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Hey guys, im a noob lol and have a question about picking a cam.
First off i have a 1979 4 bolt 350 sbc crate engine, it was bored .030 over to 355, has original crank and rods but everything else in the block is new/balanced, 10.5:1 flat top pistons, my heads are 76cc 2.02/1.6 and i was wondering what is a good choice for a cam (F/T)? pretty new to engine building so any suggestions would be appreciated?
Thanks
Joe
your engine may not have 10.5.1 with 72 cc heads most all flat top with 64 cc heads will be 10.3 or so . you never said were and when you want the cam to come in it and what your doing with this engine .drag. street . street /strip .RV. boat. mud . WHAT?
Sorry lol, i am going to be using it for street/strip in a camaro, Not sure what the cr will be in the end i was just told the pistons were rated for 10.5:1 cr and my heads are the 624 76cc heads also have a set of 882's. I just don't want to buy a cam that is too big for my set up because I'm not to knowledgeable when it comes to that. Also where i am i dont have to worry about smog laws or emmissions
well if there flat top pistons and its a 350 not a 383? it 10to3 or so with 64 heads no way with 76cc head as for cams roller hyd .roller solid . hyd flat lifter . solid lifter?
Hydraulic flat tappet
if you use a 64 cc head and have 10to1 then you can look at some thing in the hi 220s @ 050 cam and hi 400s to 520 lift .alot of cams out there .how much gear ?and stall are you willing to use ? your heads may stop you from going to of a big cam the power will move up the power band and you may not like it much on the street
so i should look for another set of heads then?
Yes. Those large chambers will not help performance. If you are looking at iron heads, take a look at Iron Eagles.Quote:
Originally Posted by 80ZJoe
www.summitracing.com/parts/DRT-10121111
For less money, you could use S/R Torquer heads, but they do not have the new combustion chamber design that a lot of people prefer.
www.summitracing.com/parts/WRL-042660-1
If you prefer aluminum, then you have numerous choices--it all comes down to how much you are willing to spend. Edelbrock RPM series is a great head for the money.
www.summitracing.com/parts/EDL-60899
I know a guy who is selling a old set of cammel humps (64cc) needing rebuilds for $200 CAN and he has a set of vortec 305 heads for $300, he said they are also 64cc and should work good on a 350? should i even bother?
Hi Joe and welcome to the forum.
Let's address some of the aspects of engine building.
1. Piston deck height. This is the dimension from the crown of the piston to the flat deck of the block with the piston at top dead center. Nominally, with a premium 350 piston, this dimension will be about 0.025".
2. Squish. This is the dimension from the crown of the piston to the flat deck of the block with the piston at top dead center and adding in the thickness of the compressed head gasket. Current thinking is that a squish of 0.035" to 0.045" works best.
3. Compression height. This is the dimension from the centerline of the piston's wrist pin to the top of the piston's crown. With a premium piston in a 350 Chevy, this dimension is about 1.560". Lesser quality rebuilder pistons will measure out at around 1.540". This will increase the piston deck height and the squish and make the motor more sensitive to detonation.
4. Stack. This is the combined dimension of the crankshaft radius, rod length and piston compression height. A common stack with a 350 Chevy would be about 9.003". That would be with a crank radius (half the stroke length of 3.480") of 1.74", rod length of 5.703" and piston compression height of 1.560".
5. Block deck height. Nominally, this dimension would be about 9.025" on a virgin small block Chevy cylinder block. So, when using a stack of parts equalling 9.003", this would result in a piston deck height of about 0.022". Combined with a steel shim head gasket thickness of about 0.018", this would result in a squish dimension of about 0.040", just in the middle of the desired range of 0.035" to 0.045" to help prevent detonation with a reasonable (nominally, about 10.0:1) static compression ratio on pump gas. Alternately, a builder might cut the block decks down to the height of the stack and use a more conventional composition gasket that specs out at around 0.040" compressed thickness. If you had a stack of 9.003", cut the block decks down to 9.003" and used a 0.040" gasket, then the piston deck height would be 0.000" and the squish would be 0.040".
