Xu7j4 Perfect Basis For A 1600 16v

[Saveit 0]

Hi,

 

Still thinking about making a 1600 16v XU engine to do some endurance racing in a 1600 class. But the big problem no matter how you go about it is pistons and rods. BUT then i read an old thread about the XU7 engine where Sandy posted the following info: 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). The pistons are short with a waisted skirt like race pistons and the stroke means that piston speed at 8000 is about the same as a 1.9 at 7250, the longer rod reduces piston acceleration at the top of the stroke as well, meaning lower rod bolt stress. It has the same valve sizes as XU10J4 and XU9J4, but the inlet ports are cast deliberately small. This restricts the standard engine, but lends itself well to more creative porting than the Mi16 allows.

 

As far as i can tell from this, the conrods in the xu7j4 engine is exactly the same as the regular 1.6 gti engine conrods. This means that by replacing the crank in the xu7j4 engine with a crank from a 1.6 gti engine you would end up with a 1600 16v engine - right? Now i would imagine that you would have to raise the compression a bit, but this could possibly be done by just skimming the head and/or decking the block? The head could then be replaced with a mi16 head or you could get it ported to perform better or as good as a mi16 head. As far as i can tell this must be the easiest route to the 1600 16v engine?

 

Correct me if i am wrong please

 

Stefan

[James_R 3]

You'll still need non std pistons to get good enogh compression, but the UX7J4 is the right place to start. I'd have a look at Dixon's build Sandy posted some picturs of modifying an Mi piston to be intruderish.

 

Mi16 head on a 1600 would be a fail, the ports woudl be like buckets = no port speed = bugger all torques

[Saveit 0]

Intruderish - which means ?

 

Hmm which head would be right for a 1600 16v engine then if the mi16 is not ideal?

[Baz 421]

RS head.

 

Intruder-ish, James means so that the pistons were machined to be like 'Intruder' pistons, have a domed top, intruding into the combustion chamber to raise compression.

[Saveit 0]

But machining standard pistons to have a so called intruderish top would only leave me with even lower CR because of the material removed from the piston? Or do you mean doing this intruderish thing and then decking the block even more than normally possible?

 

But if we were to stick with the standard 1.8 16v piston and conrod, how much would i need to remove from the block? I recon that if i deck the block so much that the piston will be level with the top of the block, then wouldnt this be enough for at least 10:1 CR? (perhaps skimming the head a little too).

Edited May 11, 2009 by Saveit

[24seven 104]

Basically starting with larger pistons in the first place. the Mi16 pistons used in Dixon's engine needed machining down because they were too tall, but by leaving material in the centre (the intrusion) the CR was kept high.

 

I was always under the impression that the easiest way to a 1600 16v XU would be to rebuild the internals from an XU5 8v into an Mi16 block, retaining the Mi16 head. That said, even if it is 'easier' then you'll still suffer oil surge and the ports on the head would be too big for the reduced capacity. Shortening an XU7 and porting the original head instead if using an RS one would be more effective I reckon (though I'm no engine builder yet ).

[James_R 3]

RS = even bigger!!

 

The best starting point wold be the XU7 head, which on the 1800 is restictive, but on a 1600 isn't so bad, also plenty of material there for making it the shape the engine builder wants it to be, plus bigger valves than the RS head and cheaper to get hold of.

 

The XU7 head (and R and RS) has a smaller chamber so you'll automatically need less intrustion in to the chamber. 36cc over 40cc or there abouts.

 

You can't take that much out the 16v heads for compression like you can the 8v heads. To do it cheaply you're limited why what compression you can get to (i.e decking the block as much as possible and skimming the head aswell and a thinner headgasket)

 

It's not easily done or everyone would have a crack at building one, good luck... not going with the iron block idea anymore??

[Saveit 0]

What compression would you recon if decking the block to level with the pistons, skimming the head as much as possible and using a thin metal head gasket? I would think that you could get over 10:1 cr?

 

No i decided to use an alloy block since it is lighter and 83mm bore iron blocks is quite hard to find here in Denmark. And people in here convinced me that the alloy block can stand the suffering. But i am working with many different ideas on how to do this 1600 16v conversion so i may return to the iron block idea at some point At the moment i have a budget of about £1800. So i have to find out how to ideally use the money.

[Saveit 0]

Do anyone by the way have some guide to piston-conrod assembly? As far as i understand the xu7 conrods and pistons are press fitted. This means heating up the pin and pressing it in to the conrod i imagine? But i read somehere that Peugeot have some description on how to do this.

[James_R 3]

XU7J4 engine 100GBP

GTi-6 valve springs 50GBP??

Newmans PH4 (or similar) 400GBP

custom pistons £500-600

TB&ecu £1500

 

 

You'll struggle to get the engine and management/induction for that money. think you could do one, not the other have throttle bodies and no engine, or and engine but not throttle bodies.

