Engine differences

JGT

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What made a 1968 350 cu. in. engine a 230 hp or a 280 hp engine? Were they made differently besides having different carburetors?
 

JGT

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1968 Buick Skylark
So if you have a stamped 230hp engine with a 4 barrel intake and carburetor then what is it‘s horsepower?
 

MelsRegal

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So if you have a stamped 230hp engine with a 4 barrel intake and carburetor then what is it‘s horsepower?
Maybe 25 more than with the 2bbl. Compression is an important factor in creating more power.
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LARRY70GS

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What made a 1968 350 cu. in. engine a 230 hp or a 280 hp engine? Were they made differently besides having different carburetors?
I see these questions all the time. Someone wants to know how much horse power they have, sometimes after they added x, y, and z to the engine. Prior to the early 70's, engines were rated in a different way than they are today.


Those HP figures were often exaggerated and manipulated for marketing purposes. A perfect example is the 1970 Chevy SS 454 LS6 engine rated at 450 HP. The 1970 Buick GS455 Stage 1 was rated at 360 HP. Both cars produced virtually the same 1/4 trap speed performance, about 101-102 MPH. Trap speed tells you how much HP the engine is actually producing. So how could one engine be making 90 HP more? It can't be, that's the answer. Bottom line, if you want to know how much HP your engine is producing, put it on a Chassis dyno. That will give you rear wheel HP, a much better predictor of real world performance. Or, take it to the track and run it down the 1/4 mile. If you want to brag about how much HP your engine is making, nothing states that better than a time slip. Here's a chart for rear wheel HP,


If you run your car at the track, note the E.T, and trap speed.

Cecil091914AED.jpg


My 70 Buick has run a best of 11.54@ 116 MPH, and it weighs 4100 lbs, with me in it. Plugging those numbers into the first calculator,

RWHP.JPG

That's about right, my engine made 602 HP @ 5900 RPM on the Engine Dyno.

Motor2FinalPull.jpg



More static compression, hotter camshaft, bigger carburetors, and free flowing exhaust is what it takes to make more HP. That is just as true today as it was back in the day.
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LARRY70GS

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What makes the compression higher?
Smaller combustion chambers, and smaller piston dish/valve reliefs. Also, stock pistons tops are actually down in the hole .040" to as much as .090" at TDC. When rebuilding an engine, it pays to strive for zero deck. Zero deck is when the piston top is even with the block deck at TDC. More efficiency and power and resistance to detonation are the result. Here's a static compression calculation for my engine,

Motor2SCR.jpg
 
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JGT

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So basically in 1968 they made a 350 engine with 2 different cylinder heads and pistons correct?
 

LARRY70GS

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So basically in 1968 they made a 350 engine with 2 different cylinder heads and pistons correct?
No, cylinder heads were the same. Piston dish volume was different. One engine was rated at 9:1 compression, and the other was 10.25:1. I can tell you even that was fudged. When taken apart and measured, the compression was less.

1968350.JPG
 

2007LucerneCXL

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Agree and a lot of the published numbers during the 60's which some had been done with a nod and wink.
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JGT

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Ok. Thanks guys. I was just wondering. Like you said in a previous post after 50 plus years different parts from different years tend to get rebuilt together like my 69 rear bumper on my 68 .
 
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