Why 4 degrees?

[hoffman900]

I’d argue it only makes the tuned lengths more sensitive and opens up holes in the power curve in order to make more peak when the intake and exhaust are in tune. More overlap area just makes things more sensitive and too much just blows fuel out the exhaust that you would otherwise want to trap and use to work on the piston.


The opening and closing points dictate the power curve.

The amount of overlap that would blow fuel out the exhaust would differ on various engines and even head styles/port flow on the same engine.

Overlap is just a tuning method. Under-valved engines are going to need more overlap to create the same signal.

Somebody said, "overlap that would blow fuel out the exhaust" ..

With a naturally aspirated engine the exhaust pressure is higher than the intake, so the exhaust is blowing into the intake. Seems like locating equal lift (maximum leak area) to minimize exhaust dilution is desirable.

If you are blowing exhaust back into the cylinder, you are doing it WAY wrong.

viewtopic.php?t=63189

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

[Tom68]

If you are blowing exhaust back into the cylinder, you are doing it WAY wrong.

viewtopic.php?t=63189

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

But you are whenever you are throttled or outside your exhausts ideal rev range, that's why I think it's funny when people start blaming all these things for exhaust up the inlet tract, even race engines have to idle.
Wesman does presumably require some street manners in this mild 300 6cyl.

[hoffman900]

If you are blowing exhaust back into the cylinder, you are doing it WAY wrong.

viewtopic.php?t=63189

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

But you are whenever you are throttled or outside your exhausts ideal rev range, that's why I think it's funny when people start blaming all these things for exhaust up the inlet tract, even race engines have to idle.
Wesman does presumably require some street manners in this mild 300 6cyl.

Oh I agree.

Bad heads need more time-area to make up for poor flowing ports, which by virtue creates more overlap.

I have laid the “why” out here many times. We ran 268* @ .050 lobes for an engine that made peak power at 6700rpm. That same lobe will support 8000+ rpm on a great flowing, modern V8 casting. We had more overlap because the IVC dictated that the lobe center was more advance than the 8000rpm example, not because we actually wanted more overlap.

[HQM383]

No, Wesman asked about 4 degrees advance, implying intake cl 4 degrees advance from equalised LSA angle install,

Tuner pointed out 4 degrees before (OVERLAP TDC) "equal lift" was considered an install point by GM presumably because cam advance has more to do with the overlap cycle than an intake highest lift point that is always around 40 degrees later than we want it anyways due to cam lobe practicality limitations.

It does seem nonetheless GM has headed more towards LSA plus around 4 degrees intake cl for intake later decades. Never mind the crazy emissions side tracks.

You advance ICL 4° then you advance overlap triangle - or equal lift 4°. Straight up is even lift @ tdc eg 110 lsa on 110 icl and 110 ecl.

[Tom68]

You advance ICL 4° then you advance overlap triangle - or equal lift 4°. Straight up is even lift @ tdc.

Yer but your overlap triangle isn't straight up with a dual pattern cam. 4 degrees TDC overlap TDC isn't a 4 degree intake cl advance.

Straight up is ... even lift at (overlap TDC) ONLY if you have a single pattern lobe that is symmetrical above that amount of lift.

I.E..A 220 220 110 with 4 degrees split overlap would be intake cl 106, = a +4 icl.
220 228 112 with 4 degrees split overlap would be intake cl 106, = a +6 icl.
220 238 114.5 with 4 degrees split overlap would be intake cl 106, = a +8.5 icl.

Stuggling here, listening to the Oreo v Statin LDL video whilst talking cams.
This is why it's truly about valve events from significant flow lift, hence they went 50 thou lobe which can now be up to 100 thou valve (so that showed a lack of foresight) Intake CL (wherever you put it) is a function of lobe design limitations, but it is relevant because it tells us open and close points (but only in its symmetrical range.

[Stan Weiss]

This is the Crane version of a Pontiac RAIV cam. To talk events and ICL you really need a Cam Dr file.

