Power And Torque Again

[pip470 61]

I think the one with the torque higher up the rev range would win as this could stay in gear longer where as the other car would have to change gear sooner, This means the car with the torque higher up the rev range can accelerate for longer in each gear slowly gaining an advantage. I think also it would be easier in reality to launch of the line with the torque higher up the rev range. One thing I find interesting is that there is a formula that can work out roughly what horse power your car is from the time and the weight or the speed and weight, so it would be easy to say as it doesnt mention torque, and the fact that the better the power to weight ratio the quicker the you will complete the 1/4 mile meaning thers only one figure that you would seem to want when drag racing, so with regards to this two cars with the same horse power and weight, they should complete at the same time no matter wether it makes the power from low down or high up torque. What do you think? I'm still with my first assumption.

[jengis 0]

My opinion on the two 1000 bhp skyline comparison -

 

If they both have the same power and weight with well chosen sets of ratios taylored to the engines then they should be fairly similar accelleration.

 

I would say the one with more torque is likely to have the advantage though because it would probably be less "peaky" (power/torque curve would be higher average accross the range of engine speeds used), but its impossible to say withought seeing an actual dyno trace and the gear ratios used.

 

editted - just noticed, DrS, that you asked you question based on the cars having identical g'boxes. More difficult to make a guess - what are the actual ratios?? are they faily low or high, spaced out or close? They may be suited better to engine A or B, or neither?

Also, you have calculated peak BHP from a torque figure at a specific RPM. OK, but in any engine the peak torque figure is very unlikely to be at the same point as peak BHP and so the peak torque figure is likely to be somewhat higher in each case than the figures you gave.

 

But as a generalisation - if peak BHP are the same (ignore the RPM at which it occurs) but one has more torque, the extra torque should be an advantage (greater spread of power)

Edited December 28, 2008 by jengis

[jengis 0]

If that is the case, I'm not surprised, as the rotational speed of the engine - providing you are in the correct gear - will equate to higher top speed. However, if you have a 1.1litre Ford Ka, do you GET THERE quicker by driving to red line or trying to stay on peak torque in each gear?

 

 

You will GET THERE quicker as well. Like I have said before. Using the higher revs means you are in, say 2nd gear not changing to 3rd - greater multiplication of engine torque in 2nd compared with 3rd means more torque at the wheels - even if you are always running the engine past peak torque RPM. This is how the theory translates to real world forces - its the turning force at the wheels that makes you accellerate.

 

You must be able to feel that when driving? hold engine at 5.5k in second then floor it. Then compare accelleration with the same test in 3rd gear at 3.5k RPM (both about 45 MPH). You can time it if you have a willing passenger too. You will see that in second gear you will get to, say 55 MPH about a second or so faster than in 3rd. Same thing if you do this through the next gears to, say, 80 MPH. If you short-shift at 4k RPM it will take significantly longer.

 

Same with top speed.... You need a certain turning force at the wheels to overcome a certain amount of resistance (resistance is exponentially higher as speeds increse). so whether a car makes 100bhp at 5k RPM or 100BHP at 10k RPM, if the 10k RPM car had lower gear ratio (by a factor of 2 in this case) in top it would make the same top speed.

[Cameron 16]

Just had a rethink, car B would actually be faster in the perfect 100% traction world. It would actually make the same torque as car A at the redline to be 1000bhp but also make more torque down low.

[jengis 0]

It would actually make the same torque as car A at the redline to be 1000bhp but also make more torque down low.

 

How would it make the same torque if the BHP is the same but at different RPM? That is not true.

 

example A was 1000 BHP at 6800 RPM

example B was 1000 BHP at 5000 RPM

 

B would likely make more torque low down, yes but definately more at its peak BHP.

A is likely making less torque generally but produces it higher up the rev range. Thats all.

