Xu7j4 Info

[Sandy 191]

I've had a few people ask me about the finer details of the 1.8 16v XU engine lately, so here are some answers:

 

Block height from crank centre line 224.5mm

Stroke 81.4mm

Bore 83.0mm

Rod length centre to centre 150.5mm

Big end journal diameter 45mm

Small end diameter 22mm (Interference fit)

Piston crown height from pin centre 33.3mm

Pistons rise flush with deck at TDC

Piston crown total volume (dish and cutouts) ~ 2.0cc

Gasket volume (1.4mm x 84mm dia) ~ 7.8cc

Chamber volume standard ~ 37.2cc

Chamber volume with 0.25mm skim (maximum practical) ~ 36.0cc

Standard CR 10.4:1

Skimmed CR 10.6:1

Inlet valve cutout 2.5mm max lift at TDC (allowing 1.5mm clearance)

Exhaust valve cutout 2.0mm max lift at TDC (allowing 1.5mm clearance)

Inlet valve diameter 34.6mm

Exhaust valve diameter 29.6mm

 

Omega Mi16 piston next to XU7J4 OE piston, earlier today...

Edited December 28, 2007 by sandy309

[James_R 3]

Cool, awesome info

 

Thanks Sandy

[pip470 61]

Inlet valve cutout 2.5mm max lift at TDC (allowing 1.5mm clearance)

Exhaust valve cutout 2.0mm max lift at TDC (allowing 1.5mm clearance

 

Sandy with the standard verniers it is possible to get the ca timing out right so, is this the standard figures i would use if setting them up with a dti on the buckets. Any help would be great.

[James_R 3]

No that's the maximum lift clearance, for running bigger cams.

[Sandy 191]

Yes, the standard lift at TDC is nowt, less than 0.5mm IIRC.

[pip470 61]

Yes, the standard lift at TDC is nowt, less than 0.5mm IIRC.

 

Is that for inlet and exhaust

[James_R 3]

Have you had an experince running 109 catcams in one? or is the compression a bit low to bother with them?

[Sandy 191]

Is that for inlet and exhaust

Don't quote me, I really can't remember! I ran GTi6 cams in my XU7J4 with about 1.2mm inlet and 1mm exhaust IIRC and it sounded and felt much better than standard timing, didn't roller it though, so purely a subjective measurement!

I should have checked it before I took the head off this one, I've got another with the head still on, but it doesn't need to come apart yet. There seems to be better valve clearance on the XU7J4 than the GTi6 bizarrely!

 

Have you had an experince running 109 catcams in one? or is the compression a bit low to bother with them?

Haven't tried, i'll be setting up an Mi16 with them in (and GTi6 head) soon though. I think in the 1.8 with standard compression, the '106 inlet cam with a GTi6 exhaust cam and GTi6 double springs or PAC-S90019's would be a good idea. The early 1.8's had fairly decent parallel sided valve springs, but the later tapered ones are pretty soft. GTi6 double springs go straight in with the top and bottom retainers. If you have the later type tapered 1.8 springs, the retainers are useless, due to the smaller diameter.

[Anthony 1,003]

Excellent information Sandy, and thanks for spending the time measuring/checking all that - you're a star

 

I don't suppose you've got similar data for a GTi-6 (XU10J4RS) engine for comparison have you?

[Sandy 191]

No worries, I've got a GTi6 engine to take apart over the next couple weeks, but it's already been played with a bit. Also I'm not sure the finer details of the RFS engine stayed the same throughout production, I've heard conflicting information.

[James_m 0]

Sandy, are the oil ways the same on the Xu7 block as the Xu9(J4) blocks? Im just wondering if they improved them over time, so this block could be used to house Xu9J4 internals and head for better oil control?

[Emmy Seize 8]

Sandy, are the oil ways the same on the Xu7 block as the Xu9(J4) blocks? Im just wondering if they improved them over time, so this block could be used to house Xu9J4 internals and head for better oil control?

 

With the described modifications (cams, inlet etc) and a 1,9 crankshaft you should be pretty close to MI16 power anyway, so why bother about the head?

