1g vs 2g compression

[1fast97gsx]

I was wondering if the 1g and the 2g had the same compression and if not what was different? I am building my motor right now and I'm looking to run about 8.5:1. I am using a 1g head with a 2g bottom end ( ) ... so I was just wondering how the 1g head will affect my compression ratio. Thanks.

 

[98RedGs]

http://www.dsmgrrrl.com/FAQs/compression.htm
Compression Results

 

[nineD5_GS-T]

Why not a 6-bolt bottom end. No point in wasting money on a 7-bolt

 

[1fast97gsx]

that wasn't the question ... my 7 bolt is perfectly fine.

 

[1fast97gsx]

ok is the 1g compression lower because of the pistons / rings being different from the 2g or because of the head? In other words ... if I had a stock 2g motor and swapped a 1g head on would my compression stay at 8.5:1 or go down to 7.8:1?

 

[Groomz]

Originally posted by 1fast97gsx
ok is the 1g compression lower because of the pistons / rings being different from the 2g or because of the head? In other words ... if I had a stock 2g motor and swapped a 1g head on would my compression stay at 8.5:1 or go down to 7.8:1?

It would stay the same.

 

[1fast97gsx]

thank you.

 

[RACER-X]

on the 6 bolt you could get a 1mm gasket and make it 9.1

 

[1fast97gsx]

with the 6 bolt head or the 6 bolt bottom end? 9:1 is what I'm looking for .... but on a 7 bolt bottom and 1g head.

 

[Groomz]

1G 7.8:1 compression + 1mm head gasket = 9.1:1 compression.

2G 8.5:1 compression + 1mm head gasket = way too high a compression ratio for a boosted street motor.

 

[1fast97gsx]

what are stock headgasket thicknesses for both 1g and 2g? I thought they were around .8 mm or so?? Wouldn't a thicker gasket then lower the compression?

 

[NOSNUSE]

To answer your question the dish on the 2g piston is smaller than on the 1 g piston which raises the compression, the head chamber is the same sizes on the 1g and 2g heads.

 

[kpt4321]

Don't use head gaskets to change compression.

 

[RACER-X]

i wasn't saying to do it that way, just trying to say how easy it is to munipilate (sorry for the s/p) the compression ratios

 

[NDgsx]

Uh running a thicker headgasket would result in a lower cr. Where are you guys getting your math formulas from?

499.25cc bdc / 64cc tdc = 7.8
I don't have real measurements handy so I'll make this up, say a stock HG has a diameter of 86mm (I know it's probably bigger, but it's an easy number to work with) and a compressed thickness of .4mm:
pi 3.14x43mm=13.69 squared=187.41x.4= 74.96cc stock gasket volume
Now a 1mm gasket will compress, we'll say .7mm installed (being more than generous). That would be 131.18cc, a dome volume increase of 56.22cc for a total of 120.22cc.
499.25bdc / 120.22cc tdc = 4.15

These are totally made up numbers and obviously WAY off, but they're just for illustration.

 

[1fast97gsx]

Originally posted by NOSNUSE
To answer your question the dish on the 2g piston is smaller than on the 1 g piston which raises the compression, the head chamber is the same sizes on the 1g and 2g heads.

Thanks that's all I was looking for.