[jengis 0]

Ah, yes I see what you are saying now about the torque at the red line. With the lazy revving engine ( B ) torque is dropping off faster so that when it reaches, say 7k RPM, it will be similar (impossible to say the same) to the more revvy engine (A).

 

Engine B would have to have a kind of power-platau from 5k to 7k (if 1000 BHP is max) and their torque values were the same at 7k. It would have very odd shape to its torque curve and, more than likely it will have slightly less torque than A at its red line in fact. But hey, I'm talking about hypothetical figures here. Not sure its helping the debate.

 

Sorry, I missunderstood you though Cameron.

Edited December 28, 2008 by jengis

[Cameron 16]

Yep, but in theory car B would be capable of making 1000bhp from 5000rpm to the shared redline of 6800 rpm. See what I mean?

 

Edit: Just seen your last post, looks like you did get it.

Edited December 28, 2008 by Cameron

[DrSarty 90 1 Cars]

Are you two enjoying this?

 

It makes a good read.

 

However, and please excuse me for raising this again, you keep on talking about gearboxes and forces at the road etc. I don't disagree one bit that that's how the power generated by the engine translates into motion, and that the different gearing focuses torque to create different rates of acceleration.

 

But this conversation all started when someone took their 205 on carbs to a RR and got (a back calculated) 145bhp result ATFW. The owner wanted to know if that was 'good' or not. Now this back calculation means we can effectively - and this is my request - eliminate everything after the flywheel. Let's imagine we are purely discussing an engine on an engine dyno, to assess how 'good' the engine is. By including the transmission system you're entering a whole new load of variables and a whole new science. I think it's best to start at the power plant and tickle the balls of danger and discuss whether a 145bhp engine is 'better' than a 135bhp engine, which has a higher peak torque figure.

 

Now instantly you may say well that's too vague, as you NEED to know what gearing and application to see how it would perform. That is in the real world totally true, hence me suggesting we play with notional cars doing something as simple as a straight line 1/4mile dash in a Newtonian type world, where these two cars simply get instant engine swaps for comparison and all other elements (gearbox etc) stay the same.

 

So, the example of the Skylines, or the 1.9 (x2) mentioned above or even two formula one cars, where one has a 850bhp engine and the other has a 900bhp engine, are quite good for theoretical tests of whether BHP is more important than torque.

 

Now I'm not baiting people here or trying to generate an argument. The question originally posed by the 1.9 owner got me thinking of a Puma article where he tuned a guy's MG IIRC, being told by the customer to aim for a BHP figure which was higher than the car that kept winning events. Ultimately when the work was done, the customer looked gutted collecting his car and seeing the RR results with a BHP figure that was something like 10bhp down on his arch rival. However once on track he destroyed his nemisis.

 

I am interested in the notion that highest is not always best, and the best way to explore that is to remove variables and focus on just the engine tuning.

 

Incidentally, does anyone have an answer for what nature of measurment device is actually in an engine or wheel dyno?

 

Rich

Edited December 28, 2008 by DrSarty

[pip470 61]

Hi rich, Im not sure I understand the question at the end thier but I think it means what actually measures the torque, well the one I'm familiar with uses water and its the force of the water used to stop the engine rotating any faster to work out the torque, its quite old but watching the operater working the machine is a great experiance, if i was to symplistacly guese how the machine works. The operator gets the engine to its desired rpm and then winds on the load until he has wide open throttle and the computers try and maintain the imputed rpm thus giving an equlibrium force in torque.

 

 

As for the torque debate, its seems an engine should be designed with a job to do and not just aim for the biggest numbers. What these threads have made me relise is that I do belive the figures are both equally important. Reading just one will only give you half the picture in how the engine will preform in its given task.

