Once again, ovalizing the primaries doesn't cause cracking. I don't know why you keep claiming that. Sure, if you crushed them over and over, in opposite planes, until it strain hardens and fatigues (note the implication of the word fatigue), then sure it will crack (brittle fracture). But fatigue doesn't occur when ovalizing.

When ovalizing you're barely scratching the surface of the 304's excellent elongation properties. That's why you never see cracking of a manifold's primaries in the ovalized area near the flange, even when they're really thin wall primaries made with tubing instead of heavy wall pipe.

 

I dunno why he thinks we're ALL wrong and he's right. Goes against everything I've ever learned. Guess his manifold is exempt from Newton's first law of motion.

 

I never said it caused cracking or even that it would crack. I said its more likely to crack. And it is more likely to crack than if it was left the way it was originally formed. Plus there is no point in going through all the trouble if its not going to net any significant gain in power. Thats the issue at hand more than anything.

And as for Pat, All the information you need is here, port size, pipe x-sectional area. You know the volume of the CC and you could calculate the EGVs using the pressure and volume of the gases. Then figure out what the change from the circular x-sectional area to the ovalized one will be. Why dont you calculate it all out and show everyone how "right" you are? All of your posts are quite frankly pompous and unnecessary.

 

Nope, I'm not the brilliant engineer going against common wisdom. I know a change in X section will cause losses. YOU"RE the one saying that it doesn't matter, your way's better, and the losses are insignificant. So why don't YOU prove you're right. Cause I've got the majority on my side. You're the underdog. Come on, this should be easy for you.

 

assume, for a moment, that squishing down the pipes will not change the material properties or lead to cracks...

having an instant transition from the oval flange to the round pipe will create an instantaneous change in the velocity and pressure of the exhaust gas.

this causes the gas to curl up around the sharp corner at the outside of the flange and reverse flow direction for a short distance in that space. the turbulent gas region will affect the smoothness of the flow out of the port. it may even be so turbulent as to increase flow resistance in the tube as compared to a smaller tube. gas flowing against opposite-direction flow is going to encounter higher friction than against a solid pipe wall. at the very worst, the turbulent flow will impinge on the original port diameter and slow down the flow more.

And just to keep you smiling, here are some silly pictures.




(this one from your friends at honda.


You may be thinking "oh but the pressure will stay constant!" and you'd be wrong. a diameter change like that results in irrecoverable pressure loss.

 

jc,

a) as jkav points out - headers / manis don't crack at the ovalized primaries, and lots of them are ovalized. They more typically crack at the collector welds.

b) if they aren't likely to crack at the ovalized spot, then it's just a question of total resistance - your sharp transition flange + bigger primaries vs. ovalized, smaller primaries.

c) the above is easy to measure with a flow bench. Why don't you do it? If there's a chance the majoriy here is right, it's worth the time and effort to do so, don't you think?

 

How about we let his fabricator build the manifold they want to build?

 

 

funny this was actually in the first paragraph of the first post. at this rate noone will discredit this statement.