Quote:
Originally Posted by CHANMADD
Mark... If you are going to build an engine that is not going to rev very high and use a cam that will make power low down on the rpms by all means build an engine with a rod /stroke ratio of less than 1.6:1 .
If on the other hand you are a driver who likes to rev your engine at higher rpm's then a better than 1.6 ratio is desirable . As you may know.. the current F1 engines use a ratio around 2.5:1 which allows them to rev to 20,000 rpms for hours on end. I would hazard a guess that the rod ratio had a lot to do with the design of these engines, but being an engineer I would imagine that I do not have a clue as to what I am talking about. A low Ratio may hold up on the street for a period of time, but if you are building an engine for longevity a better ratio is desirable. Of course if you are building engines for others and don't really care how long it will last ........then it does'nt matter at all.
I am also a little confused as to what the head size has to do with Rod/Stroke ratio???  |
As to the RPM/Rod ratio.....any Big Block Chevrolet. There's a ton of 6.385 rod x 4.250 stroke high rpm engine out in the world. (1.50:1)
AS to head size and rod ratio look at the Big 3 (well.....you know....)
Most stock engines have a rod to stroke ratio of about 1.7:1. The differences are the 351C....Big Block Chevy...(too much head) and BB Chrysler, 455 Pontiac, 455 Olds (not enough head).
The slower the head, the earlier you need to get air moving. The faster the head, the more you need to slow it down in the higher RPM range. (speed relating to the velocity/capacity of the intake port.
Rod ratio is the last thing one should worry about when designing an engine. There are exception...when using a Boss Block, for example. The cylinder length is so short (stupid short) that you have to futz around with rods to keep the piston in the hole at BDC.
You really should read that link to 460.com that I posted.