Nickp
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| posted on 23/7/12 at 07:48 AM |
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Lack of opening / closing ramps on 'performance' cam?
Hi,
Any camshaft experts in here?
I've picked up a set of reground cams for my Monte for a fraction of the £600 or so that a set of steel billet ones would cost me. I've
used a dial gauge to plot them against a std cam. They don't seem too radical with only a smidge more duration and the lift is at least 10%
higher right across its range with 16% greater area under the curve, which I think should work nicely. The big difference I did notice though was that
the std cam had about 40deg opening/closing ramps compared to virtually nothing on the reground cam. I presume this is going to give the valve train a
harder time, but how critical is it for the small mileage that I seem to manage in it these days?
http://www.guy-croft.com/download/file.php?id=10724&sid=4fb980f57c06d3321068c7aa4c4e24cb
You can see at the bottom of the blue (std) curve there is a gentle rise. I'd say that this takes up the valve clearance and gives a smooth
transition into the proper lift part of the profile. Where the 'performance' cam has a sharp transition so will be harsher in operation.
I'm wondering if the 'performance' cam would be better running slightly tighter valve clearances than std to take up a bit of the
slack and lessen the impact on and off the profile?
Cheers,
Nick
[Edited on 23/7/12 by Nickp]
[Edited on 23/7/12 by Nickp]
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Nickp
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| posted on 23/7/12 at 05:19 PM |
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No opinions? 
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AntonUK
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| posted on 23/7/12 at 08:12 PM |
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I'm not too experienced on cam profiles etc, but I was under the impression that this is typical of a re-ground cam?
Build Photos Here
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Nickp
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| posted on 23/7/12 at 08:39 PM |
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quote:
Originally posted by AntonUK
I'm not too experienced on cam profiles etc, but I was under the impression that this is typical of a re-ground cam?
You may well be right. Grinders don't want to waste material having nice soft opening / closing ramps when they can get more lift without them.
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britishtrident
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| posted on 23/7/12 at 09:01 PM |
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ISTR them referred to as "quietening ramps" from which I would assume main purpose is to reduce tappet noise
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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chillis
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| posted on 23/7/12 at 10:35 PM |
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It has a lot to do with how you measure it and the equipment used, also have you been given profile details OR valve event details?
I've measured many cam profiles over the years and they rarely match up to the quoted figures even the same profile from different grinders can
differ quite a bit for allegedly the same lift and duration, also the yanks measure a different way again.
40 deg does seem a lot just for the ramp. Is that crank or cam degrees?
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ashg
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| posted on 23/7/12 at 11:12 PM |
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I notice the file in the link is from guy crofts website. Is it a cam supplied by him? if so I wouldn't worry the chap is a legend when it
comes to building engines. He did the head on one of my lancias years back cost a small fortune but boy did it transform the car once it was all back
together and mapped.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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Nickp
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| posted on 24/7/12 at 06:29 AM |
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quote:
Originally posted by chillis
It has a lot to do with how you measure it and the equipment used, also have you been given profile details OR valve event details?
I've measured many cam profiles over the years and they rarely match up to the quoted figures even the same profile from different grinders can
differ quite a bit for allegedly the same lift and duration, also the yanks measure a different way again.
40 deg does seem a lot just for the ramp. Is that crank or cam degrees?
It was 40deg of cam rotation for each ramp.
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Nickp
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| posted on 24/7/12 at 06:31 AM |
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quote:
Originally posted by ashg
I notice the file in the link is from guy crofts website. Is it a cam supplied by him? if so I wouldn't worry the chap is a legend when it
comes to building engines. He did the head on one of my lancias years back cost a small fortune but boy did it transform the car once it was all back
together and mapped.
The cam's if definately not from Guy Croft. He is a legend when it comes to the Twin Cam, but if you even mention regrinds on his website then
prepare for the worst!!  Guess how I know? 
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Nickp
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| posted on 24/7/12 at 06:42 AM |
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quote:
Originally posted by britishtrident
ISTR them referred to as "quietening ramps" from which I would assume main purpose is to reduce tappet noise
But is this the purpose of them or is it a result of their design to smooth the transition out? I'm not sure.
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chillis
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| posted on 24/7/12 at 10:03 AM |
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I should have read your post properly first. you are using reground cams yes?
A reground or to put it properly reprofiled cam has a new profile ground into what ever material was already there. Since the new profile really wants
more metal than you had to start with there are compromises. One of those it going to be the base circle diameter and another the length of the ramps.
There are different ramp designs for hydraulic and mechanical tappets. Noise would be one consideration and valve gear wear another. The longer the
ramp the gentler it is.
I guess you pay your money and take you pick.
When possible I try to avoid reprofiled cams they can be a false economy, that said there are plenty of bmc mini boys using them.
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Nickp
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| posted on 24/7/12 at 10:57 AM |
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quote:
Originally posted by chillis
I should have read your post properly first. you are using reground cams yes?
A reground or to put it properly reprofiled cam has a new profile ground into what ever material was already there. Since the new profile really wants
more metal than you had to start with there are compromises. One of those it going to be the base circle diameter and another the length of the ramps.
There are different ramp designs for hydraulic and mechanical tappets. Noise would be one consideration and valve gear wear another. The longer the
ramp the gentler it is.
I guess you pay your money and take you pick.
When possible I try to avoid reprofiled cams they can be a false economy, that said there are plenty of bmc mini boys using them.
Yes, unfortunately the 'Twinks' cams aren't blessed with an excess of material. The base circle of these has been taken down from
26.4mm to 24mm which appears to be on the limit, but allows for the extra lift and duration. Hopefully these are mild enough to work on the std
castings but wild enough to make a difference, if you know what I mean?
They were done by a QED employee for his own engine apparently and are to their Q420 profile for the Lotus Twin Cam. Supposedly they made 160BHP in a
modified 1600, which sounds a tad optimistic to me.
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MikeRJ
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| posted on 24/7/12 at 11:46 AM |
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If you plot the acceleration of the lifter throughout the cam profile, there is surprisingly little increase for the performance cam vs the original,
so I think it will be ok. Are you uprating the valve springs or using originals?
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Nickp
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| posted on 24/7/12 at 12:01 PM |
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quote:
Originally posted by MikeRJ
If you plot the acceleration of the lifter throughout the cam profile, there is surprisingly little increase for the performance cam vs the original,
so I think it will be ok. Are you uprating the valve springs or using originals?
Pretty much what I thought, it's about 10% up everywhere so not too mad at all. It's already got Isky race springs in there as I planned
to put hotter cams in at some point after I originally built the engine. I'm probably gonna have to take the head off again to check the valve
to piston clearances as they're pretty tight with the std cams.
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