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Gains with lift beyond the point of max airflow?

General engine tech -- Drag Racing to Circle Track

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travis
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Gains with lift beyond the point of max airflow?

Post by travis » Thu Jan 09, 2020 12:04 am

This is probably a dumb question, but I’m going to ask anyway :roll:

If you have a set of heads that, on a flow bench, peak at say .400” valve lift, that only picks up like 1 cfm at each .050” lift increment beyond .400” but never backs up...is there any benefit to adding more lift without additional duration? Like say using a cam with .450” lift with 1.6 rockers, and only changing rockers to a 1.7 ratio? I get that there *could* be a minute increase in power due to the engine seeing a touch more duration at the valve...

I’ve been playing with Engine Analyzer 3.4, using the flow numbers from a set of ported 351w smogger heads with small stock valves, and don’t know if I agree with the numbers it keeps spitting out.

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Re: Gains with lift beyond the point of max airflow?

Post by KnightEngines » Thu Jan 09, 2020 1:38 am

In short, yes.
More lift, up to the reliable limit of the chosen components, is always a good thing.

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Re: Gains with lift beyond the point of max airflow?

Post by Biteme » Thu Jan 09, 2020 4:10 am

Yes.
You’re increasing the time the valve is open at the lifts where the head flows best.
And if you do it with a rocker ratio change you’re not increasing the seat duration, so you’re capturing more air and squeezing it harder, if that makes sense, provided the valve train can handle it. If you get into valve bounce you’ll lose any gain you picked up.

Personally, I’m a fan of high rocker ratios. I’ve had nothing but positive results from them.

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Thu Jan 09, 2020 5:04 am

Alot of variables I think, why does the Port stall at that lift??
I agree rocker ratio can help but the couple of degrees difference at the lift mentioned probably won't notice any difference in the street car applications we use, I used a aggressive SFT last year and changed rockers on intake to 1.6 ratio and the 420 lb/in spring only" just" controlled the 1.94" valve at.0.500" lift.
The spec engine / lift limited guys would have there ducks lined up correctly so they can make good power.
I have had engine pro software since 2011and the latest pipemax as well and both are excellent but I doubt there is enough data in the systems to give optimal results in the mild street /strip applications we are used to.
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Re: Gains with lift beyond the point of max airflow?

Post by travis » Thu Jan 09, 2020 5:42 am

The ports are tiny, and the valves are small...these are the worst of the worst LOL

Interestingly enough, I expected there to be some flow increase from the stock single angle 45* valve job to the 3 angle valve job...and there was none except for it picked up about 7 cfm at .300" lift...everywhere else it was pretty much identical.

Problem is that this particular casting is thin in all the wrong places...places that needed cut more I just couldn't.

They are better than stock by 25-30 cfm on both the intake and exhaust, so there is that I guess.

These hit 174 cfm @.400"...peaked at 177 cfm at .550" on the intake side. :lol:

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Thu Jan 09, 2020 6:09 am

There are some smart guys on this forum that can make 600 hp with a cylinder head that flows 250cfm if everything else lines up correctly.
Those heads might work ok on a small bore application 289 ci as a example.
Is this a project you are working on?
Or more just curiosity :D
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Re: Gains with lift beyond the point of max airflow?

Post by travis » Thu Jan 09, 2020 6:29 am

More of a curiosity/learning thing, to see what I could get out of them. These have been ball breakers...way too much work for very minimal gains.

They will get used on something...I just haven’t decided on what yet

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Re: Gains with lift beyond the point of max airflow?

Post by ClassAct » Thu Jan 09, 2020 9:41 am

travis wrote:
Thu Jan 09, 2020 6:29 am
More of a curiosity/learning thing, to see what I could get out of them. These have been ball breakers...way too much work for very minimal gains.

They will get used on something...I just haven’t decided on what yet


Are you just testing the port at one pressure? Are you doing other than the standard test, meaning are you just standing there and flowing the ports in one direction?

You can gain power and not gain much flow. I've actually lost flow on the bench and made more power. Way more than once.


Use the bench to test the port any way you can. You might find that your minimal gains in flow will net some pretty decent power increases. There is more to flow testing then just doing the standard 28 inches.

If the port stalls at higher lifts, reduce the pressure drop until it quits stalling and see how low you have to go.

Take the valve out and stick it upside down in the guide and test the port. See what you get.

You'll never know unless you test. And you may find that some or most of what you read about what a correct valve job/port looks like is wrong.

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Re: Gains with lift beyond the point of max airflow?

Post by dannobee » Thu Jan 09, 2020 10:51 am

The simple answer is yes. As others have stated, the time that the valve is flowing more air will help the overall flow volume.

How much work have you done to the backside of the valves? If you're limited on the port and bowl, get a bunch of junk valves and grind various back cut angles and see if the flow comes up in the low and mid lift range.

Like Class Act said, take the valve out and stick it in upside down then test. That's the most the port is gonna flow. And that ends up being your "mark" when you put the valve back in.

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Re: Gains with lift beyond the point of max airflow?