CAM-Lift---Opens---Closes--Duration
-------Deg BTDC--Deg ABDC--------- Area----ICL
0.00200 38.67 | 108.57 | 327.24 | 26.06 | 124.95
0.00400 31.84 | 98.92 | 310.76 | 26.04 | 123.54
0.00600 27.77 | 90.14 | 297.90 | 26.00 | 121.19
0.00800 24.79 | 82.63 | 287.42 | 25.96 | 118.92
0.01000 22.53 | 77.20 | 279.73 | 25.93 | 117.34
0.02000 14.78 | 65.40 | 260.18 | 25.78 | 115.31
0.04000 5.21 | 54.28 | 239.49 | 25.46 | 114.53
0.05000 1.45 | 50.18 | 231.64 | 25.27 | 114.37
0.10000 -14.18 | 33.72 | 199.54 | 24.05 | 113.95
0.15000 -28.41 | 19.15 | 170.75 | 22.12 | 113.78
0.20000 -43.49 | 4.01 | 140.51 | 19.43 | 113.75
0.25000 -61.28 | -13.92 | 104.80 | 15.29 | 113.68
0.30000 -89.31 | -41.84 | 48.86 | 7.44 | 113.74

Stan

[HQM383]

You advance ICL 4° then you advance overlap triangle - or equal lift 4°. Straight up is even lift @ tdc.

Yer but your overlap triangle isn't straight up with a dual pattern cam. 4 degrees TDC overlap TDC isn't a 4 degree intake cl advance.

Straight up is ... even lift at (overlap TDC) ONLY if you have a single pattern lobe that is symmetrical above that amount of lift.

So the variables in positioning overlap triangle @ 4* BTDC puts that out of the equation to Wesman07’s original question:

This may be an elementary question but I never got a straight answer on this. Why do cam makers recommend installing 4 degrees advanced?

As this would only be in relation to icl (maybe I’m just getting on the same page as you Tom)

Here is UDHarold answering the same question as this thread original post on another forum in 2004

I don't want them installed ANOTHER 4 to 6 advanced. I just want to make sure they are where they are supposed to be. When cams are installed, there are a number of errors that add and subtract degrees from where the cam should be installed. How the piston manufacter placed the dome and where the piston pin is actually located, how close the crank throws are actually to 90°, and how accurately was the crank key-way cut, how accurately was the timing chain, etc made, dah-de-dah-de-dah......
The only thing important is the relationship between the cam and the piston, none of these other 'errors' are important, as long as the cam is in the correct relationship to the piston. In all the cam-loop testing we have done, from 151 Pontiacs through 555 BBCs, maximum BHP and torque was achieved most often at 6° advanced from straight-up, ie---106 ICL on 112 LSA, 99 ICL on 105 LSA..... Sometimes, depending upon your individual cylinder head, 4° advanced was best. The difference was always only about 4 or 5 BHP, 5 to 8 ftlbs torque.
Lunati grinds all their cams 4° advanced, because all of the core companies, who make the cores, now provide the cores with a 4° advance off the pin........

Sorry about the confusiion....

Mike, Hello, and thanks for your support. It's always nice to have to have friends....
Say hello to the wolves for me....

UDHarold

Actually, my cam cards have NEVER said to advance a cam 4°, or 6°. What they tell is what the cam's LSA is, and WHERE to place the Intake CenterLine for BEST overall power. That point is 6° advanced from where the LSA is ground. The catch is core manufacturers changed their pin offset several years ago, and instead of offering cores with a 2° offset, they changed to 4° offset, because most cams liked that better. Because of all the various possible errors, which I mentioned in a previous post, there is no way I can, or any manufacturer, gaurantee that putting a cam in and not checking it means it is exactly where it is supposed to be. We almost all grind the cam with NO advance, the lobes are advanced in relation to the pin. This way we maximize heat-treat on the lobes. To grind extra advance into the cam lobes is to take heat-treated metal off the back side of the lobes......
I told people for years to put cams in using the 4° advance key, because with the 2° pin off-set and the 4° advance, the cam would PROBABLY be around 6° advanced. It is the job of the engine builder to verify that the cam is where the cam manufacturer suggests it to be. Putting a cam with 4° advance pin-offset in 'Dot-to-Dot' means the cam is probably between 3° to 5° advanced, and possibly 2° to 6° advanced. All numbers are possible, and this does not mean that your cam was mis-ground. What it means is that it is your job to make sure the intake CenterLine is as close to the recommended position as you can get it. Almost all cams tolerate a +/- 1° in Intake Centerline position........

Does this make anything clearer?