 

 

Which kind of takes me on to your engine a bit Rich, from the outset you said that you werent after massive power figures, Just a nice spread of usable torque, but your desicion to move to the stage 2 cam in the inlet and stage 1 in the exhaust will surely move the torque futher up the rev range thus making more power on a narrower power band. I hope you don't mind me asking, but is this what you expect or have I got it wrong? All the best Phill

[DrSarty 90 1 Cars]

Ref the rolling road, what I was jiving at was what is the machine actually measuring? For example in a gas measuring device, it may read what the compound is, but the essentially the device which measures something may just be a thermometer, measuring heat. It may be that the device inside is measuring torque, then perhaps you'll see where I was coming from all this time.

 

As for my engine, the stage 2 cam has 10deg more duration. More duration = more open valve time to induce a charge and more bang....hence, more torque. The critical tuning issue is approached by using twin variable cam pullies, DW8s as you know, aka verniers. With these on both the inlet and exhaust cam, perhaps advanced and retarded respectively, I THEN get the opportunity to tailor WHERE the torque arrives and fades off.

 

Again, this was my whole point when I (inadvertently) started this uber interesting debate, that my tuning work is simply reshaping the torque curve. To emphasize this, Peter Taylor's suggestion was tweaking the exhaust cam timing, not just by adding a stage I to compliment the longer duration inlet, but to consider retarding it to maintain the torque at higher revs, which as a direct result (again my boring point yet again), such that the calculated peak BHP would be higher which I guess again as a direct result would result in a higher top speed, as the engine can still be pushing on at higher rpm once the wheels are already rotating quickly, even in the longest/highest gear.

 

Now as my car is 90% for road use, anything over a 100mph is probably a waste, and therefore I am far more interested in getting there quickly. The only reason I conceivably have for having more BHP is to get some jollies from revving the engine harder. I don't think it'll necessarily make me go any quicker (unless it's top speed we're on about), as I already have the torque to do that, but just want more to get there quicker and explore what my engine is more capable of.

Edited December 29, 2008 by DrSarty

[AdamP 0]

I don't think it'll necessarily make me go any quicker (unless it's top speed we're on about), as I already have the torque to do that, but just want more to get there quicker and explore what my engine is more capable of.

 

'I already have torque to do that'

 

Torque higher up the rev range will be applied a greater number of times per second, therefore you will gain speed (accelerate) a greater number of times per second, therefore you will accelerate faster.

 

That is power. Power = torque/time or torque x frequency.

 

Bike engines are powerful because they apply their small amount of torque a greater number of times per second. Therefore if they're gear down they will put to the ground the same amount of energy/second (power).

 

You might find it really useful to think in terms of energy, as that's what torque is. 1J = 1Nm.

 

If you want to accelerate really quickly you need to tune the engine to make torque across a wide band high up the rev range. 80lbft from 2000-6000rpm doesn't make a fast car. 80lbft from 8000-14000 does! 80lbft at 14000 = 213bhp, 80lbft at 6000rpm = 91bhp.

 

I put it to the jury that torque is completely irrelevant when you have revs and correct gearing.

Edited December 29, 2008 by AdamP

[jengis 0]

Ref the rolling road, what I was jiving at was what is the machine actually measuring? For example in a gas measuring device, it may read what the compound is, but the essentially the device which measures something may just be a thermometer, measuring heat. It may be that the device inside is measuring torque, then perhaps you'll see where I was coming from all this time.

 

Now as my car is 90% for road use, anything over a 100mph is probably a waste, and therefore I am far more interested in getting there quickly. The only reason I conceivably have for having more BHP is to get some jollies from revving the engine harder. I don't think it'll necessarily make me go any quicker (unless it's top speed we're on about), as I already have the torque to do that, but just want more to get there quicker and explore what my engine is more capable of.

 

 

I don't know what the engineering is inside a dynamometer but it will measure the torque produced by the engine, as you suggest, by applying a metred amount of resistance.

 

On an engine test rig, measuring the actual output at the flywheel, again it will be measuring the torque directly. When on a rolling road it will be measuring the torque at the wheels in one particular gear, usually fourth. The curve shape will match what is produced at the flywheel but be different values (due to gearing increase but offset by some transmission losses, these need to be worked out and factored in to give an estimate of the engines torque).

