Cams, compression, revs and power...

[Topher-EK9]

**** hot work and debate again kozy...
this is very interesting stuff..

could you post the working of the compression ratio lift of 0.68 to get the 12:0:1.. not that i will instantly understand it but i'd like it to go through it please if possible..

thanks mate..

 

[Kozy]

Will do tomorrow mate, it's all on my work computer.

Been busy at work again this week as you can see...

 

[Topher-EK9]

ah cool, no worries mate.. not that i can digest it properly tonight anyway

 

[Kozy]

could you post the working of the compression ratio lift of 0.68 to get the 12:0:1..

Ah there was nothing special about that bit actually, it was just a quick back calculation, I just added SCR until the VPI matched the stock engine!

 

[jugbugz]

I just had my car dyno tuned for 3-4 hours non-stop. I was very happy and surprised at the results and saw this thread. Thought I'd share it with you guys.

But before that, I had a quick skim through this thread and just want to add my 2 cents about big cams and CR.

Theorectically it is essential to have more CR when your running big cams with big durations, basically anything bigger than Toda C2 cams. We've seen ppl put Toda B and Cs into stock B16a 1st gen which only has 10.2CR but made as much power as a modded stock internal B18C. But theory suggests that the power would fall flat on its face.

Secondly, where the power falls off at high rpms doesnt just come down to the cams. By experience its greatly affected by the intake, TB, IM, head, headers and exhaust pipe sizing and MANY other factors. They pretty much need to work together in harmony. And with these things, in the end, its trial and error.

Here's my Dyno results from a Dynapack after 3-4 hours of Pro tuning after installing bigger fuel injectors.

***PLEASE TAKE NOTE THAT ALL DYNO GRAPHS FROM AUSTRALIA ARE SIGNIFICANTLY LOWER THAN OTHERS WORLDWIDE, AND SOME CAN BE UP TO 20% LOWER OR MORE *** SO PLEASE DONT TAKE PEAK FIGURES INTO JUDGEMENT BECAUSE I CAN ASSURE YOU THE CAR IS PRETTY QUICK ***

My engine is the original and only 'B16B'
-stock internals except Greddy stage 1 cams and AEM cam gears dialed in to greddy specs. These cams are equivalent to TODA A.
Tuned with PFC.

My breathing mods have changed here and there, which is where I spent a lot of money on.

Things to note on the graph;
-makes peak power at 9200rpms dropping 2hp @ 9400rpm. Limiter is 9500rpm. (yeh I'm shocked! Even the tuner was surprised! )
-Flat torque and Peaks at 6500rpm and again at 8300rpm.

Yes I run a Oil cooler, oil filter relocation and Toda Oil pump Gear with modified relief valve. I get 100psi of oil pressure from 3000rpms to 9500rpm.

The next mod for this car is Toda C2 cams etc with some mild headwork(maybe) and slight bumb in CR. Leaving the bottom end as is.

 

[EK9turbo]

Nice work JB!... Graph looks great. Great HP and torque achieved.

 

[Kozy]

Theorectically it is essential to have more CR when your running big cams with big durations, basically anything bigger than Toda C2 cams.

This is the general consensus, but my question is why is this percieved to be essential?

We've seen ppl put Toda B and Cs into stock B16a 1st gen which only has 10.2CR but made as much power as a modded stock internal B18C. But theory suggests that the power would fall flat on its face.

Disciples of the high compression shrine would expect that, yet it works fine!

Nice torque curve on that engine.

Will, since you've looked in, as a tuner have you any insight into what you have to do to get a high compression engine running properly on pump fuel? In any other tuning circle that is not tuned so highly as stock, normally an increase in compression would be matched with an increase in octane rating. Our cars are already tuned for 100RON which is higher than we can get straight from the pumps, does this not create problems?

 

[jugbugz]

This is the general consensus, but my question is why is this percieved to be essential?

Disciples of the high compression shrine would expect that, yet it works fine!

Nice torque curve on that engine.

