Selecting a cam: the soul of the engine

Cams are very hard to nail on the first try…..

A couple thoughts.

Lift. The only real down side to more than optimal lift is a higher wear rate on the buckets and a little more valve train drag costing a couple hp. If you go lower than optimal, you won’t fill the cylinders and that costs a lot of hp. So, go as high on lift.

Duration and head flow. I put the 2 together because they are not independent. For a wide power band, you want the lowest duration cam that will fill the cylinders at the target hp peak rpm. The more flow you have, the less duration you need. Cams and ports have a similar effect, too big costs you low rpm power, too small costs high rpm.

A prefect 4v engine would want about 210 degrees at .050” lift to make peak hp at 7500. If the port flow is less than the perfect number, you need to start adding duration to make up for it. Once you add more than say 15 degrees to intake and exhaust, you will start to see the low-end performance dropping with little or no gains up top. You are just adding to the intake, so you can go a bit further I think, maybe 20-25 past optimal without a big bottom end impact. Since you are also increasing compression, I think 25, putting you at 235 degrees.

LSA. 107 it too small, it makes the peak number good, but hurts the low end. Euro 308s use 109 and it helps the low end quite a bit, pulling the torque peak down 500 rpm while leaving the hp peak rpm the same, although you lose a few peak hp. Since you are increasing the duration, you can also increase the LSA. With a 235ish intake cam, I would try 112 I think. Your not stuck with your choice here, you can always change it for free at the next belt service.

My engine is a little smaller than yours with a little more flow (no carbs in the way ) and also a blower motor. I think my idle cam would be 400+ lift, 220-225 duration and 114 LSA (the higher LSA help keep the boost from leaking out the exhaust port). Both your stock 328 intakes and the re-ground intakes you have would work well in my engine I think, not perfect, but pretty good. I want perfect, but with my wife watching the spending, your cast-offs re-grinds might be my best option. They are a bit low in lift, but have extra duration which would somewhat make up for it, but at the expense of low end power….but the blower gives me gobs of low-end power anyway so it’s not a big deal really. Once Web decides what they can do and for how much, lets talk before you send any cores in.

 

I'm relatively new to Ferraris and not sure what the common practices are, but we have found that with pushrod V8's, the valve job can be the key to unlocking significant extra horsepower! A multi-angle intake seat (we use 5-angles) provides shear points for the fuel as it enters the chamber and produces a more uniform fuel atomization and so, more power extracted from the charge. Radiused exhaust seats work best.

Just my humble $.02

 

The 308/328 engines come from the factory with a 3 angle valve job, seats blended and ports hand finish with about 120 grit, they look pretty good right from the factory. A few measurements and a flow bench though show the design isn’t really very good as delivered.

The main problems are that the intake port is too small at the manifold flange and the exhaust port is too big everywhere. Russ and I are both having our heads ported by a friend of mine with intake flow up 100% at .050 lift and about 20% at .400” lift, not bad….and with all the new intake flow, the exhaust port is about right, still too big, but it seems to work.

I wonder is Ferrari didn’t do the port wrong on purpose to hit emissions numbers. I had a special H-D that came with factory ported race head…but the first think to do to make more power was port the heads. The real race head flowed 138 (at 10” h2o), but the street heads had to be kept under 110 to pass EPA testing. Ferrari might have been facing the same problem.

 

I found this online and thought I would post it. Its just about verbatum of whats been discussed over more than 40 years, and is "fairly" accurate. It wouldnt matter if its a Ferrari, a Subaru, or a Suzuki, an engine is an engine. Each engine is going to operate a bit differently based upon how the builder put his engine together, but its still going to follow along these basic guidlines. The bottom line becomes how you want the car to run on the street. If your going to be driving in stop and go traffic every day, you wont like a wild cam. If you want to get the best top end performance out of it, like on a track, your not going to like a low duration cam. Most people like to stay in the middle, and thats generally between 260-290 degrees duration. But if any engine could run like a scalded cat with over 300 degrees of cam, Russ car could, he's done it all to make it a real monster, porting, compression, larger valves, carbs, exhaust. You probably wouldnt like how it runs, and street driving would be horrendous, but once it lit it would be quite a ride.

