ACCELR8

Specifically, how will a F11's torque and hp curve differ from a F10's?

F10 - 228/228 .576/.576 112 LSA
F11 - 228/230 .576/.595 112 LSA

Thanks,

Jim

ACCELR8

anyone?

2001CamaroGuy

iTrader: (6)

more exhaust will cut low end torque but can help make more top end.....

SStrokerAce

iTrader: (2)

Well the very little difference in those two cams would probably only be seen on a engine dyno in a cup shop where they can find 1hp changes on a consistant basis.

Generally....

More exhaust duration on a camshaft will allow the motor to run a smaller intake duration for a given RPM range which improves the TQ at the lower part of that RPM range and the larger exhaust duration will help keep the power on after HP peak.

The more important thing with intake and exhaust durations is how they relate to each other when you combine the lobe areas, valve diameters & curtain area, and flow of the heads. Then you can come up with a total E/I ratio and match something up to that. For some reason people don't think this matters in a LS1 so I'm not getting into it.

Bret

Ed Curtis

It does matter... Some people just don't pay close enough attention to the details...



Ed

67Firebird455

iTrader: (27)

I also believe it does matter in an LS1... I just recently put an LS1 hot cam in my 99 TA M6 and compared the two cams, visually before installation and overall power and idle. The dual pattern cams generally give more top end as they bleed off more exhaust gases, as to where a turbo cam has a reverse split duration, which allows more fuel in and less exhaust to bleed off. Lift will only affect overall flow at a specified measurement, the more the merrier isn't always true, especially on a stock-flowing head. I put a .643/.660" lift 246/253º @ .050" on a 108LSA in my 67 bird with a 455, 1050 dominator, victor with ported edelbrocks that flow 313cfm @ .650". In that light of a car, I wasn't as concerned with port velocity as I was flow, as the car would hardly be used below 3500. You get too big of a cam with too much duration, bleed off too much bottom end, run too tall of a gear or tire, and too low of a stall, it'll significantly slow you down. Choosing a cam is all in how you drive the car and the entire picture as far as lift/duration/lsa goes. Just my .02.

SStrokerAce

iTrader: (2)

Ed, you are probably only one of the ones I know of then... ;-)

BTW I like your R journal trick on cam lobes.... Nobody would ever guess that those motors have so much in common.

67Bird, A Old School Poncho is one of those motors that loves that kind of cam. Especially with the setup that you have.

Bret

LS1_PNYTAMR

iTrader: (1)

so ur saying i was wrong for maybe just buying an off the shelf cam? whats wrong with doing that? maybe i misunderstood you, but are u saying its wrong for someone to pick out a futral or comp or tsp or any of our sponsors cams and base it off mods and desired goals? i mean most of the sponsors grind cams for stock heads or aftermarket heads ect.. im pretty sure more ppl then u think understand a lot more then you think or we wouldn't have guys running 10.40's cam only, and stock cubed motor'd 6sp cars running 9's in the 1/4 mile with no power adder. i would like to think most of teh sponsors have taken into account all of the above and are not leaving anything on the table.

SStrokerAce

iTrader: (2)

No I never said you were wrong...... I was making a comment that I knew only a few people would get, don't feel bad if you took it wrong.

Actually we are just scratching the surface of what goes on with a cam, but for the most part people can understand some things in the system but most do not undestand all of them. Even I have my limits but they mostly fall withing the math and physics that have to deal with the 3rd, 4th, and 5th orders of Velocity in valvetrain dynamics.

The fast guys out there are either very smart, have tried lots of ****, have lots of money, or for the most part work with very smart people to make a good combination work. Most times it's a combination of all of them.

Bret

Greg Good

That's really not enough information. What is the seat timing? What is the duration at .200" lobe lift? Ideally, I'd hope the F11 exhaust has shorter seat timing and a little more duration at .200". Then I'd say the F11 is the one I'd pick.

Hypothetically speaking, on a low compression engine, and pump gas LS1's qualify for this, you want to be careful about running too much duration on the exhaust. The early opening kills torque. That's why you need really good exhaust ports on a street engine, so you can run a shorter cam, delay the exhaust valve opening, and make better use of your power stroke. I consider 72% of the intake and better to be good. And I'm talking mid-lift flow too. Mid-lift is just as important on the exhaust as it is on the intake.

SStrokerAce

iTrader: (2)

Even though this is rare on a exhaust valve do to it's lower mass what happens if you can't control the exhaust valve due to the more aggressive lobe?

This situation is odd since there is more valve area with that exhaust lobe due to the excess lift.... which brings with it more duration at .200

Bret

Greg Good

Well, I doubt the exhaust lobe has more acceleration than the intake lobe. If I'm guessing right, they're from the same family of lobes. Since the exhaust valve is lighter than the intake valve, acceleration rates being equal on both lobes, you'll experience valve float on the intake side first.

I most always (on a street engine) use an aggressive (intake) lobe on the exhaust. You need the "area" that a fast opening lobe gives you during blowdown to evacuate the cylinder. I want to delay the exhaust opening as long as I can, but when I open it I want it to open really fast and have as much valve lift as possible at BDC. I want fat mid-lift numbers too. "Blowdown" must be exploited to make good power everywhere and have a nice flat hp curve.