Sorry, but it was necessary to explain the above in order to get to what I am trying to explain to you. Presently, with my best guess of the parts you have in the motor, the static compression ratio is about 8.60:1. This is calculated with 727cc's in the cylinder, 76cc's in the combustion chambers, 4.6cc's in the piston deck height (@0.022"), 6cc's in the piston eyebrows and 9cc's in the composition gasket. If you used cheapo rebuilder pistons with a reduced piston compression height of 1.540", then the static compression ratio will be even less (8.29:1). If you used quality pistons and a shim head gasket, it will be a little higher (9.03:1). If it is currently 9.03:1 and you change to 64cc heads, the static compression ratio will be 10.26:1. You will then have to use a camshaft that makes power from about 2800 to about 6200 rpm's. This will require a looser than stock torque converter and a shorter rear gear to work properly. At 9.03:1 static compression ratio, you could use a street-friendly cam that might make power from 1200 to 5000 rpm's and would work with the stock torque converter and stock or slightly shorter rear gears.
The point is, you need to know what the static compression ratio of the motor is before you can intelligently choose a camshaft. The intake valve closing point, which is ground into the camshaft at the time of manufacture, is designed to work with a certain static compression ratio. If the valve closes too late, there is insufficient mixture trapped to make good cylinder pressure and the motor is a turd. If the valve closes too early, there may be too much cylinder pressure and the motor will detonate and destroy itself in short order.
Now, do you have any idea what piston compression height was used in your build? Do you have any idea what the block deck height is? Do you have any idea what the piston deck height is? Do you have any idea what the squish is?
270-h comp
or once you get some stall, gears and compression a 280-h or 305-h all great street/strip cams.
id go for the camel humps if you dont have any accesorys PS etc, if you do go for the vortec 305 heads and have your local machine shop drill them for regular bolt pattern intake OR get a vortec intake. not sure what kinda machine shop deals you can get. around here its about a $50-100 deal to drill and tap them
Thanks for the info guys, im not sure what the heights are on my build i'll have to check it out. I never heard of the squish before is that the same thing as a quench? But i have a stock converter in the car right now but i will need a new one once i finish the motor. I had a good converter but someone stole it out of my car when it was being stored at a friends house. Not sure what gears i have but i know it's a th400 with a B&M shift kit and the rear end is a limited slip. Again sorry i'm just learning lol.
The 305 heads will not breathe effectively enough to make a 350 run efficiently. Now 350 Vortec's would be a good choice as they breathe very well and make excellent horsepower.
You know guys and gals,I am just going to repeat what has been said many times before.By the time you make a used set of heads right is right and spend good money to do that,you still don't have the aftermarket heads that flow better,have thicker passages,are a better product to work with and really in some cases don't cost that much more and most importantly are a brand new set of heads.But that is my two cents worth and what direction this old boy is taking with his project.
I am constantly baffled by folks who seem to think their project has some deadline date.If only they would just wait and save alittle more money,they would get it right the first time.Also get it the way they would want the first time spending once and not twice.:confused:
Gary makes an excellent point. My philosophy may be a little more extreme than others, but I make it a point to use all new parts in a build. The only things I will re-use are the block and possibly the crankshaft. That's it. If I am spending thousands on an engine, I want the best and most reliable parts available. If I cannot afford to do it right, I wait until I have the money (or put it on my credit card--I don't recommend that).
That puts it in a better perspective for me, thanks. Maybe I'll find someone to buy the couple sets of heads i have and put the proceeds towards some new heads, anyone know what ideal heads i should go with on a budget of $1000?
