Open chat thread for Buick 350 Camshafts

Oddly enough.. Crower's turbomaster line of cams has less lift and less duration on the exhaust side for their entire line.. Granted, they are based on chevy stuff... The cam they custom made for me had a good bit less lift and duration on the exhaust side. But damn did it make more power than it should have ever made..

http://www.crower.com/index.php/catalogsearch/result/index/?cat=86&q=turbo&x=15&y=6

 

I've seen cams like that, and they're usually Chevy cams. If you have a really good flowing exhaust from the heads out, these cams work. More lift on intake, but more duration on exhaust. Buick isn't Chevy though. Heads flow differently.

As a matter of fact, if memory serves....the camshaft used in that video where a couple guys built and dyno'ed a Buick 350 and only came up with 300 HP and 350 ft. lbs. used a "Chevy" style cam...higher lift on intake and a little wider duration on exhaust. Coupled with the fact that the compression did not match the camshaft (I can't seem to emphasize this enough to people, and they don't seem to take it seriously), the engine was struggling to make power because it was working against itself with a weaksauce compression, plus was using '75 heads. Anyway...

There's plenty of cams out there that are close to straight pattern with slight emphasis on exhaust. Usually they're higher end cams, but not always. Most of the discussion I've been involved with related to mild-moderate function with some exhaust restriction assumed, which is how it usually goes with street machines or even with the heads themselves.

With a freer flowing exhaust and an I/E ratio closer to 75%, one can use closer to straight pattern camshafts, depending on RPM designation and CFM for intake and exhaust.

Stock Buick heads (1971, untouched) have a ratio of 64.64%, which means they needed to make up on exhaust (just the head alone) by a little over 10%. Stock engines tended to add even more (lift and duration combined) because they assumed a less than optimally flowing exhaust.

Stock lift is .377/.392 I/E, (.015 more exhaust) which equates to only about 4% extra emphasis on exhaust for lift, which matches the head flow @ lift (stock heads stop increasing flow past .400 lift). Stock duration is (@.050) 189*/208* I/E, (19* more exhaust) which equates to about 9% extra emphasis on exhaust; 9%+4%=13% overall extra emphasis, which is slightly more than it needs (10%) for restrictive exhaust system considerations.

There's been much talk about this topic over the years, and there's been some controversy as to which is best for what, but you just have to look at the numbers and use a little logic.

Remember 2 main things when comparing a Buick 350 camshaft to a Chevy 350 camshaft: head design (runner design, open chamber, etc.) and combustion chamber design (bore, stroke, etc.).

You can also negate some exhaust emphasis if you plan on using an "X" pipe system that you know is proven to function. This will help with your mid-high end scavenging, which makes extra exhaust unnecessary and can even hurt performance in this situation.

So really it's not a 'one size/style fits all' approach, but a custom approach based on your combination and how you intend to use it.



For mild-moderate combinations, the camshafts that will usually be excellent overall performers are the heavy emphasis exhaust cams, which take design cues off the stock cam design. Take a look at the Poston 114 camshaft and the Poston 118 camshafts and ask the people who've used them how they perform (both heavy emphasis on exhaust, as most Poston cams were in that range).

Poston 'borrowed' camshaft designs from Kenne Bell, and those camshafts were old school tech with old material designs for camshafts that wore out too fast when the ramp and lift profiles became too large. To my understanding, that is. Nowadays, the material is better so more radical cams cam be made that will last a little longer than they used to, but you're still not going to get the longevity from those cams as you will from one that takes design cues from a stock camshaft (less lift, wide LSA, heavy emphasis on exhaust, and slower ramp profiles).

You may not get the extra 10 or so HP that you would from a more radical profile, but your camshaft will last a whole lot longer.


Of course, all this becomes moot once you begin to consider roller camshaft designs...

 

Take some notes from the following Buick 350 head flow chart, comparing stock to a heavily ported set of heads:





You'll see there is zero benefit from going past .400 on intake for stock heads (we don't know, but it may have stopped increasing flow before .400 lift because it only shows from .300 to .400), and only 2 CFM is gained by going past .400 for exhaust.

Another thing to observe is the amounts gained, and the ratio of the numbers gained vs the numbers prior.

