[Adamantium]

Corky bell was and is american.

Not sure o that one. I have two guesses here.

1. that those variables might be incorporated into that figure of 1.5. perhaps super effiecient breathing will chnage that value and at the same improve volumetric effiency beyond 85%., have to consider other things that will be off direct significance such as air temperature too,this will almost certainly lower this value.

2. there is a quote which says that cubic capcity has nothing to do with how much power your engine has, only at what rpm it achieves the power that it does.

if power comes only from oxygen which it does, then a bigger engine means that per minute it can consume x volume of oxygen, if you double the rpm it will consume 2x, if you have the engine capacity it will consume 0.5x.

so a two litre at 8k consumes the same oxygen as a 1 litre at 16k which makes complete sense.

If power per stroke is therefore only dictated by how much oxygen you can get into the cylinder,anything that will make this easier should increase power, ie porting, polishing, longer duration cams, higher lift, higher boost pressure.

All these will do is make sure when you think your cylinder is full, that it really is full and at the pressure you think the turbo is providing. In essence improving the efficiency of the engine to act as a pump. Since I am working this out in my head as I go along, I think this in essence is just the same as point one, ie. it gets incorporated into volumteric efficiency.

Troube volumetric efficiency is a bit of an anomoly on a forced induction car this there is always positive pressue in the manifold due to the turbo charger (or supercharger).

makes it a bit more difficult to understand, for me at least.

It also explains why things such as porting and polishing are not as important as they are on normally aspirated cars, I suppose effectively the turbo rams the air past the restrictions in the intke path, so these restrictions are not as significant. they will however create more work for the turbo meaning the charge will be hotter.


who knows?

anybody else care to add their take on it?

 

[SkylineUSA]

I was just skimming through Maximum Boost, US copyright 1997 written by Corky Bell. And the only formula I can find is:

Lower value .052x350cidx(10+14.7)=449bhp
Higher Value .077x350cidx(10+14.7)=666bhp

.052 and .077 is the variable, of course

350 is in cubic inches, since it was written by an American, and we don't take kindly to that decimal stuff

10 is the boost pressure in psi, because we dont know what a bar is, well we do, but we drink there.

14.7 is what Corky has written down to add to the boost level, it does not going into why.

I still think it hold no merit, but since your refering to this book I thought I would throw it in

 

[Ged]

Work, 65 mile drive home, shopping meal out with the missus has kept me away for a while.

Done some thinking though and reading the above I can see part of the answer...
Original formula said 1.5bhp/cfm. So you should multiply, but you said divide. This made no sense unless it really was 1.5cfm/bhp which is what is written above. So that is that.

Beyond that I arrived at the same conclusions as above.
Where does 0.85 and 1.5 come from?
These must be approximations to cover valve overlap, blow down and ram effect due to cam timing, and other efficiencies such as air flow though the turbos intercooler plenum chamber, throttle bodies and head.

Nice to tie down where each thing is then you perhaps are able to estimate what power you should have?
Probably not achievable though. I think these two figures are what we interfere with most by changing cams, turbos etc.

Nice to disect the formula to see what it means, and how/why it should work. Guy is normally a good one for explaining numbers and units. Is there an answer here or are these ratios just averages?

 

[Guy]

OK folks it is a long one.

SkylineUSA,

Great post, you have definitely been in the UK too long as you’ve picked up a dose of our sarcasm, hope you don’t use it on the Mustang boys back home, they won’t understand it.

The 14.7 by the way is atmosphereic pressure expressed in psi.

Pegleg,

I wrote a long list of things that effect the efficiency of the engine, but deleted it by accident before I posted it, so I’ll summarise it in three categories:

Efficiency of getting air into the cylinder (cam, ports, intake temp)
Efficiency of using the pressure created (cam overlap)
Losses in the engine (friction)

What is interesting if you take the formulas and play with them is that you can do four things to increase power:

1. Increase efficiency (I’ll ignore this as it’s the most complicated)
2. Increase peak power revs
3. Increase boost
4. Increase capacity
If we take 2-4 in turn when considering tuning a GTR engine it gives interesting results. I have considered (for theory) the following medium and wild increases;

1. Medium

Increase peak power revs from circa 6500 to 8000rpm
Increase boost from 1bar to 1.5bar
Increase capacity from 2568cc to 2628cc (1mm bore increase)

These give an extra potential power capability (assuming efficiency is maintained) of:

23%
25.0%
2.3%

Add all these together and you have an increase of 57%. If we assume a de-restricted 1.0bar GTR makes 370bhp, then it will now make 582bhp.

