Mi16 Unswept Clearance Calculations

[Batfink 201]

Does anyone know the distance between the piston at TDC and the top of the cylinder on the alloy mi16?.

and also the thickness of a standard mi16 headgasket when compressed

Edited January 28, 2008 by Batfink

[ginjaspeed 0]

Off the top of my head i belive this distance is 0, but remember to include the volume of the piston cutouts in the calculation.

[B1ack_Mi16 67]

Let me see.. I have this data in an excel file somwhere

 

Block height: 224.5mm

Crank radius: 44mm

Rod length: 143mm

 

Piston pin height:

D6C: 37.1mm

DFW: 36.2mm

 

Distance without headgasket:

224.5 - 44 - 143 - 37.1 = 0.4mm + HG thickness for D6C

 

224.5 - 44 - 143 - 36.2 = 1.3mm + HG thickness for DFW.

 

I guess you're most likely to have the D6C in UK.

 

HG thickness I'm a little unsure about, I've always just used 1.3mm when calculating compression etc.

 

EDIT: Sorry, I was thinking about distance from piston top @TDC to the head-surface. So then the 0.4mm and 1.3mm are correct values, and just don't include HG thickness..

Edited January 28, 2008 by B1ack_Mi16

[Batfink 201]

well i've worked backwards on a standard mi16 head

 

swept volume (476.1233 cc) / compression ratio -1 (9.4) to get 50.652cc

minus the Mi16 head capacity (40cc) i have 10,652cc for the headgasket, bore clearance and piston cutouts

 

 

Now using this data I have worked out that my current idea for engine spec will give 9.8:1 compression which is a little on the low side, but I could do with seeing what the effects of fitting thinner gaskets would be

[Batfink 201]

woo! piston top to head surface is 2.164cc so only 8.49cc unaccounted for

[DrSarty 90 1 Cars]

If your liner protrusion is good Kev, you can always play with various thicknesses of copper head gasket.

[Batfink 201]

that would be the plan though a standard gasket will be too thick. Basically if I know the standard gasket thickness I can start to work out what the compression would be with a thinner one. I know PeterT does a large range of thicknesses as I found an old thread in the search.

[petert 591]

Whilst I can supply copper gaskets, it's better for UK customers to buy direct from the manufacturer. That way you only pay for shipping once.

 

www.ridgecrest.com.au

 

Ask for the 405 gasket. You'll need to specify the bore. For an 83mm piston you need an 83.50mm bore. The price has risen in recent months due to the China demand.

 

Be warned however, your liner protrusion needs to be good, preferably 0.004-0.005". This can only be verified without liner seals.

 

The other alternative is to skim your block and liners to obtain the desired compression height.

[Batfink 201]

Peter thanks for the info

 

can you tell me the standard gasket thickness

[petert 591]

0.5, 0.7, 1.0 and 2.0mm from memory. Perhaps also a 1.4mm.

[James_R 3]

I think a std copmpressed gasket is 1.2mm

 

QEP deck blocks so you can set your piston protrusion, if you're planning to run std pistons then 11.0:1-11.2:1 is your limit without putting big holes in them.

 

Or go forges then you can spec what you want, TDC valve clearance is another big consideration if you're planning proper cams

[Batfink 201]

what if it was on its factory gasket? I'm not sure how I can work out the affects of fitting a different gasket without knowing the original unless someone knows the cc values for the piston cutouts.

 

Would that information be in the 405 haynes manual?

[Batfink 201]

I think a std copmpressed gasket is 1.2mm

 

QEP deck blocks so you can set your piston protrusion, if you're planning to run std pistons then 11.0:1-11.2:1 is your limit without putting big holes in them.

 

Or go forges then you can spec what you want, TDC valve clearance is another big consideration if you're planning proper cams

 

Cheers James

 

To start I will just use standard parts, maybe a mild upgrade on the cam but nothing too serious to start. Does fitting a lairy cam affect compression or is it solely about valve clearance?

[James_R 3]

more overlap = less dynamic compression

 

planning to use a 6 head kev? better flow, better exhust mani, no surge, perfect ifyou're going the bodies and management route.

 

 

that on a Mi bottom end will knock up things as the chamber is 4cc smaller and you can fit 109 cams in straight off the bat, should see 200+ then no problem.

 

I think I've seen 2cc's per piston mentioned for valve cut outs on Mi's std. Also you have to consider the deck/piston hieght and again you can spec this with matt if you deck the block, also allowing you to set liner protsusion so you can keep the std h/g at £10 a pop easier and more longevity than the copper ones if you're starting from scratch that is.

[petert 591]

My standard performance rebuild is to skim 1.4mm off the block/liners to obtain zero deck height. This gives 10.8:1 with a standard head gasket and allows up to approx. 0.100" lift at TDC on the intake cam (allowing for 0.080" valve to piston clearance) without having to machine the valve pockets in the pistons. I can fit my Stage I regrind easily but the Stage II needs to be measured carefully to avoid valve-piston contact.

 

The decrease in squish height makes a very crisp engine!

 

Hope that helps.

Edited January 29, 2008 by petert

[DrSarty 90 1 Cars]

LOL: Poor old Kev. His brain must be going scatty.

 

He only phoned the other day to say how happy he was that his 205 had moved again; albeit just an empty rolling shell, with no brakes either being pushed out of his garage.

Edited January 29, 2008 by DrSarty

[Batfink 201]

i made engine noises though as I pushed!

[James_R 3]

Peter thats on the lower CR cat verions engine you're talking about the 1.4mm though ??

 

James

[Batfink 201]

so you would only deck it 0.4mm

[Batfink 201]

well without knowing whether the valves will have enough clearance if I fit a 0.5mm gasket and deck the block that will give 10.8:1 compression

If I just use a thinner gasket then 10.4:1 compression

[petert 591]

Peter thats on the lower CR cat verions engine you're talking about the 1.4mm though ??

 

James

 

Yes, sorry, 1.4mm for a DFZ, I should have said that. But as said, you'd deck 0.4mm on a D6C to give zero deck height and 10.8:1.

 

You can safely use a 0.7mm gasket on a D6C, which would give approx. 11:1.

[DrSarty 90 1 Cars]

You can safely use a 0.7mm gasket on a D6C, which would give approx. 11:1.

 

This is what I had from Pete, and it was 'kin awesome in conjunction with his cam. However, my Cu gasket eventually blew as a result of me not carefully checking my liner protrusion was ok.

 

If you do go for a Cu head gasket Kev, I still have a large tin of the copper adhesive spray you use to fit it, so don't waste your money.

 

(P.S. & mini thread hijack - Mattsav, PeteT or anyone; what's my CR gonna shape up to be in comparison please?)

[Batfink 201]

well my sum's were wrong lol and my compression calculations were 1 point too high. Without custom pistons you are looking at 9.8:1 which is rubbish

 

So i need to look at different heads. James suggests the Xu7 (the gti-6 has smaller head volume than the mi16 but I think the valves and ports will be too big)

 

more bloody sums lol

[James_R 3]

Xu7 has smaller ports different to the GTi-6 (RS) head which has larger ports and smaller valves, both have a 36cc chamber volume though.

 

[petert 591]

So i need to look at different heads.

 

What exactly are you trying to achieve?