On the heavily ported heads, the flow planes off at .400 lift, only gaining 2 CFM more @ .500 lift, then it picks up a little, but not much.
This means little is to be gained by going higher than .400 lift on intake for these heavily ported heads, not much different than the untouched heads. You gain more CFM, but @ similar lifts... (there is more to gain, but the numbers are negligible, indicating the full potential has been reached for this port job). Other port jobs may yield different numbers and at different lifts, which is why it is imperative to match the camshaft with the heads, and then the compression to the cam.

Exhaust planes off what appears to be somewhere between .450 and .500 lift. More can be gained beyond this point, but again, is negligible.

Notice by simply observing these numbers we can see that a relatively low lift cam is needed, with heavy emphasis on exhaust lift.

A .431/.453 lift cam (Crower level 3 using a 1.5:1 rocker ratio), which has .022 extra exhaust lift would certainly do the trick.

Again, all this depends on how the heads are ported, which valve sizes are used and for which set (intake and/or exhaust), etc.


For a mildly ported, or just runner cleanup and some bowl blending/guide contouring, the flow numbers should be similar to stock in terms of @ lift.

Any camshaft with an intake lift of around .400-.425 and an exhaust lift of about .015-.025 more than that is really all you need.

Once you break the numbers down, you begin to see that all these gangster .475+ lift cams are just wearing out your camshaft with increased load pressures against the lobes and lifter faces.

I understand that increasing lift beyond peak flow will allow the valves to remain open a little longer through the lifting phases, but the difference is again negligible if you consider that duration and centerline does a much better job.


Thoughts?


Edit: The ratio between intake and exhaust for the heavily ported heads is about 72% for peak lift points for each. This should indicate that as long as correct lift is observed for I/E (.400-.425 lift intake, .435-.465 exhaust), the optimal camshaft should have about 3% extra emphasis on exhaust, which shows that with more radical builds, the duration can be closer to straight pattern, while heavier emphasis on (exhaust) lift is needed.

Many camshafts aren't made this way for higher-end engines. Either my logic is way off, or people just used camshafts they figured would work based on other engine combinations they were more familiar with.


Taking the Crower level 3 cam as an example, we see the extra emphasis on lift moreso than duration is actually in the engine's favor, which explains why the camshaft seems to do so well.

Crower level 3's lift is right about where it needs to be, while the duration (@.050) of 210*/220* equates to about 5.5% exhaust emphasis. This means the heads can have about a 69%-70% ratio and the Crower level 3 cam will be right where it needs to be for a set of moderately ported heads.


According to the numbers, it's ideal.

Some more food for thought.


Edit 2: The ideal compression ratio for the Crower level 3 cam for the Buick 350 is 10.1:1 static for 8:1 dynamic.

People seem to shy away from getting the dynamic too close to 8:1; however, on an engine with optimal quench a dynamic compression ratio of anywhere from 8:1 to 8.5:1 is desirable, according to what I've read in the Chevy forums on .38-.47 quench distances. It is said that 8.25:1 is ideal for optimal quench combustion chambers.

Since the Buick 350's combustion chamber design isn't quench based due to the piston and head chamber design, which isn't as necessary with the smaller diameter bore (smallest of all 350's made) making the compression @ TDC a smaller chamber for combustion, the expansion of the flame doesn't have to travel as far to burn the fuel/air charge, reducing tendency for detonation. A dished piston is also desirable in this scenario, permitting a more even and centralized downward thrust with the flame travel.

Even so, due to the fact that there is no quench (which is only one factor that helps reduce detonation), the other factors permit the use of 8:1 dynamic, possibly 8.25:1, though I would say 8:1 is safer. Aiming for less than 8:1 is robbing yourself of potential extra power and efficiency the engine could otherwise have.

Polishing up the pistons and head chamber will net additional power as well, as it helps reflect thermal energy back toward the combustion chamber, as well as eliminate any hot spots/sharp edges/rough surface area.

For those of you who love nice round numbers, shoot for 10:1 on the Crower level 3 cam, putting you around 7.8-7.9 dynamic.

Always remember the closer you can get the engine to detonation without detonating, the maximum efficiency will be achieved. Playing it safe is always good, but just remember there's more power to be had by optimizing the numbers.

 

I see no one mentions Isky ,or schneiders cams at all.even howards cams. but they all list several nice cams for buick 350 .

