Cam timing with boost
 

Do any of you advance or retard cam timing based on n/a or boost? The cam I am using is a mild sig erson solid roller in a 535 with 360 cfm e-heads and D1SC Procharger.

Steve

Now this is a good topic. Very complex!
Managing the pressure profiles of various parts of the cycle on a boosted engine , more specifically turbo engine is a big deal imo. Interested to see what the calculator jockeys have to say about the subject.

Not nearly as simple as advancing or retarding a given Cam . Ivo depends on pressure in the manifold versus pressure in the cylinder left over from the exhaust cycle . Ivc depends on how close your cylinder pressure is to your Intake pressure.
Evo is dependent on how much residual pressure there will be in the cylinder when the Pistons coming up on the exhaust stroke after blowdown occurs ( pumping Loss). Evc will depend on the pressure in the combustion volume during overlap versus Inlet pressure versus exhaust back-pressure on the hot side of the turbo.
See complex.

There are four events to a camshaft. Not all of them will want to be Advanced or retarded I can almost guarantee it. When you advance or retard a cam you are moving all 4 the same way at the same time. Wish my intake lobes and exhaust lobes were divorced on the camshaft !!!

Isn't advancing or restarting the cam just moving the power band around?



GTO George

No. Often the intake and exhaust events require the opposite action to move the Power Band up or down. Like I said there are 4 events But just like with everything there's always one event that is Alpha in the system so by advancing or retarding the cam you can still get the result of moving the powerband. But that don't mean the events are right !

Would cam timing affect boost any?


GTO George

Blower cams, IMHO, are TOTALLY different than n/a cams. N/A needs overlap to work at higher RPM and make bigger power - boosted motors just need a tiny bit to clear the chamber. Too much and you'll be blowing fuel out the exhaust. Blower cams can make killer power with "small" intake lobes, but need bigger exhaust lobes. I've had luck with some turbo designs by having the EVO happen earlier than you may expect, it seems to help the turbo spool more quickly.

I've only designed a dozen or so blower cams, so lots to learn still. But here is an example of "advance/retard" to highlight how different it can be. A friend built a 408" LS motor. He was using stock Chevy truck L92 heads (no porting at all, no fancy valve job, just betting springs/retainers/locks), and a home made turbo with an 88mm turbo. We used a hydraulic roller, .050" specs were 242/285, and it was ground on a 116 LSA. The cam was installed on a 104 ICL - so technically it was "advanced" 12 degrees.

But I didn't design the cam, then try to figure out what the +/- should be. Rather figured out what the open & close events needed to be. the LSA & ICL were just by-products.

Oh, with a VERY loose converter, on a DynoJet chassis dyno, that cam/motor put over 1100 to the wheels.

Good Post Lee. Check out this camshaft. It was done in 1998 for the Keen's 347 engine.
Worked very well with the Vortech Supercharger stuff. Matches a bunch of your comments.

Intake Centerline 114.3 Exhaust Centerline 116.5

271/312 at .050" lift checking points

Intake open 21.5 Intake closed 70.1 (21.5 + 70.1 + 180 = 271.6)

Exhaust Open 92.5 Exhaust Closed 39.5 (92.5 + 39.5 + 180 = 312)

Cam Lift .455 Intake .457 Exhaust
Valve Lift .728 Intake .731 Exhaust

Duration at .200 = 192.5 Intake 221.9 Exhaust.

You do any camshafts of a similar design?

Tom V.

:)


GTO George

Tom, yes, I do see some similarities! That cam is like the big brother to some of my cams. Probably some shared "DNA" somewhere in the design philosophies!

internet searching,

When you advance and retard the icl you are altering the dynamic compression ratio also. Too much advance can create too much cylinder pressure which will create detonation issues unless tuned around or a higher octane fuel is ran.

Retarding it does the opposite which will lose power and lower the dynamic compression.

Instead of just crutching a centrifugal like you are saying with advance you would use all of the cams specifications like duration and lsa to create the power band you want and not just relying on ICL advance.

Same with a roots supercharger, use the other cam specifications to create the power band you want.

The other thing you're missing is the intake manifold and cylinder heads. They will also play a big part and most of the time even bigger part in the RPM range that peak torque and horsepower are made in.

