350 output?

[Best truck design]

I just got a clean 1973 GMC c2500 pickup, originally a California Truck but it has spent the last 20 years in Colorado. CLEAN with no rust, never driven in the snow.

I am trying to ascertain what the original 350 cu in was rated at for horsepower? The Fender tag shows the option California SMOG. I heard from one source it was originally rated a low 150 hp?

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[77 K20]

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This says 155hp@4000 RPM. Doesn't specify the CA version.

 

[legopnuematic]

If you look below the alternator on the block deck surface where the cylinder head meets the block there should be numbers and letters stamped on it. They will tell you when and where it was mfg, the power output and displacement aswell as a partial vin of the vehicle it was put in originally.
This is the code from my 400 SBC. T0413CLK T-Tonawanda, 04-April, 13-13th day, CLK- 400ci, 2bbl, 265hp, turbo 350 transmission
The code to the left 11J182718 is 1-Chevrolet, 1-1971, J-Janesville, 18271- production sequence.

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[75gmck25]

If the truck has a high GVW, California smog gear was next to nothing in '73. My California emissions '75 K25 only has the vapor recovery canister and PCV. There were no catalyic converters, no EGR, no air pump, etc. for my 8200 GVW truck.

I think the rating of the 350 was about 175 HP in that timeframe. It sounds (and is) lame, but you have to remember that in 1971 they started using net instead of gross HP ratings, so everything is lower than it was in the 60's.

For a mild wake-up you can swap in a modern dual plane manifold, advance the timing to about 12 BTDC, and open up the exhaust and you should be able to bring up the HP to something more reasonable. An RV cam (about 214 @ .050) will add a little more, but beyond that you need to look at work on the old low compression heads. Using much higher lift cams won't help because you don't have the compression or head flow to make them work well.

Bruce

 

[Jrgunn5150]

I tell people all the time when they are planning a build and just won't accept anything less than some lofty arbitrary HP goal that 150 hp was enough that people still crashed them into poles sideways lol.

A legit 300hp small block would shock most people, even today, especially without all the driving aids most car's have now.

 

[rpcraft]

Your basic 350 engine put out around 160 to 175 horsepower sitting in the truck until they came out with a Vortec L31 in the mid 90's. What it lacked in horsepower it made up for in torque, usually up to about 275 lb/ft on the ls9 (low emission engine) and then there was the LT9 high emission variant. Both engines made about the same power but the high emission one made it all at higher RPM's (not sure what the thinking there was) People will argue that the old engines made more power, but what changed, somewhere along the way is the way the big 3 rated horsepower. I'm not sure why exactly but I think it had to do with the emissions gestapo. I believe it was Net vs Gross horsepower and the difference was the equipment put on the engines when testing for power ratings. Things like exhaust manifolds, air cleaners, and other things that would actually be on the motor for real world use brought the power down, often times as much as 100 HP. Uncorked the engines made close to 100 more horsepower but it looked bad on paper for things like fuel consumption and what not, so they turned to net horsepower as a way to make them look like the output was lower. I am sure some old times will chime in if they are actually on the internet here, lol....

Here is a little article I found on the difference in rating over at Hagerty: https://www.hagerty.com/articles-videos/articles/2013/08/13/horsepower

 

[legopnuematic]

Both engines made about the same power but the high emission one made it all at higher RPM's (not sure what the thinking there was)

I believe the reason for higher peaks was due to the cam timing being retarded, I guess it made the emissions 'better' at the loss of low end and slight gain in the peak rpm numbers. I know that 460 BBF cam's were retarded by 4 degrees in the mid to late 70's for emissions.
https://help.summitracing.com/app/a...06/~/camshaft-basics---advancing-or-retarding

 

[bucket]

I believe it was '72 when GM changed their HP ratings.

 

[73c20jim]

My 71 Vette was rated at net.

300HP in 1970; 270 in 1971.

 

[Jrgunn5150]

I believe the reason for higher peaks was due to the cam timing being retarded, I guess it made the emissions 'better' at the loss of low end and slight gain in the peak rpm numbers. I know that 460 BBF cam's were retarded by 4 degrees in the mid to late 70's for emissions.
https://help.summitracing.com/app/a...06/~/camshaft-basics---advancing-or-retarding

Chevy didn't really retard cam timing, they just put giant open chamber heads on to drop the C/R. Ford put the pistons way in the hole and retarded the timing to keep them running on the new, much lower octane fuel.

 

[Best truck design]

If the truck has a high GVW, California smog gear was next to nothing in '73. My California emissions '75 K25 only has the vapor recovery canister and PCV. There were no catalyic converters, no EGR, no air pump, etc. for my 8200 GVW truck.

I think the rating of the 350 was about 175 HP in that timeframe. It sounds (and is) lame, but you have to remember that in 1971 they started using net instead of gross HP ratings, so everything is lower than it was in the 60's.

For a mild wake-up you can swap in a modern dual plane manifold, advance the timing to about 12 BTDC, and open up the exhaust and you should be able to bring up the HP to something more reasonable. An RV cam (about 214 @ .050) will add a little more, but beyond that you need to look at work on the old low compression heads. Using much higher lift cams won't help because you don't have the compression or head flow to make them work well.

Bruce

Yes you called it. It is a Camper Special 8200 GVW truck. 350 4 bbl but it sure doesn't run like it. No emissions equip to speak of and it is ORIGINAL. It has a canister and a PCV and thats it.

 

[Best truck design]

Ok If I were to keep the 350 is there a Good vortec or aluminum aftermarket head I can get that is reasonable for a upgrade with these (i assume) low compression pistons, for a little better performance?

 

[rpcraft]

Ok If I were to keep the 350 is there a Good vortec or aluminum aftermarket head I can get that is reasonable for a upgrade with these (i assume) low compression pistons, for a little better performance?

Yep, Summit sells GM vortec heads as does Jegs. They are so common and cheap now it's not barely worth it to try and source them from a salvage yard now days when you factor in the rebuild cost. Get yourself a matching intake and put a good performer carb with a torque yileding RV cam and you are probably doing about as good as you ever will be able to without tossing a ton of money into the block.

 

[Best truck design]

Yep, Summit sells GM vortec heads as does Jegs. They are so common and cheap now it's not barely worth it to try and source them from a salvage yard now days when you factor in the rebuild cost. Get yourself a matching intake and put a good performer carb with a torque yileding RV cam and you are probably doing about as good as you ever will be able to without tossing a ton of money into the block.

Suggestions on which heads to get?

 

[Rusty Nail]

This.

I tell people all the time when they are planning a build and just won't accept anything less than some lofty arbitrary HP goal that 150 hp was enough that people still crashed them into poles sideways lol.
A legit 300hp small block would shock most people, even today, especially without all the driving aids most car's have now.

Well said buddy, I concur.

O.P. you can cheaply,easily, and simply, change the head gaskets for a modest HP gain.
I support 305 heads on 350s if you are mechanically inclined at all that can be very rewarding because people.
#416s are /win for CHEAP.

I believe there is more power than you think to be found and had, even made, in a fresh and very thorough tune-up with modern parts. Your 1973 distributor ain't cutting mustard. Plus, if you keep your foot out of it, your gas mileage savings can pay for the parts p.d.q.

An improved exhaust syatem will pay handsome dividends.

Good luck, she's beautiful.