Subject: What is a good Cam (Moderator not included)?
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Fahrvergnugen
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posted on April 28th, 2004 at 08:37 AM
What is a good Cam (Moderator not included)?
I am contemplating a different Cam just to see what happens.
Stan's old-spec steroid cam which I am running at the moment is great and I will be trying it with a better set of heads before I go changing cams.
But I still want to continue down the development path because it is fun.
I still might ask Stan for one of his latest steroid cams but I fear that they make power too high up the rpm range.
My current combo makes power between 4000 and 6000 rpm. That's not bad but it does leave the car lacking in some crucial corners around various
racing circuits.
Jak and I run budget gearboxes. We both have rebuilt late model 1300 boxes with 4.375 ring and pinions. They have a brilliant 3rd and 4th but 1st and
2nd are too low. Consequently all the tracks are done in 3rd and 4th gear. We used to change into second coming onto the straight at Wakefield park
but last year I tried leaving the car in 3rd because it seemed easier to concentrate on taking the correct line through the corner. I ended up
getting a better run onto the straight than Jak who was directly in front of me and changing down into second. Jak and I have pretty much decided to
take these low speed corners in third now. His stroker will help pull him out of those corners.
I now want a cam that pulls from 3000 to 6500. Aircooled.net suggests a Webcam 109.
Here is their description of the cam:
Webcam 109 equivalent to Engle 125
Designed for hot street and off-road engines, works very welll with 1.25 rockers for more power! Valve Lift - 0.465; Advertised Duration - 287
degrees; Actual Duration @.050" - 260 degrees
Any thoughts?
The engine is a 1915 with 40mm inlet valves and 9.5:1 compression, 44idfs and 1 5/8th header.
I don't want a ratio rocker vs standard rocker debate here.
This sort of post is what the Racers Edge is about so please keep it clean or I will delete the post.
Bench racers, start your engines.
CYA, CT :alien
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AdrianH
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posted on April 28th, 2004 at 03:28 PM
You could run an 86B with 1.25:1 rockers which would give you 262 degrees at .050" and .478" lift.
As long as you set up the heads for the lift you can use up to 1.5:1 rockers with that cam (.575" lift).
Im running one in a 2110 it pulls cleanly from 3500 - 7000.
The other maybe worth a look is the 121/125 webcam, although it has pretty severe ramps so not so good for valve train.
The other cam you dont hear about often is the V26 engle. I think it is a berg only cam. The cam is exactly the same profile as a hugely succesfull
small block chev profile, every person I have spoken to who has used it loves it. This is a ratiorocker profile (1.4:1) Check the berg website.
Craig Paton
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posted on April 28th, 2004 at 03:48 PM
I have a new WEB CAM 86b for sale ,as well as straight cut gears and berg 1.45 : 1 rockers if your interested
Cheers Craig P.
[Edited on 28-4-2004 by Craig Paton]
AdrianH
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posted on April 28th, 2004 at 04:04 PM
Heres some more light information I copied of shoptalk early last year
There will be a pop quiz later tommorrow on the contents of this post -
It is long but worth a read
I'm going to be posting a rather comprehensive expose' on component balancing also, yet this has been one topic I've been mulling around with for a
while..Marty Staggs egg'd me on, on another thread and since it's been a source of some spastic episodes while reading replies to cam
recommendations, I figured the time is ripe............So...Here Goes...
Not many folks really understand the importance of their bumpsticks in achieving their goals, be it a 1500 SP or a 2+ liter sphincter sweller...SOOO
important are our camshafts...
I'll attempt to make this read as painless as possible..................................................
The "BIG" syndrome..........
I can't tell you why.... aside from some "Freudian" big complex, people buy into this nonsense..
Of course, I'm referring to everything from cranks to valves to ports to cams to carbs to exhaust systems, et.al, ad infinum....The only reason, in
my mind is.....People are pre-disposed to thinking.......... bigger is better.....
Taking this into consideration, I can only ask........."What are you expecting?." Once this vital criteria is determined, can we go ahead with the
rest....Don't expect a 1/4 mile mauler to provide the same economical long life as a nicely rebuilt stocker, and regardless how much we thrash the
stocker...It'll never be a mauler..For many, the holy grail of motors is one that puts up great numbers yet also, putters our butts to work through
the week without the possibility of some kind of mechanical "China Syndrome" occurring..This type of motor can be had in todays computerized age
with all the technology brought about by it, much more easily (or in some cases for the first time), than ever before...What hasn't changed is the
importance of carefully matching individual components, which when properly assembled, perform within their respective designed operating range..Also
note: properly assembled....The finest components, if assembled by some glue sniffing marsupial, will most assuredly result in being a pricey
mechanical fart.
