69-72 c10 350

[SCOTI]

How were these C10 truck motors set-up from GM? Were they flat top piston/large chamber heads? Dished piston w/large chamber heads? Dished piston/small chamber heads?

I can't remember when GM started making changes on the truck sbc's for emissions/gas compliance needs.

[HotWheelsFan]

I have no idea as to truck changes compared to passenger vehicles however, 1971 (and later) was the year engines had reduced compression. Head chamber sizes may have changed a couple years before dished pistons?

You may find better info by looking up head castings and the specs.

Bob

[SCOTI]

Originally Posted by HotWheelsFan

I have no idea as to truck changes compared to passenger vehicles however, 1971 (and later) was the year engines had reduced compression. Head chamber sizes may have changed a couple years before dished pistons?

You may find better info by looking up head castings and the specs.

Bob

I was thinking '73 on trucks since cars seemed to get the changes first but wasn't sure. That being said, there's a big difference on what head is used between a flat-top piston vs. a dish. Never had a factory early 70's C10 sbc apart to know what pistons they had.

I plan to look @ a factory late 60's early 70's 350/350 C10 pull-out combo to use for a strategic flip scenario. Knowing how these came from GM potentially helps w/the strategy.

[YellowK5]

All 3 of the 350 I have worked on recently have flat top pistons with valve pockets and large chamber heads..they were 71 to 76 engines

[SCOTI]

Originally Posted by YellowK5

All 3 of the 350 I have worked on recently have flat top pistons with valve pockets and large chamber heads..they were 71 to 76 engines

Well.... I'll find out soon enough. I'll have this 350/350 combo in the next several weeks.

[MARKDTN]

Most of the early truck and passenger 350s I have seen had flat-top pistons with valve reliefs. In fact, I may be wrong, but I don't remember any stock 350s having dished pistons-at least not any I have torn down.

[SCOTI]

Originally Posted by MARKDTN

Most of the early truck and passenger 350s I have seen had flat-top pistons with valve reliefs. In fact, I may be wrong, but I don't remember any stock 350s having dished pistons-at least not any I have torn down.

Thanks for the info as this sort of stuff is exactly what I was curious about. My C10's were 67/8's w/straight 6's.
My old '74 had a 350/350. I never cracked open that 350 since it got the job done as-is.

I figured if this 350 has flat tops, it should have decent (well, better) compression vs a dished piston/76cc head combo.

[A1971Blazer]

I think 72 was the first year that the pollution laws started to effect the 350 specs
Any 350 that I ever disassembled before that had flat top pistons with 4 valve reliefs.
Only the performance engines got the higher compression heads so most stock 350s would run on regular gas. Of course it was leaded gas and better than today's regular 87 octane.

[fatbass]

Originally Posted by A1971Blazer

I think 72 was the first year that the pollution laws started to effect the 350 specs
Any 350 that I ever disassembled before that had flat top pistons with 4 valve reliefs.
Only the performance engines got the higher compression heads so most stock 350s would run on regular gas. Of course it was leaded gas and better than today's regular 87 octane.

Correct me if anyone knows if this is nonsense but, I'm pretty sure all Chevy engines had hardened valve seats by 1972. My 1971 350 in my K10 (built in sept, 1971) had hardened seats according the the machine shop that rebuilt the heads. That was so the engines could burn unleaded without valve seat erosion since the factories knew the feds were mandating no-lead gas soon.

[SCOTI]

I googled for sbc head data. 76cc/large chamber heads were in production by '71. Prior to that was mostly 64cc stuff.

[MikeB]

Here's what I found in various places:

Truck 327s had 64cc heads, and it looks like some even had 70cc or 76cc.

However the only 350 I can find with 64cc heads was the 370hp/LT1 350, used in the Z28 and Corvette. Compression ratio was around 11:1, as I recall.

69-72 passenger car and truck 350s had 70, 75, and 76cc heads. Possibly with flat top pistons but probably with dished. Compression was probably around 9:0, and then may have dropped a little in the early 70s.

[SCOTI]

Originally Posted by MikeB

Here's what I found in various places:

Truck 327s had 64cc heads, and it looks like some even had 70cc or 76cc.

However the only 350 I can find with 64cc heads was the 370hp/LT1 350, used in the Z28 and Corvette. Compression ratio was around 11:1, as I recall.

69-72 passenger car and truck 350s had 70, 75, and 76cc heads. Possibly with flat top pistons but probably with dished. Compression was probably around 9:0, and then may have dropped a little in the early 70s.

My thought was 350's were flat tops & >64cc heads for around 9.0:1 minimum through '71. And prob '72 (as the beginning of phasing out leaded gas began), the dished pistons became the norm.

[special-K]

I know in truck 350s the HP peaked in '70 and by '72 they dropped a lot of HP. I think in '72 what came later had just begun. I see where a 70/71 350 could have 255hp and in '72 it dropped to 175hp max

[Grumpy old man]

Almost 5 years to the day I brought home this 350 I found on the right day from a friend of a friend who was parting out what was left of his project truck that he wrapped around a tree .

Originally Posted by bruceman1968
Hey Grump, You got everything you need there to positively identify your block.

