Camshaft Overlap@.050" vs Idle Quality

[Procharged 434]

Ok guys, just for conversation purposes here, what effect does the .050" overlap have on Idle quality and manners for a street engine, in any particular combination? For the example we will use a 467 c.i. Pontiac stroker, which uses a 4.181" bore, 4.250" Stroke, and 6.800" rod. Compression is 9.4-1, running headers, stock 6X-4 heads, and is a 100% Street engine that uses 91 octane pump fuel with a 2.62 low gear Super T-10 4-speed manual trans and 3.23 gears in a full factory weight 1979 Trans Am at 3800 lbs. Both cams are hydraulic flat tappets, and both use factory 1.5 rocker.

Camshaft 1.) Crower 60919.... 285/294(actual measured at .006"), 231/240 dur@.050", 112° Lobe Separation

Camshaft 2.) Lunati VooDoo 10510704.... 281/289@.006", 233/241@.050", 110° Lobe Separation

____Overlap at .006" Lift_______

Camshaft 1.) 65.50°
Camshaft 2.) 65.00°

_____Overlap at .050"______

Camshaft 1.) 11.50°
Camshaft 2.) 17.00°

As you can see, both camshafts have similar Overlap when calculated at .006" lift, but the two are very different when calculated at .050" lift. Will Camshaft 2 have a Lumpier idle than Camshaft 1, due to the 5.5° more of Overlap at .050", even though they are similar comparing them at .006"? Will Camshaft 2 have worse street manners than Camshaft 1 due to the increased. 050" overlap? Is 17° considered a lot of Overlap at .050" for a 467 cubic inch street engine? Does .050" Overlap even have anything to do with any of this?

Thanks!

[tjs44]

In my building of pontiac street engines I would take the 112 cam for sure.Tom

[ptuomov]

I don’t know the answer to any of these questions, but I do have two thoughts or really further questions: First, for idle rpm (and throttle cracked cruise rpm) engine operating conditions, is it the seat overlap or the overlap at 0.05” that better predicts idle quality? Second, is the answer to the idle quality question very different with EFI ITB stacks vs. dual plane 180-degree carbureted manifold vs. short big runner single plane carb manifold?

[Geoff2]

I wouldn't use either of those cams. Contrary to popular belief, Pontiac factory heads do NOT have poor flowing exh ports, quite the opposite.
I would use a single pattern cam.
Go the Isky cams website, Tech info: Is extra duration really necessary.

[pastry_chef]

Is 17° considered a lot of Overlap at .050" for a 467 cubic inch street engine? Does .050" Overlap even have anything to do with any of this?

No, the shelf Voodoo 704 is very streetable in a 455.

Outside of overlap, I'd prefer the Voodoo lobes over the Crower.
I've seen duration @ .200 of 140 for the Crower and 146 for the Harold designed Voodoo. The difference at .300 will probably be larger.

[Procharged 434]

Is 17° considered a lot of Overlap at .050" for a 467 cubic inch street engine? Does .050" Overlap even have anything to do with any of this?

No, the shelf Voodoo 704 is very streetable in a 455.

Outside of overlap, I'd prefer the Voodoo lobes over the Crower.
I've seen duration @ .200 of 140 for the Crower and 146 for the Harold designed Voodoo. The difference at .300 will probably be larger.

Cool, what about Idle and drivability comparison between the 60919 and the 704? Will the 704 Idle be more tame, even though it's on the 110 Separation, due to its shorter .006" duration, or will the Idle and drivability be similar between the two? I've heard a couple 60204 Voodoo, which is the BBC version of the Pontiac 704, basically same specs, except it has a little more lift, and it sounds like it has a fairly radical Idle in the 9.5-1 454 BBC I've heard. I know the stroke makes a difference, being the BBC has less stroke than the 4.25" stroke pontiac example I used here, so maybe that is some of the reason, even though they are similar in cubic inch?

[skinny z]

I'm going to venture a guess and say that with similar seat to seat overlap values, then idle characteristics are likely to be equally similar.
How the two cams perform with respect to other aspects of performance, that is obviously open to debate.

I suppose it should also be mentioned that both cams are installed on the same ICL.

[novadude]

Does a few more deg overlap @ 0.050" have more of a negative effect on idle quality in an engine with 30 deg seats (like some Pontiacs)? I'm just thinking of total low-lift flow area at the valve, and wondering if that has a significant effect (I would think it would?).

