Performance Camshafts
Discussion
Hey guys, a couple of my friends are arguing about performance cam shafts so I'm after some knowledge or pages that any of you might have to help me understand the concept.
I roughly understand that they let more fuel in per rotation? Is that correct?
How do the performance cams effect reliability? Do manufacturers of everyday performance cars such as the Astra VXR use performance cams? There seems to be more expensive ones available, is it that manufacturers build engines to a budget and would waste too much money or some other political bulls
t? Or is it emissions related?
I'm totally lost, I hope you can help!
Danny
I roughly understand that they let more fuel in per rotation? Is that correct?
How do the performance cams effect reliability? Do manufacturers of everyday performance cars such as the Astra VXR use performance cams? There seems to be more expensive ones available, is it that manufacturers build engines to a budget and would waste too much money or some other political bulls
t? Or is it emissions related?I'm totally lost, I hope you can help!
Danny
MY Knowledge is as follows
- performance Cams can be Torque boosting or Horsepower boosting and rev range related (as in peak power or mid range power)
- the Degree of the cam - e.g 260 degree cam would keep the Valve open or closed(can't remember which way it is) for 260 degrees out of a possible 360 degrees on a rotation.
Hope that helps and I hope my memory Is right
- performance Cams can be Torque boosting or Horsepower boosting and rev range related (as in peak power or mid range power)
- the Degree of the cam - e.g 260 degree cam would keep the Valve open or closed(can't remember which way it is) for 260 degrees out of a possible 360 degrees on a rotation.
Hope that helps and I hope my memory Is right
Relating to the Manufacturer's using performance cams ...... They do to some extent but they conserve for fuel economy and drive ability offering plenty of torque and peak power and not extremes of one or the other. 'Hence honda's Vtec systems gofor pure peak power but don't have much torque whereas the Rover V8 in a Landrover defender would be more torque
orientated (for obvious reasons)
orientated (for obvious reasons)
Have a look on Kent cams website, they have a table detailing the cam kits available for most popular applications. Some engines will have a number of different cams to select from, and the info will detail the powerband it is best suited to..
For example, on a vts , ( this is just for example, not real info!) there may be two different profiles available, one fast road spec, which will concentrate on a broad spread of power & torque, but maintain drivability. The reccomended powerband will probably be 3500-7000 RPM. The next step is usually a race cam, which is designed for ultimate power, with far less emphesis on the low & midrange, with a recommended powerband of 5000-8000 Rpm.
On the info section, you will see a number of different measurements. Valve LIFT is how far over STD the cam opens the valves, usually in 0.01" increments. The next figure is duration, how LONG the valve is open for, in degrees. Obviously there are limits of how much further you can open & hold open the valves for, with spring binding & piston contact being the main factors.
For example, on a vts , ( this is just for example, not real info!) there may be two different profiles available, one fast road spec, which will concentrate on a broad spread of power & torque, but maintain drivability. The reccomended powerband will probably be 3500-7000 RPM. The next step is usually a race cam, which is designed for ultimate power, with far less emphesis on the low & midrange, with a recommended powerband of 5000-8000 Rpm.
On the info section, you will see a number of different measurements. Valve LIFT is how far over STD the cam opens the valves, usually in 0.01" increments. The next figure is duration, how LONG the valve is open for, in degrees. Obviously there are limits of how much further you can open & hold open the valves for, with spring binding & piston contact being the main factors.
DannyVTS said:
Interesting read
So gains are definite, what about engine reliability ? Do other components need upgrading ?
Usually for a really agressive cam you will need uprated valve springs/tappets, especially if the tappets are hydraulic.So gains are definite, what about engine reliability ? Do other components need upgrading ?
Obviously a really agressive cam will only make good power where a standard car would be getting to it's rev limit, so you have to start looking at uprated conrods and crankshafts etc. if you want to take full advantage by revving really high.
DannyVTS said:
Interesting read
So gains are definite, what about engine reliability ? Do other components need upgrading ?
Some cams will require that you need to upgrade the springs, retainers and followers in order to cope with the extra stresses put on them.So gains are definite, what about engine reliability ? Do other components need upgrading ?
You would probably want to run an adjustable cam pulley(s) in order to fine tune the timing (advance /retard) to optimise gains.
DannyVTS said:
Interesting read
So gains are definite, what about engine reliability ? Do other components need upgrading ?
Depends what cam you go for, all of them will ideally need a remap. You can run PH3 cams on a VTS without a remap and see gains, but they won't be as much and you will have a lumpy idle.So gains are definite, what about engine reliability ? Do other components need upgrading ?
DannyVTS said:
I roughly understand that they let more fuel in per rotation? Is that correct?
Nope.Getting the fuel in is the easy bit, its getting the air in and out more easily that tuning is aiming to do.
performance camshafts exploit a few things, such as overlap, that improve engine output (torque and top end power depending on spec), but affect driveability.
This is why people talk about 'wild cams' ruining your cars idle, the engine simply cannot operate at low RPM with timing designed to get max power at the top end.
The main thing to remember about any car tuning is:
THERE IS ALWAYS A COMPROMISE
Typically if it makes more power high up it loses power low down.
If it makes lots of power if will either cost lots or affect reliability.
A great race car makes a lousy road car.
You can improve on manufacturers efforts because they have many considerations particularly cost, target market and reliability.
If it seems to good to be true (like electric supercharger on Ebay) it is a con.
