Crank And Piston (compression) Question?

[Saveit 0]

Hi,

 

Firstly, some of you may know that i have been building on an XU 1600 8v engine which ended up putting out 170 bhp at 8000 rpm. But we are thinking about upgrading to the 2000cc class instead.

 

I have a 1900cc 105 bhp bottom end with a ruined crank. I am thinking about using this bottom end with a diesel crank to reach closer to the 2000cc since the current crank is ruined anyway. Now in which engine do i find this crank (thinking it must be the XUD9 engine?) and in which cars is this engine fitted? Does the regular 1900 conrods fit this crank with regards to the big end diameter?

 

Secondly i wish to raise the compression to suit the crazy 328* crankshaft better. I have just had the head skimmed and since the lift at tdc is 5.76 i am afraid of skimming the head anymore with regards to valve/piston clearence. I read somewhere that 1.9 SRi pistons could do the job (CR of about 11:1) or is this only do-able in the 1600cc engine? Is there any pistons besides forged aftermarket pistons that could raise the compression? I was thinking about using some mi16 pistons or something but my head is 8v so im guessing it wont work?

 

A lot of questions sorry

 

Thanks guys,

 

Stefan

[Anthony 1,003]

I assume you mean the 92mm crank, found in the XUD11 (2.1 TD) engine, rather than the 88mm crank found in the XUD9 (1.9 TD) engine.

 

83mm bore x 92mm stroke will give you 1990cc

[Saveit 0]

Exactly! Thanks anthony. What is the big end dia of this crank? Does it fit mi16 conrods or regular 1.9 gti conrods?

[Daviewonder 533 3 Cars]

Would you not need custom pistons and rods due to the new crank making standard ones reach 2mm higher than normal and causing them to come into contact with the head?

[Saveit 0]

That is what i am thinking. But if using 1.9 sri pistons which i believe is flat top pistons wouldnt i be able to skim the pistons by 2mm or is this likely to cause a failure at some point? Perhaps i should stick with the 88mm crank :/ I would like the last 100cc though...

[Daviewonder 533 3 Cars]

To be honest mate ive never really looked into piston skimming but im sure 2mm would be to much to take off and still retain reliability. Im sure someone will be along soon that can help.

[B1ack_Mi16 67]

The 92mm crank do also have 26mm wide rod journals, where the normal cast cranks have 24mm wide ones.

 

So if you are to build a proper engine I would get custom conrods with 26mm wide big ends crank located..

 

Then you can make them to your chosen lenght too so pistons will sit just where you want them!

[Saveit 0]

Any slight idea how much custom rods will set me back?

 

What if i choose not to go with the 92mm crank and stay with the 88mm, would i be able to use mi16 or 1.9 sri pistons to raise compression?

[welshpug 1,662]

I would be putting my efforts towards making a 1905 engine as powerful and reliable as possible, which would give you more cash to play with than going for a custom build for extra CC when it's not a proven route to power.

 

Granted it may be a little boring going down that easier route, but it saves the expense of a totally unknown combination especially if you want to get out there and race.

[Saveit 0]

I think you are right.

 

So as i am going for a 1900cc i just need to know which pistons can be used to raise the compression. Fx 1.9 SRi - can somebody confirm?

[DrSarty 90 1 Cars]

I would be putting my efforts towards making a 1905 engine as powerful and reliable as possible, which would give you more cash to play with than going for a custom build for extra CC when it's not a proven route to power.

 

Granted it may be a little boring going down that easier route, but it saves the expense of a totally unknown combination especially if you want to get out there and race.

 

First part agree - second (bold) disagree - third agree.

 

It costs money; simple. Your best, cheapest and quickest route IMO is as Meirion has said, i.e. sticking with 'off the shelf' items and doing a clever combo and not going too lairy.

 

I'd say best to concentrate on the head*, cam profile and CR match, with good flow in of high pressure cool air and correct expulsion of gases using the simplest (even mediocre) of approaches. Well cut valve seats and careful flowing where necessary with a well chosen and timed cam I think is the way forward. Doing this will give the rewards in terms of good and usable power which lasts, i.e. is reliable.

 

* To quote Guy Croft: "All the power is in the head."

[James_R 3]

big CC'd just means power lower down, which is torques no?? not really more power different graph shape.

 

92mm crank on the 83mm bore says new shells frequently to me the rod angles :s nasty stuff!!

 

pistons wise depends on the CR you want really, I *think* 1.6 pistons give you about the max CR on std cast items, then you'll be looking at 400europ's for some forged effrot to bump in the 12:1 region which is probabaly what the head is after really.

[Lan 24 1 Cars]

A good example of that is the 106 rallye 1.3 engine and the 106 1.6 xsi engine, same head, same power about 100bhp, completly different power delivery

[James_R 3]

Less lard too!!

[Saveit 0]

Well i read somewhere that 1.9 SRi pistons would give me the highest CR possible. If using 1.6 pistons will i not have problems with the pistons hitting the head or something like that? What is the actual difference between 1.6 and 1.9 pistons?

[James_R 3]

the Dish in the crown of the piston, the 1.9 is deeper (increased unswept volume) 1.6 shallower, and SRi 1.9 pistons flat (highest) although SRi head has big chambers.

[Saveit 0]

So SRi pistons would be the best? Does anybody know the length of the SRi conrod?

[James_R 3]

1.9 length. the small end is in the same place so can be moved.

 

For a 1900 engine you want the 1600 piston on a 1900 rod, for a 1600 engine you want the SRi piston on the 1.6 rod. else you'll be melting things.

[Saveit 0]

Just did some calculations. With 1.6 pistons on 1.9 rods the CR should be a bit over 11:1 which is fine with me. But here comes my next question: How do you seperate the paticular pistons from the rods? Isnt it something with heating and freezing and so on?