Well, this is a big issue and a LOT needs to be considered. Everyone wants a nice sounding cam in their hot rod with a “racey” idle. The problem is; “race cars” that have those nasty sounding cams are completely different than cars that are driven on the street. Too many people look at fast “race cars” that “sound good” and think what a race car has is what they should run on the street, after all.. the race car IS fast, but they don’t consider many VERY important things. 1) Race cars drive on the race track, not on the street. 2) Race engines have very high compression ratios and run on race gas. 3) Race cars don’t have vacuum assisted power brakes. 4) Race cars don’t sit in traffic or drive around at anything less than their peak power RPM. 5) Race cars don’t accelerate from an idle, they launch AT their max RPM and hold it there all the way down the track. Is this how you are going to be driving your street car EVERY time you are in it? Hardly. Then obviously what a race car runs isn't what you want to run in your street car.
First and foremost, race engines are RACE engines for a reason. They may make a lot of power BUT, they ONLY make that power at a very high RPM and in a very narrow power band, usually from 5,000 – 8,500 RPM (on average), and race cars run on a RACE TRACK for a reason. They launch at very high RPMs because they HAVE TO. If they launched right off an idle, they would stumble, stall, and fall on their face. Race cars quite commonly run stall converters in the 5,000 – 6,500 RPM area and have low rear-end gears so they get TO their peak RPM very quickly. Street cars on the other hand idle a lot and run MOST of the time between an idle and 3,500 RPM or so. Sure, most of us “hot rodders” poke the throttle and run the RPMs up into the 6,000 – 7,000 RPM area occasionally, but you can’t run like that on the street from every stop sign and every stop light, so obviously what a race car runs and what a street car runs are two completely different things.
Cam profiles are not all about lift, duration, lobe separation, etc. There are street lobe profiles and there are race lobe profiles. Race profile cams are very aggressive and hard on the valve train because they are trying to squeeze out every last inch of power they can possibly get in lieu of longevity of the parts. The ramps are VERY fast and aggressive. Is it worth 10 or so extra HP to be breaking valve springs and rocker studs on your street motor? No. Then obviously a “race profile” cam isn’t the way to go as far as the aggressiveness of the lobe design.
So what about a street profile lobe that just sounds “bad ass”? Sure, you can get a cam that has a nasty sounding idle, but here’s the problem; that nasty sounding idle is caused by “overlap”. Overlap is good to have for the "scavenging effect" it causes as the RPM comes up. It’ll actually increase the effective compression of the engine and make more power. This is why radical cams “come alive” at RPMs usually around or above the 3,000 - 3,500 RPM area. That’s the scavenging effect beginning to come into play. It is because of this effect that you need to run lower rear-end gears and high stall converters, plus more static compression. If your cam comes alive at 4,000 RPM you obviously don’t want to run a stall converter with a 2,000 RPM stall. You’ll want to run a stall converter that puts you right into where your cam comes alive at, which means a 4,000 RPM stall. Well, that kind of makes your car a turd below that RPM, plus with a street engine you are limited in the amout of static compression you can run because of the lower octane pump gas. The last thing you want is detonation from running too high of a compression ratio. Without enough static compression, a "good" cam can turn into a complete turd of a cam. Everything has to be taken into consideration, which is somethig most guys don't do when they say they want a "radical cam".
An important factor no one seems to understand is that radical cams with lots of overlap directly affect the engine’s idle vacuum. A typical street engine with a stock cam will have around 18 inches of vacuum. A “performance” cam will drop that vacuum signal down to about 14 inches. A fairly radical cam will drop it down to about 8 or 10 inches. More serious cams, such as a race profile cams can often drop an idle vacuum signal down to the 4 inch area.
Engines need vacuum to run. If you have a low vacuum signal, it’ll also typically mean you have a lazy engine at low RPM’s with crappy throttle response. Sure, race cars have huge cams with great throttle response but guys that say this aren’t taking everything into consideration. Race engines have VERY high compression ratios, they have VERY light weight internal components and light weight torque converters, etc. which help the engine accelerate quickly. Street engines don’t have that, so when you put a big radical cam into a street engine, it may idle choppy like a race car does, but you can bet your butt it’ll be a complete and utter turd at anything below its peak power RPM. Now really, do you want a turd that sounds cool when it’s idling, or do you want something that may be a bit less radical but actually runs like a striped ass ape? Well then, it is essential to select a cam profile that MAKES SENSE, not one that "sounds good" just because race cars sound good.
Now an even more important thing while we’re talking about vacuum signals. Street cars usually have power brakes. Most power brake systems run off of vacuum. A typical power brake system requires at least 12 – 13 inches of vacuum to work, and they work even better with 15-16 inches or more vacuum. When you stick a “radical” cam in an engine that “sounds good”, it means it is going to have a low vacuum signal, which means your power brakes aren’t going to work worth a crap, if at all! There are a couple of remedies to this.
1) Install a vacuum reservoir that stores vacuum. These can work OK IF your cam is on the edge of not quite having enough vacuum, but they are NOT going to fix the problem if your cam is simply too big and lumpy.
2) Install an electric vacuum pump. These are noisy and expensive and they don't work that great.
3) You can opt for a hydro boost system which uses pressure from your power steering pump to run the brakes. This is a great set-up IF you have power steering, but they are also expensive.
If none of those tickle your fancy and/or you aren’t prepared to use, or do, any of those, then you certainly don’t want to run a cam that doesn’t have an adequate vacuum signal, which means a cam that isn’t that radical.
The bottom line is simple; just because a cam “sounds” good doesn’t mean the engine is going to make lots of power. In fact quite the opposite is most common. Too big of a cam WILL turn your engine into a complete and utter turd, it’ll make your car perform terrible below the 4,000 RPM range, and unless you have higher compression, a very high stall converter, and low rear-end gears, then it can very well turn your car into something that can’t get out of its own way, but hey… it sounds good when it’s idling, LOL! This is they case with about 90% o the “hot rods” we see out there cruising around. Everyone seems to over cam, over carb, under gear and under stall RPM their engines and cars. It’s better to go a little easy on the “radical idle” and gain a crap load of overall performance than it is to make a complete and utter slug of a vehicle out of it just because you want a radical idle.
Now, can you have a cam that sounds good AND performs well? Of course! There is a huge difference between a choppy idle with a low vacuum signal, and a cam that has a “healthy” idle with a decent enough vacuum signal and great performance. This what we do for a living and why engines and cars we build outperform other people’s. When you’re ready to have us build you an engine, leave the cam profile design up to us rather than what you may think you want. We are not going to send you down the road with a turd of an engine, or car. And we won’t set you up with a cam that won’t work with the kind of brakes you plan on running. This is why we custom build each and every engine specifically for each owner’s vehicle application for how it is going to be driven & used.