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North American Motorsports Pages • View topic - Answers to When is an engine Over Cam'd.

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Posted: Sat Nov 12, 2005 4:18 am 
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A racer asked me about a cam. During our conversation, he asked me how good would the engine sound with the new cam? Why does it matter?
Do we race to discover who's engine sounds better than the rest?
Something that is laughing, belching, and carrying on when it is idling is likely going to have a difficult time pulling the vacuum required to pass tech. It won't have good low speed torque either. If I was the tech man for a vacuum rule class, I would be randomly pecking off the cars that had "the sound", with my vacuum guage. It doesn't take much cam in a low compression 350 to kill the vacuum down to 15" at 1000RPM.

Guy's, I can't say it enough for you who have to use Hydraulic cams, RHOADES LIFTERS, and set at 1/4 turn past tap when COLD.!!!!!!!! Just buy the standard ones and not the new V-Max, because they are more technical than most of you are willing to deal with.

I told this guy that if he was more interested in a cool sounding cam than winning, then while he is listening to the music, he can be looking as well as hearing the music coming out of the pipes that are in his face as he stares at the business end of those cars in front of his, because he will be in the rear. HAHA


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Posted: Sat Nov 12, 2005 4:18 am 
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When an engine has a big seat duration (advertised duration) cam, and especially the exhaust cam, the killer sounding idle from the early opening exhaust valve is actually a bad thing for a low rpm usage engine. Notice when switching to a higher rocker ratio on the exhaust valve will hurt vacuum and low RPM power, but not on the intake side.

What you are hearing is the charge or mixture being exhausted while it is still very active. This is an even worse symptom with Alky because it burns so slow compared to Gasoline.

In Blown Alky, we actually have to run less exhaust cam than intake cam (though some have to chase the tuning and fuel curve all over the place because they don't) just to keep enough heat in the cylinder and keep the fire lit. As cylinder pressures go up, we also need hotter plugs and/or reduced plug gaps with fine wire electrodes. The other advantage to the shorter exhaust duration is the engine gains a TON of torque.

We find that there is so much pressure in the cylinder, and especially with 50PSI boost pressures, that we have a hard time keeping heat in the cylinder and keeping it lit. The big exhaust durations blow all of the heat/BTU's out. Though that is an extreeme environment to the fullest extent of the term extreeme, the same holds true in Gasoline applications to a small degree.

The early opening exhaust valve is simply blowing a large percentage of the available torque right out of the exhaust port. Awsome sounding but wasted energy! Though this is a crude expression, it is sort of a pre-mature ejaculation. You must keep the charge in the cylinder to do its job against the piston. Blowing it out too soon is cutting that opportunity time way short.

For those with vacuum rules, it also hurts idle vacuum. Losing some exhaust duration will also help you justify a little wider Lobe Separation Angle and smoothe out the torque curve for more tire spin control on a slick track. You will also like the way it pulls on a re-start when the engine is down in low RPM grunt mode.


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Posted: Sat Nov 12, 2005 4:19 am 
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-cap: So, what exactly is over camming?

Simply stated it happens when the valve lift exceeds the intake or exhaust port flow capability to flow air. It is when the valve is opened to a point in the lift curve that airflow no longer increases with increased lift.

Obviously, it takes flowing a set of heads on a flow bench to know exactly where this point is. Some it is 500 lift, some 700 or even 900 lift.
On most early V8 production head castings, the point of no return is approx. 500 lift. As I stated earlier, these heads wil actually back up at lifts greater than 500, while some aftermarket castings will reach their max flow at a given lift and simply flatten out as the lift increases.


When a racer is in the process of planning a new engine combo such as is likely for most right now during the off-season, and before a cam is selected, it is money well spent to flow test the heads after it has had all of the head work performed. Flow testing the head will be a very valuable step in the cam selection process.

Even a budget conscious racer should not pass up the typical $40-50 charge to have an intake and exhaust port flow tested. Just be sure the exhaust port is tested with a pipe held or bolted to the port as that effects the flow. Ideally, if you are a freak like I am, you flow test with the manifolds bolted to the head. You are not racing without maniflds bolted to the heads, so why flow test without them? I want to know what the results are when the head is as close to an as run condition as possible.