 

I agree with you that your car will accellerate fastest at the point of peak torque in one particular gear. But engineers don't tune their engines for higher peak power just to get a higher top speed, its to improve accelleration as well. There is no difference in the concept of a larger force being needed to overcome greater air resistance (max speed), or to overcome a greater inertia (accellerate a heavier vehicle) or to overcome the same inertia but at a greater rate (quicker accelleration). I personally try to avoid any talk about the higher revs meaning energy being applied at a faster rate, blah, blah, because its just theory and is not tangible.

 

My original intention was to avoide any physics talk! So I try with practical explanations - by thinking about the gearing-up of engine forces, at the expense of speed. When you are talking about a car accellerating you simply cannot ignore the gearing it has. Just like you cannot ignore the initial torque the engine itself produces. Its the sum (sorry multiplication) of all these factors that creates the resultant forces at the wheels.

 

I have explained why it is pointless to just consider torque without factoring in the RPM at which it is available. You simply won't accellerate as fast as a regular 1.9 GTi if you use an engine that produces a fat 150lb of torque between 2k RPM - 4kRPM but runs out of grunt thereafter, peaking with just 100 BHP at 5k. This will be true no matter what gearing you choose, standard or otherwise.

 

Having said all that, I can understand why you are not interested in the power output of your engine Sarty, cos you are not altering the gearing and you wan't your engine to have as much 'output' as possible over the range you want to run the engine at. The only way you can improve that is to increase torque. But, as Pip470 said, working on the torque produced at the top end will be increasing the BHP figure and by chasing the red line more you will get the benfit in accelleration as well as top speed.

 

I put a 2.0l 8v in place of my 1.6, maily because it has much more torque than the 1.6. Thats what I wanted. On first few test runs it had much more low-down grunt than the 1.6 but in timed runs I could not get it to match the 1.6 for accelleration. It wasn't running right and lacked any top end - no power!. I quicly got the fueling and ingnition sorted (plus a few other probs) and it was much free-er revving. The low-down grunt was the same but now it pulled hard to the red line and is now a bit quicker accellerating than the 1.6 was. But, it has the added benefit that its much punchier in the midrange when I'm not able to or wanting to run to the red line. Its a much better road car!

 

Yes, I am enjoying this topic!

[jengis 0]

If you want to accelerate really quickly you need to tune the engine to make torque across a wide band high up the rev range. 80lbft from 2000-6000rpm doesn't make a fast car. 80lbft from 8000-14000 does! 80lbft at 14000 = 213bhp, 80lbft at 6000rpm = 91bhp.

Well put! I find it hard to believe anyone could dissagree that this is true!

 

I put it to the jury that torque is completely irrelevant when you have revs and correct gearing.

Now there's a statement

 

Seriously though, its not irrelevant in a car designed for the everyday use, when tuning an engine for better performance. It's usually what you are concentrating most on, As DrSarty has said all allong I think.

[AdamP 0]

Now there's a statement

 

Seriously though, its not irrelevant in a car designed for the everyday use, when tuning an engine for better performance. It's usually what you are concentrating most on, As DrSarty has said all allong I think.

 

What I suppose I was trying to say was that an engine making 1lbft and an engine making 100lbft can accelerate a car at the same rate if the revs and gearing are right, therefore implying that torque can irrelevant in the search for acceleration, whereas power cannot!

[B1ack_Mi16 67]

What I suppose I was trying to say was that an engine making 1lbft and an engine making 100lbft can accelerate a car at the same rate if the revs and gearing are right, therefore implying that torque can irrelevant in the search for acceleration, whereas power cannot!

 

Exactly Same point I was trying to get people to understand in the last power and torque discussion.

