High comp 1.4

Been offered a 1.4 with a 73mm nismo headgasket for a decent price.

My understanding is that this will give a comp ratio of around 10.5:1.

How reliable would a high comp 1.4 be? I understand the 1.4's have weak piston rings anyway, so I'm guessing it won't respond well to high comp?

Would really appreciate any advice!
 

frank

Club Member
the rings just wear a bit more ihtisham, they are a bit thinner, and 1.3/1.4 ones have further to travel
any cg responds well to higher compression, but you wont gain much from the thinner gasket
the stock ones are 2mm ish, so you can workout the gain from compression mathematically
 
the rings just wear a bit more ihtisham, they are a bit thinner, and 1.3/1.4 ones have further to travel
any cg responds well to higher compression, but you wont gain much from the thinner gasket
the stock ones are 2mm ish, so you can workout the gain from compression mathematically

Ah right that all make sense, I'll try to figure the compression out accurately now, thanks!
 
there should be some online calculators
but i get it to 1348 / 4 + chamber = 377cc
and combustion chamber + gasket + piston bowl at 40cc

Okay this is what I got.

(1 cyl = 377cc, divided by the 82.8 stroke = 4.55cc per milimetre of stroke )

Stock HG is 2mm (I think?). Nismo HG is 0.5mm (I'm pretty sure on this). So 1.5mm reduction in HG thickness = 6.83cc reduction in volume

Original volume = 377/9.5 = 39.68cc
New volume = 39.68-6.83 = 32.85cc
New compression ratio = 377/32.85cc = 11.47

So 11.47:1! I obviously gone wrong somewhere...
 
yes 10.4:1 for a cg10
and about 11:1 on a cga

that makes sense as it says 10.4:1 for the cg10, but didn't mention it for the CGA3! But the person I'm wanting to buy the engine from has somehow managed to get the nismo gasket for a CGA3.

Althought I may have to check it is indeed a Nismo gasket then...
 
Thanks to all for the help.

I ended up buying the engine :) still unsure whether I am going to put it in mine or whether to sell it on. It came with a set of autosprint cams as well which are roughly the same spec as my 774's, so the only advantage to using the new engine would be that it is higher compression and less worn...
 
that makes sense as it says 10.4:1 for the cg10, but didn't mention it for the CGA3! But the person I'm wanting to buy the engine from has somehow managed to get the nismo gasket for a CGA3.

Althought I may have to check it is indeed a Nismo gasket then...

The Nismo head gasket fits both the dizzy and coilpack engines. The bore is 73mm (cga3 is 72.5 and cg13 72 if i remember correctly)
Wasnt the stock headgasket 1.2mm?
 
Okay so yes the stock head gasket is indeed 1.2mm. So redoing the calculations:

(1 cyl = 377cc, divided by the 82.8 stroke = 4.55cc per milimetre of stroke )

Stock HG is 1.2mm. Nismo HG is 0.5mm. So 0.7mm reduction in HG thickness = 3.185cc reduction in volume

So 377/ (9.5 - 1) = 44.37

44.37 - 3.185 = 41.185

(377 + 41.185 )/ 41.185= 10.15

So the compression ratio will be 10.15:1. Makes sense as Nismo advertise it as 10.4:1 on a CG10 and 10.2:1 on a CG13.

I got 10.38:1 on a CG10, 10.17:1 on a CG13, and 10.15:1 on a CGA3.
 
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