Me Personally?...I like BIG motors...I don't have to rev 'em past 5-6k, and they provide a higher percentage of "seat time" enjoyment, and since
you don't have to rev them to some ridiculous spin factor, they live...Doesn't matter if I'm trolling through traffic, cutting apexs on a
meandering mountain pass, or pouncing on some dork at a red light thinking his '03 Vette Z06 is an instrument of humiliation Par
Excellence...Fun?...Oh yeah...BELIEVE ME....it's fun, as many of you know..
Big..Small and in-between...Camshafts, valve/port, carb/injection, ignition timing and exhaust sizing is vitally critical for peak
performance......Peak... meaning everything from fuel mileage to out-put depending on the target..
How to select a cam...............................
We need to know a few things, well, quite a few things most people aren't asked, or if are, don't know the answers to...This is so important...
What is the motor displacement.
What is the Bore/Stroke configuration
What is the rod length
What is the static compression ratio
How much does the cylinder head flow on both intake and exhaust, and at what lift does the flow level out.
What is the flow differential between intake and exhaust...
What is the targeted useful rev range...2-6000?...5-8000?...Idle to 5k?....WHAT????
What is it..you ask of this motor?....
These are the essentials in choosing an appropriate camshaft...
On NA motors, I have yet to see a gain in output by adding lift beyond the flow capacity of the head...On AA motors, I've found this not to be the
case since obviously flow capacity increases are the result of a device other than mother nature. It is for this very reason, a relatively small
valved/small port head can by far fill a given cylinder to a capacity unobtainable by even the largest ports and valves on a normally aspirated
motor...You just can't spin that big headed motor to the pumping speed required to inhale the same amount of air as its artificially aspirated
counterpart at a lower R.P.M. in boost...Camshaft profiles are therefore quite different for these applications....
For NA applications...The more duration you run, the more compression you'll need, this is crucial for optimizing mid, through top end
performance..using even a 280 degree cam with less than 8.25:1 is a wasted effort..9 or even 10:1 and beyond is favored..On the flip side, don't even
think about 10:1 with a 260 degree grind..
AA motors are a different story altogether....Yes...off-boost performance still requires much of the pre-requisites as its NA counterparts..Gig
is...They're not there very long...That is...NOT if the components are appropriately matched...This applies to a loose scroll huffer hung off the
poop pipes of a 2.5 litre motor being launched at 5k+ and only has 1320ft. of tarmac to wrinkle, as well as a 1.5 litre single port that can be
pressurized by a springtime induced sneeze...
There are NO One-Size-Fits-All operatives in the automotive engineering world, or any other...When properly engineered..that component..whatever it
may be...Is there because it'll be utilized as close to 100% of it's capabilities as possible....If not...Your losing something,
somewhere..............................COMPONENT INTEGRATION PEOPLE!.............................
We need to understand the nexus between direction of piston travel, the speed of its travel and its relationship to in-out valve opening events...
The INTAKE stroke.....
At TDC, our piston is sitting still...In other words, it's hit the end of its travel waiting to be yanked back down....It picks up speed only to slow
down as it reaches BDC...O.k....Pretty simple so far huh?.....Ah contraire me amigos!....It gets a bit more complex...No..a lot more complex...You
see, as our beautiful, hi-tech slug descends down its respective bore, the intake valve is opening and our air/fuel mix starts its journey into our
combustion chamber...BUT....The majority of this precious juice gets sucked up while pressure differential is greatest...
Where does this "sweet zone" occur.....
Somewhere between 65 and 85 degrees ATDC....WOW...Big spread!...Yup!..and what, Pre'-tell, is the reason for such?....
"Piston Velocity"....
The denominators here are..STROKE..ROD LENGTH...and RPM......Now.... we know that our max slug speed is being governed by the resistance to gas flow,
and/or dynamic stress by the inertia of reciprocating components...
REAL IMPORTANT FOLKS!!!!......
Volumetric efficiency is a DIRECT result of slug velocity....
Volumetric efficiency is how we measure the effectiveness of each cylinders ability to stuff itself with about 202 vertical miles of air (per square
inch) at sea level... Now get this...The intake valve starts to close...close...to BDC, finally closing after the piston is on its way up again
...Why?...The inertia based on mass of air at that velocity...Or momentum keeps filling the cylinder with mix even after our slug is on its way back
up. Simple physical law................................................................
