We have just added a new camshaft profile to those we already offer for the 32v 928 here: http://www.928motorsports.com/parts/camshafts.php

We did a straight-up comparison to our previous most powerful camshaft grind, the 928MS 32vR3. Using the same engine, car, fuel and boost (12.5 lbs) - no other changes were made. Only the intake camshaft was changed.

I always felt that the valve overlap of our 32vR3 camshaft might be too agressive for a boosted engine, and so we set ourselves to develop a "big dog" camshaft just for boosted engines, the new 32vR4.

Compared to the R3, the new R4 cam has less lift, longer duration, and we took out 7 degrees of valve overlap.

The engine is much happier with this grind. It starts faster, idles better, and has a very linear power curve making for non-stop push-you-back-in-your-seat acceleration. Its a joy to drive - good power everywhere.

As the comparison chart below shows - if bottom and mid-range were your goal, and if you were naturally aspirated - the R3 cam might still be the right choice. We are recommending the new R4 grind for boosted cars, or those who want more power up top.

Complete details here:
http://www.928motorsports.com/parts/camshafts.php

 

Is there an R3 N/A dyno sheet?

 

Looks to me like the R4 cams loose a bunch of HP and TQ all the way up to 6,000RPM, where they begin to provide an improvement. From ~3,500RPM to ~5,500RPM, it's like a consistent 100rwhp loss! Seeing that, I would probably go with a set of R3's with a stock redline... and I think with a stock redline, the R3 cams would be faster because you would be putting down more HP to the ground on average...

Dan
'91 928GT S/C 475hp/460lb.ft

 

Carl,

Could you please answer some information.
Your site lists
928MS 32vR3 .442" / 222 deg .398" / 216 deg
928MS 32vR4 .412" / 217 deg .398" / 216 deg

How does the R4 have longer duration?

And if using S4 cores for your welded camshafts then you have 6 deg of overlap for your R3, and your R4 has an overlap of 3.50 deg.
Or if using GT cores, you have -1 deg on the R3, and -3.5 deg of overlap.
So how do you calculate your listed 7 deg of valve overlap reduction?

My stage II runs (@.050") .437" lift/230 duration and .437" lift/228 duration and this uses a LSA of 114 deg. This means that I run only 1 deg of overlap.

As to your dyno charts, it really looks like you got R3 and R4 reversed. Or didnt have the R3s correctly timed. More overlap = better top end due to proper evacuation. Less overlap, better idle, and bottom end.

Is there any chance that you could inform clients as to what the LSA is, and for your charts what you are running the camshafts at (advance/retard)?

 

Interesting.......a classic trade off of high vs low RPM performance.....given your bonneville goals, clearly this will work better.....however I would run the R3's for road racing......look at the averages....the R3 has far more average HP and torque in the typical RPM band......the R4 is much peakier R4 sure gains up high and has room to gain even more with more RPM......but at normal shift points of say 4500rpm it will get KILLED off corners vs the R3.....I doubt its stronger top end will make up for its much weaker midrange.....midrange torque really is the strength of race 928's....(don't tell Kibort).....I have seen SO many high $$$ racers with huge dyno numbers get walked by MK right off corners.....he instantly pulls a couple cars.....then it takes the whole .4 mile straight to maybe get even with him......even though they are 550whp vs 370whp....

 

Colin,

We gained duration by changing the profile of the ramps. In brief, they are more rounded than straight. So they open sooner, faster.

The base circle was also modified.

Both the R3 and the R4 cams were set to 2 degrees retarded in these tests.

The cam grind is proprietary, so I cannot provide depth of detail on how we achieved this. As you know, it costs a lot of time and money to develop a new cam. I cant just give all the knowledge away on this one.

 

Pretty much. Below 5400 rpm the R3 cams pull harder, above 5400, the R4 cams are king. We stopped the dyno runs at 6800 and as you can see the R4 cams were just still climbing and had not yet peaked. It'd be interesting to see how far they will go.... I will find that out after Bonneville.

 

Carl,

I'm not asking you to give away information, just clarify information for potential customers. Thank you for answering what camshaft timing you are running. Can I also assume that these 2 degrees of retard are CAD (Crank Angle Degrees)?

