Cam Timing Questions

[Grrrrrrr!]

I'm hoping there are some people around who have a bit of knowledge they'd like to share on cam timing and the effects it has on an engines performance. Links to articles or decent discussions also would be great.

It'd be good if we can get a good discussion of cam specs, setups and rules of thumb that could be turned into a sticky later on.

Where i'm coming from is i'm at the stage i'm starting to think about cam specs and setup for a couple of engines (3sgtes) that i'll be building up. One is going to be a relatively cheap and quick build, so the cam choice is pretty much going to be standard toyota 3s cams, but I can lay my hands on cams from gen 2 & gen 4 3sgtes, and gen 2 and 3 3sges, and I have adjustable cam gears on the way so the tuner can dial them. Second motor is going to be a bit more serious, so aftermarket cams are on the cards.

Some questions to get things started:
What effects do advancing and retarding the intake cam have?
As above, for the exhaust cam?
Overlap.. how much do you need, how much is too much?
Given the option of two sets of cams one with higher lift but less duration, and another set with more duration but less lift, what sort of power delivery does each option give?

Feel free to add your own questions, but lets keep this constructive.

[Grrrrrrr!]

http://www.mechadyne-int.com/vva-reference/papers/the-impact-of-variable-valve-actuation-on-engine-performance-and-emissions.pdf seems like a good starting point.

[Bazda]

Normally the best cam setup is what the manufacturer says.
Well with the Toda cams we use on the 4age the Toda Centerline setup seems to be the best.

Kelford cams come with their suggested centerlines, just like most aftermarket cams.

How much to adjust, well you wont know until you dyno it, see what its doing etc.

[QikStarlie]

put simply;

advance inlet - more midrange & loose peak in last usable 500-1000rpm
retard exhaust - same as above but less effect

adjusting one or both of the above directions will increase overlap. idle will be more "lumpy". piston to valve clearances will be closer.
adjusting cams in the other direction with obviously do the opposite


have always good results advancing the inlet and retarding the exhaust over the manufactures (mostly kelford 4age cams) spec's. the midrange gains usually far outweigh the small top end loss. setup on dyno is best

[atmosports]

I always thought the best way to do it was play with the timing until the valves hit the pistons or one another, then rebuild & back it off a degree or two. Idle is so overated, who wants a 1000rpm idle when you can have 2500-3000rpm??

Seriously, usually the manufacturers/grinders specs are pretty close & you end up a couple of degrees either way normally, that's providing the cams you've got are suitable for the application.

[Flannelman]

This is opening the door to Pandora's Box.

OVERLAP is the Number ONE thing to increasing any engines Volumetric Efficiency. This is experienced as torque and throttle response. Get it wrong here and nothing will save the power curve. Manufacturers don't (and most times can't) use this as it starts to destroy hydrocarbon emissions as unburnt fuel that is injected too early in the intake tract travels in past the intake valve and straight out the exhaust valve. It also leads to destruction of the Cat as it is super heated burning this fuel away.
Too much overlap gives poor fuel economy, however produces mind bending acceleration.

LIFT increase means an overall lift in the engines total air consumption, which is a horsepower increase in top 1/3 of the rev range. Severely dependent on if the associated parts, eg head, intake and exhaust manifold can deliver with the cam. No point dropping 12mm lift cams into a head that peaked and stopped flowing more air at 9mm.

DURATION - Duration is a mere measurement of either "seat to seat" or ".050" set. Some companies give a little more detail yet its simply the measurement in crankshaft degrees for how long the valve is off the seat for. I want to generalize here but I cant. See, two cams can have the same duration, yet deliver two entirely different torque/power curves as it comes down to one vital thing...

INTAKE VALVE CLOSING. It has long be believed that this point is the key to horsepower, and it is. Closing the valve later shifts the torque curve up the RPM scale at the loss of bottom end. This can be countered by increasing compression.

LSA - LOBE SEPARATION ANGLE - How far in cam degrees peak lift is separated by.

CAM CENTER LINE - intake is degrees after TDC, exhaust is before TDC.

HOW IT COMES TOGETHER...

As far as I am aware stock 4age20V cams sit at this
LSA - 125.
Centerline - 125.
Duration - 250.

Meaning - Peak lift is 125 degrees after TDC. From here its easy to see that 125 is half of 250 so INTAKE valve open is at 0 degrees or at TDC. The same is for the exhaust. How do we know? the LSA says so as the intake and exhaust centerlines are 125 degrees apart.
SO>>> 20V intake valve opens at 0 degrees and closes 250 degrees after that. Or, more accurately 250-180=70 degrees after BDC. This now shows how long the intake valve is open after the piston has stopped at BDC and now moving back up the bore for 70 degrees.
WHY HAVE NO OVERLAP? Dead easy, fuel economy and emissions set from factory. Secondary to this is VVT. When activated, the cam is ADVANCED 30 degrees. This means it opens earlier and closes earlier.
NEW LSA - 110
Centerline, ex - 125, in - 95
Duration - No changes
OVERLAP - 30

Remember what was said about two cams of the same duration giving different torque/power readings? Which cam delivers more? Trick question really as its the same cam, just its position has been changed.

