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turbogrill

High lift cams - disadvantages?

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turbogrill    0

Hi,

 

I am currently trying to pick a cam to my mild race build. Daunting task!

 

Anyhow, what is the practical implications of running a high lift cam? 

 

Let's assume that the flow/fuel delivery/compression is all good.

 

Are these valid concerns:

 

1. Higher lift is more prone to vavle floating. When messing up a downshift (5->2),  engines cams with lifts over >.500" has a higher of pistons hitting the valves?

 

2. High lift cams >~.530 requires longer valves?

 

Any other issues that higher lift cams might cause from a practical/engine builder perspective?

 

Thanks

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JMortensen    235

As NewZed says, swapping the stem seals will get you clearance for .530 lift cam. The practical considerations after seals, springs, and retainers that will allow for .530 lift really boil down to more engine wear. How much wear and what kind of mileage you could expect I can't answer, but maybe someone else can.

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Tony D    143

Everything here has totally missed the boat IMO.

 

Where is the flow data for your head? Where does the head stop flowing more air with more lift?

 

THERE is where you START.

 

Adding lift beyond that point is a calculation of the increased ramp rate to get the valve to peak flow as fast as possible for as long as possible but has relatively limited advantage.

 

 

Basically, if your head capable of even flowing more air past the limits of a 470/480" lift?

 

If not, more lift won't give you anything for the costs and effort to install it.

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clarkspeed    10

I agree. I tried to explain this recently to someone offline after the Hybrid community had recommended cams for him. Unless you are flow bench porting, it is just not there. And when you are flow bench porting, its still only marginal gain for NA street engines.

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turbogrill    0

Everything here has totally missed the boat IMO.

 

Where is the flow data for your head? Where does the head stop flowing more air with more lift?

 

THERE is where you START.

 

Adding lift beyond that point is a calculation of the increased ramp rate to get the valve to peak flow as fast as possible for as long as possible but has relatively limited advantage.

 

 

Basically, if your head capable of even flowing more air past the limits of a 470/480" lift?

 

If not, more lift won't give you anything for the costs and effort to install it.

I am having Lone wolf do the port for me. He shared some flow numbers. I think he can modify the head a little based on my needs.

 

This being my first build I want to keep things a little simple. If high lift adds a lot of complexity then I am fine to compromise on that.

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clarkspeed    10

No, thats not what I meant. Adding more than 500 lift AFTER porting is marginal increase. My point is .500 lift is a lot of lift.

Duration is another matter and I would never run 300 on the street. That is just my opionion and you can get many others. I hate over cammed engines.

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JMortensen    235

Having had a garage ported E31 and .490/280 cam I wouldn't hesitate to run a .500/300 on a similar build. An overcammed engine might be a problem, but so is having an undercammed engine. My friend who built the first engine for my Z was super conservative with his cam picks. He had this grinder who made a very high lift very low duration cam. It might have made 5 or 10 hp over stock, maybe. It was so minimal you could barely tell the difference. He had that .490/280 cam sitting around, had actually gotten it by accident instead of his usual short duration cam. I bought it from him despite his warnings about how much it would suck on the street, and when I put it in I had to have gained 40 hp and the bottom end was as strong as ever. It was a huge increase in power. Brought it back around and let him drive it and he immediately went and ordered a much bigger cam for his L18 race engine. When I later went to triples I felt like I needed more cam again, but instead of putting more work into it I ended up going V8. YMMV, but I managed to get really good results without a flowbench.

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WhitleyTune    0

Everything here has totally missed the boat IMO.

 

Where is the flow data for your head? Where does the head stop flowing more air with more lift?

 

THERE is where you START.

 

Adding lift beyond that point is a calculation of the increased ramp rate to get the valve to peak flow as fast as possible for as long as possible but has relatively limited advantage.

 

 

Basically, if your head capable of even flowing more air past the limits of a 470/480" lift?

 

If not, more lift won't give you anything for the costs and effort to install it.

 

Nope, you've missed the boat. Stopping the valve lift where the flow flat lines is a common misconception of performance engine design and is a good way to get beaten at the track (or on the street)! 