 

Aftermarket Buick V6 turbo cams (as well as all other brands) typically have less duration and lift on the exhaust.
I can personally testify that cams with longer duration exhaust for turbo application really handicaps the engines ability to make boost early on
and the engine is really lazy throughout the rest of the power band.

Exhaust design also plays a very large role in a turbo engines ability to make power as well as head porting.

Here is an article with more info:

http://www.hotrod.com/pitstop/hrdp_1011_cams_for_turbocharged_engines/viewall.html

 

I'd like to add a couple things here if I may.

The article emphasizes less overlap rather than duration for exhaust, though both play a role. Their idea is to get the intake in a position where it can take full advantage of the boost, while permitting all that extra combusted gas to be used as the 'emphasis' that will force it out the exhaust once the valve begins to open.

It is true that increased overlap will kill a boosted engine (logically) because the power will get blown out the exhaust.


Here's a couple of quotes from that article you posted:

Better flowing heads will result in more power with less boost, that makes sense (even for mild applications).

To truly get the best cam for the engine, one would need to do a lot of testing and swapping cams, or using a computer program to tune it prior to get a rounded idea, then tweak it in real world tests.

I'm still learning here myself, as we all are I think. Tossing around ideas and theories and putting our heads together seems to net great results!

So many factors determine performance, much of which focuses around the design of the parts being used, and how they perform when used in conjunction with other parts.

TA lists some cams for their turbo v6 listings, and they're mostly straight pattern cams. I figured exhaust duration and lift emphasis on turbo 350 engines because it was intuitive, along with wider LSA's and the less overlap the better. Seems I have more learning to do myself on the forced induction camshaft designs, though we must understand that the Buick 350 has a much longer stroke and different head design than the aftermarket parts (namely the heads) for the v6. This will also play a significant role in camshaft design. :TU:


As always, thanks for your input Paul. :Smarty:

 

Just wanted to move this info here where it's more relevant:

I remember reading about this some time back. He'd have been better off leaving the Mark2 cam alone at .477/.493 lift, which incidentally is pretty much the same ratio as a stock cam uses, only with .100 less lift...

Steve here on the forums (Underdog350) goes just a teeny bit faster than this setup, with MUCH less done to it and a properly matched camshaft. (and at 5200 RPM, not 6000)

His setup is hypereutectic pistons with machine work to bring compression to 9.6:1 and uses the Crower level 3 cam (which sits at about 7.5:1 DCR) with triple iron setup (iron intake, iron heads, iron stock exhaust manifolds), Quadrajet, 2 1/4" exhaust, TH350 trans with stock stall, and 3.42:1 gears. Runs 13.77@99 and gets 21 MPG and has a smooth idle... (All this info can be found here within his posts, so I'm not giving away any 'secrets')

This comes out to approximately 371 flywheel HP.

I've ran the numbers over and over and oooverr... much depends on how the heads are done, but anything ranging from stock to moderately ported the Crower level 3 is pretty much right where you want to be.

As the short turn radius gets smoothed out and the exhaust flows more, it does so at a higher lift, so exhaust will always benefit from more lift no matter how you slice the Buick 350 head. What changes most is where the duration ratios will sit based on I/E flow on the port job, but they always seem to range anywhere from 2.5%-10.5% emphasis on exhaust duration depending on port contouring.

You can obviously get away with running straight pattern cams with or without any emphasis on exhaust duration, but you're not running anywhere near where your engine will perform most efficiently.

Read anywhere about a comparison between the TA 310 cam (true straight pattern grind) and the TA 413 cam (straight pattern lift and split pattern duration) and the 413 will win out in every comparison. It has a whopping .001 more lift (which means nothing), but the reason it does better is it has more exhaust duration emphasis and a wider LSA... (110 for 310 vs 113 for 413)

Thanks for bumping this thread Sean, I was getting bored. :laugh:

It's completely understandable because there is very little camshaft engineering that focused on the Buick 350. Most cams are copy/paste from some other engine design, and it just doesn't cut the mustard for optimal efficiency. There is SO much power to be had from simply matching the parts up correctly.

Out of all the camshaft manufacturers I've examined, Sealed Power's stock camshaft and Crower seem to be paying attention to what the Buick 350 needs. :TU: That and the old KB and Poston cams that aren't made anymore because they quit making them or went out of business.

