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914World.com _ 914World Garage _ Rod Ratios

Posted by: r_towle Jan 2 2007, 11:47 AM

Hi, I searched (Phrase rod and ratio) and got over 1000 hits...
I think search just does not work right...I cant figure it out...

Anyways...
What is the optimum rod ratio for a type 4.
I would like to hear lots of opinions on this one.

Rich

Posted by: smontanaro Jan 2 2007, 12:27 PM

Try

+rod +ratio

Skip

Posted by: jd74914 Jan 2 2007, 12:35 PM

According to BrettW in this thread the optimal type IV ratio is 1.70 to 1.80.

http://www.914world.com/bbs2/index.php?showtopic=4964&st=0

Posted by: jd74914 Jan 2 2007, 12:41 PM

Hmm . . . this graph migh interest you, as well as the article I bookmarked it in a while ago.

http://www.e30m3performance.com/tech_articles/engine-tech/rod-ratio/index.htm

IPB Image

Posted by: Twystd1 Jan 2 2007, 01:18 PM

What are you looking for as far as HP / TQ..????

And at what RPM will this engine be living in most of the time?

Clayton

Posted by: Jake Raby Jan 2 2007, 10:05 PM

Optimum rod ratio is dictated by the RPM range goal for the engine as well as the cam and head work as well as the longevity goal...

For engines I design I shoot for 1.75:1 for street engines, but I have some powerful combos that run as little as 1.55:1. Our race engines that sustain RPM use 2:1 or more

There is no perfect rod ratio for the engine.

"Its all in the combo". as always.

Posted by: Borderline Jan 3 2007, 12:39 AM

Dema Elgin (local SF Bay area cam grinder) has an interesting article on engine design including rod ratios. lhttp://www.elgincams.com/campaper.html