Head flow,vs. cam lift?......

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Abodybomber

Abodybomber

Breaking street machines , since 1983.....:)
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A lot of Super Stock guys,used to/still do run higher lift cams,on stock blueprinted heads.Obviously, the ramps are quicker,more aggressive.Obviously,a shorter camshaft life. With today's bolt on,(230,240,250,cfm ) heads, do we really need such aggressive cam profiles.? This in theory.... The idea,the airflow goes up,make the cams mellower,and easier to deal with maintence and longhood.
 
The faster the valve opens, the more horsepower can get into the cylinder.
If you picture the valve opening as viewed on a set of axis, the faster the valve opens, the more "area" there is. That area equates to more go.
 
Have you seen a set of Super Stock heads these days? They are FAR from "stock". A friend that previously held many NHRA national records in Stock Eliminator is now racing Super Stock. The sets of SS heads have huge amounts of welding and porting(including port inserts) and flow approxinmately 50% more than factory as cast. Stock Eliminator heads were factory castings although it is now very common to have them only look factory cast... but that class is lift limited. So cam lobe max velocity is key to making big power.
Cams should not wear out. The only wear they get "should" be at start up. In terms of an engine that's in a musclecar from the 60s, 70s, or even 80s - longevity is now measured in tens of thousands fo miles if at all, rather than a hundred thousand miles. So expectations for these engines has also changed.
As far as the physics of a faster cam lobe - yes - controlled fastest will always best both in terms of time in crankshaft degrees that the valve is open, and in terms of the wave tuning of both the opening and closing operations individually. That's why a modern cam lobe is not only fast (typically as fast as possible given the original design and the quality of the block machining) but also has a different opening ramp vs closing ramp.
You can bet your behind that the successful SE, SS, and FAST guys make use of this technology.
 
Everything else being equal, a faster ramp profile will make more average horsepower, but not necessarily more peak horsepower.

In lift restricted classes of circle track racing they have what is known as "cheater" cams where the top of the lobe is virtually flat for a specified number of degrees. in the past this has proven to almost negate the restriction entirely.

This suggests that with high flowing cylinder heads, the ramp rate/intensity at lower lifts (0.050"-.350") is far more indicative of a cam's performance than it's peak lift.
 
this is written so cam novices have a better understanding. It is basic in the way it is written. Those of us that really understand and race cars know it is more in depth than this. Lets not get to crazy and split hairs and get super technical.

Bomber, I see kind of where your going with this from a different angle so to speak. Let me state this view point from another angle, more of a street engine stance rather than a race engine.
After reading what you wrote, and without contradicting the answers above which are correct.

It's not that the cam will wear out but the valve springs that take a beating on high lift and/or reving engines. So long as the cam is well oil feed, it'll live just fine.
A street engine that will live many many miles under all types of conditions without being serviced a lot if at all besides routine things would have a milder cam. While an increased ramp rate can be used in a street engine for many thousands of miles, the steeper the ramp, the more abuse the spring takes. The same goes with lift.

The whole valve train comes under increased scrutiny for being dead balls on accurate. Even if all is perfect, the life of the valve train is a shorter one from a race car vs the street car. The lower lift and duration ease up on spring requirements and a not so perfect valve train can survive.

Lifting the valve slower as like on the typical Chevy lobe with increase duration to meet the intended rpm operating range requires a certain valve spring pressure which is woefully weak for a fast ramp that can be used by the MoPar engines.

Power can still be certainly increased though not as much as a fast ramp cam. This is why most cam companies offer performance cams with the Chevy lobe. Longevity!

The bolt on power available from the aftermarket heads is a beautiful thing. Should you follow the same method of attack the racers in the above mentioned classes do, you should be able to find some mad power increases. But I do not think you'll like the feel of operation from the installed cam.
They tend to be a narrow rpm cam. Often nasty in idle and really crappy to drive on the street.
 
this is written so cam novices have a better understanding. It is basic in the way it is written. Those of us that really understand and race cars know it is more in depth than this. Lets not get to crazy and split hairs and get super technical.

The more air and fuel you can get into a cylinder, the more power can be made.
Ok, that was the no brainer statement.

Being that certain race classes are lift limited, the cylinder head is designed to make a max effort to increase the low lifting valve. This is mostly in the cut of the valve and seat. The cams design is to hang the valve there as long as possible to allow for a max filling of the cylinder. Power is limited. As next to the ported head.

