Look man, I think i'ts been shown that it's a mute point......there are PLENTY of motors out there that have a comparable or worse rod/stroke ratio than a 347 or any of the other strokers discussed and have gone 200,000+ miles. I think alot can be attributed to better technology but anyway you look at it 99.99% of those looking to build a "high performance stroker engine", whether it be for a hot street car, street/strip or all out race car, are not that worried about getting 150,000+ miles out of them. Piston technology, lubrication technology, engine machining techniques, etc...etc... have improved leaps and bounds in recent years. In other words, you get what you pay for......build a cheap ass stroker w/ junk parts and poor machining and it WILL NOT last very long........build it with good parts and good machine work and you will get a long performance life, but as you already know this applies to ANY engine, not just a stroker.
So what I said was not true? It is not a mute point. For every engine that goes 200k with almost as many dollars in it, 100 others blow up, break, get rebuilt every few miles. It is not as rosey as you portray IMO. It's not just money you have to put in an engine, but a lot of thought too. Some comprimises are necessary IMO to build a good street engine. All I am suggesting is build a 331 instead of a 347 to get less oil consumption and less stress on your parts. Don't have a cow. Every engine will have wear and burn oil, but the 347 will have it worse in most cases. Dave
Either way, I think this was one of the most informative things I have read on understand stroking. Thanks
I've never seen a "cylinder wall" failure in a SBF whether it's a stroker or just a stock motor, however I will give an example of personal experience, which is all I have to go by. My brother bought his 88 mustang with about 20,000 easy miles on it......well, he drove it until it had 60,000 on it and decided it was time to put nitrous on it.....we sprayed the car just about every weekend until it had 120,000 miles on it. One night the front half of the crank decided to take a trip through the oil pan. This was a typical motor w/ typical gearheads beating the crap out of it. So I guess if we would have had a longer rod it would have lasted longer????? Nope.
No need to get defensive. Everything everyone has said is true. As far as cylinder walls go, no one ever breaks a cylinder wall from too much lateral piston force. HOWEVER, the bottom of the bore can move around a lot if it's thin enough and this will lead to piston scuffing and broken skirts. The bore can also ovalize which will sqeeze the slug too also causing it to fail. Open deck blocks such as Honda suffer from a ton of bore deflection. Luckily we don't have to worry about the top end moving around, just the bottom end. So by reducing the amount of lateral force you can reduce the amount the bottom of the bore will move around, which is always a good thing. Having said that, unless you're approacing 8,000 RPMs or better, it's probably not something to worry about. For the street warrior who occasionally sees 6,000 RPM, the 5.4 rod in the 347 is plenty good enough. You're probably not going to snap off a rod at those speeds either. For rod ratio, you can go a little deeper in to the science. It can also depend on if you're going EFI or carb. A carb needs a nice strong vacuum pulse to idle properly and to have decent tip in response. EFI doesn't really care. It is true that your fluid velocity with a longer rod is going to suffer at low RPMs, because the air is elastic and if you don't give it a real hard tug at first it's going to be slow to get going. Once it gets wound up though, it's not as sensitive. I have heard of some high winding IRL engines pick up a couple ponies with a shorter rod, but you can go too short and not get enough good burn time, plus you decrease the life of the rod. That's for a 9,000 RPM 900 HP 3.0L V8 though. Not something that's very relavent for this discussion. Piston dwell time: What was said earlier about the hot gases being able to push on the piston longer at TDC was true, but the mechanical advantage of an almost vertical crank isn't much. You get your max advantage when the crank and rod form a 90 degree angle (because the rod is technically a 2 force member). The real advantage to a longer dwell is a longer burn time at MAX compression. The more pressure the fuel is under the more better it burns to point. Obviously too much pressure makes it detonate. So, if we burn our fuel under a high pressure for a longer period of time we can get all of the energy out of the fuel and into the air. That will result in more work being done to the piston. So, from a thermo-dynamic standpoint long rods are very much good. Piston accleration: Force equals mass times acceleration ( F=ma). Mr. Newton came up with this little equation and it is the sigle most important knowledge of physics anyone can possess, because everything is derived from this. Kinematics tell us that the bigger the rod ratio the smaller the piston acceleration, which gives us less force on the rod, which equals less stress. So, long rod engines will put less stress on the con rod. What does that mean to us? Now we'll have to look at the S/N (stress vs. number of cycles) curve for the con rod under a high cylcle fatigue condition. If the rod is already under the S/N curve with a short rod, then a long rod won't help. If it's over the S/N curve, a long rod could bring it down and give more life. If it's an aluminum rod, a longer rod will always help since