16v twin exhaust cam mod anyone got info for me??

currently cleaning up my kr for putting in kas once the summers out of the way, whats the crack wi the 2 exhaust camshafts on the kr? i read once that if you swap standard inlet camshaft for an exhaust one it gives more lift, anyone done it?? any info appreciated

Yeah its an internet myth. Exhaust cam rejigged as inlet cam, is no better and just hassle. I mean, chopping off the end of a cam and having to re-align the cam gear, etc? What a hassle to do.

its not a myth, it works well. however it has to be done properly otherwise you get no real gain.  also for the effort involved why not just get a decent set of aftermarket cams?  there was a guy doing them on cgti 'hotgolf' but he doesnt have the tooling anymore, cams are made of proper hard stuff  

i have a 9a, so its worth me putting at least the inlet in, this is in regards to putting kr cams into a 9a.
but the facts are worth knowing
ive just been speaking to some people on other forums about this, here's the info that i collected from different sources:

The reason they use the cam over the 9a is:

2L 16V ABF cam specs:
Intake - 219deg @ 1mm, 10.8mm max
Exhaust - 220 deg @ 1mm, 10.8mm max

1.8L 16V KR cam specs:
Intake - 218deg @ 1mm, 9.6mm max
Exhaust - 226 deg @1mm, 10.2mm max

9A pre 94 specs
Inlet - 8.8mm max

Mike "the man in the shed" from Clubgti, in a conversation i found talking of the same subject and also talking about the WUR mod, states:
"…..It's a case of making sure. Ideally you need a rolling road session to set this up properly, but it will be worth it to make sure the car is running right.

Chances are on any old car, that the fuel pressure isn't at the original factory spec any more, so it's well worth having this done.

If everything else is standard on the engine, then with the KR cam and WUR mod you should be around 160 bhp. Mine was at this spec till recently, and it's quick enough to surprise loads of flash, newer cars!!"


As someone else on the same thread wrote:
(referring to someone that was thinking of using the inlet from the KR, as the inlet for a 9a):
"………….Do you also have the exhaust cam? If you do you will get even better gains by using that as an inlet cam with the pulley chopped off."

But it's not as simple as just cutting off one end, the keyway needs machining in another place on the chain sprocket end in order for you to get it all timed up again properly. (when using the KR exhaust as the inlet for the 9a).

Also for anyone interested (that hasn't swapped cams before then here's a little guide, not by me)
http://www.clubgti.co.uk/forum/showthread.php?t=184663

So as far as i know, the ABF are best option, then the KR, but as someone said, depends what you want to achieve with it.

I'm just about to try the Exhaust mod, if i can't do it, then i'll just pop the inlet in.

de3660 said

i have a 9a, so its worth me putting at least the inlet in, this is in regards to putting kr cams into a 9a.
but the facts are worth knowing
ive just been speaking to some people on other forums about this, here's the info that i collected from different sources:

The reason they use the cam over the 9a is:

2L 16V ABF cam specs:
Intake - 219deg @ 1mm, 10.8mm max
Exhaust - 220 deg @ 1mm, 10.8mm max

1.8L 16V KR cam specs:
Intake - 218deg @ 1mm, 9.6mm max
Exhaust - 226 deg @1mm, 10.2mm max

9A pre 94 specs
Inlet - 8.8mm max

Mike "the man in the shed" from Clubgti, in a conversation i found talking of the same subject and also talking about the WUR mod, states:
"…..It's a case of making sure. Ideally you need a rolling road session to set this up properly, but it will be worth it to make sure the car is running right.

Chances are on any old car, that the fuel pressure isn't at the original factory spec any more, so it's well worth having this done.

If everything else is standard on the engine, then with the KR cam and WUR mod you should be around 160 bhp. Mine was at this spec till recently, and it's quick enough to surprise loads of flash, newer cars!!"


As someone else on the same thread wrote:
(referring to someone that was thinking of using the inlet from the KR, as the inlet for a 9a):
"………….Do you also have the exhaust cam? If you do you will get even better gains by using that as an inlet cam with the pulley chopped off."

