Another cam question, about the effect of upgrading cams

[Guest bastaad525]

Okay, what I really want to know is:

 

Swapping to a hotter cam, DOES it offer increased horsepower and torque over the stock cam, assuming the engine and other systems have been well set up to accomodate higher flow?

 

-OR-

 

Does a hotter cam simply serve to move your powerband to a different area of the rev range, but NOT really increase your power over all?

 

I would really like to hear from some of you guys who've done before and after dyno runs, to get some actual numbers. Or some track numbers showing increased 1/4 times and by how much difference it made. And if you want, please add a listing of other mods you've done specifically to the engine (i.e.: high flow exhaust or port and polished head)

[Lockjaw]

A cam offers both, increased power, and it moves the power higher in the rev range, depending on the size of the cam.

 

Someone like Timz or an engineer can give you a more technical explanation than I can.

 

I would also say it would be possible to have a cam that would make more power than stock, and keep the same rev range, and it could make more power than stock at most if not all points in the rev range, and hold the power longer.

[Kevin Shasteen]

A "Hot Cam" is not the determining factor of where your power band will surface. What determines your power band is displacement and how well your engine breathes when your valves are opening and closing at any one rpm.

 

IMHO, this is where understanding both Dynamic and Static Comp. Ratios come into play. It is possible to have a High Static Compression Engine with a hot cam and still make it idle low with your power band showing itself in the low rpm range: providing your Dynamic Comp.Ratio's were factored into the equation (DCR is determined by your Intake Valve Closing relative to Displacement of your engine).

 

If you were to read D.Vizard's book on How to Modify SBC cyl.heads (doesn't matter which mfg we are talking about-as airflow is universal to all makes and models) then on page#75 you will read where he quotes Fayett Taylor's book on "The Internal Combustin Engine".

 

Here, Vizard reports what that book says about peak power. This variable which determines peak power potential is airflow velocity. Sound travels at 1200 fps (feet per second) and the engine, with its thermodynamics, will effect that sound barrier by .55-.60. Therefor, the engine's airflow will reach Super-Sonic speeds at Velocities around 600 fps.

 

Once the airflow reaches Super-Sonic speed, within the intake port, then your power output falls as if it fell off a cliff. This "falling off" is what you and I see everytime we look at a dyno run of any engine. If you will notice the end of that dyno run where the power numbers drop-this is the point whereby that engine's airflow velocity, within the port, has reached super-sonic speeds.

 

So to understand airflow-you have to understand that all tuners are attempting to manipulate this "Point at which Port Velocity Reaches Super-Sonic" speeds. Once this point is reached it represents an airflow wall that cant be penetrated; thus-no more air-thus no more power.

 

An engine's ability to breathe determines its "Peak Potential". Your choice of Camshaft, Cylinder Head along with your intake & exhaust systems will manipulate that "Peak Potential".

 

To put it another way; if you took a stock Datsun 168ci as a baseline; you'ld obtain the same power numbers that Nissan reached. Now, take that same engine & put a cyl.head w/a smaller Combution Chamber on it...If everything else remained the same what would happen? You just woke that engine up (moderately speaking). Your engine's Airflow Velocity will reach that super-sonic speed much quicker and your power band will come on the cam much quicker: all based on the limitations of the airflow velocity that is incorporated into your engine. If the port cfm remained the same-your power band rpm would stay the same; but the engine would be more responsive.

 

This is great on the street but not much use on the race track-so what do you do? Well, you put in a cam with a longer duration-narrower LSA (DCR) that also has a higher lobe lift, install cyl.heads w/smaller comb.chambers that utilize larger intake ports, and install pistons that further push the SCR numbers upward...now you have manipulated that "Point at which Super-Sonic Airflow Velocity" will be reached and have just successfully moved your power band further up the rpm range.

 

This is all that any hot rodder/tuner is doing when they tweak an engine; they are merely manipulating the point at which that engine's airflow reaches Super-Sonic speeds. There are also many approaches to obtain the same effect.

 

The Intake and exhaust will have its effect, but the cylinder head/camshaft combo determines the intensity to which your intake & exhaust will effect your power band.

 

Once you understand airflow velocity then, as a tuner, you also have to understand that some engines bring to the table their own attributes; such as:

 

1) Push Rod Engines

2) SOHC Engines

3) DOHC Engines

4) Rotary Engines

5) *No Substitution for Displacement

 

Anyway; my .02c's worth/anyone else?

 

Kevin,

(Yea,Still an Inliner)

[Guest bastaad525]

Droppin science!!! Heheh very good article though it didn't quite answer my question! Or did it? Gonna read thru that again....

[johnc]

I think the answer we're all trying to give is: "It depends..."