 

Adding valve time-area for a given duration is always a good thing. These ports don't go that turbulent at high lifts. .480/12mm" lift is NOT a lot for these motors. On a stock L28 valve size, 12mm lift is still choked by curtain area. Lift it past this and you start to get some diffused flow into the chamber and get some added pressure recovery. 

 

Personally I don't run anything under .550" on a street motor and my competition profiles all start at .590".

 

Practical implications - More power, less of a drop after peak torque, a bit more thought involved with valvetrain setup, need decent valvesprings. 

 

Lift doesn't hugely impact on valve-to-piston issues on overrev - as long as the valvespring is correctly chosen for the cam. That has more to do with timing, closing the exhaust late (lots of lift at tdc) with not enough valve to piston clearance (So big duration with lots of overlap) 

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WhitleyTune    0

No need to be a jackass Tony. I merely disagreed with you and stated my opinions and tried to help the OP. 

 

"Adding lift beyond that point is a calculation of the increased ramp rate to get the valve to peak flow as fast as possible for as long as possible but has relatively limited advantage." 

 

The fact that you use 'ramp rate' tells me you are in over your head. Are you familiar with valve lift LVAJ diagrams and different ramp designs? And the specifics of the L valvetrain in regards to its limitations on the different curves?

 

The only time I would limit lift off a flow bench test is if the port got very unstable and turbulent. This is a much better indication of how the port will handle high lifts. 

 

I know what you are saying - added lift has diminishing returns - and this is true. But not at 12mm based of flow bench flat-line. That comes around 14-15mm with these motors. Like I said, at ~12mm lift the valve curtain area is still the choke on a 44mm valve. 

 

Good for you.

 

Thanks. Starting a cam company from scratch (including building and designing the CNC cam grinder) is not an easy task, one that I am still working on. I doubt it is ever going to be very profitable, I just want to offer modern CNC ground cams for old motors. Profile design has come a long way in the last 10-15 years and most cam companies are too busy spitting out LS cams to warrant development on older more unique stuff. 

 

Robbie

Edited by WhitleyTune

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Lurcher    10

 Profile design has come a long way in the last 10-15 years and most cam companies are too busy spitting out LS cams to warrant development on older more unique stuff. 

 

That's a large generalization of the cam grinding industry - maybe in the US, but not in Australasia...

 

12593571_1773246099576498_55085242508004

 

And the OP is probably going to stick a pair of Hitachi's on his engine, so this conversation will be a moot point anyway.

Edited by Lurcher

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Tony D    143

I found jargon, especially with engineering stuff gets some peoples eyes glazed.

"Ramp Rate" was something people could understand--you did and that was the point.

 

We are discussing a 'mild race build'.... That's analogous to 'Ramp Rate' agreed?

 

"If you overfeed the fish, the water becomes cloudy."

 

I wasn't being a jackass, just direct. Some say I could be Dutch.

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WhitleyTune    0

That's a large generalization of the cam grinding industry - maybe in the US, but not in Australasia...

 

I live in Australasia and am in the industry. It is definitely not a large generalisation. There is a huge difference between tweaking, stretching and chopping cam profiles (how they have been played with by cam grinders for years) and an engineered mathematically defined valve lift curve that is then worked back through the valvetrain geometry to produce the cam profile. 

 

What cam are you running out of interest? 

 

 

I found jargon, especially with engineering stuff gets some peoples eyes glazed.

"Ramp Rate" was something people could understand--you did and that was the point.

 

We are discussing a 'mild race build'.... That's analogous to 'Ramp Rate' agreed?

 

"If you overfeed the fish, the water becomes cloudy."

 

I wasn't being a jackass, just direct. Some say I could be Dutch.

 

I prefer to educate and discuss these things. Its hard being in an industry where your customer thinks they know what they are talking about because of internet jargon. The amount of times I have to tell someone that a larger lifter does no good unless the cam profile is optimised for it is amazing - all because internet said 'larger lifter gives higher ramp rate!"

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