One of these days I'm going to get you to see what you can do with an Alfa twin cam TK - they have it all - crappy short side radii, hemi chamber with no squish, and symmetrical ports so they've got virtually zero swirl.
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"Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds." -
Hemi is good for power if you can get some squish & compression into it - the key will be in piston design!Comment
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Sorry for the hijack TK!Originally posted by Gammaboy View Post
Intake port:
Final head flow numbers:
The left side is with a radius plate on the spigot, right side is with the carburetor and stack. Lost about 8% of flow at peak lift with the entire system in place. Nick said anything under 10% is acceptable but less would be better. Still super steady on the bench, moving only .1 of an inch of depression at any given valve lift.
Intake valve: 1.900" (~49mm) (~1mm larger than stock)
Exhaust valve: 1.475" (~37.5mm) (1.5mm smaller than stock. Also the valve has been sunk to help with overscavenge issues)
MCSA is at the carb throat-the flange: 1.77sq-in (38mm dia). Hoping the motor will peak at 7200rpm.
Both the intake and exhaust have 50* valve seat angles. Again, we are trying to minimize overscavenge, and let the ports "ramp up" at around .250" lift... which they do.
Nick still has another spare head. Someday, I'll have him work some squish into the combustion chamber, and we'll do a clean sheet as far the the MCSA size and location. One of the issues he had with this port was running out of casting thickness on the sides of the port... especially where he was trying to blow out the short side radius to get air to turn around it.
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Looking down everything
*note: nothing was tightened down, the whole thing smooths out when tightened down. Notice the nasty hook just before the SSR
Exhaust:
The .700 lift number is really .600, but with a pipe attached to the port.
Custom Racetec piston:
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Yeah, they're now doing crazy pistons like this to get squish into them - each piston is different because of the offset bores in the 2 litre (Bore spacing doesn't match chamber/port spacing believe it or not). This is a 12.5:1 slug.
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"Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."Comment
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Here's a modern Chrysler Hemi piston design (Diamond, but Racetec and CP also are being used by the top Hemi racers)
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Back on to this after clearing out a set of mild port 308 heads & a set of subi B4 heads.
Cam arrived yesterday, so I refaced the rockers & dummied it all up - less dicking around to get the geometry right than I was expecting, the longer intake valves are going to work spot on with a stock lash cap, the stock length exhausts need a .210" lash cap - coming over night from Stuart Wilkins.
Once that was all sorted I machined the spring seats in the head flat & checked spring installed height - intake needs .200" of shim, exhaust only .075" - found some crane spring locators that will only need the ID machined to fit & are .060" thick, so I can use them to locate the springs & add shims underneath to get the installed height bang on.
I'm calling that a win - 2x big unknows that could have been trouble sorted within 2 hours.
Now I'm pretty close to being home & hosed, gotta mill the head to final thickness & dummy it up on the short motor to check piston to valve clearance - which I think will be fine, due to the deeper chambers compared to the old head I have more valve free drop & due to offsetting the head the valve reliefs in the pistons will still work with the larger valves.
Gotta check anyway, but chances are we'll be fine.
No pics for now, going hard until I'm 100% sure nothing is going to trip me up at the last minute!Comment
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that looks gen 2 hemi to me?Originally posted by hoffman900 View PostHere's a modern Chrysler Hemi piston design (Diamond, but Racetec and CP also are being used by the top Hemi racers)
Originally posted by RdynoOriginally posted by TripperComment
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Just where do you find a 0.550"+ lift cam with only 260* duration? I can't get a grinder in the US to cut me anything shorter than 280* at 0.500" lift, and I'd like to get my duration down some, I've got 54* of overlap in the blown motor and I feel it's a little too much yet.From memory I cammed that one with minimal forward split & tight lobe centres (105), duration was late 260's/early 270's & lift was around .600"Comment
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That was a BMW, Catcams in Belgium ground it.
This one is 262 with .590 odd lift, ground by Clive cams with old Wade cams masters developed many years ago - I think the lobes are based on old racer brown lobes, but not sure.Comment
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We have piston to valve clearance issues
Pistons are going to need a little massage, not major, but still a PITA.Comment
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Is that a 1308a cam??
Might be the same as mine, claimed 260 deg @.50 and .585 lift.Comment
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No, it's bigger than a 1308a & is not a single pattern like most datto cams, has more exhaust duration but less lift.
It was custom ground to my specs.
Fixed piston to valve issues - a little touch up with the grinder was required, all good now.
Time to look at individual rocker arm setup to make sure each valve gets the same lift & duration - small changes in tip height & rocker tolerances can affect things more than you'd think on a finger follower type setup.Comment
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Here's one for the Datto heads, with the contact pattern in the middle of the rocker pad I had .572" lift with .012" lash, messing around with tip heights & having the contact pattern off centre (but still well within the pad) we've gone up to .592" lift.
You have to set each one up individually to suit it's rocker arm, .005" tip height makes quite a difference to lift & also affects cam timing - advancing or retarding that particular lobe compared to the rest.
If you don't do each & every rocker & valve tip you can end up with effectively 8 different camshafts in the same engine, which never works out that well.....Comment
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Okey doke, close to done.
Short motor all closed up:
Setting up each rocker arm/valve tip height individually:
Head assembled:
Rocker gear & cam fitted:
Head bolt washers ground to allow the head to sit over, head bolts turned down as well:
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