Compression Ratio for 1900

[Rallyace 3]

I am in the process of building a 1900, 8 valve engine for a rally car. I will be running a 285 degree duration camshaft, with OMEX 600 ECU. I have a lightly ported head, which I have done along accepted guidelines. I now need to adjust the compression ratio to get the best from the cam and engine management. Ideally, I’d like to do this by fitting 1600 pistons to my 1900 rods. Am I correct in assuming that standard 1600 pistons are no longer available? The use of the engine doesn’t warrant the cost of a set of forged pistons. I’m looking to achieve a final compression ratio of 11.5:1. I realise that I can achieve this with a head skim, but I’d prefer to do it with the pistons.  

My questions are: 1, Are 1600 pistons actually still available? 2, Does anyone have a set of 1600 pistons? 3, Has anyone successfully removed 1600 pistons and refitted them to 1900 rods? Any advice would be welcome.

[welshpug 1,661]

there does appear to be Mahle Pistons for the XU5 on ebay, would need to check the part numbers to be sure they are correct.

 

there is an assembly that will fit straight in without swapping pistons around, its from the low compression 1.9 engine, they have the 1.6 piston on a 143mm 1.9 rod and a large head chamber, fit the gti head and you have higher compression.

 

also there are the flat top pistons from the bx gti and 405 sri, large head chamber again but his will give nearer 12.5 I believe,   possibly more suitable for a 285 degree cam?

[petert 588]

I have used pistons from either a 1.9L DFZ or 1.6L BDY. They have a 9cc dish. As said above, use these with the normal D6B GTi head. Skim up to 2mm to achieve your desired CR. I think the part number is either 0114K8 or 0114P3. Alternatively, use Mi16 pistons and rods.

[Rallyace 3]

Thank you for your help. Much appreciated. I haven’t been able to find any Mahle pistons for the 1.6 on ebay. There seems to be no shortage of 1.9 pistons. I found a company called K Motor Shop, who appear to sell the DFZ piston. This is the web site - https://www.kmotorshop.com/en/article-list/list/motor/2870/tree-shop|263?filter=0&itemsPerPage=10&style=1

 

Would you mind having a look and see if you think it would be suitable?

[Rallyace 3]

A deadens I’m afraid. When I looked again, the dish appears to be the same as the 1.9 GTi piston.

[DamirGTI 342]

Mahle : 0397900 (0.00)

 

Production Number : 83 V 31

Compression Height [mm] : 37,5 mm

Recess Diameter [mm] : 73,5 mm

Bolt length [mm] : 66,2 mm

Recess Depth 1 [mm] : 9 mm

Top Land Height [mm] : 8,5 mm

 

.. it is 1.9 DFZ piston , currently 6 on stock here @ 109 EU per piece .

 

D

[Rallyace 3]

Thanks Damir, It is DFZ, but I’m looking for a piston with the same bowl volume as a 1600. That appears to be the same as a 1.9 piston.

[DamirGTI 342]

They're the same/identical pistons as 1.6 Gti ... same dish volume 9cc , higher CR 1.9 engines aka D6B/DKZ have piston dish @ 15cc/16cc .

 

By far easiest and cheapest route would be obtaining an set of second hand 1.9 DFZ pistons (complete along with the conrods) , since you're building 1.9 engine .

 

 

D

[Rallyace 3]

Ok. So the recess depth is 1mm, with a volume of 9cc? The info on the website says recess depth 9mm, which is also what you say above. If that’s the case, they would be great. I’ve done a quick search and haven’t come up with any second hand 1.9 DFZ pistons and rods. Thanks so much for your help guys.

[SRDT 182]

The DFZ pistons are the same than the 1.6 since 1991, that should be when the CR went down from 9.8:1 to 9.25:1 so that 95 octane could be used.

 

The 1.6 heads have 34cc combustion chambers, on the 1.9 you find 50cc chambers on the XU9S, early XU92C, XU9J1 and XU9J2. Those have flat top pistons or small dish 1.6 style pistons when it's a low CR engine like the DFV or the US market XU9J2.

The XU94C, later XU92C, XU9JA, XU9JAZ, XU9JAK and XU9M have a 34cc chambers so they need a bigger piston dish.

 

Here are some cheap new flat top pistons and sleeves sets:

https://www.serie04.com/gb/205-bas-moteur-essence-xu/119-kit-cylinders-pistons.html

[Richie-Van-GTi 72 2 Cars]

I ran a 285 at 11:1 through a head skim no bother using an adaptronic ECU. Its quite a straight forward option if you dont find the right piston combo.

[Tideee 3 1 Cars]

20 hours ago, Richie-Van-GTi said:

I ran a 285 at 11:1 through a head skim no bother using an adaptronic ECU. Its quite a straight forward option if you dont find the right piston combo.

Hi Richie .....can you enlighten us as to what an "adaptronic ECU" might look like please 

[petert 588]

Adaptronic was an Aussie designed ECU, which was bought out by Haltech. The owner/guru now works for Haltech and is the brainchild behind the R3 and R5 models.