Xu10 16v Part Swapping, Notably Heads And Bottom Ends.

[welshpug 1,657]

I've been looking at my collection of XU10 engine parts, namely a gti6 bottom end complete, as well as the top end inc 10 bent valves (hence avatar) a set of 2.0 Mi16 pistons and rods, and some Newmans cams.

 

Some quick measurements with a dial gauge showed that there is next to bugger all room in the standard J4RS piston for any worthwhile camshaft upgrades, but I remembered that I had a set of Mi16 rods and pistons about and that they have a deeper cutout and a flat topped piston.

 

This combination with the gti6 head gave something roughly like 4.9mm valve clearance plenty for some half decent cams, and what is a slightly higher than standard compression ratio if I'm not mistaken

 

now I can't seem to fathom what I've missed going through my workings out and what data I can find on both engines.

 

RFY engine;

 

40cc head combustion chamber,

 

10.4-1 compression ratio

 

1.20 mm gasket.

 

RFS engine;

 

37.2cc head chamber volume.

 

10.8-1 compression ratio.

 

1.20 mm gasket.

 

I've worked out that the RFY piston + rod with a RFS head would give somewhere in the region of 10.9-1 compression unskimmed, and low 11's -1 skimmed to 36cc from 37.2cc.

 

I do realise that they dont come flush to deck like the gti6 piston, but are flat topped, but I have heard that this allows the use of an 88mm crank to push the capacity up to 2044cc, that'll still have a fair amount of space @ TDC for some nice cams over the RFS piston if I'm not mistaken?

Edited May 15, 2009 by welshpug

[petert 586]

Sounds right to me.

[welshpug 1,657]

Thanks Peter!

 

going off the basic data above I worked out the RFS dish to be 6.64cc, and the RFY to be 5.99cc (not dished but has cutouts and sits below deck)

 

I found some information just now in a topic on here;

 

Block height = 234.8mm (At least we found it to be that when measuring)

Rodlength Xu10J4 = 152mm

Piston Compression height = 39,1mm

Half the stroke 86/2 = 43mm

234.8 - 152 - 39.1 - 43 = 0,7mm

 

Which means that in a standard XU10J4 the pistons sit 0.7 down the bore.

Adding the extra 1mm with the 88mm crank will make them sit 0.3mm over the deck..

 

So, if I use 88mm crank for a 2044cc build with no other changes, I'll have circa 42.5cc combustion chamber volume for a 13.0-1 compression ratio

 

To be confirmed, but there would be something like 3.9mm total valve clearance, less 1.5mm safe running clearance you could maybe run 2.4mm Lift @ TDC pretty safely.

[Stu 18]

 

Somehow, you have read my mind.. Ive been thinking about this exact setup for my next engine, ive got a set of S16 rods/pistons and a complete '6 engine, so coupled with an Mi crank to get a little extra displacement, should make for a good engine.

 

Ill be dummy building mine over the next month or so, so maybe we can compare notes Mei?

[James_R 3]

13:1 is a touch high in the compression department for std pistons and road fuel.

 

That said Paul Higgs is running an s16 with s16 head which works out circa 12.5:1 or there abouts and seems to be making good power and torque.

 

Personally I'd be staying with the s16 head (not head of any dropping valves like 6's on big cams) and the cmas themselves are cheaper too plus no need for spring upgrades on all the hydrolic profiles

[Anthony 1,002]

That said Paul Higgs is running an s16 with s16 head which works out circa 12.5:1 or there abouts and seems to be making good power and torque.

It's not quite that high - my quick beer mat calculations suggest 11.8:1 for Paul's 88mm crank'd S16

[James_R 3]

Std s16 1998cc CR 10.4:1 unswept = 53.1cc's

 

s16 with 88mm crank 2044cc unswept = 53.1 - 5.80 (as piston swepts 1mm high up the block) = 47.3 CR = 11.8

It sure killed two head gaskets well when it was a touch lean though

 

Score me got being uber dense this afternoon

 

s16 block with 88mm crank and new 16v head unswept - 43.3 (as above -4cc's for chamber) = 12.8:1

[sub205 5]

why not using the gasket for skimmed heads (1.4mm imho) instead of the 1.2mm, this would give a little lower cr.

[sub205 5]

repair gaskets have 1.45mm exactly.

[allanallen 528 2 Cars]

Thread Revival!

 

So what would the most sensible way to lower the compression to a sensible level if you were to fit RFY rods/pistons in an RFS with an 88mm crank? Thicker cometic gasket or skim the pistons perhaps?

[allanallen 528 2 Cars]

Thread Revival!

 

So what would the most sensible way to lower the compression to a sensible level if you were to fit RFY rods/pistons in an RFS with an 88mm crank? Thicker cometic gasket or skim the pistons perhaps?

[allanallen 528 2 Cars]

Thread Revival!

 

So what would the most sensible way to lower the compression to a sensible level if you were to fit RFY rods/pistons in an RFS with an 88mm crank? Thicker cometic gasket or skim the pistons perhaps?

[welshpug 1,657]

just give it more cam is the sensible option.

 

 

 

 

skim the pistons, means you can use off the shelf standard parts elsewhere.

 

only issue you might get going longer stroke is the blocks are very worn these days, so pushing the rings +1mm either end of the stroke than they have been going for the past 20-25 years might not work so well.