Xu10 16 Valve Head Differences

[Tom Fenton 1,541]

Gents,

 

I'm slowly thinking about a new project engine, XU10 based, so I'm interested in finding out what are the differences (if any) in the various 16v XU10 heads?

 

XU10J4RS is GTI6 head, mild cams and smaller valve stems if I am correct?

 

XU10J4 is S16 or late 405 Mi16, more cam as standard, larger valve stems?

 

Basically any other info is welcomed. Is my info above accurate or bollox? Are there any difference in combustion chamber volume? I know the GTI6 motors are very close on valve clearance, is this down to the piston cutouts or something else? Are the valve inclinations in the heads the same on them all or are there differences?

 

To give some background, I've bought a GTI6 short motor with Wossner forged low comp pistons and steel rods, I want to strap a 16v head and a big f off turbo to this, so I am just starting to think about options.

[petert 586]

XU9J4 and XU10J4 are the same family head. ie they share the same valves, springs, lifters, cams etc. They have 34.7mm inlet and 29.5mm exhaust valves

 

XU10J4R and XU10J4RS are the same family head. Both have 6mm stems. R heads are 34.7/29.5mm valves with single valve springs. RS heads have smaller inlets and larger exhaust valves (from memory) with double springs.

 

I personally prefer the earlier heads because it's possible to get bigger grinds out of the standard cams. Also, the valves don't bend if you sneeze at them.

 

The XU10J4 and XU10J4RS heads are also more desirable as they have cam sensors. Essential if you want sequential fuel injection. The XU9J4 head can be retro fitted with the cam sensor.

 

Chamber volume is slightly smaller on R and RS heads. Perhaps 36cc vrs 40cc on earlier heads?

 

Whilst RS heads flow a little better out of the box, I doubt they'd out flow a professionally ported XU9J4/XU10J4 head with 36.5mm valves. Sandy might know.

 

Piston to valve clearance is determined by the pistons, not the head. R and RS pistons are lousy. The XU9J4 and XU10J4 pistons allow up to approx. 0.100" lift @ TDC. I've never fitted an RS head to an early motor so I can't tell you what that relationship is.

[kyepan 291]

tom, it might be worth speaking to sandy, His head of choice is the xu7 i think, as apparently it has the most scope for good work to be done, and a host of other reasons he probably didn't mention.

Cheers.
J

[welshpug 1,657]

XU7J4 has same valves guides + stem seals as XU10J4R, single valve springs lower spring seat is intregrated into the stem seal.

 

Exhaust ports same as XU10J4R, inlets noticeably smaller.

 

 

Cam sensor lug casting is present on both XU7 and XU10J4R, just not drilled out or a tapped hole.

[Tom Fenton 1,541]

Peter, many thanks for that info, that is exactly the sort of thing I was wanting to know. I was already leaning towards the earlier head, mainly due to the valve stems being larger, thus giving more potential to get the increased heat from a turbo away into the guides and head, and also for the valves being that bit stronger/more robust.

Are the earlier heads 7mm valve stems?

 

Justin, Mei, although I am sure the XU7 head gives more potential for NA engines, for a boosted motor I do not see the point of going to the lengths of an expensive ported head to gain flow, instead I will use a more or less standard head, and just wind another psi or two of boost pressure into the thing.

[petert 586]

Yes, early heads have 7mm stems. The XU10J4 is the same as fitted to the T16 and makes up to 500hp easily.

[Tom Fenton 1,541]

Thank you Peter. Out of interest do you know what cam profiles the T16 used?

[TT205 42]

Can't offer anything helpful (sorry) but looking forward to the build thread

[welshpug 1,657]

Quite agree Tom, would imagine any of the other heads would work just fine, as the RFS does in the Lynx SC conversions for well over 500 bhp in the superhigh boost variant.

 

 

How early are you talking Peter for the 7mm valve stems? got a 1995 XU7 here and that's 6mm, and there's nothing at all listed anywhere about this difference.

[petert 586]

By early, I mean XU9J4 and XU10J4. The T16 profiles are tame/lame.

[petert 586]

It's common practice to use Mi16 cams in high horsepower T16 engines, or even my Stage I inlet.

[calvinhorse 870]

I know of a very good 2.0 mi16 head Tom.. It's cheap aswell

[Sandy 191]

Using the later heads can usefully reduce port section/volume and improve responsiveness for the same power potential. That would apply as much or maybe more to a boosted engine. We've had lots of chances to compare the effects of the various heads and my ported XU7J4 heads produce the thickest power deliveries and response by far, to the point where many others simply don't believe it! The ultimate flow potential of the bigger port heads at high lifts is greater, but the reality is, unless you're building a 2.4/2.5 litre engine, you'll never see the demand to use it. Flow is only one element and generally irrelevant to the end result IME where decent design 16v heads are concerned.

7mm stems do have more heat transfer potential obviously, but how many boosted Japanese engines out there are reliable on 5.5mm? Heavier valves need heavier spring pressures and so on.