You could use a straight pattern lift cam somewhere around .500 lift if the heads are heavily ported, but the intake will have plateaued off at around .400 lift (even with heavy porting...I'm not joking). Keeping it in that plateau longer is what extra lift will provide, so there's no real harm in bumping intake past .400 and even up to .500, as long as the exhaust stays within its plateau, which it will at higher lifts (exhaust seems to plateau off around .500 on heavily ported heads).

This is where a camshaft similar to the TA 413 would shine...and once you start getting into those sizes, it's time to start thinking roller (IMO) unless you don't mind rebuilding every spring and just using the engine for the summer.

When I say 'plateau' I mean it's where the CFM starts to trail off, much like how the peak HP and TQ numbers will stop gaining, though instead of trailing off and becoming less, the CFM flow on the runners just quits peaking and forms an ever so slight upwards curve, and hits a point where it sometimes doesn't gain anything with more lift.

A benefit of increasing lift past or within the plateau would be that the valve would remain open longer as the lobe goes beyond where it peaks. So you get a little more 'duration' within the plateau without increasing duration on the lobe itself. This would benefit intake more than exhaust, as exhaust needs to work as efficiently as it can so it won't rob your engine of power by closing too soon and leaving contaminated gases in the combustion chamber (overlap and higher RPM will help remove this with scavenging on more radical profiles, so too much exhaust emphasis in this scenario can actually work against you here).

This is precisely how the Buick 350 head works, and coupled with the rectangular intake runner design, a little extra lift on intake within the platuea would afford tremendous benefits on a performance engine with a larger carb and exhaust emphasis to match I/E ratio. This is why the Buick 350 can benefit from a carb much larger than the calculators say they can. (thumbs up to you Sean)

All these off the shelf cams are 'ok' as long as you build your engine around them, or select the one closest to your combination goal. You can tweak it a bit by choosing custom grinds, though most people select the simple route and just pick one that does well in most scenarios and has good ratings, and that's fine too.

However, for those who want the most out of their engine, it pays to tweak. It doesn't have to be spot-on with matched compression or best I/E ratio or whatever, but shave some efficiency off here, shave some efficiency off there, soon you have an engine that could have ran much better and you'd never even know it because it does 'good enough' with the selection of parts off the shelf.

Something to think about!

 

First, observe the time between comments, and that the previous comments/posts I made were before I had a better understanding of camshafts, though all of it isn't rubbish, some of it could be a bit off...

So take it for what it is and let it stimulate thought.




I wanted to share with everyone some thoughts I have about camshaft design, and maybe shine some light into those dark areas where we don't quite understand what's going on with that mysterious camshaft, but trust others who design them to know what they're doing to make a camshaft that caters to the desired application.

Here's a list of some popular cams I composed:


Valve timing events @ .050


Crower Level 2

202/210 108/116 I/E 112 LSA
4*A

IVO is -7.0 BTDC ( - indicates ATDC)
IVC is 29.0 ABDC
EVO is 41.0 ATDC ( - indicates BTDC)
EVC is -11.0 BBDC
Overlap is -18

Crower Level 3

210/220 108/116 I/E 112 LSA
4*A

IVO is -3.0 BTDC ( - indicates ATDC)
IVC is 33.0 ABDC
EVO is 46.0 ATDC ( - indicates BTDC)
EVC is -6.0 BBDC
Overlap is -9

Poston GS 114

214/241 110/118 I/E 114 LSA
4*A

IVO is -3.0 BTDC ( - indicates ATDC)
IVC is 37.0 ABDC
EVO is 58.5 ATDC ( - indicates BTDC)
EVC is 2.5 BBDC
Overlap is -0.5

TA 212-350

218/230 106/114 I/E 110 LSA
4*A

IVO is 3.0 BTDC ( - indicates ATDC)
IVC is 35.0 ABDC
EVO is 49.0 ATDC ( - indicates BTDC)
EVC is 1.0 BBDC
Overlap is 4

TA 284-88H

223/230 106/114 I/E 110 LSA
4*A

IVO is 5.5 BTDC ( - indicates ATDC)
IVC is 37.5 ABDC
EVO is 49.0 ATDC ( - indicates BTDC)
EVC is 1.0 BBDC
Overlap is 6.5


IVO= Intake Valve Opens
IVC= Intake Valve Closes
EVO= Exhaust Valve Opens
EVC= Exhaust Valve Closes

TDC= Top Dead Center, so B= Before, and A= After;
thus, BTDC= Before Top Dead Center; ABDC= After Bottom Dead Center, etc.

