123 replies to this topic

[EunUCh]

Its always good to hear different ideas/opinions on these subjects,the cylinder head is where it all happens and the more you look into it the more complex it becomes when you start thinking of it as working unit regarding air speed in and out of valves at a variety of revs,its also excelent to hear from people who have had the practice and knowledge in these areas of which many of us have not,keep up the good work,as for your request threeblindmice,i think 1quicklj couldnt have put it better,knowing the little that i do based on a bit of theory thats the track i would go down if it were mine,goes along with the KISS principle,from what little i found out the xu1 head apparently had a different head casting than std.Should imagine genuine heads are a bit thin on the ground but even if you dont have original u can always build up non orig as 1quiklj suggested and use xu1 spec cam/carbs/ex.maifolds etc.What 1quicklj suggested to do is almost exaclty what me mate does to his race engines and he held track record for good while too.something about those engineers at fishermans bend isnt there.sure there's always room for improvement but we can only go so far in world of compromize.
good work guys.

[N/A-PWR]

Needed to find a place for this Flowbench Design Guide,

 

and this thread 'AIR SPEED' is perfect. 

[LJ RB30]

I have a similar problem!
I bought 1 of these
http://www.flowperfo...com/system.html

Needed to find a place for this Flowbench Design Guide,

and this thread 'AIR SPEED' is perfect.

[EunUCh]

Shiit,this thread still exists,don't even remember starting it??

The DYI flow bench looks simple enough in principle to build to get some numbers.

 

One thing that me ol mate often mentioned was that we are using a constant flow source and even though people have  been 

doing these type of tests for quite some time and have had success with the numbers..are there other factors involved?

 

Of course they work, but just as a matter of interist ,i would hesitate a guess and say that even though flowing a port with or without a valve inserted will yield some numbers to the better or worse depending on procedure.

 

For example..if we flow a port/manifold/carb. under constant flow conditions we end up with a number.

This number will be in CFM ,and just say for example a combo flows 153cfm,does this mean that the particular cylinder that the combo.is connected to will make the horsepower equated from the airflow number?

 

Or, flow/ pressure(speed) would more play a part with what the cam. lobe is doing in respect to what the piston is doing through

the travel cycles of both in respect to each other in order to maintain some sort of flow/air speed?

 

What the flow bench does is give an indication of flow under the conditions we use them under,but does it really give an indication of

what the combo will flow with a pulsating condition in an engine?

No doubt they work,but i just wonder if the users of them are just not letting on what we might call a " correction factor".?

 

 

[LJ RB30]

^^ yah not wrong!

I have no intention of becoming a professional porter as obviously there is large amount of variables to take into consideration!

But for the price of the unit I got im gunna try "improve" a stock blue head for a turbo project I been gunna do for a while!
I have a few heads I can practice on , both 9 & 12 ports!
Even scored a yella terra on a freebie motor & box! 😄
So I'm gunna flow that as is then blend the throat into the bowl as it has no porting other than machining for bigger valves & clean up where the head bolt boss was replaced with a tube.

Will be a very long slow learning curve but I'm in no hurry!

[EunUCh]

Thanks oldjohnno,that explains why a larger duration/lift cam fitted to a small bore engine with the same porting/valve size as a 12 port

six won't make as much as a fast high  lift short duration on smaller cylinder,it killed something somewhere across the range but works better up higher in rpm range and the "curve" is longer/smoother but not as strong through the range.The peakiness seems to have 

moved up in the rev range?..related to the "sweetish range" in terms of flow/air speed/cam?

Ol mate said the same thing...can't see it by eye,was just a touch here and there,could not pick it,was only on an air horn they were playing with.

 

 

[Dave6179]

Wouldn't a similar stiuation exist if the head port was slightly larger than the corresponding manifold port? A small... 1mm, step up into the head would create a 'wave barrier' from running back into the manifold. Zorst ports are apparently best with a 1mm step bigger into the manifold to prevent reversion.

Cool thread man!

[EunUCh]

^ which might explain why the "back" of most intake valves these days are rather "flat" looking as compared to the earlier versions that were "conical" that tended to force the intake charge into a "cone" formation around the head of the valve as the new charge was being pushed in,even though "Smokey" says that it is ideal to have a cone shape charge,  on the hand if it is not fast enough and tends to want to head "straight down...sort of) maybe with a good balance of volume/speed that is why the mix is "nicer" and helps at a higher velocity to spread/sheer it up a bit on the intake.

 

From another point of view , the exhaust valve "sees" a flat "face" on it's way out , even though it has some pressure up it's arse they reckon an exhaust valve is more efficient than an intake valve , hence they are smaller.

Just throwing ideas around.....unlike the stuff that was flying today, better go pick up a few tools tomorrow..

Edited by EunUCh, 12 March 2015 - 07:08 PM.