Port & Polish head - high end gain low end loss?

[RyRy210]

Originally posted by Sensei:
Just some FYI for those interested...
With today's technology, costs and time have been cut down dramatically using what is called "Extrude Hone" http://www.extrudehone.com/

-Sensei

[/B]

I've actually used Extrude Hone before, which is what Ford's SVT division uses. However, Extrude Hone is more well known for being expensive, as well as being the best because everything is computer controlled. Most companies that offer port & polish, also do other things like back-Cut valves, radiused blend seats, three-Angle valve job, and hand-lapped & vacuum-tested valve seats etc. I think Gerry Johnson did some of these other mods when the heads are out, most people do. Extrude Hone is just the port & polish, nothing else. They are the best nonetheless, but are also very expensive considering thats the only thing they do.

 

[Sensei]

Yes you are correct extrude hone is expensive. Especially at first to create an actual jig if one does not exist. But time, consistency and actual gains of exturde hone has a value, which I should of clarified.

Originally posted by RyRy210:
As you all know, peak gain really doesn't say as much as a broad well rounded power curve. I started this thread with the question whether I will get high end gain, but losing some low end power if one does the port & polish. That still remains to be answered. My guess is that I will lose some low end in exchange for high end power. If this is true, then maybe honda engineers thought that more street driving is done than race driving and more low end power is desirable.

You raise a very important issue, which is often over-looked.
The answer to your question is yes you will lose low end. Your idle as well, will be extremely rough, due to improper atomization as previously mentioned.This will eventually lead to fouled sparkplugs.Another note... to take full advantage of a port/polish stepping to a colder heat range plug will be benificial as well, but this would make your low speed and idle problems even greater.

On a different note, why didn't honda use a better exhaust system & use stainless steel? better Headers? We know alot of things can be done to get more power, why didn't honda unleash its full potential? Its a compromise between cost, power, reliability, and liveability. Some people like their NSX quiet, some want to make it scream like a Ferrari. Honda had to make a happy medium.
[This message has been edited by RyRy210 (edited 06 April 2002).][/QUOTE]The cast exhaust manifold is less prone to cracking and retains heat.The heat is better contained which helps combustion, warm-ups, and prevents large amounts of the heat from dissipating in the engine compartment.The early collection of the exhaust ports aids low end as well.As you may know, these are the reasons as to why low end is loss when headers are used. The later NSX model design is much improved and has longer runner which collect latter. This as I said loses low end but the 3.2ltr has more torque to begin with so the loss of low end wasn't as great going this route. Rather using aftermarket headers I think early model NSX's would result in better performance using the later style exhaust manifolds(if they fit),but I haven't had an opportunity to try a set. Other than the early style cast manifolds, the entire NSX exhaust tubing is stainless steel. Even more the exhaust tubing is uniquely double walled and expensive for heat and sound insulation. These are one of the many small but crucial conceptions that the NSX features which goes unnoticed.

-Sensei

[This message has been edited by Sensei (edited 06 April 2002).]

 

[Gerry Johnson]

If you were to set up a degree wheel on any NSX engine, I would almost bet that the cam timing will be off, it maybe only off 1-3 degrees but never the less it would be off. Extrude hone only polishes the ports
and does nothing to change the shape of the runners or the ports, so power is gained but not like when the ports are changed and polished to increase flow.