circusboy

iTrader: (2)

I can't find any info on these questions of mine, lol.

does the amount of lift effect the power band of a cam?

if you add more lift wiill the power band go further up in the RPM range?

if you take away lift will the power band go further down in the RPM range?

I'm trying to come up with my own cam design. i realiy liked the way the GAC cam sounds at idle but don't want to spin to the moon to get the power, lol.
I want to make at least 400 RWHP . I don't want to rev higher than 6500 RPM. I want to get my power quick and keep it till red line. my car is making 342 RWHP and 346 RWTQ with the mods in my sig. Am i asking to much from just a cam swap?

I have read that the GAC cam has "lazy lobes". Is this because of the .571 lift as opposed to say a .598 lift? or is it because of a different type of lobe?

I'd like my cam to also have a long stutter. sounds like it's like it's trying to die, lol.

so far i cam up with:

FM13 on a 110 LSA
228/228 .571/.571 108 LSA
229/240 .571/.571 108 or 110 LSA

but i don't have any idea what i'm doing , lol.

can some one please educate me.

thanks in advance

circusboy

iTrader: (2)

I can't find any info on these questions of mine, lol. I posted this in the Internal section yesterday. 5 hits, no replies.

does the amount of lift effect the power band of a cam?

if you add more lift wiill the power band go further up in the RPM range?

if you take away lift will the power band go further down in the RPM range?

I'm trying to come up with my own cam design. i realiy liked the way the GAC cam sounds at idle but don't want to spin to the moon to get the power, lol.
I want to make at least 400 RWHP . I don't want to rev higher than 6500 RPM. I want to get my power quick and keep it till red line. my car is making 342 RWHP and 346 RWTQ with the mods in my sig. Am i asking to much from just a cam swap?

I have read that the GAC cam has "lazy lobes". Is this because of the .571 lift as opposed to say a .598 lift? or is it because of a different type of lobe?

I'd like my cam to also have a long stutter. sounds like it's like it's trying to die, lol.

so far i cam up with:

FM13 on a 110 LSA
228/228 .571/.571 108 LSA
229/240 .571/.571 108 or 110 LSA

but i don't have any idea what i'm doing , lol.

can some one please educate me.

thanks in advance

chirp_fourth

A 'lazy' lobe means it's probably not very aggressive, meaning that the ramp rate is not fast, meaning that the valve moves to peak slower, which is easier on the valvetrain. Power wise it's not as good, but it'll last a lot longer. Aggressive lobes 'add' effective duration, while keeping driveability a little better, so you get both benefits at the cost of a little added valvetrain wear.

Valve lift 'can' affect upper-rpm horsepower, but only if the lift is not sufficient to maximize the heads flow-lift range. For instance a .550 vs. a .600 lift wont make much of any difference in a stock head ls1, but add a set of afr's and there will be a big difference.

This is all pretty much anecdotal info, but if you want to compare, these two are prolly about the same power wise:

224/224 .571/.571 110lsa w/ aggressive lobes
228/228 .571/.571 110lsa w/ less-aggressive lobes

But at this point, you are splitting hairs even if they had the same lobe pattern.

SStrokerAce

iTrader: (2)

Guys.... the ramp speed or aggressiveness only has a small part to do with the camshaft being stable and not having valve float.

Secondly, just coming up with some random cam specs or throwing lobes together is close to DYI head porting if you don't understand what you are doing.

As for the effects of lift on the power band... it all depends on what you are looking at in terms of the motor. Valve lift is one part of the curtain area function. Curtain area is the area that the air sees as it passes thru the valve. So you would take the valve diameter x Pi x valve lift to get the curtain area. In some instances more lift shows little gains because you are already at a point where there is enough curtain area for the RPM range and the cubes you are running. Now if you want to turn the motor faster or put more cubes under the cylinder head, you need more lift OR more valve size, a lot of the time you need both.

Now when it comes to the flow curve of the cylinder head... well that has VERY little to do with the performance you get from extra valve lift. That's a long discussion as well.

Now in terms of LSA... there are some threads on this forum already talking about that but we can open up that can of worms again.

Bret

Rusted40

bits of a paper by Dimitri Elgin


FACT ONE: Volumetric efficiency is directly related to piston velocity!

Volumetric efficiency is a measure of the effectiveness of an engine's intake system and there are about 200 miles of air above the engine just waiting to fill the cylinder with 14.7 psi at sea level. The intake valve is almost closed as the piston reaches BDC, but it does not close completely until after BDC, when the piston is on its way back up the cylinder. The reason for this is because the incoming air/fuel mixture still has momentum even though the piston has slowed way down

Power is produced while the gases in the cylinder expand and cool. In most instances, the gases are at a relatively low pressure by the time the crankshaft reaches 90 degrees After Top Dead Center (ATDC), so we can safely open the exhaust valve Before Bottom Dead Center (BBDC) to take advantage of blow- down. Otherwise, the piston would have to push ALL the exhaust out

During the overlap period you will often find that both valves will be open an equal amount. This condition is referred to as SPLIT OVERLAP. On standard engines, the valves are only open together for 15 - 30 degrees of crankshaft rotation. In a race engine operating at 5 - 7000 RPM, you will find the overlap period to be in the neighborhood of 60 - 100 degrees (which also translates to more total duration)! As you might expect, with this much overlap the low speed running is very poor and a lot of the intake charge goes right out the exhaust pipe.