Since the street guys are not limited to these restrictions to hamper our efforts in the search for HP, taking advantage of the abilty to run the higher lift cam shows a direct impact on HP vs a lower lift cam. Lobe not withstanding.

Quicker the rise of the valve the more air and fuel get into the cylinder. More lift more HP.
Longer duration more air and fuel as well as a higher operating rpm band.
The above leaves out ramp rate (as far as basics of cams go)
The quicker you can get it in, the more power it can make.

Is this all ready needed?

Not really but there is a noticable amount of power to be made with a quicker ramp. The cam is more intense.

Does one need it?

No not really. But you'll probably really like it if you do get a quicker rising ramp cam.

What if opt for a slower lifting rate ramp?

You'll end up with a mellowed acting engine vs the quick ramp.

Is the quick ramp worth installing?

This depends on the person, what the engine is being built for and the target of the purpose. You can still make 400, 500 HP. It will probably just take more cam to do so.

Will I have to constantly maintain it and change out springs?

This is a mileage and abuse factor. The bigger the cam, the more you'll need to keep and eye on it. You'll notice that it will be slowing down in the 1/4 mile or that one guy you used to just beat in the street is now becoming a threat or just simy beating you.

If it is a mechanical cam, the rockers will become loud. This is adjustment time. Inspect the cam while your there. Mechanical rockers should not need to be adjusted frequently. Have no worries running mechanical cams and gear.
 
Yup, well said rumble.

I guess any question that begins with "Do we really need...?" is one where the answer for a street driven engine is usually going to be no and the answer for a competitive race engine is going to be "yes, especially if the other guys have it"

Race cars and their ever-evolving ever-improving nature pave the way for street/strip cars though, Look how many guys run W2 heads in their street mill now!
 
Thanks Frosty. I tried to break it down in a simple manor and keep it on a basic level. Getting into it deep would loose a lot of people. I know there's a lot of new to the car world guys and for many, cams are a Voo-Doo black magic.

Sometimes, the K.I.S.S. method is best.

I learned about cams from reading, then experimenting. I was part of a MoPar club that had good relations with a dealer. They sold us parts for 10% over cost and we run there name on a banner at a club meet or on the side of the car at the track.

I would run down to them and just start ordering cams. If ya feel rich one day, LOL, purchase all the cams at 284 duration for your engine and see how they operate so differently. The well know 284/.484 has a few versions.

YES! Perfect example! The W2 head was and still is one really good head that cam make your engine one mean mutha. Back when this head was first introduced, the serious race guys (or perhaps the few crazy guys, as viewed from the street guy stance... LOL!)
Would run these heads.

Most cams offered in the 70's were not so aggressive. As next to what is on the shelf today.
 
I guess using the analogy of Super Stock was what led me to think of this as a more indepth technical thing.
If the idea is to keep it simple and very generalized - if the cam used gets the heads into their power range, and assuming the heads are properly sized for the application and expected output - then it is less critical that the fatter low and mid-level lift ranges are used.
However - the faster rate of lift cams can smooth out the power curves which are exactly what street engines typically want and need to allow for compromises in gearing, convertor, and vacuum assisted options like brakes. I like using catalog grinds, and some favorites of mine were designed in the early 80s. They take less valve spring (which "frees up" power at the crank) and I can make the same peak power. But as those get larger - the "oldschool" nature becomes more evident and you start to have to think about gearing up, etc. and live with low idle vacuum. Where a modern design can make the same or more peak power by opening the valve faster and keeping it open longer while maintaining vacuum levels at idle and bringing in the torque earlier.
Look at it this way - if the same 4" ID pipe is used with a flap on the end that seals tight - you can open the flap 60% and keep it open for 10 seconds - or you can open it 30% and keep it open for 20 seconds. Either way assuming the pressure in the pipe is the same the total volume allowed to pass the flap will be equal.
 
lol if I know bomber and the guys he hangs with it will need all it can get! streetable is a short drive and a couple pulls...
 
current cylinder head rule for SS....