Post by n2omike » Thu Jan 09, 2020 11:14 am

steve cowan wrote:
Thu Jan 09, 2020 6:09 am
There are some smart guys on this forum that can make 600 hp with a cylinder head that flows 250cfm if everything else lines up correctly.
Those heads might work ok on a small bore application 289 ci as a example.
Is this a project you are working on?
Or more just curiosity :D
A Ford 289 is not a 'small bore' engine.
It has a 4" bore and a 2-7/8" stroke.
To make a 302, they stroked it 1/8" and shortened the rods by 1/16" to compensate and use the same pistons.

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Re: Gains with lift beyond the point of max airflow?

Post by CamKing » Thu Jan 09, 2020 11:19 am

Here's an easy way to look at it. Say you have a head that flows 240cfm at .400" valve Lift, and at .500" lift, it's still flowing about 240cfm.
Now start with a cam that's got a seat duration of 288 degrees, and a max valve lift of .400".With that cam, you are only seeing the 240cfm for about 1 degree.
Now make a cam with the same seat duration, and .450" valve lift. Now that cam will reach the 240 flow 18.5 degrees sooner, and stay above it for 37 degrees.
Now make a cam with the same seat duration, and .500" valve lift. Now that cam will reach the 240 flow 39 degrees sooner, and stay above it for 78 degrees.

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Re: Gains with lift beyond the point of max airflow?

Post by Tom Walker » Thu Jan 09, 2020 2:23 pm

Very informative way to explain the situation Camking. Appreciate that.

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Re: Gains with lift beyond the point of max airflow?

Post by steve cowan » Thu Jan 09, 2020 4:01 pm

n2omike wrote:
Thu Jan 09, 2020 11:14 am
steve cowan wrote:
Thu Jan 09, 2020 6:09 am
There are some smart guys on this forum that can make 600 hp with a cylinder head that flows 250cfm if everything else lines up correctly.
Those heads might work ok on a small bore application 289 ci as a example.
Is this a project you are working on?
Or more just curiosity :D
A Ford 289 is not a 'small bore' engine.
It has a 4" bore and a 2-7/8" stroke.
To make a 302, they stroked it 1/8" and shortened the rods by 1/16" to compensate and use the same pistons.
thanks for clarifying,should of said small cubic inch engine like a 289.
how much can you really do with a thin OEM casting really,we must still look at cfm demand at rpm.
for a low rpm tow vehicle can try and make some torque maybe.
i have had some small/fast ports on my bench that flow less with the valve out,so i think the so called port potential could be misleading and send you after the cfm rabbit hole.
interesting information from camking but my question is it possible to have reversion issues at IVC??
i think port size can be limiting factor no matter how much cam is thrown at it.i think the valve is required to help turn the air into the chamber even on a flowbench.
when you test at higher depressions than 28'' things change and if it converts back to 28'' you are going ok.
no argument here just my opinion and happy to admit i am wrong (maybe) :D
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Re: Gains with lift beyond the point of max airflow?

Post by CGT » Thu Jan 09, 2020 4:41 pm

steve cowan wrote:
Thu Jan 09, 2020 4:01 pm
interesting information from camking but my question is it possible to have reversion issues at IVC??
Absolutely..the piston is going the wrong direction. Increased rpm, displacement, or anti-reversion methods can allow a later one(ivc) before that point occurs...valve size, dc, seat angle etc are also factors.
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Re: Gains with lift beyond the point of max airflow?

Post by englertracing » Thu Jan 09, 2020 5:32 pm

What situation with the cam are we talking about here as there is two possibilities.
well three with rockers.
but the two for the cams,

Say we have a 250* @ 0.050, 0.500" lift cam, and we have the same profile but the nose has been ground flat which is something you might find for a lift limited class so 0.250" @ 0.050, 0.450" lift cam, I believe this is referred to as a "dwell nose lobe"
If the head doesn't pickup flow at any pressure drop over 0.400" then there may not be a large difference in power.

Now the other scenario
Say we have two cams 250* @ 0.050, one is 0.500 lift, and the other is 0.450" lift, and they have the same dwell or rather they have traditional noses, that means that the 0.450" lift cam has a slower rate of valve lift. Now remember The intake valve is chasing the piston down the hole, and in general does not get to max lift by the the time the piston is drawing its hardest (rod 90 from crank throw). In this case the faster action of the 0.0500" lift cam is beneficial, I believe the later you open the intake valve (for more mild engines) the more drastic the effect of the faster lift cam will be as they have less of a head start and will be even later to the party.

Increasing RR is most similar to scenario 2.

A question I have,
Ive heard people say if you put too much lift in a stockish engine it will be a pig and have poor throttle response.
I have always though if you run an ultra short duration high lift camshaft that it will help basically everywhere, vs an ultra short duration low lift cam.0
say 215/218 0.600, vs 215/218 0.480 using scenario 2 from above

Anyone have any insight or experience with the low rpm manners of two cams like these in a mild engine for a ranchero, bronco, el camino blazer, or whatever you like that you want to drive well.

does opening the valve an "extra" 0.100 really screw up off idle?

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