Discussion in 'Small Block Tech' started by sean Buick 76, Oct 16, 2013.
You guys are on the right track with the custom pistons, however if you think your saving money and not machining the sealing surfaces, your not.
The major cost in cutting the deck and heads is set up time. It only takes minutes to make a pass across a block or head. It may take a couple hours to fixture the block correctly. So if you cut .010" or .070" the cost is similar, if they charge by the hour which is how they should charge.
I would NEVER have custom pistons made and the try to reseal 40 year old surfaces. That's a little nuts.
Remember the basics of rebuilding engines.
Also about the thumper cam, I have a big block Chevy set up like the TV engine. Runs just like you are saying it should. No power under 3000 then runs like crazy. No vacuum, doggy. But it does sound cool. I was young and dumb then so go ahead and laugh at me!
Good point Steve.
Also, more weight on top with less taken off.
Instead of building up to deck height, build down to pistons. Either way works, though making sure the surfaces are cleaned up is a must to ensure a good seal, so while it's all set up, why not just shave'er on down...
Not to mention you may have to mill off quite a bit to get everything trued up anyway, and will ensure max life for heads since less needs to be taken off those so they're thicker, not to mention they won't be getting torqued down all warped, which may be a major contributing factor in why some are 'prone to cracking' in the first place.
Maybe over the years as the block settles the heads twist and eventually crack, depending on how badly the block twisted.
Truing them up will eliminate this for good, since the block will have been good and settled in to where it's going to be so you'd never have to worry about it again.
Lower CH and more off deck = more centralized distribution of weight, plus the use of deeper dished pistons for better flame swirl.
Though building up to deck using custom pistons is probably the best path for someone who intends on rebuilding the engine several times over the course of the block's life since the valvetrain and soft pistons being used will wear out in a few thousand miles
All good points.
---------- Post added at 01:39 AM ---------- Previous post was at 12:54 AM ----------
Here's another cam for consideration. It's kinda in-between the Crower level 2 and level 3 cams, for someone who wants a bit more than the level 2 and still wants to use stock valves and valve springs.
.280/.286 lobes (.006 exhaust emphasis)
.434/.443 @.155 (.009 exhaust emphasis)
208/216 @.050 (3.7% exhaust emphasis)
272/276 @.006 (64/60) lobe intensity
112 LSA @4* advance
108/116 I/E centerlines
Overlap @.050 -12.00
Overlap @.006 50.00
SCR @ 8:1 DCR: 9.95:1
Idle: Smooth @ ~600 RPM
Power band: 1700-4300 RPM
Peak Power band: 2700-4700 RPM
Optimal shift point: 4800-5000 RPM
Redline: 5300 RPM
Valve timing events:
IVO is 28.0 BTDC ( - indicates ATDC)
IVC is 64.0 ABDC
EVO is 74.0 BBDC
EVC is 22.0 ATDC ( - indicates BTDC)
IVO is -4.0 BTDC ( - indicates ATDC)
IVC is 32.0 ABDC
EVO is 44.0 BBDC
EVC is -8.0 ATDC ( - indicates BTDC)
Good point Steve,thats why at the end of my post I wrote,"as long as the deck and head surface is in good shape and doesn't need to be machined that is".
