High lift cam

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Ade
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High lift cam

Post by Ade » Sun Sep 13, 2015 10:50 pm

Hi all,


Hi all,

I was having a random mooch through the Haynes manual kindly bequeathed to me by Glasgowjim and I happened to notice some interesting info regarding cam lift specifications for all the different engine variants.

The B18FT has less valve lift than the other 1.7 litre engines and I was wondering about the possibility of fitting a N/A cam to my turbo engine to give greater valve lift.

Has anyone explored this possibility and if so what's the verdict?

Is there enough valve to piston clearance or would the piston crowns need pockets machining in (there's a good mm or so difference in the lift)?

Is there any difference in valve overlap or cam profile (ie duration etc)? I guess any advantage in cylinder filling gained by greater lift could easily be counteracted if the overlap and duration were not optimised for a forced induction application.

Would they even be mechanically interchangeable? ie journal diameter and spacing.

I would certainly like to experiment with this as I have another timing belt change on the horizon (ideal playtime!) and having driven the car in relatively standard form for so long I find my myself yearning for a little more power. On that note, anyone got an orange richmod/robou for sale!

Any thoughts greatly appreciated.
O.C. 480 D.

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doingitsideways
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Re: High lift cam

Post by doingitsideways » Mon Sep 14, 2015 9:13 am

Yeah, it's been done and apparently works well.

I have N/A cams in my T5 and they really help the off boost torque, but the overlap can be dialled out due to being a twin cam.
No real gains in overall power, but a good mod if you have a massive turbo, as it makes it a lot more driveable off boost.

I'm going to fit one to my turbo when I get around to it and see how it goes.
"If you can't fix it with a hammer, it's an electrical fault!"
Hammers can't fix a 480!!!

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glasgowjim
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Re: High lift cam

Post by glasgowjim » Mon Sep 14, 2015 9:19 pm

"bequeathed to me by glasgowjim"

I aint dead yet :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

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doingitsideways
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Re: High lift cam

Post by doingitsideways » Mon Sep 14, 2015 9:33 pm

glasgowjim wrote:"bequeathed to me by glasgowjim"

I aint dead yet :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:
You sure about that?

My inbox begs to differ! :lol:
"If you can't fix it with a hammer, it's an electrical fault!"
Hammers can't fix a 480!!!

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Slash01
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Re: High lift cam

Post by Slash01 » Wed Sep 16, 2015 10:32 am

Apparently the B18E N/A cam is the best however where i remember seeing that info (renault forum) neglected to state which B18E. Could be the B18E itself (early 440 1.7 carb) or the B18EP but again the cams were apparently changed after the catalyser introduction to lesson the power drop. So you have a choice of 3 lol.
There are always ample warnings and there are always subtle signs,
And you would have seen them coming but we gave you too much time.

Robou
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Re: High lift cam

Post by Robou » Wed Sep 16, 2015 10:05 pm

There is no choice at all. NA and Turbo cams are not interchangeable by design, if it were only because of the overlap.
Too old to bother
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Slash01
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Re: High lift cam

Post by Slash01 » Thu Sep 17, 2015 9:52 am

I'm sure i've read that renault guys have swapped the cams from n/a B18's into the turbo's. I've also read that the F3P cam is a good one from the Clio RSI. Don't shoot the messenger pmsl
There are always ample warnings and there are always subtle signs,
And you would have seen them coming but we gave you too much time.

Robou
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Re: High lift cam

Post by Robou » Thu Sep 17, 2015 7:07 pm

I should have been a little more precise: Mechanically the shafts can be swapped. There are lots of guys outside doing stupid things and even making them public, in doing so giving proof of their stupidity. But what is always missing is the glorious end. Only vague remarks remain, because, let us be honest, nobody likes to admit the failure after all the trouble been invested.

And about the clever remark of "doingitsideways" concerning the twin cams: If you manipulate the timing of both camshafts in order to minimize the overlap, that is a good thing. Anyway, you understand the problem. But then what happens? Breathing is out of order as well as injection timing and ignition timing. Detecting an off turbo increase of torque is a coïncidence, anyway not something we are all after, in contrary.
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doingitsideways
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Re: High lift cam

Post by doingitsideways » Thu Sep 17, 2015 9:10 pm

I was more illustrating the point that it works on a twin cam engine, as the overlap can be dialled out.
The N/A cam mod is quite popular in T5s, as the duration is NEARLY the same, but lift is quite a lot higher.
I'm still experimenting with mine, but so far 2° retard of each cam seems to work really well.
Probably worth adding though that I have a fairly heavily modified cylinder head.

All this is relative anyway, as the single cam in a B18FT cannot be adjusted.
"If you can't fix it with a hammer, it's an electrical fault!"
Hammers can't fix a 480!!!

Ade
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Re: High lift cam

Post by Ade » Fri Sep 18, 2015 5:09 pm

So......

It's been done but there seem to be mixed views on the value of carrying out such a modification!