BUT WAIT...
Ive searched high and low for this nugget of information and found it a few days ago.
FORMULA ATLANTIC CAMSHAFT SPEC
LSA - 99
CENTERLINE in - 98, ex 100
Duration 302
OVERLAP - 104

Better yet... intake valve open - 53 BTDC intake valve close 69 ABDC
Exhaust valve open - 71 BBDC exhaust valve close 51 ATDC
Peak power is around 9500-10000rpm
20V comparison (VVT OFF), IVO - 0 BTDC IVC - 70 ABDC
EVO - 70 BBDC EVC - 0
(VVT ON) IVO - 30 BTDC IVC - 40 ABDC
EVO - 70 BBDC EVC - 0
Peak power is around 7400-7800rpm.

Whats the same> power stroke - set at 110 degrees.
> non VVT setting intake valve closing is one degree different. (VVT switches off above 7000rpm, so this is relevant)

Extra? Atlantic engine used 11.5 comp, up 1 point on Silvertop, 0.7 Blacktop.
Atlantic engine lift is somewhere above 11mm on a 16V head. Silvertop is only 7.9mm and Blacktop 8.1mm

So, the Atlantic engine was able to produce 240hp, up from 140-150hp 20Vs. How? >increased lift - more air in for the top end, >longer duration - Kills bottom end for top end by shifting the torque curve higher up the rpm range, >larger overlap for greater cylinder scavenge and >higher compression.
RESULT = 100+Hp more 2000rpm higher up the rpm range. Or 71% power increase with a 26% increase in rpm. Never forget that this is peak power, not average power.

This is by no means the final word on camshafts. All it hopefully will be is a guide and a warning that smaller duration and a tighter Lobe Separation Angles will deliver more average power over the rev range than other cams that are longer or wider. The others may create more "peak power", but its average power across the entire rev range that accelerates a car faster.

[jondee86]

Excellent contribution Flannelman... thanks for taking the time to
write all that down.

Cheers... jondee86

[Grrrrrrr!]

Excellent contribution Flannelman... thanks for taking the time to
write all that down.

Cheers... jondee86

+1, and also thanks to QikStarlie.

So to keep this discussion going.. (and to help me figure out what to do...)

One of the options I have are gen3 NA cams, which are 252deg / 9.8mm intake & 240deg /8.2mm Exhaust, with (if my calcs/internet numbers are right) 119/113 LCA. giving an LSA of 116 degrees. These have smaller durations than even the mildest upgrade cams offered by kelfords (258/258) for the 3sgte, but more than the standard 3sgte cams in any generation.
I've keyed in the details of a few other 3sgte cams (GSC and Kelfords) and they seem to be running LCAs of 108/112 +/-2. and LSA of 111ish degrees.

If i decide to run the gen3 NA cams, should I be trying to move them to similar LCAs as the 3sgte cams.. So advancing the intake cam ~10degs, and leaving the exhaust alone as a starting point?

[jondee86]

This is an article that I collected a long time ago from somewhere. It is
written for single-cam engines (pushrod V8's) rather than twin-cam engines,
but there is some useful wisdom on cam timing problems...

Symptom Problem Solution

1. Power brakes and other vacuum accessories don't function properly.
Excessive overlap
Wider LDA or less duration decreases overlap and increases vacuum.

2. Vehicle is sluggish off the line, but runs great as engine speed increases.
Camshaft is too large.
Intake closing and exhaust opening points greatly affect low-end performance.
Going to a smaller cam will help the low-end. Tightening the lobe separation
while decreasing duration may help even more.

3. Rough and unstable idle causes engine to occasionally stumble and stall.
Too much overlap
Wider LDA or less duration decreases overlap and increases vacuum.

4. Vehicle runs strong off the line, but "gives up" as engine speed increases.
This symptom may also be caused by a valvetrain stability problem (see No. 7).
Not enough area under the curve; intake closes too early
Retarding the cam will cause the intake to close later, but installing a larger
cam is the best way to increase area. Wider LDAs typically help, and a more
agressive cam sometimes hold on longer as long as the valvetrain remains stable.

5. Good low and high-speed performance, but engine lays down in the midrange.
Overlap problem or mis-matched components
Not enough overlap prevents exhaust headers from working effectively. Also, if
the heads flow well downstairs but the cam is designed to work upstairs, the
result can be a flat, lazy torque curve. Start by examining the combination and
if everything "matches," try going to a tighter LDA.

