cam choices SK2 pro or tuner 2?

[Kozy]

Pro1s are known to work well on stock block H22s with around 11:1 compression. Anything over 11 should be fine, 12.7 is probably a massive overkill.

 

[jesse888]

Nice knowledge cheers. Handy calc aswell!

 

[godfridge]

hey vtec6000 any chance you can dig out some tuner 2 graphs? this is something iv considerd though its hard 2 find graphs for tuner 2's
thanks

 

[Vtec6000]

Sorry I forgot, will try remember next day i'm on the dyno. You can expect around 210-215bhp with the Tuner 2's. A slight head skim helps these work well. With stock compression gains aren't massive.

 

[rs250nut]

Sorry I forgot, will try remember next day i'm on the dyno. You can expect around 210-215bhp with the Tuner 2's. A slight head skim helps these work well. With stock compression gains aren't massive.

The gains will never be that great with stock compression and aftermarket camshafts, the reason being is that you are effecting the dynamic compression ratio. Because the hotter camshaft has a longer duration and higher peak lift the inlet valve is left open longer on the compression stroke effectively reducing the dynamic compression ratio. This is why a mechanical change in compression ratio is needed with like you say a head skim or a change in piston cc. Also worth mentioning is the way the cams are timed up can effect the compression ratio (dynamic).

 

[Vtec6000]

The gains will never be that great with stock compression and aftermarket camshafts, the reason being is that you are effecting the dynamic compression ratio. Because the hotter camshaft has a longer duration and higher peak lift the inlet valve is left open longer on the compression stroke effectively reducing the dynamic compression ratio. This is why a mechanical change in compression ratio is needed with like you say a head skim or a change in piston cc. Also worth mentioning is the way the cams are timed up can effect the compression ratio (dynamic).

Pretty much yes. But more than compression the biggest factor I've seen effecting 90% of builds and why they don't work so well is their breathing mods aren't sufficient. "I want a race spec engine but want to keep my twinloop so it's not loud" lol. Everything works hand in hand and having one part of your setup wrong holds everything else back.

 

[rs250nut]

Pretty much yes. But more than compression the biggest factor I've seen effecting 90% of builds and why they don't work so well is their breathing mods aren't sufficient. "I want a race spec engine but want to keep my twinloop so it's not loud" lol. Everything works hand in hand and having one part of your setup wrong holds everything else back.

I agree, a change of camshafts should never even be considered if the basic breathing mods have not been carried out even though these should be the first parts changed with a performance engine build. Most of the time people should research how fitting these performance parts will effect the way their engine makes power.

 

[davidglanza]

would pro 2's make a car fail nct/mot on emmisions test?

 

[godfridge]

Ok so not rrally worth it then? I had them in a b16 before . Thoughts you can get not far off those figure with a remap? A dc5 couldn't pass my Jordan with tuner two's. And even then it made me think they must be even better in a b18

 

[Kozy]

I doubt anyone bothers figuring out their dynamic compression ratio when speccing cams, the numbers commonly chosen for builds suggest most of them are just plucked right out of thin air with nothing more than a 'more is better' thought process on it.

Does anyone even know what the DCR of a standard B series is?

Most of the time people should research how fitting these performance parts will effect the way their engine makes power.

I could swear you told me that was pointless and you're better off just bolting bits together and seeing what happens?

 

[rs250nut]

I doubt anyone bothers figuring out their dynamic compression ratio when speccing cams, the numbers commonly chosen for builds suggest most of them are just plucked right out of thin air with nothing more than a 'more is better' thought process on it.

Does anyone even know what the DCR of a standard B series is?



I could swear you told me that was pointless and you're better off just bolting bits together and seeing what happens?

I'll get my coat...............

 

[Kozy]

I have nothing more too add really, it just seems a bit odd to try and replace something you've lost when you don't know how much you had in the first place... :dunno:

 

[rs250nut]

I have nothing more too add really, it just seems a bit odd to try and replace something you've lost when you don't know how much you had in the first place... :dunno:

????

 

[Kozy]

Fit cams - reduce DCR. You then try and make DCR back with raised compression.

If you don't know how much DCR you had to start with, how do you know how much you need to replace?

Given that these engines are designed to run on 100RON, and the best we can get is 99RON, there's probably not a great window to increase the compression before you need to start pulling timing, unless you eat into the safety window which on a road car probably isn't advisable.

Or, does it not matter and you can just bung some 14:1 pistons in there and get 'a good tune'?

 

[rs250nut]

Most of the time the fuel is going to be the limiting factor, hence why with alcohol running drag cars the compression is up at around 16:1-18:1 . When at the track with my old Renault 5 gtt it made me laugh when a member of a car club caught me tipping a whole bottle of octane booster in the tank, " I would not do that mate unless to want to go bang" still makes me laugh thinking about it now when I told him it was my insurance he looked at me all funny.

 

[Kozy]

Most of the time the fuel is going to be the limiting factor, hence why with alcohol running drag cars the compression is up at around 16:1-18:1.