Profiler heads are probably the best aluminum head for around $1000. Do not even consider ProComp heads no matter how attractive the cost--absolute junk.
www.profilerperformance.com/sbc-heads-176.html
Iron Vortecs are less expensive and a very good flowing head but you will have to use a Vortec intake manifold.
www.summitracing.com/parts/SUM-151124/
PBM iron heads loaded for under 800.good head for the money could look in to them iron killer heads brodix bro1020001 or the RHS in ironQuote:
Originally Posted by 80ZJoe
I've looked at a ton of SBC heads and am impressed with the RHS (Racing Head Service) cast iron heads for the money. Let's assume you can zero deck the block to the pistons for zero piston deck height. Let's further assume you have 6cc's in the flat-top piston eyebrows, a run-of-the-mill Fel-Pro composition head gasket that compresses to 0.040", 1 5/8" long tube headers through the mufflers of your choice, an Edelbrock RPM or Weiand Stealth intake manifold mounting a 750 CFM vacuum secondaries carb of your choice, these heads....
http://www.summitracing.com/parts/RHS-12301-01/
(making a static compression ratio of 9.35:1 with the flat-tops), and this cam & lifter kit....with the cam installed 2 degrees advanced....
http://www.summitracing.com/parts/CRN-100132/
I don't like to spec flat tappet cams any more, but will use one here just for simplicity and because it is relatively cheap. Follow all the precautions given in the link at the bottom of this post.
I have factored the published flow of these RHS heads by 0.95 in order to present a realistic head flow. Sometimes the manufacturers fluff up the flow a little with tricks of their own, like larger bore pipes than the engine builder will be using. For instance, when's the last time you saw a 4.200" cylinder on a 350 Chevy??? Anyway, I feel that this DynoSim is pretty near to realistic to what a real motor would generate on a real dyno. I've done several hundred of these exercises now and I think I have a pretty good feel for reality.
RPM HP TQ
2000 146 383
2500 186 390
3000 237 416
3500 295 443
4000 346 455
4500 387 451
5000 421 441
5500 430 409
6000 410 359
Peak volumetric efficiency 93.7% @5000
Peak BMEP 192.9 @4000
This motor makes some pretty good cylinder pressure as evidenced by the BMEP, so zero decking the block for a 0.040" squish is MANDATORY if you expect to operate the motor on pump gas. No whining please. Just do it. Use a 2500 stall converter and 3.73:1 rear gear and you'll tear the tires off. This is one of the better 355 street/strip motors I have DynoSimmed. Great cylinder heads for a 355, they really pack the cylinders.
http://www.crankshaftcoalition.com/w...ips_and_tricks
For ignition timing, establish TDC on your damper with the timing tab you will be using. Here's a tutorial from Isky as to how to do it as you are assembling the motor and finding TDC to degree the camshaft....
http://www.iskycams.com/camshaft.php
If the damper won't degree properly, the inertia ring has more than likely slipped on the hub. Over time, the elastomeric material that separates them breaks down and will sometimes allow the inertia ring to move in relation to the hub. If that has happened, you really need to rebuild or replace the damper. I always use an OEM damper because the bore is correct for a press fit onto the snout of the crank. Some aftermarket damper hubs are bored either too tight or too loose. If the fit is too loose, the harmonics that are set up in the crank each time a cylinder fires will not be dampened properly from the hub to the inertia ring and crank failure can result. If yours needs rebuilding, send it to Damper Doctors to be rebuilt or if you don't have one, call 'em up and order the correct rebuilt damper for your application.
http://www.damperdoctor.com/Merchant...egory_Code=CHE
Anyway, start with 14 degrees at the crank and 20 degrees centrifugal. Use a kit from Summit to tailor the curve. Also, install a Crane adjustable vacuum timing cannister and a Crane limiter plate. The HEI cannister is 99600-1 and the plate is 99619-1.
Thanks, I'll search the local shops first to see what they have or can get cause i hate ordering parts from the internet and heads would be imaginably pricey for shipping. But i'll keep yas posted about what they have. Here is a pic of the pistons i'm using, what should i do about the surface rust on the deck? it's not as bad as it looks from the pic but is there anything i can do myself without ruining the deck or would i have to have a machinist shave it or something? It's not pitted so i don't think it would be a hard fix.
http://i1013.photobucket.com/albums/...101_1838-1.jpg
Awww, you've messed up already. Those are cheapo rebuilder pistons with a 1.540" compression height. Geez, I wish there was some way that you fellows knew to ask someone who knows this stuff before you buy this junk. To get to zero deck now, you'll have to remove about 0.045" from the decks instead of 0.025" if you had used the correct 1.560" pistons. Then the decks start gettin' a little thin and may not hold a head gasket and you have to whittle the heck out of the intake manifold to get it to line up and yadda yadda.