This may be already known to some or most, but I'm including for sake of completeness for those
who perhaps do not know.

I've committed most of these numbers to memory, for use as a convenient mental reference for basis of comparisons to other camshafts and any I may wish to create.

The numbers are incidental--any cam can be pretty much anywhere. Whether it works or not, and how it works--that's the question...


Onward now to my descriptions and understanding thus far on this data. Bear in mind that this is a disclaimer that my information may be incorrect based on erroneous understanding, and will be corrected later if such is discovered or pointed out.

I'd also like to add that any comments, ideas, suggestions, or corrections are all welcome and will expound our understanding even further.



Firstly on how the timing is set up, which was a fundamental misunderstanding on my part a while back, which has since been corrected.

LSA= Lobe Separation Angle and is the distance, measured in camshaft degrees, between the center of the intake and exhaust lobes. To find the center point, take duration @ .xxx for each lobe (same distance for each, .006 and .006, .050 and .050, etc.) and divide by 2. This gives the center.

This is the reference point that will be used to set up the camshaft timing with the crankshaft. The installed timing, whether advanced or retarded, is measured from the crankshaft.

Bear in mind that the crankshaft turns 2 revolutions per 1 revolution of the camshaft.


I'll use the Crower Level 3 camshaft as an example:

Intake lobe 210*/2=105* @ .050 installed at 4*A (advance) with 112 LSA is 108* ICL. 108-105=3, for 3* ATDC installed point (or -3* BTDC).

This is @ .050, so the intake lobe has been lifting for a little while BTDC, and will continue until 33* ABDC (@.050), where it's closing. When it closes (this closing point @ .006 is where the dynamic compression is measured for effective stroke and CID), the piston is swinging around to TDC for the compression stroke and ignition.

Now the fuel is burning (based on timing, octane, compression, etc.) and expanding as the piston is moving down, converting this expansion of gas into rotating energy.

Now the exhaust valve is waiting its turn. It will be open @.050 when the piston reaches 46* BBDC. If the fuel is still burning, it will expand further out into the exhaust. This is where the engine can lose power if the exhaust valve opens too soon, and is based on the rate at which the fuel burns (higher octane burns slower, so you'll want a later opening point for exhaust, I'm presuming).
Though you don't want it opening too late, otherwise the duration on the exhaust lobe may overlap on the other side and remain open too long, creating unnecessary overlap with the intake valve opening again--though this is actually desired for higher RPM power bands when coupled with scavenging, so the exhaust will help draw the charge down from the intake before the exhaust valve closes.

This can create a Volumetric Efficiency greater than 100%, which equates to more atmospheric pressure and a sort of 'scavenge-induced boost.'

Back to the exhaust valve. It's now evacuating the burn gas out and will be at -6* ATDC @ .050, which is 6* BTDC. With this cam, overlap at .050 is -9*, so the intake and exhaust valves are both closed for 9 degrees @ .050 (closed for 6* BTDC and 3* ATDC = 9* total); however, there is still overlap below this lift. On this upward stroke the exhaust is finishing its evacuation and the intake is preparing to open, which happens before TDC, which is what causes the reversion.


So now we come to WTF does all this mean?

It means, in a nutshell, that performance cams shift opening points on intake earlier so the piston can scoop up as much air as possible and take advantage of the exhaust closing for scavenging so it has greater than atmospheric pressure feeding the intake stroke. It then creates a denser air/fuel mixture for combusion and thus greater power stroke energy.

However, since the intake is opening so soon it affects intake vacuum because reversion negates vacuum by filling it with more gas (some of it could be some burnt exhaust gas that wasn't properly evacuated...)

This is why timing is so critical in getting the combination operating as efficiently as possible. The wrong camshaft will kill your engine's performance and economy.

Opening later creates the reverse, which is greater vacuum but at a power cost. It won't draw in quite as much air/fuel. To compensate for this, a longer power stroke coupled with the environment to support it (greater compression and octane) and greater exhaust emphasis to function later.