2. Wild

Increase peak power revs to 10000rpm
Increase boost from 1bar to 3bar
Increase capacity from 2568cc to 2771cc (1mm bore increase, 2mm stroke)

These give an extra potential power capability (assuming efficiency is maintained) of:

53.8%
100%
7.9%

Add all these together and you have an increase of 232%. If we assume a de-restricted 1.0bar GTR makes 370bhp, then it will now make 1228bhp.

OK so what does this prove then?

One, that this theory holds some truths, since the figures look reasonable, provided you ignore the efficency issue, which is to specific to be described and is where massive gains and losses are made.

Two, You will never gain much through extra capacity, since it is impossible to make substantial enough increases (even with the 3.0 OSG kit, which would restrict revs, through long-stroke). The real increase in power are achieved through boost and revs.

Guess what, that matches what Formula 1 told us decades ago, they ran 5bar boost on the 1.5 litre engines to get 1500+bhp and now use 18,000rpm+ to get power instead. If you want to make real power there is no other way. The trick is to maintain efficiency when you do it and ensure reliability. The problem with boost is heat and the problems with revs is mechanical stress on components and internal friction losses that multiply at the square of revs.

Hope my ramble is of interest to someone.

Guy

PS I work in a bank dealing room and have no engineering qualification, so I can of course be talking complete nonsense……..

 

[SkylineUSA]

Hey Guy,

14.7psi, so thats where you get the bar figure from, duh. Thanks for that, I just learned something. And that is what its all about.

Oh, remember I am English, I just talk like I am an American


Tony

 

[Syed Shah]

Re: OK folks it is a long one.

Two, You will never gain much through extra capacity, since it is impossible to make substantial enough increases (even with the 3.0 OSG kit, which would restrict revs, through long-stroke). The real increase in power are achieved through boost and revs.

This is true, on most examples, such as the Supra and Skyline.

But, displacement can still be a HUGE advantage.

How? Simple, limit the use on the downfalls of displacement, mainly long-stroke limiting the max revs of the engine.

The best way to do this, is to only gain displacement through increasing the bore, instead of the stoke, this way, you gain extra displacement, while still allowing the engine to rev high.

The problem with this is that nearly all blocks cannot really be bored out very much, because of the gaps between the cylinders, which if made to thin (ie boring out the block too much) will reduce the integrity of the block, causing it to crack. So 1.5-2mm is probably our max (I would say 1.5mm on a Supra, but have never seen a RB26 block, so cannot say exactly for you guys).

But, you can still gain a decent displacement increase on most blocks using this method. A small increase in displacement by boring alone would probably allow you to spool up a turbo a couple of hundred rpm less, giving you a larger power band, and any gain in this respect is worth having.

BTW, what is the exact bore of the RB26, and what is the stroke length?


As for how to make displacement a huge advantage, and how to make the best use of revs and boost: Well for this, we would probably need to build our own block and engine from scratch;

The best thing would be an extremely short stroke, so it can easily rev very high without the extreme stress this causes on engines not built for it. But to make up for this, we would need a very large bore, which would not be a problem, as we are designing it this way rather than doing it to an existing block not strictly designed for it. This way we would end up with what we want: A large displcement engine, that can still rev. Because we are getting our extra displacement from the bore of each cyclinder, rather than an increase in the stroke. Also, due to that large displacement, we would also have loads of torque!

So, with that done, we would have created a large-dispalcement engine, that can rev like hell, so not only would it spool up a very large turbo very quickly due to the displacement, but it would also rev extremely high, giving you the ability to have an extremely large turbo that is still streetable and useable.

Next thing to do: Make it suitable for handling large amounts of boost; to do this is much simpler. As we all know, boost causes a lot of stress on the engine (heat, pressure etc), so we just need to make everything strong enought to handle boost, manic revs etc

For this, we need to make our block, and all the engine materials as strong as we can, forged block, titanium pistons and rods etc, ALL the components. Remember an engine is only as strong as it's weakest part. So the valvetrain etc must not be forgotten, it must all be upto the job.

Remeber that there are also other parts that need to be uprated and matched to a high boost/rev/displacement setup. Things like cams must be able to handle the revs, as stock cams on high revving cars simply run out of breath. We must also make sure the whole thing is cooled well. As very high boost causes very high temps. A massive rad, oil cooler and FMIC would be required.

