V-tec

You can alter the rev point at which the V-TEC switches to high lift, long dwell operation but this is pointless. If the high-rev operation mode worked at all revs then there'd be no need for it, would there?

If you ran the car in high lift mode at all revs it would eat fuel and be very torque shy.
 
But just getting it to kick in a 1000 or so RPM lower down can make a big difference to the drive. It's a bit like adding a fast road cam I suppose.
 
waynne said:
But just getting it to kick in a 1000 or so RPM lower down can make a big difference to the drive. It's a bit like adding a fast road cam I suppose.
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That's what VTEC is!!! A set of fast road cams for use at high revs, with the tamer ones for low down and midrange flexibility. If it worked properly 1000rpm lower then Honda would've set it to engage 1000rpm lower.

VTEC is only there to partly get around the compromise of fixed valve timing.
 
Yeah, I have to agree with HDi on this one,
It's not like trying to have a turbo spool sooner, cams are a completely different ball game that are desigined to work at there best in a specific part of the rev band, if you had it come on the performance cam sooner you may find a dip in the torque curve between the transition which would be extremely anoying (or at least for me it would be)

Your best bet is to speak to a specialist tuner as they will advise on such things, you never know with a remap moving the timing a bit might be beneficial,

Hondata I supposed to be good although they are an american company, I suppose it wouldn't hurt to send them an email
 
Even getting a turbo to spool early can be challenging. Without adequate exhaust gas flow there's nothing to spin up the impeller. This is where superchargers come into their own.
 
Variable valve timing and variable valve lift systems are only there to try and offset some of the compromises made in a fixed geometry system.

My car has BMW's double VANOS which varies intake and exhaust cam timing independently of each other, all the way across the rev range. It also takes into account other factors such as throttle position and load.

But if I were to cripple it and leave it set in max revs / max throttle position I expect that the low and midrange torque would all diminish and leave me poor performance. Probably it would also chew up petrol at a very high rate.

Locked in it's low rev low load position the car would lack torque and performance as the revs rise.

As it is it works very well and the power delivery is pretty linear considering it's a naturally aspirated engine.
 
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On a VANOS equipped engine a remap might be benefical to you,

Celtic quote 204 hp and 230 lb ft, the increase in power isn't much but the increase in torque should be felt,
 
jarrus said:
Quite possibly, was just a thought though,
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I did have a look at the figures. Some people say that my car, being double VANOS M52 is rated at 212bhp provided I run on 98 RON or higher.

I thing this is wrong. I thought that single and double VANOS engines have same rated power & torque but the double VANOS one has peak torque at slightly lower rpms.

Anyone any the wiser?
 
But is that just because they run 'em on 87 RON fuel in many cases and we have 95 RON as our minimum in the UK?

I know there were some significant engine differences in the US cars. Some US E39s had the M52 engine with a cast iron block. Mine is definitely an alloy block and head with steel bore liners.

Perhaps there are more differences of which I am currently unaware.

It does go quite well for a heavy car with nothing more than a 2.8 litre N/A 6 to pull (more correctly - PUSH) it around.
 
Our fuel ratings are slightly different, I think 87 AKI (US octane rating) is the same as our 95 RON,



I'm not sure why they have lower powered engines than us as the e46 m3 is exactly the same as ours,
 
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I've been to the us a a few times now here how it works

They have Regular, plus and super rated at 87 aki 91 aki and 93 aki respectfuly,

our regular 95 RON is the same as 91 AKI and our super 98 is the same as there 93,

That's how I've read it.
 
I'll take that as correct because it's the first time I've been aware of different labelling. It is well within the realms of reality - let's face it, a US gallon is different to a UK gallon.

What is AKI?

RON is Research Octane Number.
 
Anti Knock Index, is an average between RON and MON

Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load, as it is determined at 900 rpm engine speed, instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON, however there is no direct link between RON and MON. Normally, fuel specifications require both a minimum RON and a minimum MON.

Better now? :)
 
jarrus said:
Anti Knock Index, is an average between RON and MON

Motor Octane Number (MON), or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load, as it is determined at 900 rpm engine speed, instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON, however there is no direct link between RON and MON. Normally, fuel specifications require both a minimum RON and a minimum MON.

Better now? :)
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Thankyou - that's the kind of answer I like.

So are such tests still carried out with single cylinder 4 stroke test engines which allows the compression ratio to be adjusted mechanically?

If so, then AKI seems to be a better thing to consider because it takes account of real world operation. MON and RON, despite being accurate, are largely meaningless then.

You're onto something here.
 
O yeah absolutely, us on this side of the pond always look at the highest figure, where as the Americans take an average out of to effective tests of petrol/gasoline,

I'd imagin that the compression ratio in the engine can be varied some what but from my research though it seems that most the time the engines static compression stays the same and it's the ignition timing that is altered as said previously.

I think next time I put some diesel on my car I will have a look at the petrol pumps and see what the small print on the labels say, my usual filling station is Esso as it's the closest to me, there aren't really any places close by that do "super diesel" like BP ultimate and v-power, but if I'm in need of diesel and I'm going the gym that day there is a Total garage near buy that sells there EXCELLIUM diesel and I've used it and it's just as good as Ultimate, (i've always thought V-power was no different to standard diesel) and it's funny how they market it, exactly the same as ultimate, hell it could even be the same stuff....
 
Weird that is, I didn't think different diesels made your car noiser.

Personally, I hadn't noticed any difference in the noice, but then again you know how noisey those XUD's are.... I'm not going to deny it, they sound like a bag of spanners on a cold morning, although when warmed, they are supprisingly quiet.
 
154916d1230595979-honda-o-volkswagen-vtec_yo.jpg
 
I've driven Honda's with VTEC valve timing. I my experience it doesn't kick in, anymore than a turbo should be felt to 'kick in'.

It should be a linear transition from one set of valve timing and valve lift parameters to another set of parameters.
 
I've driven an Accord with vtec, but only a standard 143bhp 2.0, so there wasn't so much a kick as a bit of an increase.

however my Clio 172 had a similar system and there was definite step change and marked increase in acceleration.
 
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