Porting suggestions please!

[stevek]

Looking at the picture below and considering the following information:

Intake:
40mm valve
36mm port diameter
38mm at intake manifold

Exhaust:
34mm valve
28mm port diameter
34mm at exhaust manifold

Bore x Stroke:
82.07 x 75.48 mm (1598cc 4 cylinder)

Desired:
3 angle valve cut to support 12.5mm lift



How would you go about modifying these ports to get the most and best quality flow out of them at approx 7500-8500rpm?

Cheers,
Steve K

[sir yun]

i would suggest posting this as well on the speedtalk board.

what kind of head is it ?



as you have casts i would first determine min cross sectional area to see where you are at size wise for you intended purpose.

the basic port looks like it is a good basic shape.

i'd guess that the changes will be very subtle and i suspect the valve/valveseat bowl and a minor bit of SSR shaving/widening to be the place to look for the most gains.

of course the flow should be good w. manifold fitted to the head.

good luck.

do you have a scrap practice head as well?

[automotivebreath]

Hi stevek,

Size and shape of the throat are top priority, normally 88 - 90% of valve diameter
for the intake valve. Shaping the throat, valve and seat angles and chamber shroud
are all critical.

Plenty of material can be removed at the valve guides to streamline the boss.

With the RPM you want to run; the SSR needs attention to prevent separation.
This is be best done with a flow bench and a pilot probe measuring localized port
velocity. I can't offer anything specific, with the heads I'm accustomed to doing,
(SBC) I widen the apex of the short turn and lay back where it approaches the
throat. I do this with out a flow bench only because I have templates to go by.
(It would be nice to get a look at a properly ported head).

As for port CSA, FlowSpecialist or David could point you in the right direction,
hopefully they will join in.

[olNick]

What do you use to make these cool looking casts Steve?

regards,

nick

[stevek]

Thanks for the comments guys.

The product I used is a silicone rubber #8421 from a company in Brazil called Avipol Comercial Ltda. It costs about USD$15 a liter with the hardener.

Intake port profile looking down the port:


Actual port view:


Intake port profile showing valve bosses:

What do you make of that bump just above the valve seat?

Exhaust port profile:


The exhaust port goes tall where it has been pinched, thus maintaining the same port area.

I haven't burretted the ports, but when I was pouring the product in it was about 100cc for the intakes and 80cc for the exhausts.

Cheers,
Steve

[sir yun]

what kind of engine is this off ? looks like a bike head.


it looks like there are some core shifts directly around the seat. i'd say there are gains to be found there.

seats (like allways) should have priority. but without testing&developement you're pretty much bound to choosing a set of angles and hoping for the best.

In your position I would guess a single 45 degree intake seat with no topcut, a short as possible 50(? failing that 65) degree downcut to define the seat with and then painstakingly sculpt a radius blend keeping the downcut to 45 deg. sharp.

use some magic marker on the valve..lap it in (no grinding paste) to reveal contact face .. cut back the valve at 30 degrees.

go you your local church and burn a candle because this is all a guess (not a wild guess but a 100% guess nonetheless).

at least this way leaves material for a more conventional 3 angle seat if it is all wrong.(but i have faith in this setup

do you have a picture from the chamber and the inside of the port from the chamber side?


oh ..i'd be very wary of working with a big grinder here (mine is a 740watt 240v 8 lbs.. rather hefty) .. a dremel type tools might not work fast but i have ported several cast iron heads with only a dremel type tool and a carbide bit. and it does a good job for detailing work like this.

just take all the handle bits off that way you can reach into the ports even with the short burrs.

[stevek]

Just a short update:

I sent the head of to be flow tested and here are the results:
Lift is from 2mm to 12mm, flow is in CFM@10"

Stock


Removal of casting flash, minor bowl blend, lightly profiled guides:


Comparison of before and after the minor tidy up:


At 13mm of lift (.325 L/D) it flows 99.1cfm@10", if I'm right that's about 156cfm@28".

Considering the valve won't be lifted much higher than 12mm, do you think a three angled valve job would help or hinder flow?

[stevek]

Anyone?

What size margin would you use for each of the angles?