All this would equal one very cool engine: I would imagine something like an 8l V12 (or I12 if you could find an engine bay long enough to fit it!) with a 15k rev limit and a couple of T88s bolted on. A 2-stoke version of this engine would also be very nice. (if your feeling generous, I wouldn't mind this for Christmas )

So if created correctly, displacement can be a great advantage, although most of the time, as Guy said, it is not.

Also, just a bit of advice: If you must increase your engine displacemnt on your Skyline, just do it slightly by boring out the block. Creating a long-stroke RB26 is really destroying the only thing it has going for it (apart from being connected to the such an impressive 4WD system): revs.

 

[MarioGTR]

Maximum power / theoretical power profiles

I have stated what I wanted on the other thread, so I'll let that die.

Onto the subject at hand. This thread is more like it, the way it should be. All good information and a discussion. To this, I have no problem contibuting to.

First and foremost, all of the theories listed, such as Corky's, are valid to a point, the point being that they don't consider one very, very important aspect. That being efficiency. It is just quantified as a simple percentile value, when in fact, by todays standard - it is the efficiency of a given engine combination (which also includes the fuel used) that can provide a massive differential to the power output of a given engine.

Going back to basics, engines are simply air pumps. They take air from and inlet stream, perform some processing (combustion) and then expell it via an exhaust stream.

If you were to take an engine, give it positive oil pressure (very important) and turn it with another locomotive supply on its crank - it would pump air. Infact, this is what we do when we profile a base engine in testing. You would be amazed how such a simple test can provide meaningful insight into how efficient (or not) the pumping capability of an engine can be gauged. The only problem is speed - you can't really turn an engine in this fashion to 10krpm plus - which is a pity, especially when the camshaft specifications we use are designed to work up in that region.

The other problem with these theories is that they don't allow for the contribution of fuel - I can gain over 15% in power output on the same engine by adding what we call 'jungle juice' - a concoction of Toluene/Xylene and Nitromethane (very small amounts). The only way to quantify this increase in the above algorithms would be to push up the 'efficiency' - which from memory Corky quantified as "...between 0.52 and 0.77..."

Time and engineering have changed. The world was once belived to be flat, it is not. It was once believed that an engine put 33% of its power out the crank, another 33% out the exhaust and 33% was lost to parasitic drag and converted to heat that was discharged via the cooling system.

The RB26DETT profile is actually as follows:

24.8% of ingested fuel energy was converted to crankshaft power.
5.1% was attributed to internal friction and parastic drag loss.
5.3% was radiated into the surrounding airstream in the engine bay.
34.8% was determined to exit the exhaust headers (I won't disclose what work was extracted to run the turbos, that is a whole can of worms).
30% was lost to the cooling systems, both oil and water.

Note that this profile was done on a stock RB26DETT at low boost (if I recall correctly, it was at 7 psi of positive boost pressure).

The other thing that the magic efficency coefficient doesn't seperate, is the dynamic compression ratio, which has a profound effect upon power production. This encompasses the static compression ratio, the camshaft overlap and duration - which, I should add, are heavily reliant upon the engines breathing ability (ie: volumetric efficiency) at the rev range required. It is no good having 300+ degree camshafts when you can't rev the engine that high to make use of them - a mistake like this isn't covered by the aforementioned theories, so would give artificially inflated projected power figures.

Onto what Syed and others have stated. I am in total agreement with you - an increase in displacement is a waste of time - I have always maintained that the RB26DETT (and the 2JZ-GTE) are both small displacement motors, hence they make all their power from their revs, it is a waste to compromise this in the pursuit of 'there is no replacement for displacement'. There is, and it's called *boost*, baby!

Another interesting tidbit: We have tried everything from de-stroking to 2.4 litres through to a full 3.2 litres - in the end, we stuck with 2,700cc. We used 87mm x 75.7mm - because, for reasons I don't have time to explain, an 86mm bore provides almost perfect combustion burn on Gasoline fuel (have a look at all of the best engines of the last 20 years, there is a reason for an 86mm bore - even the BMW S220 in the McLaren F1 utilised this) and the 75.7mm stroke (a 2mm increase) still allowed us to retain massive rev capability without any disturbing harmonics. Infact, the reason I limited the revs to 11,500rpm was the valvetrain assembly was borderline - I am seriously considering butchering a BMW double-vanos head in the near future... but I digress.

Engine power is not a simple affair, especially when your talking in excess of 1,000 BHP from a small displacement motor. The cooling system in itself is a massive problem. Strengthening the hard parts to accept the boost and revs is the easy part.

