All the power is in the head. Part 5 - Inlet porting (2)

GC porting, development, valve and seat work, combustion chambers, cams, head construction, etc
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Guy Croft
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All the power is in the head. Part 5 - Inlet porting (2)

Post by Guy Croft » Sun Sep 03, 2006 10:34 am

The second and final phase of typical development to improve flow over standard.
In part 1, I carried out a series of preliminary tests, basic modifications and flowtests to establish the potential of the inlet port on the Fiat TC 1592cc cylinder head - things like testing the bare port flow and manifold flow, improvement to the short side radius, opening out to valve correct seat diameter, opening out the valve throat. In this section we'll see how these steps are taken further and how the port - chamber region of the inlet side is fully developed and checked ready for building-up.
Attachments
013 DT 1592 prelim deshroud.jpg
Deshrouding the chamber adjacent the inlet valve. The highest lift flow (See graph, part 1) is a long way from bare port flow. After this mod flow drops, a sign that the short-side radius may be wrong.
013 DT 1592 prelim deshroud.jpg (39.38 KiB) Viewed 16872 times
013A DT 1592 inlet seat proximity to head face.jpg
The cast-iron inlet seat will interfere with the machining of the head face so I'll need to recess it by grinding down the top edge into the alloy.
013A DT 1592 inlet seat proximity to head face.jpg (103.5 KiB) Viewed 15974 times
014 DT 1592 test valves radiused OE 41.7 & POS.jpg
The penny-on-a-stick valve at right showed up some gains under 6mm lift or so, but the modified production valve was definitely better at higher lift. I opted for OE valves with 30 degree back grind.
014 DT 1592 test valves radiused OE 41.7 & POS.jpg (52.49 KiB) Viewed 15950 times
015 DT 1592 test valve Cosworth style rear profile.jpg
This 'tulip' shape, with 30 degree angle on the rear of the valve was useless in the TC head, nowhere near as good anywhere as the other two.
015 DT 1592 test valve Cosworth style rear profile.jpg (39.07 KiB) Viewed 15943 times
016 DT 1592 inlet ports standard spec.jpg
View of the standard 1592 inlet port. A big port fro a 1600, too big maybe. The size was reduced on later (131) models to 36-33mm.
016 DT 1592 inlet ports standard spec.jpg (54.4 KiB) Viewed 15931 times
017 DT 1592 inlet port matching and shaping.jpg
Matching to gasket size and smoothing the internal region this takes it to 35.4 vertical x 35 horizontally. The metal is taken off sides and roof, not port floor.
017 DT 1592 inlet port matching and shaping.jpg (42.32 KiB) Viewed 15924 times
018 DT 1592 race guide fitting.jpg
Pressing a GC race guide in the development port, head has been warmed to about 50 deg C and the the guide bores in the head lubricated with copper-based anti-seize.
018 DT 1592 race guide fitting.jpg (37.66 KiB) Viewed 15921 times
019 DT 1592 race guide in fully developed port.jpg
View to the port fully finished at 80 grit and the aerodynamically superior race guide in place. The bare port flow is now 102.6cfm compared with 91.1 standard, nearly 13% more, my average for a good job with 42mm valves.
019 DT 1592 race guide in fully developed port.jpg (55.74 KiB) Viewed 15907 times
020 DT 1592 brush honing guide after fitting.jpg
The guides have to be checked after fitting, valve must drop under its own weight and be a snug fit. I use brush hones to correct any tight sports - which there usually are on old heads - even with perfect guides.
020 DT 1592 brush honing guide after fitting.jpg (117.73 KiB) Viewed 15905 times
022 DT 1592 inlet port fully developed outer view.jpg
Port finish is 80 grit, developed with Ataband and split fork deburrer, wetted with WD40. No real point in going finer - makes no difference to flow.
022 DT 1592 inlet port fully developed outer view.jpg (23.73 KiB) Viewed 15894 times
023 DT 1592 inlet port matching one to another.jpg
Now the difficult bit - making them all the same before moving on to seat work. Note that the two jobs are essentially separate. Do the port first then the seats..
023 DT 1592 inlet port matching one to another.jpg (116.68 KiB) Viewed 15889 times
024 DT 1592 inlet seat ground to true valve diameter.jpg
First thing is to grind the seat out to true valve diameter, see how wide the contact face becomes.
024 DT 1592 inlet seat ground to true valve diameter.jpg (26.02 KiB) Viewed 15873 times
025 DT 1592 top grinding seat at 20 deg to enhance flow & recess seat.jpg
