Kevin Shasteen Posted June 9, 2001 Share Posted June 9, 2001 MikKZ; that sounds like a killer small block! What I cant get out of my mind/discount; is the article (I forget who found it first)-it was about "The Small Block Chevy Should Have Built" where the engine was build to alledged impossible spec's then ran on cheap pump gas & w/high comp.ratio w/out detonation. To me that proves there is something to longer rod's & their ratio; but then why all the fuss about it? Either there is irrefutable evidence or someone has pulled the wool over the eyes of a lot of people....including myself! Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
DavyZ Posted June 9, 2001 Share Posted June 9, 2001 Mike kZ: I agree; you have one killer small block; great website too! Kevin, that was an article AFR has on their website (I think). They destroked a 400 sbc to 350 ci, using a 327 crank. Sweet motor. If those specs are true, I'd love to have one. High compression on pump gas; yowza! David Quote Link to comment Share on other sites More sharing options...
Guest Night_rider_383 Posted June 9, 2001 Share Posted June 9, 2001 pparaska... Thanks man. Yeah this little 383 should be a real screamer. The parts is running up high $$$$$ but she's gonna make some power and i feel if i keep the revs under 7 grand and do all the reg stuff like oil, plugs etc this thing should last long enough to where i can drop it under the hood of my kid's 1st car with maybe just a freshing. (19 years old, no kid for another 5 years atleast) lol. Yeah from what i heard theres two reasons chevy went to the larger journals and one you hit the nial right on the head. The other was to keep there price down. I guess they looked at it like this if all our small blocks used the same cranks with just diff. strokes we can save blank amount of money per year. If you stop and look at it for a min the cranks on sb's are almost the same on the large journal years. 267, 305, 350 used the same strokes, 307, 327 used the same, the 302 used a diff one as well as the 262, and we all know the 400 is totaly diff. All the stuff about rod angles looks great on paper but in real world cases the rod angle don't really mean alot unless your in pro racing where the engine is reved high and has alot of power and the piston loads are in the higher range. On your streeter what does a 1.8:1 r/s/r over a 1.5:1 r/s/r mean. NOTHING. Youll never know the diff. if you drove both engines around town and if they was both the same all but the rod angle. Vause your streeter dont see rpm over 5000-5500 any way. What he said about all the angles is right 100% but the only it really matters is in like nhra pro street or faster class drags, Nascar, bush, etc where the rpm can see the up side of 7500-9000 rpm. Look at the 400 sbc it had the worst rod stroke ratio and rod angles of any sb chevy built and we all know how long one of them things can last. Yes that don't last as long as say a 350 and yes the cyl. wear is greater and everyone looks at the reason why is cause of the rod angles and ratio. This could be true but my thoughts on it is cause of harder use. 90% of all the 400's was put through @*&% with towing, racing, etc Mike kZ.... Sounds like a sweet engine you got bud. Not bad numbers out of it at all. Our 327 has alittle more hp but alittle less torque. 453 hp@6200 with 480.4 ft lbs @5400. I wished i build for more low end like yours but it will all work out lol. Heres a few specs on it. 9.78:1, forged trw flat tops, crane power max 272/284 with 454''/.480'' lift. 1.6 rollers brings lift to .484''/512'', 1965 double hump heads, full race port work with enlarged intake runners, smooth polished exhaust ports, race bowl work, manley valves, alum intake, re-jetted edelbrock 600 cfm carb. It don't do too bad 14.39 in a 73 chevy c/10, 4700 lbs plus me, 3.08 open rear, th-400 trans, 2800 stall, Gets only 10 mpg but i'm working on ways to get more Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 9, 2001 Share Posted June 9, 2001 Okay, so Rod Angularity only comes into play at higher RPM's(?); then this is one more piece of the pie to the Rod/Stroke Ratio theory. I agree that most 400's were put thru the ringer w/heavy foot drivers that usually didnt own the vehicle (employees driving tow trucks/service trucks..,ect,ect). Looks like the controversy continues-where will it end? Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 9, 2001 Share Posted June 9, 2001 I always thought the rod angularity problem wasn't one of power, but of wear. I was under the impression that bad rod angles make the bore wear out faster on the right and left sides of the bore? It would seem the longer stroke on the crank would put the rod at a more extreme angle at 90 and 270 degree from bottom dead center? That was my understand of rod angularity and why it can be a problem. Is that wrong? Regards, Lone Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 9, 2001 Share Posted June 9, 2001 What intrigues me the most about the higher rod/stroke ratio is the purported better octane tolerance - in other words you can either run lower octane gas or hight compression on the same gas than a motor with a lower rod/stroke ratio. Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 10, 2001 Share Posted June 10, 2001 That alone is the very issue that keeps me leaning toward the whole idea that there is something to the rod/stroke ratio (longer rods being better) & why I like the article "The Small Block Chevy Should've Built". I'ld just like to know (I guess only a piston mfg knows this) is exactly how minimal a piston compression height is considered too minimal for an engine on the street where durability is an issue/as opposed to a race engine that will be rebuilt on a weekly/monthly basis(?). Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted June 10, 2001 Share Posted June 10, 2001 My tenous understanding is that the longer rod motors tend to have different piston acceleration and dwell times at TDC. This effects power, wear, and knock tolerance. Longer rod motors make more torque and apparently don't knock as easily. IMO if you're building a motor from scratch and have a choice ot build a longer rod go for it so long as cost doesn't go through the roof. In my case I simply set a HP target and let the builder decide. I'm NOT even sure what length rods I ended up with but it should run close to the number. The only thing I would NOT want done is to put the rod pin into the ring package and not to have a real short piston. With high rod ratios a short piston is liable to rock and the pin in the ring package - well that's obviously not good Other than that I let the builder decide. Sure, a roller cam and longer rod might have gotten me more power under the curve but I'm not bench racing this puppy, I'll be driving it. As was stated earlier - chances are if you drove two nearly identical motors back to back you'd probably not notice the difference just due to rod ratios. Know that longer is better to a degree but don't go nuts with the cash trying to get an extreme Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 11, 2001 Share Posted June 11, 2001 Wiesco had been playing with short skirted pistons and was seeing some real power and durability (used in a few indy cars as I understand it), but I also wondered about the rocking of such a short design, I'm sure with less skirt, weight would be decreased and maybe a little less friction if the skirt was dragging. I can't recall they're take on it and how they combated the potiential wear from the thing rocking in the bore unless they used slightly tighter clearances.. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 14, 2001 Share Posted June 14, 2001 pparaska wrote: "...and if you're going to be buying rods, why not build a 350 with 6 (or 6.2 possibly?) inch rods to get the rod/stroke ratio in the (better) 1.7-1.8 range. Broader torque curve (improved breathing characteristics, etc.), less road angularity, better detonation resistance (for the same static compression ratio)." I must be missing something regarding the improved detonation resistance. As the r/s ratio increases, the piston speed near TDC decreases. All things being otherwise equal, this makes an engine MORE knock prone as opposed to less. With a shorter rod, the increased piston speed increases the volume of the combustion gas (after TDC) faster, dropping the peak pressures and temperatures. Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 14, 2001 Share Posted June 14, 2001 I didn't make that up. I've heard this before and although I don't believe everything I read, I do put some stock in the writer of the article "The 350 Engine Chevrolet Should Have Built". Read the first column of the second page of that article here - it's about the only place I can cite right off to back up my assertion above. Actually, I think the reduction in peak pressure and temperature that you point to with a shorter rod actually hurts detonation resistance - if the combustion space is growing more rapidly after TDC with a shorter rod, then the conditions for a good burn (swirl, turbulence, sufficient pressure and temperatre) means decreased combustion efficiency, and more tendency for knock. I think I see your reasoning that higher pressure and temperature are what can cause detonation, but if it hasn't occurred already on the compression stroke (due to correct tune, octane, swirl, etc.) than it has no reason to go unstable and start detonation after a good start from the spark plug. That's my theory, I have no idea whether it holds water . Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 14, 2001 Share Posted June 14, 2001 Everything I've read about Detonation indicates that Swirl, [(Quench & Squish)sometimes considered the same thing] combined w/an appropriate compression determine detonation. The sources I've read claim that an engine's Quench has the most effect/non-effect on detonation; anything over .060" Quench & your pushing for disaster-even at a 9.5:1. Most SBC's piston deck clearence are usually at .022" in a SBC, plus the .038" gasket crush thickness ant you're at .060" already-when the piston is lowering itself in the cylinder-the pressures are decreasing & this phenomenon combined w/a High Quench clearence causes determines. I've read where even turbo engines can benefit from a .010" Piston Deck Clearence-keeping the compression the same by altereing the piston/dishcc's. This would allow the piston to maintain its Quench/Squish for a longer period of time. By Deck Milling the engine to near "0" piston deck clearences to maintain better Quench...you're fooling the engine/this is basically the same thing you're doing by increasing the Rod Length-your are increasing the Dwell time of the piston during its Quench/Squish: Better Effieciency/less loss of cyl.pressure = more power. I'm not sure about the wear factor-jury is still out on that one. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted June 14, 2001 Share Posted June 14, 2001 I thought the article spoke about actually being able to run the engine w/less timing advance due to the piston "Dwelling" at TDC for a longer time span-this allowed the timing to be altered...in a less radical manner. Yes/No(?). Any other ideas? Kevin, (Yea,Still an Inliner) [ June 14, 2001: Message edited by: Kevin Shasteen ] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 15, 2001 Share Posted June 15, 2001 I don't know the answer. I agree that turbulence and swirl are important - and it seems a short rod motor has more of it than a long rod motor. The short r/s means higher piston speeds, hence more turbulence. What I've seen looking at cylinder pressure versus crank angle data is that knock generally occurs about 10 - 20 degrees after TDC (at say 2000 RPMs). The mechanism for knock is that for temperatures and pressures above a certain level (related to octane rating), the fuel air mix spontaneously ignites and does so all at once, as opposed to burning uniformly. As a result, the peak pressures spike up, which is what beats up the engine. Once the fuel and air mixture start burning, the radiated heat of combustion heats up the remaining air fuel mixture. This increases the pressure (the combustion chamber and the gases behave almost adiabatically). So even if you have a good spark and lots of turbulence, if you advance the timing too much, the peak pressures and temperatures inside the combustion chamber cause the remaining air-fuel mix to light off spontaneously and all at once. I agree with Pete and Kevin about longer rods improving combustion efficiency. I read the Hot Rod article and don't know what to make of it. Bob Quote Link to comment Share on other sites More sharing options...
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