78-79 cam part numbers? / 16V cam specs
I just recieved some 79 cams to upgrade the lackluster cams in my US 81:
https://members.rennlist.com/porken/79Cams.jpg These will hopefully push me over the 200RWHP barrier: https://members.rennlist.com/porken/16Vcamspecs.jpg The 11/10 degrees extra duration should allow me more latitude in cam timing too. ... 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? |
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 |
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? |
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! ... 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. ... I guess a tangental question would be: which is better, lift or duration, or when is one better? |
Should have the lifters face polished by a machine shop so the you don't increase cam lobe wear or lifter wear
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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. |
toofast928,
Good idea, I'll check into that. I was wondering how to deal with different used cam/follower combos. ... 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. |
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 |
My head hurts now...
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.) ... 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. |
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 |
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. ... https://members.rennlist.com/porken/camdiagram.gif 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 ... 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. ... 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 |
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 |
Here we go. 85/86 Euro S cams (like the ones I have for sale) are the most aggressive.
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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.
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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
Originally Posted by PorKen
toofast928,
\ 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. |
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