Get IVO to a few degrees ATDC, IVC around 30-35* ABDC for a longer compression stroke/combustion cycle (this will vary based on a few factors), EVO timed where the fuel is about spent and EVC BTDC so there's minimal overlap.

It's important where the piston resides in relation to the 75* 'sweet spot,' which is the point where the piston starts to speed up for the upper portion of the crankshaft rotation. (Edited for clarity and mistype)

This is another subject that may be of interest, because it plays an important role in piston movement and speed in relation to the crankshaft position, which improves intake draw and exhaust evacuation.

Briefly, the piston moves slower (up and down) for the lower half of the crankshaft rotation (180*) than it does for the upper half. This translates into piston movement that will travel further and with greater speed for the upper portion of the piston stroke vs the lower half, though 'half' is only relevant to the crankshaft itself, and not the stroke of the piston.

This is because the rod moves more side-to-side on the lower part of the stroke than it does on the upper part, which equates to less up and down movement for the greater side to side, and vice-versa for the upper part.

This rod/stroke ratio plays an important role in camshaft design because it shows where the piston will be during its 'optimal' area for travel and speed, which is where you want your camshaft specs to revolve around.

This is for my mild setup idea, though obviously there's a huge range of alterations that can be done based on what one needs.

This is also where experience will come in handy for those who grind cams professionally, though research can reveal a surprising amount of data in this area... (as well as some math figures to sort out a few disparities)

There's a sweet spot to be found depending on how you want your engine to behave.

I'll come back later to edit any mistakes or typos, this is enough for now to get a nice little chat started for those who wish to participate.

Remember this is an ongoing process, and there's still plenty to learn.


Gary



Oookay...The Wallace site I used for those numbers has the ATDC and BBDC backwards...

So that thows a few things off...again. But this time it's not my fault. I can figure this **** out once I get all the tools I use fixed!

I was wondering why the last two numbers weren't lining up in my mind....now it makes sense! lmao

 

Awesome!

 

This can all be overwhelming and confusing, so narrow it down to a few things.


Take the numbers you know exist for popular cams that people have good things to say about, and analyze those numbers and compare them based on your knowledge of how the camshaft behaves.

Adjust up or down to suit for a custom cam, OR just use the camshaft that's reputed to work well.

This information will at least help to understand the differences (and similarities) between the different camshafts.

Something else to consider is the earlier the intake valve closes, the greater the dynamic stroke and compression will be.

If you analyze the numbers, you'll begin to see how the camshafts behave and what compression would best suit them.

I hope this information serves to help more than hinder understanding, as my descriptions may or may not be the best way to put it.

Please correct me on any mistakes anyone...if anyone's interested enough to dig this deep into it.


G

 

Actually Gary,the piston moves slower on the top of the stroke AND the bottom of the stroke. This is referred to as piston dwell(lets call it PD),PD on the top and the bottom of the stroke can be changed by the lenght of the rod. A longer rod will have a longer PD time compared to a shorter rod.

As the crank rotates around with a longer rod to stroke ratio,the rod accuates back and forth less leaving the piston at TDC longer than a shorter ratio. This is because with the longer rod to stroke ratio,the piston will actually reach TDC a faction of degree before the crank gets there and will stay there another faction of degree after the crank starts moving down. This reversing of piston direction with a rod to stroke ratio will create a dwell time at the top and the bottom of the stroke.

If the piston was attached directly to the crank without a rod,then there would be no dwell time as the piston will move as fast as the crank. Throwing a rod in the mix puts the piston futher away from the crank and an extra pivot point,and the futher away it is the more the dwell time will increase.


Here is a link that will explain in lenght PD and more;

http://victorylibrary.com/mopar/rod-tech-c.htm

A long read but VERY infomative.


Derek

 

Thanks Derek, I'll check that out. Meanwhile, I'm discovering the calculators I've been using at the Wallace site threw me off a bit on some of the timing events...

Seems I'm encountering setbacks and stumbling blocks to my learning, but I'm determined to get it anyway. It may just take longer than I'd anticipated.

 

That link I posted will be A LOT more helpful in your quest than that calculator site,take a break from that site and look at the other one. The link I posted is only 1 page of many,of the many questions that you have.:TU:


:beer

Derek

 

I'll check it out later. I'm about as beat up mentally as I can take it for a while.

