Help. Where to start Mi16 build?

When I am on a computer I can post the catcam specs sheet.

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I found them. I personally think they're a bit small for even 12.5:1 on 98. Certainly a conversation you should be having with your engine builder.
 

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Thanks.

In basic terms you mean that that cam is unlikely to open and let enough air in?

What would you recommend? A different cam, gasket, piston? There would be an option better than just throwing different fuel at it all of the time I presume...

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I think the inlet valve will close too early, creating excessive combustion pressures for 98 fuel. I would get the CR down to around 11.5:1, as an educated guess, with those cams. Without doing some dynamic compression ratio calculations, it's hard to know. Having a thin head gasket is good, as it decreases the squish distance. Excessive squish distance, caused by a thick head gasket, fitted in order to reduce the CR due to a high dome, is bad. Poor flame travel.
 
Thanks Peter. That is interesting, as the 12.5 CR is direct from Pug1off. I am checking with them why, and why we are so much higher.

"The compression we use for normal pump gas here (95-98 RON) is around 12.5:1 on this spec. If you’re using the stock 86mm crank you should find the pistons very close to this, give or take minor differences in the chamber. "
 
I'm just curious so I can work out the dynamic compression ratio for you. I doubt PEC makes rods for XU10J4R, thus most likely are RS versions which are 158mm C/C. What is the part number of the pistons?
 
Thanks!! Pec rods G00176. I am usually really good at Google, but can't find these. I can find G0017 though which is as you say 158mm. Pistons have W4256 marked on them.

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Primarily because the Dynamic CR is 9.46 and should be sub 9.3? Ideally 9.1? Do you have an example DCR calc screenshot from an optimal build?

Unfortunately I don't have any real experience to make up my own mind. I'll phone Pug1 tonight before liaising back with the builder.
 
9:1 and 98 works, provided it's tuned correctly.
 
Righto. There is agreement that 12.5+ is too high for hydraulic lifters. 12-12.4 is being recommended. And the suggested way to achieve being to take a skim off the piston crowns, rather than increasing squish area.

I appreciate the advise on here; what skim will give this CR range and a good overall setup; does this give better DCR params, and will the cam inlet problem still exist and limit timing options? My engine builder is good and I am sure he could calc and give advice, but the experience with XU10's obviously lives on this forum.

Thanks.

Cheers.
 
It has nothing to do with the hydraulic lifter, just the closing point of the intake valve and static CR. I'd be removing most of the crown, aiming for a static CR between 11.5-12:1.
 
Thanks. Only repeating the words from the parts supplier re the lifters. Cheers again.
 
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