[Kevin Shasteen]

Originally posted by bastaad525:

Okay, what I really want to know is:

Swapping to a hotter cam,

1) DOES it offer increased horsepower and torque over the stock cam?

2) Does a hotter cam simply serve to move your powerband to a different area of the rev range?

Have you ever noticed when an auto mfg comes out w/some new sports car that they will have a street version of that car then a race version of that car? Both cars will utilize the same engine configuration yet neither engine's output is similar in any way. Yes is the obvious answer.

 

This is where it pays to have a little knowledge about the engine your are tinkering with. It always helps to know your cylinder heads ability to flow; as in having a cfm flow chart and knowing its chamber volumes. This way you will have some idea as to its strengths and its weaknesses. This should give you some kind of an idea if/when your modifications have surpassed your cyl.heads ability to add to your modifications.

 

To answer your questions on your previous post-Yes to #1 if your engine in its stock configuration was "suffocated" (detuned) from the factory to begin with. Then it will depend if all the factory did was put in a milder cam. If the factory detuned your engine to create a milder version for the street-then a "hotter cam" should wake up your engine. However, if your engine was not detuned to begin with and was built to maximum performance for that street aplication-then a "hotter cam" wont necessarily do anything except move your power band higher up the rpm range.

 

This is also where it pays to recognize patterns; such as the difference between smaller displacement -vs- larger displacements. On smaller displacements you can manipulate both the torque curve and the hp curve substantially, whereas on a larger displacement-say in the neighborhood of the big blocks, you wont really be manipulating the torque curve. You can add to it-but, usually a big block's torque curve is usually going to be broad and very torquey. Yet, what you can manipulate on a big block is that engine's hp curve. You can make your big blocks hp curve pick up where the torque curve drops off.

 

Think of torque as an engine's ability to work and the hp as the engine's ability to work fast...or slow if the engine has been detuned.

 

Does that help at all(?) or am I still dancing around the issue?

 

Kevin,

(Yea,Still an Inliner)

[johnc]

A simple way to check on your engine's "state of tune" as delivered by the factory is to calculate its horsepower per liter and compare it with one of the industry best - the Honda S2K engine.

 

Honda S2K engine - 240hp / 2.0 liters = 120hp per liter.

 

Dodge Viper V10 - 500hp / 8.3 liters = 60.25hp per liter.

 

The above would tell you that there is much more room for improvement in the Viper engine then in the Honda engine. For comparison, a 5.7 liter small block Chevy would have to be making 684hp to match the Honda and the Viper would have to make 996.

 

For the Nissan L28 we have different horsepower numbers, but let's use the most optimistic one:

 

170hp / 2.8 liters = 60.7hp per liter.

 

That will tell you that there is a lot of room for improvement and you can also brag to your friends that the Datsun makes more horsepower per liter then the Viper. You ultimate goal would be 336hp for the L28 to equal the horsepower per liter of the Honda.

 

So far I don't think anyone has achieved that in a normally aspirated L28.

[Lockjaw]

I hate to say this, but I don't think comparing a datsun and a SBC is the same, nor would it be fair to compare a Vtec honda engine to a datsun.

 

The cams in the datsun engines are so mild that increasing the lift and adding about 10 to 20 degree's would make a nice difference. Not to mention adding some more compression.

 

Also the stock cam was not designed for max performance. It is a compromise design that has to take into account the "majority" of drivers, not to mention emissions and fuel economy standards. Also, don't forget warranty issue's as well.

 

There is no way I am going to be conviced that the stock cam will make the same power as a larger one, all things being equal. There is always room for improvement.

[Guest bastaad525]

I dunno but since installing this cam, and tuning the carbs using a exhaust gas sniffer computer, the car still feels slower than it did with the stock cam. At least when driving on the street. Am I gonna have to drive this thing like a S2000 now? Heheh those guys get like NO power until they're up in the high RPM range. My conclusion that is that though the hotter cam may be making more power, that the stock cam may well have been the better cam for people who live in the city and do most of their driving in traffic.

[Lockjaw]

Well there are always trade off's when going to a larger cam. You could advance it using the number 2 or 3 position on the sprocket.

 

If your cam is a larger one, you should have added some compression.

 

I got my engine running last night. Flat top ZX engine with a milled p79, round port header, su's, and a big crower cam. Once it is broken in, then I can give you some idea of what it will do.

 

What helps with larger cams, besides compression is a light flywheel and 3.9's or steeper in the back.

 

One of the things I haven't thrown out there yet is the Lobe separation angle on the cams. I was reading about that, and there may be some merit to having a little wider lobe separation angle. My crower is on a 110, but alot of the cams out there for a datsun engine are on 108 or 107. Usually all things being equal, the wider the love centerline, the better the idle quality. I am sure there are power charactoristics as well.