What LSA are the camshafts ground at?
What LCA are the camshafts ground at?
For both of those, if you just let us know what cores you had welded and ground we can get that information easily, unless these have been modified by your grinder. Though this is something that should imho be posted on your site.

Also your statement about making the lobe rounder vs straight changes the ramp rates (and too high of a ramp rate can be very dangerous for life of cam). And yes effects the duration, but that should show up on your site still, you list R3 @ 222 duration, and R4 at 217. Your numbers appear to be measured at .050" but this is not clarified, are these numbers at .050"?
So what you are saying is that your R3 would have 222 duration @.050" then 200 duration say at .100" lift, and 100 duration @.250"
But your R4 would have 217 duration @.050" then 202 duration @ .100" lift, and 150 duration @.250".
This is fine and I understand this. However this is not where overlap is measured.
My question is to confirm where you have managed to pull 7 deg of overlap from. My numbers still stand, if running a S4 camshaft core, you have only removed 2.5 deg of overlap, if running a GT core, you have removed 2.5 deg of overlap for an even further increased number.

The only way that I could see you saying that you pulled 7 deg of overlap is if you were talking absolute numbers from the MOMENT the lifter starts to move (industry standard is always measured @.050" lift, and for EU .040" or 1mm lift. ). But even then, these numbers would be tough to line up.

So if you could answer, how you managed to remove 7 deg of overlap as your numbers currently posted do not reflect this.
What is your LSA?
What is the LCA? (less important but still good to know)

None of these questions are giving away ANY proprietary information.

 

I am assuming the new one makes more power . I am not sure which chart is which, since hp=red and Tq=blue

 

Just go up to the chart above that one and you can see the R4 cams HP and Torque curves all by themselves.

I will make the notation on the comparison chart more clear - thanks for the catch.

 

I do not have a dyno sheet for the R3 cams in a NA motor, sorry. It just hasn't come up yet.

 

Those are definitely application-specific cams. Averages about 50 hp/80ft-lbs torque lost from 3000-5500 rpm over the R3's and no hp/tq advantage until 6000. That is the "meat in the sandwich" for track and street cars. Would be good for Bonneville or drag racing with a tight ratio gear box.

 

I agree.

That's the beauty of having several to chose from.

 

Carl:

Just when I think I've got a pretty good "handle" on what makes engines work, something like this comes along and I get completely lost. How can cams that make 100 less horsepower and less torque, everywhere below 5,200 rpms have "very linear power curve making for non-stop push-you-back-in-your-seat acceleration" over the cams that have higher torque and horsepower?

To me, this is like saying: "I had two inches removed from my ***** and now it is longer."

Help me understand.

 

No problem, Greg. Let me see if I can help you understand.

The R3 camshafts have more mid-range on my supercharged motor, as shown. But, also as shown, the HP peaked and started to fall off at 6000 rpm. They would be a better choice for a road racer with gearing to concentrate in the 4500 to 6000 rpm band. I certainly have enjoyed road racing with them this season!

However, for my upcoming Bonneville event, I need the peak HP to be at peak RPM. The most important power band for me at this event is 5800 rpm and up. So, the R4 camshafts are a better fit for the application.

Now lets look at the Torque curve. The R3 cams present their peak torque from 4200 to 5400 rpm, and that's pretty good. But the torque curve of the R4 cams is even broader and more linear from 4200 to 6200 rpm. Because you don't race, you might not understand the value of a near constant power band.

Race engines with peaky power bands are harder to drive, because the power will come in suddenly when the engine hits its peak, and should that happen in a corner, it can cause a spin and a shunt. But engines with a long, constant power curve are easier to drive - you can throttle-on through a corner and know that the rise in torque is constant with the increase in RPM - there are no surprises.

Anybody who has raced a turbo can tell you how challenging it can be if the turbo happens to come in mid corner! Not fun. So, for the average driver (read ME) a flatter torque band is more predictable and easier to drive.

In conclusion - its not that one camshaft is "better" than another. It depends on the application, and one camshaft may be more appropriate for the task at hand than another.

By creating a new camshaft grind all I have done is increased the choices available to the 928 owner.