it to the end customer. If you are purchasing an aftermarket cam, INSIST for the cam spec sheet, better see if you can get it degree'd just to verify the specs.
PS: This is all I could think of for now, guys please feel free to add if I have missed out on something.