CALCULATING DURATIONS

Let us review the four strokes and add some timing events to calculate the total valve duration. For illustrative purposes, we can discuss a good street cam with a 268 degree duration and 108 degree lobe centers. (The lobe center angle is the angle in camshaft degrees between full intake cam lift and full exhaust cam lift). As we discussed above, at the end of the fourth stroke both valves are open and the next stroke is the intake stroke. Referring to fig. 1, we see that the intake valve began to open at 26 degrees BTDC. The piston moves down the cylinder after the crankshaft passes TDC, and the valve reaches full lift at 108 degrees ATDC (lobe center). Note also that the intake valve is still open when the piston reaches BDC. We can start to add things up now. The crankshaft has rotated 180 degrees from TDC to BDC on the first stroke and the intake valve opened 26 degrees BTDC, so the total crankshaft rotation so far is 26 + 180 = 206 degrees. We started with a 268 degree camshaft so that tells us when the intake valve will close: 268 - 206 = 62 degrees ABDC. Note that even though the second stroke is the compression stroke, we see that it starts while the intake valve is still open!

FACT TWO: In the lower RPM range, the engine does not have any compression until the intake valve closes. As the engine speed increases, there is a ram or inertia effect which begins compression progressively sooner with engine speed.

Now, we compress the air/fuel mixture and ignite it at the proper time in order to maximize the push down on the power stroke, or stroke three. Remember, I said most of the cylinder pressure is gone by 90 degrees ATDC, and you can see that with our 268 degree cam, that the exhaust valve begins to open 62 degrees BBDC, that is, before the exhaust stroke actually begins. So adding again, we have 62 + 180 (stroke four) = 242 degrees. Thus at TDC at the end of the exhaust stroke, the intake valve has opened but the exhaust has not closed. The exhaust valve remains open for 268 - 242 = 26 degrees ATDC. With the intake valve opening at 26 degrees BTDC and the exhaust closing at 26 degrees ATDC we have a total of 52 degrees of overlap.

VALVE TIMING EVENTS - ORDER OF IMPORTANCE

Let us now take the four valve timing events and put them in order of importance. The LEAST important is the exhaust valve opening. It could open anywhere from 50 degrees to 90 degrees BBDC. If it opens late, close to the bottom, you will take advantage of the expansion, or power, stroke and it will be easier to pass a smog test, but you will pay for it with pumping losses by not having enough time to let the cylinder blow-down. You must let the residual gas start out of the exhaust valve early enough so that the piston will not have to work so hard to push it out. Opening the exhaust valve earlier will give the engine a longer blow-down period which will reduce pumping losses. But, if you are only interested in low speed operation, say up to 4000 RPM, you can open the exhaust valve later.
The next least important timing point is the exhaust valve closing. If it closes early, say around 15 degrees ATDC, you will have a short valve overlap period. Less overlap makes it easier to pass the smog test, but it does not help power at the higher engine speeds. Closing the exhaust valve later, in the vicinity of 40 degrees ATDC, will mean a longer valve overlap period and a lot more intake charge dilution that will translate into poor low-speed operation. Some compromise must clearly be made to determine just how much overlap one needs to use. Many factors such as idle quality, low speed throttle response, fuel economy, port size, and combustion chamber design must be considered in making this choice.
A somewhat more important timing event is the intake valve opening. Early opening allows for a greater valve overlap period and adds to poor response at low engine speeds. Now, for the high performance enthusiast, low engine speed could mean 3000 RPM, but I would not consider such an engine as appropriate for normal street use! If you are not concerned about passing the smog test, then early intake valve opening will help the power output of the engine. That is, earlier valve opening will have the valve open further when the piston reaches maximum velocity and that, in turn, will increase volumetric efficiency.
I must stop now and ask you a question about your engine. If a 1500 Cortina head does not flow much air above 0.350 in. of valve lift, and it is possible to have the intake valve open that much by the time the piston reaches maximum velocity, WHY DO MOST PEOPLE THINK THEY WANT AT LEAST 0.500 in. VALVE LIFT???
Now, the last timing event is the most important, and the most critical to engine performance - THE CLOSING OF THE INTAKE VALVE. This event governs both the engine's RPM range and its effective compression ratio. If the intake valve closes early, say about 50 degrees ABDC, then it limits how much air/fuel mixture can enter the cylinder. Such an early closing will provide very nice low speed engine operation, but at the same time it limits the ultimate power output as well as RPM. Another problem with early intake valve closing that most people do not consider is that if you have a high compression engine, say 10:1 or higher, you will have more pumping loss trying to compress the mixture. This might even lead to head gasket and/or piston failure! These observations suggest that if you close the intake valve later the cylinder will have more time to take in more air/fuel and the RPM will move up. That seems simple enough, doesn't it? The later the intake valve closes the higher the RPM and therefore the more power, MAYBE? It turns out that if the intake valve closes past 75 degrees ABDC, you could lose most of your low-speed torque and if your static compression ratio is only 8:1, the engine will not be able to reach its horsepower potential. This should give you a better understanding of why the intake valve closing is the most important timing event.

