Guest Anonymous Posted May 22, 2003 Share Posted May 22, 2003 To all concerned; I know that the accepted safe piston speed is 4000fpm. I also know that this number is used as a redline for bottom end strength but, there is a question,.....If the "Effective Stroke" value (in inches) drops as the degrees ABDC of intake valve closing increases, is it not true that this action (in effect), because it reduces the stress on the reciprocating parts involved, actually lowers that stress and therefore also effectively reduces the "Piston Speed Redline" value so that actually more RPM's can be realized without component failure?.....Or does the fact that the advantage of later intake closing is eventually overcome at high RPM, negate what I am thinking? What is the deal here? Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 22, 2003 Share Posted May 22, 2003 Valve events have zero to do with it. There is some compression relief TDC on the compression stroke, but on the exhaust stroke you're looking at all that mass being slung around at TDC with no opposing forces to speak of. 4000fpm (average speed I presume) sounds like a general rule of thumb number. But it's not speed that kills, it's the sudden stop. i.e., peak piston acceleration is more important than average piston speed. Allowable peak piston acceleration will depend largely on piston and rod design and construction. I would hope that the bottom end is stout enough to handle all the pistons and rods can. What kind of setup are you thinking of, and what redline are you hoping for? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 22, 2003 Share Posted May 22, 2003 Yes Mr. Baldwin, I get your drift. especially about the whipping action. What has been bothering me in the back of my mind is that I have searched online and am not finding any data that explains how some engines are capable of 7-9000 rpm long enough to be useful in extended competition. I can listen to a formula 1 engine and of course hear the high rpm's and know that they must have a pretty short stroke; Then I can listen to a 300+ mph dragster and hear the more normal rpm sound. What is happening to my mind is that I keep reading how cams are good for 7-9000 rpm and the guys who are talking about them and some apparrently running them, and I wonder where all the data is to substantuate and confirm such engine performance physically and how practical it might be for a street engine shall we say for even as little as a 5000 mile life expectancy? And I wamt to see some data in that area plotted against various stroke lengths. I am thinking things like modus of elasticity and tensile strength and 'G' forces gainst a complex reciprocating mass. As for my intentions engine-wise; It is a "Normally Aspirated" Dart Big M, 4.625 bore (machine lightened pistons), aluminum rods, 4.750 stroke (lightened crankshaft). At this time I personally don't think even 6500 rpm would be safe using this setup without a Girdle, but there again, info online is very sparce in that area. You speak of "Hope" for the bottom end (and I know you speak of surface hope) but under that surface is where I must go for my answers. Where are the dissertations concerning Splayed Mains, two vs four bolt mains, Girdle time and block filling and if it is girdle time then is it also filling time and etc. All this vs normal aspiration, supercharging and exotic fuels, all this I need to put in my mind for reference so I can feel that I have at least "some foundation" for my decisions in this area. I don't ever want to see any smoke and/or flames enveloping the car at selected high rpm's or hear the sound as if a sledge hammer were striking a 55 gal. drum as I approach peak rpm.....LOL. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted May 22, 2003 Share Posted May 22, 2003 rod bolts and rods normally fail under tension on the exhaust stroke where theres no effective compression slowing the piston down as it plays crack the whip. you can run an engine useing premium forged parts for very brief times at speeds of 4500fps piston speeds if the pistons and rods are light weight. now on a 4.75" stroke bbc engine thats about 5700rpm. I sure would not exceed 6000rpm if you intend that engine to live long! LOOK here, http://www.prestage.com/carmath/calc_pistonspeed.asp http://em-ntserver.unl.edu/Mechanics-Pages/Luke-schreier/unzip/Tension%20and%20Compression%20in%20Connecting%20Rods%20VI.htm http://victorylibrary.com/mopar/rod-tech-c.htm http://www.grapeaperacing.com/GrapeApeRacing/tech/rodslength.cfm Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 23, 2003 Share Posted May 23, 2003 Dont forget that those who constantly find themselves running their engines on the ragged edge are ALSO CONSTANTLY rebuilding their engines. If/when their engines are not rebuildable-then they are replaced. If you're only building a street engine...you may want to rethink utilizing alluminum rods(?). Do you really need above 5500rpms on a street engine? You will not find nor get "all the info" you need as the pro teams who are running on the ragged edge like to keep their secrets...SECRET. You will have to read magazine monthly issues, internet sites & thread/posts till your eyes hurt: eventually you will have enough of a foundation to base your opinions. Experience doesnt come cheap: somebody's got to pay the piper. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 23, 2003 Share Posted May 23, 2003 Well Grumpy, the engine is going to live for at least 5000 miles because I am asking questions. I may shorten the stroke and I may not. On dyno 2000 I have a nice 2250 rpm under the curve with 5250 right in the middle of the sweet spot. I can drop the power band back enough to keep the 4.750 stroke and stay with the 4000 ft/min rule and still get plenty of action, or I can push it to the 44-4500 ft/min. you mention and be on the edge. I am testing the water on this issue in here and on websites right now. I really appreciate your Links and have read them all thourougly. My conclusion right now is that your figure of 5700 rpm is a reasonable max. I have a cam lined up that pulls from 3250-6500 rpm (according to the build) but with the stroke I mentioned plus the gearing, I simply don't need to wind that high, besides, the bottom drops out pretty good after 5700. I just wanted to get some feedback on that piston speed to see if it really was a bonified figure or just a groupie biased one. And so now I will assume that all USA V8's running real strong on the street with the higher rpm's are either "on the edge" or will fade in the strech because of their shorter stroke and/or higher gears. Well, maby I'm all wet there in some cases. Anyway, running a 1.76 powerglide the rpm "fallback" from 5700 would be 2250 rpm putting me 200 rpm above the "turn on" of 3250, that'll work! I feel better about the whole thing now, Thanks. