Unequal camshaft duration 4AGE

[oldcorollas]

cam grinders keep their specs "secret" because they are in it for the money.
racers keep it secret so they can be "better" at their "hobby" than other people

Na to SC to turbo are very different in cam needs, but you can think about it from firts principles (although of course KM does not agree )

to say simply......
NA, for a given revs, you need overlap to take advantage of exhaust scavenging, where the tuned exhaust helps to remove burnt gas from the cylinder, and also helps to pull the intake charge in by giving it a bit more energy (kinetic from velocity and potential from the lower cylinder pressure).... what size in/ex cams chosen are mot to do with the relative flow of the ports... a (relatively) poor flowing exhaust needs more cam.... as we all know...

SC also uses exhaust scavenging (can/should use) to clear the cylinder of dead gas, but since there is more pressure in the intake ports (compared to NA) when the intake valves open, the higher initial flow of the SC motor vs the NA motor can help to give the same cylinder clearance with less overlap. so you can get away with a smaller overlap on an SC than NA, and still have same RPM limits before cams choke....
or.. with same cams/overlap, the SC will work to higher rpm...

exhaust opening time affects (well.. many things but...) the losses of the engine.... earlier opening valve will allow gas out earlier (duh), which will slightly reduce the cylinder pressure on the exhaust upstroke... whilst it may not seem much, reducing inefficiency in engine is as important as improving the amount of air stuffed in in gaining power. so while you can probably get as much air into engine with later opening exhaust (but same overlap) the losses on exhaust stroke will be slightly higher.

from intake side, because of the pressure, longer intake duration (but same overlap) = more time to stuff the air in.... but depending on many things, too long may not give the best flow due to ... i guess easiest word is harmonics....
for exhuast cam, earlier closing means less time with both valves open and less time for the charge being blown in to escape past exhaust valve.. but same as NA, at higher rpm, this reduces the time for scavenging/blowing spent charge out....

anyway
from a starting point of balanced cams (not necessarily equal duration or lift tho), and way simplified.. (ie relatively equal overlap)

relatively larger intake will increase the ability to stuff air into cylinder and increase power, but at higher rpm, the exhaust cycle might start to restrict, due to losses on exhaust stroke, and remaining charge in cylinder.

relatively larger exhaust cam will reduce inefficiency due to lower exhaust blow down(?) pressure, and so will increase power output by making engine more "efficient", and reducing remnant charge in cylinder (dilution/restriction of intake). at higher rpm, the intake might start to restrict the power in terms of what gets into cylinder, but the larger exhaust will still mean higher power due to lower losses...

this also means same power with less fuel/air needed. (ie, does it easier)
whereas, larger intake than exhaust might take a little more fuel and air to make same power due to inefficiency (more power, but works "harder")

and of course, moving the cams around for a given duration will also have effect due to changing overlap, but thats a different story...

whilst the exact cam specs (not just duration and lift, but the shape of the curve.. ie ramp rates and the actual movement of the valve (shape of curve)) used in the latest hobby racing engines are secret, different grinders use different profiles, durations and lifts to achieve almost the same results (ie, in various racing series... ie, one make restricted series such as sayy.... nascar or V8taxis or pro-stock or whatever)..
ie there are many ways to skin the cam cat and get same result (more gross power and higher losses, same net power but less losses)...
and whilst people may be secretive about grinds due to money, the actual basic physics of engines has not changed much.. just the optimisation to reduce the losses on each engine )

anyway, i hope i have given you a bit to think about..... because i honestly don't know for each engine what works best. BUT, think of it in the different parts....
overlap (and the relative position of the overlap to TDC)
exhaust opening time and losses.
intake opening time and "stuffability"
ramps rates (changing "effective duration", ie area under lift curve.. which changes actual duration requirements)

and what you are trying to achieve (more absolute power... more efficiency at given power level, more area under torque curve etc), and what you want to sacrifice



EDIT: and if you want to read more intersting stuff, look up Miller cycle.... which actually sarifices output/capacity, but increase actual efficiency at a given power level by abotu 15%.... and sicne we are talking about SC engines.. you can kind partially apply it to otto cycle as well.. to get a bit of a hybrid cycle..... (which, by having longer longer intake, but short overlap, you migth be doing now anyway )

edit2: persoanlly, for road car engine, i would go for wider torque band and lower losses/better efficiency.... btu of course in class racing, you migth be losing out to those with higher power/capicity... however, if you haev intake restrictors, it changes the game again and then relatively lower output for larger engine, but less losses can be more attractive

[30psi 4agte]

Stu is on the money......... Yet Again

I guess in the end you can do all the theroy in the world and ask for as many opinions as possible but it will only get you so close to your objective. It will come down to alittle trial and error on the end as EVERY engine will react different to certain mods.

>Like i said in my previous post mabe it is worth ordering two exhaust cams as they are interchangeable and trying the longer duration on each side (EX and Inl) to get a good idea of what is better suited to your needs.

I do think differing duration is the way to go !