I surely wouldn't cut corners like that on a full race or a high performance street build,but for a mostly street limited strip engine if the deck and head surfaces check out decent with a machinist straight edge with some good hand stoning,the inexpensive .040" Fel-Pro blue perma-torque head gasket is more forgiving on surface finish with being able to seal on a mild build under 10:1 compression ratio would be fine. And for the extra compression height of a AutoTec forged piston would still be lighter than a off the self sbb 350 piston.(the weight part is for Gary,they aren't adding compression distance on a heavy off the shelf piston design)
Another senerio to use these pistons would be if say your good running rebuilt engine were to start losing fuel economy and then started running sluggish after a couple of tanks of fuel and come to fine out that the float has been stuck opened dumping way to much fuel washing out the rings and glazing the cylinders. A compression test shows that the rings are bad and when you take it apart you find out that the bores are now out of spec.(because thats what happens when fuel washes the oil off of the cylinders excessive wear happens fast) Your running .040" forged pistons and there aren't anymore oversizes available,what do you do? Do you start fresh with a different block and put another $1,000 + into machining plus new rings to re-use your rotating assembly,or would you buy a set of Auto-Tec pistons that could be ordered .043" oversized("at no extra charge") and just have your block re-honed?(and rebalance if the new pistons are way lighter) Even with a rebalance it would be aroud $200 less,not including the cost of a different block which could be another $100-$500 depending on what you can find and you still take the chance that the new to you block is good to use that is good enough to bore .040" over without core shift.
Chances are that a 40 + year old engine isn't a virgin anymore anyway and if the previous machining checks out flat....o No:
As for paying per hour for machining,as long as there is a set hours for a certain machining process is charged that would be fine. If they timed the guy that is doing the job and charged you for how long it took that guy to do the job vs the other guy that can do it twice as fast,I would think a set price would be more fair?(FYI it usually takes less then 1/2 hour to setup a block for decking,sometimes less depending on what was setup up on the machine before changing it over to do a block but would take much longer if they charged per hour):eek2:
---------- Post added at 10:54 AM ---------- Previous post was at 09:56 AM ----------
The AutoTec piston will still be LIGHTER than an off the shelf piston. With your lower centralized distribution of weight statement why wouldn't you just build a sbc with a lower deck height in the first place if you don't want the piston to go up as high as it can in a sbb?uzzled:
"Not to mention you may have to mill off quite a bit to get everything trued up anyway"
Actually not as much as you might think,in some cases as little as .005" would be all it would take to clean and true up the deck surface. In this case the better piston is a great choice to keep the deck surface thicker and much more stabil than a hogged down deck surface.:Brow:
The major contributing factor for heads cracking is overheating and detonation,this will cause the heads to warp and being under a clamped load of the head bolts will cause them to crack because the deck remains flat,NOT from the deck surface "twisting". When an engine overheats there is way more heat in the heads than the block causing the expansion rate of the heads to be much higher than the block making the heads warp and twist on the lesser changed deck.
"Truing them up will eliminate this for good, since the block will have been good and settled in to where it's going to be so you'd never have to worry about it again"
This is FALSE,if a engine overheats there will ALWAYS be a chance that a head can crack.(period)
"Though building up to deck using custom pistons is probably the best path for someone who intends on rebuilding the engine several times over the course of the block's life since the valvetrain and soft pistons being used will wear out in a few thousand miles "
I'm not sure what "soft pistons being used will wear out in a few thousand miles" you're referring to,but the ones I have mentioned are 4032 forged that are more wear resistant and are run with less side clearance than a forged Speed Pro off the shelf piston. And what does the valve train wearing have to do with pistons?o No:
I was going from the angle of an unknown core block, not one that was running OK but needed some help. Of course if the block was trued prior with few miles it should be fine.
I think unless the engine was abused you will find it won't take much cutting to true it up.
Where did these deck height dimensions come from? Are they from prints or actual measurements?
I think the ultimate build plan would be increased height pistons with the least cut from the deck to true the block. Measure the old piston position before disassembly for your base line, deck the block to get flat surfaces then order the pistons. It's pretty basic stuff.
Then you need to have it balanced if the piston weight changes.
I think Gary is going to the extremes with less weight and mass centralization of weight. Good to remember if you have the choice but really we're not in the chase for the cup. I am a fan of lowering rotational weight to extend the engines life.
I went with extremes to show pros and cons within the spectrum of variances. It doesn't mean that this is absolute and must always be done, or that any particular build combination will always follow these guidelines or must do this or that in order to do it properly.
I offer suggestions to solutions, and am not (always) basing my suggestions off experience. This should tell you that my view can sometimes be wrong, but doesn't mean that someone with experience will be right, either.
