Gasflowing of cylinder heads

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Gasflowing of cylinder heads

Postby pepa on Mon Apr 19, 2010 4:29 pm

We have covered the basics of cams and the management systems around them in the previous issues. So now what more can you do to your aspirated car? Well there is the usual route that everybody will recommend and that is to make it breathe even better. Immediately the next sentence will contain the phrase ‘gasflowing’. Now what is this and what does that achieve. As I mentioned in the previous articles – an engine is simply an air pump. To make it get more air in it helps to remove the restrictions in the intake and exhaust air paths. The main aim of gas flowing is to make this airflow as efficient as possible. Now why is it needed – can’t the manufacturers do this right?
Well the answer is twofold. The first problem is this thing called mass production. The engineers design the ports and intakes as good as possible and it’s great in paper form. But somebody has to make it into metal and the process is a casting. Because of the way a head is made there are always two or more parts of castings that have to be joined and some machining have to take place. Now in mass production there are several castings and there will be ones that are better than others will. There will also be better machining and worse so almost no 2 heads that come out of a factory are exactly the same (this also explain why some cars simply perform better than others straight off the factory floor). The first aim of doing a gas flow job is to remove these imperfections from the castings and to basically get the port shaped and clean as it was designed. This is also called blueprinting, as the aim would be to get the metal product looking like the engineering blueprints would have been.
The second objective is to possibly improve on the original design. Now while this is not always possible and sometimes result in something worse this it the point where experience and testing comes in. When a tuner starts with a gas flow for a specific car he/she? should know beforehand what is going to be done to the rest of the motor. Is the capacity going to be bigger than it was before – what cam is going to be used – is it going to be carburetor or injected etc? It is no use starting with say a 1.8 head and you make the ports bigger – you install bigger valves and the end result is going to be used on a 1.3 motor. That engine will be dead and will probably only start performing at 8000 rpm. The main reason for this is something called air speed.
When you take a plunger of a certain size and you suck air through say a 10mm pipe the air will move at a certain speed through it. If you make the pipe bigger to say 15 mm and using the same plunger and pull it at the same speed you still move the same amount of air but it will travel through the pipe slower. So why do we need airspeed? This helps with how well your cylinder is filled with air. The higher the airspeed the better the cylinder fills (remember the cam story and why it works) so if you end up making the ports and valves too big for that capacity motor it will actually perform worse at lower rpm than it was before you started changing things. This is why it is important to use reputable tuners as they would know what works and what does not (mainly through trial and error!). A head that has been opened too much is useless except for maybe a serious rpm racecar and will cost you to replace it. So you do port and valve size work according to the requirements of the customer and considering the other modification to the motor.
Without changing anything in port sizing and by simply matching the manifolds to the head and cleaning the casting up, considerable increases can be had, because the airflow through the port is smoothed which help promote airspeed. The result is a motor that is smoother and often lighter on fuel at cruising. It will most definitely make more power as well. As with everything so far – it is always a compromise some way or the other. You will flow a race engine slightly differently to a street motor because racecars do not spend time in traffic jams and do not need to be performing well under 5000 rpm. Also if you use the extra power made available from the flow work the car is likely to be heavier on fuel. But generally speaking this is one of the most worthwhile exercises you can do to a cylinder head and rates high in bang for buck. Of course all of this will again require the same consideration to tuning as would a longer duration cam as you are now putting more air into the motor which will require more fuel.
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Re: Gasflowing of cylinder heads

Postby CDB on Mon Apr 19, 2010 4:44 pm

some good info there pepa
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Re: Gasflowing of cylinder heads

Postby DRIFTWORX on Tue Apr 20, 2010 10:02 am

I must say well said!!!!

i have a few options to add on

To improve the airflow the following litle things make a great improvement on any standard based head

multi angle valve seats

Skimmed down and polished valve stems

polished valve faces

polished combustion bowles

polished and ported exhaust ports

cleaned and flow matched inlet ports

skimming the head down alot!!!!

adding a decent cam to compliment the head job,

just by doing these litle things to your head you wil have a noticable improvement in power and fuel economy

itl also give you a bit more torque to do the things you like , speeding

you can even go as far as having al the valves balanced on a scale to ensure they are all the same weight.

converting to solid lifter setup with a oil spray bar can give you an extra 3k rpm ( very tricky modification!!! ) ive only done ten and they rock,

then people forget that you must compliment al this with a decent intake system that has been cleaned out and flow matched, ad a decent branch and exhaust, and make sure you got a high flow air filter otherwise its al a waste of time.

and on fuel injected cars adding a modified throtle body wil double the effect you get merely because you motor gets more air

alot easier
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Re: Gasflowing of cylinder heads

Postby Krakie on Tue Apr 20, 2010 10:55 am

DRIFTWORX wrote:converting to solid lifter setup with a oil spray bar can give you an extra 3k rpm ( very tricky modification!!! ) ive only done ten and they rock,

What does this cost, and cams will have to be changed as well right?
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Re: Gasflowing of cylinder heads

Postby DRIFTWORX on Tue Apr 20, 2010 8:10 pm

that stuff costs big bucks and, only for the quartermile and track junkies

for racing purposes only!!!!!!

the convertion goes for extra 3K over and beyond any other work gets done

and that should be minimum5k for a wel done head, ( not just a port and polish ) excl spray bar

also wil need fully blue printed motor..

otherwise you gona be taking the crank pieces out of your dashboard!!!!! :bom:

i can get t hat done for you too, dont stress. ( the blue printing part )

normaly charge bout 2k per motor for the blue printing, ( include balanced and ligtned pulleys )
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