Hey Guys, been roaming the site and searching the web for this info, but unfortunately my decision will indefinitely depend on consensus. This post is the short and sweet version (5x shorter than the original), so forgive me for being blunt.

A15 in 1200 GX Coupe for daily highway driving, drags, drifts, and serious mountain sprints.
*I'm building her for torque* to suite all these conditions better.

She has a dry sump, the block's water and oil ports sandblasted, block bored to 77mm (during last service). Forged 'rods and pistons (Just in case I do eventually supercharge her), copper head gasket, coaxial valve springs, fuel injection, msd coil packs, and finally - before assembly, all moving parts will be weighed and balanced to be identical.

Now for the questions:
1 - I want to increase the stroke to 88mm rather than bore her out mainly because she's being built for torque and so that I can get a longer service life out of the block. Not to mention it should take quite a bit more punishment. This a solid idea?

2 - Knife edge the crank?

3 - If everything from the crank up is balanced, would a harmonic balancer still offer sufficient benefit?

4 - Considering local station's fuel is 93/95 octane and the motor has a longer stroke, what compression ratio should I be aiming for? I was thinking 10-10.5:1.

5 - I understand cams very basically, but I'm uncertain what I should opt for. I've been thinking of longer duration for the longer stroke, plus some duration for overlap (for pulse tuning).

6 - Is it worth enlarging the ports on the head? I understand more air+more fuel=more power, but this is still limited by valve size, and I'm also afraid of sacrificing torque.

7 - That sparks the next question - Correct exhaust diameter. Supercharging is my only form of forced induction if I do eventyally go that route, so branches and full free-flow are a must. Just not sure on the diameter (Also dependent on the former question) and 4-2-1 or 4-1? No cat's necessary in SA!

8 - ITB's or Single throttle manifold with MPFI? Both cases have an equally imbalanced affect on the crank.

9 - Fueling. I have no idea on the ideal air-fuel mix for this engine. Also, high pressure or high flow injectors?

10 - And lastly, would the B140's diff and gearbox handle this kind of hammering? Remember - Drags, Occasional Drifts, Serious Mountain Sprints, and Daily Highway time.

If you took the time to read through this, I'd like to express my gratitude and apologize at the same point. I could not have put these questions separately, or the bigger picture would have been missed. Many MANY thanks.

PS: I work for a living just like you gentlemen, but my living's for my GX!

For camshaft, consult with the camshaft vendor. Tell them the exact RPM range you are looking for. Their advice should be more experienced than anyone's on here.

*I'm building her for torque*

Boring it out will increase torque faster than a longer stroke. Just 2mm overbore is about as effective at building torque as a 6mm stroke increase.

Why knife edge the crank? That is usually one done when revving over 8500 RPM to reduce pumping losses.

Harmonic balancer won't help increase the power or reliability in any way. Unless revving over 7500 RPM -- which would not be a "torque" motor.

Air/Fuel mix:
* 12:1 for max power/full throttle
* 14:1 for cruising (steady throttle)
Same as any gasoline performance engine.

B140 uses the H165 diff. Plenty strong. The gearbox is strong enough for naturally aspirated use, but not for hard supercharged use.

Thank You Sir!
I have read much of your input on many topic on this website, and I'm sold. I am curious about one or two of your answers though. Please don't think I doubt you! I'm simply curious and would like to learn from you!

You said increasing the bore would provide more torque than increasing the stroke. Now it was my understanding that a wider crank angle meant more leverage on the crank. This would sacrifice revolutions though. Where increasing the bore would leave you with a shorter crank rotation for the larger piston being forced down. This would in turn increase the revolution limit and also increase the revolution rate. So this being said, wouldn't it need more revolutions to enact the same amount of force on the crank, thereby raising the revolutions for peak torque?

Secondly, is there a possibility you might know how much punishment a "well-looked-after" B140 gearbox can take? I received 2 emails not to long ago confirming that the diff handled over 350nm in a circuit car, and 327nm in another everyday car for 57,000 miles so far with no hassles.

I am eager to read from you again =D

Quote:

The B140 uses a 60-series gearbox, i believe. Look on the left (driver's side) of the gearbox for a "60" casting to be certain.