aluminum does not have infinite life like steel or iron can (ferrous vs. non-ferrous metals) if the stress is low enough. Piston clearance and ring tension: High revving race engines love to go together loose. The more they clatter and carry on at idle and the more oil they burn the better. If NVH (noise vibration harshness) is an issue for you and you don't want the neighbors complaining every time you fire up the beast and smoke them out then you'll want to run a tight piston to wall clearance with an offset pin and a high tension oil ring. If you want to pass emissions, you might also want to make sure there's not much blue smoke coming out the back too. If the pin is pushed up into the oil ring that's not the worst thing. It's not the best, but you can get a ring kit that takes this into account so it still scrapes the wall like it's supposed to. No worries there. All engines burn oil if you have a PCV (positive crankcase ventilation) system. This is simply from the windage, hot oil, and other things that makes the oil airborn and increase pressure in the pan. If you're not burning it, then it's oozing out the valve cover breather. No engine ever in the history of the world is going to have 100% oil retention. It's just impossible. There are lots of things you can do with baffling and filtration to get the consumption down though. That's why some valve covers have that steel wool stuff in the breather hole. It's so the air can get out and the oil sticks to the wool and falls back down into the valve train. Piston Force: The longer the rod, the more likely it is to buckle and fail from excessive piston force. Now, I have only seen rods fail in this manner due to detonation. Under normal load, I have not seen a rod fail from buckling assuming everything else is great. A lot of times the small end of the rod will fail because the oil isn't getting all the way up there, or the pin is flexing enough to bind the rod or scuff the small end bearing. Either way, things normally bend first then rattle around a couple of times until they break. Rods will also fail in compression from buckling because of a hydro-locked cylinder, but this is normally from them sitting out in the rain over night and then someone hopping in and firing it up. More of an accident than a design flaw. You can also hydro-lock a cylinder if you put a TON of fuel into it, but I don't think any of our engine will even flow that much fuel. Block failure: The number one cause of short deck windsor block failure is a cracked main web. These blocks are good to 500ish HP depending on who you talk to and are definitely the weak link. The crack generally starts out in one of the mains because it has been stressed too much too many times. Then the crack propogates into the cam journals then into the lifter bores and then starts going front to back and splits the block in half. Fairly common for these things. Normally when a main starts to let go things move around a lot and you can whack the cam with the rod generate debris scuff a bearing and all hell breaks loose with the rotating assembly before the crack propogates far enough to split it all the way in two.
Man i have been gone a while. sorry I Feel the same way. if you are so busy that you cant check your oil every once in a whila and add some. buy a honda.
After all the Websites I have been to, I'm going to say Rod Ratio is probably the most mis-understood part of building. Seems most people just hear a part of the equation. I have heard people say everything from "smokey said so" (that was 30 years ago) to just repeating what they read about more time at TDC. It's about matching, are longer rods better? Answer is NO! but then again could be yes. Depends what your doing. Ever hear bigger isnt always better? Just as going from 8:1 to 9:1 compression makes more of a difference then 13:1 to 14:1, the same holds true for rod ratio's, going over 1.70 in a street motor is pointless. Your better off matching your system. Head port sizes play an important role when selecting rod ratio, in some cases shorter rod ratio's are an advantage. Knowing your rod ratio is so over embellished. Leave it to the guys spending 75,000 on a drag motor trying to pull an extra 1-2 horsepower.
awannabeegrabber, Not sure what you mean since my honda burns more oil than the grabber and dirties it faster. (must be the wet clutch cause it doesnt smoke)
LOL...as long as we are getting off topic, a "mute" point is one that is not made. A moot point is one that is not relevent. Back to our regularily scheduled programming.....
I'm glad Maverick.to has so many smart a**es!! I bet most people here could sit on a block of ice cream and tell us what flavor it is!!!!
How old is your honda. The new ones burn no oil, they end up getting like 40mpg. I dont no about the wet clutch thing. it could be possible
83 honda magna. (wet clutch is a motorcycle part) it doesnt smoke so im not sure where the oil is going. but its negligeable, just more than the mav.:evilsmile
Ok. i was talking to a racer down at the strip last weekend. MIDNIGHT DRAGS. there were some amazing rides there. I asked a guy about what he had, He replied with a 350 in a ford mustang. I asked why. he said he did it quick because he had a 502 at home and he used the 350 for that night. So we talked about his 502 and he said he did the opposite of stroking the motor. His 502 had like 400 cubes. i was puzzled, we got to talking and he said that he have a shorter crank for more rpms, he ran 9s with a small block 400 with the same set up just set to a 327. Ever herd of this???
