PorKen

I just recieved some 79 cams to upgrade the lackluster cams in my US 81:



These will hopefully push me over the 200RWHP barrier:



The 11/10 degrees extra duration should allow me more latitude in cam timing too.
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Anyhu, I checked in the WSM to verify the numbers stamped on the end of the cam, and it shows the numbers for 78-79 US and ROW as 928.105.155.07 and 156.07.

Mine are stamped 155.06 and 156.06?

Anyone notice the numbers stamped on their early cams?

toofast928

Hi Porken, Sorry I can't be any help but I'm behind you all the way. Are you running the Euro throttle body? Gave me a noticeable increase in midrange and high RPM.

Tony

Old & New

The 07's are an updated part / part number, according to the PET.

Certainly worth a shot, but did you have no luck obtaining 80- Euro cams?

PorKen

toofast928,

No euro parts, yet. I'll see how the cams do.

Eventually I have to pull the engine or at least the heads, to replace the exhaust studs, so I can put headers on!
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Old & New,

Thanks for checking. It might be something like the woodruff key, which, according to the WSM, changes sometime in 79 to a parallel key.

I haven't really tried to find euro cams, and I couldn't pass these up for the price. There is not as much as lift as the euro cams (safer?), but they have more duration.

I needed to change my leaky cam tower gaskets anyways, so I thought it would be a good time to swap.
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I guess a tangental question would be: which is better, lift or duration, or when is one better?

toofast928

Should have the lifters face polished by a machine shop so the you don't increase cam lobe wear or lifter wear

Old & New

Ken,

A quick search yielded:

http://www.auto-ware.com/combust_bytes/camspecs.html

-and-

"Longer duration improves top-end power but almost always sacrifices low-end torque. Lower duration improves low-end torque and makes the car idle better, but it limits top-end power, and you can get only so much valve lift with a short duration cam due to the rate-of-lift limitations of the lifter."

So, more of both are "better", to the point of affecting idle, drivability, emissions and component longevity.

PorKen

toofast928,

Good idea, I'll check into that. I was wondering how to deal with different used cam/follower combos.
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Old & New,

I did some web searching too, and found similar info.

Here's another quote from googling for "CIS cam duration" (here): "In simple terms, a camshaft's lift determines how far the valve rises from its valve seat. The lift has a dramatic effect on low R.P.M. performance, but has a lesser effect at higher R.P.M.s.

Duration is also important. If you looked at a long duration you would notice that it is wide and blunt. This enables the valve to stay open for a longer time or duration. Duration has the opposite effect of lift. The longer the duration, the more the R.P.M. horsepower will be boosted. However, it is at the expense of lower R.P.M. horsepower."

Other bits I gleened about longer duration:
*Increases performance with small valves
*Reduces effective compression
*Lowers manifold vacuum

And lift:
*Big valves need more lift to unshroud them

What I finally understand is: longer duration moves the torque peak higher, which makes more horsepower because you have more work (TQ) done more often (revs).

Since I'm a torque fiend, I should be able to advance the cam more, and still have more power on top than I do now.

Dennis Wilson

There is one other part of the cam equation I've never gotten a fix on and that is overlap. Could someone chime in and explain how it affects torque, HP or driveability?

Thanks,

Dennis

PorKen

I get different values than the spreadsheet above for exhaust duration, plugging in WSM specs into an (online calculator):

78-79 US (ROW) M28-3/4 (1/2), HP219@5250/TQ245@3600 (HP229/TQ250)
Stamped: 155.07/156.07
Intake opens: (-8) BBDC, closes: 55 ABDC, duration: 227, centerline: 121.5 ATDC, advanced: 6.75
Exhaust opens: 38 BBDC, closes: 2 BTDC, duration 220, centerline: 108 BTDC
Overlap: (-6), separation: 114.75 {extremely wide}

80-82 US (ROW not S) M28-13/14/15/16 (09/10), HP220@5500/TQ256@4000 (HP229/TQ271)
Stamped: 173.01/174.01
Intake opens: (-12) BBDC, closes: 48 ABDC, duration: 216, centerline: 120 ATDC, advanced: 8.5
Exhaust opens: 32 BBDC, closes: 6 BTDC, duration 218, centerline: 103 BTDC
Overlap: (-6), separation: 111.5 {moderately wide}

80-83 ROW S M28-11/12, HP300/TQ263
Stamped: 187.03/188.03
Intake opens: (-9) BBDC, closes: 52 ABDC, duration: 223, centerline: 120.5 ATDC, advanced: 6.5
Exhaust opens: 37 BBDC, closes: 2 BTDC, duration 219, centerline: 107.5 BTDC
Overlap: (-7), separation: 114 {wide}