UDHarold

Jim,
Exactly where each cam likes to run is according to how it was designed. Just because some cams are all 300° at .020 and 264° at .050 does not mean they will all run alike. Most of my most popular roller cams have at least 3 distinct LSA at .020, .050, and max lobe lift. The 2 most popular families, the 288/296R and the 310/314R, are 1.5° retarded at .050 from the nose LSA, and 3° retarded at .020,--- ie, 100° ATDC at the nose equals 101.5° ATDC at .050, and 103° ATDC at .020. All these numbers are correct, and this is the reason I tell customers to degree them in off the nose. It's easier to find, and is very accurate. The other numbers are then there automatically.
Symmetrical cams ALWAYS make more top-end power when retarded a few degrees, because the intake opens later, putting in less reversion (Heard this before?), and shuts later, allowing more cylinder filling(Heard this part,too?). I just always designed the retard at low-lift into the design.
Generally speaking, whosever cam you have, follow their general instructions on installing the cam. This is only put you into the ballpark for the ultimate power from that cam. Once you have achieved your best times, playing with the lash will determine whether or not to advance or retard the cam, and that can determine whether or not you need a larger or a smaller cam.
Good Luck, and Happy New Year!

UDHarold

[Tom68]

You advance ICL 4° then you advance overlap triangle - or equal lift 4°. Straight up is even lift @ tdc.

Yer but your overlap triangle isn't straight up with a dual pattern cam. 4 degrees TDC overlap TDC isn't a 4 degree intake cl advance.

Straight up is ... even lift at (overlap TDC) ONLY if you have a single pattern lobe that is symmetrical above that amount of lift.

So the variables in positioning overlap triangle @ 4* BTDC puts that out of the equation to Wesman07’s original question:

This may be an elementary question but I never got a straight answer on this. Why do cam makers recommend installing 4 degrees advanced?

As this would only be in relation to icl (maybe I’m just getting on the same page as you Tom)

Here is UDHarold answering the same question as this thread original post on another forum in 2004

I don't want them installed ANOTHER 4 to 6 advanced. I just want to make sure they are where they are supposed to be. When cams are installed, there are a number of errors that add and subtract degrees from where the cam should be installed. How the piston manufacter placed the dome and where the piston pin is actually located, how close the crank throws are actually to 90°, and how accurately was the crank key-way cut, how accurately was the timing chain, etc made, dah-de-dah-de-dah......
The only thing important is the relationship between the cam and the piston, none of these other 'errors' are important, as long as the cam is in the correct relationship to the piston. In all the cam-loop testing we have done, from 151 Pontiacs through 555 BBCs, maximum BHP and torque was achieved most often at 6° advanced from straight-up, ie---106 ICL on 112 LSA, 99 ICL on 105 LSA..... Sometimes, depending upon your individual cylinder head, 4° advanced was best. The difference was always only about 4 or 5 BHP, 5 to 8 ftlbs torque.
Lunati grinds all their cams 4° advanced, because all of the core companies, who make the cores, now provide the cores with a 4° advance off the pin........

Sorry about the confusiion....

Mike, Hello, and thanks for your support. It's always nice to have to have friends....
Say hello to the wolves for me....

UDHarold

Actually, my cam cards have NEVER said to advance a cam 4°, or 6°. What they tell is what the cam's LSA is, and WHERE to place the Intake CenterLine for BEST overall power. That point is 6° advanced from where the LSA is ground. The catch is core manufacturers changed their pin offset several years ago, and instead of offering cores with a 2° offset, they changed to 4° offset, because most cams liked that better. Because of all the various possible errors, which I mentioned in a previous post, there is no way I can, or any manufacturer, gaurantee that putting a cam in and not checking it means it is exactly where it is supposed to be. We almost all grind the cam with NO advance, the lobes are advanced in relation to the pin. This way we maximize heat-treat on the lobes. To grind extra advance into the cam lobes is to take heat-treated metal off the back side of the lobes......
I told people for years to put cams in using the 4° advance key, because with the 2° pin off-set and the 4° advance, the cam would PROBABLY be around 6° advanced. It is the job of the engine builder to verify that the cam is where the cam manufacturer suggests it to be. Putting a cam with 4° advance pin-offset in 'Dot-to-Dot' means the cam is probably between 3° to 5° advanced, and possibly 2° to 6° advanced. All numbers are possible, and this does not mean that your cam was mis-ground. What it means is that it is your job to make sure the intake CenterLine is as close to the recommended position as you can get it. Almost all cams tolerate a +/- 1° in Intake Centerline position........

Does this make anything clearer?