But it's not as simple as just cutting off one end, the keyway needs machining in another place on the chain sprocket end in order for you to get it all timed up again properly. (when using the KR exhaust as the inlet for the 9a).

Also for anyone interested (that hasn't swapped cams before then here's a little guide, not by me)
http://www.clubgti.co.uk/forum/showthread.php?t=184663

So as far as i know, the ABF are best option, then the KR, but as someone said, depends what you want to achieve with it.

I'm just about to try the Exhaust mod, if i can't do it, then i'll just pop the inlet in.

All the above assumes longer duration = better performance?

paul take from it what you want.
i cant be bothered writing to you as you argue EVERY post that gets posted on the internet, ive seen you on Clubgti doing the same too.
you were useful, but now just annoying.

im glad i dont own a mk1 anymore and moved onto a corrado so i dont have to watch your comments all the time.

i think your just embarrassed as people have proof and seen gains from it, when you said it was just a myth as your too lazy to try it yourself.

i've de ticked "notify me when a reply is posted"
because i dont care what you have to write.
people can take the information and use it, so good luck to you all giving it a go.

it proves to be a worthy gain, and i'll be doing the same along with other mods during this week.

Thanks for that but I'll stick with my original advice - its a myth. The KR inlet cam is a compromise of ultimate top end power and mid-range torque, sure the exhaust cam plus vernier pulley or equivalent setup could probably post a higher top end power figure, but the mid range would suffer, so acceleration would suffer.

Too lazy to try it - maybe so? There's lots of things I've NOT done to my car, but I'm happy enough, after all I have other things to do anyhow. So I can't say the above is from personal experience, but I have read many threads on CGTI and others about it and I'm able to look at these and read between the lines, rather than take everything at face value.

Cam duration and lift; and the interaction between the exhaust cam and inlet cam (well, gas flows) is a complex area and worthy of debate. I'm quite happy to participate in that debate in an adult manner and offer my views, but if you don't want to, I can't really stop you.

I don't argue with EVERY post, just trying to demystify things…..

paul_c said

 . . . its a myth. The KR inlet cam . . . sure the exhaust cam plus vernier pulley or equivalent setup could probably post a higher top end power figure, but the mid range would suffer, so acceleration would suffer.

Cam duration and lift; and the interaction between the exhaust cam and inlet cam (well, gas flows) is a complex area and worthy of debate. I'm quite happy to participate in that debate in an adult manner and offer my views . . .

. . . just trying to demystify things…..

First and foremost, it is no myth. Second the topic is about the exhaust cam being converted into an intake cam as I understand things, so any discussion on the KR intake is irrelevant really I think. Before the question comes up as to how I know, it is because I have done the modification some years back. I no longer have the modified camshaft or the 16v for that matter, but I still have a picture or two if the modified camshaft lying around. You can debate the worth of it, that is a fact nobody can deny, as it is some work and hassle. But fact also is that it makes more power than the factory cams, either the PL, KR or 9A. That it makes its power at higher engine speeds is no downfall as all "performance" camshafts do the same thing by nature (physics) and it loses no more power in the lower engine speeds as does an aftermarket performance camshaft. Just how you determined that losing mid/lower engine speed reduces the engines ability to accelerate is a topic for another discussion, but it doesn't.

True, camshaft design and function is a complex topic and I would doubt that there are all that many "backyard" mechanics willing or able to talk camshafts. It's easy to throw a few words like duration and lift out and call it a day, but they are only two of about 15 different factors designed and machined into a camshaft. One thing is understood by most or every cam grinder or motorhead though, "the bigger the area under the curve, the more the cambers can be filled and the ability to make more power exists (torque really but we'll stay away from there). Everything being equal, if the duration is longer or the lift is higher or both in this case, the area is greater under the curve so it can make more power.

Any ill feelings between you and the other poster is just that, between the two of you and has no bearing on this response. But regardless of the hassle or cost, the modification does work and is no myth of any kind. But that word, "demystify", is another issue. I think I understand what you were trying to convey, but I don't think it is a word really? Could be wrong.

