With the new block on the horizon, and the capacity for a large bore and a stroker crank, I started thinking about what would be a good combo for me. The engine will be turbocharged so major cubes are not needed. Some things I have thought about; A larger bore will move the walls away from the valves. A shorter stroke will allow higher RPMs A longer rod will reduce the rod angle A stock 455 has a rod length to stroke ratio of 1.69 and a rod angle of 17.2 From what I've been able to find on the internet, 1.69 is low and 17.2 is high. I've tried some different combos and came up with this; Bore = 4.4 Stroke = 3.8 Rod = 6.7 (reduced stroke by .1, so I added .1 to rod, which will move piston up .05) Cubic inches = 462 This has a rod/stroke ratio of 1.76, rod angle of 16.5 (same as a chevy 327) Bore = 4.5 Stroke = 3.7 Rod = 6.8 Cubic inches = 470 This has a rod/stroke ratio of 1.84, rod angle of 15.8 (close to ideal according to link below) I found this on the web and I'm sure there is more info out there; http://victorylibrary.com/mopar/rod-tech-c.htm Any thoughts or information to share?
I believe your thoughts are correct.I think Rod angle is very important. The 500+CI Buicks have never run like you would think,With only getting the CIs through Stroke the good rod angle is lost.(At least thats what I believe). Wayne Emmott :grin: 70 STG 1 Conv 12:80s 78 Skyhawk STG 3 7.80s ?
The problem with what we have is a deck that is too tall to shorten the stroke. If we could drop the deck it would solve our problem. It would give a shorter pushrod too. Your using a bit heavy of a piston using the stock rod. A 6.800 rod on the stock stroke would be better but then do the math for a 3.7 stroke with a 7.0 rod. For a power adder it is not the way to go. 1.75 is as high as you want to go for a power adder going by the general rule of thumb. I looked at doing the same thing. I haven't found the answer yet. You can alway try it to see how it turns out but the math works out against it.
There are alot of opinions on this subject some like long rods some like shorts ones.It's all about the way you like to build a motor your head design cam timing compression power band and nitrous or a blower etc. From what I have seen in the motors I have inside knowledge of any thing in the 1.6 1.7 range works good.Over 1.75 the piston dwells to long at tdc expecially if you run a power adder.In a circle track motor or endurance application long rods are good keeps wear down.
I made a couple of charts in Excel then overlaid them to get the green area. The numbers on the left in each cell is the rod angle, the number on the right is the rod/stroke ratio. The blue cells represent rod angles of 17 degrees or less. The yellow areas represent rod/stroke ratios between 1.6 and 1.75. The green areas are where the two overlap. As you can see, there is no area where the rod angle is below 17 degrees AND the rod/stroke ratio is below 1.7. Ain't life grand! :laugh: It looks like the factory components are a good compomise, but I would like to increase the bore size to help with the air flow. http://www.popularhotrodding.com/enginemasters/articles/chevrolet/bigblock/0305em_turbo_bb/ But, he ain't talking! :ball: (and 10,000 RPM is too much for me!)
Get the crank you want, get the piston you want, and put a connceting rod in to "Connect" the two together. People take too much emphasis and time on what size rod and stroke ratio and blah blah blah. I wish I could still find the article written by Rehr Morrison. (If I do I'll post it) It talked about stroke to rod ratio, and how most of it doesn't mean squat. He tried all sorts of combo with different length rods, and got the same EXACT power numbers and same amount of cylinder wall wear. If fact in the dyno numbers from all three combos, all you could see was one line. In the bottom is said "this is not a misprint, the gains and losses fromm the different rod to stroke ratio's are so slight, they don't even show up" His bottom line, get your crank, get your piston, and put a connecting rod inbetween. If you've got a 100,000 mile motor, well yah rod to stroke ratio will probably be a concern, but very slight. A local guy who bracket races has a BBC with a terrible 1.41:1 rod to stroke ratio. It makes 1200 HP and runs great. As far as cylinder wear, its no different then their previous, "longer rod motor" My point, the advantages you gain from a long or short rod motor are so minute, you might as well not worry about it. Spend more time worrying about other things for you car that count.
I second this opinion. SOme people sepend too much time working with the quote, ideal rod length to stroke ratios. I n the scheme of things , it just does'nt matter that much. Jim Burek P.A.E. ENTERPISES
Yes! One less thing to worry about! :TU: Now, how much benefit is it to have a larger bore to move the cylinder wall away from the valve? o No:
A search of the Internet (Google) turned up precious little on the Reher-Morrison article. The title of the article is "Shattered Myths & Racing Truths" and was found to be discussed on this website: http://hotrodders.com/t5070-15-1.html go about 1/2 way down the page for some more technique discussion. Looks to be a Chebby site but they too came to the conclusion that rod length/stroke ratio amounts to a whole lot of nothing. Craig
Of course everyone likes more cylinders but there was a chart somewhere showing all the production engines ever made. The Chevy 4cly iron duke motor has the best BS ratio, with 2nd place going to the 60* 173 2.8 V6. The 60* [degree] motors have an edge. As a 2.8 owner I can say it rev's like a two stroke. It revs fast and hard. Combined with a stick shift tranny, the fast reving n good gearing makes up for the lack of stock power. RPM'sXGear's=Fun I relate it to owning a 600 motorcycle. As long as you use the full RPM band and the gears right, its fun. Dog it off the line or short shift and you might as well give it up. ------- But the problme with the BS ratio thing is you need the parts to take advantage of it. By the numbers the 173 2.8 is an easy 14000 RPM motor, but there are no parts made that could hold up to that. Even though by desing, It could. Its why most people go for the biggest bore and longest stroke they can get. Then juice or turbo it.