So take it for what it is.
What I will do is offer possible reasons or answers to things that aren't always known, even for experienced builders.
Heat will crack heads, yes. But it's not the only way they can crack. No one can sit here and say that it is ALWAYS as a result of this or that when there's variables to consider.
I find it rather funny when I offer up suggestions or ideas and if they vary from what someone plans to do, there is intense focus on what I said as if I were speaking directly to them.
There's more than one way to go about doing things, particularly when (as Steve said) the block is unknown. That's all I was getting at really. If you already know what you're working with then your path will be clearer.
Because I don't want to build a Chevy? Missing the point entirely as usual, if a person's sole goal was centralized distribution of weight, they'd be better off with a Subaru boxer engine.
Yes, in some cases it could be this, and in some cases it could be that (thanks for clarifying my point). Thicker block material would indeed be a benefit for extreme building, though saying you need the deck as thick as possible and then turning around and boring it as much as possible and thinning down the crank journals for a stroke job is sorta like talking about of both sides of your mouth.
The benefits and risks should be obvious.
I never said that twisting was the sole and only cause of head cracking. I only pointed out that it could be a contributing factor.
You're right. I should have worded this better, particularly when it was going to be scrutinized with such zeal.
This was tossed in more as humor than anything. Valvetrain being the typical 'cam chewer' profiles, coupled with typical softer forged pistons both contribute to a shorter engine life. This was the point.
Again, I was speaking more in general, not directly toward you or your engine project.
No need to get all defensive, I'm not criticizing your skills or methods. You are one of the few people with whom I would actually place trust in my engine build.
Gary, I appreciate your take on things and get what your saying. I believe the other guys do as well.
I would build a Subaru but they offer too many piston options. LOL
Don't care much for boxers, the dog or the engine.
Moving this info here from another thread for easy reference:
Here's the stock specs for analysis:
IVO is 19.0 BTDC ( - indicates ATDC)
IVC is 71.0 ABDC
EVO is 79.0 BBDC
EVC is 34.0 ATDC ( - indicates BTDC)
Overlap is 53
IVO is -15.0 BTDC ( - indicates ATDC)
IVC is 24.0 ABDC
EVO is 40.0 BBDC
EVC is -12.0 ATDC ( - indicates BTDC)
Overlap is -27
Stock cam has asymmetrical lobes, so the timing is all over the place depending on the lift of the lobes.
Speed Pro's Stock Buick 350 camshaft:
.243/.253 I/E lobe lift
.377/.392 I/E valve lift @ 1.55 stock rocker ratio
270*/293* duration @.006
189*/208* duration @.050
112.75* LSA @.050
109.5*/116* I/E centerlines @.050
114.25* LSA @.006
116*/112.5* I/E centerlines @.006
This equates to a 1.75* retard setting @.006 and 3.25* advance @.050
Can anyone see why this camshaft confused me earlier on when I was trying to learn camshaft basics using this as my learning foundation? lol
---------- Post added at 07:37 PM ---------- Previous post was at 07:05 PM ----------
If the LSA and centerlines were the same @.050 as they are @.006, this is how the timing events would
IVO is -21.5 BTDC ( - indicates ATDC)
IVC is 30.5 ABDC
EVO is 36.5 BBDC
EVC is -8.5 ATDC ( - indicates BTDC)
Overlap is -30
If the LSA and centerlines were the same @.006 as they are @.050, this is how the timing events would
IVO is 25.5 BTDC ( - indicates ATDC)
IVC is 64.5 ABDC
EVO is 82.5 BBDC
EVC is 30.5 ATDC ( - indicates BTDC)
Overlap is 56
So @.006, the stock cam appears smaller than it actually is with the asymmetrical lobe design for better vacuum and idle quality, while @.050, the cam appears larger than it actually is with the asymmetrical lobe design for better performance characteristics.