VI208TBC
3970010
L10

L10 is the casting date
L = December
1 = December 1st
0 = 1970
Your block was cast on December 1st 1970

3970010 in 1970(or 1971 see below) is a 350cid.

VI208TBC is V1208TBC
I's used for 1's is very common when found stamped on Blocks.
1208 = December 8th
Your Block was cast December 1st and assembled on December 8th in 1970.

Casting Date codes are the day, month and year they say they are, but Suffix codes go by Model Year. Your block is December of 1970 which is the 1971 Model Year. So when you look up TBC you have to do it for 1971.
In 1971 TBC = 350cid, 255hp, 350auto, LS9, 4bbl, 10,20 C or K
So you have a 1971MY 350 Truck motor.
Great price. BTW

This thread shows what I found inside .
http://67-72chevytrucks.com/vboard/s...d.php?t=752595

[Grumpy old man]

After 5 years of constant project creep I'm still working on it . I've come close to pulling it back out and just to find out what pistons are in it , But I can't tear apart a good running engine . Maybe it's time I bought a bore scope ?

[special-K]

Originally Posted by Grumpy old man

After 5 years of constant project creep I'm still working on it . I've come close to pulling it back out and just to find out what pistons are in it , But I can't tear apart a good running engine . Maybe it's time I bought a bore scope ?

For my '67 project I have a freshly rebuilt '68 truck 327. Freshly rebuilt in '07 that is. I plan to crack it back open now. Back then I used 64cc iron heads and the choice of cam was based on using the TH400. An M22 crept up so I want to do some top end changes now anyway.

[Rickjz]

Originally Posted by special-K

I know in truck 350s the HP peaked in '70 and by '72 they dropped a lot of HP. I think in '72 what came later had just begun. I see where a 70/71 350 could have 255hp and in '72 it dropped to 175hp max

The reason for the HP drop in 1972 is that they started listing net HP as opposed to gross. Basically the same engine.

[Warrens69GMC]

Originally Posted by Grumpy old man

After 5 years of constant project creep I'm still working on it . I've come close to pulling it back out and just to find out what pistons are in it , But I can't tear apart a good running engine . Maybe it's time I bought a bore scope ?

Rent one at Autozone. Ends up being free after you return it.

[MikeB]

If there are actually any left, I'd like to tear apart a previously unmolested 69-70 truck 350 to see piston type, gasket thickness, and actual deck height. You can easily tell combustion chamber volume by removing a valve cover and looking at the casting number.

I say "truck 350" but C20s and C30s may have had smaller camshafts along with lower static compression than C10s, achieved with either dished pistons and/or 76cc chambers.

[Yamariv]

I'm looking for a period correct"ish" 350 for my truck and have been watching this thread closely. So if I'm understanding this right, a mid 70's low compression block was the same as the earlier high compression block, it was just the heads and pistons that changed in the smog era for low compression?

I have a line on a 1974 350 out of a Monte Carlo, if the above is true then maybe I should grab it and put high compression heads on it and flat 1970 pistons and I'm good to go?

[Grumpy old man]

Originally Posted by Yamariv

I'm looking for a period correct"ish" 350 for my truck and have been watching this thread closely. So if I'm understanding this right, a mid 70's low compression block was the same as the earlier high compression block, it was just the heads and pistons that changed in the smog era for low compression?

I have a line on a 1974 350 out of a Monte Carlo, if the above is true then maybe I should grab it and put high compression heads on it and flat 1970 pistons and I'm good to go?

Ahhh, There's a little more to it than that . That 74 monte engine had about 165 hp , Probably a 2 barrel carb and was a smog motor

[Yamariv]

Originally Posted by Grumpy old man

Ahhh, There's a little more to it than that . That 74 monte engine had about 165 hp , Probably a 2 barrel carb and was a smog motor

So no easy way to getting her up to 1970 Compression and specs w/o too much money invested?

[MikeB]

Just found this at the GM Heritage Center website:

There were several 350s available in 1969. The TurboFire 350 had 9.0:1, 10.25:1, and 8.0:1 compression depending on the vehicle. The 10.25:1 engine was listed as an available option only in the El Camino.

The High Torque 350 had 8.0:1 and 9.0:1 compression and was used in HD trucks.

Start here with pdf document page#52: https://www.gm.com/content/dam/compa...olet-Truck.pdf

You can find all kinds of specs here.

[MikeB]

Originally Posted by Grumpy old man

Ahhh, There's a little more to it than that . That 74 monte engine had about 165 hp , Probably a 2 barrel carb and was a smog motor

Don't forget that HP and TQ specs went from "SAE Gross" to "SAE Net" in either 71 or 72. That alone would drop HP ratings by 20-25%. But throw in lower compression and emissions controls and you may be down 30%.

Somewhere In my searches I ran into ratings for Gross and Net numbers listed for the same engines, but I forget where that was! One that I think I remember is a 307 was rated 200hp Gross and 155hp Net.

[special-K]

Originally Posted by Yamariv

So no easy way to getting her up to 1970 Compression and specs w/o too much money invested?

Sure there is. Just do as you planned, flat tops, better heads, and cam. Those were the things that defined "smog motor". Anything else is added externally.