[foundnemo25]

Well I was trying to answer the question that quite a few people asked. The 1.9 HO head on the 2.0 SPI block. Well we all know that they will bolt together but no one actually did it. After assembled I did a compression test even though the motor is on the stand. Cranking it over by hand it showed 130 (+/-) 5 across the board. If I get a chance to actually put it in a car to check the clearance of the intake manifold which should clear with no problems. I just thought while I had time on my hands that I would do something constructive and answer the long sought after question. It seems that the compression is a little higher than the 1.9 spi hybrid motor, if I were to say actual compression I would say between 8:2.1 - 8:5.1 which is still good for turboing. Now if I can get it into a car it will be ran with megasquirt so I wouldnt need a cam sensor. Figure that you would have the full Hemi combustion with the 2.0 displacement which would be the best of both worlds. Just my opinion. I will keep you guys informed when I get it in a car and hook a turbo to it.

 

[UnexplodedCow]

With that kind of compression test I'd wager it's more around 9:1 as a stock 1.9 HO engine gets around 135-ish PSI on a test.

 

[foundnemo25]

With the 1.9 spi hybrid motor it shows compression are 120-125 which is not that far off from that. 9.1 compression would be around 160-180 range depending on the cam lift.

 

[UnexplodedCow]

Along with head port shape and such. My current engine is a CFI, bored 1mm over, with heavily milled head, and the compression ratio math indicates a 10.3:1 compression ratio, yet it only gets 155 psi (all cylinders) on testing. It also will not run cleanly on regular gas...nothing but pings. 89 octane will run it, but it will be super weak, and 91+ it thrives on. The rings had .012" gap, were properly fitted, with new valves, and properly ground seats. The gasket is not leaking. Go figure, eh? I think it's just the intake design and ports that restrict the life out of the engine.


Edit: I've also seen people with very clean, low mileage stock CFI engines get about 130-135 psi on testing. HO engines typically get the same, too, although some get up to 150. The CFIs that are around 150 or so when compression testing usually are higher mileage, rough running pieces that have carbon coated chambers.

 

[foundnemo25]

True I do agree with you on that one. There are a lot that affects the actual compression test itself and you reall cant tell the actual static compression from the compression test. But one thing is for sure it cant be no more that 9:1 compression. Seeing that you have a larger displacement with the domes head would give you more space for air to take up. Best case is around 8:5. Either way would still be better off boost than the 1.9spi motor.

 

[UnexplodedCow]

I agree that it would be better. A little more displacement, and the HO is a good head. Good times.