Compression Stroke.......................
Easy...The slug compresses the mix to a degree required to allow our spark plugs to ignite it....Once this happens.....Precision timing of our spark
is required..
Power Stroke................................
Well, our air/juice mix has been compressed, the plug fires and the piston is pushed downward by these expanding gasses. In normally aspirated (NA)
motors, the gasses reach a relatively low pressure state at around the 90* ATDC crank angle, Turbo/Supercharged motors (AA) a ways further...This is
where we want to start opening the pooper..This is so we can take advantage of the inertia or blow-down, and expel as much of these end gasses as
possible to leave as much clean room for the up-coming inlet charge with minimal dilution...If we didn't start opening the poop valve, we'd be
relying on the piston to push ALL of it out..Which leads us to.........
The exhaust valve is already opening up at a pretty good clip....Our piston is now on its way up with a vengeance, and well.......If that exhaust
valve is not wide open as the piston hits max velocity, it'll be up against a wall of dirty air and now has to exert more effort (pumping loss) in
clearing it out....Well, as that ascending piston slows as it gets to TDC, the pooper is almost shut......But...........Heavens to Mergatroid!!!
The intake valve is starting to open!...Yup folks...We've advanced to..............(music sans Rod Serling)......
.....The Overlap Zone ..
In this zone we find the intake and exhaust valve opened an equal amount..or ...properly... split overlap...
On garden variety mundane, civilized street motors, aka stockers, both valves are in the air only about 10-15 to 25-30 degrees of crank rotation
versus 60-100 and more for a 8000+ revving shrieker! It also makes for a turd as far as lower r.p.m power is concerned, after all...A lot of that
precious charge goes right out our big *** exhaust....Now we'll revue all 4 strokes again.... BUT, this time with some valve timing events tossed in,
in order to determine our valve timing duration...Fun huh?...Well, it is for me at least..
We're not talking lift here folks ..
Let's say we have a mid displacement, good punch motor....Fitted with a 268* duration cam, ground on a 108* lobe center angle...(LCA is the amount,
in degrees, between the highest lift points on the intake and exhaust lobe)...As I mentioned above...BOTH valves are open at the end of the exhaust
stroke...The intake valve starts to open at 26* BTDC....As the piston crosses over the TDC point, the intake valve finally hits wide open at 108
degrees ATDC, (cam installed "straight up"). And know what?...It's still open at BDC...Now some K-1 math:
The crank has rotated 180* from TDC to BDC, and the intake valve opened at 26* BTDC...So...26+180=206...Now remember..We have a 268* cam in this pup
sooooo....It also tells us where the valve will close.....268*-206*=62* ABDC... So, we've compressed the A/F mix and (hopefully) ignited it at the
right time..Recall earlier, I said most of the cylinder pressure has dissipated by around the 90* crank angle ATDC...you can see, with this 268* cam,
the pooper starts opening at 62* BBDC....BEFORE the exhaust cycle actually begins......K1 addition again..62+180=242.......At TDC......the end of the
exhaust stroke..... the intake valve has opened, yet the exhaust hasn't closed yet..It stays open for 268*-242*=26 degrees ATDC....NOW...The intake
opens at 26* BTDC and the exhaust valve closes at 26* ATDC...What do we know?...We have 52 degrees of overlap.....BOTH valves are open for 52 degrees
of crank rotation......O.k...so far, so good....
Most of you guys are real bright so I know you have no problem following along, or even being bored in reading this speil, but it's for the benefit
of everybody understanding what's happening in relation to their motors, and how cams play a role..
Now, that (hopefully) you understand the basics, let's address valve timing events...
Sequence of valve timing events in ascending order of importance......................................................................................
Opening the pooper.............
Without Doubt.....Exhaust valve opening is at the bottom of the list...It can open anywhere from 45 to 95 degrees before BDC. If we open the pooper
close to BDC, we can take advantage of our expanding gasses to a higher degree...BUT...This is a fine line to walk, as we pay for it in pumping losses
since we minimize the benefits of blow down...We just don't have sufficient time to allow all end gasses to escape, leaving the piston doing overtime
in pushing them out on the way up...Next in line, and understandably so, is.....
Closing of the pooper....
