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Increasing Torque


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compresion  and engine stroke are big players when you try to increase torque. Also head work can increase torque if you do it proply but it will most likelee move it up the rev range . most mods will do this Cams are grate at improving hp but they will move torque curve up in most cases .but the best way to increase torque is a turbo or supercharging by a long way

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Modifying the ports is a good way to go. My green car was built for torque so has had the head worked to suit, basically not too big in the ports and short run into the chamber. The head was originally built by a rally guy, so it was optimised to produce torque over power.

 

My engine throws out 210 ft/lb at about 3600 and currently makes max power at 5800 so is a big lazy truck motor that pulls better than a 14 year old school boy.

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You should really try and tell us where you want the torque increase to be.

 

A V8 feels strong and throttle responsive because it has gobs of low rpm torque. A rotary in a HQ like the ones sold in Japan would have been awful to drive....no low rpm torque to speak of ie gutless.

 

High rpm power is actually the product of torque multiplied by engine revs, and when you look at it like this, to make decent power, you'll require a head that breaths well at higher rpms. There is a limit to the amount of air a head can flow. The size of the port and the camshaft profile will determine this. So by using a big port and a big cam profile, you will improve torque but at ever higher rpms. The bigger ports and cams only work at higher rpms because it's only then that the airspeed through the ports is high enough to generate sufficient inertia to prevent the negative effects of reversion. At anything below these 'effective' rpms, the head isnt flowing fast enough, the big overlap is bleeding dynamic compression and torque will decrease. This isn't where you want to go if your looking for a 'tractor' or 'torquey' engine, one that generates good power (think the formula) at low rpms, say around 1800-2800rpms.

 

On the highway in 5th, doing 100-110km/h, squeeze the throttle on a tractor engine. Now do the same with one of the 'other' engines and see what happens, or doesn't happen. If a low rpm torquey bastard is what you think you want, read on.

 

It was suggested to use a turbo or supercharger for low rpm effect. It will work, for sure, but you'll have to drop compression and use a stockish cam. With a NA engine, keep the stockish cam and keep the ports stock and you'll be on the right track. Add some compression but don't go too high as the dynamic compression will cause the engine to detonate unless you modify your cooling system, use higher octane fuel, water injection, colder plugs and run mechanical advance without vacuum advance because it may overadvance momentarily.

 

Advancing the ignition timing and cam timing will boost low rpm torque. 20 degrees static ignition timing with a dizzy with 14 to 16 degrees mech. adv. will work, all in by 3000rpm.

 

Use a 6-2-1 header for better torque spread. A 6-1 header is usually 'tuned' for higher rpms. A 2.25 or 2.5 inch pipe will work just fine.

 

Your intake setup will also have an effect on torque. My Arizona Z intake has been designed to boost low rpm torque and I wonder how many Aussies have tried this manifold for themselves. It works very well for me but required some unique tuning strategies to get it working properly. AFR's are also important for torque production as go too lean and the engine will ping, too rich and be slugish. The AFR's will determine ignition advance. A small Holley 4 barrel was used, small venturis and multiple barrels took care of both low rpm and high rpm scenarios.

 

Just some stuff....... ;)

 

Did I lose power? Compared to what? A stocker? No, the thing has more power at max/peak power rpm's than before, but more significantly the torque curve has muscled up exactly where I want it to be. Responsive, economical, docile and reliable are important aspects for my streetcar.

 

Just wait 'till you drive it.

 

Cheers :)

 

 

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not bad the last l28 i did for the engine day made 190 kwatw at 6200 torque is close to 300 at 3500 and it made 150kw at 4200 not bad for 2.8l

 

Peter, I am having some dramas with number 2 leaning out and running a bit too hot, so the timing at the.moment is set at 2 deg btdc to keep a safe tune. The only problem with the log manifold with the inherent problems in getting even flow down each runner.

 

In the next month or so those issues will be sorted so expect  to see more torque and maximum power closer to the 6800 the 74 deg cam normally produces power at.

 

Also helps that the bore is 89mm to help with the torque.