I'm off now as we are racing at Indy on the Gold Coast this weekend. I'll wave to you all on TV.

Mario.

 

[ColinM]

If higher revs are the key to making more power (along with boost) then pneumatic valves would suuely be a good way of getting much more than 12000rpm, like F1 engines. I assume that the cost is astronomical but hey, we are talking practical theory here. Check here for some info -
http://www.indiacar.com/nfs/technical/pvengine.htm

 

[323GT-R]

Short Stroke Engines...

Regarding building a short stroke engine for high Rpm use, this is fine in theory, but remember that the torque produced is related to the length of the stroke, since this is produced by the piston pushing the con rod down onto the crank, hence a longer lever = more torque. For an ultimate drag race engine, this may not be so much of a factor, but for road use or circuit use, the engine needs a usable power band.

I remember years back reading a piece about F1 engines, giving loads of calculations as to what the maximum achievable Rpm was, funnily enough it was around 15,000, wonder what the Ferrari / BMW engineers would make of that now...

The equation shown, is this based on typical engine efficiencies and other factors, or optimum (if someone knows)? As has been stated, there are a huge number of variables which are not taken into account, it's just whether they have been assumed as typical or optimum values.

 

[Adamantium]

I know they use pneumatic valves but what about solenoid controlled valves? is there no advantage in this?


Incidentally to the guy who mentioned a 2 stroke motor.

cant say a lot about this but as a patent attorney in the motor industry, I come across a lot of interesting ideas, most rubbish, btu some phenominal. One that i wanted to share with you with the prospect of joining the crankshaft to the valve train by use of an automatic gearbox, with a 2 to 1 reduction. By incorporating this with some form of vvt, you have an engine than can smoothly switch over from two to four stroke, when conditions are suitable.

I havent looked at the details of this, as it is not my client, but I know it has been filed, so can say what I know already. A working model has been built, and rsults so far have been incredible, interms of power extraction, and emissions which is the main driving force behind most engine related patents these days .

Seen some great developments in variable geometry turbo chargers, but those I cant talk about.


This capacity increase thing does interest me.

I am wondering if Mario can elaborate to some extent on the physical problems that having a less or more than square con rod ratio creates.

I have often read people saying it "isnt good" or the pistons speed must not exceed 3000ft/min or something like that, but no one ever explained to me what happens when you go beyond the realms of what is considwered ideal.

Funnily enough I still know nothing about rb26. I run the flat four from the impreza which starts off at 92mm by 75, in the process I have increased bore to 100mm and stroke to 79 to yield 2.5 litres instead of 2.

I am now wondering if I should not have stroked it further to 81mm as this would have yielded a similar con rod ratio to that which I had before.

If you strengthen everything sufficiently enough, is there any other reason why it wont rev as high? I can appreciated it has a lack of willingness to rev, but how noticable is this when the engines are side by side?

I am still convinced that a 25% increase in displacement will be worthwhile purely from a drivability point of view. I am fitting what by impreza standards is a very large turbo, but similar engines should still allow me a bar of boost by 3/3.2k revs.

I also like the fact that the longer stroke means that cc for cc Ido achieve better torque. The consensus being it is at the expense of revs. Does this make the car worse? or just worse for extracting the highest power figures?

Ultmiately it is too late, as the crank is being made, and I can do nothing about that. I am hoping for >500bhp and lbft, and have seen similar results doing almost the same thing, whether the engine will be happy at its previous 8k redline I dont know. I do know that the peak power has dropped to around 6300, but if that remains usable on the road and track, I dont know that this is such a bad thing.

 

[SkylineUSA]

22B,

Your a patent attorney, I have one of those, but she is a US Patent Attorney

Those flat 4s are great engines, all give you that. Sounds like you are going to have a monster on yor hands.

"I am still convinced that a 25% increase in displacement will be worthwhile purely from a drivability point of view. "
I believe this as well.

Personally, I am with 22B about the usable power at lower rpm levels. I will gear my GTR the same way. I like torque, thats my downfall.

Its all depends on what you want. To get one thing, you always have to sacrifice some where else. I want drivability over anything else. Working on engines is one thing, but I want to drive the car, not work on it all the time.

 

[Adamantium]

I like power too, torque isnt enough on its own, otherwise I would have a diesel of some kind.

To me that must be a serious push factor towards stroking despite the consensus of the thread to be boring.

I would agree with this to some extent, but cc for cc, an increase via sroking is going to yield more torque. I still want to know what exactly is the downside to breaking the theoretical piston speed limit and the problem with a con rod ratio that puts more lateral loading on the piston, if the components can take it.