If our exhaust valves close at say....15-20 degrees ATDC, we obviously have little overlap..GREAT low end running and efficient at low revs....If we
keep that pup open a bit longer...say 40 ATDC...Our overlap period is substantially larger, which results in dilution of the upcoming inlet charge,
leaving a puttering pansy of a motor down low...
Intake Opening............
Important...Real Important....If we open this pup early, it obviously translates to more overlap (I'm not talking about installing the cam in an
advanced position...I'm referring to moving the intake lobe in relation to the exhaust lobe) again, sacrificing low speed performance for high speed
benefit...This is where we get our power gains..This earlier valve opening results in the valve being open further as the piston reaches peak speed,
allowing better cylinder filling...Better cylinder filling = higher volumetric efficiency....ha-ha-ha....I have you thinkin' about rod length huh? I
better....You should already see how vitally important it is........
Intake Closing..........
Here's the Big Wazoo..The most important event.. It determines both rev range and effective, dynamic compression ratio...If we close the inlet
relatively early at oh, about 45* ABDC, we hamper cylinder filling. We get real nice drivability but don't make much power and don't rev at all...A
good long life street motor cam for Grand Ma's low compression 1600 type 3 automatic..Note, I said low compression. Know why? Peak cylinder pressures
skyrocket with higher compression ratios. Huge pumping losses occur just trying to compress the mixture...A sure-fire way to morph a motor into a
horizontal mortar launcher..SO...We close the intake valve later giving the cylinder more time to suck up its life giving seed....And...since we're
giving it more time, we're also raising its RPM, and since we're raising its RPM, we're sucking up more seed, and since we're sucking up more
seed, we're making more power... All is fine and good, to a point....Once the valve starts seating past about the 75-80* point forget about low speed
output...Also, you can see from all of the above, that you MUST have substantial static compression to take advantage of these more radical cams...If
not...milder grinds yeild higher performance gains............ In any case...This is the most important valve timing event.
Hopefully, I've provided some insight on how your cam choice is paramount to the end result...I could immerse myself deeper on this subject...It
certainly is comprehensive...READ what I wrote....2..3..10 times if you need to...I hope it helps...When in doubt, call your cam grinder or discuss
these variables with your builder...To just install a certain grind based on..."So and so runs that cam and it works real well", is a dopey reason
unless so and so has a reasonable duplicate of the motor you're building with the same performance criteria, and most importantly, has done the
appropriate calculations in determining what profile matches expectations/performance...For anything but a dedicated race motor, with all of the
required matched components that go along with it...much less camshaft will provide far more performance...
Posted by Joe Sumen
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Fahrvergnugen
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posted on April 29th, 2004 at 12:24 PM
Thanks for your responses Craig and Adrian. Adrian's last post is very educational. I like the point about matching cams to compression. I've heard
a lot of people say that you don't really get 10:1 compression because it bleeds off with the overlap. I'm glad somebody has actually explained that
in detail. I'm going to have to read that post again to fully comprehend it.
I don't think I'll go with heaps of lift ratio rockers CM pushrods and all that jazz. I'll probably keep it simple with as light a spring pressure
as I can get away with. I'm not going any bigger than 40mm inlet valves.
I'd like to hear from some more people who've used ratio rocker cams like the 86b that Craig mentioned with 1.25 rockers. I'm not that interested
in valve lift over .500.
When I emailed Aircooled.net I asked if I should go for the 121/125 cam but the 109 is what they came back with.
Adrian. Have you had your car on a dyno? I'm more interested in the shape of the curves rather than the hp figures. What are your other engine
specs?
CYA, CT
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Craig Torrens
A.k.a.: Craig Torrens
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posted on April 29th, 2004 at 10:46 PM
CT, if you want to sell your cam, let me know and I will buy.
Thanks
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posted on May 1st, 2004 at 08:14 PM
Quote:
Originally
posted by Craig Torrens
CT, if you want to sell your cam, let me know and I will buy.
Thanks
Surely Craig after all your excellent promotional work on this forum Stan would give u a free cam wouldn't he?
Congratulations to Ben Durie for breaking the hillclimb record at Ringwood in his stroker beetle!
AdrianH
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posted on May 2nd, 2004 at 02:56 PM
Never had it on a dyno. The engine is a 2110 82 x 94, 5.4" rods, CB cnc oval ports, 48 DRLAs, 1 5/8" exhaust. Comp ratio is 9.2:1 with a .040" deck
height. Cam is installed straight up (86B) and lifts .555" with 1.45:1 rockers.
