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| Modified Heads 12g940 https://www.ausmini.com/forums/viewtopic.php?f=2&t=88727 |
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| Author: | kiwiinwgtn [ Thu Feb 26, 2015 8:02 pm ] |
| Post subject: | Modified Heads 12g940 |
I am possibly going to be burnt at the stake for asking this but here goes. I have two 12g940 cylinder heads with 1.44 inlets ans standard exhausts ported to the letter to Vizard Specs from the yellow bible. I have been doing some reading some of the thoughts around porting Mini heads in 2015 and there appears to be a move away from going that big and using smaller valve sizes. So given we have better fuel in 2015 and better electronics to provide spark and control dwell etc is the Vizard spec head now obselete. To add some context I am talking about on a road car. My engine is 73mm bore, Re13 cam shaft, 1.4 rockers (rolla) 10.5:1 compresion, electronic igntion Would there be any gain in performance down low in using a different head with smaller ports and valves I am no longer interested in top speed but more looking for a quick weekend car. Kiwiinwgtn |
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| Author: | Morbo28 [ Thu Feb 26, 2015 9:12 pm ] |
| Post subject: | Modified Heads 12g940 |
:popcorn: Edit: okay sorry looks like we don't have the 'popcorn' smiley here. I'm very interested to see people's thoughts here. |
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| Author: | VulcanBB18 [ Thu Feb 26, 2015 9:27 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
Hey kiwiinwgtn Firstly, "better fuel"? I think the old leaded-super was a much friendlier beast to the A series, but we can still do fine with 98 or 95 unleaded. Yes Viz's stuff is long in the tooth now, but he did back-up most his work with flowbench and/or dyno tests, so while things have moved on, anything done to "his spec" should still be quite a reasonable performer. One thing I've noticed with the benefit of time with Viz's stuff is that it is really aimed at "peak power racing engine" rather than "nicely hotted up fun road engine" and so following some stuff verbatim leads to some sad faces. However, I think you could do nicely with one of GR's smaller cams, and pay attention to intake & exhaust performance and I'm sure the "Viz spec" heads will work just fine. Fortunately he did pay attention to low lift flow, which really helps road manners. My recently built 1022cc engine has a 295 head that was taken to Viz specs on 1275 valve sizes (always bugged me that - young fella I was and I didn't communicate properly that I wanted the other end of the mod spectrum!) which is a bit overdone for road use, but with attention to intake & exhaust systems and cam specification/timing, the result has been awesome! tl;dr - Just use 'em I say! cheers, Jacob |
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| Author: | drmini in aust [ Thu Feb 26, 2015 10:00 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
I'm running a Vizarded Mk2S head (+ bathtubbed chambers) on my 1360 with a 282 cam, 1.5 rockers, and a 45 Dellorto (36mm chokes). Now I've jetted it right, it pulls smooth from 50kmh in 4th gear at part throttle. Valves are 35.6 inlet and 31mm exhaust. I do have another head with stock valves and ports, but this thing is too much fun as it is. Redline is 7500 these days. 
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| Author: | mini_mad_matt [ Thu Feb 26, 2015 10:01 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
There may be a performance gain with a different head yes. But You can't really say the head is obsolete because then you would have to say so is the engine. The heads sound like they were made to be good heads back in the day, so they should still be good heads yea? I say just use the head in the best condition and if your not happy with the way it's working then maybe look into a different head. No point discarding 2 worked heads just because people have found a possibly slightly better way to do the same thing unless your not happy with the power and it's delivery. |
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| Author: | TK [ Thu Feb 26, 2015 11:22 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
"Yes Viz's stuff is long in the tooth now, but he did back-up most his work with flowbench and/or dyno tests, " Yes he did. It wasn't trial and error but research and development. |
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| Author: | kiwiinwgtn [ Fri Feb 27, 2015 7:10 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
Obsolete may have been a two harsh a comment. Ones in use and the other will be a spare. I have a few minis so was thinking more for my next engine. |
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| Author: | Phil 850 [ Sat Feb 28, 2015 6:12 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
So for a "good" road motor do you use the standard 12G940 with LCB extractors, good cam, 1.5:1 rockers and a decent manifold & Carb. Would that be Brisk, reliable and driveable ? |
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| Author: | TK [ Sat Feb 28, 2015 6:56 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
yes near stocko head (get rid of the casting marks in ports, clean top of port, and the smaller curve on the bottom of the port entering the combustion camber)., Add mild cam, stock rocker ratio, lightened flywheel, hs6 carb, lcb. Should be very nice. |
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| Author: | Phil 850 [ Sat Feb 28, 2015 10:12 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
Thanks TK. When you say the "small curve at the bottom" I presume it is the tight radius where the valve seat is cut as explained in DV's yellow book. If that description makes sense 
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| Author: | TK [ Sun Mar 01, 2015 7:21 pm ] |
| Post subject: | Re: Modified Heads 12g940 |
yeah that's it Phil. Works seriously well mate. |
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