Russ, I havnt used my adjustable cam sprockets yet. If it gets down to the wire and you cant find any, let me know.

CAM PROFILES:

WHAT WILL WORK FOR ME?

These are very general guidelines for a modern, four-valve per cylinder DOHC,

four-cylinder engine of between 1600 and 2400cc's.



240 DEGREES OF DURATION, 0.390" LIFT, 15 DEGREES OF OVERLAP:

Typical stock cam works well from 700-6500 RPM, smooth as can be. Relatively low emissions.



265 DEGREES OF DURATION, 0.420" LIFT, 30 DEGREES OF OVERLAP:

Good street cam, pulls well from 4000-7000 RPM, slight lope to idle. Will idle at about 900 RPM.

Might pass a smog test. Might work with ODBII. Works well with most bolt on power modifications

like adjustable cam pulleys, header, exhaust, air intake. Cars feels fun to drive on the street and

is most likely more responsive than stock almost everywhere in the power band.

Most people should stop here!



280 DEGREES OF DURATION, 0.440" LIFT:

Mild race cam, pulls well from 4500-8000. Idle at 950 RPM with a definite lope.

Could pass a smog test with tricky fuel and ignition management, most likely OBDII will not like this.

Car might not feel good from a seat-of-the-pants perspective. Higher compression (10:1), adjustable

cam pulleys, headwork and headers become a big plus at this point. Special matched valve springs

are most likely needed.



290 DEGREES OF DURATION, 0.460" LIFT:

High RPM lobe of a VTEC cam (duration only) really wild street cam or mild race cam,

power band from 5500-8500. Idle lopy at about 1200 RPM. Most likely will fail HC and CO part of

smog test. ODBII system may experience some serious emotional problems. Higher compression

(11:1), adjustable cam pulleys, headwork, headers and other stuff become almost mandatory.

Racing valve springs needed. Compression puts engine almost to the point of not working

with pump gas.



305 DEGREES OF DURATION, 0.500" LIFT:

Full race cam, power band from 7000-9500 RPM. Idle lopy at about 1400 RPM. Smog? Hah!

OBDII system giggles and spews failure codes before becoming catatonic. High compression

(at least 12:1), headwork, short runner intake manifold, custom tuned header, bigger injectors,

high-powered ignition and stiff valve springs become mandatory. Car won't run on pump gas any

more because of compression. Close ratio transmission necessary due to narrow power band.

Car is just about undrivable on the street unless it's certain streets of Long Beach in April.







Duration of a cam is measured on the cam by dial indicator and degree wheel when the dial indicator reads 0.003" lift. Why 0.003"? It is because it is really hard to see when a dial indicator first starts to move versus degrees on a degree wheel when measuring a cam. The opening point is spread out over quite a few degrees and it is pretty hard to nail the exact opening point--0.003" is an easy spot to pick where you can get a definite reading.

Sometimes cam makers will state duration differently. Commonly, the makers of domestic cams will pick 0.050" as the measuring point for the cams duration. This is because some engine builders feel that the sloppy pushrod and floating rocker arms that domestic engines sport pass a lot of slop into the equation, and 0.050" is a more accurate point to take a cam duration.

Some Japanese import cam makers use 1mm or 0.040" for the same reason. Duration taken from these points of higher lift will be quite a bit less than advertised duration. A cam with 260 degrees of duration will have a 0.050" duration of around 215 degrees. Some cam grinders use .030" or even something like 0.020" because they feel that that is the best place to measure duration.

When purchasing a cam, find out how the duration is measured. For instance, a cam with 260 degrees of advertised duration is a good, mild street cam. A cam with 260 degrees of duration at 0.050" lift is a full race monster.

 

What about dual or even multi-pattern cams?

For example, could it be beneficial to have a different profile on the intake versus the exhaust on a 2-valve engine? I used to have a Crower cam that was made like that...but I just had to take their word on it that it was good for anything.