 

[SkylineUSA]

Side loading is bad. Even if the components can take it. You will decrease the life expectancy of the engine do to wear. This is what I have read at least.

You know whats funny about the RB26DETT. I never see anyone talk about cam profiles. You buy some generic cams, and throw them in. In the states, we live off of cam profiles. all I see is 256, 264, or 272 and XX.X amount of lift and that is it. I have spent weeks looking at different cam, and how they will react on the engine, even in boost applications. I wonder why that is?

 

[Guy]

BHP

Now this is what a great thread is all about.

I'm off to the USA for a week or so on holiday, so won't be adding any more for a while, but I eagerly await reading this when I return.

Guy

 

[lightspeed]

Don't forget that more side loading on the piston also increases friction.

Piston speed limit is all about the strength of the piston/rod/pin - the acceleration/deceleration forces on changing from up stroke to down stroke are very large- if the piston velocity is too high then the piston/rod/pin will not last too long.

 

[Syed Shah]

I will gear my GTR the same way. I like torque, thats my downfall.

To be perfectly honest, if you want torque and not BHP, you are wasting your time with your RB26 engine.

It was not designed to be a torquey engine at all, and was always designed to make lots of power at high rpms. If you want low rpm torque and power, get a Viper or something similar. No amount of stroking (even to 3-3.2l) will ever give your a high torque RB26, at low rpm.

Like I said earlier, revs IS the strength of the RB26, take it away and what have you got? A 2.8-3l, low torque, low BHP engine. Not really what you want.

 

[SkylineUSA]

Am I thinking that I will be able to produce a RB26 that can match the torque of a 426 Hemi, No.

I totally agree with you that the RB26 was not intended to be torquey, but then again its all relative.

If you think I am wasting my time, I better re-think my approach.

 

[Adamantium]

how about a fully strengthened 2.5 flat four with 8.5: compression running 2.7 bar of boost?

good for 550lbft and 550 bhp

 

[Syed Shah]

2.7bar? On what fuel? Becuase you'll have all sorts of problems on anything less than race gas.

Also, whereabouts in the rev range will the 550lbfts of torque be?

Out of interest, are these figures SAE or DIN? Because in the states, lightly modded (i.e still stock turbos) Supras are getting 450-550ftlbs of torque, while on the UK system, its more like 400 max.

Also, what is your new rev limit? On what turbo (and at what rpm will it start making positive boost, and full boost?).

Thanks

 

[Adamantium]

2.7 bar is absolute peak, balls out for a laugh boost, which the engine can take. It has taken more so far.

those figures quoted are at 2.1 bar.

This is running 97 ron super, not race fuel, with NF octane boost in a concentration of 1ml per litre.

Det is only a problem if you run the ignition, you can use this octane of fuel, you just have to be prepared to retard the ignition a bit. Ie. map accordingly.

Must stress, this was done on an engine dyno, and prior to the use of water injection, which will be added on the car for a little extra safety only, not for the purposes of advancing ignition further.

Peak torque I believe was at 4200 rpm, and all figures quoted here are standard UK bhp and torque,

This is not an engine in a mild state of tune. The engine mods so far must have set me back almost half an R34. The turbo also is far from standard. The mapping has been done using a pectel T6 ecu which in total must have cost me around 4k. To my knowledge I have left no stone unturned in terms of doing the job right first time.

Once assembled and running I will post a spec and some pictires. Cant see that ever happening as this all started when the standard engine threw a big end at idle and that was in january. Been driving round an £800 205 ever since, and occasionally an S2000 lent to me by my father.

Having seen cems gtr (I believe I was the one who persuaded him to buy it ) I have often considered junking the impreza and all this expense that has come with it, just to buy an R34, since I like them so much. Sadly I have a strange love for the 22B (not really an impreza fan, in fact prefer lancers) but the 22B has so much charisma, I cant imagine ever getting rid of it. So instead I thought I would make it an even more special 22B, my goal being drivability and then outright performance. In this respect it works, The pectel will allow me to reduce boost to make it less of a monster , and this feature is fully programmable so doesnt have to affect spool up, the extra 25% capacity brings in the much larger and newer design turbo significantly before the old engine managed to, making it nicer to use on the road.

This is all theory of course, as the engine hasnt been in the car yet.

The figures also dont relate to my engine, but to an identical one built in tandem with it. The only difference being mine has stronger head studs instead of bolts and stronger rods.