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Posted: Sat Nov 12, 2005 4:19 am 
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Since the race season is over, I am certain there will be plans for new engine combinations by almost every racer. Since most racers did not consistently win during the season, they need to carefully evaluate their present engine combination and make changes.

This applies mostly to racers who never made enough power to make it to the front regardless if they won or not once they got to the front.

If the car was not consistently running in front of the pack, then one would be a fool to simply freshen his engine for the next season without changing the cam. It did not keep up with the Jonses' this year, so why would you assume it will next year? Evaluate if your racer beat other racers off the turns, but lost them near the end of the back stretch because they caught you, or if they simply out ran you from the start.

This can tell you where the engine is lacking. A trip to the local Chassis Dyno will tell you the same thing. The two things you can change that will make the most difference to the engine's on track performance and acceleration is #1 the cam, and #2 the rear gear ratio. Incidently, those are two of the cheapest items one could buy.

IF you are building a new car and new engine, then you are buying these two items anyway. Time to buy the right gear and cam. You can buy right, or you can buy again.


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Posted: Sat Nov 12, 2005 4:19 am 
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Just because you might have been a consistent winner in the previous season, don't think that your competition is simply going to be contempt freshening their engines and running behind you again. They are going to make whatever changes they feel need to be made to beat you! Therefore, if you are a consistent winner, you still need to find Horsepower in the new combination to better yourself.

I see winners get lax and think they don't need to change anything. They will ask questions such as "why do I need to change anything? I am winning." You need to see their look of bewilderment when I suggest they need to step it up. They are shockingly optomistic competing in a sea of sharks. LOL! You have to stay on your toes with your engine program because your competition is gunning for you. I can assure you that once they tear an engine down, they are going to step it up with the intent to beat you. If you maintain the "Statuesque", your fast car will eventually lose. Update accordingly.

I won't mention names or teams here, but I have witnessed this attitude and arrogance of an acquaintance of mine who is a Pro category racer. He used to be one of the most successful racers known. Now, he seldomly runs quick enough to qualify and is sent home on the trailer! He has lost almost his entire Engine Lease program because of this. I told him the solution a couple of years ago when he asked me for help. To my knowledge, he has yet to try it. My wife just shakes her head every time she watches a televised event and his team fails to qualify for the show. She say's that is what he gets for not listening.

Touché!!


The time to prepare for battle is not after the battle has begun. The time is now.

Here is a slogan to race by: I've upped my standards. So...Up yours!

I look forward to each and every potential opportunity during the off season.


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Posted: Sat Nov 12, 2005 4:20 am 
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There is a big advantage to buying the right cam instead of the traditional and inexpensive shelf grinds which are mass produced. THey are not really even good designs. Many are sucked in by the so-called cam designers (which they are not) claiming they use a computer to designtheir profiles. Though that is true with some of them, understand that a cam is simply a series of mathametical curves. The computer is not any better at designing cams than a live person who knows how. They can simply complete the task 10 million times faster. After all, a computer program is only as good as the programmer. Garbage in, Garbage out. They will only compute what the program and program designer tells them to. Therefore, they can't design a cam any better, so don't buy into the marketing hype some companies claim in order to sell you a mass produced piece featuring a grossly inflated duration specification.

Just like the aftermarket Hydraulic rollers out there. One in particular produces some reasonably intense lobes. The down side is that they are BRUTAL on the valve train! Which is why the valve train is noisy, too! We design them even more intense than they can. The difference is we know how to design them and we know how without making them brutal.

I love to pick on one giant in particular because they advertise many of their seat durations (advertised durations) on Hydraulic cams at .006. However, if you check one of their finished cams, you usually have to check it at .008 for their number that they are advertising to be accurate. This means that the cam is a bigger advertised duration than what they are publishing. It also means that is is not any bigger at .050 or .200, just at the seat. If you understand cams, you will understand that I am telling you that the cam is bigger when you measure it at .006 then at .008 which means that it is lazier than you originally thought you bought.

Here is an example: If I have a published advertised duration of 288 @.006 (Six Thousandths of an Inch), and a duration @.050 of 234, but when I actually profile check the lobe with a computer analysis program called a Cam Doctor and I get 288 @.008 as opposed to 288@.006, and my duration @.050 is still 234, the cam is showing it to be less intense of a ram acceleration. Why? Because the 288 is at .008 not .006.