[projectpug 0]

Very good read keep it coming

[jengis 0]

What I suppose I was trying to say was that an engine making 1lbft and an engine making 100lbft can accelerate a car at the same rate if the revs and gearing are right, therefore implying that torque can irrelevant in the search for acceleration, whereas power cannot!

 

I agree whole heartedly! That's what I have been trying to say from the outset but sometimes it just isn't understood, despite my best efforts

[Cameron 16]

As true as that is, its immensely impractical.

 

In the real world you won't be able to rev your 1lbft engine to the 10 million rpm needed to make the same power a 100lbft engine could make at much lower revs.

 

Take the bloke with the MG (iirc) who wanted 10bhp more than his rival. He could have gone to an engine builder that could guarantee the power output he wanted, but he probably would have lost the race. The interesting fact from that story is that he was initially disappointed with his lower than expected power figure, but obviously the engine builder knew otherwise and the bloke went on to thrash his opponent. Why would that have been? If he had chosen to regard torque as irrelevant then maybe it was the hand of god pushing him along, but the fact is although he had less peak power he clearly had a better spread of torque meaning the in-gear acceleration was better.

 

The point I'm making is you just can't ignore either torque, rpm or power. Not if you want a complete understanding and therefore the edge on your competition. The formula for power involves torque and rpm, and therefore the formula for torque uses power and rpm. The two (or three) will always go hand in hand.

[AdamP 0]

Of course I'm being highly theoretical in my explanations, an engine isn't going to make 80lbft from 0 to 14000rpm, but in order to understand properly what happens you need to assume that it does. What we want to aim for is not a torque curve but a flat torque line. Ideally an engine would make exactly the same torque everywhere in the rev range, as theoretically it isn't affected by RPM. However once you get really into the practical side of things you find that restrictions and compromises limit the combustion when the engine is pumping at certain rates (after all... and engine is just a pump!) and the air / mixture is moving at different speeds

 

What the chap in the midget has adjusted the flow compromise to create slightly more torque lower down, possibly at the expense of torque higher up the rev range. It can pretty much be guarantied that had he adjusted for the same amount of torque further up in the rev range, increased the rev limit and changed the gearing he WOULD have been faster. However it's cheaper to go for a bit more in the middle.

[pip470 61]

All excelent stuff from the usual suspects, thank you. Rich sorry to go on about this, Like I said to you in person its going to be hard to see what has had the greatest improvement to your engine as you are doing a few things at a time, however holding the valves open longer with more duration will like you say create more torque but that will more than likely move the peak torque higher up the rev range at a sacrafice for lower down torque. When the car is accelerating from lower revs, the engine wont actually like the valves being open longer there fore the toque will be less, If I was tuning a car for what you have set out to do, a nice spread of torque from low down which will inevitably make it run out of puff higher up the revs, i would be reducing the duration and maybe looking at a rally cam as they are designed to be able to pull out from really tight corners and accelerate as quick as possible, I think with your engine now you are tailering it for more power (or more torque) at the higher rev range at the expense of torque lower down. Theres a few ways to get torque accros the rev range such as a supercharger or variable valve but I imagine only one of them will be realisticly probable. I just cant belive this stage two cam with more duration will do what you set out to do. I wonder if peter t could explain why I am wrong as I probably i'm so I need a little help in this area please. Sorry to use you Rich, its just Ive folowed you're thread very closely and met you so had the chance to chat to you too so I hope its ok to use your example for this power/torque explination as it seems we are all agree the realtion ship between them so I just wanted to put this knowledge into a praticle example, How do you move/tailer the torque curve for a given task to do? Drag racing track car sprinting rallying ect ect.

[Mandic 0]

I agree whole heartedly! That's what I have been trying to say from the outset but sometimes it just isn't understood, despite my best efforts

 

[DrSarty 90 1 Cars]

No-one ever disagreed Mandic & Roman - and we're glad you're still watching too - but one thing that is at the crux of it all is our friend physics again, because it is all about energy...and to an equal degree entropy.

