Hey wassup guys, I know that when you add performance parts to enchance performance, such as Intake, header, or exhaust and etc. it will weaken your low end hp, and increase the high end hp. But I don't understand why, can anyone give me a better understanding of this? Since most performance parts are made to flow better, if theres more flow during anypart of the rpm range, why couldn't the extra air and along with extra fuel transmit to extra power? Why couldn't the extra flow from I,H,E improve the low end power, just like a bigger size engine, isn't it the same because there's more air in there just like the bigger engine? Also, for example when you install performance cams for any engine, why does it only improve the higher end power?, and even hurt low end power. Thanks for your time

 

bigger diameter piping will increase the amount of air flow but will slow them down . . same as water pipe big pipe will have slow flow while small pipe will have fast flowing what we want is high velocity of air and not only big volume . .

as for cams it depends on the profiles of the cams. . high lift high duration cams will improve air flow in higher RPM hence make power . .

this is my novice explaination im sure the mod here will give you a better picture

 

Like VTEC said, you want to shoot for air velocity. Remember back to your physics classes where PV=nRT, basically pressure and volume are inversely proportional. Air flow in itself does not hurt performance but if you increase the port volume that the air has to travel through and don't increase the pressure moving the air through that port, then the velocity will decrease. So what we try to do is to make the port shape more efficient so we don't have to remove a lot of material and decrease velocity. Ideally a port would be smaller than stock but flow much more air and that would make more torque and HP. That is basically what a supercharger or N2O does, move more oxygen in without increasing the port volume.

 

Great explantion guys thanks! I also have another question regarding cams. Say putting some toda specbs on a b18c motor. Why couldn't they just stick with a stock primary cam lobe instead of changing it to more aggressive? I mean isn't the stock lobe more better and more power for the low end, whats the point to alter the primary lobes, i thought vtec motors are designed to keep the low end power and have a stock idle? Is there any cams out there that has a stock primary lobes but has a very aggressive vtec lobe? What I want is a type r stock primary lobe with something like a toda spec b vtec lobe. Thanks again

 

Honda engines make power by revving high. Pair that with the VTEC system and it's go go go.

 

I'm just 'trying' to answer your question as i'm not very long in this :P the mod here will sure give you a better answer and i will too learn from it .

If im not wrong its because the stock Vtec cam doesn't make power till above 10K RPM but those after market cam does hence they gotto change the profile to make power for higher RPM even for primary cam lobes which made the idle at higher RPM too. for example Stock cam switches to Vtec at about 4500 - 5500 RPM where those after market cams 'may' switch into Vtec only at 5500 - 7000 RPM which totally move the whole usable powerband higher.

Sorry if i were wrong :P

 

Crower makes VTEC cams with a stock primary and secondary.

 

If i'm correct theres 3 cam lobes on the vtec cams. Hey KangaRod you said Crower makes vtec cams with stock primary and secondary? So on the cams theres primary, secondaries and vtec ? or theres just primary and secondary(vtec)? How does the cam perform with a stock primary or secondary compare to others? thanks

 

In a normal overhead cam motor, there is one cam lobe per valve. The cam spins which moves a rocker arm up and down which controls the movement of the valve to which it is attatched. In a motor with 4 valves per cylinder, the primary lobe is attatched to one valve and the secondary is attatched to the other.

In a VTEC motor, there is an extra cam lobe and rocker arm between the primary and secondary rockers; this is called the mid lobe and rocker arm and is not actually attatched to valves. Before VTEC is engaged, the mid rocker arm freewheels. It has a part called a "lost motion assembly" under it which acts similar to a valve spring.

When VTEC is engaged, an oil pressure switch opens and little pins inside the mid rocker arm lock it to the primary and secondary rockers, thus changing the effective cam profile.

If you have a cam with stock primary and secondary lobes, it will behave identical to stock before VTEC is engaged. The only difference is that once VTEC kicks in you get a more aggressive cam profile than the stock mid lobe provides. If you have larger primary and secondary lobes, you get a more agressive cam profile all the time.

 

OK say that we're comparing two toda specb cams, one that has stock primary and secondaries and the other is just a straight toda specb that also has aggressive primary and secondary. Comparing the two, what are the disadvantages and advantages between the two if installed in identical engines and cars? Won't the cam with the stock primary and secondary make a better useful rpm powerband? Wouldn't it start out a bit quicker since it has more power on the low end?And does the straight toda specb cam or the one with stock primary and secondary make more midrange power? But what will happen in results in the whole race during the 1320? thanks for reading