101 reasons you should dyno your stock car.

[shiroitenshi]

From my experience, the A/F jumps around because the car is jerking and not because a/f is jumping causing car to jerk.

And this jerk if it happens will always happen only in vtec transition point or part throttle in higher rev like 7k, 8k rpm etc.

I don't exactly know why it happens but i know for sure if cam gear settings are not optimal setting for your specific engine build, compression etc, this will always happen and also if the vtec point and iginition + fuel map is not ideal it will happen.

My 1st cam i used was Jun2 and Jun3. Both this cam had crazy mis-fire or jerk during vtec transition and part throttle. No matter how we set the cam gear, it could not be eliminated with retaining good power. all this was done in old skool style with a re-chip ecu.

The EK i know for sure, after install S300 and did a good tune and setting vtec point high the vtec transition was smooth and alot less jerk at part throttle.

My recent cam installation on the Buddy clubs, when the camgear setting not ideal, it was jerking like hell in vtec transition. Now solved with only camgear setting.

Hmmm.. sound interesting.. but I need to ask what causes the car to jerk in the first place? I can only estimate that it's due to either fuelling (looking at the tuner increasing fuelling only to find that it jerks after a certain range only serves to make me think that it's the injectors). As for the cam gears timing.. you might have a point, but in my head, it works out the following...

Cam gear wise, you move the powerband by delaying or advancing the valve open/close timing, which in effect, change your dynamic compression curve, so fuel and ignition requirements change, so assuming that the jerk is due to cam gear settings, it still could be tuned out with tuning.. but not with this 1.8l setup.. fact is, you know how many tuners I brought it to, chris, and they couldn't eliminate the problem completely.. finally just did the shortcut way of reducing power to compensate.

 

[shiroitenshi]

chris,
u actually said the solution, prolly u didnt realise this chris. its the vtec transition point that makes the jerk. the primary cam profile on the cams especially JUN are meant to be pushed betwen 5800 to 6800. this may sound absurb for newbies but the power hasnt died yet at the mid range. the rest of the rpm are pulled untill 9200rpm. but for street setup (mild modded) no doubt between 7800-9200 the engine is dying to be pushed which wasnt meant to rev that high either. cam gears do help with the power band but not make more power as ppl believe.

i think the toda c2 should be good in all ranges, aint that right chris? hee hee hee

C2 isn't that high, J101.. it's comparable to S2's and BC's 2nd stage cams, if you look at the actual durations at 1mm.

The primaries are higher.. (pre-vtec) and actually similar to the Toda D's.

Those advertised durations really play havoc on what people think on cams..

The initial ramp (I think that's what they call it in cam terms) usually affects the advertised duration.. the less aggresive the ramp rate, the more duration the cam will appear to have when using advertised(zero lift) specs.

That's why you'd be surprised to see how much 'advertised' duration the R cams have, due to it's 'not so aggresive' ramp rate.

Which is also why the R cams seems to keep the rocker arm wear to a minimum. :P

Actually your idea is a bit different that mine.. yeah, it manages the power band, but how it does it is what I think of the most.

My idea of cams is that it regulates static compression.

Why stock pistons with stock compression and stock cam lose power at high rpms (other factors not withstanding) is due to the fact that the quick valve closing times were not allowing the engine to flow the air in the amount sufficient enough to generate power.

Due to the inertia of flowing air, at high rpms, the flow actually helps the exhaust gasses exit the engine faster and replace it with fresh air from the intake tract.

In a stock unit, the flow is severely retarded due to the fact that the valve is already fully closed with the exhaust gasses still in the combustion chamber (I'm not sure this is possible, but for now, it is in my head), choking the flow, and generally reducing power. (or in another way, not filling up the cyclinder with enough air density to generate proper 'power')

So what's this got to do with high compression pistons?
Interesting note, this.. and I did think about it a lot, and I could only come up with the idea that due to the fact the overlap and intake closing times are also longer, the swept volume is reduced drastically (In my head, the compression stroke only begins the moment the intake valve closes fully.) Funny how the 4 strokes don't seem so straightforward anymore when I think of it in detail.

so, if the intake valve closes like 45 degs ABDC, it effectively removed half (or was it a quarter? must go look and remember at the cam/crank relationships again)of the swept volume, reducing compression (for that particular stroke.. which will bring it to the point of diminishing returns if you keep increasing it.