Undoubtedly. This is why I always question high compression builds on engines that were designed to run at around 11:1 on 100RON from the factory. If the fuel is the limiting factor and we can't even get what the standard engine is designed for, then serious increases in CR with lower octane fuel are going to start requiring timing to be pulled at WOT which will start cancelling out the gains unless you're willing to pay for additives or race fuel.

Obviously, reducing the DCR with long duration cams is going to require some additional compression to make it back up, but with too much being detrimental, how much should you add to compensate for what has been lost? It's usually a lot less than you think, and this is what no-one seems to figure out, it often seems like a 'pick a number between 12 and 14' and let the tuner sort it out kind of deal.

You also have to question if a DCR figure calculated from the VTEC profile is even relevant. Pressure loss from port reversion as a result of a late EVC at >6000rpm is going to be negligible, the cylinder pressures at this speed are going to be more in line with the static CR which if you've gone super high on lower octane fuel, is going to be heavily into knock territory.

DCR is typically attributed to low engine speed performance, at this point we're on the primary and secondary lobes, with a far shorter duration and a far higher DCR. The drop in DCR is also far less with aftermarket cams than in it is on the VTEC profle. For instance, Pro2s VTEC lobe would see a 1.5% drop in DCR over stock cams in a B16B (4.2%when degreed on the same lobe center), but the secondary lobes would only drop it 0.7% (2% on stock lobe center)

So if we average that out and say Pro1s need 2% more compression to put the engine back where it was stock, then you'd need to take a B16B from 10.8 to 11.0. Despite this, tuners say that won't make any power with that and you need closer to 12:1, which throws further questions at the validity of DCR...

I dunno, maybe just plucking a number out of thin air really is the best option...

 

[rs250nut]

Thing is there are so many variables, when the engine is running on the high lift lobe you will gain from greater cylinder filling but with a trade off will be bleeding off cylinder pressure, for instance if you are running pro 1's the intake cam shaft is open on the compression stroke to 50 degrees abdc. Whats more advantageous? This is where real world testing comes in.

 

[Vtec6000]

@Kozy, Take this example. B18C with 12.5:1 static CR. Stock type r camshafts. What effect do you think this will have on power output compared to stock compression ratio using same cams?

 

[Kozy]

At low revs and low throttle, the cylinder filling will be low, increased compression can be used without pulling timing, or even possibly with added timing, to net a reasonable gain in power, much the same as you could at high altitude. I'd expect to see around 5-10lbft gain in the range of daily driving duties which is what people notice and like. Fuel economy would most likely improve.

As the revs and throttle increase, the cylinder filling increases and so do the cylinder pressures. I don't know the knock limit of 99RON, but my workings suggest the standard engine sits at around 700psi peak, so assuming we don't want to exceed that given we're a point down on RON, then I'd expect you'd need to start pulling timing and /or adding fuel between peak torque and peak power, which will reduce gains, possibly even back to stock output depending on how finely tuned the OE map was.

Another point to consider is that if this compression is to be made from the pistons alone, it would require a 10.5cc dome all else being equal. That's a significant blockage to overlap through flow at TDC, which can and will impede cylinder filling. In addition, any additional mass on already hugely stressed conrods will be contributing to more rod stretch at TDC which will increase the effective compression ratio even more.

All things considered, I'd expect to see no significant gains in peak power, possibly delivered at lower RPM and with a plateau of power right around the top of the rev range. An increase in EGTs and fuel consumption. Probably lots of nice pops and bangs from the exhaust due to hotter gases and more unburnt fuel.

At WOT at low revs, I think the fact that the small lobes can only feed about 80% of what the VTEC lobes can mean that the timing can still stay pretty aggressive as the cylinder pressures will stay pretty reasonable. Overall I'd expect the difference in torque between high and low cams to diminish to develop a much flatter torque curve, fuel consumption will improve during daily driving and increase along with EGTs under high RPM WOT.

I guess it all depends on how much breathing space you've got with the standard engine to increase ignition advance before it starts knocking. The more you can use, then the bigger the gains from increased compression, but if the standard map is already quite close to MBT then there's probably not a lot to be gained without other compromises. That's something you as the tuner no doubt have experience of, and I can only hope to learn. An S300 is on the shopping list for the ATR, so hopefully I can start testing ideas soon...

I'm now prepared for you to tell me I'm totally wrong on all counts...

 

[Vtec6000]

Well here is Dyno sheet for setup we're discussing. It has Wiseco 12.5:1 pistons, everything else is stock(cams etc)

Rpm on sheet is out by 200rpm so imagine the curve moved back 200rpm. Rev limit is 8800.

You have many valid points but cylinder filling at low rpm's certainly is not low and it's at these low rpm's that the engine required most timing to be retarded in order to prevent detonation. Power wise it's making in around what I'd expect a good healthy b18c with stock pistons to make with same bolt on parts.(4-2-1 manifold and catback exhaust, catalytic converter still in place) it made one of the smoothest torque curves I've seen from one of these engines to date. Worth mentioning I guess this was tuned on 95 octane fuel.