 

What head are you running? How about engine spec's in general?

[Guest bastaad525]

Heheh LJ for once I'm ahead of some suggestions. The cam is on the #2 position. I have added quite a bit of compression, pushing 10.3:1 probably more as the head has been rebuilt twice and I"m sure at least shaved a little. I also have a stock flywheel that has been lightened to about 16 lbs, and a 3.9 rear end

 

The motor is an early L28 block with flat tops, bored .060 over, with an N42 head, pretty much stock except polished, tuliped stainless valves, some minor (very minor) polishing of the ports and bowls, and of course the cam. I don't know what the seperation angle is. Intake/ignition/exhaust/clutch/suspension all upgraded to performance parts.

[yo2001]

Originally posted by Lockjaw:

[QB]One of the things I haven't thrown out there yet is the Lobe separation angle on the cams. I was reading about that, and there may be some merit to having a little wider lobe separation angle. My crower is on a 110, but alot of the cams out there for a datsun engine are on 108 or 107. Usually all things being equal, the wider the love centerline, the better the idle quality. I am sure there are power charactoristics as well. QB]

What idle quality? Your car still thumping some potato aren't you? Anyway, smaller LSA suppose to give more power in high speed but loses low speed effieciency also because there are more valve overlap.

[DAW]

Bastaad525, I think you should look into the cam timing more closely, given the type of problem you're facing. First, what hole the cam is in on the sprocket matters only in re to where the cam is actually timed to. In other words, what you really need to know is where the index line on the front cam thrust cover lies in relation to the V-shaped notch on the cam sprocket. Factors at play here are chain length (stretched vs new vs new replacement not to spec, etc), sprocket (crank and cam) wear, cyl head thickness, over or under-shimming of cam towers. The wild card is whether your replacement cam pin is identically placed at manufacture to the Nissan cam you removed. This last one requires a degree wheel to confirm. You'll be able to compensate for any discrepency easy enough, but you'd have to check it first.

 

Leave the dowel in hole #2 where you have it and check the line/notch position. Always rotate the crank smoothly to #1 cyl TDC position to keep chain tension on. You may find that you have selected #2 hole but the cam is timed closer to stock location or even retarded, especially if the head has been milled but not shimmed.

 

From your description, it sounds like you may be looking for some cam timing advance to help driveability and low-end power, so consider the trial & error tuning route and advance to hole #3 if you don't have a degree wheel. With flat-tops and a milled N42 you don't have an endless piston-to-valve clearance so you don't want to be off too much in either direction. DAW

[Guest bastaad525]

I took a look but I couldn't see the mark on the front of the cam itself. Gonna have to go take another look with a flashlight. Again, I will say that the guy who installed the cam has been doing this kind of work on Z's for some 15+ years. All the work he's done on my car has been top notch. I watched him do the work and saw that he payed a LOT of attention to lining everything up when he reinstalled it. If there were problems like a stretched chain or what have you, he would have let me know. I don't think there was however, as he checked everything before taking the cam off and at TDC, the timing mark on the crank, marks on the cam sprocket and timing chain, and the V mark and mark on the cam front all lined up perfectly. He showed me that.

 

In regard to the seperation angle of the lobs, not sure that this is a good indicator, but the cam IS a stock cam just reground to new specs, so I"m gonna guess that the seperation is the same as a stock cam?

[DAW]

You need to verify it yourself and it's easy to do. That way you can ask yourself, "do I believe what I'm told, or my lying eyes?" Warning though, adjusting the cam timing is easy but you must block the timing chain when you reposition the sprocket or you will lose the chain and make a lot of otherwise unneccessary work for yourself. You can't disturb the crank once you've blocked it, so you would turn the cam a small amount using a large adjustable wrench on the square lugs on the cam so that you can slip the repositioned sprocket onto the cam dowel. DAW

[Lockjaw]

I have always heard a tight lobe centerlibe made for a more choppy idle, and more topend power, but the last thing I read on the subject suggested perhaps that wasn't the case with the import engines.

 

I have my own personal likes and dislikes when it comes to centerline, and like to stay around 110 on NA, and 112 or so on turbo.

 

I am not an N42 fan, but it sounds like you have plenty of compression. I think you should go to a larger cam. I like billets personally, and am fond of crower cams. The stoutes normally aspirated Z I ever rode in had a crower cam, I had a regrind from crower that rocked, and I have 2 now, one for my turbo car, and one in the 260, and it hits like a MOFO.

 

My buddy just got one a little bigger than mine,also a crower. I think they get 180 for a billet.