valve sizing question

[Anonymous]

Have Oz head. Don't want to go overboard on intake valves and risk rupturing the water jacket on #1 cylinder. Based on that, is there any benefit to going with oversided exhaust valves only? Or is it an all-or-nothing affair? Want to build as much reliable power as I can while still keeping it streetable.

Other things to do- porting and bowl work as recommended by Falcon 6 Handbook. New seats, guides, etc. Gonna try to get some flow bench work done to balance out flow across all cylinders. Headers & exhaust port divider.

Any other suggestions?

--mikey

 

[AzCoupe]

Don't want to go overboard on intake valves and risk rupturing the water jacket on #1 cylinder. Based on that, is there any benefit to going with oversided exhaust valves only?

The #1 exhaust where the problem occurs, but only occasionally. I know of only two cases where the water jacket was ruptured, but its an easy fix. It can be reached from the backside and built up, through the t-stat hole.

Here's a pic of the oversized valves installed.

 

[Anonymous]

Hmmm.... food for thought....

Next question: Are there any drawbacks to the oversized valves in terms of low end power and torque? Streetability is a key concern over pure top end. I'm more concerned with getting a fat power & torque curve through the midrange. Looking to make my redline b/w 5000 and 5500.

One other thing to note (that will improve driveability)- I'm planning to eventually run this with an EFI setup.

thanks

--mikey

 

[addo]

The blokes I have used for machine work tend to think there is a valve size limit for efficiency in these heads, but they're looking more from a circle track viewpoint. There are so many inferior aspects to the chamber design compared to newer engines, that it's hard to see why every bit of flow wouldn't help. You can go even bigger than Mike's sizes, in theory. I had a post on it with some calcs by SR, but they were lost in one crash.

Design the cam factoring in flow specs, and it should be fine.

Regards, Adam.

 

[CobraSix]

I have oversized in my Oz head, just like Mike described. No problems to date, and fun as hell. Lot's of umph.

Slade