Which is why stuffing big cams in a low comp stock engine is like causing controlled compression loss and the loss of power.

Yet people still do it, and claim they make power... hmm.. placebo effect maybe?

 

[zaki]

Yup.. exactly.. cruising b4 vtec and wot is perfect.. same story with yours zaki.

And I suspect the A/F jumped around due to the sputtering of the injectors.. looking at the AF reading, the a/f started reading lean gradually (in the span of 1-2 secs (mind you, this is at part throttle, not WOT run) before the a/f became something like 10.5 then the jerks started, and then only did the a/f ratio jumped around.

It actually felt like a rev cut.. except more severe in the sense that it actually 'slows' down the car. (of course, that could be attributed to having a car that runs on 205/50/15 tires. :P)

Same problem lah zaki.. the way you decribed it similar. I suspect it's some problem with the rechipped ecu putting too much enrichment during the vtec crossover point.

How much is the fuel pressure? IMHO, it's not due to the injectors. What I can think of is the rechipped ECU is not suitable for the cam. In my case, it cannot be the cam since it follows the kilang spec.

We love to have big duration, high lift, wide overlap cam. At WOT, the scavenging effect does the job well. we may have 100% or more volumetric efficiency. but at low load, the VE is lower and reversion may be the cause of my (maybe your) problem. the pressure inside the manifold fluctuates due to reversion (usually reversion is associated with poor idling at low rpm, but i think it still has effect at higher RPM at different load). that makes the a/f jumping too lean too rich too lean too rich.

 

[shiroitenshi]

How much is the fuel pressure? IMHO, it's not due to the injectors. What I can think of is the rechipped ECU is not suitable for the cam. In my case, it cannot be the cam since it follows the kilang spec.

We love to have big duration, high lift, wide overlap cam. At WOT, the scavenging effect does the job well. we may have 100% or more volumetric efficiency. but at low load, the VE is lower and reversion may be the cause of my (maybe your) problem. the pressure inside the manifold fluctuates due to reversion (usually reversion is associated with poor idling at low rpm, but i think it still has effect at higher RPM at different load). that makes the a/f jumping too lean too rich too lean too rich.

Fuel pres is at 4 bar at idle. means vac hose off, 4.5 bar. Still think it's not the injectors ah zaki? Even 3.5 bar is pushing it, this is 4.5 oh.. and was only able of getting high 11s on the AFR (occasionally, means can't maintain it)

(this is the same setup in the '1.8 peak whp thread') Can't reveal the details specifically, but it's a very very high compression engine. Supposed to run on race fuel, but sorting out the road tune first. Initial impressions are good, it pulls hard enough with a higher FD to rival a very torquey B20 setup.. But loses out on higher end power (haha.. this has got to be a first (O_o)).. a B20B pulling away at the higher rpm range than a B18C with a higher FD.. :P

So, based on the findings so far, we're going to swap in bigger injectors and go for a retune.. hopefully for better results. I have no delusions of having 230whp for this ride, but I think 210-215 should be at least achievable..

Actually it's not a chipped unit, but an original mugen OB2b box.. not a copy/clone whatever. VTEC point is 5.2K.. and the curve at WOT is actually smooth even though engaging comparatively early, and there's a smooth transition of torque climb.. from the torque maps.. I can see how the engine gives out the torque relatively early at the low cam (the dip is at 4-5K, as opposed to the usual 5-7K rpm we usually see (on tuned setups)

The suggestion was that he use back the original ECU with unichip piggyback, but since he want's to use the mugen box anyway.. so that one owner's choicelah lah... But for the third tune, I'll probably bring a stock unit along so can test as well.

