How does it work. Long duration cams

[panic-mechanic]

Right - following on form the mythbusters thread I promised to look for an article I wrote for S&S many years ago. Well here it is. If you get bored quickly - don't start.

To cam or not to cam.
Terms you need to know:
TDC - top dead centre - when the piston is at the top of it stroke
BDC - bottom dead centre - Piston is at the bottom of the crank stroke.
BTDC - Before TDC
ABDC - After BDC
We often get asked that question in the club and it's never a simple answer. But let's first look at what it is and what makes it work. Hopefully most people will know what a camshaft is. It's that funny looking shaft that has odd lobes all around the thing. The purpose of a camshaft is to open the valves in the engine which basically makes an engine breathe. Camshafts turn at half crankshaft speed. End of the day all an engine is, is an air pump. So what that comes down to is that the better you can fill the capacity of the motor the more power it will make. Now let's look at cams. They will make the valve(s) stay open for certain duration of the time that the crank is turning. Quick explanation - 4-stroke engine is Intake - compression - power - exhaust cycles. You want the intake valve open during the intake cycle - both closed during the compression and power cycles and the exhaust valve open during the exhaust cycle. Each of those cycles will last 180 degrees of crankshaft rotation. So if you take TDC being 0 degrees then the intake cycle really last till 180 degrees or BDC. Then the compression cycle starts. That will last till TDC - spark happens and now you have the power stroke - that lasts till BDC then the exhaust cycle starts which lasts till TDC and all over again. Now these cycles are not as clear cut as exactly 180 degrees as there are areas of basically dead air movement at around TDC and BDC. Through the years engineers have studied the airflow inside a motor and found that you can open the intake valve before the exhaust valve is closed and use some of the scavenging effect of the exhaust air rushing out to start the intake cycle off. This is called valve overlap. So now already the intake cycle starts at BTDC. Then they found that because air is rushing into the intake port it carries momentum and it doesn't just stop immediately when the piston is turning at BDC - so you can close the intake valve ABDC and fill the cylinder better. So now already you can have intake cycle of say 5 degrees BTDC + 180 + 40 degrees ABDC to give you 225 degree duration. Same then happens with the exhaust. You can open it before the power stroke is finished, as combustion is complete - and you can close it after TDC to help the intake cycle. Standard cams run around that duration for reasons of economy - compromise of driveability and power. Now you get a cam with longer duration - which increases the area ABDC that the intake stays open. What happens now is that at Lower RPM some of the incoming air (mixture) is pushed out the open intake valve due to the fact that the piston is rising into the compression stroke and the valve is open. Effectively you have dropped the compression ratio. Why it works is that at higher RPM the speed at which the air is coming into to cylinder is so high that you do not get the reverse airflow - thus filling the cylinder to basically more than it's usual capacity. This is the reason why you get bad idle with long duration cams - there is a lot of valve overlap and the cylinder is being filled only partially - so you are running a low compression motor with bad combustion. The longer the cam duration the higher up in the RPM range the point is reached where airflow speed beats reversal. That is the reason why you lose bottom end power and the power moves up in the rev range. It now also means you basically have to rev the motor higher to reach power peak. If the duration is long enough you might reach a point where the power is made after where the normal rev limiter is so then you have to either move the limiter or use a shorter duration cam. All in all it's a compromise and any modification you make falls in the area of personal choice. Some people cannot handle the lack of drivability and the Fuel consumption that a 288 cam will give you and other can't live without the power it gives at higher rpm and don't care about the other losses. So when it comes to cam duration it's a case of seeing what you want and like or dislike and live with it.

[panic-mechanic]

And here was a follow on about gasflowing.


