Cr Ratio On 1.9

[Hardcharging 0]

Doing a road rally next month so I need to make some progress soon !

Having some probs with my 8 valve 1.9

I have new engine to replace blown one but don't know the origins of it.

CR Ratio is onlt 8.5 the motor has new shells rings ect.

I will need around 10.5 for my cam to work well.

Can anyone tell me which engine I have ?

Is it the Cat one?

How much should be skimmed off the head.

Or can you tell me how up the CR on this engine?

I also have a good set of Mi pistons . Can I use them ?

Any advice will be gladly recived .

If this is the wrong section ,Sorry!.

[unariciflocos 49 1 Cars]

As far as I know it's the Gentry engine that has 8.4 CR. If this is the case then a D6B head will give you 11.1 CR. If it's another kind of engine maybe 1.6 pistons with a smaller pit may be a solution. Best way to measure the CR or see how much you need to skim is to measure the squish volume and the chamber size in the head using plexi, a seringe and water.

[mattbenselin 0]

The GTI XU9JA (D6B) engine had a c/r of 9.6:1, the XU9JA/Z (DKZ) had a cat and c/r of 9.2 while the Gentry XU9J1/Z (DFZ) had a c/r of 8.4.

 

If you have the DFZ you will need to swap the heads like Andrei said, or you could put the Mi pistons (must have the Mi rods too) to raise it a little but not really worth it. Try giving QEP a ring to ask about combinations and CRs.

 

In the Gentry they changed the pistons, combustion chamber volume, cam and management I think so not just a straight swap of any one thing to make a GTI engine. I think you will need to skim too much off the head to bring the CR up enough making it weak. This isn't much use but a 1mm/40thou skim on a D6B/DKZ head raises the CR to 10.5/10.1 respectively so getting that starting from CR8.4 would require a lot more taken off.

 

Best and safest/most reliable way would be to start with a D6B engine I'm afraid. I found my engine was DKZ and thought about swapping pistons but was easier and cheaper in the end just to find a good D6B.

 

Matt

[Hardcharging 0]

Thanks for that chaps !

We are going with the Mi pistons and rods .

[petert 601]

Mi16 pistons in a DFZ don't really give the CR much of an increase. The DFZ piston has a 9cc dish and sits flush with the deck. An Mi16 piston has valve cut outs of approx. 2cc and sits 0.4mm down the bore, so another 2.1cc. So you're only 5cc in front. By my calculations, this will only result in 9.0:1 CR. DFZ is 8.4:1 std.

 

I would definitely fit the Mi16 pistons, but also skim the head. You can take up to 2mm. I would take 1.75mm.