A set of stock cylinder heads and your intake manifold that is apart of that blower no matter what the cam timing is due to the runner length, plenum volume and runner design just won't make anymore peak power past 6200-6300 as Pred Z said.

That is why people will change out from the stock style type intake manifolds on say a nitrous car or a N/A H/C/I car to a single plane so that they can rev the motor higher while still staying in the peak power range of the motor. This is achieved by the shorter runners in the single plane and more plenum volume.

Your intake has long runners and less plenum volume therefore making it limited in the amount of rpm and peak power it can make along with making a lot of usable low-mid range torque.

GTO George

George sincerely not trying to pick on you or or your thoughts if that's what is in the text above. But most everything that was in that post is complete garbage. Magazine article type myths. Don't drink the Kool-Aid.

Not going to comment on everything as to the complexity of the explanation but I will say that in most cases when somebody goes from a dual-plane manifold to a single plane manifold their biggest gain is because they have effectively doubled the size of the carburetor that the motor now recognizes. The motor now operates at a higher pressure/ far less pressure drop in the intake manifold. It's not a runner length issue, its not a plenum volume issue. Just a pressure issue.

Hell im not trying to drink anything.........just trying to learn.
Again (just trying to learn)...........advancing or retarding the camshaft (2,4 degrees or whatever) does that affect Boost in a blower car.


GTO George

I get it, and my comment was not directed at you personally.

And to answer your question.........yes ,but it's circumstantial. Depends on the timing events of the camshaft and the resulting pressures( on each side of the valve) before and after those events, all 4 of them.

George pressure is resistance to flow. Now are we getting our boost pressure because of head/manifold/cam timing restricting flow between the blower and the cylinder or are we actually achieving the same cylinder pressure at (swept volume) as our boost pressure. Same cylinder pressure at swept volume as boost pressure is all you could ever hope for. !

George I have tried advancing my cam to as far as I could from the cam card recommended 110 . Went as far as 106, and what I learned from that is , Yes I got a couple of more cranking psi when advancing it but what really stood out was it made the turbo spool sooner and was a lot more valiant down in the rpm range . Wound up fracturing all the rod journals on the crank. The turbo went from being all in spooled @ 5000 to being all in @ 4200 when advanced. Bearings looked like the first day I put them in so it wasn't detonating either. After that I read on Yellow bullet that spooling and making power too low in a engines rpm is not good. Kind of like putting a ten speed bike in 10 gear and having the power in your legs to spin the tires from a standing stop, It would be real bad on your ankle's. lol Im no expert, but that's what I have experienced with advancing a cam..

subscribed.

John, as I was degreeing in the cam I was thinking about all the events and an N/A IVO would want to be open earlier than a boosted motor because a boosted motor has forced induction. On the other hand an N/A motor may need the EVO sooner to help blowdown and evacuate the exhaust gasses BUT could a boosted motor benefit from a little later EVO to take advantage of the high cylinder pressure at that point and maybe produce a little more HP. You are right about the massive tug-o-war going on in there. I was wondering about the specific cam I will be using. Right now I degreed it as specified on the card and even called the manufacturer and he said to do it to the cam card. I'm not trying to break records BUT if I can take full advantage of this cam then that is what I want and doing it now is what I will do because once it is in the car it will not come back apart.

That camshaft was actually smaller vs the previous camshaft installed (The camshaft above has less intake duration, more exhaust duration, less overlap.
The Keens were turning their 347 engine 9000 rpm in 1998 race season.
It was not a problem making the bower they needed with the supercharger, it was getting rid of the exhaust and having a clean fresh charge for the next combustion event.

The engine also had to have a large stepped header installed to remove the exhaust and this was even with the Motorsports Race head used on the engine. The whole system had to work.

So yes the DNA is similar on what works. I worked on that camshaft design with Don Hubbard for the Keen Brothers program. Don Hubbard wrote The Book on Camshafts.
"There's also Don Hubbard's Camshaft Reference Handbook. Regards, Chase Knight."

Anyone actually know who Chase Knight was or what he did.

Tom Vaught

How in the hell are you supposed to figure this out!!!! Does all this take into account velocities at different RPM points? I guess you would use probes to gather the info needed? Vaught and Wilkie I am not.