6. Engine runs strong throughout its range but noses over big-time near max rpm.
Insufficient exhaust duration or valvetrain dynamics problem
If there's not enough exhaust duration, the piston is forced to pump out much
of the spent charge on the exhaust stroke. This pumping action robs power
from the engine. By opening the exhaust sooner, more of the spent gases can
exit near the Bottom Dead Center, and less power is required to push out the
remaining gases.

7. Engine pulls strong to redline in lower gears, but as vehicle speed increases
the engine won't accelerate beyond a given rpm.
Valvetrain dynamics problem
At times the valvespring's natural frequency of vibration matches other
vibrations in the cam and valvetrain. When this occurs the spring can no longer
control the valve. In low gears the engine blasts through the bad spots, but at
higher speeds acceleration is too slow so the engine can't power through.
Change the spring, cam, or both.

8. Engine performs OK everywhere, but not as well as expected.
Mismatched cam for the application
One of the most common cam/valvetrain-related problems, it can typically be
fixed only by matching the cam correctly with the engine, choosing lobe profiles
with the most area that are still able to maintain stability.

9. Power peaks earlier then expected, then gradually falls off to the redline.
Cam too small
The cam may need to be larger on the intake on the exhaust, or both. With a
solid cam, run a lash-loop to see if tightening the lash (increasing the valve
duration) helps. Also try different rocker arm ratios.

10. Power curve goes up strong to a certain level, than levels off for the next 1,000 rpm.
Restrictive intake or exhaust hinders air-flow
Changing cams won't help this problem. Look at the airflow numbers and see
if they go up to a given number and stop. If so, there's a restriction in the inlet
and exhaust tracts. Do not confuse this with a decrease in airflow at the extreme
top-end; that's a sign of valve-float (see No. 7).


Definitions:

Lobe center is the amount of camshaft degrees between the point of
maximum lift on the intake lobe and the point of maximum lift on the exhaust
side of a given pair of cam lobes. As an example, lobe center is calculated for
cylinder number one only and does not deviate between number one and the
other cylinders in the powerplant. To make a representative sketch of lobe
center, draw a line between the very center of a camshaft intake lobe and then
draw a similar line through the respective exhaust lobe for the same cylinder.
The number of camshaft degrees between these two imaginary lines is the
camshaft lobe center.

Also called lobe displacement angle (LDA), the lobe center has a definite bearing
on how a particular camshaft will operate in a specific powerplant. If the lobe
center of the camshaft is increased, the valve overlap will be decreased. The
overlap decrease is created because the exhaust timing will occur earlier and the
intake timing event will occur later in relation to crankshaft position. Conversely,
if the lobe center or displacement angle is decreased, overlap increases. Note that
lobe center cannot be changed once a camshaft has been ground.

Definition: Lobe centerline should not be confused with lobe center or lobe
displacement angle. The term "lobe centerline" refers to an imaginary line drawn
through each respective lobe but does not combine the separation angle between
the intake and exhaust lobes in a given pairing. Lobe centerline can be altered by
advancing or retarding a camshaft, while lobe center is a figure that cannot be altered
since it is incorporated into the camshaft when it is designed and manufactured.

Cheers... jondee86 (I fkn love coloring )

[d1 mule]

I suggest rotary / 2 stroke

Problem solved

[jondee86]

https://www.youtube.com/watch?v=IcO_2pLqYqw



Cheers... jondee86

[Flannelman]

I suggest rotary / 2 stroke

Problem solved

They still are governed by the same open and closing points similar to an engine with a cam as the rotor/piston open and closes the ports.

While overlap is finger pointed for a great deal of low speed issues, it still produces more torque over a wider rev range than either exhaust valve open or intake valve close which is determined by duration. Determining how much overlap your engine needs before low speed issues become a problem is a fair bit more than most believe.

I also need to point out I have given wrong info on 4age 20V cam details. ST and BT run 250 duration but ST runs 125 centerline while the BT runs 120. Also the Exhaust cam is set at 109 LCA giving 16 degrees overlap for ST and 21 for the BT. VVT on is 46 and 51 respectively.

On the V8 front, large overlaps were commonly used with single plane manifold. Single plane are when all runners share the same plenum under the carb, where duel plane splits a V8 in half, feeding 4 cylinders per split plenum. Fitting a single plane means a cylinder that is on its induction stroke can pull exhaust fumes into it from its opposite cylinder that is in its overlap phase. Again, this adds to the lack luster vacuum and poor idle quality with large overlap cams. That was needed back in the 80s and 90s for power, big overlaps and large open single plane manifolds. Today, with computer generated flow modeling, old school carby V8s have a far better choice of duel plane manifold. These manifolds have the same or greater flow than the old single plane back in the day so provide that same power AND because they stop the exhaust dilution by splitting the intake in half means low or no idle quality issues and vacuum needed for brakes.