adjusting cam timing for higher rpm?
Turbo Mini Forums

Just about to rip the engine out of the mini to find an oil leak before avon and figured i might aswell have a tinker while its out.

I'm currently running a ph2 cam and a 6.5k rev limit, plan is to up the limit to 8k but will i need to or see any benefit from tweaking the cam timing to suit? Ideally i'd like a custom cam but i aint got a fooking clue where to start with that one.

I'm thinking of retarding the timing to 103 instead of 108 or have i got it arse backwards?

the whole reason behind wanting to try 8k rpm is because the GT20 is showing no signs of dropping off at 6.5k rpm.

how she looks currently..

I'm also interested in this

If something is worth doing, it's worth doing half of.

Advancing the cam usually brings the power band in eariler.

Edited by Vegard on 10th May, 2010.

aaaah i got it back to front then....worth a try 5 degrees advanced then? or just stick as it is and up the limiter?

i would leave it as it is, my experiemtning with cam timing showed optimising for higher RPM flow REALLY hurt spool times, and from that graph, your spool times are awefull already! obviously totally different engines but sure it will apply! i would shoot for your 8k goal and see how it rolls, if it tapers off after 7500, then you will have a nicer torque curve anyways and 500rpm less stress on the engine :)

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

advancing the cam timing moves the power band DOWN the rev range ,eg an inlet at 110 moved to 106 atdc pk lift is advanced 4 degrees .
mowogs example is actually retarded 2 degrees in going from 108 to 110.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Nic, time the cam in at 112 deg use a 2 deg offset key from minispares

did you time the cam in at 108 at first? if so the chain will have streatched making you at 110 so the 2 deg key will sort it. to 112deg

that will get you to where you need to be!

that how i get my top speeds as my cams in at 114 deg with the 13s and 2.95 final drive

Funnily enough, I measured what the cam was timed in at in MOT. Not a slouch that either

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I was always under the impression that, where cam timing is concerned, advancing the cam meant moving the timing to a lesser number, and retarding, moving it to a higher number?

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So i did read it right? lol, Cam timing is complex enough with fixed lobes never mind two seperate cams

Edited by Sprocket on 10th May, 2010.

remember the inlet cam that we time is timed ATDC,

think of it as a linear event, the exhaust opens, then closes (nearly) the piston comes to tdc then the let opens, if the inlet is say 110 deg after TDC timing it to 100deg ATDC will mean it opens 10deg sooner.

and just to confuse matters....

the reverse is true of the exhaust cam lol

yeah it's always been timed at 108 degree's on the nose, i will double check it on wednesday when i get chance to lift it out as it's all disconnected ready to go now.

already have vernier gears fitted so adjusting without keys isn't an issue.

cheers for the advice and info so far guys, will think it all over and decide when it's out i guess.

On 10th May, 2010 Sprocket said:
So i did read it right? lol, Cam timing is complex enough with fixed lobes never mind two seperate cams

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I don't think your cam timing will sort your revs,
are you using the bog std mety turbo manifold?

If so you'll have big troubles to pass the 190, it's simply restric too much your exhaust.

I would let my cam timed at 110 to help on spool. It'll make so little difference to retard this cam if your working on your exhaust (exhaust valve, port, manifold).

Which are yours?


last note: if your engine hasn't been rebuilt since your first build, you'll certain end in a big kiss by going trhu 7000 on std pistons/rod/crank at this level of power and without frquent freshing. by opening it you should already find toasted bearings at copper stage on the piston load side, making already your pistons misaligned to your crank. I would fresh it up and would invest in light pistons/rods (like acralites / sccomponents)

fabrice

good power, what boost is that on?

Team Racing

From a turbo point of view I think the cam has less effect on rpm limitations compared to head and turbo spec.

The PH2 should be ok for 8k, and looking at the GT2056 map upto 240bhp at 20psi is well within its high efficiency region.

So why is your power dropping off at 6.5k?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

the thin lines the torque, power keeps going all the way to the limiter. i think it was just levelling rather than dropping, will know for sure when it goes to the rollers again i guess with a higher limit.

Fab, the bottom end has done over 30k (block, pistons, rods etc) the shells and thrusts have all been checked over and replaced as necassary regularly. Last time they were checked was about 400 miles ago when i fitted the the GT20. It's highly likely that it might grenade itself, but i just want to see how far i can push a fairly stock motor tbh. the rings/bores are getting a bit loose now and blow by is increasing so just want to give it some treatment this season and rebuild over the winter with lightened internals.

Spec is std metro manifold with jimsters T2 adapter plate to allow the GT20 to fit, home made elbow/diwnpipe, 31mm stainless exhausts in a well modded mspd head.

i'm planning on checking the cam timing to make sure it's still right and leaving at 108 now then and just see how it goes on the rollers/quarter at the higher limit. Not hoping to set any records or anything like that just want to see what it'll do in a full fat road car.

I would port/change that exhaust manifold, as said it's definitely restricting power at the 190 marks.
Your cam exhaust valve/port turbo turbine flow are ok ( as Steve said, you'll certainly find it now at 110°, because of stretching) exhaust valve , port, and turbo have the right flow,but your manifold is now not large enough to let that much flow outing.
A good test is to reduce your boost to 15/16 psi and see if your power will continu to climb up to 7500/8000,you should end in the same power level,but gain in rpms.
Then at this level anything messed regarding ign timing /a/f ration is 10 % lost at least , Harry's found in playing with timing that the best power was at 30°/31° max advance, anything above and you loose power/torque.