[kingmick]

Hobby, lmao. 99% of people that play with cam grinds do it for a living not a hobby.
Engine builders and race teams.
Takes money, time and experiance to get it all perfect.

[30psi 4agte]

Hobby, lmao. 99% of people that play with cam grinds do it for a living not a hobby.
Engine builders and race teams.
Takes money, time and experiance to get it all perfect.

lol I beg to differ all the blokes that i know of have played with them for the hell of it and to gain performance none of these bolkes do it for a race team of a living.


I think there are more hobbiests out there rather than race teams.

[kingmick]

What play with 10-20 diff grinds on dynos?. Sorry i meant the ones that do there own and and get them ground to spec in numbers of diffrent types and test them.

[oldcorollas]

Hobby, lmao. 99% of people that play with cam grinds do it for a living not a hobby.
Engine builders and race teams.
Takes money, time and experiance to get it all perfect.

sorry, i meant australian racing is a hobby....
ie "yay, i won a national title with half a field"
state series, national series... it is all just a hobby...

anyway, the cam grinders may not want to tell cos they do it for a living (as i said.. in it for the money).
"race teams" (hobby or not) feel they have something to hide as they will "lose their edge"

Mick, what you are talking about is empricial testing. ie, make 20 different sets of cams and just test.... if a bit more thought is put into it, you should be able to get away with a lot less cams
i agree that it takes time, money and experience (or lots of testing) to make it better , but there is no such thing as "perfect" on an engine, it is all compromise.
there is no argument that some emprical testing is needed on every engine, (in other words, it is duificult to isolate and take account of every difference on every engine) however, just making a bunch of cams and testing is not as good as using a slightly more scientific process

regardless if you are an engine builder, a "racer" or someone doing it for fun, the basic physics of engines are exactly the same.

as you must agree, not all cam grinders who "do it for a living" are good at making cams.
as i tried to say, different profiles make a difference, and there is not one "perfect" cam, there are many ways to achieve the same results.

however, the BASIC reasons and effects of changing certain aspects of the process of opening and closing valves is universal and has been around for a looong time.

so.. how about discussing that, instead of just saying that only people who participate in hobby racing, or those who grind the cams, are the only ones who understand the process, btu they won't tell becuase they are ghey and feel the need to be secretive

so.. of the 20 cam grinds you got made for your 4AG, what differences did you specify?

[kingmick]

everyone can have there view.

[Billzilla]

so.. how about discussing that, instead of just saying that only people who participate in hobby racing, or those who grind the cams, are the only ones who understand the process, btu they won't tell becuase they are ghey and feel the need to be secretive

Mate you know I race cars as well, and I have the most powerful Suzuki G13B in Aus in my class.
We spent over ten years getting it like that, do you think I'm just going to tell everyone how to do that because I'm a nice guy?
No, they have to work for it like I did.

Racing is war, there's first and then there's lost.

[oldcorollas]

everyone can have there view.

sure, but saying you (or others) know and won't tell you is no fun for anyone
it doesn't help one bit.

so what is your view on the effect of altering opening and closing times on overlap and losses and cylinder filling for SC engines? and what about different profiles (in terms of deviations from sinusoidal and the effect on cylinder filling by moving the lift to conicide with different piston velocities etc).

not trying to be antagonistic (as you mentioned in previous thread), but if you CAN help and contribute to discussion of these kind of things... why won't you?

[oldcorollas]

Mate you know I race cars as well, and I have the most powerful Suzuki G13B in Aus in my class.
We spent over ten years getting it like that, do you think I'm just going to tell everyone how to do that because I'm a nice guy?
No, they have to work for it like I did.

Racing is war, there's first and then there's lost.

yup, i totally understand that, but there is no reason for you to not assist others understanding of effects of changing different cams to affect the way an engine operates.. ie the direction people go...
i know you are one of the few that actually went to the effort of getting information out there (and your pages are very well read)
as you said, it took ten years to work out the peculiarites of your particular engine, to get that last 2-5%, but i think it is good if more people understand the method of how to find out for them selves, and what steps they can take to work out which cam to choose next...

as we all know, people here are likely to only try maybe (for arguments sake) 5 or 6 cam combinations max... and doing it for fun, not to win races but still, the basic reasons for altering the asepcts of a cam are always the same..

but as you also know, even with that basic knowledge, it is difficult to know which side of the performance peak you are on, and which direction to go to reach that peak... that is up to each person to find out .. (same for any experimental work where you are trying to optimise certain traits)

so i reckon this is a good place to discuss the basic reasons for changing certain things in certain directions... but as you say, not the place to say XYZ cam from mob B works really well at this 10X lobe angle and whatever else....
but also not the place to say "you don7t know and you won't find out, cos the "professionals" won't tell you...
engine performance understanding has gone from a black art, to a grey art, and the lighter it gets the better

[Billzilla]

Another quick example -
I was talking with a very well-known engine builder a few days ago (Mick knows who he is) as to how my new con-rods were progressing. He said they'd be alone any day now, but he questioned as to why I wanted such long rods.
I figured that if he didn't know, he bloody well should have so I just ummed and ahhhed and vaguely answered.
I still don't know the real root of the question ....