With the wide lobe intensities, another RPM dynamic variant comes into play: at lower RPMs, the cam appears smaller while at higher RPMs it appears larger, based on the blowby around the valves between .050 and .006 lifts.
This would create a very wide power band since the cam is (albeit mildly so) 2 cams in 1, being smaller when it needs to be and larger when it needs to be.
I thought this was pretty clever engineering.
No worries Gary,I wasn't getting defensive,I was just trying to be as acurate as I know the information to be. My post wasn't meant to be an attack on you in any way.My lacking confuser(computer)skills combined with my writing style could be taken the wrong way at times,so I hope you didn't take what I wrote to be offensive.
I figured you were mostly speaking in general,as I was trying to be corrective in general,I probably should of used blue instead of red for highlighting your quoates. Not sure how to get the blue boxes like other people and you use.o No:
And thanks for the vote of confidence in my abilities. Be careful about learning to much about cams,Comp Cams might have to hire you and you'll have a really long drive to Memphis every day to work. That would be cool to be able to buy a good Buick cam from them though.:TU:
It's ok Derek. I understand a lot more than one may initially believe.
You see that list of icons (buttons) above the text box here where we type? Those icons are shortcuts for commands (basically they're links that execute a series of commands with one click, much like a hyperlink or other icons on the computer, blah blah blah) and will let you pull up sub-menus for text size, font, color, etc.
You can form the text with sentences lined up to the left, middle, or right. See the icons just to the right of the "B" "I" and "U"?
The smiley face brings up the same icons you'll see to the right here with a list of emoticons (emotional icons as they're referred to).
So anyways, you can get your different colors for texts there.
To quote anything, type in a simple command for quotes using the brackets [ and ].
Type in the word 'quote' in-between them to begin a quote, then type in a /quote inside the brackets to end the quote.
It will put the words in those little quote boxes.
Type [ quote ] words words words words [ /quote ] only remove the spaces between the brackets [ and ] and the quote and /quote. I wrote it like that because if I left the spaces out, the computer would have seen the command and made the quote box, like this
If you don't type in anything, the computer sees it as nothing to 'say' and it negates (deletes) the quote box.
Thanks for your vote of confidence with the cam grinding thing, but I'm sure they just have guys there who set up the core, type in a code into a computerized grinder, and rap off several dozens of shelf grinds for the warehouses, or something to that effect.
I doubt they'd have need for another brain to pick apart their current designs because they already know their designs are for 'show' more than 'go'. In this case, 'sound' more than 'go'.
I'm discovering there's as many opinions on camshafts is there are (well you know the saying about opinions and how everyone has one).
Safe bet is to just go with some off the shelf grind instead of trusting someone like me that no one knows.
Which is good, since this is more of a learning discussion than anything.
I'm also discovering that the more I dig into it and the more I explain, the more I'm losing my audience. So there's that to consider too.
There's a lot to it.
Hey thanks for explaining how to post gooder.
I wasn't talking about you actually in the shop grinding cams,I was talking about you being a tech rep. on the phone helping people design a custom cam for their app.,and being a cam designer for new cam lines. I'm sure they already have people out in the shop running the machines,thats the easy part,the hard part is designing the lobes.:TU: (if you can handle an office job that is)
Hey guys I had this grind suggested to me a while back by a guy who grinds erson cams. Tell me what y'all think it would do for sound, Mpgs, vacuum, and tq power range. I wanted a cam with a mix between the 212 and 284. Would you Guys change anything and why? How does this compare to other cams?
---------- Post added at 12:51 PM ---------- Previous post was at 12:41 PM ----------
214/220 duration at .050, lobe sep would be 108, intake centerline is 104. Lift would be .457/.488.
Thanks for the suggestion. I may look into that.
---------- Post added at 09:50 PM ---------- Previous post was at 09:44 PM ----------
I'll be happy to give you an analysis. Maybe not tonight, I'm feeling kinda blah tonight.