 

I mean it's about the storage of energy (potential) in the fuel, and the generation of more potential via compression, which once ignited generates kinetic energy in the form of an explosion, which then remains kinetic as it pushes down the piston(s), transferring to crank (where a little is scrubbed off and turned back into potential in the flywheel), continues through clutch, FD, driveshaft, hub, wheel and tyre, where the final transfer of kinetic energy takes place between the surface of the 'road' and the tyre.

 

Now if I've stated the obvious I'm sorry, but it's because I'm focussing on energy, the key to it all. As rightly said, the units of measure we are using basically simplify into a representation of energy. Hence it must be perfectly obvious to anyone, that if you have an engine spinning at what might be called super RPM (in road car terms) say 14,000rpm, because of the mathematical derivation of horsepower including a multiple of RPM, then there exists a high amount of energy, so of course it will accelerate you or make you go fast.

 

This in effect is how it is done in track orientated cars such as F1 and other motorsport geared cars as they are using a combination of high RPM AND, as high as possible torque figure generated in that band of the rev range to generate as much energy as possible. Surely this explains it in its simplest form and shows our learned Balkan friends that we're not total dorks. One could possibly argue too that a larger amount of potential energy is also retained in the flywheel which would help matters, unless of course the flywheel has been wasted excessively.

 

Now, and bear with me please, taking the above as red, which concedes that BHP is important as it represents energy which is quite obviously increased with RPM (but almost purely mathematically), the key ingredient in both the real world and mathematically is the rotational force the engine generates, torque.

 

Pip470 and Jengis seem to see exactly what I'm saying, and their explanations are clear and understandible. I've never said BHP is irrelevant (it reflects energy at rpm), and I've never said the higher the peak torque the better (which some people seem to think I've always been saying). People here are now talking more about what I said when this all (gladly) kicked off, which was wanting to see the shape of the measured torque curve and discussing how that can be shaped to suit the application. This is why I asked about RR equipment and what critical measuring device is at work, which I suggest it could probably be proven to be a torque meter, which in effect, on its own, proves my whole argument.

 

In summary I am picturing F1 engine technicians wanting to improve an engine. Now I'm not an F1 fan - although I do find the technology fascinating, even more so since this topic started - but they have certain restrictions such as displacement and rpm (3.0ltr & 19k IIRC), but the figures aren't that critical. So their engines 'idle' at 8,000 rpm, so for me that makes an 11,000rpm rev range which isn't wildy off the scale we have. These technicians may certainly want 950bhp instead of 925bhp, because shock horror, it represents (potentially) tranferrable energy to go from tyre to track. Hence, yes, I totally agree, BHP IS IMPORTANT; more could certainly mean better, faster whatever.

 

But these guys have a formally imposed rev limit - and to some extent so do we, as manufacturing tolerances, component balancing skills and accociated costs begin to restrict our goal to allow an engine to rev higher and higher to become more 'powerful' - so where are the technicians going to concentrate their efforts? Imagine one technician who for an example has his F1 engine's torque curve infront of him, and he experiments and finds a way to wind the spark plug out and secure it one thread back into the head, and this magically raises the torque curve uniformly 3lb/ft all the way along the line. This engine is then more powerful, period. Yes, it will have now a slightly higher torque figure at peak RPM to plumb into the BHP formula, giving a higher peak BHP figure. This then agrees with the notion that more horsepower = better. But what has really changed?