I know why I want long rods, he shouldn't have to ask!

[Billzilla]

yup, i totally understand that, but there is no reason for you to not assist others understanding of effects of changing different cams to affect the way an engine operates.. ie the direction people go...

Oh yeah I'm happy to give a bit of direction here and there.
Sorry for the snip but to keep it short the guys that make a living out of this just generally aren't willing to part with too much information. A slip here or there can open up a whole new path for people, to let them catch up. They just don't want that to happen, so they don't say much.
Mick may well be too tight-lipped, but wee'll have to deal with that.

An example of how far some people will go to get more power from their engines - The Supertaxi mob, as you'd expect, use very good flowbenches to flow the heads to make them work better. Some time ago they reached the limits of the vacuum systems, so some of them now run pressure instead of vacuum and also up to 55" flow, just to really get that last little bit out of the head.
They've been so successful that there really is now nothing much left to gain, and all they do is play with cam timing for the different tracks.
That's just one small story.

[oldcorollas]

but he questioned as to why I wanted such long rods.
I figured that if he didn't know, he bloody well should have so I just ummed and ahhhed and vaguely answered.
I still don't know the real root of the question ....
I know why I want long rods, he shouldn't have to ask!

did he not know? or did he (partially) know but pretending not to so he can try and find out more on the sly? it must be hard to trust anyone in such an industry....

in a secretive industry like race engine building (or turbine blade manufacture ), there must be a certain amount of double bluff going on (i also do it when visiting certain labs and companies and there are certain american profesors who are well known for doing such thigns and then writing paetents on stolen info )

if i am blatantly wrong about the basic physics of things, i hope you racer types would take the time to say what and why (without stupid reasons like "read about it in 10 years" )

to me an engine is just a mechanical air pump, to be optimised by changing different parameters, and understanding those parameters is interesting

i am sure that anyone reading this would appreciate your input into the basic reasons for stuff... like generalised effects of cylinder filling and scavenging with unequal cams..

(i am also surprised that an engie builder would ask such a question, but perhaps he was just curious of you were on the "right track" or not... )

[30psi 4agte]

Hmmmm this thred is starting to become WWF Royale rumble

Sir Bill (NO pun intended I have utmost respect for you and your teachings! It certainly pointed me in the right direction years ago)
i tend to agree with OC Things like running longer rods certainly isnt something new there is heaps of info out there as to why you would do such a thing but acting like it is a big secret when its not isnt helping the guys that are still learning and look to this site and others to gain valuable knowledge.


Share the knowledge....... After all thats why we are all here !

[Billzilla]

did he not know? or did he (partially) know but pretending not to so he can try and find out more on the sly? it must be hard to trust anyone in such an industry....

in a secretive industry like race engine building (or turbine blade manufacture ), there must be a certain amount of double bluff going on (i also do it when visiting certain labs and companies and there are certain american profesors who are well known for doing such thigns and then writing paetents on stolen info )

if i am blatantly wrong about the basic physics of things, i hope you racer types would take the time to say what and why (without stupid reasons like "read about it in 10 years" )

to me an engine is just a mechanical air pump, to be optimised by changing different parameters, and understanding those parameters is interesting

i am sure that anyone reading this would appreciate your input into the basic reasons for stuff... like generalised effects of cylinder filling and scavenging with unequal cams..

(i am also surprised that an engie builder would ask such a question, but perhaps he was just curious of you were on the "right track" or not... )

Yeah the thought of him trying to pick my brains ran across my mind, so I thought either way I'll shut-up. But I did ask him what the rod-ratio of an F1 engine was, and he seemed to know.

Anyways - Yeah, given free reign over what to pick, I'd go for a little more lift and a little less duration on the inlet compared to the exhaust.
No, I haven't actually done all that, I've only had the opportunity to muck around with equal-lift & duration cams both sides but in sims (yeah I know, bloody sim, etc) they seem to favour those numbers.
My reasoning for this would be that the exhaust port flows something like 75% of the inlet on a typical 4AGE, so it needs a bit more duration to get the right flow out of it.
However, they are less sensitive to exhaust cam changes than they are for inlets, so I'm only really guessing sorry.
As mentioned, every engine is different and the only way to be sure is to test every profile you think might be close.
Test one engine and you'll get one set of cams that work nice, try them with another engine and they may well not be.
That's why you can really only give general recommendations in a place like this. Try a set of 272's in the engine, yeah they'll work fine. 288's might be better, they might not. But we know that 272's work pretty good for the vast majority of people.
Forced induction engines are even more 'random', as there are no two inlet systems the same on most engines.


And FWIW I know I'm on the right track as an almost identical engine to my new one has been built by a friend in Holland, and it makes 248hp on a reliable engine dyno.
Reckon I can't wait to see it running?