[panic]

Vizard suggests that the overlap "window" (interval - OL nominal degrees, height = OL max lift) effect is roughly proportionate to the square of the degrees of shared timing (IVO BTDC + EVC ATDC).
For comparo, the effects of different OL (in "dimensionless units"):
30°: 9
45°: 20
60°: 36
75°: 56
90°: 81

15° difference is significant...

[pastry_chef]

Cool, what about Idle and drivability comparison between the 60919 and the 704? Will the 704 Idle be more tame, even though it's on the 110 Separation, due to its shorter .006" duration, or will the Idle and drivability be similar between the two? I've heard a couple 60204 Voodoo, which is the BBC version of the Pontiac 704, basically same specs, except it has a little more lift, and it sounds like it has a fairly radical Idle in the 9.5-1 454 BBC I've heard. I know the stroke makes a difference, being the BBC has less stroke than the 4.25" stroke pontiac example I used here, so maybe that is some of the reason, even though they are similar in cubic inch?

Using the shelf cams, the Crower will have smoother idle.

If you don't mind the sound of Rhoads lifters and setting them with a feeler gauge you may consider Rhoads V-Max to smooth the low end.
https://www.rhoadslifters.com/Pages/VFlatTappet.html

Another option would be to have the Voodoo ground on a wider LSA if you want.

[skinny z]

Using the shelf cams, the Crower will have smoother idle.

Given the same seat to seat duration and overlap and assuming they are installed on the same ICL, what would lead you to this conclusion? Would the difference in duration at .050" have that much of an impact?

[Procharged 434]

Cool, what about Idle and drivability comparison between the 60919 and the 704? Will the 704 Idle be more tame, even though it's on the 110 Separation, due to its shorter .006" duration, or will the Idle and drivability be similar between the two? I've heard a couple 60204 Voodoo, which is the BBC version of the Pontiac 704, basically same specs, except it has a little more lift, and it sounds like it has a fairly radical Idle in the 9.5-1 454 BBC I've heard. I know the stroke makes a difference, being the BBC has less stroke than the 4.25" stroke pontiac example I used here, so maybe that is some of the reason, even though they are similar in cubic inch?

Using the shelf cams, the Crower will have smoother idle.

If you don't mind the sound of Rhoads lifters and setting them with a feeler gauge you may consider Rhoads V-Max to smooth the low end.
https://www.rhoadslifters.com/Pages/VFlatTappet.html

Another option would be to have the Voodoo ground on a wider LSA if you want.

Thanks! Am I correct in thinking that the Pontiac 467 would idle tamer than the 454 BBC with that 60204(basically same camshaft as 704), due to the Pontiac having a 4.25" stroke vs the 4.00" stroke of the 454? How much will a 1/4" more stroke tend to tame the camshaft?

[pastry_chef]

Would the difference in duration at .050" have that much of an impact?

It seems so.
I've heard both cams idle, Crower is for sure smoother.

[pastry_chef]

Thanks! Am I correct in thinking that the Pontiac 467 would idle tamer than the 454 BBC with that 60204(basically same camshaft as 704), due to the Pontiac having a 4.25" stroke vs the 4.00" stroke of the 454? How much will a 1/4" more stroke tend to tame the camshaft?

I think more may come into play there, maybe valve sizes as well.
Hard to compare.

[Procharged 434]

Thanks! Am I correct in thinking that the Pontiac 467 would idle tamer than the 454 BBC with that 60204(basically same camshaft as 704), due to the Pontiac having a 4.25" stroke vs the 4.00" stroke of the 454? How much will a 1/4" more stroke tend to tame the camshaft?

I think more may come into play there, maybe valve sizes as well.
Hard to compare.

Again, thank you. Your first post above, you said the 704 is very streetable in a 455, so even though it may have a little more sound at idle than the Crower, it will still provide plenty of vacuum for power brakes in a daily driver, and make plenty of low end power, especially with a 4spd manual trans? I think I had seen Paul Carter, a very well respected pontiac builder, say that the 704 camshaft was very explosive when you step on the throttle in the 455-467 Pontiacs, and he actually seemed to think the Idle of the 704 wasn't all that radical at all, but I know that depends on the person, some people's "radical", isn't bad at all to someone else.