 

So Pip> Yes, if you want me to say it, we seek more peak BHP for my engine. As stated, I have the low down grunt, and in fact I will get more as it's unavoidable with the longer duration inlet cam. But I can now increase the volumetric efficiency of the engine, or to be more correct get it nearer its '250bhp' flow potential (a restriction imposed by the head apparently - but fine for most people's use and one of the advantages of the Mi16 head) by having also increased exhaust duration to expel the waste. More in - banged - then out, must simply be the recipe for a better performing engine, hence BMEP. But by altering the cam timing, overlap etc, we can tailor where the torque peaks and tails off, which we will indeed push to the right in search of continued torque in the higher rev range. The natural by-product of that will be a higher BHP figure although in essence - and this is my whole point - it's merely a representation of how the torque has been engineered to be high, or in my case STILL high, at the higher rpms. So what I'm aiming for is not a figure, it's a continued pursuit of a torque curve which starts high and rises smoothly, even steeply, but most importantly keeps either rising further up the revs more than before, or plateaus at around 4.5k and stays up there until 5.7k before it begins to fall off. What we don't want is a sharp fall-off, which is what I had previously, based on the engine being starved of air and fuel due to the ITB and runner sizes.

 

Phew . I hope I'm viewed as a contributor to this discussion, rather than a stubborn old fool. I'm enjoying reading all of the comments and look forward to replies and seeing where this goes next.

 

Rich

Edited December 29, 2008 by DrSarty

[pip470 61]

Stupid back button just erased my full post, Oh how I hate that back button

 

Ill re write a much shorter version. Definatly a contributer Rich mate, Fantastic right up again.

 

Ok I can't help but dsagree with you saying "As stated, I have the low down grunt, and in fact I will get more as it's unavoidable with the longer duration inlet cam" Please can I try and give what I think to be the correct reasoning using an example. I love the extremeness of formula one engines, they really push the boundaries. So I dont know if you know this but genericly they have tiny strokes, almost like a sewing machine, now this must mean the pistons are quite large to get to the required 3ltr capacity. Now what fasinates me is the speed the air and fuel mixture which must be quite a sizable amount to sustain that amount of power must be traveling at. If I try and get my head round it I come up with lets say an engine doing 18000rpm, I make a cycle of its four strokes induction, compression, ignition, exhaust to be hapening at 9000rpm, so with that 1 cycle happens 150 times a second, To me that is getting a large chunk of fuel and an even larger chunk of air into the cylinder 150 times a second. Simply amazing. These engine run massive duration cams, hence the reason they idle at 9000rpm. Below this speed the air speed in the runners is not enough to provide the said amounts of fuel and air resulting in the lumpyness described by many people who fit uprated cams. This brings me onto your engine, air speed in the runners. Longer duration with your cams will increase your volumetric efficiancy but only where the engine is most efficiant (peak torque) which will be at a new rpm more than likely higher than your previos peak torque figure, unfortunatly the efficiancy of your engine wil suffer lower down in the rpm. (not to the extent of the formula 1 engine lol). I really think its impossible to gain through out the rev range, unless there are other changes such as the upped compression ratio which might be your thinking but as I understand, you will not be upping your compression ratio from your last rolling road result so I can discount this. Ive stolen this little snippet from wikipedia to highlight what vvt does,

 

At high engine speeds, an engine requires large amounts of air. However, the intake valves may close before all the air has been given a chance to flow in, reducing performance.

 

On the other hand, if the cam keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. This will cause unburnt fuel to exit the engine since the valves are still open. This leads to lower engine performance and increased emissions. For this reason, pure racing engines cannot idle at the low speeds (around 800rpm) expected of a road car, and idle speeds of 2000 rpm are not unusual.

 

The profile, or position and shape of the cam lobes on the shaft, is optimized for a certain engine RPM, and this tradeoff normally limits low-end torque or high-end power. VVT allows the cam profile to change, which results in greater efficiency and power

 

Honestly rich I cannot wait to see your new improved engine, its going to be a beast and these types of discusions are what I look forward to listning too on the euro trip, beer flowing, maybe a camp fire and a few discussions also on how big the universe is (how i digress, sorry). I have to say i very rarely actually take part in these discusions because i will confess that the whole subject blows my mind and all that I know is either read from hours of free time being a security guard lol or thought out in my own mind so I dont feel it appropriate to say to anyone they are wrong just like I am not saying you are wrong Rich, it just doesn't work like that in my head so I cant wait to be corrected and shown a new way of thinking about it.

