I had an A14 in my old 1000 coupe - it's not exactly difficult. Certainly not compared to the difficulties, and expense, of fitting the A14 crank to the A12 block.

I could almost understand a rally competitor doing it though, because they're restricted to using the standard or homologated block with free internals. But for a street engine it seems an awful expensive way to avoid the need for a mod plate.

And even after all that trouble, you won't quite end up with the same result as a normal A14, because your rod to stroke ratio takes a fair bit of a battering (but I don't know what length rod Dodgeman used - didn't he get some weird rare A series rod from USA?). Which essentially means reduced safe rpm limit, reduced mechanical efficiency, and makes the engine less sensitive to valve timing - meaning you won't get full advantage out of your sporty reground cam. And following on from that, I reckon it would reduce volumetric efficiency too. If I was going to rally a 1200, I'd stick with the A12 crank and 76mm bore.

Well, let me see.
Mod plate, what's that. The only one here to mention mod plate was yourself, so that not an issue, just a red herring.
Since i am boring the block, i needed new pistons, so i bought A15 ones. Nothing hard about that.

Difficulty & expense in fitting the A14 crank? Surely you are joking. It's simplicity itself.
I swapped something that i didn't need for the crank, so stop spreading stories about "expense" & the machining was done in 35 minutes for free. As for dificulty, it just fits up the same as a stock one. I suspect that you are thinking of something else. It's neither expensive nor difficult in this instance.

The rods? I don't know about weird, Perhaps you could elaborate on what is weird about a stock A series con rod. Yes, they are rare here in Australia, because the 1237cc A12a engine was not sold here. Tell me more, most particularly about the weird part.

Rod angle increase, yes, but at street speeds, it shouldn't be a problem for me. It hasn't been a problem for the only other example of this engine that i know of. My engine will be red-lined at 6,500 as this is the mark on my stock tach & the other engine is regularly run to more than that. In fact, it gets flogged mercilessly, but surprisingly, it would seem, it still runs good. Very bloody good.
It's the torque that i'm after, not dazzling revs, & all in a sneaky 1200 block.

Reduced volumetric efficiency? With a bore & stroke of a stock A14 with a 1mm overbore, & an improved 12GX head, you will need to provide a detailed explanation before i will swallow that.

Less sensitive to valve timing? Again, an explanation will be necessary.

The only special machining required was to chuck the A14 crank into a lathe & reduce its overall diameter by a few milimeters. Basicly we cleaned the dags off the counterweights. Big deal.

Basicly, everything in this engine carries a stock Datsun part number. It's just an innocent little 1200,... honest, so i don't know what you mean about "going to all this trouble." No part of this exercise has been any trouble, but ALL of it has been FUN,...... for me.

Talk is cheap when decrying a design, but if you know why all of the points noted above are negative ones, please let us all know, in exquisite detail, so that others don't make the same mistake.

If i was going to rally, i wouldn't use this engine either, but i'm not rallying, i'm just street cruising, so it will be OK for me.

whoa, I didn't mean to insult your rods - I take it back, they're perfectly normal A series rods. albeit from the other side of the planet. All I was saying is that I was not sure what length rod you had used (but they had to be short), and I couldn't recall if you said they were A13 or A12a rods, I just knew they were out of one of those oddball A series engines.

As for this...Quote:
I don't know what I was thinking. Yes, simplicity itself! So easy in fact, I think I'll go do it tonight. Just pop it in me lathe... ah, hang on... will this here angle grinder do?
I seem to recall your mate did this for you in his home made lathe, but for 99.9% of us machining doesn't come cheap. You say it took 35 minutes to machine the crank. An engineer however, is going to charge for time spent measuring the block and crank, and double checking everything to make sure it actually fits after the operation, then there's the trial fitment, which will involve a dummy assembly of the bottom end (crank, rods and pistons), which I'm sure the engineer would also insist on so that he knows it's not going to come back. Conservatively, you'd be looking at 4hours, and at cheap charge-out rates that bill would come to arond $340. did I mention that's a real conservative estimate?

Then you have to balance the reciprocating assembly wether its just going to be a street motor or not. But that's probably simplicity itself and free too... For the rest of us, you'd be looking at another couple of hundred. This would be an optional extra if you were building a street A14.