You can't there is no math for it , that's kind of the point. Well I take some of that back there is math for it but it's so circumstantial on so many different things dynamically that it's almost impossible to come up with calculations.
You have to try stuff notice Trends and follow the data path. The problem is is you can't get fixated on one part of the system. It doesn't work because that part of the system is dependent on another part of the system and so on.
One of the biggest things that I see in this thread is people want to refer to a boosted motor as such a boosted motor. Shouldn't do that it's a turbo motor or a blower motor , 2very different approaches as well as requirements.

A blower motors Ivo realistically should be able to be open earlier than NA because it has more pressure in the intake manifold vs NA.

Now on a turbo motor could be just the opposite. Because of the back pressure on the hot side of the turbo connecting to the combustion chamber by way of overlap. Can't open the intake valve until the pressure in the cylinder is lower than the inlet pressure!
On a blower motor the back pressure on the exhaust system connected to the combustion chamber through overlap is at atmospheric pressure.!!!!!!!

OK, so I am learning something here and it does make sense, can't thank you enough. I will keep this cam 4* advanced.

Ivo is only 1 event. Just sayin.
Usually the two Alphas are ivc and evo.
Whats the cam like ? Blower ?

If you want to spin yourself out degree the cam and find out where .001 of valve lift is on ivo ivc evo and evc. Then look at where the Piston is in the bore at those numbers. Bet you will think you screwed up, but you didnt. Lol

Marcella is correct on this one.

The Math just gives your general concepts. You have to do a SYSTEMS approach on the specific engine and typically every system is different. So you look for what the engine is trying to tell you, not some math equation.

A boosted Engine just means that it has a pressure ratio higher than 1.0

There is a world of differences between how a belt driven supercharger and a Turbocharged engine operate and how fast they can make torque and horsepower.

But a guy who understands how the engine works can move between one system and the other because the physics does not change, the math changes but not the physics.

Just saying. Corky Bell wrote books on both Supercharging and on Turbocharging and they are very good because he understands the physics and can explain it very well in his books.

Tom V.

Then after you do this you can get fixated on trying to get the same or more area under the curve and trimming up those 4 events. Become obsessed with valvetrain component weight so you can maintain control with more valve acceleration.

Or just wish you had a 4-valve motor after calculating its curtain area versus time/ crank degrees vs A2 valve motor. 4 valve motor is a turbo best friend because of this. !

While not a blower cam this graph shows a cam install by the card, 6 degrees advanced, and 6 degrees retarded and the piston position. I could not find the graph that showed the valve relief position as well.

Stan

@.050 238- 246 LSA 112 ILC 108
io 11
ic 47
ec 27
eo70

Blower is a D1SC procharger which this motor will outgrow.

What really gets me is how fast a piston moves just by spinning it by hand verses 7500 rpms and more, then the air column has to stop at the intake valve then accelerate into the bore. I know there is an inertia effect going on but the fact that these defining moments are there, are mind boggling.

Brings me to another question, do heads need to be flowed to to come up with the best cam design. I have very close approximate numbers on my heads but never actually flowed. The car in question is in my signature and I think it should run mid to low 9's. current cam is 264-270 @ .050 740 lift on 110 lsa. 11.9 comp. Tiger heads was said to flow 440 cfm and I don't know at what lift but probably 850-900 lift. It is still street driven with occasional trips to the track.

John,
Just to go off on a tangent a little here. The top lines in the attached graph shows the shows the same valve lift curves as my last graph. The second line is the vertical valve drop for a head that has a 14 degree valve incline angle while the third line is the vertical valve drop for a head that has a 24 degree valve incline angle. How much if at all does the actual valve drop come into play?

Stan

Interesting old thread on Speed Talk, with UD Harold.

Cam and Airflow

:)

Vertical valve drop?? Explain

John,
I do not know what the technical term is or if there is one.

What I mean by vertical drop is how far down the bore the valve moves verses the amount valve is off of its seat.

With a zero degree valve incline angle. vertical drop = amount valve is off of its seat.

With a 90 degree valve incline angle vertical drop will always be zero.

Stan

That was a good read.!