Discussion
http://www.wighat.com/fcr3/camtruth.htm
Restricted Flow Case
The subject always comes around to the modification of a stock engine. By stock engine, I am referring to the typical restrictive factory stock (or very mildly modified) intake and exhaust capabilities. There are differing opinions as to what can be done to a restrictive stock type engine to increase performance. These opinions range from 'doing nothing', because it is a waste of time and money to attempt helping such a poor breathing set-up, to the alternative of working within the constraints and finding extremely respectable performance. Though aimed at stock set-ups, this category can very easily encompass many configurations, even all-out race engines. A restricted engine can be thought of as an engine that is limited by its components, manifolds, heads, or carb/EFI configuration to allow the full-displaced cylinder volume to enter. This classification primarily applies to the inlet side of the engine, where cylinder filling occurs. After all the peripheral parts are chosen/assembled, there is only one component that controls how well the air exchange is carried out, the camshaft. How is the typical camshaft swap in this situation viewed?
The rationale for 'doing nothing' focuses in three distinct areas: drivability, RPM, and overall power capability. The drivability issues come about because of the idea of the engine loosing all of its low-end power or torque characteristics. The RPM issues come about, because of the need for the engine to turn higher rpm to make power. This is closely related to the low-end power loss associated with the drivability issue. And last, is that the overall power capability of the engine is low. This last area is deeply grounded in the idea of flow equals power, so why bother with the compromised breathing capability of this type of set-up.
What Can Be Expected From A Restrictive Design?
Adding a performance-oriented camshaft to a restrictive stock-type engine set-up will require timing events that focus on increased cylinder pressure and lower RPMs. Lower RPMs will require earlier intake valve closing values, yet still enable excellent cylinder filling at these lower RPMs. By addressing cylinder filling and pressure as design criteria, low RPM torque in maintained and usually increased. Drivability is maintained, if not enhanced. In a track situation, the drivability may not be an issue but the cylinder pressure maximization is still the goal.
If there is a question about how much power a restrictive engine set-up can produce, look at the sanctioned racing events that require stock breathing characteristics of the cylinder head/s and peripheral equipment, yet allow revised valve timing events. How is it that a 'stock' class drag car can run in the 11's on the ¼ mile, yet the average hopped up street car cannot seem to even break into the 12's. It's about engine requirements. On a side note, it is common for a lot of these combinations to be shifted well below 6500 RPM.
Restricted Flow Case
The subject always comes around to the modification of a stock engine. By stock engine, I am referring to the typical restrictive factory stock (or very mildly modified) intake and exhaust capabilities. There are differing opinions as to what can be done to a restrictive stock type engine to increase performance. These opinions range from 'doing nothing', because it is a waste of time and money to attempt helping such a poor breathing set-up, to the alternative of working within the constraints and finding extremely respectable performance. Though aimed at stock set-ups, this category can very easily encompass many configurations, even all-out race engines. A restricted engine can be thought of as an engine that is limited by its components, manifolds, heads, or carb/EFI configuration to allow the full-displaced cylinder volume to enter. This classification primarily applies to the inlet side of the engine, where cylinder filling occurs. After all the peripheral parts are chosen/assembled, there is only one component that controls how well the air exchange is carried out, the camshaft. How is the typical camshaft swap in this situation viewed?
The rationale for 'doing nothing' focuses in three distinct areas: drivability, RPM, and overall power capability. The drivability issues come about because of the idea of the engine loosing all of its low-end power or torque characteristics. The RPM issues come about, because of the need for the engine to turn higher rpm to make power. This is closely related to the low-end power loss associated with the drivability issue. And last, is that the overall power capability of the engine is low. This last area is deeply grounded in the idea of flow equals power, so why bother with the compromised breathing capability of this type of set-up.
What Can Be Expected From A Restrictive Design?
Adding a performance-oriented camshaft to a restrictive stock-type engine set-up will require timing events that focus on increased cylinder pressure and lower RPMs. Lower RPMs will require earlier intake valve closing values, yet still enable excellent cylinder filling at these lower RPMs. By addressing cylinder filling and pressure as design criteria, low RPM torque in maintained and usually increased. Drivability is maintained, if not enhanced. In a track situation, the drivability may not be an issue but the cylinder pressure maximization is still the goal.
If there is a question about how much power a restrictive engine set-up can produce, look at the sanctioned racing events that require stock breathing characteristics of the cylinder head/s and peripheral equipment, yet allow revised valve timing events. How is it that a 'stock' class drag car can run in the 11's on the ¼ mile, yet the average hopped up street car cannot seem to even break into the 12's. It's about engine requirements. On a side note, it is common for a lot of these combinations to be shifted well below 6500 RPM.
I actually like n/a engines cammed to an inch of their life with no low down torque 
If you can throw in a lumpy idle then I'm even happier.
One car I had built used a 1.8 but dynod at 250bhp N/A (stock is about 120bhp) - considerably worse than standard under 4k rpm but screamed from then on to the red line (just under 9k).
But I can see why other people would hate that.
Whilst I do have supercharged cars I do find they lack the charms of a properly sorted N/A even if they are ultimately more powerful/quicker.
If you can throw in a lumpy idle then I'm even happier. One car I had built used a 1.8 but dynod at 250bhp N/A (stock is about 120bhp) - considerably worse than standard under 4k rpm but screamed from then on to the red line (just under 9k).
But I can see why other people would hate that.
Whilst I do have supercharged cars I do find they lack the charms of a properly sorted N/A even if they are ultimately more powerful/quicker.
ads_green said:
I actually like n/a engines cammed to an inch of their life with no low down torque If you can throw in a lumpy idle then I'm even happier.
One car I had built used a 1.8 but dynod at 250bhp N/A (stock is about 120bhp) - considerably worse than standard under 4k rpm but screamed from then on to the red line (just under 9k).
But I can see why other people would hate that.
Whilst I do have supercharged cars I do find they lack the charms of a properly sorted N/A even if they are ultimately more powerful/quicker.
Excellent post!!! If you can throw in a lumpy idle then I'm even happier.One car I had built used a 1.8 but dynod at 250bhp N/A (stock is about 120bhp) - considerably worse than standard under 4k rpm but screamed from then on to the red line (just under 9k).
But I can see why other people would hate that.
Whilst I do have supercharged cars I do find they lack the charms of a properly sorted N/A even if they are ultimately more powerful/quicker.
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