THERE IS ALWAYS A COMPROMISE
Typically if it makes more power high up it loses power low down.
If it makes lots of power if will either cost lots or affect reliability.
A great race car makes a lousy road car.
You can improve on manufacturers efforts because they have many considerations particularly cost, target market and reliability.
If it seems to good to be true (like electric supercharger on Ebay) it is a con.
You also need to improve the airflow into the engine. This might mean porting the head, fitting larger valves, using a bigger throttle body/individual throttle bodies and probably a different exhaust system.
Tuning an engine is about matching the various components - a set of wild cams with no other modifications will be horrible to drive and unlikely to give much in the way of increased power.
Tuning an engine is about matching the various components - a set of wild cams with no other modifications will be horrible to drive and unlikely to give much in the way of increased power.
A magazine I read once summed it up thus:
A camshaft, in the traditional sense, affects the engine speed at which the engine is running most efficiently. The camshaft itself has an engine speed range at which it is most efficient, and this range is smaller than the engine itself is capable of, say a 3000rpm band, where the engine itself has a 6000rpm band.
The camshaft design determines where in the 6000rpm band the 3000rpm of maximum efficiency will lie.
Since most cars driven on the road will spend most of their life below about 3500rpm, and will do a lot of stopping and starting, you want the car to be responsive and driveable at lower revs, so you might specify a camshaft that works best between 2000 and 5000rpm. This car will feel nice and torquey and responsive, It might feel a bit strained above 5000rpm but it will develop its best torque at lower revs. If you rev it above its best working area, it will start to struggle to fill the cylinder with mixture in the shorter time available, hence a drop in torque and a feeling that the car is running out of breath.
Power is pretty much torque times revs, so if you are after more power you can fit a cam which has its efficiency band further up the rev range. Then when you get to 5000rpm, instead of starting to struggle for air, so to speak, the engine will feel very responsive and eager to rev more. This makes the car faster simply because, by moving the torque peak to higher revs, you make the engine more powerful.
The flipside is that now below, say, 3000rpm, you drop out of the bottom end of the efficiency scale. The engine again has breathing problems, this time (I think) because the airflow is too free so the air movement becomes sluggish and again fails to fill the cylinder effectively). It will give the car a lumpy idle, mean you need a lot more revs to pull away, and will mean if you put your foot down at low revs the car won't feel responsive until you start getting into the camshaft's working zone. It would feel a lot like multivalve engines used to. Lots of performance at high revs but sluggish at low revs.
The effect this will have on longevity would be partly down to quality of the camshaft, and, because you have to run at higher revs to find the performance, the engine spends more of its life in higher stress conditions.
The ideal situation here, of course, would be to run one cam profile at low revs and then switch to a harder cam at high revs, which I believe is the original working philosophy behind Honda's V-TEC system.
The early V-TEC engines still ended up being very peaky, but then in my experience Honda engines were peaky before V-TEC came along anyway, so that might just have been the compromise they always settled with anyway. At least V-TEC ran smoothly at low revs, whereas a hard cam can make a car quite difficult to live with on the road.
A camshaft, in the traditional sense, affects the engine speed at which the engine is running most efficiently. The camshaft itself has an engine speed range at which it is most efficient, and this range is smaller than the engine itself is capable of, say a 3000rpm band, where the engine itself has a 6000rpm band.
The camshaft design determines where in the 6000rpm band the 3000rpm of maximum efficiency will lie.
Since most cars driven on the road will spend most of their life below about 3500rpm, and will do a lot of stopping and starting, you want the car to be responsive and driveable at lower revs, so you might specify a camshaft that works best between 2000 and 5000rpm. This car will feel nice and torquey and responsive, It might feel a bit strained above 5000rpm but it will develop its best torque at lower revs. If you rev it above its best working area, it will start to struggle to fill the cylinder with mixture in the shorter time available, hence a drop in torque and a feeling that the car is running out of breath.
Power is pretty much torque times revs, so if you are after more power you can fit a cam which has its efficiency band further up the rev range. Then when you get to 5000rpm, instead of starting to struggle for air, so to speak, the engine will feel very responsive and eager to rev more. This makes the car faster simply because, by moving the torque peak to higher revs, you make the engine more powerful.
The flipside is that now below, say, 3000rpm, you drop out of the bottom end of the efficiency scale. The engine again has breathing problems, this time (I think) because the airflow is too free so the air movement becomes sluggish and again fails to fill the cylinder effectively). It will give the car a lumpy idle, mean you need a lot more revs to pull away, and will mean if you put your foot down at low revs the car won't feel responsive until you start getting into the camshaft's working zone. It would feel a lot like multivalve engines used to. Lots of performance at high revs but sluggish at low revs.
The effect this will have on longevity would be partly down to quality of the camshaft, and, because you have to run at higher revs to find the performance, the engine spends more of its life in higher stress conditions.
The ideal situation here, of course, would be to run one cam profile at low revs and then switch to a harder cam at high revs, which I believe is the original working philosophy behind Honda's V-TEC system.
The early V-TEC engines still ended up being very peaky, but then in my experience Honda engines were peaky before V-TEC came along anyway, so that might just have been the compromise they always settled with anyway. At least V-TEC ran smoothly at low revs, whereas a hard cam can make a car quite difficult to live with on the road.
Edited by Alfanatic on Tuesday 25th January 15:38
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