We have covered the basics of cams and the management systems around them in the previous issues. So now what more can you do to your aspirated car? Well there is the usual route that everybody will recommend and that is to make it breathe even better. Immediately the next sentence will contain the phrase ‘gasflowing’. Now what is this and what does that achieve. As I mentioned in the previous articles – an engine is simply an air pump. To make it get more air in it helps to remove the restrictions in the intake and exhaust air paths. The main aim of gas flowing is to make this airflow as efficient as possible. Now why is it needed – can’t the manufacturers do this right?
Well the answer is twofold. The first problem is this thing called mass production. The engineers design the ports and intakes as good as possible and it’s great in paper form. But somebody has to make it into metal and the process is a casting. Because of the way a head is made there are always two or more parts of castings that have to be joined and some machining have to take place. Now in mass production there are several castings and there will be ones that are better than others will. There will also be better machining and worse so almost no 2 heads that come out of a factory are exactly the same (this also explain why some cars simply perform better than others straight off the factory floor). The first aim of doing a gas flow job is to remove these imperfections from the castings and to basically get the port shaped and clean as it was designed. This is also called blueprinting, as the aim would be to get the metal product looking like the engineering blueprints would have been.
The second objective is to possibly improve on the original design. Now while this is not always possible and sometimes result in something worse this it the point where experience and testing comes in. When a tuner starts with a gas flow for a specific car he/she? should know beforehand what is going to be done to the rest of the motor. Is the capacity going to be bigger than it was before – what cam is going to be used – is it going to be carburetor or injected etc? It is no use starting with say a 1.8 head and you make the ports bigger – you install bigger valves and the end result is going to be used on a 1.3 motor. That engine will be dead and will probably only start performing at 8000 rpm. The main reason for this is something called air speed.
When you take a plunger of a certain size and you suck air through say a 10mm pipe the air will move at a certain speed through it. If you make the pipe bigger to say 15 mm and using the same plunger and pull it at the same speed you still move the same amount of air but it will travel through the pipe slower. So why do we need airspeed? This helps with how well your cylinder is filled with air. The higher the airspeed the better the cylinder fills (remember the cam story and why it works) so if you end up making the ports and valves too big for that capacity motor it will actually perform worse at lower rpm than it was before you started changing things. This is why it is important to use reputable tuners as they would know what works and what does not (mainly through trial and error!). A head that has been opened too much is useless except for maybe a serious rpm racecar and will cost you to replace it. So you do port and valve size work according to the requirements of the customer and considering the other modification to the motor.
Without changing anything in port sizing and by simply matching the manifolds to the head and cleaning the casting up, considerable increases can be had, because the airflow through the port is smoothed which help promote airspeed. The result is a motor that is smoother and often lighter on fuel at cruising. It will most definitely make more power as well. As with everything so far – it is always a compromise some way or the other. You will flow a race engine slightly differently to a street motor because racecars do not spend time in traffic jams and do not need to be performing well under 5000 rpm. Also if you use the extra power made available from the flow work the car is likely to be heavier on fuel. But generally speaking this is one of the most worthwhile exercises you can do to a cylinder head and rates high in bang for buck. Of course all of this will again require the same consideration to tuning as would a longer duration cam as you are now putting more air into the motor which will require more fuel.

[panic-mechanic]

Ah look - here was one that looked at the managements and cams - better sit down with some coke and popcorn here can be tough to read

Hello again. In the last issue we investigated the use of Long duration cams and why they work. So now you have hopefully gone and begged a lift or ten in cars with different cams and decided on buying that 288 you always wanted. So you storm home and you just see tools flying to get that cam installed. You get all the timings right and start the car. First thing you most likely notice is that it won't idle so nicely. Well the reason for this is you have now just totally changed you engine characteristics and the management can't cope. So let's look at different managements etc. with cams.

Firstly the good old carburettor and mechanical & vacuum advance distributor. You'll find that when you put a CO meter on the car it is now slightly lean. So you will have to increase the idle fuelling a bit. That will already get the idling better. You can also advance the timing slightly to now cater for the fact that you are basically running a lower compression ratio motor now and due to a lack of vacuum the timing is much slower because the vacuum advance is working less. When you load it on a dyno you will also see that at the RPM where the cam starts producing power there is a tendency for the fuelling to go lean. So if you have a 2 stage carb it's most likely that you will have to increase to fuelling on the 2nd stage. The timing might now become a bit of a problem as you might find that it wants to ping(pink,detonate whichever term you prefer) with the increased timing for the idling. The way to correct this is to modify the distibutor's maximum advance on the flyweights so that it decreases the allowed max advance it will allow. That way it will let you use the advanced timing earlier to recover the bottom end somewhat and then reduce the total overall advance on rpm to keep it from pinging. This will be almost mandatory if you also raised the static compression ratio as suggested in the last article to recover some of your bottom end.

Then there are 3 or 4 different injection systems that is common to VW and other cars in how they work. There is The K-jet system whih is a mecahincal injection system and there are EFI's namely Digifant; MP9 and Motronic.

Looking at K-jet. You will find this one the most forgiving to mods of any system installed on a car. It might be sligtly rough in idle with the cam installed but it will run fine. Running it on the dyno you might find that it is also slightly lean but this system is almost the only one that will actually compensate to a fair degree already without you having to tune it much. To explain how to achieve the tuning on K-jet is an entire article on it's own so I wont do it now. The timing part of it is the same on the 8v VW's as the part for cars with carb and mechanical ignition as the ignition system is basically identical. The 1.8 and 2l 16v had a mapped electronic ignition system and there are some shops like Dastek that can map these to suit your cam.

