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Discussion Starter #1
I have fitted a Eaton blower to my 2.4 CIH, and naturally now, I need to overhaul it, so I thought about lowering the compression a bit. What would the preferable ratio? I'm thinking build it like a turbo and go around 8 or 8.5:1, what you say?

Depends on the boost level.. hm. That I have not managed to foresee yet. Anyone good with that sort of calculations here? :)

The 2.4 pistons compression height is 31.5mm? I was about to order a set of 10mm longer rods, and order a set of custom pistons, but I guess a PCH of 21.5mm and with a bigger dish might be unrealistic. What do you think?

And the head gasket, a lot to choose from, original size is around 1.1mm?
 

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I have fitted a Eaton blower to my 2.4 CIH, and naturally now, I need to overhaul it, so I thought about lowering the compression a bit. What would the preferable ratio? I'm thinking build it like a turbo and go around 8 or 8.5:1, what you say?

Depends on the boost level.. hm. That I have not managed to foresee yet. Anyone good with that sort of calculations here? :)

The 2.4 pistons compression height is 31.5mm? I was about to order a set of 10mm longer rods, and order a set of custom pistons, but I guess a PCH of 21.5mm and with a bigger dish might be unrealistic. What do you think?

And the head gasket, a lot to choose from, original size is around 1.1mm?
It definitely depends on the boost you run, and whether you are intercooled or not. The 'old school' reasoning was that every 3 psi of boost equaled roughly one compression point. So with 6 psi (.408 bar) of boost you would have a theoretical compression ratio of 11.4:1 with the standard 2.4 pistons. Of course unless you have special fuel or you retard the ignition timing a lot, this would be a problem.

But if you chose 8:1 or 8.5:1 compression as a starting point, that wouldn't be a bad place to be.
 

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Discussion Starter #5
Here is a picture, this is taken a few days ago.

As you can see I have swapped out the stock 2.4 injection system for a astra 1.6is system that uses a map sensor, no flap box!

The coke bottle is there only as eyecandy, :p No, I had the hose mounted just before the original flap box, but I found that there was building up some oil in the cooling pipes and I dont want to fill the intercooler with oil, so i have to figure out something else to do with that. Might just get a filter and a return line to the block.
 

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Discussion Starter #6
It definitely depends on the boost you run, and whether you are intercooled or not. The 'old school' reasoning was that every 3 psi of boost equaled roughly one compression point. So with 6 psi (.408 bar) of boost you would have a theoretical compression ratio of 11.4:1 with the standard 2.4 pistons. Of course unless you have special fuel or you retard the ignition timing a lot, this would be a problem.

But if you chose 8:1 or 8.5:1 compression as a starting point, that wouldn't be a bad place to be.
Ok, for now I have a megajolt ignition and a astra 16is injection system, so I will run only 0.2 bar, until this thing is approved at the dmw. Then I will use my brand new 7" wheel on the crank(and upgrade with megasquirt and the works), and the compressor will be maxed at 5600 engine rpm, compressor will then have 14000, the compressor is rated a litre pr rev. The goal is to use 98 octane fuel.

I have tried a few blower calculators out there, but I'm not sure if the result is correct. It says with a ratio of 2,5 I'll have 17.9 psi (1.24 bar) boost. That would be cool if that was somewhere in the ballpark.
 

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I had these made some years ago by Venolia. They are 8.5:1 compression ratio for a 2.4 litre CIH engine, and rings have been lowered for high boost use. I also had the piston crowns and skirts coated by Swain Coatings.
 

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Discussion Starter #9
I had these made some years ago by Venolia. They are 8.5:1 compression ratio for a 2.4 litre CIH engine, and rings have been lowered for high boost use. I also had the piston crowns and skirts coated by Swain Coatings.
Do you think they still have a recipe for those? Those are made for standard rod sizes? I would prefer coating too, but not sure if anyone over here can provide that for me.
 

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Do you think they still have a recipe for those? Those are made for standard rod sizes? I would prefer coating too, but not sure if anyone over here can provide that for me.
Yes, they were made for standard length 134 mm rods.

I'm sure they still have the job number, but since these were ordered back when I had my business, they would not be available to the general public. They keep custom designs proprietary.

That said, if I gave you the "job number" to reference they could easily look them up. However I would have to find the original invoice first. I'm sure I still have it, I'm just not sure I know where to look for it.

As far as the coatings, they could be done in the US before shipping to you if you orders from them.
 

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Discussion Starter #11
Yes, they were made for standard length 134 mm rods.

I'm sure they still have the job number, but since these were ordered back when I had my business, they would not be available to the general public. They keep custom designs proprietary.

That said, if I gave you the "job number" to reference they could easily look them up. However I would have to find the original invoice first. I'm sure I still have it, I'm just not sure I know where to look for it.

As far as the coatings, they could be done in the US before shipping to you if you orders from them.
Ok, would be great if I could use your job number, else I have another option to send a piston to ROSS where I bought the pistons I have in my other kadett, I'm pretty happy with those. That would take some more time tho.

How hard would it be to get the dish calculations, could be a bit bigger, I'm thinking 8:1 for my setup.
 

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The optimal CR really depends on what fuel, the level of boost, and the peak cylinder pressures you can contain. Secondary considerations might be how knock resistant your chamber is, coolant temp, duty cycle (drag racing or endurance).

To bookend this - 150+ bar peak pressures (super strong headgasket/block/pistons/crank) , methanol, and drag racing, and 29 psi boost you could likely handle 11:1 or higher CR (near ideal spark)

110 bar peak pressure, 98 RON pump gas, endurance racing, 8 psi boost and 8:1 might make sense (significant spark retard to prevent knock)

For a datapoint, there is a new 2014 2.0L AMG-Mercedes that makes 355hp on premium with turbo (18 psi) DI, 150 bar cranktrain. It has a 8.6 CR and very nice 4V chamber.

Just $0.02, good luck
 

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Discussion Starter #13
Plan on using 98 octane unleaded. Original size head gasket (0.8mm?). And I think original size piston compression height, then the conrods aren't too expensive.

Anyone good with calculations? I think a dish depth of 6.5mm would be ok with a bore of 96mm. Anyone know the original dish size? Searched the forum and one place said 11cc and one 7 something ml..
 

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Plan on using 98 octane unleaded. Original size head gasket (0.8mm?). And I think original size piston compression height, then the conrods aren't too expensive.

Anyone good with calculations? I think a dish depth of 6.5mm would be ok with a bore of 96mm. Anyone know the original dish size? Searched the forum and one place said 11cc and one 7 something ml..
11.8 cc seems to be sticking in my head. I know I've checked them numerous times.
 

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Haven't found the invoice from Venolia yet, but I did find this picture I took. The Venolia piston dish volume is 21.8 cc's. The 2.5 head I prepared with big valves is 55.6 cc chamber volume, FWIW.
 

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