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 Post subject: Camshaft tech.
PostPosted: Sat Feb 14, 2004 8:26 am 
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Here is a short explanation of some of the terms,and what they mean.

Duration
This is the amount of time,in crankshaft degrees that the valve is open. Most often, duration is expressed as an 'advertised' number,which, for the purposes of comparing one cam to another, is almost completely useless.

Duration at .050"
This is a known constant way of measuring duration. Unfortunately, too many manufacturers, or retailers don't use it. The valve event is measured from .050" lift, on the opening ramp, to .050" lift on the closing ramp of the cam lobe. If all cams are measured in this way, then you can directly compare one to another.

Lift
Pretty simple. The amount that the valve is open, either in inches, or mm.

Lobe separation
The distance between the intake, and exhaust centerline in cam degrees.

Image



What does a performance cam do for me?

Duration.
Generally speaking, the duration will determine the useful RPM range of your engine. As duration is increased, the power band moves up in the RPM range. What you gain on one end, you will lose on the other.

Lift
Increasing the lift will almost always result in increased torque, and horsepower. It has been said that lift = torque, and horsepower.

Lobe separation.
Decreasing the lobe separation(moving the lobes closer to each other) will benefit low,and lower midrange torque and horsepower, but create a rougher idle, and peakier torque curve. Increasing the lobe centerline will reduce overlap, broaden the torque curve, provide a smoother idle, and better top end power.


Some things to consider.
Because of the large valve area (and excellent cylinder head design in the case of the GT DOHC), the 4 valve/cylinder motors are much more duration sensitive than the 2 valve/cylinder motors.In other words,the same cam will net very different results on the two motors. The 4 valve motors produce more power with much less duration, and overlap, but will also start to lose low RPM power in a real hurry as duration at .050" increases beyond ~210 degrees (on the GT DOHC).

A little FYI on the grind/regrind process.

Many people think you just take a little off the bottom (base circle), to get more lift, or you can tell the grinder what numbers you want, and he will custom grind it.

This is how it really works.

The cam grinding machine is a kind of copy machine.
If you have ever seen a copy lathe in a wood shop, for making spindles, its very similar.
When you grind a cam, you need to use a master template. This template has the lobe shape, which determines the lift, and duration.
During grinding, the entire lobe is ground, and the new shape takes on the charachteristics of master template.

How do you increase lift?
Take more off the bottom than you do off the top.
The lift is determined by the total lobe lobe height, minus the base circle diameter.
Its an exageration, but if you leave the tip of the lobe, but take material off the bottom, and sides(reduce the base circle diameter), then the lift is increased, as is , obviously the duration.
The lifter rests in a different place, but will open further.
How cam the lifter just re-adjust?
Hydraulic preload.
The GTi has substantial lifter preload, and there is alot of room for base circle reduction, and increased lift, or in other words, a completely reworked lobe shape.

If you still cannot grasp the concept, picture the lobe to be a rectangle, taller than it is wide.
Place a triangle inside the rectangle.
This is how the lobe will be re-profiled.
Grab a vernier caliper and measure the width of the lobe (to reflect the base circle diameter-this will be the smallest lobe number).
For the GT, it will be about 33mm
Now measure the total height.
This should be about 40.5mm
Subtract the 33 from the 40.5.
This is your lift.
Imagine taking material off the sides and bottom only.


The number one myth about reground cams is that they will wear, because, or if, they are not properly hardened after grinding.

The cams are cast iron, and require NO hardening after grinding.
The only post grinding process is something called parkerizing, which gives them that flat black.grey look. It is a type of surface treatment that etches the metal, and enhances lubricity (oil sticks to it better) during startup.

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Last edited by suprf1y on Mon Apr 09, 2007 10:38 am, edited 1 time in total.

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PostPosted: Fri Mar 19, 2004 6:27 am 
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Perhaps you could elaborate on cam construction? Like the difference between building up the lobes for a regrind as opposed to not building up. How is each process done? Benefits over one to another?

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PostPosted: Tue May 04, 2004 1:58 pm 
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i found this gr8 camshaft article in the Tech Section of the club4ag forum.

http://www.club4ag.com/faq%20and%20tech ... _story.htm

it helped me alot to understanding..

by!

