Cam Timing Is Out By 4 Degrees On Mi16

[pete1986 2]

Iv recently had a petert stage 1 inlet cam fitted in my mi16, along with verniers and some other goodies. When my mate was doing the cam timing though, there was a bit of a mix up. What we thought were the correct figures turned out to be wrong. They were dialled in at 114 for the exhaust cam and 110 for the inlet cam, but we later found out the inlet should be 114 as well. So at the moment it is too advanced.

 

My question is, how will this affect the running of the engine?

 

The reason i ask is that it seems quite gutless in lower revs, then at about 5k it goes on a mad one! Also, sometimes it turns over very slowly when starting.

 

Thanks in advance

[Anthony 1,000]

As I understand it, advancing the inlet cam brings the power band down the rev range, giving stronger mid-range at the expense of some top-end.

[projectpug 0]

http://www.quickbrickmotorsports.com/prod_camtool.html

 

Not a bad article on how changing the timing effects power in the rev range. Anthony is right though advancing it does bring the power band down.

[petert 550]

114 is far too retarded. My cam should be installed at 109 degrees. Even at 110 deg., it should be exciting however. I would question the ability of someone to accurately time a camshaft using the lobe centre method, on an Mi16 installed in a car. It would be far more accurate (and easier) to use the lift @ TDC method. You should have 0.065" @ TDC if the cam is installed correctly. Use the same figure for the standard exhaust cam if you have verniers.

Edited January 20, 2009 by petert

[mattmk1 0]

Just a question that ive always wondered about. When fitting aftermarket cams or altering the cam timing, do you not throw the ignition timing out slightly - as rotor arm runs from cam? Could be why his car is slow turning over if it does it when warm - has knocked ignition timing too far advanced.

[jengis 0]

Just a question that ive always wondered about. When fitting aftermarket cams or altering the cam timing, do you not throw the ignition timing out slightly - as rotor arm runs from cam? Could be why his car is slow turning over if it does it when warm - has knocked ignition timing too far advanced.

I believe Mi 16's and modern ecu's use flywheel timing triggers. So therefore perhaps not the issue in this case.

 

But yes, timing should be set to the engine characteristics and as max compression will be at a different stage in the cycle. If cam timing is altered it may be wise to alter ignition accordingly to engine mods. But not the problem stated.

 

Aftermatket cams are usually ground with an OE shaft profile as a base so the drive will be at the same angle as OE for the given specs, so it's up to the builder to specify the ignition changes (in an 8v for example)

Edited January 21, 2009 by jengis

[petert 550]

I can see what mattmk1 is talking about. The distributor on an Mi16 is fixed. Therefore theoretically, if you advance/retard the inlet camshaft you are moving the relationship between the rotor button and the distributor cap. However practically, the change is minute and the spark will still jump across. In it's extreme this is called rotor phasing and can be an issue on regular distributors when aftermarket ECU's are used. For example, in an 8V distributor, if you move the initial timing position from 10 deg. BTDC to 70 deg. BTDC, the rotor button will be half way between two posts.

[pete1986 2]

Thanks for the replys everyone.

 

Petert, so if my cam is timed at 110, but should be at 109, it is retarded by 1 degree. Will advancing it by that 1 degree make much difference? ie. bringing the power band down. Or could it be that it is actually retarded by more than 1 degree due to the acuracy of the timing method used?

 

It is pretty quick as it is, but it doesnt fully get into its stride until 5k rpm then it hits the limiter before you know it. I would prefer it to kick in a little lower. Raising the rev limit could be a soultion i suppose, with the aid of your chip. A rolling road may be usefull to see what its doing.

[petert 550]

Or could it be that it is actually retarded by more than 1 degree due to the accuracy of the timing method used?

 

109 would be better, but I think it's more about the accuracy of the method being used. Consider how much dwell there is at maximum lift? Can you get back to me with the current lift @ TDC?

 

In the meantime, just advance the cam 1 degree (remember that's 2 deg. crank, so 108 LCL if you're right) and see what happens.

Edited January 21, 2009 by petert

[pete1986 2]

My friend is positive that the timings were done accuratly, it was done with the engine out of the car as well. He's a good mate of mine, i trust him.

 

What are the timings for the standard pulleys, both #3 and #4? If one has the desired timings then surely it would be better than fcuking about with verniers.

 

Another concern is that there is a tapping sound coming from the inlet cam.

[Richie-Van-GTi 70 2 Cars]

sorry for the slight hijack, whats the best way to ensure the lift at TDC is accurate when using hydraulic lifters? or is it best to switch to solids for more accurate results?

[welshpug 1,622]

Shouldn't matter if they're hydraulic or not, the cam still pushes the top surface down the same amount, even if there is no hydraulic pressure there to hold them open when you turn it over by hand

[petert 550]

#3 = 111 deg.

#4 = 107 deg.

 

The cam is ground 1 deg. advanced however. So with a #3 it will be 110.

 

Did you recondition the lifters before fitting the cam?

[pete1986 2]

So neither is of any use What about the #2 pullley?

 

The valves were re-lapped and seats were re-cut. I was told that the lifters were ok, there wasnt any tapping before all this was done...

 

If i were to get the cam timing advanced to 109, so advanced by 1 deg, will it actually make a noticable difference?