A couple of shots of a 16v Integrale Evo 2 head I am preparing.
Brief is optimum flow for high lift cams, high (30 psi) boost. it's straightforward to get improvements in the 136 (std bare port flow) to 150 or so, but beyond that the porting has to be done with great care (and takes MUCH longer). Rush it and you're going to break thru into a coolant gallery, and the higher the flow the more any deviation from a sleek internal aerodynamic profile fights against you.
To put 150 plus in perspective: in development terms the Integrale/Coupe 16v head is relatively straightforward to work on. By comparison, with a 16v Vauxhall XE 2 liter head, on the (1mm smaller) production 33mm valves that kind of flow (with a good valve-in response) is not easy to achieve, and if you get it and fit the right cams it's good for well over 238bhp even normally aspirated.
I think the most you're going to get out of an Integrale with OE size valves fitted is about 164, and to do that you're going to need to lift the valve to 13mm, anyone who claims much more, well, I'd like to see it in the flesh. And does it need more flow? Well, you can always chase more, but on a turbocharged engine? Not really.
There is no direct relationship between airflow on this engine and power, all I know is that a loss of airflow on the flowbench is a bad thing and reducing losses - especially at the high port velocity of a turbocharged engine is a good thing. I also know that a turbo engine will produce a lot more power for given boost than one that has not been gasflowed, and good valve-seat work will greatly enhance the throttle response.
But this job is not just performance enhancement, it includes inlet valve overhaul, race springs to replace the OE ones (for higher rpm limit) new Nimonic 80A exhaust valves to cope with the high exhaust temperature, new race guides, head reface etc.
The std head flow peaks around std cam lift of 8.2mm actual and springs coil bind at 11.6mm actual valve lift, so allowing even only 1mm safety clearance between coils (2mm is better) that means, for what it's worth, you could only put actually 10.6mm lift cams in a head with OE springs and get away with it.
I checked the shimming on the C&B cam and it looks like I need 1mm top hats on the inlet, which will shim in the mid range OE 33mm shims, that's fine. It's not a bad idea to have them anyway as the bucket gets very close to the head at 12.7mm lift without them.
porting, development, valve and seat work, combustion chambers, cams, head construction, etc
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- Bare port flow test after initial porting, around 151 cfm, better than standard (136) but not good enough. No mods to valves and sets at this time, just enlarged ports, knife edged splitter and 80 grit smoothing. Both barrels should flow the same.
- MM 16v Int on flow test @ 151cfm.JPG (145.36 KiB) Viewed 19093 times
- Here the head is at 162.3cfm (at 10") - the increases coming from enlargement thru the splitter in the critical upper and side regions.
- MM 16v Int part finished inlet.JPG (151.77 KiB) Viewed 19086 times
- Blowing down the inlet port to examine behaviour of air over the port floor and short side radius. Not a true representation of what happens but still useful. As the air speed increases a vortex develops (RH barrel).
- MM 16v Int inlet blow thru.JPG (126.93 KiB) Viewed 19060 times
- Honing the'Trojan' guides after pressing, with head at 50 deg C and some copper-ease in bores. Some guides are tight, that's good. Brush hone gives oil retention and relieves the high spots nicely.
- MM Int guide honing.jpg (117.34 KiB) Viewed 18934 times
- Valves should just fall under their own weight. The guide bores often go tight. I prefer to have the bores tight and hone them rather than have a loose in-situ fit.
- MM guide-valve fit checks.jpg (115.1 KiB) Viewed 18924 times
- GC 16v Integrale type race guides fitted, honed and ready for seat grinding. I rarely do race seats with old guides.
- MM Int GC guides ready for seat grinding.jpg (118.23 KiB) Viewed 18926 times
- Trial grind tells me how concentric the guides are, these are excellent, this grind was microns only and it has cleaned up well. Rough removal/fitting or poorly-made guides can throw the seat miles off centre.
- seat prep 002.jpg (107.33 KiB) Viewed 18908 times
- Seats top cut at 20 deg, dual effect of helping lower lift flow and dropping contact face deeper into head - helps with race cams with small base circle.
- seat prep 003.jpg (109.07 KiB) Viewed 18902 times
- Grinding contact face out to true valve diameter at 45 deg with the Peg10 grinder, my favourite seat tool these days.
- seat prep 004.jpg (114.62 KiB) Viewed 18890 times
- Contact face now at true valve diameter, ready for narrowing throat grind to a 1mm contact face and lap, then back grind on inlet valves.
- seat prep 007.jpg (96.63 KiB) Viewed 18881 times
- Here doing the throat grind that narrows the contact face down and provides an effective transition for the airstream from the parallel lower section to the contact face
- Int 16v seat prep 08.JPG (169.08 KiB) Viewed 18757 times
- Finished seat, 20 x 45 x 1.75 x 75 deg - I have not found a setup any better, a good compromise of low and high lift flow. Opening out the lower throat parallel 0.5mm made no difference, it's big enough on those valves.
- Int 16v seat prep 09.JPG (155.43 KiB) Viewed 18743 times
- Evo 2 head set up for valve-in tests with final configuration.
- Int 16v rigged for final valve-in tests.JPG (153.05 KiB) Viewed 18722 times
- I'm using the actual GC triple race spring outer for the lift tests, to get take it over 12mm, so it's a good opportunity to measure the installed height of the spring. Err on the safe side with the measurement..
- Int 16v checking outer spring inst ht.JPG (147.83 KiB) Viewed 18716 times
- Final valve spec is 45 contact face narrowed to 2mm with 20deg back grind. A 30 deg back gring on a good condition or new valve leads to a very wide back-ground region and isn't as good as the confined 20 grind shown.
- Int 16v valves with back grind.JPG (160.16 KiB) Viewed 18701 times
- Without top hat shims the bucket get very close to the head at 12.7mm lift, the bucket at left has bottomed on the head.
- Int 16v buckets.JPG (157.49 KiB) Viewed 18686 times
- Final spec compared with standard Integrale head at 10" depression. New flow is everywhere better and esp at hig valve lift.
- 16V Integrale flowtests 06.120.jpg (65.88 KiB) Viewed 18678 times
- Trial shim with Colombo & Bariani 12.1mm lift inlet cam.
- Int 16v trial shim .JPG (137.29 KiB) Viewed 18665 times
- My own race spring seats with flat bases are going in this head.
- Int 16v race spring seat.JPG (160.82 KiB) Viewed 18663 times
- Final shot of head on test with rig running, operating with valve at the max lift it will take with test springs fitted.
- 2006_1125Image0025.JPG (37.5 KiB) Viewed 18643 times
- Doing a bit of deshrouding inside the fire ring at the areas marked out (black). This did help the higher lift flow.
- 2006_1125Image0021.JPG (156.52 KiB) Viewed 18640 times
- I make a lot of notes like this aide-memoire stuck to the board in my build room - 16v spring and valve height instalation data. Easy to forget vital fact. Never assume you'll only ever do one engine of that type.
- Int 16v useful info.JPG (16.96 KiB) Viewed 18633 times
- Standard Integrale head on flowtest to enable comparison with Myles' unit. This is approx the valve lift at where flow peaks.
- Int 16v std port on flowtest.JPG (37.85 KiB) Viewed 18560 times
- With standard valvetrain this is where springs 'box' (bind). You can't lift that high, you need at least 1mm and preferably 2mm between coils or the springs are going to fracture sooner or later. There's no point anyway, with standard ports.
- Int 16v max inlet lift.JPG (31.19 KiB) Viewed 18523 times
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