If you check it at .006, it is more like 295. Imagine now that the 295 cam (which is 9 degrees bigger advertised than the 288 that they published), but it didn't grow any bigger in duration anywhere else. Otherwise the 234@.050 would be 243 if everything was on the right side. It is lazier then they show it. Why would anyone install a cam to add advertised duration only? Why would any educated person buy a bigger cam if all they were getting was something that was bigger at the seat but not any bigger anywhere else? They would not do it knowingly, which is what I am trying to illistrate here.


They are doing this with the numbers because they know it is a lazy design. The smaller the seat duration is and at the same time the bigger the duration @.050 and 200 is, the more intense the ramp is. Therefore the more power including low end the engine will make at all RPM's.

I hope you can see what I just did. Are you pissed yet? Now you understand one of several reasons why these cams never deliver what they are marketed as being able to deliver. You can also see why they kill more low end power than you thought they would. You have just been sold a cam by a cam company who knows very little about actual cam design, but knows a whole bunch about creative marketing.

Buying this crap without understanding, is going to set you back financially and usually competitively as well. And as I said before, making a choice about which cam to buy based on a lift and Duration @050 comparisson against other cams, is basing your decision on only 20% of the facts. THe problem is that most cam companies do not publish the .200 numbers. Can you guess why? Many also don't post at what point they measure the seat or advertised of their Hydraulics. By now you should be able to guess the answer.

Call some of them, I bet most of the techs on the phone won't have a clue what you mean when you ask what the duration at .200 is.
If you buy based on price, then you deserve whatever does or doesn't happen. I am not saying a cam has to be expensive to work. I am saying that when you buy a $39.00 to $99.00 camshaft that was designed 25-35 years ago, you shouldn't be too upset or surprised when it doesn't cut the mustard. You might even be inexperienced enough with racing and engines to feel that it does. You must have never had soemthing to really test it against. Forgive me for being blunt here, because I will simply say that you get what you pay for. Try one of my designs and I will give a money back guarantee that you will never buy from "Them" again!


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Posted: Sat Nov 12, 2005 4:21 am 
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within 5 years you will find that wet flowing cylinder heads for R&D purposes will be the norm. This process is almost entirely the source of all of the recent developments in chamber designs and 50-55 degree valve seat angles. The wet flow bench will show fuel displacement trends of a head. Does the port pitch the fuel to one side of the chamber? Does it pitch it right at the plug making the plug wet and hard to light?

You will see a big change in head designs in the aftermarket soon because of this equipment. You will see 25-28 degrees of total timing be typical for best power.

All of this is available now even in production vehicles. The aftermarket has this technology, but it is still in its infancy and is therefore more common in Pro-Stock and in Cup engines because it is still cost prohibitive to most racers. In ten years, Vortec heads will be the typical small block Chevy head for Street Stocks. I really don't see why they are not allowed now because they are less expensive to build than an old closed chamber casting. I feel they are not allowed because of ignorance. A car equipped with them is not going to be that much faster. Just more reliable. If tracks are trying to keep their respective classes affordable, then choosing to ban these Vortec heads is a big dis-service to the class participants in my opinion.

It is sad that I can't even run a cylinder head on my race car that I can find in a thrashed work truck or Suburban everywhere I look and on any day of the week I choose.

I know that statement may piss some people off, but I tell the truth.
Reducing the cost of maintenance has to be considered in making decisions about how to keep a class such as Bombers, Limited Modifieds and Street Stocks affordable, right? I guess I need to complain to the SIMS people about the Limiteds, eh?

I wish I made the rules, because if I did, the spectators would have a much better incentive to go and watch the races. I am not saying that races are not already exciting to watch. They are. The cars would be making considerably more power, and the engines would be much more reliable. And the cars would be more exciting to watch because they would be faster. What spectator wouldn't want to see that?


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Posted: Sat Nov 12, 2005 4:21 am 
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What lifter preload do you racers set the Hydraulic lifters to? I.E. how many turns past zero lash do you turn the rocker arm adjusting nut?

1/8, 1/4, 1/2, 3/4?

I know that the factory spec is 3/4 turn. I also know that even on a factory stock engine with stock cam there is a very noticeable difference in a 3/4 turn adjustment vs a 1/4 turn.

I also know that some racers run 1/8 turn or even less. This is dangerous because it lets the lifter plunger ride against the snap ring which will fly apart if it gets into valve float.


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