Port comparison

[rpmag]

I have recently tested 6 different ports on a flow bench at 25" H2O. The ports are known to have a poor short-turn radius that is too tight. The port modifications were attempts to overcome the flow seperation that occurs in the std port.

The std port flows:
in: .05 .1 .15 .2 .25 .3 .35 .4 .45 .5
cfm: 26 51 74 96 115 127 136 139 142 144


One modified port flows:
in: .05 .1 .15 .2 .25 .3 .35 .4 .45 .5
cfm: 25 50 73 95 112 127 141 154 163 167

My query is in regards to possibility of onset of flow seperation. In the std port the volume of flow per .05 in of lift starts to decrease at .2-.25 a 12 cfm increase, at .25-.3 there is a 9 cfm increase and .3-.35 there is a 3cfm increase.
From this I get the impression that the flow is perhaps starting to seperate at .2/25 and the flow seperation get progressively worse, i.e. has greater detrimental effect on the overall flow rate.
Whereas the modified port reduces the impact or amount of flow seperation at the same lifts.
Is this a reasonable train of thought?

 

[patprimmer]

Low lift flow is mainly dependent on the shape of the back of the valve and valve seat area of the port. Flow at high lift is more influenced by the port itself.

Regards

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[rpmag]

But what level is high/low lift? Std cams lift to 10mm, so more .25 and more is 'high' lift?
Same valve and same single angle seat dimensions used in all tests. Port mods made to port floor only.

 

[ivymike]

if you calculate minimum flow area vs lift, the results might give some idea of how to pick "low lift" vs "high lift" values for your geometry.

 

[patprimmer]

Half inch lift is not much for an American V8.

I would be a truckload for a 4 cylinder 16 valve about 1.5 to 2.2 litre engine

Regards

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[rpmag]

It is a 2lt 8v engine from mid 70's.

 

[patprimmer]

rpmag

What have you been smoking?

2lt 8V?

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rpmag]

Pat:
1: I do not smoke and I am unsure of what you are querying.
2: The heads from a 2 litre, 8 valve engine are used as the basis of a magazine article. They are used because they have a known problem, they are cheap and are representative of many heads of that period, these engines (8 valve, 4cyl) still form the basis of much of club level motorsport and marque classes.
3: the article series is looking at different solutions and what results are gathered. The intention is to start broadening the technical enquiry, which in current Australian magazines has been lowered to the stage that a porting article is 7-800 words, a photo of a head, a bloke holding die grinder and a finished head that then purports to flow X horsepower. None of which is particularly enlightening.
4: yes I could use 16v heads. Infact I could report of a 1600cc NA Honda engine that makes 147kW, but that is a $20k engine (not counting development cost) and not really in most people's budget.

 

[ivymike]

I'm sure he thought you meant that it was a 2L V-8 engine (American) from the mid-70's, which would have been pretty unusual if it existed at all.

 

[Warpspeed]

rpmag definitely said 8V not V8. It all seems perfectly clear to me, and I don't smoke either.

 

[patprimmer]

Sorry. I read it as a typo for V8.

2 litre 8 valve 4 cylinder should have slightly lower lift than an American V8, but considerably more than a 16 valve 4 cylinder.

0.4 sounds pretty fair for high performance road car and 0.5 or a little more sounds about right for a race engine.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warpspeed]

Hehehe Pat, did you know dyslexia is more common amongst highly intelligent people ?

 

[patprimmer]

It's also much more common among men than women.

I wouldn't dare to suggest that our two observations might be related. ;-)

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RRBD]

Remember, a port the flows well at low lifts will also flow backward well too (reversion)You need to try a few things to determine what is happening, I would try moving the head a small amount so the valve is closer to the centerline of the cyl. bore and retest, this will tell you if the valves are becomng shrouded at mid to high lifts. I try to make intake ports most efficient at peak flow demand, which on most american v-8's is around 75 degrees atdc. This is the point where the piston is traveling the fastest, and will have the highest differential pressure between the cylinder and atmosphere. (Engine's dont suck air, what you feel is the effect of two different pressures trying to equalize)

Just my two cents

Scott