KR inlet cam vs cut down KR exhaust cam is a fair comparison to make here (see original post).

GrimyFingers said

Just how you determined that losing mid/lower engine speed reduces the engines ability to accelerate is a topic for another discussion, but it doesn't.

Acceleration is directly proportional to power. Power = torque x speed. Hence, at higher engine speeds, the engine will produce more power until the rev limit is reached, or another issue (able to deliver fuel, gas flow too turbulent, friction losses) become more significant.

So, there is no argument, power is a good thing and also there is no disagreement that max power is achieved higher up, than lower down, in the rev range.

Pretty much every aftermarket cam looks to maximise power. However the gas flow at high rpm is not the same as the gas flow at low rpm; also the nature of the flows are very different once you're at part throttle (but we'll leave that aside for simplicity). So, cam manufacturers optimise performance for high rpm, naturally leading to high power at that rpm. BUT there is a compromise, in that power at low rpm might be down a little. Notice how manufacturers have been keen to work around this, with things like variable lift, variable valve timing, etc

So, for racing on a circuit, or getting a high headline figure on a dyno run, great, use a hotter cam, make more power.

BUT

In racing from a standing start, the power at low rpm is also critical because the car must accelerate initially using low rpm (unless you have some fancy clutch). It is this critical aspect which must also be taken into account too.

And it has to be said, part-throttle and low rpm usage is 95% of driving, especially in a 16V in a Mk1! So you cannot simply ignore this in seeking a max power figure. This is why I reckon, even forgoing a lower dyno power figure or even a couple of tenths on the 1/4 mile, the original KR cam is "better".

To be totally fair, I have to say that my posting about any discussion on the KR intake was irrelevant was a bit harsh and not well said on my part. The intention was to stay away from talking intake camshafts as the original topic was asking about converting the 16v exhaust cam into an intake cam. And as you requested I did return and re-read the original post and reference to lift of the KR camshaft was made. What you stated was not all that off topic and de3660 also covered cam specs. It appeared to me that the discussion was possibly going to head in a different direction and I made a poorly written statement to try to direct things back on tract. The fact that it was in the quote I did from you was only due to a ?two birds with one stone? kind of thinking (you had both areas I was responding about). So if it bothered you all that much then forgive my jumping the gun and being a bit tactless. If you know the tale of the frog and the scorpion then you might understand, it?s just my nature. As I stated in the past, I?m not above being wrong and don?t mind saying so if I am.

Also to be totally fair and honest, the rest of your last post really makes little sense to me in relation to what you quoted me saying. Now I?m no physics major and math was not my best subject in school, but I can?t really find anything you could refer to as a ?counter? or ?in support of? to what you quoted me saying. I do get the feeling you have been reading some of Thomas Barber?s old writings though.

I also have to confess to making a boo boo in the text that you quoted. It might or might not change things, but might make having a discussion on the topic more clear and to the point if there will be one. I used the words ?mid/lower engine speed? in the quote you did when speed was not the intended word. What I wanted to say was ?power? in place of the word speed. Now if that changes things for you then fine and dandy, but if the feeling is still the same then we can discuss it further. Believe me; I love to talk/discuss cars. I am not an expert on any one automotive subject nor am I what you might call dumb in any of them either. If you want to have a discussion, and I welcome one, then please clear up what you have written. Explain a little as to just what the rest of all that is about. Everything in your last post can not be based on my poor use of a word that I made in your last quote of me.

?Power = torque X speed? ?

ok put simply:


EXHAUST KR CAM
- good top end power (good for pub talk/dyno runs)
- not optimised for lower rpm or part throttle (poor driveability)
- emissions problems due to overlap
- not a simple bolt on modification
- needs setting up properly


STOCK KR INLET CAM
- optimised as a good compromise for all areas of running (high/low rpm, part throttle too) (good driveability)
- also produces better power at low rpm than  a wild cam
- better power at low rpm is good for acceleration IF you need to accelerate from low rpm