[Formulajones]

It's not uncommon. If chain/gear wear occurs the cam retards.

Did you check it during the first install, or are you just now checking the first cam as it's coming out?

I ask because sometimes parts aren't made exactly. You can have a cam gear or crank gear that isn't machined exactly to spec with a keyway not quite where it should be, or possibly a keyway on the cam or crankshaft that isn't exact. Any number of these things will throw off the ICL which is why they should always be degreed. So it could be a case of the timing chain is in perfect working order, it's just that one or more of the scenarios mentioned might not be to spec to begin with.

[Steve C.]

A fwiw, Lee Atkinson later replaced the 288/296 Ultradyne hydraulic flat tappet cam. It was replaced with a Ultradyne solid flat tappet cam that was a single pattern 280/280 at .020, 247/247 at .050 and like the previous HFT it was also ground with a 108 lobe separation. I believe he picked up about 2-tenths and about 4 mph with the change. He reported no big change in driveability despite the 16 degrees additional duration and before he sold the car it was running low 11's at about 119 mph. Harold Brookshire often suggested Pontiac cams with a 108 lobe separation.



.

[Formulajones]

16 degrees additional duration on the solid would make that very similar to the hydraulic it replaced when you figure the lost duration when lash is figured in. So similar drivability isn't surprising. That's actually a good comparison between a solid and hydraulic and what a solid brings to the table.

[Steve C.]

Yes, excellent point.


.

[jimmy daniel]

I’m going to side with Cliff on his theory simply because he’s done soooo many!! He’s not guessing!

[Steve C.]

Within a discussion of whiz bang bug zapper ignition....

"Advancing the cam 2 degrees helped 2 tenths (.20) of a second, for less than ten bucks! I’d like to buy a couple seconds at that price"
John Mino
Pontiac record holder

Within a reply to John.....

"Changing cam timing by advancing (or retarding) the cam can provide some increase in performance as evidenced by John’s experience. In general, the larger displacement engines do not respond as well to cam advance due to their already abundant low RPM torque. Also, many aftermarket cams are ground advanced, and they may not favorably respond to further advancing."

"However, engine configuration, vehicle weight, actual cam timing, gearing, converter type, etc., all have an effect on cam operation, so shifting the timing of your cam may be beneficial. You must have a repeatable baseline of performance before trying this change so the cam timing effects can be accurately compared."

Jim Hand
http://www.dapa.org/drag-racing-with...ader-feedback/

In short, it's all combination specific. And the blurb on the subject from Comp Cams is a general statement or concept obtained by inference from specific cases.




.

[GTO JONES]

I'm going to put something else out there on cams. What about the 4-7 swap, thought and theory. .

[Cliff R]

You must have a repeatable baseline of performance before trying this change so the cam timing effects can be accurately compared."

Something like the runs listed below, made 23 minutes apart on a "test and tune" Friday night at our local track:

R/T: .505 .514
60': 1.6230 1.6289
ET: 7.3169 7.3188
MPH: 94.35 94.36

So here in lies the problem for testing this sort of thing with a street driven car. Few, and I mean very few of these cars are set up for drag racing where they can hook solid and make repeatable runs. It took me nearly two years of racing pretty much every week (during the season) to nail down the suspension modifications and find the right tires to get my car to run that consistent.

Once I got the car to hook I started testing parts, which including moving the camshaft 4 times to see what effect it had on ET and MPH. Even then you can't get all that done on the same track on the same day, so you've got to average the runs you make and compare them to what the car typically would run in similar track and weather conditions. This leaves enough room for error that for sure some Troll or disgruntled Forum member with a bad attitude toward folks who are doing good with this stuff and trying to help out others jumps all over your posts with smart-ars comments like this:

"Cliffy,
Your results are misleading & bias so your worthless posts are dismissed.

As you know your time is better spent writing a book or serving tables."

Yes, that the reward you get for the all the hard work and willingness to share it with others in Public Forum.....FWIW......Cliff

[pastry_chef]

Originally Posted by Steve C.

In short, it's all combination specific.
.

x2

I'm sure we can all agree optimal intake valve open or close will fluctuate through the RPM range, within a given combination.
The ideal valve close at 3500 RPM won't be the same at 4700 RPM.

The same flux is true with the exhaust valve events.

The center of open and closing is the centerline.

Add (intake center + exhaust center) then divide by 2 = LSA.

[Cliff R]

+3 and we can use some "old" technology to bring modern variable valve timing into the equation by using Rhoads lifters and high ratio rocker arms.

To this day it surprises me that folks building these engines with flat cams don't take advantage of that scenario.

Most of the negative press on Rhoads comes from the associated noise when using them.

If you upgrade to the V-Max variety they added an internal steel shim/spacer to limit plunger travel and designed them as short travel "high performance" lifters. They also fast bleed off rates like standard Rhoads lifters. They are designed to be adjusted with the plungers bottomed out and lashed very precisely much like solid lifters.

