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Vc496

4K Small Port Head Ported Compared To Large Port

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Being spending a bit of spare time working with a 4K small port head using the std 36mm intake and 29mm exhaust for a good friend.

After carryout some tests on the small and big port heads found that the bigport airspeed was way to low so I decided to rework the smallport and to find that it outperformed the big port. Modified the small port intake to the correct cross sectional area required for the valve size great average airspeed  through out the port . Exhaust was a bit of a problem (no air speed on the floor)but with some out of the square thinking got it working really well to.  

1st pic std intake bigport cyl 4. Cly 8 modified smart port using std 36mm valve with good air speed across the entire port.

2nd pic std exhaust port cyl2. modified exhaust cyl7 using std 29mm valve with good airspeed across the entire port.

 

 

IMG_0239.jpg

IMG_0238.jpg

Edited by Vc496

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Our ole 4k seat removed areas marked off for welding and then lots of grinding lots of grinding 

IMG_0320.JPG

Edited by Vc496

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That's a great increase in the exhaust!  Do you compare notes with oldeskewltoy?

Datsun found the same with their SSS back in 1969/70s, the big-ports never got enough revs up to really use the ports size, and they went to a medium ports afterwards.

What cam size are you planning this around?

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No I have not compared any notes just spent many hours modifying the exhaust port both in shape and in the chamber. Intake was easy.

Found a lot in chamber design hence why it is getting welded.

Yes you are right the std big port air speed is way to slow(virtually none across the floor and slowly got better towards the roof). If you ran a bigger valve with the untouched port and turned it 8000 plus it would work well.

That why I stayed with the small port and std valve and modified it. 

Good airspeed all the way through the lift up to 500 which will give good power all through to approx 7500 with good throttle response for coming out of corners.

Hopefully I will have the trial head digitised and then be able to tweak the ports on cad and run cfd on them and hopefully have a cnc program for them.

May take a while eventually I would like to be able to do a CNC head and CNC manifold package.

Cam shaft I have not yet decided but will be in the 450 to 500 lift range and duration at 50 somewhere between 240-260

Should be able to run good compression without milling to much of the head due to the chamber design.

Edited by Vc496

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Interesting work. Did you have an MS Excel output of the flow data, Valve Lift vs CFM? Was thinking of putting it into a program like Engine Analyzer Pro and compare power curves for different camshaft profiles.  

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Bruce

Here are the figures all tested at 28

Std 36 mm intake and 29 mm exhaust

EX                                                            Intake

100           46.5                                       53.8

200           84.4                                       93.2

250           97.9                                       111.4

300           105.8                                      125.1

350           110.8                                      134.2

400           115.3                                      141

450            117.1                                      146

500            120.5                                      147

 

 

 

Edited by Vc496

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