This stuff is entertainment to me, it would be cool if I could make money doing it lol
I have dreams about this stuff, calculating things in my sleep. No worries about it giving me headaches. I love this stuff.
I need to take some refresher courses on math though so I can get back into some meaty problems involving physics and quantum mechanics.
People used to laugh at me for being a nerdy type, but hey you'd never guess it by looking at me
Hope you get to feeling better!
Ok maybe just a teaser...
I was actually doing some calculations on different grinds last night before retiring, and came up with some interesting combinations you wouldn't think you'd get with varying LSAs and centerlines.
I noticed some patterns between common camshafts and figured they made them that way for x reason and y audience with z application goals.
I also noticed a lot of people seem to do things out of 'habit' or 'familiarity' when creating something, and there's good logic behind this since it gives reference points to base ideas from. I do this too when designing or altering existing objects. Trick is to not let this become a rut and only allow ideas inside a limited realm.
Instead of designing a cam based solely on lift/duration/LSA/centerline numbers, I've found it best (for me) to design it around timing events, and then match it up with numbers that fit well together and compliment each other.
I'm not saying there's sacred geometry involved or anything, but... ok well maybe a little, but there's also an element of harmony, like music, with numbers that fit better than others. It can be all over the place with this so it's not a 'magic' set of numbers, just ones that resonate better with others.
Still plenty to learn, always plenty to learn.
It looks like I may be on the right track with this, since the engineering behind the stock Buick 350 camshaft seems to have originated from calculating where the valve timing events needed to be at a particular lift, and then just did the math and solidified the numbers wherever they happened to end up. This would explain why the numbers are all over the place.
The larger the cam is, the closer together things become since there's less room between events for variations. This is why you typically tend to see narrower LSAs on larger duration cams.
Where the centerlines are installed is important too, so while a cam may fit certain desired locations @whatever* advance or retard install, altering it will shift everything so that maybe the intake is now better, but the exhaust is now out of whack, which would require a regrind...
So it's best to get everything all nice and set up where they need to be for the application and then designate an installed centerline for optimal performance. I believe cam makers already do this.
This is still basic stuff guys, and it's geared around the Buick 350. When you start getting into other engine designs, everything changes dependent on bore, stroke, head runner style, angles of runners relative to the valve, size and even shape of valve, CSA in relation to valve curtain, windowing around the valve stem/guide bosses, unshrouding, combustion chamber polish, piston shape (dish? flat? dome?) and combustion chamber design (quench? no quench?) all play important roles as to how the fuel/air charge will travel down from carb to exhaust pipe, maintaining proper mixture until it reaches the cylinder, compresses/combusts/evacuates all at optimal times.
My focus though now is for the Buick 350 with the limitations and benefits that exist with its design.
---------- Post added at 10:14 PM ---------- Previous post was at 10:14 PM ----------
Thanks Paul. I will. In a bit of pain.
May turn in early tonight.
Thanks Gary id like to know what you think of that combo
I have found that the stock 350 cam and the gs cam are both optimized for the stock head flow. When you start porting on the heads you actually lose power. 1,92/1.55 valves in the stock head give a slight power increase and small tube headers really wake it up a 350. Port matching the intake to the heads on a stock 350 also makes a big difference.
as for many of these cams they are all good the issue in a Buick 350 becomes stock head flow above 4600 rpms.
I have found that wide lsa cams do better on capitalizing on the 350's long stoke to get a broad torque band also keeping the dynamic stroke around 3 inches seems to be a sweet spot for torque and hp.
but then again it also depens on what you are planning to do with the vehicle as there are many other factors to add in in order to achieve you desired results.
just some of my thoughts...
Another mild cam, in-between the Crower level 2 and level 3, but a bit closer to the level 2. Been trying to come up with some numbers for this 'in-between' cam and I think I've pretty much hit it this time.