Using a feeler gauge between the rocker and valve tip the installer/tuner then has very precise control of the leak down available to each valve. You can also control or limit the bleed-down available and associated noise that goes with it. Set at .030", for example they will make no more noise fully warmed up with the engine heat soaked and oil thinned out as a flat tappet solid cam set pretty close to the same specs. For less noise they could be set at .020" and even tighter if you want pretty much no noise at all. Of course you start to loose the bleed down and variable valve timing feature the closer you get to zero lash.

The end result when using Rhoads lifters/high ratio rocker arms is that you can produce power very similar to a well chosen hydraulic roller cam at much less cost. I did back to back dyno runs to verify this and found that investing $1000 in a HR set up with the same .050" specs as the flat cam being replaced only netted 3hp/4ft lbs torque improvement, and that was on a 468CID engine with 10.48 to 1 compression and 260cfm KRE aluminum "D" port heads........Cliff

[GTO JONES]

I know I'm going off the track a little but can someone explain the 4-7 swap and the advantage.

[pmd400]

Took the car out to break cam in today. After break in I set the timing back to where it was with the old cam, 12 deg initial plus an extra 22 mech. Spent a couple of minutes to set the idle. It now idles with 15” vac at 700rpm rather then 14”. The car is dead smooth when sitting at the stop lights, no chop to the idle. Can lug the engine a lot more now without bucking. Can easily cruise at 40mph in 5th gear at 1400rpm. So idle, off idle and cruise is a lot smoother now. Now as far as pinging goes. The old cam would ping from before 3000rpm. It continued to ping until I let my foot off. This cam seemed to ping at 3000rpm and was gone at 3250. I then ran it up to 4000rpm without issue. So it has definitely improved. Today was 90*F. I might back the timing back 2* and see how it responds

[ponyakr]

Originally Posted by GTO JONES

I know I'm going off the track a little but can someone explain the 4-7 swap and the advantage.

Apparently, very few Pontiac guys see it as a benefit. Since you never read much about it.

https://www.google.com/search?q=what...hrome&ie=UTF-8

The first I even thought about it was after seeing several Howards HR 4-7 swap cams listed on the Summit sight.

https://www.summitracing.com/search/...rder=Ascending

[Cliff R]

Tom Vaught (nearly as I can remember) put up some information on benefits based on crankshaft loading from the 4/7 swap deal.

Far as making power, I've done a few 455 builds with 4/7 swap camshafts and haven't seen any benefits far as making more power. In other words the dyno numbers were on par with previous engines with near identical CID, head flow, cam spec (without the 4/7 swap).

Same thing with the longer 6.8 rod stroker set-ups. We did two 455's back when the KRE heads first came out. One had Pontiac 4.21" stroke and 6.625" rods, the other 4.25 and 6.8" rods. CID was close, compression, same cam, heads, head flow, intake, headers, carb/distributor.

Both of those engines made dyno numbers so close to each other you couldn't really tell one from the other........Cliff

[pastry_chef]

Originally Posted by pmd400

This cam seemed to ping at 3000rpm and was gone at 3250.

For some reason this 9.5 compression 455 with 288 @ .006 is more sensitive than normal.

I've seen a few use the 4/7, 2/3 swap but not compare back to back.

Here is a comment from Jim Butcher:

Originally Posted by 66bonne

Ditto. Tested a couple of cams for P-Dude. Exact same specs but one had the 4-7 swap. What a difference with the swap !! Much smoother idle and the revs are crisper. Love it.
Jim

The dyno man at Hendrick Motorsports says little improvement on a mild build but the 4/7 will accelerate better.

[Formulajones]

Dad is curious. Just did a cam swap for him and the new stick with Harold lobes is a 4-7 swap.

Many years back we used a friend/machine shop that tested back to back 4-7 swap on his 406 sbc roundy motor and stated he found no discernable difference on the dyno. But I've heard others say there is. Biggest benefit I've heard is crankshaft harmonic improvements so less transmitted to the valvetrain. Just swapping 2 cylinders around though has me questioning that. But interesting none the less.

To take that a step further, another engine builder local pushes the LS firing order swap telling me his dyno testing has shown as much as 20 HP improvement. Now we are talking changing the entire firing order where I could possibly believe there might be some sort of change there. But not many trying that either since the cam core is $1,000 so it's not cheap. We've found nearly 20 HP with just carb spacer changes so it's hard to justify that small gain spending $1,000, if it's really there.

[tom s]

Does the 4-7 swap get effected by properly clocked headers?Tom

[gtofreek]

Typically, the circle track guys like the 4/7 swap because when they come out of the corners and punch the throttle, they claim it doesn't try to blow the tires off as easy. On a dyno, they will make about the same power. The 4/7 swap can also help with main bearing life. Because of the size of this cam, the only core available that could handle the grind was this core with the 4/7 swap.

Tom, yes the firing order change can affect the way a tri-Y header works, but with 4 tube into 1 collector, it doesn't matter.

[Formulajones]

There ya go dad, straight from the man himself

Your cam is so big, it was only available in the 4-7 swap

That'll make him feel good, thanks Paul

[GTO JONES]

OK, less fire this thing up, push rods will be here tomorrow they say.

Thanks Paul.