Top grind at 20 deg; test showed later that 30 deg was better, except at very high lift (well outside useable lift range).
025 DT 1592 top grinding seat at 20 deg to enhance flow & recess seat.jpg (59.19 KiB) Viewed 15860 times
026 DT 1592 inlet seat top-ground at 20 deg.jpg
Alloy available for refacing is now just visible at the '6 o'clock' position of the inlet seat insert. Of course this takes the valve deeeper into the head, can present shiming problems for the unwary..
026 DT 1592 inlet seat top-ground at 20 deg.jpg (31.92 KiB) Viewed 15844 times
027 DT 1592 inlet seat throat after 70 deg grind - thru.jpg
View thru throat with 70 deg grind to pull contact face back to 1.5-2mm wide. See how doing this gives me more metal to work with on short side radius.
027 DT 1592 inlet seat throat after 70 deg grind - thru.jpg (112.9 KiB) Viewed 15849 times
029 DT 1592 OE late valve back grind at 30 deg.jpg
029 DT 1592 OE late valve back grind at 30 deg.jpg (20.58 KiB) Viewed 15842 times
030 DT 1592 inlet valve back ground and lapped.jpg
With the valve grinder set at 30 deg I carefully develop the back grind.
030 DT 1592 inlet valve back ground and lapped.jpg (9.44 KiB) Viewed 15832 times
031 DT 1592 inlet seat lapped after 70 grind.jpg
The best way to do the back grind is lap the valve to its seat (at proper dimensions) and then grind right up to the lapped region.
031 DT 1592 inlet seat lapped after 70 grind.jpg (27.28 KiB) Viewed 15826 times
032 DT 1592 inlet seat lower section ground at 85 deg.jpg
Giving the lower throat region an almost parallel grind to open out its diameter. Doing this to the lower section helps the run-in of air into the 70 deg section.
032 DT 1592 inlet seat lower section ground at 85 deg.jpg (20.88 KiB) Viewed 15815 times
033 DT 1592 inlet seat throat diameter - final.jpg
Measuring the final - larger - configuration of the valve throat - narrowest diameter. How much bigger it will need to be varies from head to head and much depends on the optimum throat angle.
033 DT 1592 inlet seat throat diameter - final.jpg (114.13 KiB) Viewed 15812 times
034 DT 1592 finished valve and seat, throat.jpg
Here the intrusion of the 85 deg grind has been fully fettled out and that region is now finished.
034 DT 1592 finished valve and seat, throat.jpg (117.67 KiB) Viewed 15813 times
035 DT 1592 inlet seat top relief - burr.jpg
Roughing out with a small burr around the top of the seat - avoiding my careful top grind.
035 DT 1592 inlet seat top relief - burr.jpg (118.15 KiB) Viewed 15804 times
036 DT 1592 inlet seat top relief - 80 grit .jpg
The relief dressed at 80 grit. The bung in the plug hole tells you that this head has just come off test on the flowbench..
036 DT 1592 inlet seat top relief - 80 grit .jpg (121.1 KiB) Viewed 15803 times
037 DT 1592 protector gasket .jpg
Not a bad idea to tape a head gasket in place when doing deshrouding..
037 DT 1592 protector gasket .jpg (115.02 KiB) Viewed 15787 times
038 DT 1592 inlet seat top relief - 120 grit.jpg
Final look of recessed and deshrouded inlet at 120 grit. 80 grit looks horrid in combustion chambers. A lot of work to bring the early chamber up to the exit flow of the later, bigger one.
038 DT 1592 inlet seat top relief - 120 grit.jpg (114.04 KiB) Viewed 15776 times
040 DT 1592 measuring tip hts with vernier.jpg
This job allows me assess whether I can shim it or not. If I've done my seats well, even by eye, tips should be very close to each other. I can grind valve tips to equalise, sometimes necessary if one seat/valve has been extensively reground due to wear/c
040 DT 1592 measuring tip hts with vernier.jpg (111.04 KiB) Viewed 15758 times
041 DT 1592 tip hts measured.jpg
If you're good with seats this is how close you can get them. Std tip heights are about 40.5mm inlet and exhaust. This is common to sohc and 16v too - they share the same spring and spring seat.
041 DT 1592 tip hts measured.jpg (109.8 KiB) Viewed 15778 times
DT 1592 inlet flowtests phase_03.jpg
Final Test 31 spec, poor perfomance of POS valve and superior response of 30 deg top grind visible. It's can be hard to get valve-in flow closer to bpf in the 8v TC, you sometimes have to lift 13mm or more. Way better than standard though.
DT 1592 inlet flowtests phase_03.jpg (73.05 KiB) Viewed 15612 times
DT 1592 inlet flowtests top grind chart.jpg
The top grind is better than 20 deg and best left sharp as this chart shows. It's something I only looked at quite recently, I think the 30 top grind interacts with the 30 deg back grind.
DT 1592 inlet flowtests top grind chart.jpg (85.88 KiB) Viewed 15623 times

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