Next step for my 350

It's not complicated. All cams have their lobe centers separated by a certain number of degrees. When there is an even split between intake and exhaust positions, the cam is considered to be 'straight up' with no advance or retard, at 0*.

When a cam has 'advance built into it', such as the Crower cams, the cam position will sit at 4* advance when 'lining up the dots', or setting it to "0*". Advancing it further adds to this, which is what I was talking about.

As was mentioned, if you use a degreeing wheel, this becomes a moot point, as the cam position will no longer be subject to being measured by the cam gear.

Symmetric lobes are pretty straightforward. When you get into asymmetric (depending on the type of asymmetry), it can get a bit more complicated.

The Federal Mogul CS647 cam, for example, sits at 3.25* advance @.050 and 1.75* retard @.006 when using the 'stock' cam gear, which is set to 'straight up' or '0*' advance/retard. There is NO advance/retard built into the gear. This is a common misconception with OEM timing gear sets, at least with Buick 350's. I got this information straight from the lead engineer from Melling.

The timing gear set is also synchronized with the camshaft, so there is no degreeing or guesswork involved in its installation, unlike the aftermarket cams.

You could, of course, use another timing gear set or use a degreeing wheel to set it up in different positions.


Gary

 

Absolutely right. When one realizes all the manufacturing processes involved, and even if tolerances are tight, it's mind boggling to consider how much dimensional stack-up there can be with all the different processes. Everything from the crankshaft keyway, the gear keyways and camshaft grind all have allowed tolerances. When the planets line up just right, things are close to nominal. The planets hardly ever line up "just right", though!

Devon

 

OK decided to stick with the 350, as if there was ever any doubt.

Ordered Auto tech pistons with same CD 1.85 as SP hypers and increased the dish to 16cc. SP hypers were 15.5cc. Also increasing the bore to 3.845 to get correct piston clearance. I think I will remove the combustion chamber lump also to drop a little compression. I did not make the chambers equal cc size before but will do it this time. Will reuse the big valve heads but will put the level 3 cam back in installed exactly as it was. My thinking is the big valves will help mid lift flow some but not really hurt the velocity at max lift since the throat area becomes the restriction around .400" lift.

 

Are all the new parts legal for the "stock" racing class? If not might as well port the flock out of the big valve heads and make that thing run 12s!



Derek

 

Refer to page #3 of this thread...


Gary

 

Steve, the 180-185 lbs. of cranking pressure still bugs me. It shouldn't be that high with 10.12:1 compression and your IVC point. Something was overlooked, either by you or I, in calculating the compression ratio. Either that or the online calculators are wrong, or our (or my) understanding of DCR vs octane requirement is flawed. Anything is possible. I just want to get it sorted for the record.

Anyone else have input on this?

As far as larger valves and lower lifts/flowing heads, I recall a thread that I either started or commented in, regarding this topic. It ended up being me stating that larger valves can benefit lower lifts, even stock, since it would help with increasing airflow while not hurting velocity, particularly with a wide lobe profile between .050 and .006, giving the valve more breathing room while the valves were partially open/near closing/opening.

Larger valves (or multiple valves) increase air volume exponentially within the valve curtain, requiring less lift to flow the same amount as smaller valves with higher lifts. This is a similar design with multi-valve modern engines with low lift overhead cams, if memory serves. Paul will certainly chime in on this to correct me or add more info if I'm wrong or leave anything out.

Partially open valves would also maintain or even increase velocity, which means the stock cam would benefit from massaging and larger valves, as long as there is sufficient swirl.

Essentially, instead of increasing cam/valve lift, increase the diameter of the valve itself while improving airflow quality (velocity, less turbulence). More power is achieved and the valvetrain lasts longer.

This would be especially beneficial to the Buick 350, which flows optimally at lower lifts anyway, making higher lift cams even less needed than with stock sized valves.


Gary

 

Engineers have observed that air cannot really flow through the intake at speeds exceeding 650 feet per second. This appears to be a critical speed at which it takes more power to shove air through the intake than you get by burning the air in the cylinder. For engines that burn very efficiently, the speed could be as high as 710 feet per second. an inefficient burning engine may have a critical intake speed of only 600 feet per second. An efficient burning engine would be a 4 valve per cylinder Cosworth Formula 1 engine. An example of an inefficient burning engine is a Ford Model T sidevalve engine. A maximum intake speed of 650 feet per second works very well for engine developing peak power between 4000 and 8500 rpm.

Now sit back and think about what you have just read because I will use it to explain the two most important concepts in engine design:


1.The faster you rev your engine, the more power you will make UNTIL the intake air speed reaches 650 feet per second.



2) The larger the intake valve, the faster you can rev your engine before the intake air speed reaches 650 feet per second.



