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M
mini-valver
Ben, as i said, only really dealt with vauxhall 8v's and renault 16v's are new to me. On an 8v 290 is lively but still driveable.
M
mini-valver
True. Good for power without being to OTT though.
M
mini-valver
How often do you get a true profile though.... My kent 285 is brilliant but im running 40's so its hard to tell how stable the idle would be with just a cam. over 3k though and it pulls hard up to 7500 until the cam starts to drop off around 8. a milder cam would start to dip much earlier wouldnt it??
I always get a true profile as i dont read the bullshit advertised duration that UK cam companies use to sell cams.
a good 285 should not dip that early.
Like i said, understanding cam design properly is complex and because of that cam companies over simplify the explanations so people dont feel afraid of just buying a cam without any actual knowledge of what is going on.
a good 285 should not dip that early.
Like i said, understanding cam design properly is complex and because of that cam companies over simplify the explanations so people dont feel afraid of just buying a cam without any actual knowledge of what is going on.
M
mini-valver
Did'nt know that! Understand them to a point, in that i know how they work etc but all duration is beyond me!
Im happy with mine though so it's all i can ask.
Im happy with mine though so it's all i can ask.
Camshafts are one of those topics in life which disprove the old rule that you can get 80% of the results for 20% of the cost – you really need to pay for the best, which is why Ben and Schrick quite legitimately charge so much.
Traditionally cam design was all about lift, duration and overlap. The holy grail was a design which went straight up to maximum lift, stayed there for the required time and then shut immediately – christened many years ago by an eminent designer as the flying brick. Unfortunately the stresses and strains that this created meant that it was a recipe for disaster.
Modern design techniques have moved the subject on a long way and nowadays it is possible to get bit nearer. It has always been easy to get lift, by using gradual opening and closing curves, but the duration (and overlap) is unacceptably long, moving the torque and power way up the rev range, and even beyond the other characteristics of the engine The usable power band then becomes ridiculously short and the area under the torque vs rpm curve is smaller than a more sensible set-up.
One way of helping the situation, and to obtain a greater average flow area, is to go for an asymmetrical profile, in which the opening side of the lobe is more gentle than the closing side.
The designer may also need to allow for the relationship between the cam profile and the rockers or fingers, as they do not necessarily provide a simple multiplier effect. This is in particular why a regrind, which by definition has to reduce the base circle diameter, is in general not a good idea – hence the need for the more costly solution of ‘billet’ cams. The other nasty side of a regrind is that it is modifying parts which have already been heat treated, and will need retreating – very difficult to get 100% right.
Cam design needs to be matched to the weight of the vehicle, the bore and stroke and sensible working rpm range, and hence also the gearing. For instance a Hyabusa engined Caterham weighs under 500 kg and can live with totally different characteristics from a Clio at over double the weight. This situation can be aggravated because when specifying the usable power band most drivers (even in F1) have little idea of how low they actually go in the real world – even on the track. Unless you have data logging, I promise that you will be out by quite a long way – and don’t forget that there is no point in revving way beyond peak power to compensate, as yet again the useful area under the curve will be less.
So as I said you pay for what you get, but also need to be sure that you know what you really need – hence the need to listen to people like Ben who have taken into account all the factors. Sounds a bit like a plug for him, which it is, but only because he has convinced me that he is 100% on the case
Traditionally cam design was all about lift, duration and overlap. The holy grail was a design which went straight up to maximum lift, stayed there for the required time and then shut immediately – christened many years ago by an eminent designer as the flying brick. Unfortunately the stresses and strains that this created meant that it was a recipe for disaster.
Modern design techniques have moved the subject on a long way and nowadays it is possible to get bit nearer. It has always been easy to get lift, by using gradual opening and closing curves, but the duration (and overlap) is unacceptably long, moving the torque and power way up the rev range, and even beyond the other characteristics of the engine The usable power band then becomes ridiculously short and the area under the torque vs rpm curve is smaller than a more sensible set-up.
One way of helping the situation, and to obtain a greater average flow area, is to go for an asymmetrical profile, in which the opening side of the lobe is more gentle than the closing side.
The designer may also need to allow for the relationship between the cam profile and the rockers or fingers, as they do not necessarily provide a simple multiplier effect. This is in particular why a regrind, which by definition has to reduce the base circle diameter, is in general not a good idea – hence the need for the more costly solution of ‘billet’ cams. The other nasty side of a regrind is that it is modifying parts which have already been heat treated, and will need retreating – very difficult to get 100% right.
Cam design needs to be matched to the weight of the vehicle, the bore and stroke and sensible working rpm range, and hence also the gearing. For instance a Hyabusa engined Caterham weighs under 500 kg and can live with totally different characteristics from a Clio at over double the weight. This situation can be aggravated because when specifying the usable power band most drivers (even in F1) have little idea of how low they actually go in the real world – even on the track. Unless you have data logging, I promise that you will be out by quite a long way – and don’t forget that there is no point in revving way beyond peak power to compensate, as yet again the useful area under the curve will be less.
So as I said you pay for what you get, but also need to be sure that you know what you really need – hence the need to listen to people like Ben who have taken into account all the factors. Sounds a bit like a plug for him, which it is, but only because he has convinced me that he is 100% on the case
J
jbaddeley
I've got schrick and SMT. Great on road and track. No worries in traffic, slightly lumpy on tickover but not an issue.
J
jbaddeley
My Cams were done by Yozzasport. Very good package.
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