CAM SELECTION REQUIREMENTS

So, now you ask, "What do I need to know to make a proper camshaft selection for my particular application?" The list is long. First of all, in what RPM range will you want power: 1-4000 RPM, 3-6000 RPM, 5-8000 RPM, etc.? What is the size of the engine? What are the bore and stroke dimensions? How long is the center-to-center distance on the connecting rod? How much piston pin offset is there? What is the static compression ratio? In the cylinder head, what is the maximum air flow (in cubic feet per minute or CFM) in the intake track with the intake manifold and carburetor installed? At what valve lift does the air flow level out on both the intake and exhaust valves? What is the percentage of air flow of the exhaust versus the intake? What are the valve sizes? What are the lengths and sizes of the intake and exhaust systems? Once you have this data, you should be able to make a logical cam choice; but sometimes you might have to face the reality that your basic engine parameters are wrong for the RPM range you are after. How can a layperson look in a cam catalog and make an intelligent choice? First the parts supplier must supply the proper information in order to help the customer choose the right camshaft for his/her application. But, in addition, you need to be prepared with the right information about your engine and what you ultimately want to be driving


Just about any engine would benefit from a prepared cylinder head, a good exhaust system (with a relatively small diameter for street use), and maybe a little larger carburetor. As you increase the RPM band, you'll need to increase the compression ratio and add some more duration to the cam. The more duration you add, the more compression you'll need and that combination will increase the upper mid-range and top-end power. It is very important to keep your combinations balanced; for example, you can not use a 270 degree camshaft with 8:1 compression. 9.5:1 would be a lot better. Conversely, you can not have 10:1 compression and use a cam with only 250 or 260 degrees of duration! As soon as the duration is above 270 degrees, the standard exhaust system will likely restrict the breathing ability of the engine. As a result, it may become difficult to make the idle mechanism work properly due to reduced vacuum and extra exhaust back pressure.

circusboy

iTrader: (2)

man, there is a lot great info in here. i'll have to try an read it when i'm sober, lol. thanks again for the replies.

keep'em coming

Old SStroker

Interesting thoughts by Elgin. I don't think this was written recently.

I have seen some very successful engines run on pump gas with SCR over 10:1 and durations at/under 270 (@.006), so times they are achangin'.

I was hoping Dimitri would get deeper into his "FACT ONE: Volumetric efficiency is directly related to piston velocity!"

SStrokerAce

iTrader: (2)

lol.... I always thought that the basic pricipal of a NA motor was the law of physics where the air will move from high pressure to low pressure. His opening statement doesn't reflect that but the rest of that section does.... so what's up with confusing people?

Bret

treyZ28

Isn't that how EVERY engine (or any pump) works? Has someone discovered a way to violate a rule of thermodynamics (1 or 2, i forget) and get something to flow from low to high? HVAC companies might be interested in employing you Either way, flow will go from high pressure to low pressure. Whether that "high pressure" is negative or positive relative to atmosphere is irrelivant. Just a nit-pick.

As far as all this stuff goes, as its been said; there is no free lunch, especially in NA.With NA, lower specific outputs (hp:l) in a given engine size (well, I guess its just more power in a given engine at this point) will generally have a flatter torque/VE curve.
You'll start tuning things like valvetrain events, runner lengths/diameters etc to a specific RPM and it "wont work" in other places. Think of it as a sand box. You can make a big mound or a flat surface.

Valve lift, ramp rates and effective durration; you change one, you change all of them. You cant have the same lift and ramprate and decrease your durration. Steep cams really beat on hydro-lifters. Its why solid lifters have an edge on hydros.

As far as separation angles, ideally- you'd pick everything else and that would just happen. with a given stroke and rod length, you'll have your valvetrain events move around a bit. Different heads will have different charactoristics. Ideally, peak valve lift would occur a bit before max piston volocity.
Realistically, emissions and other factors play a role. A big one is lacking powerful simulation softwear and tons of experience. I've never really heard of people basing LSA off lift or vice versa.

Id honestly suggest taking an off the shelf cam, I know its cool to say you have a custom cam. Its also cool to win races.

Adrenaline_Z

^ I doubt Bret was implying the low to high pressure movement...in fact,
I know he was not.

You might want to check his background (hint: engine...cough...builder/tuner...cough)

treyZ28

I know brett

It was more or less saracasm and the second part agreeing with him. Guess it wasn't well displayed.

SStrokerAce

iTrader: (2)

Z, Why do you think my ignore list consists of Trey? One day he will have enough self esteem to not try and pick fights on the internet on those days where his rash flares up.

treyZ28

If you want to talk about old times, maybe one day, you'll stop calling people up and asking them to stop promoting other site vendors because they get stuff so much cheaper than you and you cant compete with them.

But yeah, I'm glad to see you're not crying anymore. Hows that film degree treating you?

circusboy

iTrader: (2)

i guess i'll just stick to whats proven.