Tech Tips with Stormy Byrd
A Camshaft Primer:
What I am going to talk about is directed mainly toward American small block V8 engines with 8.5-9.0 compression that are for street use, street gears etc.
Getting into racing cams for the track would cover too many variables such as oval track-drag racing-off road etc. Also the engine type: turbocharged – blown – injected – carbureted, cylinder heads-exhaust; and where you need the peak power band.
This primer is for camshafts destined for street use. Obviously big blocks can use a tad more lift and duration, but stay within the recommended lobe centers given below.
When choosing a cam for the street, you need two things: good idle/vacuum and good low-end response. Stick shift cars can generally get away with a little more “cam” than their brothers with automatics. With the excellent selection of hydraulic cams available, forget about solid cams these days. Set it and forget it as Ron Popeil use to say, selling his rotisserie ovens on late night TV.
Let’s face it, a street car needs to idle at a stop light and pull good to 4500 rpm. This is where you need your torque band. A cam should also be compatible with the given intake setup, exhaust, carb, gears, etc. The numbers presented here are numbers that come from much R&D from those camshaft manufactures. Always call your favorite cam maker to get dialed in for your combination.
Lobe Centers: Generally an American V8 for the street will like a cam with 110 - 112 lobe centers. This lobe center will also work for street blown applications and will give better low end response. Cams with lobe centers of 104 – 108 are more suited for short oval track when rpm is high and you need that power band coming off the corners.
Duration: The more duration you put into a camshaft for the street, the less vacuum you’ll have for accessories like power brakes .Lower intake vacuum also messes up air and fuel mixing below the carburetor causing the fuel to drop from suspension. Bigger duration cams will also facilitate the need for a “higher stall converter” to combat poor fuel atomization and bad idle.
Cams made by most camshaft manufactures for a decent street idle range from 260 to 284 degrees maximum duration. Remember the more duration the lower the intake vacuum, the worse the fuel atomization.
Hot cams will run anywhere from 290 to 330+ degrees duration.
Lift: Consider your valve train: springs – pushrods – rockers, rocker studs. The more lift, the more strain on the valve train. While many aftermarket street cams can be run with stock springs, I would suggest using what the cam manufacture recommends as they are normally very close to stock in dimensions and pressures. Most of those springs are relatively inexpensive. Many of the “RV” or “street” cams are generally in the vicinity of .390”-.470” lift range and will normally work without having to notch the piston for valve clearance
Later on if you think you could have used that "bigger cam," you could always bolt on a set of higher ratio rocker arms. A change from 1.5 to 1.6 could quickly add as much as .050" more lift; this would also change the opening duration times a little, however it's a quick bolt on piece.
Always consult the cam manufacture if changing to a higher rocker ratio, as piston to valve clearance could be compromised.
Take a look back at the infamous Chevrolet Duntov 30-30 cam. Lift was around .400” and duration was around 230-degrees. Springs were rated at 80-lb closed and just over 200-lbs over the nose. This cam kicked ass! It idled great and pulled hard to 6500+ rpm.
Rocker arms: If you stay within a manufacture’s street cam recommendations you will generally be able to utilize the stock OEM units. Aftermarket rockers with “true factory ratios,” while not necessary, can help bring everything closer to ‘blue-printing’ what the manufacture intended to do but because of production cost, didn't.
Pushrods: Most aftermarket “street cams” will work in harmony with stock pushrods; however, if you’re worried, good aftermarket units can be purchased from Jegs or Summit for around $40 a set!
Remember: It is easier to “over-cam” than under-cam for the street!
Of course if you have a better intake, exhaust, ignition, and cylinder heads, you can get a little more aggressive with a cam profile. Remember, though, where that car lives - in traffic on the street, stoplight-to-stoplight.
Over the last 36 years as an ASE certified mechanic I have seen people come into my former shop after being convinced by their local speed shop to install that .550 lift, 320-degree duration cam with 106 lobe centers, an 850 Holley double pumper, and Victor Jr. manifold with stock heads. The result: works great at 4000+ rpm on up then noses over at 6500 rpm. Oh, and plus the fact the car wont idle and has no vacuum for power-assist brakes.
If you want that “rump..rump” sound, utilize the above "street" numbers, set the idle low and tell your friends you’ve got a “roller” in it.
So, for good low end response and idle, the cam for your American V-8 should generally start with a lobe center between 110- 112, duration between 260 and 284-degrees and lift around .390”- 470.”
Remember: ALWAYS install a new cam with new lifters from the cam manufacture. Never mix new and old parts! And don’t forget to replace the old timing chain with a new one.
When breaking in a cam you’ll also need an oil additive with ZDDP (zinc-phosphate) as today’s oils have less and less of these components that makes oil “slippery.” Redline – Lucas products- Justice Brothers and even STP. Yes, STP is loaded with zinc, use it!
When breaking in a new camshaft it is also important to keep the engine rpm cycling from 1500 to 2300 rpm. The reason for this is that the camshaft in most cases gets its lube from the oil tossed off of the crankshaft. A new cam needs to “burnish” the lifters to the cam face while being splashed by the crankshaft. This is most important with a new cam as it can be ruined in minutes if this procedure is not followed to the letter.
A great addition to the above would be a “dual plane” manifold as its power band is from off- idle to 4500 rpm. Carburetion should lean toward an Edelbrock AFB 600 or Holley equivalent with vacuum secondary, dual exhaust and an updated ignition, such as offered by MSD, to complete the package.
When it comes to fuel injected engines, call the camshaft manufacturer for their recommendations as the new breed of late model engines can be run with more radical camshaft profiles on the street because of new technology and factory hydraulic roller cams/lifters.
Many good aftermarket heads are now available for the street these days but here again sometimes “too big” can be bad for the street as air velocity needs to flow enough at idle to atomize the fuel properly. Be careful and if you do go the aftermarket head direction do not port and polish for street use as fuel can puddle at low rpm when driving on the street. Rather, gently deburr high or rough spots in the ports, but that, and how air actually flows, are another topic.
We’ll get that advice from one of the pioneers of cylinder head research, Larry Ofria of Valley Head Service, a big maker of horsepower for 50 years.
NDW - by Stormy Byrd; Photo by Little Redneck Photography