After being wrong the first time about something so stupid and now the calculator on that website has numbers backwards...I feel mentally raped right now.

I've got it sorted out pretty much for myself as far as how I see it, but explaining it to someone else has got me all tongue-tied and whacked out.

Maybe I will take a break afterall.

If not for me, then for those who are trying to make heads or tails of my posts! haha

 

Derek

Gary was referring to the piston acceleration and not the dwell time at TDC or BDC.

For Buick 350 maximum piston velocity occurs at 75* before and after TDC.
That leaves 75* to accelerate to piston max velocity from TDC and 105* to BDC.
So "G" forces at TDC are greater than the "G" forces at BDC.
In fact for rod to stroke ratios less than 2, the max "G" forces do not occur at BDC but offset at both sides of BDC.
The amount of offset increases as the rod/stroke ratio decreases from 2.

Interesting stuff

Paul

 

I'm not sure if that is what he was referring to?

If the piston reachs maximum velosity 75* after TDC,for 15* it will remain there until it passes the 90* mark where eventually it will have to stop just before 180*(dwell) to reverse directions. So I would think on the way back up the piston would hit maximum velosity 75* after BDC and remain there until the after 90* when it will have to stop again to reverse directions once again. I wouldn't think something rotating in a circle with a dwell time on the top and the bottom wouldn't reach maximun speed after 90* and have to come to a stop to dwell?

But haven't really ever looked into where max piston speeds occur before,so............? It would make more sense if they occurred 180* from each other when dealing with a circle.o No: But that circle doesn't take into effect the crankshaft position in relationship to the rod,that I quess could make it work that way?

Derek

 

Oh ja. Herr Muller ist der Meister. Klar interessant!

Paul's knowledge of engines is truly amazing.


And Derek's knowledge is pretty impressive too.

Yeah that's what I was referring to Derek. I think they'd both play a role though.

---------- Post added at 03:50 AM ---------- Previous post was at 03:44 AM ----------

The velocity I'm referring to is the speed and travel on the upper end of the stroke vs the lower end of the stroke.

The piston is faster and moves more distance on the upper 180* of the crankshaft rotation than the lower half, but because of rod movement side to side on the lower half is more, so it soaks up more movement for the rod so the rod moves less up and down inside the cylinder. Opposite of upper 180*, where the big end of the rod doesn't move as much from side to side and therefore has more travel and speed in and out of the cylinder from 75* to TDC on the up stroke and down stroke.

This is the area you want to get your valve timing around so it capitalizes on the faster piston speed in this area

http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

 

Yeah,forgot about the angle of the rod,the more of an angle the more the rod acts like its shorter. Nice link,I can see it clearly now,especially now knowing that the rotation is asymetrical.ou:


Good stuff!!:beer

Derek

 

Looks like Gary's break time is over.

Welcome back.
Lots of great info. Now if we can just get someone to make the parts we need. Aluminum Stage 2 heads with adjustable rockers and a SP1 style intake.
Since the 350 is almost an exact 7/8 scale 455 it can't be that hard since the design work has been done and proven on the 455.

All comes down to $$$$$$$$. How many of these parts would sell.

 

Many things to consider when designing a cam, for sure.

Getting intake valve to close at the ideal location but not cut too deeply into the dynamic stroke and dynamic CID, yet keeping dynamic compression within parameters conducive to the type of fuel usage (while keeping intake reversion as low as possible), basing that off intake lobe total duration and opening point in relation to TDC and overlap reduction, while figuring out where best to get exhaust valve to open to end the power stroke (but not too soon), and how long it needs to stay open (duration), while comparing all this to the needed lobe lift in relation to runner flow and valve shape/size--in relation to I/E ratio.

Not to mention flow quality, not just flow quantity.

Shuffle shuffle, juggle juggle! Numbers all over the place.

Though in this whole mess there is an ideal place for these events to occur based on other parameter of engine performance.

This is all fluffy talk but necessary to describe what is needing to be done.

So onward goes the research and learning.

Gary


Edit: all in all...The Crower Buick 350 level 3 cam (or one with specs very similar to it) comes out on top in every comparison I've made thus far for street engine performance and economy in every day usage (all aspects considered), though the TA 212 is a close second. This is my personal opinion.