The most torque Nissan used these with was the A15, which was often rated at 83 ft-lb (112 Nm) torque depending on year etc.

The next size up gearbox is the 63-series which Nissan used up to 112 ft-bl (152 Nm). These came in A14-powered B210 5-speed cars (1976-1978) and are suitable for supercharged engines. The 63-series gearboxes were designed for the L16 engine and can easily handle more torque than the 60-series boxes.

Quote:

That is the theory. But don't forget practical reality.

Yes, you are partially correct -- if the displacment doesn't change. A 1488cc engine with long-stroke, small bore will make more torque than a 1488cc engine short-stroke, long bore. But in reality if you increase the engine size via stroking or via boring, either way you will increase the torque. And the torque difference between 82mm and 88mm stroke is not huge when the CCs don't change.

For example:
* 82 mm stroke x 76.00 bore = 1488cc, 83 lb-ft (stock A15)
* 88 mm stroke x 73.36 bore = 1488cc, 85 lb-ft perhaps with careful camshaft tuning

This is with a stroke difference of only 7%. Compare that to a 33% difference in strokes with two different 6.2-liter small-block GM V8 engines, which might be good for 30 ft-lb torque difference. But since HP is lower, it is a still a performance trade-off. It won't necessarily accelerate faster.

Quote:

And there is no "sacrifice" of RPMs. The factory stock 82mm stroke A15 can rev to 9000 RPM repeatedly. And an 88mm stroker can still rev high, the Nissan factory 88mm stroke crank revs to at least 8000 RPM, more than a "torque" motor needs.


The main factors of long-stroke vs short-stroke:
1. the rings will last relatively longer with the shorter stroke
2. The next most important factor is the the side loading (and in neither case is it very important for the A15)
3. the last actual real effect is the leverage. yes, it is real, but increasing the CCs of the engine has more effect on HP and Torque than this leverage effect. The only time it becomes important is when:
* class racing rules prohibit going to more CCs. That's when the professionals start juggling stroke/bore ratios
* fuel economy. Car manufacturers are judged on average fuel economy, so a 0.1 increase in fuel economy can be a huge win for a 1,000,000 unit run of motors

If your goal is acceleration performance, go with increasing CCs. If you are meeting a certain CC limit (racing class rules) then worry about bore/stroke ratio. The same goes for rod/stroke ratio - the effect is real, but minor compared to increasing CCs.

Were you planning on running a lightweight flywheel? there's some debate between hillclimbers about using light ones and although I use a light one I believe a heavier one is more suitable for maintaining engine rpm under load and general driving. What I do like about light flywheels is the emphasis it puts on compression braking and the feel of shifting gears, but the latter may be more to do with method and the solid side bushings I placed in the box.

Hillclimbs, go medium to heavy flywheel, go square stroke, dont think long will make a difference and it will last longer.It's easier to play with ya diff ratio and box ratio to get the right medium for you requirements. Suspension also is a key factor. Dont put so much factor on engine HP , your gears will compensate.. ps have fun anyway !!

Thanks Guys.
You gentlemen are really filling in the blanks for me.

I guess what my bore stroke question comes down to is: Do I bore her another 2mm to 79mm or do I stroke her to 88mm? Either increases the cc. Right now she's the underdog in her class (Circuit and KOTM), and class won't change 'til I cross the 1900cc mark. Mind you, how close can I get to having her bore/stroke square? I'd be satisfied if her cams are cut to limit her at 7500-8000rpm, as long as she has sufficient GRUNT (I grew up with RB30's and V8's, so chassis-twisting torque over HP for me, thanks).

The reason I ask about the diff and 'box is so that I won't have to buy others later. If the gearbox and diff can take the many different types of consistent punishment, then I'd be satisfied on buying extra CWP's and servicing the gearbox often.

Oh and yes, if her torque is sufficient (which it already is) I plan using a medium to light flywheel. Not too light though.

Thanks once again for the replies!

The following is opion/based on experience (but I haven't worked on a million a series dattos specifically). It's not the last word, I'm not perfect. I've tried to provide reasoning explaining anything I've said, but read it all with a critical eye, because ultimately whatever you do with or to the engine your the one who will be responsible for how it turns out.

