Cam Lobe Wear Question

[The Dan]

So effectively all lift does is get more air in/out because the valve opens more but still opens and closes at the same time.... Correct?

Where as a larger duration will extend the time in which a valve is open and there for move the power to a different point in the band... Correct?

Also duration is calculated by the amount of engine degrees that the inlet or the exhaust is open for while LSA lobe separation angle is the amont of overlap of the inlet and exhaust...correct?

These are half startment half question replys btw

Yep, you pretty much have it there.

Advertised duration is different from duration at 0.050 open as well. Ramp rate, advertised duration, duration at 0.050 and overall lift all have an impact on what the camshaft will be like in the engine. Two cams with the same 0.050 duration but different advertised duration will have different efficiency at different RPM.

I apologise if this makes things more confusing but it's just to point out that looking at a cam that says 270 x 11.4 tells you nothing about what the cam will achieve. Knowing all the information is critical to knowing exactly how it will perform.

LSA is important for scavenging effect as the boost pressure or inlet fill will push the exhaust gasses across the top of the piston and out the exhaust while the valve is still slightly open. LSA has other functions but this is part of it.

Timing the camshaft is just as important as getting the lift and duration correct.

[GTR_JOEY]

awsome cheers for the reply

can u go a bit more detail into duration and advertised duratation? examples and why we have it like that maybe?

trying to get my head around it

thanks

[The Mafia]

Thanks also for the replies elite, will help me understand breadsticks even more.

Cams have alway been a but of a confusing area for me.

[The Dan]

awsome cheers for the reply

can u go a bit more detail into duration and advertised duratation? examples and why we have it like that maybe?

trying to get my head around it

thanks

A good example would be a Tomei camshaft. Their catalogue may refer to a camshaft being 260 deg and 9.15mm inlet which is a Poncam for a GTR. The 260 degrees is from the point where the cam lobe is lifting @ 0.050 (50 thou) until the point at which it is closed to 0.050 (still open slightly). The advertised duration may be something like 295 degrees because it is measured at 0.004, 0.006 or sometimes up to 0.020. It depends on the manufacturer and the application the cam is being used (solid vs hydraulic) as to where they report their lift. Most try to stay at the 0.050 for ease of comparison but some will still report advertised durations. If you get two camshafts with the same total lift and advertised duration but different lifts at 0.050 inches, the one that has the smaller lift at 0.050 would indicate the ramp is very fast because it has to get from the smaller lift at 0.050 to the overall lift which is the same on both shafts. This means the valve is opened at a much more accelerated rate. Air speed into the cylinder is slower but the cylinder can draw it in much more quickly. The engine with this cam will make power a little earlier even though the duration and lift can be reported as the same.

A slower ramp means air speed increases more efficiently into the cylinder and much more smoothly at higher rpm so the power is made slightly later.

You can still get a pretty good idea of what a cam is going to do from the basic lift and duration that the manufacturer - especially the japanese brands who don't give you any real information on the profile but it's not always the case when you are buying custom made or cams that are made locally

*edit* I should also point out that the timing of the lobe is very important as well. Having them open and close at the wrong time is just as bad as having the wrong lift and duration for the turbo that is fitted (camshafts should always match turbo the same as torque converters should). We recently dialed in a set of Surecams on a GTR that was making about 450hp at the wheels. The lobe was way off. So far, in fact, that we had to move the camgear on the belt one whole tooth and then adjust it further to get the correct opening at TDCE. It made a further 80hp when we did

[The Mafia]

Information gold mine thanks again elite

[GTR_JOEY]

cheers Dan

very helpful mate

Got so many more questions but i dont wanna annoy the sh!t out of you

Edited December 27, 2011 by GTR_JOEY

[fatz]

A good example would be a Tomei camshaft. Their catalogue may refer to a camshaft being 260 deg and 9.15mm inlet which is a Poncam for a GTR. The 260 degrees is from the point where the cam lobe is lifting @ 0.050 (50 thou) until the point at which it is closed to 0.050 (still open slightly). The advertised duration may be something like 295 degrees because it is measured at 0.004, 0.006 or sometimes up to 0.020. It depends on the manufacturer and the application the cam is being used (solid vs hydraulic) as to where they report their lift. Most try to stay at the 0.050 for ease of comparison but some will still report advertised durations. If you get two camshafts with the same total lift and advertised duration but different lifts at 0.050 inches, the one that has the smaller lift at 0.050 would indicate the ramp is very fast because it has to get from the smaller lift at 0.050 to the overall lift which is the same on both shafts. This means the valve is opened at a much more accelerated rate. Air speed into the cylinder is slower but the cylinder can draw it in much more quickly. The engine with this cam will make power a little earlier even though the duration and lift can be reported as the same.

A slower ramp means air speed increases more efficiently into the cylinder and much more smoothly at higher rpm so the power is made slightly later.

You can still get a pretty good idea of what a cam is going to do from the basic lift and duration that the manufacturer - especially the japanese brands who don't give you any real information on the profile but it's not always the case when you are buying custom made or cams that are made locally

*edit* I should also point out that the timing of the lobe is very important as well. Having them open and close at the wrong time is just as bad as having the wrong lift and duration for the turbo that is fitted (camshafts should always match turbo the same as torque converters should). We recently dialed in a set of Surecams on a GTR that was making about 450hp at the wheels. The lobe was way off. So far, in fact, that we had to move the camgear on the belt one whole tooth and then adjust it further to get the correct opening at TDCE. It made a further 80hp when we did

and the exact reason why any engine builder always asks for the detailed cam specs prior to intalling the f**kers...cause if you dont have them you are f**ked potentially

[The Dan]

and the exact reason why any engine builder always asks for the detailed cam specs prior to intalling the f**kers...cause if you dont have them you are f**ked potentially

yeah pretty much. I haven't seen it because we don't often play with standard cams but I have been told even the stock camshafts in RB26's and 25's are way off for lobe angle and lobe timing. Always pays to check.