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PostPosted: Sun May 16, 2004 8:53 am 
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Not a bad article, but there are some misleading statements, and some statements specific to the 4ag motor that shouldn't be considered when talking about the Suzuki motors.
Quote:
Reground stock cams have a reduced base circle which changes the valve train geometry, requiring many special mechanical modifications to make it work properly.


Not in this case it doesn't. Only the height of the lifter is changed, and since it is straight up, ands down, no geometry is altered. On a rocker arm application, geometry is changed, sometimes in a positive way. In this Toyota application, no special modifications are required to make it work properly. Only shims are added. Total bullshit statement.

Suggesting that the Formula atlantic engine builder is using billet cams, therefore it is the only correct way is nonsense. With their budget, they can likely afford custom made camshafts. Is your application the same? I doubt it.

The talk of 'turbo cams' is also misleading, and drives me nuts. The example given of what the Honda's are running tells you the lobe centers as being 108-112(pretty standard) and a Vtec duration of 235. What exactly is a 235 duration? Is it at .050" lift??
Later in the table of cams, it shows the stock cam as being a 'good turbo cam'.
This is exactly the kind of misleading bullshit that inexperienced people read, and believe. In many cases there is no difference between a turbo cam, and a non turbo cam. The important thing to consider when choosing a cam is the RPM range in which you are operating.
I get alot of people worried about 'too much overlap' on their turbo cars, when in 99% of the applications, it is not even close to being an issue.
If you are turboing your car, then you are looking for something more than stock. Why would you even consider running stock cams if you go to all the trouble, and expense of a turbo install?
I am not bashing you for posting up this article, but inasmuch as the article does provide some good basics, it was pretty obviously not written by an engine builder, and really only helps perpetuate some myths that do alot more harm than good.


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PostPosted: Mon Apr 23, 2007 2:59 am 
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suprf1y very useful info :thumbsup:
didn't think it can work this way , have few questions :

how much a stock lifters can pop up to reduce to gap in regrinded cam, let's say i would like to grind my cams to cultus specs so + 1mm lift ?

and how far u can increase the lift on stock lifters and valve springs in GTi ?

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PostPosted: Mon Apr 23, 2007 8:11 am 
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swifterrr wrote:
suprf1y very useful info :thumbsup:
didn't think it can work this way , have few questions :

how much a stock lifters can pop up to reduce to gap in regrinded cam, let's say i would like to grind my cams to cultus specs so + 1mm lift ?

and how far u can increase the lift on stock lifters and valve springs in GTi ?


The lifters have, if I recall, about 3mm of hydraulic preload.
Cultus cams only have .5mm more lift, and stock duration.
IMO, they are not worth the effort, unless you can get them for free.
Get a good profile, if you're having some custom ground.
I have used up to 10mm lift with no problems.
I haven't gone further than this.

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PostPosted: Sun May 27, 2007 4:57 am 
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Quote:
I get alot of people worried about 'too much overlap' on their turbo cars, when in 99% of the applications, it is not even close to being an issue.
If you are turboing your car, then you are looking for something more than stock. Why would you even consider running stock cams if you go to all the trouble, and expense of a turbo install?


Hi Suprf1y,
After reading a few posts similar to this of yours over the last few years, I decided to have my turbo engine built with non stock cams. This engine feels very powerful from mid to high RPM but i'm having problems with idle. I understand that cams can give you a rough idle and hard time getting a decent idle but I would like to try and work around this because of the benefits in the higher RPM range.
I'm running a standalone ECU and find the idle only starts to become stable at around 32 degrees advance :shock:, anything below and it's all over the place.
I have been told this is due to "overlap", which can also cause faulty AFR readings.
I would really like to hear your thoughts and advice on this as I know you really know your stuff about cams.
Many Thanks
Phil


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PostPosted: Sun May 27, 2007 9:58 am 
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R.I.B. wrote:
After reading a few posts similar to this of yours over the last few years, I decided to have my turbo engine built with non stock cams. This engine feels very powerful from mid to high RPM but i'm having problems with idle. I understand that cams can give you a rough idle and hard time getting a decent idle but I would like to try and work around this because of the benefits in the higher RPM range.
I'm running a standalone ECU and find the idle only starts to become stable at around 32 degrees advance :shock:, anything below and it's all over the place.
I have been told this is due to "overlap", which can also cause faulty AFR readings.


