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Re: Bore a12 how far can you go
No life (a.k.a. DattoMaster)
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2003/12/3 7:56
From Christchurch NZ
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I recently read in a mopar performance small block mopar "A" engine hot up book that longer rod ratios made more mid range torque. Thanks the Harry, I now understand why. Perhaps this explains why, when I first got into Datsuns, all the "old hands" I spoke to locally told me that the A14 was "The one" to build for a goer. However, popular opinion on this site seems to have been to the contrarary of this. (Leaning more in favour of the A15)
All that aside, I can respect Chris's reasoning for builing this engine. And should there be any shortcomings in midrange torque or whatever, I'm sure his Hemi powered rod will more that make up for.


Posted on: 2005/4/7 10:47
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Re: Bore a12 how far can you go
No life (a.k.a. DattoMaster)
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From Southern Tablelands N.S.W. Australia
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Well, i must say thank you to those who have added their own thoughts to this debate, but more importantly, i will offer an apology to L10_B110 if you feel that i have decended to a level of personal attack. It was not intended.

I was thinking only this morning that this was good as i'm sure we all enjoy a good "robust debate" as long as we don't decend to the level of abuse & name calling, but you gotta admit, anyone who asks if they can modify a crank with an angle grinder has got to be a bit suss..
I, like you, can quite happily become very passionate about some subjects, but i don't wish to make outright enemies over it.

OK, to clarify,... I am well aware of just about all the points raised,[yeah, i know, i'm a tease] as i ran my own engine development sideline business when i lived in Sydney. It was known as MoPower Engines & i specialised in street legal, improved performance small block Chryslers, although the odd Big Block & Polysphere came through. I worked in conjunction with Riverstone Engine Reconditioning when it was part owned by a friend who was trying to develop an air cooled V8 made from an assortment of parts, including a '52 Ford 8BA crankcase. He was bored some days & was doing this just to see if it could be done. It was well advanced & mostly assembled when the business was sold due to the severe ill health of a partner & the project was junked. They were imaginative, resourcefull, & great people to work with.

It was Riverstone that did all of the machining on the first version of my 1200GX engine, including the flywheel work & rod little-end boring too. I did all the assembly work in my airconditioned & filtered assembly shop. Does that make me an "engine builder?" I'll leave that to you.

I had a lot of research & reference material on all of this stuff, I probably still do, but it's been packed away for years.
I also learned many years ago about the point where maximum piston speed is reached too, & why it is so,... so now you know of someone who will support you on this point.

Many of the points raised are particularly valid in a maximum performance engine, but in something that runs at more liveable rev limits, these limits of efficiency are normally never reached, & are therefore, as i said, somewhat moot. In this particular application, it's all a bit of a yawn really.
The existing Datsun 1200 /1434cc engine that we have here has, as i said, performed adequately, & well, for a year or more, [so far,] & is being flogged just about every day.

However,...... if i was on a tight budget, then swapping a used A14 into my chassis is cheaper, & if i was looking for a cost-no-object, balls-to-the-wall 1400cc engine, then the A14 is definately the way to go.
But neither of these things apply, & my little experiment will fill MY criteria quite nicely. It even has novelty value at a barbeque, & now, it would seem, has become a pivot for a good old debate on engine design. I love it.

Oh yeah, we knew that the static compression ratio was somewhere between 9 to 1 & 10 to 1, which was in the zone for me. Feral was kind enough to accurately calculate it for us. It's very close to 9.5 to 1. Not too far off for the finger-counting maths we did. It's all good

I accept that the points that you have raised are most valid, however, i also feel that you have missed the very point that some others have picked up on in the last few posts. [bless their little molly lubricated hearts] It's not for racing,... it's for fun. Why?... Because i can.

D
I had a chuckle when i read your post as you must be reading my mind.
The GX head now has larger valves, but the ports are mostly unmodified. They're big enough for street duty.[Thanks Feral]
I have a Bosch electronic distributor for it [Thanks Feral]
I have Iridium plugs that are indexed [Thanks Feral]
I have an adjustable cam sprocket so as to help optimise engine efficiency. It's a tuning aid. [Thanks Feral]
I have roller rockers Not for ultra high rpm, but for a little more valve lift with the relatively modest cam timing that i plan.
It's the extra "cam" you have when you don't have much cam.
Two custom harmonic balancers are currently in use here, but mine will have a standard pulley size.
I will run factory [based] EFI if i can get one at an affordable price.

It's all good fun.

Posted on: 2005/4/7 12:37
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Re: Bore a12 how far can you go
No life (a.k.a. DattoMaster)
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From South Africa, Bloemfontein
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Dodgeman

Through reading this thread it sounds like you know what you are going to do and have thought about all the things that could go wrong.
My comment: Go for it and let us know how it goes on the dyno.
This is something very interesting namely, A12 turned into a A14 using factory parts.

Also as you have stated, you mentioned a racing version of this engine.
Hell, if it can race for so long then it MUST be good enough for street duty.

Guys, don't be so hard on each other.
This is what the site is all about.
Trying new stuff and testing it to see how it works.
Although I must say that all the replies about this subject has brought up some interesting view points on how engines work.
Thanks to all for boosting my engine knowledge.

Posted on: 2005/4/7 13:14
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Re: Bore a12 how far can you go
Just can't stay away
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From Auburn, Washington
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Quote:
While I can't remember all the details, I do remember that the dynamics of the piston at times of critical valve events are more favourable to performance engines with longer rods for a given stroke. Obviously only within a certain range, but I seem to recall that many many years ago race engine builders aimed at 2:1 rod to stroke ratios, but I think a figure around 1.8 is more flexible and realistic.


What you are describing is the fact that a longer rod causes the piston to dwell at tdc and bdc longer. This may or may not be desirable. To me, it is desirable. It causes the flame front to push on the piston longer meaning you can extract more power from a longer rod. It decreases the sideloading on the piston which means you have less friction and your pistons last longer. The drawback is that you move your torque peak up the rpm range. This may not be desirable in your particuliar street engine.

Having said that, there is one thing very good that happens as the rod ratio approaches 2:1. The engine becomes more octane tolerant and you'll find that you can run cheap gas and lose less than 2% power when you drop several grades of gasoline.

I edited some for clarity

Posted on: 2005/4/7 15:26
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