If it 'must' stay NA, and is deliberately going to be made to work at more all round user friendly rpm range then the long stroke crank is worth a look. It'll likely cost you more than running a diy sc14 supercharger on a std stroke a15, and produce less torque and less hp, than the supercharged option, and also not last as lnog as the 'budget/ghetto supercharged a15) but that's just the way it goes.

It's also worth noting that if you do go to a supercharger, you'll need to run a lower compression ratio than you would with an NA 1.7 and a different cam (less overlap, less duration, and specifically for supercharging, you'd run a little more exhaust duration than you would for any given intake duration for an NA engine. You'd also not be needing or using twin webers (or if running efi, a single throttle body in front of the supercharger and an injector in each manifold runner instead of itbs). You'd not need the longer stroke, the supercharger will pump in all the air you need, so the capacity of the engine is a little less crucial. So aside from knowing a fairly mild a15 with supercharger will make more power than the stroked NA 1.7 ish sized motor, there's also the issue that not a lot of the bits could be retained, so if you found yourself still wanting more grunt, then it'd be easier and way cheaper to just pursue forced induction from the beginning

Now for 'real' racing you will get to the point as far as engine capacity goes, that it's just so big (like around what 1.7 litres if you went with a 2mm oversize bore and 88mm stroke) that no matter how well ported the head is, the head is just not capable of properly feeding all that capacity at higher rpm, and the increased friction from the longer stroke would combine with that and cancel out most if not all of the gains of the extra capacity.

But you aren't looking at those rpm levels so a properly "pocket ported" head will do the trick and be capable of supplying enough flow to feed that much capacity. Pocket porting is basically focusing the work on the bowl area (around the valve/valve seat and valve guide boss area of the intake and exhausts) these areas are essentially a 'bottleneck' and flow a lot less than the main 'straight' section of the port. So you effectively work on those areas to minimise as much as possible the obstructions. you won't be opening up that straight main section of the port and as a result of there being no increase in the cross section area of that part of the port (and those more restrictive regions won't exceed that size/area/flow of the main part pretty much no matter how much time you spend porting them) so since that area isn't increased, the flow velocity won't be compromised, meaning no loss of low/mid range output and efficiency.

On a similar note the added friction from the longer stroke is far less of a factor/penalty at lower rpm ranges. Same story goes for rod:stroke ratio. Shorter rods mean more rod angularity and so more 'side thrust' and more friction, power losses and stress/wear and tear on the bore walls and the piston thrust face on the skirt region. In your case presumably you wouldn't run shorter rods, but a longer stroke with the same length rods so it's 'like' running relatively shorter rods. Again, at more reasonable rpm levels it's just not any real worry.

Lighter flywheels mean quicker throttle response, and with low enough diff gears (like 4.875:1) well the difference in acceleration in first gear can be noticeable. The gearing (first gear combined with said diff ratio) is just so low that a heavier flywheel will actually manage to slightly reduce how quickly the engine can spin to redline. By second gear the effect is reduced a lot, and by 3rd and 4th and 5th, it's negligible. For a purpose built hillclimber, the lighter flywheel is definitely the go.

Now presuambly the engine combo/rpm range/usage would actually rule out using 4.875 diff ratio, probably 4.1:1, maybe 4.375 (but the latter is imo highly debatable with the longer stroke) but certainly not 4.875. WIth this in mind, much like how the effects of a super light flywheel is reduced progressively to nil as you go up through teh gears, well with 4.1s the advantages will be minimal. GIven the longer stroke (if you go ahead with it) and the desire for long engine life, you really can't aim for anything beyond 4.1:1 diff gears imo, and furthermore you'd definitely want to be running a 5 speed with an overdrive 5th, not a 1:1 5th (though admittedly those boxes/gearsets are darn