Will, since you've looked in, as a tuner have you any insight into what you have to do to get a high compression engine running properly on pump fuel? In any other tuning circle that is not tuned so highly as stock, normally an increase in compression would be matched with an increase in octane rating. Our cars are already tuned for 100RON which is higher than we can get straight from the pumps, does this not create problems?

Thanks for the compliment!

Like many things, everything has a theory of physics. Guess its just how we are taught.
I guess things can always be fine tuned to offset the balance - Power can still be made, but not to its fullust as you already know.

Here's some good information about static CR and cam duration relationship that I learnt from this post.
Static CR & Intake Cam Duration Relationship - Team Integra Forums - Team Integra

Normally you could pull out timing to reduce detonation, basically make less power and run it safely. Theres still a limit to that though. My friends fully built K26 engine needs E85, no choice with high compression.
I don't think theres anything you can do to those with stock ek9 ECUs running on 98ron fuel. My friend's stock EK9 runs on 98ron and is knocking all over the place in low rpms. He won't be able to help it until he gets Tuned or get some 100ron fuel.

It would be interesting to see what Will says, hes the PRO!

 

[Kozy]

Saw that on my travels, good link that one JB, but it's still looking at it in the basic sense, simply that you are losing DCR/cranking pressure and must claim it back. This is valid if you drive around town all day at low engine speeds (in which case why are you buying hairy cams?!), but where does a track car spend most of it's time in the revs? What are the contributing to the cylinder pressures at these speeds?

 

[jugbugz]

Saw that on my travels, good link that one JB, but it's still looking at it in the basic sense, simply that you are losing DCR/cranking pressure and must claim it back. This is valid if you drive around town all day at low engine speeds (in which case why are you buying hairy cams?!), but where does a track car spend most of it's time in the revs? What are the contributing to the cylinder pressures at these speeds?

I'm not very certain on the theory so I'll leave this to Will to put it into words.

But what I can say is RPM increases cylinder fill efficiency. In lower rpms the airflow velocity is low, the pumping energy isn't great enough to flow efficiently of give it enough momentum, thats why big lobe cams don't make more power at low rpms compared to a smaller lobe, thank god for Honda and VTEC!

On any engines, bigger cam lobes will only operate efficiently at high rpms. Lowering the the VTEC point on our engines with big cams will in most cases loose power. Ofcourse this also depends on the engine capacity, rod/stroke ratio, compression etc and the tuning of the airflow. The B18C rod/stroke ratio isn't ideal for high rpms, but its great for torque as the short stroke is more powerful than a long stroke on the B16B. So really, theres just way too many factors to point out.

This is probally all the information I can give to your question. I hope it relates

 

[Kozy]

I'm not very certain on the theory so I'll leave this to Will to put it into words.

But what I can say is RPM increases cylinder fill efficiency. In lower rpms the airflow velocity is low, the pumping energy isn't great enough to flow efficiently of give it enough momentum, thats why big lobe cams don't make more power at low rpms compared to a smaller lobe, thank god for Honda and VTEC!

Spot on.

High RPM sees the inertial effects of the intake and exhaust scavenging on overlap increasing VE in a form of mild supercharging, increasing effective displacement and overcoming the reduction we saw at low RPM. In the rev range long duration cams are designed to work at there should be no need to increase compression as we are aiming to generate a mild supercharging effect.

Scale this idea up a bit to consider a turbocharged application, where we drastically increase VE, are we going to be increasing compression there? If not, why not?

 

[jugbugz]

Spot on.

High RPM sees the inertial effects of the intake and exhaust scavenging on overlap increasing VE in a form of mild supercharging, increasing effective displacement and overcoming the reduction we saw at low RPM. In the rev range long duration cams are designed to work at there should be no need to increase compression as we are aiming to generate a mild supercharging effect.

Scale this idea up a bit to consider a turbocharged application, where we drastically increase VE, are we going to be increasing compression there? If not, why not?

Im not sure why your asking questions that you know the answer to but hey lets play along lol

Fuel is the limit as to how much compression there can be in the cylinder before it self detonates which is as bad as pinging. Adding forced induction onto an engine will increase its compression ratio. All this information can be found in the Force Induction threads.