[mattbenselin 0]

What about a cheaper route like throttle bodies from a bike and an ECU like Megasquirt. I dont know the regs you would have to build it to but would be an alternative.

[Saveit 0]

I was planning on sticking with the original ECU and sticking some bike carbs on it since i have some R1s laying around. But what do you think?

[Saveit 0]

And i have already found some wossner pistons that i think will suit (LINK). But in Dixons thread Sandy appearently machined the standard mi16 pistons due to them being to big. Then these high comp wossner pistons will be much too big? I have no problem buying aftermarket custom pistons, but i will need to find some that i know is at positive fit (perhaps with minor modifications) before buying them. Otherwise it is a waist of money.

[mattbenselin 0]

Original ECU for what: the 205 GTI or (I presume) the XU7 engines Sagem SL96 (JP4) or Magnetti Marelli 8P1A (JP)? You will maximise the results by using throttle bodies over carbs and using a fuel+spark ECU but your budget will suffer. I am using bike carbs with a Megajolt for just this reason. I presume both the XU7s ECUs will run spark without fuel and you can use the carbs for the fuelling, but you may still be better off with a standalone ECU and the MS can be built for +/- £100 I think.

[Saveit 0]

I was planning on using the existing 205 gti (jetronic) management and just doing the distributor conversion like you do on an mi16? I have absolutely no knowledge on how to build this megajolt system. But perhaps i could pay you to fix something up for me ? Send me a PM if you feel like it.

[Baz 421]

What about a cheaper route like throttle bodies from a bike and an ECU like Megasquirt. I dont know the regs you would have to build it to but would be an alternative.

 

Why go all that way to then half-ass the rest of it with crap?

[mattbenselin 0]

The Jetronic only runs fuel and presumes all components used are the standard items especially the AFM. This means you can't use it with throttle bodies, and using carbs means you dont need an ECU at all. Using a dizzy will work but does not allow you to fine tune the spark advance and very effective and noticeable gains can be made by using an electronic distributorless ignition system. Both the Megajolt (spark only, use with carbs) and Megasquirt (spark and fuel, use with throttle bodies) can be bought as a kit to be built by yourself or as an assembled and complete unit. Have a good read and see what you think. Personally I don't build them though have just finished modifying my own MJLJ V4 and am very pleased with the ease of setting the system up.

 

the parts you will need are easily available:

 

- MJLJ or MS ECU

- Trigger wheel (triggerwheels.com)

- Ford EDIS components: (All ford stuff can be obtained from a scrap yard for very little money)

- EDIS ECU

- VR sensor

- Ford or Peugeot coil pack + HT leads

- TPS sensor if using TPS (alternative would be MAP)

- Coolant temp sensor

 

- If using MS then injectors and all injection associated stuff

[mattbenselin 0]

Baz the reason I suggested this is the limited budget available for this build and the outcomes he wants.

[James_R 3]

You be better off building a good 8v than a cheap 16v 1600

[Saveit 0]

Matt - thanks a lot, will look in to it!

 

James - Yeah and 8v would be the easiest route since i have a lot of components for it. But we want at least 160 bhp (170 bhp would be ideal) from a 1.6 engine, and i have only seen few making that kind of power from 1.6 8v. At least i dont know how to pull that kind of horses from a 1.6. Ive seen guy croft do it (174 bhp at 9000rpm) but firstly a head from guy croft surely most be way over my budget, and secondly 9000rpm on an 8v for 4 hours in a row (endurance racing) doesnt sound that tempting. But please do feel free to tell me otherwise

Edited May 11, 2009 by Saveit

[Batfink 201]

I've roughly planned by 1600 16v build and quite frankly theres no way to do it cheap.

I will be fitting custom pistons and rods as its the only proper way to do it.

 

Kev

[Saveit 0]

Why custom rods? I would think the standard 1.6 rods would be fine?

 

Could you perhaps PM me with a bit more info on your setup (if you dont wish to give away your secrets to the public yet ) like pistons, base engine to build from, head and so on? And will your run it on throttlebodies or?

[EdCherry 34 1 Cars]

I seriously considered this also, if your going to do it you need to chuck some money at it, it isnt something that will be a good budget build. Was looking for previous builds and power figures etc etc but couldnt really find anything which also put me off a bit.

[Saveit 0]

A read a thread somewhere about this conversion and those different engines mentioned made between 190 and 220 bhp. I think 3 examples or so was given. So it is possible to get good results from this.

[Sandy 191]

The XU7 rods are the same as the XU5, 22mm pins though, not the 20mm I said in that quote!

 

It's all fine except the pistons. You'll need a crown height (distance from pin centre to block deck) of 37.5mm, which coincidentally is the Mi16 height. The intruder needs to be at least 5cc net. The rods need to be narrowed slightly at the small end and bushed ideally, but that does leave them very thin over the pin, so proper rods would be preferable really.

 

For a 1600, you have to consider using the TU 16v, because it will be a much simpler build.