Also, on a 4-valve engine, could you have two different profiles for the intake valves - one for good idle and a second for high-speed power?

The Corvette ZR-1 4-valve engine is made this way; the high speed secondary intakes are blocked of by a vacuum servo at low RPM and have a substantially higher duration than the primary intake valves.

 

A three angle valve job was hot stuff when these cars were new.
We use a custom built wet-flow bench which allows us to analyze the fuel flow and suspension as well as simple airflow. Trust me on this, the 5 angle valve job makes a difference.

 

With that setup, I do trust you - but do you have an idea of how long this treatment lasts? In other words, do the advantages of the 5-angle grind "wear off" after a few miles?

 

Valve face height or penetration into the chamber makes a difference on low lift flow on the exhaust valves. I see so many sunk valves during a valve job that hurts power and they dont seem to even realize it. Its a small but important detail, make sure the exhaust valves seem to sit high on the seat rather than flush with the chamber face. I agree 100% on the valve seat angles as well.

 

It should last as long as any valve job.
Re: sunken valves, this can noticably increase the chamber volume - more than you would think. This obviously in turn decreases compression and power.

 

I don't like 5 angle valve jobs because they don't flow as well as radius seats. The quote I always like is "I don't care if you're Jesus Christ himself, without air, you aren't going to make hp". You can domp in as much fuel as you need, but the air is another matter.

 

Not so. Sinking the valves helps flow and hp on every head I've ever seen numbers on. It works best of course if you mill the head or change the pistons to get the compression back, but it generally helps anyway.

 

There is no reason in the world the exhaust profile needs to or even should match the intake profile.

 

Total duration is not a particularly useful way to spec a cam. The reason has nothing to do with slop in the rockers or anywhere else. The problem is that to prevent the valve from slamming or bouncing, the cam needs to have acceleration/deceleration sections at the lead and tail end of the cam and every vendor/maker uses different standards. So my 250 can might be your 260 cam. Once the cam gets to .050” lift, it’s out of the accel/decel ramp area allowing the cams to be compared pretty accurately and is the number that should be used instead of total or .003” duration.

Also 2v cam numbers will be about 20 degrees more than 4v numbers for the same result simply because a 2v engine has bigger and heavier valves that need to open further to work, and that takes a bit more time.

 

Forced induction will behave somewhat differently, but in a NA motor, increasing airflow alone does not guarantee power. In fact, the reverse can be true in some cases. Fuel and air have to work together. I have seen a 20+ HP gain with virtually no increase in dry airflow, attributable to fuel management in the ports, seats and chambers.

Do you really use a radiused intake seat?

 

Read this article.
http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/
It tells you how to calculate the lobe centre angle.
It is spot on for my 456.

 

I do use radius intake seats and have oh geez, 15 year now.

There are a lot of variables (carb v EFI, port velocity, ect) so I don't doubt your results.

 

Virtually all the Ferrari with DOHC engines, have different lift and duration one each cam. Plus, they are infinetly variable individually. IOW, you can alter timing on either cam individually.

I cant see what different profiles between the two intake or exhausts on a 4 valve would accomplish, as the intake and exhaust ports are siamesed. I believe this is what actually killed the 5 valve motors, its just to complex for the small gain in power.

The .003 lift thing I posted above was off the information I cut and pasted and are not my words. I just felt that it was good "general" information, and thought I would share it. Ultimately whatever cam you are going to use, should be measured in such a way that it comapres with the current part. If Ferrari use .50 mm valve clearance to measure 244 degrees duration, this figure should also be used with any other cam grind to make a logical comparison.