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 23, 2003 Share Posted May 23, 2003 Hey Kevin! I am doing an original Hot Rod effort here! The whole car is a build for accelleration, the top speed just comes with the package. The alum. rods are for accelleration as is the crank, pistons, cam etcetera. That is why even for the street I am imitating a dragstrip build for the most part. These days I believe such is called a "Saturday Night Special" (a street car that's not good for much else other than drag racing). As to the 5500 rpm, that's cool but I'll take what I can saftely get there.....LOL Why don't you let me help you do a conversion on your in line?.....LOL. Thanks for the reminders Kevin. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted May 23, 2003 Share Posted May 23, 2003 First off, HOLY CRAP that is a BIG engine! Now for more pertinent stuff. Design rpm ranges for camshafts have NOTHING to do with structural concerns. Only for getting mixture into the cylinders and exhaust out. You don't *have* to be a structural engineer to put together a big motor that will survive, but it would help if you had the assistance of an EXPERT in the field, rather than putting it all together yourself and hoping for the best. As far as hope for the bottom end, I was thinking of NA L6 motors. This is a deep-skirted design, and the bottom end is very stable. Your monster motor may need that girdle for stability. Again, rule-of-thumb maximum average piston speed doesn't account for a lot of what goes on in the motor. Specifically, it doesn't account for the effects of rod length on peak piston accleration. It also doesn't account for the actual strengths of pistons, rods, crank, block. I think you should find a knowledgable, successful engine builder experienced with building reliable monster motors like yours for the street, and open your wallet. It sounds like your engine is way to specialized for way-too-general rules of thumb regarding safe engine speed. What is happening to my mind is that I keep reading how cams are good for 7-9000 rpm and the guys who are talking about them and some apparrently running them' date=' and I wonder where all the data is to substantuate and confirm such engine performance physicallysnip I am thinking things like modus of elasticity and tensile strength and 'G' forces gainst a complex reciprocating mass. snip At this time I personally don't think even 6500 rpm would be safe using this setup without a Girdle, but there again, info online is very sparce in that area. snip You speak of "Hope" for the bottom end [/quote'] Quote Link to comment Share on other sites More sharing options...
Guest Luigi Posted May 23, 2003 Share Posted May 23, 2003 I think that some of the questions you are asking can be solved by talking to your crank manufacturer. As well as the company that make the rods. Aluminum rods tend to be "softer" and thus absorb some of the stress that occur as the rod changes direction. there is something else I would like to add. A REALLY good engine simulation program will go a long way towards dialing this combo in. NOT desk top dyno. you are gonna hafta get either engine analyzer PRO or Alan Lockheeds engine expert. other than that, build it! Just my thoughts luigi Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted May 23, 2003 Share Posted May 23, 2003 ENGINE ANALYZER PRO software I bought. ($490) its a p.i.t.a. to work with but does give very good info! you might want to try the new DD-2003, if moneys tight, its not nearly as percise but still its better than DD-2000 heres other options http://www.engineprosoft.com/ http://www.motionsoftware.com/minigide.htm http://www.rapidline.com/pcver.htm http://homepages.ihug.co.nz/~don_s/software.htm Quote Link to comment Share on other sites More sharing options...
Guest Thurem Posted May 24, 2003 Share Posted May 24, 2003 From what I have gathered, the pistonspeed limit of 4000 ft/min. is the max speed the oilfilm will support before breaking and allowing direct metal to metal contact (insert expensive noise here). This is not the final word though as far as I understand, because "they" keep developing new oils and materials that will withstand higher stress. The average piston speed is somewhat easy to calculate. Stroke * RPM / 6 = pistonspeed in Ft/min The actual piston speed will be higher in the middle of the stroke and lower and stop at TDC and BDC. Thure Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 24, 2003 Share Posted May 24, 2003 Thure; I had forgotton all about ball bearings until you mentioned the oil. I never thought of the oil viscosity at all. That is a very profound point! Thanks for bringing it up! Quote Link to comment Share on other sites More sharing options...
Oltmann Posted May 24, 2003 Share Posted May 24, 2003 The Honda S2000 has a avg. max piston speed of 4965 fpm. I think it uses a standard 30 oil. I wish I knew how they did this. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 24, 2003 Share Posted May 24, 2003 Oltman; I comission you to search out this phenomena and report back to me, Spare no expense and my God will reward you (I am in good standing). Quote Link to comment Share on other sites More sharing options...
Oltmann Posted May 25, 2003 Share Posted May 25, 2003 S2000 Engine parts Check out #3--talk about a girdle! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 25, 2003 Share Posted May 25, 2003 Let me see..... I think I'll buy the dipstick first, just to make a commitment you understand Ya, that is some layout. The DOHC is not fair of course, unless I can have one free! What is the bore and stroke of that simple device? Quote Link to comment Share on other sites More sharing options...
Guest Thurem Posted May 25, 2003 Share Posted May 25, 2003 Let's somebody make that S2000 into a S4000 V8, now I think we are talking. 480 hp 10krpm 4 liter V8, SWEEEEEET. Thure Quote Link to comment Share on other sites More sharing options...
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