Quote:

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

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.

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.

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.

Quote:

spot on.

the L16 / L24 have a 1.8:1 rod/stroke ratio, which is, according to many an expert, the "perfect" rod / stroke ratio for a powerful NA engine that not only revs hard, but produces useable torque in the midrange.

1.57:1 is a very short ratio indeed, and i think overall driveability will be compromised unless it's cammed & carbed up to make up for poor cylinder filling otherwise. and engine like this would CERTAINLY respond well to boost though.

HOWEVER

i can see Dodgeman's point. not wanting to cut the car for originality leaves you with few options for more power.

but i'm with L18_B110 here. similar situation is when i think to myself "why put an L18 crank, rods and pistons in a +2.0mm L16 block?" when you you could just use an L18 to start with. sure, if you wanted to keep a 1600 in immaculate condition with original numbers then yeah, go for it. otherwise, anyone else would just swap in an L18.

this thread has gotten all too technical for me.

Well the A14 block and a15 are the same, the rods are the same but the pistons are taller on the a14 by 3-5 mm? (77 vs 82mm stroke) correct me on that one.
However "around" 10mm difference? on the rod length in this case seems that it might not be a big deal in regards to the a14 crank.
If 1600cc a13 are possible then a 1420cc a12 seems more than reasonable.
Time will tell and we hope it works out for Dodge as we do for feral in his crazy challenge but hey feral use argon next time ;).

Everyone put down my uncles project of a 427 cube windsor. Specially since he had to use modded 400 cleveland crank, chrysler 360 hemi rods (just 150mm long) and custom pistons and clearanced w351 block, home made harmonic balancer. But that engine ran for 18 years without a hitch and made around 440 hp and 13.4 second quarters in an old f100.
The rods where too short according to calculations but it didnt stop him embarrassing many flashy posches and other exotic and "correct" machinery.
That thing had a 4 speed manual no auto and the torque it produced was speechless.

If there is lesser dwell time at TDC (which seems like there will be) he might be able to get away with it with higher velocity porting (please read: not larger but better angled atomised fuel delivery which is a slightly cleaned up a12gx head) and maybe some fancy timing setup (higher energy ignition and why not some greenfire plugs as well ;). Also this setup will maybe require a harmonic balancer for the side thrusting (as Dodge did point out to me that he was fully aware of this).
In the end we will see.

For Dodge, this exercise will beat a non factory non engineered a14 in costs hands down. Lets not forget originality.
Bring it on I said ol chap

Harry thanx for those calculations it will be interesting to see if it is 1.57 or 1.6 with exact measurements and whether it matters in our much loved A series and not small block v8s.

I guess that's where hot-rodders and racers differ. I wouldn't build an "improved performance" engine with such a big compromise built into it just for the purpose of aesthetics. Especially when there is a better factory alternative available.

anyway, I had an hour to spare and just finished typing this up...

OK, here goes. First some basics that we can probably all agree on. although I'm sure some of them will be contentious...
1) The amount of power an engine can produce is largely determined by how much air/fuel it can pump.
2) The main factors (variables) in pumping air and out of a given engine is the movement of the piston, and the timing of the valve events.
3) The dynamics of how the piston moves is determined by the crank's stroke (or more correctly the crank pin radius) and the rod length.
4) during the course of the 4 stroke cycle, the piston will come to a complete stop 4 times.
5) the remainder of the time the piston is accellerating. (decelleration simply being -ve accelleration)
6) the dynamics of how the piston accellerates is determined by the crank pin radius and rod length. (Yes, I know I'm repeating myself)
7) piston speed (well, probably more correctly the instantaneous accelleration of the piston) at and around the valve events is largely responsible for determining the dynamics of the intake and exhaust gasses.

and some more complicated facts that are really hard to get your head around...
8) If the piston travels the full length of the crank's stroke in exactly 180 crankshaft degrees, it stands to reason that at exactly 90 crankshaft degrees the piston will have travelled exactly half its stroke in the bore, yes? Well it doesn't. I bet you don't believe me. every mechanic I ever told this did not believe me either. Unfortunately my memory, not to mention my maths skills are not up to the job of explaining this, but it is true nonetheless.
9) the piston will always move more than half the crank's stroke in the first 90degrees of crank rotation. How much further is determined by the relationship of the rod length to the crank pin radius (which is consistent with rod to stroke ratio).
10) therefore, the piston is moving faster in the first half of the crank rotation, than the sencond half.
11) max piston speed occurs when the angle of the rod is tangetial to the motion of the crank pin. The shorter the rod you use, the earlier (in crank degrees) this happens.
12) now all of that was to get us to this point -> This has a few real world implications (that I can remember); reduced max operating speed because the safe peak piston velocity will be reached earlier, and reduced mechanical efficiency because the piston has less time to exert force to the crank around the optimal angles, and thirdly because piston speeds at times of the most important valve events are higher, the engine is less sensitive to valve timing.

That is why "I reckon" that volumetric efficiency will be comprimised with the short rod A14 crank combo you're running. Maybe you can see now why I didn't bother to explain all that in my first post, and just said "I reckon"... which is why I suggested you read up on it for yourself. The details get sketchy with time, and my explanation is definitely lacking in clarity and vital chnks of info, but I'm pretty sure I have the facts straight.

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. Rod lengths under 1.6 were though of as poor according to my memory. And your rod to stroke ratio comes out to about 1.57:1, but I used less than 100% accurate rod length figures in that calculation, but it shouldn't affect the results to the quoted accuracy.

And now the rest of have seen the essense of hotrodding. Sometimes it's more about, "Can it be done?", rather than cost, ease or leading edge performance. Sometimes, it about what you got and what you can do with it.

I think Dodgeman has the true hotrodder spirit. Too many people think hotrodding is about bolting a few mailorder billet parts on and going with it.

I appreciate the engine-uity put forth Dodgeman

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understatement of the year!

I'm not about to start taking engine building advice from someone who selected all his parts for the assembly without so much as calculating the compression ratio.

I think you're getting overly defensive, and starting in on personal attacks which I'm not about to be drawn into. All I am saying is that the shorter rod to stroke ratio you are forced to run is a less than optimal compromise. It also goes against the convential wisdom of performance engine building, which you obviously are not aware of.

there is a big difference between a mechanic and an 'engine builder'. There's much more to it than selecting various components that will fit together.

Just to clarify this for you, because you're not the first to incorrectly think I'm saying "that thing will never run"... I'm absolutely certain you will be very pleased with the fruits of your labour into which you have obviously invested so much pride. But the fact remains, the same parts on an A14 block with std A14 rods, will have much more potential. And until you did that, you will have learnt nothing about this from personal experience. But its just a very mildly tuned street engine so at the end of the day, it isn't going to matter all that much.

All I was doing was pointing out some of the consequences of reducing rod to stroke ratio in a 'performance' engine. If you really want to know more about it and refuse to read it anywhere but here, I'll get to work on my assignment tonight, or if it's quiet today I might be able to make a start sooner. I think I made it pretty clear I was less certain about the negative impact on volumetric efficiency than the other effects, but it is a natural progression from the reduced sensitivity to valve timing events caused by the different piston dynamics resulting from the shorter rods. But volumetric efficiency is certainly partially a product of valve events.