Edited January 7, 2008 by Emmy Seize

[James_R 3]

You could just bolt a GTi-6 head on an Mi bottom end, the head should reduce the surge issue and you'd gain come compression and have very large vlave cut outs. Although the extra throw on the crank wouldn't be so good for longevitity compared to the XU7 set up.

[James_m 0]

With the described modifications (cams, inlet etc) and a 1,9 crankshaft you should be pretty close to MI16 power anyway, so why bother about the head?

 

You'd need custom or at least different rods and/or pistons to get some kind of usable compression ratio with the 88mm crank. Plus i already have all the mi16 bits. and im not sure which management you could run something 1.8 on. Mappable only i suspect.

[welshpug 1,657]

Sorry to drag this up again but having been to service on a rally and seeing what the 205's are up against I was thinking about 16v XU5's, but I'm a bit confused now!!

 

I've had a few people ask me about the finer details of the 1.8 16v XU engine lately, so here are some answers:

 

Rod length centre to centre 150.5mm

Big end journal diameter 45mm

Small end diameter 22mm (Interference fit)

 

ok, so the same size pin as an Mi?

 

but

 

The standard XU7J4 is a bit of an odd ball. It has 81.4mm stroke and 83mm bore (1761cc), the same size rods as the 1.6 8v (150.5 long, 45mm big ends, 20mm interference fit gudgeon pin).

 

not the same size as the Mi16!

 

 

(note that all references to Mi16 here are to the 1.9, i.e 83mm bore)

 

XU5 and 9 8v is 20mm gudgeon pins?

 

which press into the piston and the conrod floats on the pin, the XU7 fit the same way, but the Mi16 doesn't and is also a different size?

 

 

so even if 1.9Mi pistons were the same size they fit the Conrods differently, does that matter?

 

came across these http://www.forgedpistons.co.uk/Products/Product.asp?id=142 which are mi spec pistons but have a 20mm Gudgeon pin.

 

many thanks to those that can help

[Sandy 191]

They have 22mm pins, it was brain fade on my part. The XU7 rod is interference yes, the Mi16 is floating. You can however use the Mi16 piston/pin pressed into an XU7 rod as an interference fit. I mapped an 8v XU7 last tuesday that has been competing with this arrangement for about 7-8 years, revving to 8500rpm. It' was less than 10bhp down on when it was built, so seems to work ok! If you've got Dave Walkers Engine management book, you'll see it on pages 53, 78, 93 etc.

[welshpug 1,657]

ahh lol!

 

hmm, Xu7 rods, XU5 crank Mi pistons, XU7/10 head

 

gonna have a play methinks...

[Batfink 201]

Welshpug - i'm not sure its possible to make a 16v xu5 without using forged pistons to get the compression back up as its rather low with standard mi16 pistons

[welshpug 1,657]

yeah I think that's the conclusion I've come to so it wouldn't be cheap, but then not as expensive as it could be!

 

not sure exactly what the compression ratio would be as yet though.

[welshpug 1,657]

I'm not so sure if it is any lower now!!!

Edited May 20, 2008 by welshpug

[Batfink 201]

off the top of my head a straight swap of parts gave a 8.6:1 compression ratio so mi16 high compression pistons were essential. Problem then is a racy cam then needs more compression than standard

[welshpug 1,657]

compression ratio is higher than that with the head I want to use Batfink

 

though probably still not high enough for wilder than std cams, good enough for a trial engine.

[TVH 0]

They have 22mm pins, it was brain fade on my part. The XU7 rod is interference yes, the Mi16 is floating. You can however use the Mi16 piston/pin pressed into an XU7 rod as an interference fit. I mapped an 8v XU7 last tuesday that has been competing with this arrangement for about 7-8 years, revving to 8500rpm. It' was less than 10bhp down on when it was built, so seems to work ok! If you've got Dave Walkers Engine management book, you'll see it on pages 53, 78, 93 etc.

 

Can I just press in the xu9j4 piston/pin to a xu7/xu5 rod (these rods have same Pug OE part number) without any other modifications?

[welshpug 1,657]

exactly the question I wanted to ask but it seems from what sandy said of that engine they are, any mods though?

[Guest Puges]

Which pistons i have to use to get compression ratio like 8.0:1 - 9.0:1 ? I'm going to build turbo engine to my cti.

Edited October 5, 2008 by Puges