If it were mine, I'd remove those pistons and sling 'em over the fence, than get on the horn and order some decent pistons like these that would make 9.35:1 with a 72cc head....
http://www.kb-silvolite.com/kb_car/p...tails&P_id=156
But hey, it's your motor, do as you wish. Pat McCarthy may have cut some decks this thin in the past. Maybe he can tell you what to do.
your talking 045 off the deck thats a bit but. i have cut off 030 on the sbc i care not to cut any blocks too much .on the race blocks i have cut 100.off the deck of a hurt 10.200 race block there just thicker then a 9.800 deck just more iron .but.. my mill is made for cutting big heavy cuts still takes a long time and wears the cutter on the wheel .so it cheaper to get a better CH piston so there s on need for a heavy cut some cast piston are very hard to get to a O deck
That sucks, I didn't technically mess up i was lied to lol, i was told they were really good pistons.... f***ing BS :(
Tech - those last heads and pistons you recommend would give an effective combustion chamber of 79cc right (72cc + 7cc)? Does your calculator give the dynamic CR with that combo?
I'm getting 8.75 DCR with my homegrown calculator with the cam intake closing at 36 degrees ABDC . . .
tech has a new dyno program he may have a dynamic sim on it ? i know he did use the KB pistons that is the one i use till i get $500 for my new dyno program
No, I have been using the Keith Black calculator for several years. I don't think it matters whose you use, as long as you stick to one calculator and know what kind of number it takes from that calculator to tolerate pump gas.Quote:
Originally Posted by SBC
On the second line of post 19, you can see where I assumed 6cc's in the eyebrows. This would have been fairly accurate with a quality flat-top piston. I didn't have a clue as to what piston he had at the time I wrote that post, but was just swinging the bat through to see what we had. I further allotted 9cc's for the 0.040" gasket, so the entire volume would be 72 + 6 + 9 with a zero deck. If you figure an overbore of 0.030", you have 727cc's in the cylinder. 727+72+6+9=814. 72+6+9=87. 814 divided by 87=9.35:1 static compression ratio.
Using the KB calculator, if you enter 9.35, along with a 5.703" rod, 3.480" crank and 49 degree ABDC intake closing point (36 @ 0.050", advanced to 34 and with 15 added, which is what is called for by the calculator), you get a Dynamic Compression Ratio of 8.282:1, which is in the range of 8.00 to 8.30 that I shoot for on the KB calculator to tolerate pump gas.
http://www.kb-silvolite.com/calc.php?action=comp2
I just noticed that the KB piston I linked is actually 7cc's instead of 6cc's. There is probably 1 cc or more variance in the combustion chambers, so I'm gonna let it ride. It ain't rocket surgery.
Cool - I was wondering how the timing advance would affect everything and the 2 degrees alone wasn't making a big difference. The extra 15 degrees brings it into pump gas range as you said. THATS the factor that I haven't been considering.
Is there a rule of thumb as to how much timing can be added before everything is out of whack?? Seems like I have read posts suggesting as much as 36 degrees in some cases.
The main reason why on my build I am not using KB pistons is the design promotes carbon build up on the ring lands.Seems to be just a bad design.I spoke to Mahle some more to find you can run those pistons at 4.029 vs 4.030,one thousands tighter that limits or eliminates cold forge piston slap because of the coating.One tip they gave me was to NOT use anything like carb cleaner to clean the pistons before the install of them.That kind of cleaner lifts off the coating.Of course they are making claims the coating last for the long term where on another thread I had concerns posted.The piston/ring design on the Mahle hands down seal without any carbon build up.They also told me they don't build cast pistons or pistons without the coating.Yeah I think in this case I found the age old saying.............."You do get what you pay for".The Mahle of course costs more.
