Cylinder Head Gas Flowing?

[Chris_uk]

Ok so I seen something on TV the other day about modifying a cars Cylinder Heads by the use of Gas Flowing, it was done to a 1.8 Lotus Elise and boosted the BHP from about 120 to over 150, I was wondering if its worth doing to my Mazda 1.5? ive been reading a few web pages and some say it helps, others say its a waste of time and money. Any thoughts on this idea guys?

Chris

 

[George Patches]

I really doubt you'll be able to pick up 25% more power like that Lotus. A modern cylinder head is a pretty advanced thing and while gains can be made, I don't think they'll be as drastic, but still every bit as expensive.

 

[Racebrewer]

5% to 8% power increase sounds more reasonable unless it is a really poorly designed head.

It is a very common process in the states and the results depend a lot upon the skill and knowledge of the guy doing the porting. "Going overboard" can do more harm than good.

David Vizard has written about the process and what he has learned over the years.

I'll see what links I can find for you.

For a ton of "Hand's on" in, try looking at the forum on Flowbenchtech.com

John

 

[Danielcut]

On our cars I'd think it'd be more trouble that it'd be worth unless you've maxed out every other performance option and were still looking for more.

 

[AN7]

You watched wheeler dealers

By porting and polishing the head can flow more air/gas, BUT, all depend from the setup of the motor, camshafts, cam timming, etc.

So maybe the head can flow the air needed for the 150hp but it is not sure that the current setup could accomplish that.

 

[Chris_uk]

Yes AN7, it was indeed that very show

Ahhh so I think ill scrap the idea for now then, just toy with the idea of this new remote tuning option ive come across here in the forums. Need to save some pennies first though

AN7, do you reckon that with the stock exhaust and the CS SRI, the 2 has more pull lower down? I seem to have lost the sucked into seat feeling since I had my new exhaust installed, I do seem to have a bit more on the higher rev bands though, although it doesn't seem to have the same kind of feeling as before the exhaust install.

Chris

 

[jeffmsp]

well with n/a piston engines, running a larger intake pipe, larger exhaust pipe and porting the cylinder head will shift the power band from stock.

stock is typically designed to provide the flatest torque curve possible over the usuable rpm range for easy daily driving. If slapping a big intake or exhaust pipe on a car was really that good of an idea for the everyday end user Mazda would have done it themselves.

modifying the diameters of the pipes and ports significantly effect powerband. IE with larger everything you typically lose low end power and gain top end power.

The length of the intake pipe also plays a key factor in tuning (converting from a short intake to a long intake makes a difference in resonation characteristics).

Usually people look into this stuff and run some simple calculations to find the right combination by factoring in some basic variables (desired peak HP RPM, intake pipe diameter and length, exhaust pipe diameter, port sizes/shapes, exhaust pressure etc) to make max power at desired RPM before they start buying parts.

In performance applications you typically sacrifice power and response "under the curve" IE 1000-3500RPM to gain power in the top end as this is where you spend all your time when you are racing.

In non performance driving (IE not redlining your car every gear) the stock setup may actually make more power @ X rpm then a modded setup, especially when dealing with modified ports, manifolds, camshafts and anything else that drastically alters the engines volumetric efficiency (VE).

so while that lotus in the show (I watched that too btw) gained some peak HP, you can bet it would be down on power in the low end. not to mention it would have poor low rpm and cold start emissions (larger ports = poor airflow at low rpm = poor fuel atomization and fuel scavenging).

It is always important to size your mods to the actual CFM that will flow through the motor. IE: No sense in having a intake/exhaust/cam that can support 400 CFM @ 7000RPM when your motor flows 150CFM @ 7000RPM etc.

Its all about matching things correctly to get the best gains.

There are tons of books and online info regarding tuning n/a engines if you guys are interested google has everything you would ever need to know.