3TC oversized valves

[brucey]

Calculating flow potential of 42mm intake valves:

From "How to Build, Modify & Power Tune Cylinder Heads"


Calculate valve seat inner diameter (assume a simple 45 degree angle seat)


Valve seat id. = valve diameter - (seat width x cos(45))

For a 42mm valve with a 1.5mm width seat

Valve seat id. = 42 - (1.5 x cos(45)) = 41.1mm


curtain area = pi x diameter x lift

For 41.1mm valve seat id. at 1mm lift (in m^2):

curtain area = pi x (41.1/1000) x (1/1000)
= 0.000129119 m^2


Flow bench calculation. Constant of 213685.34 for 25" of water at 15 degrees, and 1013.25 millibars atmospheric pressure.

cfm = A x C x 213685.34

assuming 95% flow efficiency for the valve area, i.e. C=0.95 (coefficient of discharge).

cfm = 0.000129 x 0.95 x 213685.34
= 26.211 @ 1mm valve lift


Max lift of curtain area (assume 1/4 of valve diameter)

0.25 x 41.1 = 10.275mm lift

valve flow potential

cfm potential = valve flow x valve lift
= 26.211 x 10.275
= 269.318 cfm @ 10.275 mm

convert cfm from 25" to 28" of water:

= 269.318 x sqr(28/25)
= 285.019

so the valve can flow 285.019 cfm at 0.419" lift.
Doesn't include the flow reduction from the 8mm valve stem and guide, but is well over 200 cfm, from what is normally achieved when porting. Port size is the restriction.

[ctrain]

i wonder if its possible to get an aluminuim welder to weld up the pushrod holes so that they are a few mm smaller on the sides giving more room to port the intakes, the pushrods dont need that big hole do they, would they be fine with a maybe 5-6 mm of gap between the rod the the wall?

[brucey]

i wonder if its possible to get an aluminuim welder to weld up the pushrod holes so that they are a few mm smaller on the sides giving more room to port the intakes, the pushrods dont need that big hole do they, would they be fine with a maybe 5-6 mm of gap between the rod the the wall?

Maybe that could work, weld beads along the wall to give more material to work with.

I had a closer look at the stock valve seats which look like they have angles: 30 45 60 degrees. The width of the 45 degree cut is about 2.5mm. The diameter at the bottom cut is about 36mm. It's not really blended with the throat which is about 35mm. If the bottom cut was blended the potential flow of the stock valves could be ~206.6 cfm @ 28" of water at 0.367" lift.

Though there is a limitation when widening the port in the vertical direction due to the cooling holes in the port floor, and the thickness between the port wall and the base of the valve spring. Looks like there is an allowance of 29-30mm. It looks possible for the cooling holes to be filled in with welding to make the port larger. I'll put up some photos to give a better idea.

[MorGo]

The port between pushrods is 40 mm wide so leaving 2 mm per side amounts a 36 mm wide port.Yes,making something else than round port is the key but there is a limit on that too.Welding the outside of ports is no can do (at least widening) because the pushrods should be thicker and there is not much room for the stockers..
T-head is a port limited.With extensive modifications one can have more port area but then it would be cheaper/simpler to move to 2T-G.Or some other engine..

[brucey]

Here are some photos of a cross-section of a 3TC head. From a T18 (TE72 corolla). Has EGR in the exhaust ports

Chamber 1:



Other half of chamber 1 looking from front of engine:



Looks safe to remove the whole ridge around the valve guides, and shape the roof of the port, being careful with the thickness between the bottom of the valve spring and the port wall. With the floor of the port there are two holes, which can limit the width in the vertical direction in the port. Could weld these up half full to widen the port. The hole closest to the inlet (manifold face) is just empty space and doesn't really serve as a purpose. It's covered over by the head gasket; might be a casting feature during manufacture. The second shallower hole is a coolant passage. It doesn't have this on the exhaust port side. I reckon its purpose is to heat the inlet port for better fuel atomisation; similar to heating the intake manifold.
Not sure if these holes are as deep as an early 2TC head. The early heads are meant to have bigger ports. Is anyone able to confirm this?

Photos of head surface showing push rod hole spacing (note coolant hole under inlet port is blocked up with deposits):





The two middle push rod holes don't have much space, so the wall cannot be welded, or it would be very minimal. Yes port between pushrods is ~40mm. What's a rule of thumb for a safe wall thickness?

[brucey]

Got these valves from streetsportindustries. Good valves for the price, and reasonable postage.
EV8 stainless steel. +3mm oversize, 44mm intake and 39mm exhaust. Swirl polished and undercut steams.





Going to get them machined down to 1mm oversize and also back cut.

[ctrain]

hey brucey, how much did it cost to get them machined down and back cut, im thinking of getting the same as yours but i can get 1mm oversize valves from BRD Racing for $120 + shipping from america.

[brucey]

hey brucey, how much did it cost to get them machined down and back cut, im thinking of getting the same as yours but i can get 1mm oversize valves from BRD Racing for $120 + shipping from america.

I had the head reconditioning/port work/pressure test/harder springs as a package. It was included in the porting/cutting valve seats work, so I didn't really get charged extra to resize and back cut the valves (little discount).

$120 is a good price, but I thought BRD only had stock size and 45mm intake valves? Euro export can do $25 for each valve to machine down to 1mm oversize.

[ctrain]

mind if i ask how much all the headwork cost? BRD do all different sizes from stock up to 39mm exhaust and 45mm intake

[brucey]

About $750

pressure test $40
gasket set $100
overhaul (clean up, valve steam seals etc.) $300
crowcams springs (holden) $80
port work $180
shaved head to 63cc $50

I supplied the stainless steel valves. Were resized and back cut. The three valve seats angles were cut 30 45 70.
Valve guides were removed for basic porting work. Gasket matched. Couple of hours work on the inlet ports and an hour on the exhaust ports, probably a bit more. The work involved probably could of cost over a grand, but I got it a little cheaper. The guy who did the work has his own workshop and self-employed, so less overheads.