 

My experiance has been that there is a very fine line with the duration specs on a cross flow, hemi combustion chambered engine. Very easy to get into a over scavaging situation and loose all torque. I agree with James, a dual profile and on the 4V a scatter pattern is the direction I am heading to eliminate this problem.
One would have to draw me a picture of how sunk valves flow better. I guess I simply do not understand the dynamics of that theory. I always use over height seats with longer stems to get away from that situation.
If it is a race engine you want, scrap the "shim over" cam followers and go to the shim under style. My experiments show that the valve float and flutter begins quite early in the rev range with the heavy OE setup. Eliminating all the extra weight allowed me to obtain insane rev's and use utterly obsurd cam profiles in the 4V engine. In my experiance, most of the high wear problems are caused by float due to the extra weight and the resulted hammering of the lobe to the follower. If one looks very closly at the dyno results you will see the tell tale signs of valve float and spring flutter and in my case far earlier than I expected given the springs I use.
I dont want to think of how many lobes and followers I hammered to death testing cams before I found this. This alone justified my keeping one engine as a dyno mule only.

Best of luck,

Dave

 

Dave, what ratio of intake v exhaust flow do you normally run?

The stock QV head (and I think 2v head) have very large exhaust ports, that don't flow anywhere near what a port that big should flow, but still are 92% (about 100% with the CIS connected) of the intake flow....which seems very very high. I know with the blower, I've been pumping 50% more air and fuel than I should be for the power I make and I think the exhaust flow is the cause. When the heads finished the exhaust will be down to about 78% of the intake, which I'm hoping with a little more LSA the blow-down problem will be gone.

I started sinking valves out of necessity, big valves with high lift, long duration cams tend to send the valves crashing into each other unless you sink them - .100” on the 2.7l 911 I did 10 or 12 years ago. I was scared to death about losing flow, but I had to get clearance between the valves. What I found was that the flow did drop at first, but with a little cleaning up the head around the seat, the flow was actually quite a bit higher than when the valves were sitting proud. I’ve found the same thing on pretty much everything I’ve messed with since. The best explanation I have is that when the valves are sunk a bit the head can function like a diffuser after the valve to help the flow slow and expand into the cylinder.

Dave what rpm and on what engine(s) did you notice it? I wasn't planning to make that change to my qv since I'm sticking to an 8k redline, but maybe I should consider it.

 

Both velocedog and Newman have the most current information regarding valve seats. This is an Aurora IRL head done by Darin Morgan of Reher-Morrison. You will notice the lack of radiused seats. The exhaust valves are not sunk into the head either. Valves are Del West. Here is a post from Darin.

I have yet to see an instance where a full radius seat made more power than sharp angles or one sharp angle at least. I use a semi radius seat but I leave at least one sharp definition angle under the seat and sometimes two. If you ask Flotz, Myself, Warren, Ikie, Chapman, Bill Jones, and anyone from Dart or Brodix, you will find the general consensus is that radius seats do not work in a high performance engine. I have never seen a case where a full Radius has worked better than a "correct" sharp angle. On the wet flow bench a Radius seat will not form what we are now calling a shear ridge. There are a couple of places within the intake port and chamber that help shear the wet fuel as it enters the chamber. Without them, you get a puddled mess of wet fuel that wont burn very well. The last portion of Bill Jones post touches on this.

The exhaust however is different. The correct radius seat has always proven to be better.

I even tried a radius seat again last year on one of our test engines. It lost 15lbs/hr of fuel flow and killed the engine 12ft/lbs and about 23hp.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
FAX-468-3147
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There maybe some misunderstandings or the use of the term "radius seat". When I say radius seat, it is 1 radius in the port, 1 flat for the valve to sit on and a second radius (not generaly the same as the 1st) into the chamber.
I have never used a full radius seat on anything because it leaves a point contact sealing surface that lasts about 1 race on the track and 1 week on the street, it's just bad engineering unless it's a cost is no object project. Whether or not the flat helps with fuel managment, I honestly don't know, it appears it does, I use it to get normal valve seat life.

In the photo, the valves are definately sunk down into the head and the cumbustion chamber cut to unshroud them on the sides, it looks just like every head I've been invloved with for the past 10-12 years. The exhaust valves are more proud than the intakes simply because the valve is thicker at the edges, which both improves flow and valve life.

 

A complete re-reading of this thread sure does bring into focus some of the many problems with the idea of an electromagnet driven valve system, as was discussed a week or two in the past.