 

Phill

[DrSarty 90 1 Cars]

Nice one Phill.

 

I'm not really trying to prove anyone wrong, because I don't know enought to be any kind of authoritah!

 

However. I have 11 'o' levels, 1 'ao' level (in maths) and 3 'a' levels, including physics, applied and pure mathematics. This doesn't make me a guru or expert, but it should show I have the grey matter to reason and perhaps argue. I learn everyday and love it.

 

There is no practical plan or reasoning behind my engine...fact. It's all taken from advice and guesswork, which shows I listen and am prepared to experiment.

 

Tom Fenton's 1.6 turbo is an example. He's applying practical knowledge, with what from I can see is an experimental 'you win some you lose some approach', which I think helps us all progress.

 

Good luck Tom.

Edited December 30, 2008 by DrSarty

[jengis 0]

Good reading!

 

I too am no expert and have little practical experience building engines. It is something I tried to grasp during uni days when I had too much time on my hands and I wanted to reason why some cars have high BHP figures for small capacity (typically Jap stuff) versus larger engined but relatively low BHP. And furthermore, why it seemed that 0-60 times diddn't match what would be expected of the high power-to-weight ratio's, like honda Vtec Civics etc.

 

I remember reading an Autocar road test of the Mitsbishi Colt Cyborg ZR vs the Peugeot 306 Rallye. On paper the Colt, with its screaming 1.6l MIVEC (variable valves thingie) made a claimed 173 BHP! It weighed a fraction less than the 306 which, as we probably know, makes a claimed 167. So it had a higher BHP and a higher power/weight....so it should have been faster, right?

 

Obviously in-gear accelleration wasn't going to be its strong point but even flat out through the gears it was slower. I'll dig out the figures (wet surface):

 

Car - Colt / 306

0- 60 - 8.4 / 7.8

0-100 - 24.6 / 20.7

30-70 - 7.5 / 6.8

 

qtr mile - 16.8 / 16.3

 

I guess my point is that the Colt was not able to make best use of its high revving engine. Perhaps its gearing was not low enough (looking at the quoted ratio's I would say they are pretty low enough!), or perhaps it wasn't making the claimed 173 BHP (probably a lot of truth in that) but most importantly, the max BHP is figure does not tell the whole story. There was no torque curve printed but peak torque is quoted @ 7000k, with the red line only 1200 RPM higher. Very peaky indeed! The average BHP in the range of RPM's used when sprinting through the gears is probably only around 155 BHP.

 

Now compare that with the 306 Rallye engine (GTi-6, for those unfamiliar). It has a peak of 167 at 6500 and peak torque at 5500 RPM. With its closely stacked ratios and high rev "ceiling" at 7250 RPM it is well able to keep the engine up near peak power when sprinting and because is is not as much of a BHP "peak" it probably averages over 160 BHP.

 

Now I would have expected the two cars to be closer matched than the timed figures sugest, and I strongly suspect the 306 was well run-in (wheras the Colt was probably fresh off the ferry). But it was telling that the jurno's said the Colt felt like it had 150 BHP wheras the 306 more like 180! Thats all down to the larger engine having a greater spread of torque so it has a strong midrange.

 

5 years later I bought a 306 Rallye! (Now sold -Where are you now T596 PEF?)

 

 

Now, I see this thread going more towards the tuning of a particular engine for performnce and as I have little experience here I will try and stay out of it. Mr Pumaracing has said more that I can on this and his musings are well known to this forum.

 

It's been a great discussion and I hope I explained WHY I think measuring the power produced by an engine is important and that power figures can be directly related to the amount of accelleration, wheras torque figures are only important if the gearing or RPM range are not changable. BHP figures are not marketting hype, so long as you understand that a single peak figure is not giving you a complete picture of the engines performance.

 

Cheers,

Kev

Edited December 30, 2008 by jengis