The above two concepts lead to the most important conclusion:

YOUR ENGINE'S MAXIMUM POWER IS DETERMINED BY YOUR INTAKE VALVE AREA.







Yes, it is the engine with the biggest valves that wins the races, not the engine with the most cubic inches of displacement. A 180 cubic inch Formula 1 engine with 32 inches of intake valve area makes 720 horsepower and a 427 cubic inch racing Ford with only 28 inches of valve area can only make 600 horsepower. It is interesting to note that the Formula 1 engine has to spin at 13,500 rpm for maximum power and the Ford engine at only 6800 rpm for maximum power. This illustrates the following important concept:

Valve area determines total potential horsepower and displacement determines how fast your engine has to rev to produce maximum power.



Let me explain the above concept. Suppose we had a single cylinder engine with a valve area of one square inch, and at 5000 rpm the piston was moving air through the intake valve at 650 feet per second. If I rev the engine faster, I will not make any more power because it consumes too much power to shove the air through the valve faster that 650 feet per second. If I double the area of the piston, than air will be going through the intake valve at 650 feet per second at only 2500 rpm. If the intake valve remains equal, the bigger the piston the sooner the intake speed reaches 650 feet per second. The horsepower will remain the same with the small piston at 5000 rpm or with the big piston at 2500 rpm.



http://www.strokerengine.com/StrokedEngines.html

Really god read.



Derek

 

Relax, Derek. I defended you in another thread that got deleted recently, so I'm not your enemy here. I already know the things you are talking about. Essentially it's displacement moving through a specified area (intake runner, past the valve, etc.). Air flow is the name of the game, but not just the amount of it, but the quality of it. Whether you're talking about large cubes and small heads with low RPM, or small cubes large heads and high RPM, the engines WILL behave differently even if they make the same 'horsepower', and you won't get where you want to be if you mismatch parts within a particular combination, depending on your desired outcome/application.

Increased valve size can improve lower RPM engines too (comparing similar displacement), particularly with low lifts for both valve lift and head flow @lift, because velocity is retained while increasing volume. Similar principle behind the tall, narrow runner design (which many people do not understand, so it comes as no surprise this is being misunderstood).

You are suggesting increasing head flow in any way possible, yet still using the same combination. To benefit from this, one would have to match the other parts with the increased flow@lift in order to raise velocity back up, which means larger cam, headers, etc. which Steve won't be using. If he follows your advice with his combination, he WILL lose power because his engine's powerband and parts won't be sufficient to adequately use the heads.

Buick heads behave differently than Chevy heads, and so must be treated differently, particularly for milder combinations such as this. When 99% of your flow happens below .400 lift, you must match parts and build accordingly.


Gary

 

Gary calm down, I was just pointing out a cool article about valve size and how it relates to making HP. I wasn't trying to go against your info, I was just trying to add to it. And Gary, I am never your enemy anywhere. Nowhere was I trying to say to increase the lift like a sbc, I get it the sbb heads are low lift flowing heads. Did you read the info in the link?

I was only suggesting porting his heads if he couldn't run in the stock class anymore because of the AutoTec pistons then maybe the level 4 cam might work better with some headers because if he can't run in the stock class he can install headers.

And thanks for defending me in the other thread, you were right I only wish the best for Mark.



Derek

 

All's well.

I did check out the link, and I concur: very good read and source of information.


Gary

 

Valve curtain area is Valve Diameter x PI x Valve lift which is linear not exponential. I suspect you where thinking valve area.

It doesn't calculate for me either especially with the cam retarded by 2 degrees.
That puts the DCR at 7.3

As far as 650 ft/sec in curved manifold runners and intake ports, not happening. Wet flow support at velocities much above 350 ft/sec also not happening.
Horsepower potential determined by valve size is a simplistic view.

Here is a more complete picture.
As you read through this article keep in mind that the Buick heads falls under the worst case of nearly flat (or vertical) valve angle with a low intake port.
This is largely because (IMO) the Buick block is too high causing low induction locations for the sake of hood clearance.

http://www.superchevy.com/how-to/engines-drivetrain/1005chp-cylinder-head-design/

Some of this co-insides with Gary's comments about matching components and setup.

Paul

 

When you say it does not calculate do you mean it does not make sense the damage was caused by detonation or are you thinking something else? The numbers did calculate to a value correct? Was this value to be considered a 93 octane safe number? Also it should be noted it was a rural gas station I got the fuel from, maybe it was not 93 as advertised.
This weekend I will CC each individual chamber and determine if #3 had a smaller chamber than the others.
There was no other damage or indication of detonation in any other cylinder. Other than the slight polished spot on the upper bearing halve.

