More compression or flat tops

[ptuomov]

So is the point that if you hit the velocity limit with flat-tappet lifters, then you're making at least some compromise between lift and duration? My thinking is that if you hit the flat-tappet velocity limit, you're at the corner solution there and then you're probably making at least some compromises relative to durability, duration, lift, etc.

[CamKing]

So is the point that if you hit the velocity limit with flat-tappet lifters, then you're making at least some compromise between lift and duration? My thinking is that if you hit the flat-tappet velocity limit, you're at the corner solution there and then you're probably making at least some compromises relative to durability, duration, lift, etc.

No compromise in duration or lift.
Since you have to accelerate quicker to the max velocity, you will need more spring pressure to control the valve, and that will reduce durability.

[ptuomov]

So is the point that if you hit the velocity limit with flat-tappet lifters, then you're making at least some compromise between lift and duration? My thinking is that if you hit the flat-tappet velocity limit, you're at the corner solution there and then you're probably making at least some compromises relative to durability, duration, lift, etc.

No compromise in duration or lift.
Since you have to accelerate quicker to the max velocity, you will need more spring pressure to control the valve, and that will reduce durability.

I agree that you can choose where to compromise. For an engine with a long expected service life, like a production motorcycle, I'd expect them also to compromise a little bit on duration (making it longer) and peak lift (making it lower) to not exclusively compromise on reliability/durability once they hit the velocity limit.

[CamKing]

I agree that you can choose where to compromise. For an engine with a long expected service life, like a production motorcycle, I'd expect them also to compromise a little bit on duration (making it longer) and peak lift (making it lower) to not exclusively compromise on reliability/durability once they hit the velocity limit.

In a production engine, there should be no compromise. You design the valve lift curve you need, and then design the follower diameter large enough to allow you the velocity you need. I do a lot of OEM cam development, and the designers have an idea of what the valve lift curve needs to be, before they design the rest of the valvetrain, so there's nothing limiting them, that will require compromises. If they think the optimum cam will need a 1" follower, they don't design a .900" follower. If they think they will need a 1.7 rocker, they don't design a 1.6 rocker.

[DCal]

So the p/s boys are getting the compression as high as they can. Every inch possible.

Steve, Pro Stockers are running 14.8 to 15.3 unless they are lying to me. Their domes are .150 or less so they could get more CR if they wanted.

[ptuomov]

I agree that you can choose where to compromise. For an engine with a long expected service life, like a production motorcycle, I'd expect them also to compromise a little bit on duration (making it longer) and peak lift (making it lower) to not exclusively compromise on reliability/durability once they hit the velocity limit.

In a production engine, there should be no compromise. You design the valve lift curve you need, and then design the follower diameter large enough to allow you the velocity you need. I do a lot of OEM cam development, and the designers have an idea of what the valve lift curve needs to be, before they design the rest of the valvetrain, so there's nothing limiting them, that will require compromises. If they think the optimum cam will need a 1" follower, they don't design a .900" follower. If they think they will need a 1.7 rocker, they don't design a 1.6 rocker.

Although I've never done this, my impression is that people designing production engines compromise on everything, but don't want to make big compromises in any individual area.

[CamKing]

Although I've never done this, my impression is that people designing production engines compromise on everything, but don't want to make big compromises in any individual area.

That's probably more common on smaller engines, where they may not have room for fitting the correct valvetrain. The OEM engine I'm making cams for are large truck and industrial engines, so that's not an issue. The engines are designed to make a given amount of power, at a given RPM, using a given amount of fuel, and last a given amount of miles. If it meets all those requirements, there's no compromise. Of course, I could design a more aggressive cam, that would make more power, and reduce the life of the engine, but that's not what the engine is being designed for.

[Steve.k]

IMG_3632.PNG

So the p/s boys are getting the compression as high as they can. Every inch possible.

Steve, Pro Stockers are running 14.8 to 15.3 unless they are lying to me. Their domes are .150 or less so they could get more CR if they wanted.

I would imagine prostock on north side of 1" lift. They have huge valve releif so they make it up with small dome. I know the ps fords have basically no combustion chamber so that's another part of reason.Thanks Dcal.Prostock head looks deep in chamber that would help to.

[CamKing]

I would imagine prostock on north side of 1" lift. They have huge valve relief so they make it up with small dome. I

They don't have as much valve relief as you would think.
Due to their relatively short duration, and wide LSA, their lift at TDC is around .280" on the Intake and .320" on the exhaust

[Steve.k]

Yes i can mill these heads to 55cc easily without a drastic flow change. They are 64 now. So yes thats the answers im looking for. Even with a deep relief and mid 13 compression we maybe further ahead than custom dome to get is up in 14+ area.

Personally, as long as the dome does not hinder flame propagation or cross-flow within the chamber, the dome size shouldn't be an issue.
The problem is that most big domes, do create some kind of hindrance.

Walter thanks again. Its not a huge dome so we will live with it. Just thought maybe not much difference in flat top hp and save a little messing around. Later down road you have a piston that fits the head without worrying about this custom setup.

[ClassAct]

I agree that you can choose where to compromise. For an engine with a long expected service life, like a production motorcycle, I'd expect them also to compromise a little bit on duration (making it longer) and peak lift (making it lower) to not exclusively compromise on reliability/durability once they hit the velocity limit.

In a production engine, there should be no compromise. You design the valve lift curve you need, and then design the follower diameter large enough to allow you the velocity you need. I do a lot of OEM cam development, and the designers have an idea of what the valve lift curve needs to be, before they design the rest of the valvetrain, so there's nothing limiting them, that will require compromises. If they think the optimum cam will need a 1" follower, they don't design a .900" follower. If they think they will need a 1.7 rocker, they don't design a 1.6 rocker.

Some good stuff in here Mike. What happens when you just run out of room and let's say you just can't get the follower diameter you need? What happens then?

[rustbucket79]

I understand your apprehension chopping on such nice looking slugs.

[ptuomov]

Some good stuff in here Mike. What happens when you just run out of room and let's say you just can't get the follower diameter you need? What happens then?

I think (but don’t know) that they compromise by having longer than desired duration, lower than desired peak lift, and a little worse than desired reliability due to higher accelerations and spring loads. As long as the compromised system is within the design requirements on all dimensions, they’ll call it a day and move on to the next project.

[CamKing]

Some good stuff in here Mike. What happens when you just run out of room and let's say you just can't get the follower diameter you need? What happens then?

If it's a rocker arm/finger follower type valvetrain, you just increase the ratio, and that reduces the required follower diameter.

[Steve.k]

So Mike more than likely make as much or more with flat top, less compression and matched cam for compression!