That said, I'm talking about more exotic ultra light flywheels here. The good old trick of using an a12 flywheel (which is slightly lighter than the a15 one) has no real 'drawbacks' and they are plentiful, so you might as well use one. The gain in throttle response won't affect in gear acceleration much, but the quicker response can help with regard to launching the car from a standstill/various shifts. The ultra light flywheels also mean the rpms drop a lot quicker so it is harder to keep the engine rpms up, and it makes them a lot less user friendly in heavt traffic (it's not unusual for tractors - that have to potter along at very low speeds, and also can get slightly bogged or whatever - it's not unusual for them to have much heavier flywheels - the inertia in the heavier flywheel will prevent the engine rpms from dying and stalling when you hit a bump or whatever. Anyway, the a12 flywheel just isn't much lighter than the a15 one, and heavier than a race spec one, it won't incur the driveability issues, so again, go for it.

knife edging a crank is only a big deal for much higher rpms in general. Additionally, generally the more weight in the crank, (when it's not ever going to see sky high rpms) the longer it will last, so I'd definitely leave it as is.

Out of curiousity, what is the plan as far as the crank itself goes - is there some company out there offering a custom (possibly billet) long stroke crank for the a-series, or are you taking an a15 and having the rod journals welded up and offset ground to attain the longer stroke?

Since the capacity is larger than an a15 (and a lot bigger than an a12) - in general you'd aim for more airflow headwise (though the rpm limitation helps avoid some of this) . Also a cam that would see a particularly grumpy idle on an a12 will be smoothed out a bit in an a15, since at any given rpm range the a15 (or stroker a17!) will need more air/fuel to feed it. So look at a cam that is something above what might be considered mild, but something short of full race. I'd suggest that perhaps something with 280 - 285 degrees seat to seat duration (and as much lift as they can safely achieve for that duration without risking lifter/valvetrain issues) Quite often the sort of cam that would see light of day in a rally engine would be a good option (but that wuold be the biggest you'd typically want to run, and certainly a slightly milder one could be justified). A pretty good rule of thumb here is if there is ANY doubt at all, go smaller on the cam duration not longer.

As a very very general rule of thumb, when you go longer and longer on the stroke, the cam lobe separation angle tends to want to be a little bit narrower. Nothing drastic here. If a particular cam (approx rally spec) had 110 degrees lobe separation (it's probably narrower to start with on an a series spec cam 110 is merely used for sake of example) then with an 88mm stroke you'd want to perhaps close it down to 108. This has to be decided upon ahead of time (obviously) and the cam has to be ground to suit. You can't (of cuorse) alter lobe separation on a single cam engine, not like you can with dohc where you can individually time BOTH cams.

This narrower lobe separation (all else being equal) will result in a slightly rougher idle. Initially that might not make sense. But what happens is that at idle, the throttle plates are closed so very little air can be sucked into the cylinders. The tighter lobe sep means more valve overlap (period where the exhaust valve isn't yet fully closed but is close to closing, and the intake valve has already started to open - so both are open at the same time) - well the exhaust pipe has no 'throttle plate' in it, so at idle, whilst the intake throttles are closed, the engine can and will suck some air (or exhaust gases, or a bit or both) back in through the exhaust port. even if it was air, it was from the exhaust, so it isn't carrying with it a well distributed fuel mixture to burn, so idle is slightly compromised. Not night and day, just trying to be up front about it. Ironically once the throttle plates ARE open (even just at cruise rpm/power levels, and certainly at full throttle) the tighter lobe separation angle (within reason, obviously you can go too far) will lead to improved mid range torque without costing much if any peak power. And that's worth far more than peak power in 99 out of 100 situations even on a circuit.