Quote:
Duration.
Generally speaking, the duration will determine the useful RPM range of your engine. As duration is increased, the power band moves up in the RPM range. What you gain on one end, you will lose on the other.



This is whats happening.
You can't have smooth idle, and performance at mid/high RPM, both at the same time.
This becomes more of a problem as displacement becomes smaller, and valve area becomes bigger.
Larger motors are more capable of handling the overlap period, than smaller ones.
You don't see false AFR readings, but you do see some pretty rich conditions during idle, from the overlap.
The overlap being discussed is a period when both valves (int/exh) are open at the same time.
Not great for idle, and static compression, but as RPM increases, so does the efficiency of this setup.
Nothing you can do.
Bottom line, the small bore GT motor is very susceptible to small amounts of overlap, and you can't really have good mid to upper RPM power without it.
What are your cam specs?
If you can open up the lobe separation, you may be able to smooth out you idle, a little.

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PostPosted: Thu May 31, 2007 8:43 am 
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Sorry for the delay on getting the specs for the cams...
The duration at .050" lift is 210, Lift is .340
Many Thanks
Phil


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PostPosted: Fri Jun 08, 2007 5:25 am 
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Hi Suprf1y,
What are your thoughts on these cams? Should they make quite a difference at idle?
So far my best idle is at 1000RPM (or higher) with 32 degrees timing.
I've also been told to try richening the mixture at idle, rather than keeping it stoich.
Many Thanks in advance
Phil


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PostPosted: Fri Jun 08, 2007 6:53 am 
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Sounds like good advice.
Thats a nice cam profile that should make you excellent power from the low midrange to 8500+ RPM

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Jun 24, 2008 4:50 pm 
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Now - I could be wrong - I've never changed a cam before, but I believe there is a bit more to it than just removing the old cam, installing the new one and getting the timing right.

Isn't there a recommended "break-in" process? Specific lubricants and not allowing it to idle but running it at 2000+ rpm or something along those lines?

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Jun 24, 2008 9:11 pm 
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Not really.
You're thinking about small block Chevy stuff.
Assembly lube is good, good oil is important, but with the Suzukis, just slap it in, and go :-P

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Jun 24, 2008 9:42 pm 
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I always keep a mix of 10w40 and assembly lube around in a little syringe kind of thing, so yeah you should lube it, but its no worse than starting it up after it sat for a few weeks im sure. but really, its that simple, ive changed like 5 cams and can do it in my sleep already

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 Post subject: Re: Camshaft tech.
PostPosted: Mon Jul 07, 2008 10:26 pm 
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i had read you can cut the timing cover in half so you dont have to remove pulleys,but how do you line he belt back up does that not matter as long as the 2 marks on the crankgear and cam are marked?


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 Post subject: Re: Camshaft tech.
PostPosted: Tue Jul 15, 2008 2:47 pm 
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im new here so i hope i dont get bashed, im looking for a person or place to buy a performance cam for my 1992 geo metro 1.0 liter. cam some one give me a contact # or something to someone that can help me, thanks


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 Post subject: Re: Camshaft tech.
PostPosted: Tue Jul 15, 2008 4:07 pm 
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Click on the link in my sig.
Email, or PM me.
Let me know what you want to accomplish, and we'll try to pick the right cam to do it.

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 Post subject: Re: Camshaft tech.
PostPosted: Wed Jul 16, 2008 8:55 am 
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suprf1y wrote:
Click on the link in my sig.
Email, or PM me.
Let me know what you want to accomplish, and we'll try to pick the right cam to do it.

i sent you a PM , i drive this car 65-70 mph about 90 miles a day. thanks


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 Post subject: Re: Camshaft tech.
PostPosted: Sun Sep 14, 2008 10:45 pm 
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I found this thread very interesting.

Has anybody looked into different ramp profiles for opening the valve and closing the valve (involving just one cam lobe for a mental image).