The more torque you can make the easier it is for the engine to pull up from a gear change and e.t. good.

SStrokerAce

iTrader: (2)

Right but this is what I was talking about....

A shorter seat and higher .200 with the same lift is working like a Max Area lobe and those things aren't the most fun to control.... Granted you are probably about have about 20% less mass to control vs. the intake.

Yeah I see your point on the lobe profile.... Wouldn't running a tighter LSA do the same thing for you rather than running the cam with a wider LSA and having it advanced to get the same ICL?

I also think there is something to be said about lengthening the exhaust pulse in some setups too, that rapid opening is nice if you have a perfect header oh say like one from Pro-Fab or a cup shop but most times these guys don't. Let alone the header match up the firing pulses which is almost impossible on a split crank V8.

Bret

Greg Good

Forget about the header for the purposes of this conversation. The cam is the nerve center of it all. It tells the head when to flow. All the header has to do is be the right diameter to keep the velocity up, but not be much of a restriction, and be the right length so harmonics are exploited.

Fast opening has always worked for me on the exhaust. I've never seen a situation where a lazy exhaust lobe made more power than a fast exhaust lobe, although that's what a lot of cam companies will give you on a solid roller unless you request otherwise. Hydraulic rollers are a different story. They commonly use the same lobes on both.

Running a wider LSA, AND advancing the cam (as in your post) is the opposite of tightening the LSA and supposedly leaving the intake lobe centerline where it was. It advances the heck out of the exhaust opening. Not really what you want on a low compression engine, IMHO.

SStrokerAce

iTrader: (2)

I like this idea, like a Comp NC lobe.

To put my example better:

A 110LSA, 108ICL and a 112ECL (110LSA +2)

Then keeping the same ICL

A 108LSA and a 108ICL and a 108ECL (108LSA 0)

The former will fit the bill of "The early opening kills torque" idea.

Since what you are saying fits into the 110LSA, 108ICL and 112ECL theory, add on to that "you want to be careful about running too much duration on the exhaust" how are you supposed to get any overlap? You can't run a narrower LSA because it makes the EVO to early and at the same time keep the same IVC. You can't run too much exhaust duration, the big loser here is overlap then.... Only way left to get more overlap is too keep the IVC and open the intake valve sooner, increasing the advance on the cam and intake duration.... which is more likely to loose you TQ, than the early EVO. It sounds like a never ending downward sprial?

Bret

Greg Good

No. The tighter the LSA, the later the exhaust valve opens (provided the cam is installed "straight up"). That's why a tighter LSA cam is generally better for torque. You gain in two areas that induce more torque, an earlier intake closing, and a later exhaust opening.

The wider the LSA, the earlier the exhaust opens. The more the cam is advanced, the earlier the exhaust opens. Get it?

Now, back to your original question, the difference between 228 and 230 is very small at .050". I'd like to know what the seat timning is and how much lift at BDC both exhaust lobes have.

SStrokerAce

iTrader: (2)

It's late and my orginal post on that was right on that track,

then I mixed one thing up in my head and the whole thing went in the can...... When the EVO number increases it's getting earlier thats why its a BTDC deal.... For some reason that wasn't in my noggin.

So same example as above without me confusing everything afterwards.

I was begining to think there that all the laws of motors were getting thrown out. Yep, that's the laws....

All that overlap and early IVC and late EVO is good until you run into a problem with too much overlap polluting the incoming air/fuel charge in the standard 3500-4000rpm dip area. Then you have to do something about that, either with anti-reversion (backflow) or cam specs.

Bret

Greg Good

That's right. Too much overlap. Specifically too early an intake opening can muck up things during overlap. A lot of guys worry about overscavenging during overlap. I think that is the least of the problem with overlap. Exhaust gases blowing up into the intake port when the intake valve opens is the real bogeyman. I use valve jobs that flow as little as possible as low lift in reverse, and as late an intake opening as practicable.

Having a low residual pressure in the cylinder from a really good exhaust stroke helps too.

SStrokerAce

iTrader: (2)

I understand the cuts you put on a valve and VJ on the intake to prevent this but are we talking about the same things on the exhaust too to prevent revearse flow at low lifts there too?

How about the effect on rod length and therefore dwell realating to this area too? Then again when the overlap happens effects this too.... a advanced cam will cause the overlap area to happen earlier on in the cycle so is that going to be a disadvantage or advantage depending on if you have lots of dwell or a little bit of dwell.

A longer rod would push the exhaust out of the cylinder faster since it gets up near TDC a bunch faster also creating..... "a low residual pressure in the cylinder from a really good exhaust stroke"


Bret

Greg Good

The tendency these days is to make the rod shorter. With the awesome flowing heads we have now the shorter rod gives a stronger "signal" to the intake ports and gets the port velocity up higher. The rod length is just another tool we use to "tune" the intake port cross section to the engine. The shorter rod moves away from TDC quicker and displaces more volume, drawing a little more on the intake port. It makes the port think it's on a larger engine. That lets us get away with a slighly larger cross sectional (and better flowing) port.

I haven't yet worried about backflow on the exhaust port. If the header length is tuned correctly we "should" have a low pressure at the exhaust port during overlap.