Digifant was a Full electronic management system with mapped fuelling and timing. It had a mechanical flap & potentiometer type airflow meter. Inputs from here would be read off the map for the fuelling(also used throttle position). You can adjust the airflow meter to compensate for the fuelling but the only way to modify the timing was to install a piggyback chip like unichip from dastek or Uni5 from Perfect Power.

Mp9 came on the polos and the after '96 upgrade of the mk3 where everything that VW offered had injection on. This system uses 3 inputs to read the fuelling and timing map. It uses absolute manifold pressure; Throttle position and RPM. Absolute manifold pressure(AMP or MAP as some call it) is a reading taken inside the manifold after the throttle body. On idle with the throttle closed it will be a vacuum. On aspirated cars on full throttle it will be the atmospheric pressure of the air outside depending on where you are - so 1 bar at sea level and about 0.8 bar at the reef. If you remember I mentioned that a high duration camshaft reduces the amount of vacuum that an engine produces due to the valve overlap. If you look at the tuning map of an EFI system it will use this AMP to to reduce the fuelling for idle and on partial throttle positions to achive good economy and emissions. By now destroying that vacuum you have the situation that the fuelling goes too rich at idle and part throttle. This will cause bad consumption - bad idle and surging at partial throttle with the longer duration cam installed. It will now also need more fuell at the point where the cam starts working and there is no way it will compensate automatically ast it does not know that you changed the motor's fuelling requirement. The timing also gets affected and the same problems crop up as for the mechanical systems. Not enough advance on closed and part throttle and possibly too much at load and wide open throttle (WOT). You can adjust the base fuelling and the base timing on these systems if you have the VW diagnostic tool(VAG1552) but that will make the idle richness worse if you make it richer and the full power lean worse if you make it leaner. The only way to correct these are to chip them - again by piggyback. There are apparently peopel that can get into the actual system chip and map but I have yet to see it done. I'm not saying it can't be done. So for the home tuner this is bad news as it is going to cost you much more than the cam in chipping and dyno costs. By the way - Opel corsas are in the same boat as these guys. They use a motronic box but it works on exactly the same inputs and principals.

Then there is the Motronic systems found on VR6's and a Lot of opels - Bosses,Superbosses, TS's, Astras also on Bmw's, mercs etc. These systems use a hot wire air mass meter, Throttle position sensor, Rpm, Lambda and Manifold pressure to do management. On top of that it has knock sensing as well. These systems are almost good for correcting for a cam. The airflow meter will see that there is more fuel needed and the motor's fuel requirement has changed due to the increased airflow. At cruising on constant throttle it will read Lambda(air/fuel ratio) and correct that to run economically. If the timing becomes a bit too much it will retard that to a safe level. The only place they might suffer a bit again is at idle. Although these systems will cope with what you have done it might still be possible to extract a few horses here and there with aftermarket tuning and chipping.

At the end of the day what this all comes down to is this. An engine is an airpump first of all. To make the most power it needs to burn an air/fuel mixture of around 13.2 parts air to 1 part fuel. To run economically and clean it needs around 14.7 parts air to 1 part fuel. To be able to make more power you have to burn more fuel in the right ratio. To be able to burn more fuel you have to get more air into the motor. That is why every good modification start around making the motor digest more air. For that more air you are then able to add more fuel and if your mod successfully adds air you have to get more fuel otherwise it will be making less and even damage the motor due to being lean. For the same reason you cannot simply add fuel and think it's going to make more power.

[panic-mechanic]

Oooh ooh and look at this beauty - glad I saved this one. Hard to work out at times. This was a post I made on the board many moons ago about CR and long cams.. The youngsters can learna few things here too.