As for the reversion.. I'm not sure it occurs so readily unless overlap is very severe... in which case, I don't think the cams overlap are that extreme to cause a lot of reversion, considering they aren't running at very low rpms like 1-4K.

Interesting note about the reversion though, I might have to look it up. Though the fact that just before the vtec switch point, it started leaning out do make me think that it's the injectors though.. and comparatively, the target horsepower exceeds the capacity of the injectors by quite a margin already. And that's being conservative with the BSFC value at 5.25 already.. and a 280lph pump. (O_o)? (I know.. so big ah?) but seriously.. in tank pumps are the way to go.. inline fuel pumps are noisy and although it's slight more in complexity in installation, the in tank pump is the best.

I have heard an inline pump noise.. and trust me,, having border304s and that pump humming in your ear is not fun at all.. not to mention the lack of soundproofing material.. so add the tire noise of semis to the equation. ouch!(>.
Anyway.. forgot to make sure during that time, but I think what happens is that the jerking is caused also by the vtec turning off (rpm reduced to less than 5K, VTEC off) and then on (rpm started increasing again), messing the fuelling.. Should have wired an led light to the vtec solenoid to see how the vtec is engaging or disengaging.

What happens during the jerk is that at 5.2K part throttle, the rpm needle actually jerks back to lower rpms.. it's almost like a speed cut, except it happens in VTEC point only.

Most people that test drove the car said that it felt as if the car jerks like it didn't have enough fuel as well. Which has always led me to thinking the injector sputtering, which would cause such behaviour.

My butt is particularly insensitive.. so I don't usually rely on my butt dyno sense.. I did take the car out for few spins though, and there was a sense of flat spot just before the vtec engages then the jerk, but I don't really rely on that feel, like I said.. my butt really insensitive..

 

[J101]

chris,
aiya..should have told you to snap some pix, for record purposes. hehe

The Skunk2 Pro retainers had a 0.3mm bigger base than Omni and fitted Toda Springs very well with minimal free play. It fitted bettter on the toda valve springs then Omni, Crower and Brian Crower.

 

[J101]

shiroi,
im eating my breakfast while reading this and suddenly i feel full-lah..haha
when i said c2, im thinking of street application with mild mods and definitely affordable realistic setups. i cannot say toda-d or skunk pro 2 as they require more than just high compression and good tuning. it would be good if we can see smaller cams like toda A2 or jun type 0 and type 1 to benefit simple mods and fast daily results.

as long theres no graphs, u can say its a placebo effect.. ha ha

Which is why stuffing big cams in a low comp stock engine is like causing controlled compression loss and the loss of power.

Yet people still do it, and claim they make power... hmm.. placebo effect maybe?

 

[shiroitenshi]

shiroi,
im eating my breakfast while reading this and suddenly i feel full-lah..haha
when i said c2, im thinking of street application with mild mods and definitely affordable realistic setups. i cannot say toda-d or skunk pro 2 as they require more than just high compression and good tuning. it would be good if we can see smaller cams like toda A2 or jun type 0 and type 1 to benefit simple mods and fast daily results.

as long theres no graphs, u can say its a placebo effect.. ha ha

Actually J101... the C2 isn't that far off from the spec D.

IF check the durations at 1mm, and I think you'd be surprised at them.

I do have some strange vibes about the D's though.. Ericks put on his website 250 primary and 300 secondary, and I thought that if this is the case, this is a very big cam, if he is quoting 1mm duration numbers, and quite a normal (high performance) cam with higher primaries if it's an advertised duration..

But looking at the cam sheets of the Toda Ds, these numbers don't appear at all.. They're closer to C2 specs that I first thought, but still slightly bigger though.

So the local Toda D's don't appear to have the same specs as Ericks, advertised or not.

Any thoughts on this?