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i was on a web site the other night and they were saying the best rod to stroke ratio is 1.75. most stroked out fords are around 1.50. which is the as far as you can push this ratio acording to them, at this ratio your rod is starting back up the cylinder at a 45 degree angle. which causes sever side wear. just thought i would throw this against the wall and see what falls off. richard ([email protected])
 

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"BEST" can vary from one situation to another. 1.75:1 is a good compromise for a typical hot rod engine. Sometimes you end up having to live with something less than what you would really like to have. Rod ratios of 1.5:1 or less are definitely getting into the danger zone. Each engine, usage, and parts combination will tolerate a little more of less than the next.
 

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The popular 4.300" stroke w/6.800" rod is 1.58 ratio . Which works nice .
The 4.150" stroke w/6.800" rod is 1.64 ratio , if you want a longer ratio .
 

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the reason i brought this up is some guys are running 4.5 stroke and 6.7 rod which is 1.49, courous some feed back from some of these guys as to how its working out.richard
 

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Hey Lem, does this difference in rod ratio affects HP in the higher rpm Range, say 5000-7000 rpms? Is it wiser to use a 4.14 crank vs a 4.3, in a hot street/manual transmision, light car? (2800 lbs)
 

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rpenny said:
the reason i brought this up is some guys are running 4.5 stroke and 6.7 rod which is 1.49, courous some feed back from some of these guys as to how its working out.richard
These engines run just fine and there is no issue.

By the way, the factory rod ratios for the 460 & 429 are 1.71 and 1.84 respectively, whereas the factory non-stroked chebby 454 rod ratio is a less than spectacular 1.53. Imagine stroking that. Sad...very sad.

Paul
 
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Rod Ratio

Richard, I run a 4.5" stroke with 6.7" rods & I haven't had any problems.
 

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rpenny , it is a matter of context ...do you want to drive it on the street or drag race it ?
About any thing will work 1/8 mile at a time . If it is on the street the 1.64 ratio will be better . Also , the truck late model blocks and race blocks have a longer cylinder which works nicer with the long stroke/short rod stuff .
 

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hey thanks guys. loved the chebby ratio, and i agree it does depend on what the application is. iam just an old dog still enjoying the learning side .richard
 

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Certainly "BEST" varies from application to application.
An example is the 500 inch PRO STOCK engines which used to run a rod/stroke ratio in the 1.8's however, as the cylinder head ports kept getting larger and larger that higher rod ratio with only 500 cubic inches could no longer start the airflow in the port fast enough so, they went all the way to the 1.5's in order to make it work for them; (although in a very NARROW rpm band).
That was more of a plus than the extra "cylinder wall loading" was a minus to making more flywheel horsepower so, it works very well. In other applications it works exactly the other way; every engine application IS different. Some it matters a lot and others it hardly matters at all.
 

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Rod Ratio, 400 Chevy.

Personally I don't think there is an ideal rod ratio, what's good for one engine is not necessarily good for another. I feel that the effects of rod ratio are very much overstated but that if it does have a measurable effect it goes something like this:

If you have a large volume effective intake tract and a rather restrictive exhaust port it's better to have a lower rod ratio, a shorter rod and a longer stroke. Why? Because making the rod shorter makes the piston approach and leave the area at or around TDC more quickly but it produces the opposite effect at the bottom of the stroke, the pistons motion changes more slowly with the shorter rod. What this does is work the intake side harder while giving the exhaust a little bit more time to do it's thing. The exhaust lobe can have a chance to get the valve open a little bit farther before the piston really gets going back up the cylinder thus helping out the exhaust side.

Does a 4.500 stroke 6.700 rod combo work? Absolutely.

Remember a 400 Chevy engine has a rod length of 5.565 inches with a stroke of 3.75 or 1.48 and they ran 100,000 miles easily enough.
 

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I hope shorter works.....

Mine is 1.438 :shock: 6.835" rod, 4.75 stroke. The only thing I can do is raise the deck.
 
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