CYLINDER HEADS (April 15, 2013)
Must be correct casting number for year and horsepower claimed,
per NHRA Technical Bulletins or NHRA-accepted. Cylinder-head
casting must also be on NHRA runner volume list as published on
NHRARacer.com. Porting, polishing, welding, epoxying, and acid-
porting permitted. Grinding and polishing in combustion chamber
permitted. Welding and/or applying epoxy in combustion chamber
prohibited. Spark-plug hole must maintain the stock location, size,
and angle as machined by the OEM; spark-plug adapters
prohibited. Valve-guide centerlines must maintain the stock lateral
and front-to-back location as machined by the OEM. Valves must
maintain stock angle; valve-stem angle must remain stock, +/- 1
degree. Cylinder head must be able to hold combustion chamber,
intake and exhaust runner volumes per NHRA Specifications. Any
aftermarket steel valve permitted; must maintain stock head and
stem size; titanium valves prohibited. (OEM sodium-filled valve may
be replaced with titanium, provided weight is equal to or greater
than original.) Valve diameter permitted to be +.005-inch or -.015-
inch from published NHRA Technical Bulletins. External
modifications prohibited, intake side of head may not be cut into
any part of valve-cover bolt holes (except for SS/AH). Valve-cover
bolt holes must remain unaltered and in their original location
(except for SS/AH). Welding or epoxying permitted on external
portion of runners for repair only, maximum 2 runners per head.
Heat riser passages may be blocked off from intake-manifold side
of cylinder head or in exhaust port. The following are permitted:
polylocks, jam nuts, screw-in or pinned studs. Any valve job
accepted. Exhaust plate permitted between header and cylinder
head, maximum 1/2-inch; may not protrude into exhaust port.
Cylinder head may have all seats replaced.
 
Stock eliminator heads..........

CYLINDER HEADS (April 15, 2013)
ENGINE
Must be same year and make as car used, aftermarket NHRA-
accepted cylinder blocks permitted. Equipment other than original
factory-installed prohibited. Any special equipment export kit
(superchargers, dealer-installed options, etc.) automatically
disqualifies car. Engine must remain in stock location — height,
setback, etc. Cylinder bores must not exceed .080-inch over stock.
Bores are measured at top of cylinder where ring wear is not
evident. Crossbreeding parts prohibited. Normal balance job (i.e.,
one piston/rod assembly untouched) permitted. Otherwise
lightening of component parts prohibited. All carburetors, manifolds,
heads, etc. must be tightened to prevent any air or fuel leaks.
Vacuum lines must be securely connected or blocked off. Stroke
tolerance is +/- .015-inch. Stock OEM or NHRA-accepted
aftermarket crankshaft mandatory. Aftermarket crank must retain
OEM configuration (i.e., billets, knife edging, etc. prohibited).
Lightening of crankshaft other than normal balance job prohibited.
Cylinder blocks may be sleeved. Aftermarket SFI Spec 18.1
harmonic balancer mandatory in AAA/S through G/S and AAA/SA
through G/SA. See General Regulations 1:2.
SUPERSEDED AND/OR REPLACEMENT PARTS
Superseded parts are restricted to cylinder heads, intake manifold,
crankshaft, cylinder block, and transmission only when
manufacturer lists such parts in its published parts book, notifies
NHRA of said change, and change is accepted by NHRA.
Must be correct casting number for year and horsepower claimed,
per NHRA Technical Bulletins or NHRA accepted. Porting,
polishing, welding, epoxying and acid-porting prohibited.
Combustion-chamber modifications prohibited. Cylinder heads are
additionally restricted in that they must retain original-size valves at
original angles +/- 1 degree and must be able to hold original
cylinder-head volume per NHRA Specifications. Runner volumes
may not exceed the current Super Stock cylinder-head volumes as
listed on www.NHRARacer.com. Regardless of the poured volume
measurement, any modifications to intake or exhaust runners
prohibited. Any evidence of modifications from the original castings
will be grounds for disqualifications as determined by NHRA in
NHRA’s sole and absolute discretion. Any aftermarket steel valve
permitted, must retain stock head and stem diameters. Only
engines OEM-equipped with sodium-filled valves may use sodium-
filled replacement valves. Titanium prohibited. Hardened keepers
permitted. Lash caps prohibited. Valve-diameter tolerance: +.005-
inch or -.015-inch from NHRA Specs. The following are prohibited:
spark-plug adapters; cylinder-head studs; any grinding in ports or
combustion chambers; removal of any flashings; sandblasting or
any other modification to cylinder head; any film coating of intake
and exhaust runners; any film coating of combustion chamber.
Runners and combustion chamber must retain OEM appearance.
Final acceptance as determined by NHRA in NHRA’s sole and
absolute discretion. External modifications prohibited. Intake side of
head may not be cut into any part of valve cover bolt holes. Valve-
cover bolt holes must remain unaltered and in their original location.
Heat riser passage may be blocked from intake manifold side of
cylinder head. Blocking passage down in valve pocket prohibited.
The following are permitted: polylocks, jam nuts, screw-in larger-
diameter rocker studs or pinned studs, bronze-wall valve guides.
Valve spring umbrellas optional. Cylinder head may have all of the
seats replaced. Any valve job permitted,O-ringing prohibited.
Exhaust plates prohibited.
 
yeah..read all that...and figure it out...probably why stock and SS heads cost so much .....1st..the head guy gotta be able to read and comprehend......
 
