camshaft profiles

S

steve09

Track Warrior
Points
67
Car
Honda NSR 125R
in my rather basic knowlage in car working this is how i see it.

a normal car has one or two cams, SOHC or DOHC.

the inlet ones are the ones im talking about.

a normal cars the car has one camshaft lobe profile and Vtec has two,
one for normal driving and one for when the Vtec kicks in.

if you get a remap on a Vtec i've heard that you can lower when the Vtec kicks in.

what I want to know is if you were to take your Vtec cam (or get a new one) to somewere like kentcams, can they change JUST the Vtec Lobs to race profile?
I hear if you get race profile on a normal road car it becomes lumpy and an ass to drive at low revs, but as the Vtec kicks in high revs it should only have positive effects, would this be a good idea?
 
Probably not as the changeover would be quite brutal. And you'd really struggle to keep the emissions in check. If you alter the VTEC parameters and engage the long dwell lobes at lower reves then you'll be losing power.

That's the whole point of the VTEC system. If it was beneficial to engage at lwoer revs then Honda would have done it that way.
 
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hmm, hadnot thought about that, would a fast road profile be better or would it be better to get both profiles changed while i am there to ease the change over?
 
Honda engines are already in a pretty high state of tune. It's only thanks to modern injection and management systems that they're as smooth as they are. Stick a pair of dellorto carbs on a VTEC unit and it'll be rough as hell.
 
fair play. advice well taken.

so you say to leave well alone unless going for a full on race set up
 
other than cam profiles, which you have said can cause problems with emmisions and change over.

what is the best way to get more power out of a vtec engine?

im not talking forced enduction cos i dont think my insurance can take that hit at this stage.

im talking about small subtle mods to give that little bit of extra ompf top end.

and tipically what sort of revs does the vtec kick in? 5200rpm?
 
It's not so mch that the VTCE kicks in. It's there all the time. THere are two distinct operating modes, normal and high RPM. The changeover point is over 5000rpm. I remember driving one of the first Prelude 2.2 VTECs in 1998. THat changed over at 5800!!! Peak power was 185bhp at something like 8400rpm!!!!!!

Freeer flowing air filters always help. Sports cat will reduce back pressure. all these things are important on high revving engines as the valves are (compared to lower rpm) only open for a very short amount of time so you need to get air/fuel in and exhaust out very quickly.

If you then get it chipped or remapped (taking account of the physical mods) you will probably see about 15bhp more at the top end. Low down, very little gain really.

Also, using 98RON petrol will make a difference with these engines.
 
Some of the later VTEC engines have 2 VTEC zones to get your head round! It does depend a bit on the engine though.
 
might just leave it and do a couple of small mods like air filter and exsaust, that sort of thing until i have got the funds for a turbo.

anyone know of a good place to get a full stainless system with twin DTM back box?

2.5inch diamiter a good size for the engine?
 
Powerflow did my prelude for £340 that was with the 3.5 twin slash

is the 2.5" the bore or the tailpipe sizes ?
if its the bore id say that was too big for a 1.6
 
bore.

thats why i asked, incase it was wrong and anyone else knew the best size without a serious drop in backpressure and power.

perfect size anyone?
 
I don't think you'll get much more from a VTEC engine with a turbo in terms of flat out bhp. You might find it'll help the bottom end. One thing that VTECs are is torque shy.
 
hohum..... might just leave it as is for the moment, it has 160 bhp as it is so i prolly wont need much more,(just found out thought it was the 109 one) and in a year or so get a bigger and better car.
 
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