The relationship between long duration cams and compression ratio is as follows. A cam's duration is measured in degrees of the crankshaft travel since top dead centre(TDC) of where the cam starts to open the valve and to the point where the cam closes the valve. The agreed standard is to measure those degrees after the valve have achieved 1mm of lift away from the seat and when the valve is 1mm before closing. So if you have a 236(standard G-grind) it stands to reason that the valve will close 236 - 180 degrees after tdc(assuming the cam lets the intake start to open on tdc-most don't- it starts to open about 24 or so before tdc but for ease of calc lets leave that) - so 56 degrees after the crank turned at the bottom or of the pistons's travel up the sleeve does the intake valve close. Both valves being closed now it means the compression stroke. Now take a 288 - only after 108 degrees of crank movement after bottom dead centre(ABDC) does the intake valve close - that only leaves 72 degrees of compression stroke as opposed to 124 degrees for the standard cam. In effect this will lower your effective compression ratio. Why does it work then?. The speed of the air rushing in the port of the open intake will at some point be higher than the effect of the rising piston wanting to push the air out of the open intake valve. At this point you feel the effect of the cam working as it lets more air into the chamber. This effect depends on things like intake runner design - length etc. That is why short intake runners and long duration cams can make things worse than better - a short intake runner is not condusive to high air speeds - neither is a too big intake runner (for that reason why you might lose power going to 50mm tb's instead of 45's that made power well). So to counter this effect of a lowered compression ratio some guys will raise the compression ratio to the reasonable limit of standard fuel (around 11.5:1) because this will recover some of the bottom end that the cam loses. On the other side of the coin - a higher compression ratio means more fuel/air mixture being present in the chamber which aids power and make for a stronger motor at top end as well. The problem with that is that you now have to watch the timing advance to stay out of ping with the motor on wide open throttle and high rpm. Here is where programmable systems comes into it's own - you can advance the timing low down to aid acceleration and pull it back slightly at high RPM wide open throttle to avoid pinging.

[GolfGTI]

Good grief, absolute brain overload. Will have to read them all over and over again but awesome articles PM. Thanks

Looking at K-jet. You will find this one the most forgiving to mods of any system installed on a car. It might be sligtly rough in idle with the cam installed but it will run fine. Running it on the dyno you might find that it is also slightly lean but this system is almost the only one that will actually compensate to a fair degree already without you having to tune it much. To explain how to achieve the tuning on K-jet is an entire article on it's own so I wont do it now.

This is one article I would really like if you ever did write it. Once again, thanks for all the info you are sharing with us. Back to the top of ther page then.....

[panic-mechanic]

I did at some point. Problem is you need to buy and make up pressure gauges and stuff which is normally not something guys want to do for a once off.

[Hotdubz]

can someone please sticky this

[sjs]

Thanks for all the info Panic .

[Life937]

Great Post!! Keep them coming

[panic-mechanic]

No I'm finished now. You okes know everything I do now.

[Kaktus]

Great stuff! Ta PM!

[dood786]

can someone please sticky this

Glued

[GolfII GTi King]

Great to hear from the Master again.
Thanks PM.

[VW MAN]

Great to hear from the Master again.
Thanks PM.

to me, still the one of the best advisors ever....man is a legend.

[ShardOfJade]

Great info, thanks.

Some of that I knew, but it seems I had some holes at very important spots.

[nasti]

Yoh brilliant stuff ! Very informative . Thanks Panic mechanic . Gonna read it all over again .

[128kw]

No I'm finished now. You okes know everything I do now.

Yeah right its gonna take alot more than this info overload to know what you know

Thanks for the info

[HASSEN]

I really missed you on the forum PM, guys pay careful attention to what PM says. You will learn a great deal. The man is a genius.

[CRASH_IT]

WOW!

Could you maybe tell me how to tell the difference between the cams you get? eg Cut, Split, Billet, Estas, *** etc? Are there makings for each to look out for?

Im in the market of purchasing one and dont want to be screwed over by a fake or purchase a cut cam!

[panic-mechanic]

There is no standard. But just know that billet cams don't have VW marking on. SO if you find a cam with engraved numbers for the duration on the end but it has vw stamps then it is a cut. By far the easiest to know that you have the real deal is to go directly to the importer - so for estas get it from Sportcam in the cape..

[CRASH_IT]

Going to look at a estas cam shaft, Do these ware at all? What can I measure, taking along a vernier to check!

[panic-mechanic]

I suspect you meant wear. No a cam should not wear - if it does there is a problem. Speak to nellis at sportcam. Perhaps he can give you meaurements you can take with a vernier.

[CRASH_IT]

Found some info on how to tell it a estas camshaft!
There should be a little egg looking thing which is actually a Cam Lobe!
I could only get this small pic, hope it serves it's purpsose.

[Abnormal]

Found some info on how to tell it a estas camshaft!
There should be a little egg looking thing which is actually a Cam Lobe!
I could only get this small pic, hope it serves it's purpsose.

??

I dont understand all cams have to have cam lobes!

or is that part painted green supposed to have a marking that looks like a cam lobe?

[panic-mechanic]

or is that part painted green supposed to have a marking that looks like a cam lobe?

That is correct...
That is their logo - look at the website then you'll see what it looks like. http://www.estascamshafts.co.uk/