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the 74 should make at 5900  76 hi lift cam in the motor above makes power at 6200 has 88 mm bore timing is 14 static and 28 total all in at 3800  has 13to1 comp . it funny as this motor with 10 to 1 had the same timing  .sounds like your setup is not quit right. manifold design and size, and exh play a major part in this as does the head and combustion chamber some head are better than others

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the 74 should make at 5900  76 hi lift cam in the motor above makes power at 6200 has 88 mm bore timing is 14 static and 28 total all in at 3800  has 13to1 comp . it funny as this motor with 10 to 1 had the same timing  .sounds like your setup is not quit right. manifold design and size, and exh play a major part in this as does the head and combustion chamber some head are better than others

 

With the injection a 76 deg cam doesn't really work in my motor and the 74 is nicer. Exhaust is a handmade 6-3-1 system into 3" pipe exiting out the right at the end of the door. The system was made by Andy at Penrith Muffler Man many years ago to match the engine.

 

Injection is turbo log manifold with Haltech F9 computer. I am looking at upgrading to Motech when the dollars allow.

 

The last build made max power at 6800. The current motor has a pretty flat torque curve and power doesn't drop off quickly after 5600 so I rev to about 7000 before changing up without drama.

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Torque = Moment or Turning Force – is a function of the perpendicular force around the point of rotation and the distance to the point of rotation.

 

In the case of an internal combustion engine, the force is a function of the pressure in the cylinder during the burning of the fuel (petrol & air mix) AND the area of the piston (as Lurch was alluding to).  The higher the pressure or the larger the piston area (or both), the greater the force creating torque.  Additionally, the ‘stroke’ or the offset of the crankshaft journals from the axis of rotation, is the distance over which the Turning Force is acting.  Hence, a longer stroke will increase torque.

 

So this brings us to the next problem, the pressure in the cylinders is dynamic not constant.  And more in relation to your question, how do you increase the average pressure applied to the piston during combustion?  Firstly, because there will be a time in the combustion process when the pressure will be at its highest, we want to time the piston travel (crank to conrod angle) such that this pressure peak generates the most torque (this is why ignition timing is so important and why programmable ignition is worth its weight in unobtainium).  Factors that can affect the pressure profile in the cylinder include (but are not limited to) the amount of fuel sucked or pushed (if supercharged*) into the cylinders, the chemical properties of the fuel, the amount the fuel is compressed before ignition (although I believe this changes the burn rate rather than the actual thermal energy output), the shape of the combustion chamber, etc.  The biggest influence here is the amount of fuel in the cylinder before combustion.  Remembering an engine is basically just a big reciprocating air pump, meaning this is all about a combination of mechanical factors (valve opening & closing times, valve sizes, valve durations, port flow characteristics) and fluid dynamics.  Plenty of people on here have knowledge about getting an L-series to be a good air pump.

 

To summarise, your options include:

  • Increase Piston Size
  • Increase Engine Stroke
  • Ensure optimal ignition timing for all rev ranges (programmable ignition required)
  • Increase the amount of fuel in the combustion chamber (messing with cams, valves, ports, inlet and exhaust manifolds, etc)

 

* Turbo is short for Turbine driven supercharger.

 

 

NOTE:  I reserve the right to be proved wrong about any or all of this by someone much smarter than myself.

 

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hi, i dont know a lot about the l28, but generally smaller Ø inlets and exhaust will allow greater air speed into the engine, giving better torque in the low rpm. but being small, they limit hp potential.

 

im putting a holden 5L v8 into my patrol, i asked a very knowledgeable bloke about a good combo to get me all my torque into the low rpm range, like 2-3k rpm, where i think it would be best in my patrol. he recommended staying with the stock manifold and even exhaust (for the airflow reasons mentioned) and just changing the cam. the cam he suggested to me wasnt a standard grind. the lobes were a 'mild' profile, you could say a stage 1 cam, but they are normally ground on 112 LSA for the 308 and he suggested i get it on 108 LSA and install it 6 degrees advance. here is a quote of his logic, you might find it useful.

