What are the internal differences if any between the GS350 and the standard 350 motor? Are there cam and head differences like the standard 455 vs the stage 1 option or was it just a 4bbl carb and gearing?
There is no difference. A 350 4 barrel is the same engine regardless of if its on a GS or a Skylark. Even the gearing was like that of a Skylark. Ive had plenty of 3.08 peg leg GS-350's
I was under the impression that the GS 350 had higher compression pistons (10.25:1) and the standard 350 had lower compression pistons (9:1), and that the GS 350 engine could be ordered on regular Skylarks as well? Info from here: http://www.socalgs.com/wildcat/septoct02.pdf
A 2.56 is not really like a 3.08 the 70 GS 350 had a different cam, carb,,distributer,and hi compression pistons that the base 4 barrel did not have. Trans had slight changes also. 71-up they got lame
There is no evidence I could find for a GS specific cam for any year in the GM parts books. As far as I can tell only compression differences up to 1970.
A 1970 SP code 350 could be had in either a Skylark or a GS, so the engine wasn't GS specific. Yes, there was a lower compression 350 4bbl available in the Skylarks coded SB.
No "GS" specific engine mods, other than the dual snorkel breather and dual exhaust and maybe some distributor curve differences. Other than badging and gearing, GS350 was essentially a standard issue Skylark 350. I don't believe there was a GS 350-2 though; they were all 350-4. Only difference was in 1970, where there were 2 different engine types, the "9:1" (in both 2 barrel and 4 barrel) and the "10.25:1" versions (4 barrel only). Only cam differences were 'supposed' to be over the years, not within the years. All replacement and OEM cams use the same part numbers for those years, so same cam. Cam change happened in 1975 I believe, when it got even smaller and topped out at 4200 RPM in order to aid with emissions control and catalytic converters. All 350-2 and 350-4 were same in '68 and '69, with the 2 barrels having "9:1" and 4 barrels having "10.25:1". I believe '71-'74 were essentially the same except for the addition of the EGR (exhaust gas recycling) valve and the air pump starting in '73 I think. The '71-'74 were rated at "8.5:1" and '75-'80 were rated at "8:1". Actual compression ratios were lower than rated. There was a head transition within this '71-'74 period, where it got thicker and resisted cracking more. We suspect it was in '73, though others here will have more info regarding this. Gary
Like Buick64203 said: "A 1970 SP code 350 could be had in either a Skylark or a GS, so the engine wasn't GS specific. Yes, there was a lower compression 350 4bbl available in the Skylarks coded SB" I believe the stamping is located on the face of the block that is exposed between the #1 and #3 spark plug if it's in the same place as on the 455s.
I must be special . . . Does anyone have a picture of this area? I've been sticking my fingers around the block to try and feel for raised letters but I'm having trouble finding it! Can anyone take a picture or a 350 and circle the area in red for special people like me? Or is this something that can't be seen with the engine in the car?
You can see it with the engine in the car. Unless the block was milled during a rebuild and the letters got milled off.
thanks for all the info guys. I found my s/n. mine is an SO code which had me confused, I was looking for the SP or SB. I looked in my chassis manual and found that SO is a 2 barrel motor with the lower 9:1 compression. it is listed at 230 bhp. the SB is listed at 285 bhp. same compression, only difference I could see is the 4 barrel carb. so by swapping to the 4 barrel as I am in the process of doing, should make a noticeable difference? Some other threads I have read on here were leading me to believe that the seat of the pants results may not be what I was expecting...
There is no doubt that the 4bb intake and carb swap adds Hp, but there is also a slight loss in low rpm torque.
Are you saying it has been observed that the 2 larger barrels of the 2 bbl carb help low end torque more than the smaller barrels of the 4 bbl? I've not tested every possible combination, but I've seen the opposite effect.
