XU10J4 ACAV with XU10J4RS intake / exhaust manifold?

[Tseize 0]

I have not found exactly the same conversion in among the different topics, so that's why I opened this one.

 

I am thinking of buying such an XU10J4RS intake manifold that has got already the necessary small adjustments for fitting it to RFT/RFY engines. Plus the GTI6 injectors. And at the end an engine remap, of course.

But basically I do not intend to buy the exhaust mainfold unless it is really needed.

 

Pros:

• You can get rid of the usage of the unbuyable ACAV membranes (even if I like them). It is a strong reason. 
• More power? (Or only at higher revs?) I was told (by the seller  ) that you can feel the difference even in a basic setup (without exhaust manifold and remap).

 

Cons (or at least these are my fears):

• Lost of mid-range punch? The ACAV is like having a (very) small turbo boost effect at around 3500 RPM, that's cool.
• Because of the resonator in the intake should you change the exhaust manifod as well otherwise the mid-range torque will be poorer than in the standard engine? Or is it not necessary due to the different cylinder heads? 
• As I read the XU10J4RS has got quite a few other modifications in the cylinder head compared to the ACAV (I do not care about the ones in the bottom end  ), so I do not expect at all that this change alone would entirely cover the gap in the power between ACAV and RS, but at least spending ~800 EUR you would like to see some noticeable gains.
• IMHO the rolling road figures of an original XU10J4RS are not extraordinary compared to my old, but rebuilt ACAV engine (90.9 kW @wheels measured several times on different dynos).

 

And yes there are other ideas in my mind for the next year, like the discussed XU9 crankshaft (but I do not intend to touch the bottom end until there is no problem), or some professional headwork, or the proposed milder KENT or Cat cams could give 10-12 extra bhp after remap, so maybe this latter would be a more cost effective approach.

[petert 630]

I would just swap inlet manifolds to begin with and retain the standard XU10J4 injectors. I have a replacement chip for the ECU that makes a nice difference. I sell them to enthusiasts for just cost + shipping. Later, if you decide to swap cams, crank etc. then change the injectors and ecu.

 

 

[SRDT 232]

You can't fit the RS exhaust manifold on the ACAV head as is. It's probably easier to sort out the 9/10 studs problem on a XU9J4 manifold. Many aftermarket ones have the double pattern.

[petert 630]

It is indeed difficult to adapt the exhaust manifold and not worthwhile. I made an adaptor wedge plate many years ago, to suit a 205. However, you’re better off just buying a new 4-2-1 long pipe design.

 

http://www.taylor-eng.com/conversion/conversion_parts.htm

 

 

[welshpug 1,721]

mi16 doesnt have a shove mid range, more a lack of bottom end, gti6 has more torque, and over a wider band.

 

I have fitted a gti6 inlet to a 2.0 mi16 in a 205, never had it mapped or dynod but it went well, no comparison to the acav inlet unfortunately as the engine was supplied bare.

[Tseize 0]

The inlet manifold and the injectors that I intend to buy are sold in one package. Neverthless I am curious about your chip, @petert, may I ask you to send me the details in PM?

At least now I've realized that the bigger injectors would be also needed for increasing the power (however I do not know how much free capacity the original RFT/RFY injector has got), 'til now this was not so obvious, even if it is a basic principle of tuning.

 

 

[petert 630]

I take it the RS injectors are 2nd hand then? They'll need servicing before you can do anything with them, if they've been sitting around.

 

The XU10J4 injectors are good for approx. 175hp max. 

[Tseize 0]

Good to know. I'm aiming for 180-185 Bhp at the crank in the long run in order to achieve a sub 8s 0-62 mph. This would be far from the perfomance of my old XU10J4TE engine setup (max. 1.5 bar boost, ATD chip, GTI6 gearbox) , but it will be enough and I don't want to replace the block in my actual car.

Edited July 20, 2025 by Tseize

[petert 630]

The key point in tuning an XU10J4 is removing the 1mm of deck clearance. The 1mm results in poor flame travel and why it’s doughy and flat. This can be achieved by either skimming 1mm off the deck or fitting an 88mm crank. The reward is a responsive engine with a flatter and improved torque curve. CR is approx. 11:1.

 

 

Edited July 21, 2025 by petert