From what I see in that article is they worked in a .400 range in rod length.Ok to make a short stroke 455 to work with a light piston with a cd of 1.350 and a stroke of 3.70 you would need to go from 6.6 stock to 7.350 inch rod thats 3/4 of an inch thats excessive but to get the piston light It would need to be done,If you mean to tell me R-M would put a 7.350 rod on a 3.70 stroke I highly doubt they would.I don't think there is a perfect rod to stroke ratio but a 1.98 r-s that the above would provide is way out of the ball park.So you mow .250 off the deck and pull the same amount out of the rod you still have a 7.10 rod and a ratio of 1.91 this still sucks.I assume R-m was working with a 454 with a stock 4.0 stroke going from a 6.135 to a 6.535 rod the r-s ratio goes from 1.53 to 1.63 not 1.69 to 1.91 or worse.I don't think you want to throw in what ever fits and I know R-m wouldn't. My above 455 specs where with a 10.550 deck and the piston at zero deck
10inchbuick said; Buicks4Speed said; I wonder if there could be some minor changes made in the casting and a run made with a shorter deck? Then the excess could be milled off the top and keep the deck thickness. (just thinking outloud) What I'm trying to acheive is better air flow and the ability to rev higher, but really the air flow is the biggie. If a larger bore will help air flow, then that's what I need to do. It doesn't take lots of cubes to make power with turbos and the engine is at 462 now. There are small cube V6s out there making well over 1000 hp so the "need" for more cubes isn't there. Lawrence Conleys Tweaked II is making over 2000hp with a 4.4" bore and 3.62" stroke. http://tweaked2.com/ http://www.hotrod.com/techarticles/engine/113_0401_turb/index5.html It looks like one of the chioces in my first post with a piston with the pin moved up might be the way to go and let the rod angle and rod/stroke ratio fall where it may. Is there anything I'm overlooking? o No:
From what I understand the deck on the new block is .750 thick so you could remove .250 as I mentioned in my last post.This would bring you to 10.250-10.300.I would still shorten the rod a little maybe 6.950 with a 1.480 cd with a 3.700 stroke and a 10.300 deck.The piston would be .020 in the hole and this would be a 1.87 r-s.With a 4.500 bore and a 3.7 stroke it would be a 470.With a turbo I think you could get away with it.I still don't think it would be good for a nitrous motor.
FWIW Mopar Performance said that 1.85 was the best R/S ratio for a drag race engine. I have no idea what it is based on but that is what they said in their "Engines" book. Smokey said use the longest rod you can, but he was talking endurance engines at that point.
I'm sure I don't remember everything correctly, but I read somewhere that F1 cars have a stroke of approx 2" and a rod length of approx 6" for a rs ratio of 3, and that they turn 18,000rpm! They produce around 1000hp out of 180 cubes, no turbo. I'll try to find the info again as it was interesting but not really information I could use in my Buick! :laugh: If there's something I can do to make the engine better the first time around, that's the time to do it instead of having to buy parts 2 and 3 times to "get it right". The other side of it is I'll probably have more power then I'll know what to do with, anyway! ou:
F1 do all the elite stuff. I believe they don't even run a round piston or conventional valves. On the new block. Works for me. I like it! :TU:
The key is 18000 rpm for three hours or so.At 18k piston dwell at tdc isn't that important. Plus they ONLY make around 850 HP at 3 litres :eek2: .They don't even run valve springs the valves are hydraulicly operated and the motor cost 250k plus
Rod-to-stoke and cams..... So how much do you adjust your cam if you go with the 3.7 stroke and 4.500 bore over what you would normally run?? Will it run like a 440 and make more low torque with a weaker top end?? I have my thoughts but curious if anyone else has thoughts on this. It always seems that Buicks make good power numbers in the 260 duration range and low 270's on the intake. Where do you think an adjustment needs to be made if any? We look to turn our Buicks up with the new block but if they wont make any more power whats the point?
Does anyone know how to calculate how much stress would be removed from an engine at a given RPM by destroking it X amount? I have searched everywhere for this, but I can't find it. My thoughts were exactly the same as Alan- destroke it, use ultralight rods and pistons, internally balance it, and go with as big of a bore as possible to let the heads breathe. Add boost, and it would be BAD! Also, wouldn't it be possible to do away with the block girdle up to the 600-650hp/6500max rpm level by using this type of setup? It has to tweak the block less- less mass thrown around and all. ________ Affair Live
Well, I ended up with a bore of 4.5, a stroke of 3.9 and a rod length of 6.7, for 496 cubes. ( The rod/stroke ratio is 1.72 and the rod angle is 16.92). I guess I'll just have to deal with the extra cubes! :laugh: A friend of mine has a BBC with a bore of 4.6, a stroke of 4.25 and a rod length of 6.385, for 565 cubes. The rod/stroke ratio is 1.50 and the rod angle is 19.44 degrees. He runs 4.8 in the eighth and mkes over 1000hp naturally aspirated. Uncharted territory? o No: The only thing that seems to be the problem is what Buicks4Speed posted before about the deck being too tall. It appears that blown (and nitrous, too) engines like the shorter rods to reduce the dwell time at the top of the stroke. A longer rod will increase the potential for detontion. It looks like the deck could stand to be as much as .500 shorter.