.434/.443 @ 1.55 lobe .280/.286
266/272 @.006 62/58 lobe intensity
IVO is 25.0 BTDC ( - indicates ATDC)
IVC is 61.0 ABDC
EVO is 72.0 BBDC
EVC is 20.0 ATDC ( - indicates BTDC)
Overlap is 45
204/214 @.050 108/116 I/E 112 LSA
IVO is -6.0 BTDC ( - indicates ATDC)
IVC is 30.0 ABDC
EVO is 43.0 BBDC
EVC is -9.0 ATDC ( - indicates BTDC)
Overlap is -15
Power Range (Shift Point): 1600-4200 (4700-4900)
Static compression ratio of 9.75:1.
Effective stroke is 3.08 inches.
Your dynamic compression ratio is 8.00:1 .
Your dynamic cranking pressure is 158.97 PSI.
Static compression ratio of 9.44:1.
Effective stroke is 3.08 inches.
Your dynamic compression ratio is 7.75:1 .
Your dynamic cranking pressure is 152.55 PSI.
Static compression ratio of 9.13:1.
Effective stroke is 3.08 inches.
Your dynamic compression ratio is 7.50:1 .
Your dynamic cranking pressure is 146.16 PSI.
Timing numbers are based on a 108* ICL.
The intake valve (@.050) opens 1* sooner and stays open for 1* longer when compared to the Crower level 2. This gives it a 2* longer intake cycle.
Exhaust valve opens 2* sooner and stays open 2* later when compared to the Crower level 2. This helps to compensate for the extra intake charge, as well as the added exhaust emphasis needed for closer to stockish type heads (better than the Crower level 2 does). Adding in the extra lift on exhaust accentuates this effect even further.
Compression stroke is around the same @.050 but is a little shorter @.006, more in-between the level 2 and level 3 cams, so a higher compression can be used when compared to the level 2, but lower than the level 3's requirement.
Summary: the 'in-between' camshaft which is slightly closer to the level 2 than the level 3, with the benefit of retaining the best of both cams.
---------- Post added at 06:24 PM ---------- Previous post was at 06:16 PM ----------
I'm about to do an analysis on this, but I'll give you my first impression before doing so:
6* separation, 108* LSA, 4* advance, mid-.400's int/high .400's exh.
Narrow power band for sure, but would be pretty intense within this power band. Would 'need' a small stall and Stage1 springs.
Need more info for a thorough examination, such as .006 durations.
First off, here's what the timing events look like. This is what you should pay attention to most.
IVO is 3.0 BTDC ( - indicates ATDC)
IVC is 31.0 ABDC
EVO is 42.0 BBDC
EVC is -2.0 ATDC ( - indicates BTDC)
Overlap is 1
Depending on where your .006 numbers are, this cam would probably have a slight lope, maybe barely noticable.
Intake opening is same as TA 212, closing is 4* sooner than TA 212. Smaller intake charge, but longer compression stroke @.050.
Exhaust opens 7* later than the TA 212, closes 3* sooner. This means the combustion stays a closed circuit a little longer, and evacuates for not as long, as the TA 212.
So what does all this mean? First I'd like to mention something about a pattern I've seen with performance cams regarding overlap. According to my observations, if the overlap occurs more before top dead center rather than after it, the cam is a little less dependent on scavenging for its power, so that would make this cam better suited for use with small diameter primary headers or a well cleaned out set of manifolds.
The exhaust emphasis on lift also helps this aspect.
Whoever designed this camshaft seems to know these things too, or at least aimed toward a more 'budget friendly' performance cam.
Give me more info and I'll add more.
Well Gary that's really all I have. One can never tell the whole secret... Lol. Naw that's all he gave me. I haven't noticed him on the board in quite a while. I forget how to spell the name but think it was supremifi or something. Honestly I just want to notice the lope only once I put my auto in drive. Not a aggressive cam just something to make me smile everytime I put it in drive. So 1 or 3 degrees might make that happen. At the same time I don't want to push the power band way up beyond my usable street torque.