0.2 Skimmed Off Head Cr Increase?

[speedtripledan]

In building a new engine up Silvertop 2.0l zetec i,ve had to have the head skimmed at which point they had to take 0.20mm off. would this have any real effect on cr ? if so how would you work it out.

In the build i have also added new fz2002 kent cams which should be good for another 20bhp, what i,m trying to do is figure out the best map for my nodiz as it seem to "pink" at lower rpm when trying to accelerate in 5th for instance at 2000rpm higher up the rev range it goes like shat off a greased stick! Is pinking to much advance or not enough

 

Would going up a heat grade on the standard plugs be of any benefit? the engine was dyno'd at 175bhp before the head skim and cams addition so way over what ford originally put out in the mondeo.

 

cheers

[tractor]

pinking it to much advance so valves doing a little jig

[Guest chris brown]

Pinking is to much advance. Don't let it pink or you could end up with a hole in a piston

 

Must type quicker

Edited February 27, 2016 by chris brown

[Shaft]

compression ratio is worked out from the volume of the cylinder (for this example we're omitting the volume of the combustion chamber in the head)

 

Work out the cylinder volume of one cylinder at BDC then again at TDC (Calculate from bore Ø x stroke) the difference calculates to the compression ratio.

Work out again but subtract the 0.2mm from the stroke. this will then show you the difference.

[Guest 2b cruising]

Hi Dan.

0.2mm is not enough to bother about with compression ratio.

Pinking actually starts well before you can hear it by human ear so you are out more than you might think.

It is also one of the easiest ways to burn a piston out.

It is caused by to much advanced ignition.

Without a rolling road and if you have no settings for your new cam, back off your advance until you can no longer hear it, then one or two degrees more.

Until you can get it sorted properly on an RR, it is better to be safe than sorry.

To many things for an amateur, (no criticism intended so I hope no insult taken), things like fuelling, cam timing, octagon levels ect ect ect need to be taken into consideration for an untrained racing engineer to get right. Even they prefer RR these days.

Better saving up for a session on RR than spending money on bling.

If you can't get it done before Scotland, take the safe way out. Unless manifold starts glowing red or lots of backfiring through exhaust, you have not got to much retardation to do any damage.

All the best mate and enjoy completing the tour this year.

Regards, Ken

 

Must type much much quicker.

Edited February 27, 2016 by 2b cruising

[Guest 2b cruising]

Taking metal from cylinder head will not make any difference to swept volume.

Combustion chambers on modern petrol engines are not the same shape as the cylinder bores so cc of chamber before and after regrind needed to work out comp ratio.

Snapper Paul is good with this formula.

Forgotten all my engine testing formulae as never used since leaving college.

Once exams were over forgot all about that kind of things. Doh. How come sense comes so late in life.

Edited February 27, 2016 by 2b cruising

[Longboarder]

I agree 0.2mm (8thou for us English) should have so little effect on CR you do not need to consider it. Apart from new cams have you done anything else to the engine? Where did the Nodiz map you're running come from? Have you made any changes to porting, exhaust, inlets or the carburation?

What parameters is the Nodiz reading? Revs of course, TPS or MAP for load and engine temp?

I would agree pinking demands you reduce the ignition advance. On mine I only get 22^o at 2000 rpm, 17 at 1600 and 12 at 1200. Max at full load 31 above 3200.

 

What is engine temp doing while this is all going on? Does it get hotter than it used to? Might point to running weaker due to the improved breathing of the engine.

 

Nigel

[Guest lotusPaul]

175bhp..what's the current specs of the engine including induction and exhaust?

[speedtripledan]

The spec at the time was 45 webers and a bespoke exhaust made by Martin keenan. That figure was from torquetune Ollerton 146bhp at the wheel using the standard 20% loss equates to 175bhp, it made more with bigger chokes but was very lumpy in the mid range.

[speedtripledan]

remapped the engine today and it is much improved, still needs fine tuning on a dyno but good enough for now

[Guest lotusPaul]

DanE

 

have you checked coil bind on the valve springs. Memory tells me that standard springs bind at about 10 to 10.5mm. Your lift on the FZ2002's should be a little over 11mm.