Lets go back to NA application

Speaking of volumetric efficiency, its always such a challenge to hit or surpass 100% VE on naturally aspirated motors. So many factors with cam overlap, airflow tuning etc, it was theorectically not possible long long ago until new theories arose.

What we know is where peak torque is gained at a certain rpm, its also where peak VE is gained. Building an engine to make broad hp and torque is always such a challenge. Ever since i started playing with hondas, i wouldnt care if i never get to drive a turbo ever again. Modifying an underdog 1.6L is just so challenging and is a different experience compared to my DC5R. Everything comes down to trial and error.

 

[Kozy]

Im not sure why your asking questions that you know the answer to but hey lets play along lol

Haha, I do have a good idea of what the answers are to the questions that I am asking, yes. I don't know anything for certain, only making educating guesses, and putting the ideas out for discussion. The questions I am asking are not aimed at you directly, just to anyone reading in general. Hopefully people reading will answer the questions themselves and come to their own conclusions which we can then talk bollocks about for hours on end. That was the idea at least...

Fuel is the limit as to how much compression there can be in the cylinder before it self detonates which is as bad as pinging. Adding forced induction onto an engine will increase its compression ratio.

Exactly, so you lower the compression ratio to keep the cylinder pressures within the limits of the fuel!

Lets go back to NA application

Speaking of volumetric efficiency, its always such a challenge to hit or surpass 100% VE on naturally aspirated motors. So many factors with cam overlap, airflow tuning etc, it was theorectically not possible long long ago until new theories arose.

Totally agree, not only is 100% difficult to achieve, it's also pretty hard to quantify exactly what VE you are acheiving at any given point. It can be done, but it's certainly not straightforward! I guess what we should think about is an increase over the peak VE as stock. So 105% VE should be thought of as a 5% increase over stock, whatever that might actually be nominally.

Back to the relation to forced induction. You increase VE with boost, which increases the cylinder pressures (compression ratio stays the same ) so you reduce the SCR to return the pressures back to within the limits of the fuel you are using, but with a greater effective displacement, which gives more power.

The same principals apply with NA and cams. You're trying to increase the effective capacity, (albeit marginally compared to FI), which works to increase cylinder pressures the same as boost would. You're never going to need to reduce compression to account for this, such is the marginal increase in VE that you are likely to achieve, but why is it percieved to require raised compression for big cams to work?

 

[jugbugz]

Haha, I do have a good idea of what the answers are to the questions that I am asking, yes. I don't know anything for certain, only making educating guesses, and putting the ideas out for discussion. The questions I am asking are not aimed at you directly, just to anyone reading in general. Hopefully people reading will answer the questions themselves and come to their own conclusions which we can then talk bollocks about for hours on end. That was the idea at least...



Exactly, so you lower the compression ratio to keep the cylinder pressures within the limits of the fuel!



Totally agree, not only is 100% difficult to achieve, it's also pretty hard to quantify exactly what VE you are acheiving at any given point. It can be done, but it's certainly not straightforward! I guess what we should think about is an increase over the peak VE as stock. So 105% VE should be thought of as a 5% increase over stock, whatever that might actually be nominally.

Back to the relation to forced induction. You increase VE with boost, which increases the cylinder pressures (compression ratio stays the same ) so you reduce the SCR to return the pressures back to within the limits of the fuel you are using, but with a greater effective displacement, which gives more power.

The same principals apply with NA and cams. You're trying to increase the effective capacity, (albeit marginally compared to FI), which works to increase cylinder pressures the same as boost would. You're never going to need to reduce compression to account for this, such is the marginal increase in VE that you are likely to achieve, but why is it percieved to require raised compression for big cams to work?

Depends if our stock engines do hit 100% VE then yes we could base it off as that. We could assume all engines that hit 100hp+ per litre would hit 100% VE at some certain RPMs, however, on NA engines it only happens on a very narrow RPM window. I remember Endyns built K series hit 137% VE Naturally Aspirated! Amazing really...

Its perceived to be as a general rule for general engines. Honda engines have the high RPMs to makeup for better VE, therefore insufficient CR disadvantage is substituted with High RPM, cam tuning, etc etc, basing this on what was said here. Correct me if I'm wrong.