83-84 US S M28-19/20, HP234@5250/TQ263@4000
Stamped: 203.00/204.00
Intake opens: (-11) BBDC, closes: 46 ABDC, duration: 215, centerline: 118.5 ATDC, advanced: 8.5
Exhaust opens: 25 BBDC, closes: 2 BTDC, duration 207, centerline: 101.5 BTDC
Overlap: (-9), separation: 110 {moderate}

84-86 ROW S M28-21/22, HP310/TQ295
Stamped: 211.00/212.00
Intake opens: (-6) BBDC, closes: 54 ABDC, duration: 228, centerline: 120 ATDC, advanced: 10.5
Exhaust opens: 43 BBDC, closes: 4 BTDC, duration 227, centerline: 109.5 BTDC
Overlap: (-2), separation: 109.5 {moderate}

(See below for an explanation of what separation and advance do.)
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Dennis Wilson,

Overlap is where the intake and exhaust valves are open at the same time. At the right engine speeds the exhaust gases exiting the cylinder will help pull the intake charge in and the exhaust valve will close in time so that fuel/air will not continue out the exhaust. At other times exhaust gases are left over in the cylinder, or the mixture is wasted out the exhaust.

High overlap can cause reversion pulses back down the intake, which most fuel systems don't like, eg. MAFs see twice as much flow, one out, and one in.

In order to run a large amount of overlap, you need to use individual throttle bodies!

As you can see above, the 928 cams have no overlap.

Dennis Wilson

Knew what overlap was, but wondering why? Guess it is just the result of longer duration cam lobes. Brings back memories of Duntoff (sp?) cams and 57 Chebbies.

Dennis

PorKen

It's not so much duration, but how much lobe separation (10) which determines the amount of overlap.

The closer the intake and exhaust noses are, the smaller the amount of separation, and the more power can be made.

Even the euro 84-86 cams are not very aggressive at 109.5 degrees.
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1. Max Lift or Nose
2. Flank
3. Opening Clearance Ramp
4. Closing Clearance Ramp
5. Base Circle
6. Exhaust Opening Timing Figure
7. Exhaust Closing Timing Figure
8. Intake Opening Timing Figure
9. Intake Closing Timing Figure
10. Intake to Exhaust Lobe Separation
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Lobe Separation Angle
Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight

Tighten
Moves Torque to Lower RPM
Increases Maximum Torque
Narrow Powerband
Builds Higher Cylinder Pressure
Increase Chance of Engine Knock
Increase Cranking Compression
Increase Efective Compression
Idle Vacuum is Reduced
Idle Quality Suffers
Open Valve-Overlap Increases
Closed Valve-Overlap Increases
Natural EGR Effect Increases*
Decreases Piston-to-Valve Clearance

Widen
Raise Torque to Higher RPM
Reduces Maximum Torque
Broadens Power Band
Reduce Maximum Cylinder Pressure
Decrease Chance of Engine Knock
Decrease Cranking Compression
Decrease Efective Compression
Idle Vacuum is Increased
Idle Quality Improves
Open Valve-Overlap Decreases
Closed Valve-Overlap Decreases
Natural EGR Effect is Reduced*
Increases Piston-to-Valve Clearance

*Some exhaust gas is left in the cylinder after the exhaust stroke.
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Effect of Cam Advance/Retard

Advance
Begins Intake Event Sooner
Open Intake Valve Sooner
Builds More Low-End Torque
Decrease Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance

Retard
Delays Intake Event Closes Later
Keeps Intake Valve Open Later
Builds More High-End Power
Increase Piston-Intake Valve Clearance
Decrease Piston-Exhaust Valve Clearance

Dennis Wilson

Thanks Porken. Reason I asked was that I noticed an overlap on my 931 when I removed the head last weekend. Hadn't noticed it befpre on my 924 NA. Turns out that the (false) overlap was due to bent valves in #2 and 3 cylinders. Still puzzling over how it happened since the timing belt hadn't slipped or broken. No marks on piston and the motor drove OK (down on power) as long as I kept it out of boost.

Dennis

heinrich

Here we go. 85/86 Euro S cams (like the ones I have for sale) are the most aggressive.

JP Rodkey

Just wanted to add that I replaced my tired '79 Euro 4.5L (original M28.01) with an '84 4.7L - but put the '79 cams in the later engine. The car idles and runs great. MUCH peppier and noticeably more power.

mark kibort

Longer duration on the 928s didnt really change the torque or HP curve much. It did shift the torque curve up a little, but the real change was that we got the same peak torque, at near the same rpm, but the hp was flatter and there was more of it and it went out farther.

I have a set of dyno runs for the 84 stock, euro intake with cams and then 5 liter upgrade. no downside for the cams and intake all shown on one dyno sheet.

mk