OR, you could drop in the A14 engine. And then spend the five or six hundred dollars you saved yourself on stuff that will make it go faster. Anyone who owns a hacksaw and an electric drill can do the conversion - That is simplicity itself! Or if you want to get really fancy and make it look factory at first glance (that's all your A12 block will do anyway), just unpick the mounting brackets off the x-member and weld on some 120Y ones - that will invlove such exotic tools as an electric drill, cold chisel and a hammer. Then take it to someone to weld it up - might cost you a carton.

All this begs the question - why did the Datsun engineers go to the trouble of using a taller block and longer rods for the A14?

It's a pretty big assignment to explain how the rod to stroke ratio affects engine performance on a web forum. It has taken much more cleverer people than me chapters to explain this. I think if you go read the Racer Brown stuff Datsport has one thier website, you'll get a good broad grounding in this and other aspects of engine building.

OK, it's apparent that you haven't played with too many of these, so i will add what little i can to make it simplified.

The rods are the same length as standard 1200 /A12 ones, with the exception of the larger wrist pin eye. My existing 1200 GX engine uses A14 pistons with the little end opened out to take the larger pin. This time i elected to go with a factory stock part. A13 [big bore version] & A12a rods are dimentionally interchangeable

The A14 crank will fit the 1200 /A12 block without alteration. There is quite enough room in the blocks that we tried.
The lathe work was't to allow the crank to fit the block, but to ensure that the counterweights miss the bottom of the pistons when the pistons are at BDC.

Could you do the necessary mods to the crank with an angle grinder? Hell yes, you could do it with a hand file if you were really really patient, but i seriously question why you would have an angle grinder in your engine assembly area. Is this the best engine work that you can do?
The the only part that actually needs work is the small part of the counterweight that would intefere with the piston. The best way to check this is to simply assemble an old A12 rod & piston onto the crank [with a suitable bearing] & rotate it around the journal. Then grind away the part where it interferes. Repeat for the other three journals.
Even a blacksmith could do that. That's all the dummy fitment that was required in the first engine, so we can put that small fortune back into our pockets. Wasn't that simple?

Balancing is always done on all my engines as a standard procedure, so what's the problem here? Don't you balance yours?
The A15 pistons should rise to be almost flush with the block, so this is not a special part of the build. Just standard rebuild stuff here. The A15 pistons were selected because they are shorter in the pin to crown measurement & a dummy trial fitup showed that it would work, so the first engine was built from leftovers.

For me, saving money on a cost effective & very practical A14 transplant is not the prime objective here, although it could, & probably should be for many,... geting the combination of parts that i want IS the prime objective.
I try to save money by using what little skills i have gathered after almost 40 years as a mechanic, & by doing as much as i can myself.

Now you seem to have overlooked the fact that i have not asked, nor even suggested that you,... or anyone else for that matter, should duplicate this engine, nor do i suggest that anyone should spend money on having engineers build engines for them un-necessarily, only you are suggesting this.

It's an exercise that will cost ME about the same as a regular "improved performance" engine buildup & will take roughly the same investment in time, effort & other resources. Since i am not looking for ultimate performance, the points that you labour upon, like rod angle & the alleged reduction in "mechanical efficiency", along with this reduction in sensitivity to valve timing [whatever that's supposed to mean] are all rather moot.

We have one of these engines running here in a 1200 coupe already & after more than a year of flogging, it still runs strongly. Mine will be in a milder state of tune & I expect that it will serve me well in its intended role.

If it doesn't work, then i will know why from first hand experience, instead of coming up with a great confection of rhetoric revolving around some airy fairy theories about "reduced volumetric efficiency" based on nothing more than a foundation of "I reckon"

You seem to be obsessed with absolute minimal costs & blacksmith engineering, & for a low cost project, i'm sure that this approach would be fine for you, but for me, this car is a plaything & i want to do as good a job as i can. Quality is always appreciated, & it's all fun.

The criteria for its existance?
No visible or un-necessary home grown engineering
To make the finished product appear to be a factory built car if possible
To assemble a maximum capacity engine for this car built from readily available standard Datsun /Nissan parts, & based on core components already on hand, with a minimum of special engineering.

I'll be sure to let you know how it runs.
The End

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.

Quote:



understatement of the year!

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

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.

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.

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.