Xu10J4 & J4R/rs Blocks

[JeffR 51]

I have been offered an XU10J4 iron block from a 306 S16 (155hp) for cheap & was wondering if it's the same as a J4R block from a GTi6? It'll only be used if the J4R block won't bore to 88mm.

 

It has piston cooling sprays but are there any minor differences I should be aware of? Maybe cambelt lower cover, etc.

 

Thanks

[camgti 56]

Hi Jeff,

 

As far as I know they can come with or without spray bars. If yours has them thats great! They are otherwise pretty much the same.

 

I have a J4r in my 205 and the only other differences are more to do with the head and stuff that bolts to it. Otherwise the same.

 

Are you building a monster 88mm job? I have some 88mm pistons I will eventually fit to my 92mm crank in an iron block too! Very interested to see hpw you get on!

 

Cam

[JeffR 51]

Yeah, I think the heavier 405 needs as much horsepower as I can wring out of it! Would like 250+ with 88x88. Piston spec is as yet undecided as are cams & CR.

 

I think an 88mm bore would get the best out of the big valve head too.

[petert 586]

Isn't 88mm flirting with danger? Some blocks do and some blocks don't? (reminds me of a song)

 

I'd make it 87x88 and put your head straight on. It will make well over 250hp. Are you going to run E85?

Edited July 24, 2014 by petert

[JeffR 51]

I hadn't considered E85 as being a 'must have' for this new build tbh.

 

While I understand it has some advantages and might be appropriate in some circumstances, I think the disadvantages are also considerable.

 

Advantages-
*E85 has a RON rating of approx 105 RON & can run a richer air/fuel ratio making more power
*have a cooling effect so intake charge is more dense & produces more hp
*reduces the potential for detonation

Disadvantages-
*less energy by volume compared to straight unleaded
*need 30-40% more fuel by volume to produce same amount of power
*larger capacity fuel system including fuel injectors, pump, etc required
*is hydroscopic (water attracting)
*not kind to steel or some types of rubber components in fuel supply system
*requires an API SN spec engine oil

 

I'd probably stump up for a dry sump system before changing the fuel type.

[welshpug 1,657]

I know a few engine builders that wont go past 87mm due to issues with 88mm.

 

can you do 92mm?

[JeffR 51]

Is that a 2.1 crank from a XUD11?

[camgti 56]

Yep 92mm from XUD11. I got mine from French Connection.

 

There are a few guys who have run 88mm without issues.

 

Who are the guys who have had issues?

 

Cam