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View Full Version : I would look at larger intake valves.


Dessertrunner
06-02-2011, 12:25 PM
I have no experiance with engine valve but Matt has mentiond to me that our engine could take larger dia valves. What I would like to find out is how much larger can they be. Also what amount is everyone shiming the existing valve in height.
If I was going to put larger valves in the heads would it be worth using slightly longer valves at the same time then I would be able to keep the existing lifters?

Love some help at this point.
Tony

Dessertrunner
06-09-2011, 02:10 PM
Givent the lack of comment you must be busting to know, you can't change the valves as they are slow close to touching now. I willpost a image on the weekend showing what I mean.
Tony

RallyBob
06-09-2011, 04:55 PM
On Jack Laverty's EG33, we went with .5 mm oversized Supertech valves, since they were a no-cost upgrade option. I would have prefered at least 1 mm oversize (intake and exhaust).

However, given the weakness of the exhaust flow compared to the intake flow, I would rather use stock intake valve diameters, and go much larger on the exhaust valves (2 mm is not out of the question IMO). I feel there's a bit more power to be had this way.

The exhaust side was only flowing about 65-70% of the intakes (the straight ports outflow the dogleg ports), and that was after a lot of porting work on the exhaust ports. Intakes were barely touched by comparison.

Dessertrunner
06-15-2011, 09:34 PM
High Bob,
After looking at the intake valves I think there is stuff all to gain from that change. So you are right the outlet valves need some attentation.

Is there some sort of ratio on airflows relationship between inlet & outlet sizes?
Tony

RallyBob
06-16-2011, 06:45 PM
High Bob,
After looking at the intake valves I think there is stuff all to gain from that change. So you are right the outlet valves need some attentation.

Is there some sort of ratio on airflows relationship between inlet & outlet sizes?
Tony

Yes, I have found that the exhaust should generally flow 75% to 80% of the intake to be able to make the power the intake ports can support.

As is, the SVX heads only flow 65% at .450" valve lift. So they respond well to exhaust porting and to a more aggressive exhaust cam profile.

XT6Wagon
06-16-2011, 07:05 PM
My personal view is unless you are going to spend the time and money to properly develop a motor (lots of testing of lots of configurations), its best to stick to stock valve sizes. Exception to this is when your stock valves are an odd size and a slightly bigger size is common and cheap as dirt.

Why I say this is that many people in the Small block V8 world would buy heads with the largest valves possible. And make unimpressive power. Often it wasn't just the valves they screwed up on, but it was a fairly major source of thier poor performing engine. The extremely large valves looked awesome on a flow bench, but when faced with a real engine, didn't do anything. Too much of the valve was shrouded by the cylinder bore and what intake charge managed to get past it, didn't flow in in a proper efficent way.