If this motor came stock with a 4bbl, can anyone guess on compression? Looking to see if it's any higher than my 71 model.

Thanks

 

The only way to know is compare the dish in the piston side by side.

Just like valve sizes, you gotta take the head off to make sure.

 

true, BUT

yes, the compression dropped in 1971 compared to earlier years.

So, if both are stcok, the 1970 is likely on the order of 10:1 vs at best 9:1 for 1971.

 

Very true..



I'm gonna take "highschoololds" question very literally and peer into it a little more. Hopefuly I'm not being too ****.

What if someone told him it was a factory four barrel from either year. But instead, it was a two barrel motor (lower compression) and stuck a year correct 4bbl manifold and carb on it?

The only way to know is to take the head off.

 

I was thinking of taking borescope and compression gauge when I go look at the motor. I just wanted to see if what I had read was right, or if it was a waste of time to even go look at it.

Value?

 

Yea Josh, a 70 motor could certainly have more compression.

Just make sure you know what yer looking at...have fun.

 

Well I have had the heads off my 71. So I know how big that dish is...huge. Would it have flattops or the smaller dish. I'm thinking my 71 had the 23cc dish?

 

it would have a small dish unless its a w31 motor but not likely

 

So, theoretically, 9.0-9.5:1?

 

Yes

 

Not exactly correct.
All 71-72 350s had 68 cc head and 23 cc dish, cr was around 8 to 1, maybe a tad less.
70 350s had a 68 cc head and either a 6 cc (10 to 1 +/-) or 14cc (9 to 1 +/-) Cr. Actual cr on the low comp is closer to 8.5 to 1.

 

X2 with captjim . With the pistons being down in the hole about .025 to .035 and chamber being at 68 cc with a .022 shim gasket you will be around 8.5 to 8.7 to 1. Now if you got the heads to a true 64 cc and .010 deck height and .040 head gasket you will be in the true 9 to 1 area. close to 9.5 to 1 with a .022 head gasket .

 

I pulled my 72 apart and did the math with the big dish pistons. It came in at right about 8.1:1. I've seen a few other "9.0:1" 350's and they were pretty close to that when checked.

 

Thanks for all the information.