Cam timeing over advance? symtoms or problems?
Turbo Mini Forums

can anything actually bad happen from over advancing your cam?
i added a few decrease when i had my box off to swap the FD but i also changed from unleaded to ethanol
i felt the car had plenty of top end but was lacking in the low non boost rpm so i swapped the FD for earlier boost and also added about 3-4 degrees to the timing for a bit more low end grunt

now its done that just fine and the results are good but i was thinking maby its got a side affect? it cranks 210 psi on a hot compression test and 1 bar boost it seams fine but can this much cylinder pressure be hurting things? there is no sine of det due to the fuel im thinking mor on the lines of burning up things valves seats pistions turbine wheels surely the early timeing puts more heat into the engine rather tha dumping ot in the exhaust

A few degrees swing on the cam timing on the old A series wouldn't normally make any difference, unless of course you are using a scatter cam. That is getting back to the basics of the Siamese port problem where two cylinders perform slightly better than the other two. Swing the timing one way one pair of cylinders perform slightly better while the others slightly poorer, the net result is the same. Swing the timing the other way, and the same thing happens. Obviously it depends on how much you advance and retard before it really does start to make a noticeable difference, for better or worse, I wouldn't know.

what cam are you running ?

274 or 247 what ever is it the Kent brand one i allways mix the numbers up cbf looking atm its in at about 107 not 112 so 5 advanced read on the crank..

the first time i had it in at 112 with an (old) duplex chain that had been ran for about 3 years as a semi daily so i figured any "stretch" had already happened and id just go with straight up timing like i say this worked but it was a bit gutless down low combined with the old metro T3 and 2.9 FD on 98 octain it cranked over at about 195-200 psi with a stock 202 head

i changed probably to Manny things at once to really get down to it but any ways

its now in at 107 degree with a brand new IWIS duplex chain set 3.1 FD between E100 and E85 fuel depending on whats around sometimes form the pump some times from the barrel new head with more compression now cranks 220 PSI hot valves seats bowls lost of stuff different on the head n intake main

so its not a matter of how the cars come across more low end grunt but a question of is it potentially hurting something

im mostly thinking about the cylinder pressure and heat thats being held in the cylinders its 11.75 CR and 15 psi ive not had any problems yet but most guys i speak to say its a waiting game my self im probaly gonna just run it as its real nice to drive donno what the power is but its going to the dyno in a month or so once i get closer to getting my license back...

supposedly on Ethanol your fairly safe if you stay below 25:1 for a dynamic CR and im at a little over 21:1 when on 15 psi

A few degrees either way will trade top end and bottom end torque. The quoted timing figure is what the can manufacturer felt was the balance for their test engine. Many of us are using NA cams on turbo engines, so IMO you should only consider the quoted timing figure as a starting point. Swapping a some top end for more torque lower down makes perfect sense in a road going turbo engine - something I plan to test on my setup.

You seemed to say you advanced the cam and got more torque lower down, but I was sure it should be the other way around. Anyone confirm which way it is?

If the lower part of the torque curve (the area you improved) is nowhere near as torqey as the peak torque, IMO, I doubt you have anything to worry about. Detonation is (largely) down to cylinder pressure, but if the torque is relatively low at that point, then so must be the pressure. If you've lost torque higher up, the VE has gone down in that region, so less air going in, less chance of detonation, I'd imagine.

Edited by PhilR on 25th Feb, 2016.

im not really that knowagible on the stuff i just wing it really but at the currtent setup it feels like a much bigger cc engine as it dosent take much if any gas or rpm to get it off the line and the top ends seems to flatten of a bit but its not really a screamer as the cam is advertised to run out at 6k and to be fair its a 1098 crank if it should last imo best kepped around the 5k for regular shifting... that last crank near broke in two from shifting at about 7.5k every shift for 3 years.. id well i think but that was na

any way off the point

so if the change from 112 to 107 is really not a huge jump than i think im fine with it as my impressions on ethanol are amazing its really hard to make the engine ping ive swung the timing a bunch each way just to see what would happen and it really dosent care much besides a slight loss in "by the seat of my pants" power ive only been messing around myself and i know crap all about tuning besides loud matalic knocking is bad

but i guess the next thing is to stop fooling around and see what the professionals say and what it puts down in black and white for numbers.. it sure feels fast to me i regrett not fitting an ATB form quafe

maby its the added cylender pressure or the head flowing better at low air speeds maby its the fuel maby the cam in at 107 not 112 or a combination of them all

id like to get an EGT in there to see what that is but id think if its anything like the ice cold carb and intake than its at a safe number the carb and mani nearly allways have condensation on them and feel really cold evan at idle just the volume and type of fuel evaporating i guess i need to get out and take some pics and update my build log havent done that since the loss of license

Ethanol has a crazy high knock rating. I wouldn't risk listening for knock with just your ears though. Detonation can be happening before you hear it. Best get some det-cans or sensor on there. Are you planning to get it set up on a rolling road?

Edit that, I'm not thinking straight lol.

I would have gone the other way to 115 degrees

Edited by Sprocket on 25th Feb, 2016.

yeah it will be set up on the rollers i have just been playing really

the way i think about cam timeing is the crank is staying where it is and the valve event is being moved so it hapens a bit before or after the piston is at tdc ie full valve open at say 112 vs 107 meaning the valve is actualy opening sooner and of cause closeing sooner so with it closeing sooner its farther down the bore as the pistion come up makeing more cylender pressure

pulling cam timeing i thought was to make the valve hang open longer so the valve stays open till the piston is up the cylender more before it closed

looking at the way the valves open and close shows that most of the "filling" of the cylender happens as the pistion is on its way up! so it makes sence that a screammer needs that valve to stay open a bit longer and a low rpm unit to closer ealyer as the air is just moveing slower so its not got the sepped to continue filling the cylender as the pistion is tyring to push it back out
when the valve opens it takes a while for the air to actualy start moveing

this is all just my understanding so dont know if its how it really works or what but yeah wanted to say

Yeah, that makes sense. I had it backwards.

So, if you advance the cam, the inlet closes sooner after BDC and your dynamic compression figure will be higher. If this helps low rpm VE at the cost of high rpm VE, I can't see that you'll do any harm despite the increased dynamic CR. Does that sound right?

You're running Megasquirt? You could autotune and save the VE table with the current cam timing, then retune with different cam timings. The changes in VE tables should give a good indication where you lose and gain torque. Assuming your peak VE goes down, I'd guess you'll be safe.