Too help refine the calculation here are the actual numbers:
compression taken with all plugs removed and throttle blades closed.
1. 195
2.185
3.37
4.165
5.175
6.185
7.177
8.190

Cam events:
Intake open; spec 5.0 BTDC actual 3.5
Intake closed; spec 41.0 ABDC actual 43.5
Exhaust open; spec 53.0 BBDC actual 51.5
Exhaust closed; spec 1.0 ATDC actual 3.5

Maybe the mistake I made was not trying to equalize the chamber size and #3 was even higher than the others.

 

So the numbers mayhave even been higher if it was done w throttle open as is usually done

 

Thanks for posting the actual cam timing specs. That clears up the misunderstanding.
When you said the cam was degreed 2 degrees retarded we took it to mean 2 degrees from straight up which puts the intake lobe center at 114 degrees ATDC.
What you meant was 2 degrees from the spec on your cam card which puts it at 110 degrees ATDC.

At 114 degrees ATDC the DCR is 7.3 which equates to far less that 180 psi cranking pressure.
That's what we meant by not equating.

At 110 degrees ATDC the DCR is 7.6 which yields a higher cranking compression but 180 psi to 195 psi is still too high for a DCR of 7.6.

The only other reason for the high cranking pressure is some of the lifters have lost oil and the plungers are sitting low in the lifter.

180 psi is about the limit for pump gas.

 

Thanks for clearing that up Paul. My semantics can be a bit off sometimes, since I do this all from memory, and I can get a bit absent-minded from time to time... :laugh:

The calculations are WAY off for the specs given compared to the cranking pressure, and as I said before, comes out to around 11.5+:1 SCR with a ~70*ish IVC, and that was with 180-185 lbs. We now see that some are 195+, which screams detonation in my mind... and also explains why some pistons were affected and not others (one to the point of destruction), since the compression figures range ~25-30+ lbs. between cylinders. Imagine...if Steve's engine ran so well like this, how well it would have ran 'blueprinted'!!

This is actually a testament as to how durable those hypers really are. They stood up to incredible punishment.

So it turns out that my suspicions about cam installation were correct afterall...

It's good to get these things ironed out for clarity so the record isn't tainted with misunderstandings and disinformation.


Gary

 

Gary

You have seen me do the same thing when I'm in a hurry trying to do several things at one time.
I've gone back and re-read my post, "What in the world was I thinking" then doing a fast edit hoping no one has read the stuff yet.

Concerning cranking compression, you missed the part about some of the lifters being without oil and allowing the plungers to bottom out, the ones that have been sitting with open valves.
That will shorten the duration and cause the cranking pressure readings to be high and all over the place depending on how far down the plunger is in the lifter body on various lifters.
The 165 reading is probably the only correct one.

Paul

 

lol, glad I'm not the only one who does this. ou:


And yes, I did overlook the part about the lifters.

As I said, it's good to get this ironed out for clarity. Good to see we're looking out for each other. :TU:

Even with 165 psi, that's still 10.8:1 SCR @70* IVC, and sits at around 8.25:1 DCR. Could be doable with polished combustion chambers and ideal/near perfect quench...but 8:1 is about the limit for this combustion chamber type, even with ideal conditions. On 93 octane, that is.

For 10.12:1 SCR and his IVC point, he should have been sitting on near ideal DCR of 7.73:1 which comes to 152 PSI. In case I've made a mistake, I'm getting this from the Crower level 4 cam's IVC point of 68* when sitting 'straight up' in the timing gear (with 4* advance 'built in'), retarded 2* for 70* IVC.

We also know that using the timing gear can be *less* than 100% accurate...but Steve said he used a degreeing wheel.

I just thought of something else...Steve gave .050 valve timing events...I don't suppose something was overlooked with this, as the figures I give are supposed to be at .006. He set things up @.050 so maybe the other figures weren't measured or just guessed at?

Just trying to toss out some ideas.


Gary

 

Hmm.

I punched in Steve's timing events @.050 into a wallace calculator and came up with this:

Your cam has an Overlap of 6.00 degrees
Intake Duration of 226.00 degrees.
The Exhaust Duration is 234.00 degrees.
The Inlet Cam has an Installed Centerline of 108.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 116.00 degrees BTDC.

It's installed @ 108, which means it is 'straight up' in the timing gear, or 4* advanced.

This would put DCR even higher at about 7.87:1 and 156 PSI, still less than 165.


Gary


Then my silly self notices it's 1.5* offset from that, so no deal on that idea. Another ou: on my part.

Your cam has an Overlap of 7.00 degrees
Intake Duration of 227.00 degrees.
The Exhaust Duration is 235.00 degrees.
The Inlet Cam has an Installed Centerline of 110.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 114.00 degrees BTDC

But still doesn't compute, as here are the specs again with 1.5* as Steve lists.

 

165 was just a guestamation. The problem is how to get an accurate cranking pressure reading with hydraulic lifters that have bled down?

I see you are not taking any chances on errors and using an off line editor like Word and pasting it here. LOL

Paul