For instance in the early 80's we had special cams ground for SBC engines and they had a slower ramp profile on the opening side of the lobe and a faster lobe profile on closing the valve. This mostly had to do with high spring rates and the need for lower torque profiles for circle track. By speeding up the closing of the valve on the intake lobe we were able to increase the static compression at low rpms and still maintain high rpm reliability as well as building power in the high rpm range. It made for a flat torque curve.

Seems like a cam such as this might be advantages for our little 3 cylinders.

Just food for thought.

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 Post subject: Re: Camshaft tech.
PostPosted: Sun Sep 14, 2008 11:23 pm 
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Quote:
Has anybody looked into different ramp profiles for opening the valve and closing the valve

Yes, I do regularly.
My most modern profile, the 222/365 performance cam makes very strong midrange power, yet works fine with the stock computer.
Idle is rough, but power is good, and plug fouling is not an issue.

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 Post subject: Re: Camshaft tech.
PostPosted: Fri Oct 03, 2008 6:10 am 
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I ran the 210/.340 spec cams (mine were designated Cosworth 553/D2) for 3 years, 45,000kms and in 13 just-for-fun competition events...I found they were good for a 70% street / 30% competition car. They were fitted back in 2001.


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 Post subject: Re: Camshaft tech.
PostPosted: Sat Jan 24, 2009 12:52 pm 
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hears a good link regarding cam terminology:
http://www.aperaceparts.com/tech/camterminology.html
i found it useful...

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 Post subject: Re: Camshaft tech.
PostPosted: Mon Nov 02, 2009 3:21 pm 
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OK, I'll show myself a dummy. How is reducing the lift of the intake valves any different from closing the throttle a bit, or restricting the intake at some other point?
I'm trying to see why I should regrind my perfect stock cam for lower lift. If the lobes were rough, I would do it. As it is, a redrilled 10 degree cam sprocket is all it gets. I hope to chisel the guys who have the local smog shop for some exhaust gas analysis before it comes up smog time again. If the CAT cannot keep up, I can go back to stock. The new drilling and timing mark are to be 175 and 180 degrees from the old ones.

What I am asking, assuming the ECU keeps an appropriate mixture, is why lift should matter at all in low throttle situation, or why lower lift would help trained economy drivers.

Thanks, Bob


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 Post subject: Re: Camshaft tech.
PostPosted: Tue Nov 03, 2009 9:29 am 
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drbobw wrote:
OK, I'll show myself a dummy. How is reducing the lift of the intake valves any different from closing the throttle a bit, or restricting the intake at some other point?
I'm trying to see why I should regrind my perfect stock cam for lower lift. If the lobes were rough, I would do it. As it is, a redrilled 10 degree cam sprocket is all it gets. I hope to chisel the guys who have the local smog shop for some exhaust gas analysis before it comes up smog time again. If the CAT cannot keep up, I can go back to stock. The new drilling and timing mark are to be 175 and 180 degrees from the old ones.

What I am asking, assuming the ECU keeps an appropriate mixture, is why lift should matter at all in low throttle situation, or why lower lift would help trained economy drivers.

Thanks, Bob

I'm curious about this too. I understand why an economy cam has less duration, but why less lift? Unless the lift has to be reduced in order to get the desired duration.

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 Post subject: Re: Camshaft tech.
PostPosted: Tue Nov 03, 2009 2:00 pm 
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This might help (and further searches will reveal more):
http://en.wikipedia.org/wiki/Active_Val ... rol_System

"i-Active Valve Lift System (i-AVLS) is a version that supports variable valve lift. It includes 2 intake lift profiles depending on engine speeds. AVLS-equipped Subaru engines have 2 intake valves per cylinder, but AVLS only controls one of them, leaving the other in high-lift mode at all times.

At low engine speeds, each of the two intake valves for a given cylinder run on a different camshaft profile (the engines are 4-valve per cylinder type). One valve is operated by a low-lift, low-duration lobe, while the other is actuated by a high-lift, high-duration lobe. This increases air speed causing a smooth idle, while at the same time promoting a swirl factor, increasing efficiency."


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