So I guess the lesson here your trying to lay out is, big cams can be made to work even if the CR isnt high enough?

 

[Kozy]

Not a lesson per se, because I don't know I am right, but certainly as I see it, the whole 'big cams need massive compression to work' thing is a bit of a myth, which I feel like busting....

 

[jugbugz]

Not a lesson per se, because I don't know I am right, but certainly as I see it, the whole 'big cams need massive compression to work' thing is a bit of a myth, which I feel like busting....

Well, if you have a push rod that only spins to 6500rpms, then Big compression is needed. Then again, i've also seen locals dropping big cams into stock bottom GM V8s and make crazy HP numbers.

I've also heard from some retired engine builders who build 4age motors and say 11.0:1 CR is plenty **** loads for big cams to run good and warn about high compression brings forth detonation problems especially running on pump fuel.

Its definitely not a HELL NO thing to do, just depends on the engine, cam specs, tuning etc.
I have to say though, the b16a 10.2CR stock motor had to engage vtec at 7000rpms with Toda C cams, limiter 9000rpm. The peak power was only like 5hp better than another b16 with type R cams but the low and mid range gains were huge! Making it look like a B18 when you overlay the graph with another B16. Considering that it was a stock motor 1st gen B16a never been opened up, is quite amazing really.

If I hadn't seen these things myself I wouldnt have believed it was possible. Its usually the low budget built cars that discover these things.

Sometimes too much theory limits what you can do.

So which one of those people in there are you Kozy? lol

 

[Kozy]

Totally agree, it does vary across engines as you say. I am focussing on the B16B/B18C as a case here, due to already being relatively high compression, high speed and tuned for higher octane than we have readily available etc etc.

So which one of those people in there are you Kozy? lol

One with the beret I reckon. I do have a leather jacket though...

 

[jugbugz]

Totally agree, it does vary across engines as you say. I am focussing on the B16B/B18C as a case here, due to already being relatively high compression, high speed and tuned for higher octane than we have readily available etc etc.



One with the beret I reckon. I do have a leather jacket though...

haha

I agree with you too.
Increasing CR for big cams on our engines would make the most out of the cams in all RPMs across the board. The downside is, higher octane fuel, and you need a tuner that knows what hes doing and atleast hours on the dyno. Otherwise the results isnt even worth all that trouble and money opposed to just dropping big cams onto a stock motor.

The combination of airflow parts also is critical, which greatly affects power/torque curve, where peak power/torque is made and where it dies. You see heaps on dyno graphs online hitting big peak numbers yet the powerband is just wierd with dips here and there. And you have some that rev to 11,000rpm but the power starts dying at 8500rpm.

The main point is, just because you've spent money and upgraded a certain part, doesnt mean it will perform better or work well with your combination.

The best form of measurement is a hub dyno(dynapack) where wheel size, tyre size, strap tension doesnt get into factor. Get a base line from your car and work from there.

Anyway getting off track... Good info here

 

[Topher-EK9]

The combination of airflow parts also is critical, which greatly affects power/torque curve, where peak power/torque is made and where it dies. You see heaps on dyno graphs online hitting big peak numbers yet the powerband is just wierd with dips here and there. And you have some that rev to 11,000rpm but the power starts dying at 8500rpm.

i wish i could add to the knowledge being given here, but sadly i can't. I am loving sitting back and reading it though.....slowly

However, I do look at alot of dyno graphs and i have a kind of photographic memory so to speak, but there are so many strange dips in graphs that i see that sometimes i play out in my mind how it would feel to drive that car, when in mine, with those dips and peaks all about the graph..
what i am getting at slowly, lol, is the graph you placed up looks so smooth and flat and consistent like it'd be such a free flowing, predictable, enjoyable engine to drive, basically thanks for giving me an insight into why i notice this..

enjoying this info muchly guys please continue .. is this a Sticky yet ?

rep added to you both.

 

[Kozy]

enjoying this info muchly guys please continue .. is this a Sticky yet ?

rep added to you both.

Cheers bud.

Don't think it qualifies as a sticky, it's only conjecture, no solid info.