Wel i guess the funds are gonna go toward new pistons now :(
I'm not sure what your're asking, but if you're talking about how much you should advance or retard a camshaft to get the characteristics of the motor where you want them, a rule of thumb there is that if you have to advance or retard more than 4 degrees, then you have chosen the wrong cam.Quote:
Originally Posted by SBC
I'm not sure what your're asking, but if you're talking about how much you should advance or retard a camshaft to get the characteristics of the motor where you want them, a rule of thumb there is that if you have to advance or retard more than 4 degrees, then you have chosen the wrong cam.Quote:
Originally Posted by SBC
well that s BS there telling you.... must of been the broom pusher grab the phone ? i have used there cast piston that had NO coating on them and they do or did make pistons for PBM and they are not coated as i have used a set in a 355. botom line is how are you going to run a coat piston 001 less if you can not messure it for size real size?? its coated . if there 2618 there going to move if 4032 you can fit them closer to the wall for what your doingQuote:
Originally Posted by 1gary
mahle made the cast pistons chevy used in 90s and maybe even now
No kidding guys.I just talked to them and was informed no cast pistons available.Check it out your self:1-888-255-1942.
i do not need to call them:3dSMILE: i bored a 351 ford out 040 so 4.040 last year PBM sent me mahle cast piston not coated in a mahle box NO Kidding .i mic the piston so i had a good look at them ..do they coat them now... well they may now.. BUT they own clevite now so hard to say whats going on thinking i did a 460 030 over as well with the mahles as well not coated casters
SBC has asked a question on PM about the cam we used above and the calculator on the Keith Black Pistons site. My answer is way too long for the PM, so I will publish it here on the board.
Quote:
Originally Posted by SBC
First off, rump-rump is the sound of the motor being inefficient. It's the sound that results from the speed of the motor being out of the operating zone for that particular cam. It's the sound of fuel/air mixture being blown back up the intake tract to confuse the venturis as the piston ascends with a still-open intake valve. Not that rump-rump is bad. It just indicates that the cam was not designed to operate at the rpm you are operating it at. Once the RPM's increase, the motor comes "up on the cam" and all is right with the world. Personally, I consider it "poser" to choose a cam based only on rump-rump without regard to engine efficiency or power.
The cam I used in the DynoSim was very close to the correct choice for the motor in my opinion. It's the....CALCULATOR....that requires the additional 15 degrees in order to make it work.
There is duration at 0.050" tappet lift and there is duration at seat-to-seat (On a hydraulic cam, usually shown as 0.006" tappet lift. On a solid cam, usually shown as 0.020" tappet lift. This is also shown as "advertised" duration.)
Let's say a theoretical cam has a duration @0.050" of 200 degrees. Let's further say that at 0.006", the duration is 230 degrees. (The difference used here is too radical to be a real-world cam, but I just need to do it this way to explain the calculator). We have 30 degrees of difference between 0.050" and advertised duration on the lobes of this cam. We are dealing with the intake lobe for use in the calculator. So, the lobe would have a difference of 15 degrees on the opening ramp and 15 degrees on the closing ramp of the same intake lobe. So the calculator is asking you to add 15 degrees to the 0.050" closing point that you have to enter into the calculator in order to get the valve closer to its seat position. As you know, we cannot begin compression in the cylinder until we close the intake valve. That's just the way the calculator is configured and something we have to work with to use the calculator.
On a real-world camshaft, the difference between 0.050" and advertised might be anywhere from 70 degrees (35 degrees on each side of the lobe) down to as tight as around 40 degrees (20 degrees on each side of the lobe) and even a little less on some radical flat tappet roundy-round cams. If you think about this, you can see that there comes a point when the lift is so radical coming off the base circle of the cam (where you set lash) up to 0.050" lift, that the edge of the lifter could dig into the ramp of the lobe. Back in the day, the fast guys introduced special aftermarket mushroom lifters for a Chevy that you had to insert from the bottom (the cam bore). I'm told that a spot-face operation was also performed on the bottom of the lifter bore. This presented a wider footprint for the lobe to work on so that the lobe had no lifter edge to contend with. Today, it is common practice to enlarge the lifter bore and use larger diameter lifters, such as perhaps a 0.904" diameter Chrysler lifter in a SBC motor instead of the stock 0.842" lifter diameter.
