Engine Work Ready For Later Upgrades, Decked, Valve Pockets?

[benny205mi16 19 1 Cars]

Hello,

 

I am getting ready to take my engine (1.9 MI16 alloy block) to Gardias engine services for some work to be carried out,

The block decked by 0.4mm to increase the compression, the flywheel and crank balanced and also the valve pockets in the top of the pistons deepened.

 

But here is my problem I have not done any of these mods before so I am in new territory, I have searched and found out that 0.4mm is the best for the compression on these engines, and due to funds I am going to have the pistons done for the valves but at first run standard cams but with the future plan of cams and throttle bodies.

 

My questions are, will the engine run ok with a decked block but other than that a standard setup?

and when I rang up for a chat with Paul Gardias he said I would need to tell him how much extra I wanted taking off the piston valve pockets,

So from this I assume I will have to decide the final spec of my engine, as in which cams, and then I can work out the depth needed, can anybody help me with working this out or point me in the direction of any help?

 

Thank you for any help, I am lost a bit.

Ben

[welshpug 1,621]

You need to work out what cams will work on standard sp

rings, then see what lift they have @tdc, then how much space you need, then how much meat there is in the crown.

 

I'd be looking newman piper or kent.

Edited October 6, 2012 by welshpug

[Henry Yorke 269 3 Cars]

I might be being dumb here, but compression is based on the capacity in the cylinder head squish zone volumetrics. If you deck the block you reduce the capacity and increase compression. If you pocket the pistons you increase the capacity and decrease the compression. One will offset the other to an extent. If volume from pocketing = volume removed by decking then there would be no impact overall. However I suspect that pocketing would be less than decking anyway.

 

I am guessing you would benefit from a pair of vernier pulleys too to compensate for the decking. This will give you a better chance of being able to run it on standard management too, plus you will probably need them for your new cams anyway.

[petert 549]

Ironically, the number you need to know is 205. That is total distance the inlet valve clearance in thousands of inches for a standard DC6 or DFW engine. You can convert to metric if you want, but it's easier for me in inches. From that you deduct the lift @ TDC for the cam, the result being the theoretical valve-piston clearance.

 

A standard Mi16 has 0.032" lift @ TDC with a #2 pulley.

 

eg

0.205" - 0.032" = 0.173" (which is heaps of clearance)

 

For my Stage II regrind:

0.205" - 0.105" = 0.100" (that is acceptable, but very close to the 0.090" limit)

 

If you deck the block it become more complex. A 0.4mm (0.015") skim would not bring the valves exactly that much closer, as the valves are inclined. However for safety, use the full amount.

 

 

For my Stage II regrind:

0.205" - 0.105" - 0.015" = 0.085" (that is unacceptable, being under to the 0.090" limit)

 

What is the 0.090" limit you should ask? The generally acceptable limit for a hydraulic lifter is 0.080". However, that's actual, not theoretical. The valve is closer to the piston after TDC. The amount must be determined during a dummy build. However, for what you're doing, allow 0.010". Thus 0.090" at TDC is equal to approx. 0.080" at 6 deg after TDC.

 

Taking 0.4mm off the block nets approx 10.8:1. It's no use choosing a huge cam for that much compression anyway. Cams that would suit that much CR would have somewhere between 0.060" to 0.120" lift at TDC. Choosing the worst:

 

0.205 - 0.120 - 0.015 = 0.070" (0.020" under)

 

This means you need to take a 0.020" (0.5mm) from the inlet pockets. I'd take 0.030".

 

You'll loose some CR deepening the pockets, so you'll end up with probably 10.6:1 anyway. Talk to Paul, he knows his stuff and will probably suggest taking a bit more than 0.4mm, meaning the pistons will sit proud of the deck at TDC.

 

The new engine will run fine on the standard cams.

 

I wouldn't buy Kent, Piper or Newmans.

Edited October 6, 2012 by petert

[welshpug 1,621]

I wouldn't buy Kent, Piper or Newmans

 

I guess not, being the other side of the world, and making your own cams

[benny205mi16 19 1 Cars]

Thank you Petert,

You have been more than helpful,

I was intending in contacting you about some cams at a later date.

I'll build with the intension of fitting one of your cams later, so I'll work out the clearance with your measurements, which cam of yours would you reccomend I put with throttle bodies?