 

tight lobe centres gives more overlap

overlap is what makes torque

increase overlap increase torque

increase duration increase rpm and hp

use small duration eg 218 to keep rpm low and tight lsa to keep torque high

small pipes and inlet with long small runners give more torque which is what u want not power

no porting needed small is best your on the right track

 

and the guy that recommended this cam can be found here, if anyone doubts his info he is pretty good: http://www.purnellperformance.com.au/

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don't mean to be a ass but some of the tec BS hear makes me giggle as any one can read a tex book and have a go .in stead of bagging each other i will be i the shed building a l28 that will be faster than any one hear will no how to drive ,there are people that do and people that read about the people that do it... nuf said.

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The air fuel mix is never 'sucked' in. There is 14.7psi of pressure around us all the time (at sea level) that will force or push the air/fuel mix into the void created by a descending piston , so its only at pressures above 14.7psi, generated by a turbo or supercharger that the supercharging effect can begin to take place.

 

However, the volumetric efficiency of an engine off boost will determine its torque potential too. There is always a loss of flow through the induction system. The importance of engine modification is to try and reduce these losses and bring the actual flow as close to the theoretical maximum as possible.

 

Yep - I should have worded that better.  The amount of fuel (petrol & air mix*) entering the cylinder is a function of on the pressure difference between the cylinder and behind the valve.  The greater the pressure difference, the more fuel will be pushed into the cylinder once the valve opens.  In the case of ‘charged’ engines, this pressure difference is significantly increased.  Unfortunately, this is where it starts to get into mass flow rates, density, temperature, harmonics, laminar & turbulent flow, open and closed systems, etc (AKA fluid dynamics and thermodynamics), but I'm really rusty and would get even more of that wrong, so I'm not even going to try.

 

I guess for making the distinction between NA engines and supercharged engines more pronounced, I used the term 'sucked' to emphasise the increase in torque from having more than ~1 atmosphere of pressure difference (ignoring harmonics) pushing the air & petrol mix into the cylinders.

 

 

* Obviously, with EFI the amount of petrol added to the air flow is determined by the ECU and the parameters set by the tuner/manufacturer.  In the case of direct injection the petrol goes straight into the cylinder and not via the inlet port and past the valve.  And for carburettors, the venturi affect determines the amount of petrol added to the air flow (subject to jet sizes).

 

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don't mean to be a ass but some of the tec BS hear makes me giggle as any one can read a tex book and have a go .in stead of bagging each other i will be i the shed building a l28 that will be faster than any one hear will no how to drive ,there are people that do and people that read about the people that do it... nuf said.

 

Peter fair point, and I agree.  However, it's a bit difficult to impart years of practical experience on someone else at the best of times, let-alone via an internet forum...  So I guess the best anyone can do on here is sprout technical info.  At least it might help others make slightly more informed decisions.

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  • 1 month later...
  • 1 month later...

Torque can be increased without sacrificing power by any of the following:

(a) increase bore size (b) increase stroke © raise compression (d) fit a supercharger or turbocharger.

 

Cheers

 

Gordon Dobie

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I would run a super light flywheel on it.

Once you are moving i dont think it effects torque at all and will just let the engine rev up faster. I've run a super light flywheel on a street driven zed before and it was fine.

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Mate, I would go light, light, light with your flywheel. The stories about them being hard to drive on the street and hard to launch are just that, stories!! It's a lot more important to make sure your tyres are square to the road at launch, than worrying about your flywheel weight! Tyre compounds are where you will make up real time here. My 1600 has a very light flywheel and is usually dicing with a MR-2 for fastest 2wd to the first split at hillclimbs and we often beat 4wd's. A big torquey 6 should be better again. Get that weight off the crank and it will love you for ever!! The boy's are right it's all in the head and don't be worried about building a 'screamer' it takes a lot of race miles to wear out a L series Datsun. If you want to stay in the same class as you run now, have a very close look at the first three on Mr.Dobies list.

 

Hodgo

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I run a 4kg billet flywheel on my new motor with 4.1 diff, very easy to launch and revs up super quick. The only down side is the revs drop quickly between gears, but that's easily fixed by heal and toeing. I definately say lighten the flywheel.

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