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| Long rod and offset grinding crank? https://www.slantsix.org/forum/viewtopic.php?t=18672 |
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| Author: | Bren67Cuda904 [ Wed Jul 19, 2006 6:40 pm ] |
| Post subject: | Long rod and offset grinding crank? |
I really like the long rod idea, and the the offset grind of the crank. Can I do both? Is there a piston available for this combo. I don't think the KB268 would work anymore. I really know very little about it. I am compiling different combinations to present to my builder for final approval and then to build. I trying to save some money by doing much of the research for him. I want to get him in the ball park and let him take it from there. Are these 198 rods hard to find/get? Does Doug D have them on hand? |
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| Author: | Jeb [ Wed Jul 19, 2006 7:06 pm ] |
| Post subject: | |
198 rods are pretty scarce, especially considering that not many 198's were built in the first place. I think Doug used a Chevy Vega pistion. The normal piston for the long rod 225 is a 2.2 piston. Have read "Stroking the Slant Six" in the article's section? It list part numbers and everything. |
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| Author: | Ron Parker [ Wed Jul 19, 2006 7:10 pm ] |
| Post subject: | |
The 2.2 Chrysler pistons will work on the 198 rod . The pin location is the same as a Slant Six. You can get them in 1mm oversise or 2 mm oversise. I think the 1mm puts you about 40 thousand over and the 2mm about 80 thousand oversize. But im not sure my racing buddy Bagel can answer this. Thanks Ron Parker  It Aint Over Until I Win |
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| Author: | Bren67Cuda904 [ Wed Jul 19, 2006 7:56 pm ] |
| Post subject: | |
I have read all the articles. I like the long rods because they allow for more time to let in fuel air mixture in and more time to exhaust gases out. The piston spends more time at the top and bottom of the stroke. This seems like a big deal to me, especially for a NA engine. Offset grinding = more stroke = more cubes which is always good. I also want pistons that are more tolerant to nitrous. What is the total distance from piston hitting the head and center line of the crank? I don't want to be more than 10:1 CR |
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| Author: | panic [ Wed Jul 19, 2006 8:15 pm ] |
| Post subject: | |
"The piston spends more time at the top and bottom of the stroke." No, only near the top, time spent near the bottom is less. The difference in position for a 225 rod vs. a 198 rod is only a few thousandths of an inch. For example, at 30 degrees ATDC the difference is less than .004". The difference in rod ratio is only 4.5%, just below what is considered to be the margin of observable change. You do realize that to offset grind the crank and use 198 (or any slant) rods the crank must be welded? |
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| Author: | Bren67Cuda904 [ Wed Jul 19, 2006 8:53 pm ] |
| Post subject: | |
If time near the top is more so is time near the bottom. The crank rotates in a perfect circle to the best of my knowledge. If an unground stock crank is ground .025 (offset) there should be no crank welding needed. .005 for the polish = .030 total. Inside of the journal gets most of the grinding. The question here is whether the 198 rods will work and not crash into the head/valves. |
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| Author: | DusterIdiot [ Wed Jul 19, 2006 9:47 pm ] |
| Post subject: | Depends on the head... |
Quote: The question here is whether the 198 rods will work and not crash into the head/valves.
If you have a nice unscathed 1963 Truck head like I had with a 68cc combustion chamber...probably not...now with a ported polished job with a cut to make a 40 cc chamber you might be beggin' for it... You can always dish the pistons a bit... -D.Idiot |
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| Author: | slantzilla [ Thu Jul 20, 2006 7:36 am ] |
| Post subject: | |
I have used 198 rods w/ 2.2 turbo pistons in two uncut blocks. Deck height on both was -.028". 
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| Author: | Doctor Dodge [ Thu Jul 20, 2006 9:35 am ] |
| Post subject: | |
Quote: I have used 198 rods w/ 2.2 turbo pistons in two uncut blocks. Deck height on both was -.028".
This matches what I have seen with the stock stroke, 225 "long rod" combos I have built.If you off-set ground the crank to .030 U/S as discribed and did some careful measuring and block deck "clean-up" resurfacing, you can get to a zero deck height condition. Match that with a closed chamber head and the correct head gasket thickness and you will have a "trick" engine that has a light piston, a nice rod ratio and a quanch / squash zone. The only trouble with this combo is the fact that there are no closed chambers cylinder heads and the compression ends-up in the 12 to 1 range. (when using a flat top piston) DD |
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| Author: | argentina-slantsixer [ Thu Jul 20, 2006 12:45 pm ] |
| Post subject: | |
doc, would you elaborate, draw or just enlight me about WICH shape should a closed combustion chamber have? I've been reading this for years and I can't exactly figure out mainly due to my lack of experience with other engines than the /6. |
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| Author: | DusterIdiot [ Thu Jul 20, 2006 12:54 pm ] |
| Post subject: | Closed... |
closed is just that, they look a lot like a cylinder head with just enough chamber for the valves to move in with no shrouding and little else...or they are just a "shelf" on one side (the side opposite the spark plug...so as the piston comes up it drives the mixture right at the electrode). There are some interchangeable terms you can look up like "quench head" (The Ford guys talk about the Boss 351's chamber and it's quenchability lots), or "swirl port" (the magnum engines got this), Chevy for a while bantered about the "Soft head"(aka swirl ported)... -D.Idiot |
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| Author: | sixinthehead [ Thu Jul 20, 2006 1:53 pm ] |
| Post subject: | |
When offset grinding, I think you only get half what you take off the crank. For example, if you cut .030 off of one side of a new journal, your new center is .015 "higher" than the original. Now in larger terms for clarity; say our circle is 10 inches in diameter and you cut 2 inches off of one side - the center of the circle has moved to 4 inches from 5. So, in your engine, you should still have "room at the top" even with an offset grind. Either way, you will have room to adjust your CR by decking. |
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| Author: | Bren67Cuda904 [ Thu Jul 20, 2006 6:10 pm ] |
| Post subject: | |
I definitly want to avoid 12:1 CR, but your talking about flat top pistons, right? If I used the KB268 piston (18cc) wouldn't the CR be around 10:1 even with the offset grind and 198 rods? Offset grinding the crank .030 does move center .015 . I didn't beleive it until in plotted it in Autocad. |
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| Author: | Bren67Cuda904 [ Thu Jul 20, 2006 6:15 pm ] |
| Post subject: | |
After offset grinding and a .080 over bore. (I believe thats a standard piston 1 mm over size) What would my cubic inches be, for the mathmaticaly inclined? |
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| Author: | zedpapa [ Thu Jul 20, 2006 8:28 pm ] |
| Post subject: | |
i had been toying with this idea also. only my idea was to have a set of custom rods built at 7.000" long and using the stock piston pin but going to a smaller bearing diameter to facilitate more offset when grinding the crank. the stock bearing diameter is 2.187". going to a 2.000" diameter bearing size would allow increasing the stroke +\- .093" to get a 4.218". my only question now is are bearings available for this size? i want to say that nascar engines use this size bearing, but i can't remember. also from everything i have read in Hot Rod and CarCraft, it seems that smaller bearings are better suited to higher performance. with a bore of 3.480 and a stroke of 4.218 ci comes out to 240.71. found the calculators at http://www.supermotors.net/vehicles/cal ... /index.php i just think if you are going to the trouble and expense of doing this, why not go all the way? (and get more cubes!) zedpapa |
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