805moparkid said:
whats and exhaust plate?
Click to expand...

after all the hi-tech b s, and not saying these guys are wrong, but, there is absolutely no sense in haveing more cam than your head will flow.
if your heads flow (for instance) 340 @ .600 lift, there is no point inrunning higher lift than .600 plus your lash. duration ?? that`s another story, betterleft to your choice for your engine :hello2:
 
LOL @ Tony!

Moper, your one of the guys here that can cover a lot of area. I'd be hard pressed to argue with you, Tony and a handful of other guys here. I just took the question on from another angle.

For general purpose performance, one needs not go crazy trying to be a scientist figuring out numbers of flow and lift. Getting the most out of it would need a good bit of brain power. Then there's splitting hairs between everything else for what should be and what is and what does perform best. And then how and why it failed to do the expected.
The brain could go Ka-Boom!

If the bomber wants to really nail down some power, then get that cam that rockets the valves up and hangs'em high for a while on some high flow counter parts, in and out, squeeze that mix good and away you go!

While that basic recipe could be a disaster waiting to happen if your so foolish to "throw" parts at the problem, it is the basic idea of how power is made.

The question for the Bomber is, "Where are you going with this and where do you wanna be at builds end?"
 
famous bob said:
after all the hi-tech b s, and not saying these guys are wrong, but, there is absolutely no sense in haveing more cam than your head will flow.
if your heads flow (for instance) 340 @ .600 lift, there is no point inrunning higher lift than .600 plus your lash. duration ?? that`s another story, betterleft to your choice for your engine :hello2:
Click to expand...

Bob, there is a line of thought as to why you would want more lift than the head flows BUT I do not subscribe to this line of thought for street and mild strip cars Not earning or chasing money. The extra stretch is not needed for a pretty hairy scarey ride.

A buddy of mine ran into the mid 10's easy enough without making use of every last CFM of head flow from his W2's. it was just a good combo well exacuted (sp?) in a light car.

Also pushing an engine so hard wears out parts quicker. A pair of high school freinds run a rail. I think it's super gas, but I forget. There currently running 500 cubes with a plan to go (much) bigger. I asked why the expense? They answered, "A bigger engine doing the same or better job with less effort and stress! Duh!"

So I sat In The corner quietly wearing the dunce cap for the night.
I missed it! LOL
 
well I can understand having more lift than needed for the same reason you shift past peak hp, your snapping that valve open farther for the same given time (assuming roller and that that grind is doable).
 
famous bob said:
after all the hi-tech b s, and not saying these guys are wrong, but, there is absolutely no sense in haveing more cam than your head will flow.
if your heads flow (for instance) 340 @ .600 lift, there is no point inrunning higher lift than .600 plus your lash. duration ?? that`s another story, betterleft to your choice for your engine :hello2:
Click to expand...

I think theres a benefit to running a little more lift than peak flow of your head, say your 340@.600 if your cam only has .600 lift peak flow is only reached for a split second if you went .625 lift or so the peak flow will be hit twice and there would be more average time spent around peak flow.
 
It's really more of hanging the valve there longer in the peak is area than it is trying to pick up peak flow twice since the air and fuel are coming in At such a rate. The air is now jamming down. Ram effect.

The idea that the air flow slows down only to luck up again doesn't make sense to me. For a street ride, this is a bit far to go IMO at least.
 
Really what I was trying to say depending on the head, on the theoretical 340@.600" head probably will flow close to peak numbers plus and minus 0.050", so a cam that has more lift that just peak will spend more time in that peak flow window, but like the Airwolf head that flows 300@.500" and 326@ 1" unless your trying to extract every last HP you'll probably end up with .550"-.650" lift cam.

Factory seem to be going with big head flow smaller cam look at the new hemis heads flow more stock than all but the most serious race heads to get good power from a relatively small cam, if I was building a street engine I'd go witha little more head flow to be able to run a smaller cam to achieve the HP goal than the other way around.
 
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