What robou says about overlap is what I was kind of concerned about. A turbocharged engine and NA equivalent will have very different overlap requirements (turbo requiring less as there is a compressor helping to fill the cylinder so there is limited value in using exhaust gas inertia to scavenge/fill the cylinder, potentially too much overlap could shove good mixture out the exhaust port having a detrimental effect!)

Has anyone actually got first hand experience of a B18ft with a NA cam? Do you gain back what you lose from the extra overlap in lift? Guess its not ideal though if there's a big difference in overlap between the two shafts.

Robou....

On the subject of the twin cam T5, when you say the ignition timing would be affected by altering the cam timing, could you clarify for me please. Does the T5 take its ignition input data from the cam and not the crank or do you mean simply that the stock ignition timing would not necessarily be ideally suited to a variation in valve timing?

As regards injection timing, it is my understanding that with port injection, the timing of the injection is not particularly critical. There have been a myriad of different things tried over the years, including timed, continuous and 'semi continuous'.

I believe Marelli-Weber developed a sequential timed port injection system but found no practical difference in power or driveability, only a small improvement in emissions and fuel economy. This system was used on the ford cosworths among other things.

Our bosch LH2.2 falls into the category of 'semi continuous'. I believe the ignition signal is used as a trigger for the injection, which, when the system was in the developmental stage, opened all the injectors at once, once every revolution of the crank. The bosch engineers found that this led to issues with latent fuel in the ports and so changed the system to deliver half the fuel every half revolution of the crank. In practice this resembles continuous injection and it is certainly not accurately timed to coincide with inlet valve opening etc. but is nevertheless more than satisfactory.

Purely out of academic interest, what is the nature of the injection system on the T5, does anyone know what system it is?

By the way, I'm basing my information about the jetronic on an old book I have, (a history of automotive fuel injection) but if anyone knows better from ACTUAL experience (with scopes etc) then please do correct me if I'm wrong!
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Slash01
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Re: High lift cam

Post by Slash01 » Fri Sep 18, 2015 6:45 pm

As I say from what I've read on the Renault forums the n/a swap is a workable option. With regards to the efficiency of it is rarely talked about.

Would reprofilling the shaft to reduce the overlap and adjust the duration but keep the lift be a workable solution?
There are always ample warnings and there are always subtle signs,
And you would have seen them coming but we gave you too much time.

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: High lift cam

Post by Ade » Fri Sep 18, 2015 11:11 pm

If one were to get into having the shaft reground then it would be more practicable to have the turbo shaft done. You would lose too much material if you were to try and alter the overlap as this is defined by the angular difference between the high point on the exhaust and inlet cam for each cylinder. For instance, if you wanted to decrease the overlap by 5 degrees then you will end up with a lift that is no greater than the point on one of the lobes which is 5 degrees around from the point of maximum lift. Hence you would inevitably lose some of the lift in reducing the overlap.

Counterintuitive as it may seem, it is possible to increase the lift of a camshaft by removing material......

You leave the ramp and lift parts of the profile more or less untouched and remove material from the dwell side of the profile then re shim the valve clearances accordingly when refitting the shaft. If you remove, for arguments sake, 20 thou from the radius of the dwell and then re shim accordingly, then you have achieved 20 thou more valve lift. Of course this means specialist regrinding of the shaft and undoubtedly custom shims as they would have to be quite a bit thicker than any standard item availble for tuning the working clearance. Of course having the turbo shaft reworked in this way means that you maintain your basic valve timing and overlap and simply add lift and in reality this would be the truly 'engineered' solution, not a compromise that sort of works! Interesting that so many renault people seem to have success with this given the fundamental differences. I would be very interested in the actual differences as measured between the different shafts. Does anyone have spare (worn/damaged even) examples of the shafts that they would let go for a reasonable price. We have a wonderful metrology department at work am I would be able to get some actual dimensions and data to give some substance to this subject!
O.C. 480 D.

Robou
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Re: High lift cam

Post by Robou » Sun Sep 20, 2015 8:42 pm

@Ade
I was merely reacting on twin cams, not on T5 especially, I do not even know what that is. Also I did not mean to claim the ignition timing was affected by altering the cam timing, because ours is a flywheel sensor, but that it is not correct anymore because of the different breathing.

And about injection timing, it indeed does not make much difference whether is of the batch type, like ours, or timed as far as engine output is concerned. Timed is more or less introduced because of emission laws, EPA cycle testing and it was easy to imply with modern electronics. But at changed valve timing it "could" happen that at some cylinder the injection is too early.

Another point to consider is that valve timing is measured on the cams, not in real life where closing highly depends on the valve springs. With higher lift the closing time, especially at high revs, increases the overlap.

In contrary to what you believe, I believe that our Jetronic only at starting, and depending on engine temperature, revs and number of revs, performs a double injection.

But all this is very complicated with too many dependencies. I better leave this discussion with a well meant: Hands off.
Too old to bother
480 Turbo midst '91

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