Track Tac

General lifter / head question...

D

Devil-D-Dawg

New member
On the topic of ratio lifters, does upgrading a head with larger valves do the same work as adding ratio lifters? OR does adding a cam with significant lift negate the need for a ratio lifter?

If one is trying to build an easy breathing motor, can you forget about the ratio lifters and just focus on the porting / valve size, and cam?

I understand that, when getting to the high side of compression (and low side of clearances) there could be interference between valves and piston. I have no intention in cutting recesses into a piston but I am looking for the deepest "breaths" possible.

Thoughts?
 
I think you mean ratio rockers, not lifters. Lifters are the small round things in the bottom side of the engine, which ride on the cam libes, rockers are in the head. To answer your question, no the valve sizes have nothing to do with lifters or the cam. Ratio rockers are a way to get more lift at the valve than using a bigger cam. Some people like to use ratio rockers to get more lift, while others prefer to get a bigger cam, and some like to use a bigger cam and ratio rockers both together for max lift at the valve. For what you are wanting, I would look into a high lift cam and a set of ratio rockers both, since you want to get as much air/fuel into the motor as possible. You could upgrade the stock size valves to a 27/25mm combbo, but if you do that I would at least do some mild port work and put a bigger better carb on it than the stock carb, such as a Honda fx390 carb or a tillotson 304wx
 
TYPO - I meant rockers / not lifters.

I am using a 390 carb. The head has 28/26mm - full port and polish.

I'd like to stick with the bulletproof Champion rockers - they are solid, tough, and inexpensive. If my head flows well with oversized valves, and I have a tall profile cam - is there any reason to add a ratio rocker? My point is, are things really going to breathe any better if I push that valve another millimeter or so? There has to be a point of diminishing returns, right?
 
the point of diminishing return comes with engine failures.
yes big valves add breath as do all the other things you mentioned Rockers included.
you are nearing that point .
The other thing is after a certain point the gains get smaller for each modification..
Diminishing return again.
The carb may be worth looking at now.
Or more cubic inches.
 
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Good points by flattop.....and yes devil, every little extra bit you can push that valve open is gonna allow the engine to take a bigger breath
 
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