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Posted:
Fri Nov 30, 2007 1:52 pmby 106-1194218389
Boy do I agree with Larry! Years ago I was trying to break into the head porting business and was criticized by the nay-sayers because my ports were not "pretty". I generally leave my ports with a carbide finish and do not smooth them with cartridge rolls to be pretty so I was really hammered on to the point it affected my business. What was really funny is the cars running my heads were kicking butt. A car I did heads on and intake system won at Road Atlanta in SCCA F production 3 out of ten years and always finished in the top 3. Were my ports "pretty" #### no they just won.
John
Posted:
Fri Nov 30, 2007 2:26 pmby SWR
Posted:
Sat Dec 01, 2007 8:23 amby larrycavan
Posted:
Sat Dec 01, 2007 8:51 amby jsa
[quote="larrycavan"][/quote]
Larry,
Nothing against the company, I simply stated to beware of bore adapter size as it might not be obvious what that means for a YB engine.
Consensus on the YB is that valve shrouding is an issue, and a larger bore adapter inflates the flow readings.
The flow readings they claim for a standard YB head are 15% above the readings I have gotten for a standard YB head.
You make many valid points in their defence, however I still maintain my concern about their results.
My biggest concern is that someone unaware of the effect of bore size for a particular engine's results might look upon those results more favourably than due.
It is also worth noting in _general_ that CNC gives excellent repeatability, but that in itself does not mean the product is automatically best of its kind. It could just be repeating less than stellar port shapes. I'm not saying the product in question is stellar or less so, just use of a non representative bore adapter raises questions.
Posted:
Sat Dec 01, 2007 10:27 amby SWR
Posted:
Sun Dec 02, 2007 2:32 pmby 106-1194218389
What is a sad thing is that CFM is not the only story. A sewer pipe flows a lot of air. You have to pay attention to velocity and turbulence, how the air enters the cylinder etc. I have been listening to a CD I bought "Porting By the Numbers" an interview with Darin Morgan. In the interview he states that the NHRA Pro_Stock heads are actually smaller now then they were just a few years ago. He also points out that the exhaust valves on these 500 cubic inch engines are now only 1.800" where the stock off the shelf BBC heads are 1.880" He also dyno'ed an engine with 2 sets of heads. The ones that flowed more air lost 150 hp at 9500 rpm. They had a little turbulence .150" above his maximum valve lift but it killed the heads. So CFM is not everything. The time slip at the end of the drag strip is the best criteria.
Posted:
Sun Dec 02, 2007 7:21 pmby jsa
Posted:
Sun Mar 22, 2009 10:37 amby msj442
i just now got around to reading this thread and holy crap. its funny how i thought we were all for the same thing. i guess i know now that even if you post a comment, advice,etc. it will always get shot down no matter what it is. ive learned to just read and not post lately.
jmo, max
cool link larry.
Posted:
Sun Mar 22, 2009 12:13 pmby jfholm
The one thing I like is we may not always agree but that is a good thing. We learn from these discussions. That is what is good about this forum there really is no contention or arguing, just good discussions. I think that is why the flow bench itself has turned out so good. We don't always agree on something but we are adult enough to discuss it and the cream always seems to float to the top.
John