I was surfing and came across this post on www.chevelles.com by Harold Brookshire, known as UDHarold (world-renowned camshaft engineer and designer). It's the first time I have ever seen a chart outlining the limits of rate of lift compared to lifter diameter.....
"UDHaroldMar 31st, 05, 3:42 PM
Since if there's anything I know, it's History, here goes.....
Prior to the widespread use of computers, very few mushroom cams were made. The earlier designers had enough trouble making cams follow their normal lifters, much less an extra-wide one.
By the mid-70's, NASCAR racers had learned enough to know that the Chrysler .904" tappets allowed more aggressive lift curves than the .842"-.874" tappets. NASCAR's compromise?---Let everyone use a Mushroom lifter. Chevrolet went to .960", and NASCAR settled on that, even though Chrysler had some 1.000" ones. Those were used in drag racing.
In 1978 I designed the Comp Cams' 310/318 mushroom cam, 268/276 at .050, .390"/.410" lobe lift. In 1980 Buddy Baker won the 1980 Daytona 500 with this cam, and it is still the fastest Daytona 500 ever run. NASCAR went to restrictor plates, and then to .874" max tappet diameter.
Cams with flat-bottom lifters, either hydraulic, solid, or mushroom, are design-limited by velocity. Here are the max safe velocities(more or less) for the various lifter diameters:
.842" .00705"/°
.874" .00733"/°
.904" .00759"/°
.960" .00808"/°
There ARE tricks around these numbers, but not all cam designers know them, or else how to use them right.....
Cams with rolller lifters, either hydraulic or solid rollers, are design-limited by acceleration and base circle diameter. A peak acceleration rate that may be un-makable for a .900" base circle may be usable for a 1.100" base circle.
There are obviously tricks around these limitations, also. The hard part is knowing the tricks, not the basic theory, and when and how to use the tricks....
UDHarold"
If you'll go to the calculator and play with it, you'll begin to get a sense for what works and what doesn't. Start by using the same static compression ratio, rod length and stroke, changing only the cam timing by 5 degrees each time you run a new calculation. If you run a few dozen of them, you'll begin to see the effects of less cam and more cam. For instance, start with a 350 Chevy. 3.480" stroke, 5.703" rod length and a generic 9.0:1 static compression ratio. Start with a very short cam that closes at 20 ABDC and add 15 to see the results. Then use a cam that closes at 25 and add 15, then 30 and add 15 and so on. After you have run the range with those figures, change up the static compression ratio to 9.5:1 and run through them again. Then 10.0:1, then 10.5:1, then 11.0:1. If you are writing down the results, you'll begin to see a pattern. Like I'm saying, the more you use the calculator, the better feel you will have for the relationship of static compression ratio to cam timing, what works and what doesn't.
In the final determination, it is probably best to consult with the tech guy at the cam grinder of your choice and discuss the details of your vehicle and your engine build before you pull the trigger on a choice. But it most certainly helps for you to have an idea of where to start. We see fellows all the time on this forum and I'm sure it's the same on a hundred other forums where they come on to tell us their tale of woe about the car not having any power after their world-beater rebuild and change to a "double-throwdown, John Force camshaft" in their 8.00:1 small block Chevy. You realize right away that they have chosen the wrong cam without having a clue as to how things work in the motor. You also know that they used short, cheap rebuilder pistons and have a squish somewhere around 0.080" to 0.100". The only thing keeping the motor from detonating itself to death is the fact that they used too much cam for the static compression ratio and the cylinder pressure is zip.
I would urge everyone reading this post to also read through (several times) this tutorial written by Dimitri Elgin, one of the old-time cam grinders....
http://www.elgincams.com/campaper.html
Outstanding post.Thanks.Quote:
Originally Posted by techinspector1
Quote:
Originally Posted by techinspector1
Hi tech, thanks for the links to UDHarolds post. He is a wealth of knowlege. There is a small typo in your post above you may wish to change to avoid confusion, no disrespect intended.
Cheers
Thank you. I swapped the 200 and 230. Now it makes sense....I think:whacked:Quote:
Originally Posted by Rimmo