UDHarold

Jim,
Exactly where each cam likes to run is according to how it was designed. Just because some cams are all 300° at .020 and 264° at .050 does not mean they will all run alike. Most of my most popular roller cams have at least 3 distinct LSA at .020, .050, and max lobe lift. The 2 most popular families, the 288/296R and the 310/314R, are 1.5° retarded at .050 from the nose LSA, and 3° retarded at .020,--- ie, 100° ATDC at the nose equals 101.5° ATDC at .050, and 103° ATDC at .020. All these numbers are correct, and this is the reason I tell customers to degree them in off the nose. It's easier to find, and is very accurate. The other numbers are then there automatically.
Symmetrical cams ALWAYS make more top-end power when retarded a few degrees, because the intake opens later, putting in less reversion (Heard this before?), and shuts later, allowing more cylinder filling(Heard this part,too?). I just always designed the retard at low-lift into the design.
Generally speaking, whosever cam you have, follow their general instructions on installing the cam. This is only put you into the ballpark for the ultimate power from that cam. Once you have achieved your best times, playing with the lash will determine whether or not to advance or retard the cam, and that can determine whether or not you need a larger or a smaller cam.
Good Luck, and Happy New Year!

UDHarold

Yer there's some interesting points from a grinders practicality point of view.
First quote also showed why working with overlap TDC can be important, variation there is piston to valve and could put you close to contact if not checking intended installed position.
If somebody was to throw a cam in without checking installed position and got a smog gear with 7 odd degrees of retard built in they might be in for disaster.

On small blocks I always at some point after timing chains on and before heads are on do a quick straight edge across the lifters for one cylinder check, ( I always degree cams, can't help myself ) simply put a short straightedge across the lifter tops, rock the motor till you have equal lift and look at the piston position, if it isn't almost at TDC you've F'd something up and better not bolt the heads on.

[Tom68]

HQM383.. I bought an old HJ with a 253 2 barrel way back that was gutless, put valve stem o-rings on it because it smoked on start up, found out the cam was a tooth out whilst doing it so corrected that....thing was still gutless, I'd already drilled the main jets to get rid of the lean surge. Put a factory 4bbl manifold and Q'jet on it and it really woke up. I guess valve events with restricted breathing aren't very important ?

[barnym17]

MY guess with other breathing restrictions you may well hit a point that a good cam cant improve,but I also think in that case a bad cam can really hurt it.

[digger]

If you are blowing exhaust back into the cylinder, you are doing it WAY wrong.

viewtopic.php?t=63189

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

But you are whenever you are throttled or outside your exhausts ideal rev range, that's why I think it's funny when people start blaming all these things for exhaust up the inlet tract, even race engines have to idle.
Wesman does presumably require some street manners in this mild 300 6cyl.

case in point on some vanos bmw engines at WOT the centrelines are in the 70 degree range at low rpm but at same rpm cruise its more like 130 degrees so the throttle opening/load matters. From i can tell its the mass, at part throttle with less mass to exhaust the engine has way too much exhaust and the pressure drops too quick and thus you get a reversion pulse instead of suction. So you dont want to get sucked into the idea that tight LSA cams are good for low rpm therfore would work well on the street as its true only at WOT

[Tom68]

So you don't want to get sucked into the idea that tight LSA cams are good for low rpm therefore would work well on the street as its true only at WOT

We probably should refer to them as higher overlap cams.
I think 305s had one cam as tight as 104 but it had very little duration.

[digger]

So you don't want to get sucked into the idea that tight LSA cams are good for low rpm therefore would work well on the street as its true only at WOT

We probably should refer to them as higher overlap cams.
I think 305s had one cam as tight as 104 but it had very little duration.

better to say high overlap + tight LSA as that makes the EVO and IVC better for low rpm

[hoffman900]

So you don't want to get sucked into the idea that tight LSA cams are good for low rpm therefore would work well on the street as its true only at WOT

We probably should refer to them as higher overlap cams.
I think 305s had one cam as tight as 104 but it had very little duration.

Someone should find a dyno graph that doesn’t start at 3000rpm for a street engine

[Tom68]

So you don't want to get sucked into the idea that tight LSA cams are good for low rpm therefore would work well on the street as its true only at WOT

We probably should refer to them as higher overlap cams.
I think 305s had one cam as tight as 104 but it had very little duration.

Someone should find a dyno graph that doesn’t start at 3000rpm for a street engine

Is it that the dynos don't have the water regulation to cover the wide range ? Sounds fixable with some creative engineering.
Or more about getting the engines to take load ? Just need a good dyno driver that can balance the throttle input, I know that then becomes a variable.

I'd hate to add another post, so answering the following question on page 11, coz people keep posting, even random posts like "why 10 pages" which if answered will add to the page count.