The compression ratio you can safely run depends on a lot of things, fuel octane. head material (alloy means you can run higher comp than cast iron) chamber design (closed chamber head, with some quench areas will allow the higher comp ratio, but you might not be able to get it low enough since there's much more capacity being squeezed into the same chamber size, so the increase capacity leads to more compression. If however you can get dished pistons that still have quench areas intact (i.e. the dish is a similar shape to the chambers with some flat areas surrounding them, not a full dish as such). if you can get that sort of piston dish, you can run more comp. Bore size (generally the larger the bore, teh less comp you can run but even at 78mm the datto engine is a relatively modestly sized bore, it's not till you get into bigger 4/6 cylinder regions that it becomes a big issue. The other factor is camshaft duration/intake valve closing timing. Very very generally speaking, the later the intake valve closes, the higher compression you can run. SO with the sort of cam duration (and later intake valve closing point timing) you'll be running, you can run more static compression. You shouldn't have much trouble with 10.5:1 with that sort of cam timing (approx 280-285 duration) and I'd almost make a case for a touch higher if you had access to 98 octane, but you don't so 10.5:1 should be ok. If you can't run a closed chamber head/matched piston dish shape and the resultant significant quench areas and/or you can't run it so that the piston at tdc is no more than 45thou from the flat sections of the head deck (which is a combination of block deck height, piston crown height, and head gasket thickness. Look up quench on various car sites to learn more but basically if there are large flat areas sandwiched together when the piston is at TDC, then it works as if the fuel was much higher octane, but if the piston/head don't get that close to each other at tdc it just won't work. Ideally you'd aim for a tighter gap than that, but then, with thermal expansion, the possibility of very slight piston rock at TDC and all that, you would risk them actually making contact and that would be game over. Anyway, if you couldn't get decent quench then you'd have to reduce the static comp ratio to be safe. around 10:1 would be more inline possibly even less (and if you can't run over 10.0:1 then you really start to lose out at higher rpms (bigger cams not only 'allow' more comp ratio, they more or less 'need it') - and this dropoff in power can actually mean that if you (for arguments sake) had to go down to around 9.5:1 compression, you'd actually get a better performing all round combo with a smaller cam (perhaps around 275 adv duration or thereabouts)


Exhaust wise, the 4 into 1 headers in general tend to make the most power (but a bad 4>1 will lose out to a good 4>2>1 setup). There's a set available through hurricane 4 into 1 with 38mm primaries. Primary pipe diameter is by far the most critical factor in matching engine capacity/rpm and thankfully the maths behind it has been worked out by a bunch of people literally decades ago. Anyway 38mm primaries on these headers (they also make a 4-2-1 which apparently has 35mm primaries, which would be too restrictive for even a stock cammed a15 to be honest) will find their own peak efficiency (where they boost torque the most at about 4200rpm. Obviously they aren't that 'narrow' in their range, and whilst 4220 is technically their peak rpm point, they will happily and usefully work to optimise torque across a good 2000rpm or so either side of that. They are very very marginally too narrow, but nowhere near enough to lose sleep over and are off the shelf. Ironically their primary pipe length is a touch short for an a15 (a street/mild competition rpm range one). Whilst primary pipe length doesn't have anywhere near the overall influence that diameter does, running shorter pipes will tend to bias the rpm range upward a little. SO in this case they actually are a fairly good option. they come with a 2inch collector which is about right too.

One throat/barrel (webers or itbs) per cylinder always produces the best throttle response and wider powerband, whereas a larger plenum and single throttle body tends to see peak power *(if optimally sized). For any sort of circuit/climbing work the itbs/webers are for sure the way to go

drivetrain wise - there's two issues - weight of car/engine output being the first. But there is also shockloading - in other words even with a stock engine, if it is revved up hard and the clutch is let off too quickly, that sort of shock will eventually break the diff or the gearbox. so what I am saying is that whilst the 60 series box will last ok for a street a15(and maybe a17) IF the driver treats it very considerately - no harsh launches and a slightly restrained lift off of the clutch after gearshifts - it won't die overnight. But if it is seeing hill climbs, any rallying (where the grip can get loose then grab really hard every few meters) and drag racing/drifting, you're going to see the end of the gearbox a lot sooner. I reckon it'd be a good case of where at least a 63a box (which can be found with an a series bellhousing, thuogh they are rarer) or a 71b box conversion (tehre's a thread on that conversion on this forum, but it's still in very early stages so you'd be doing it as a one off, before there'll be a how to write up (or in the much longer term possibly the option to have the bellhousings cut/welded so the 71b boxes can be bolted up.

Good advice jmac.


But note the effect of *minor* stroke changes:
Quote:For the planned 6mm stroke increase, we are looking at what? 200 RPM of difference? In the SBC V8 engines they talk about strokes in the same range as A15 (which is 3.23") but with changes on the order of 25 mm (going from 3" to 4"). That makes for much larger RPM/torque effects than a mere 6mm change.