are the 403 small block and the 350 pretty much the same engine, or is the 350 stronger.

 

the 76 and older 350 blocks are stronger. as far as power the 72 and older will make the best 350. in 77 they took much of the casting out of the webbing of the mains.

 

i was also told that you can put 350 heads on the 403 and make better power. i don't know which heads but i am sure that someone will have better info coming.

 

so my 403 in my 77 cutlass is a little souped up with a 4 barrel carb and eldelbrock parts, and long tube headers with 2 1/2 inch dual exaust, so it moves and sound pretty good, but ive been told to keep a close watch on the cooling sytem because of the webbed mains.

 

If you guys are not running 11's or faster, with 10+ compression, DO NOT WORRY about the 403.
Think of the 403 is a .300 over bored 350.
Yes, the took a bunch of material out of the main bearing webs, as they also did on 77^ 350's.
Running the 403 is like a 50 hp boost compared to a 350, JUST because of the bore/cubic inches. The factory saddled it with poor compression to keep it down. The 350 heads addresses the compression problem, 403 heads will make good power if you have better pistons.
Jim

 

You are correct. The 77-80 350 blocks have the same windowed mains as the 403 does.
The 68-76 blocks are all the same. Same casting number, same metal used in the casting. It's just the 73-76 got the #8 heads and lower compression that killed the stock power numbers.

 

well, im not racing it or anything like that, its just fun to sometimes punch it off the light with somebody beside me and see there shocked expression..... when im suddenly gone.

 

Putting 403 heads on a 350 will kill any kind of power.

Typically 403 heads are 83cc's where the 68-72 heads are 68cc's a 15cc increase is a lot

 

Could you explain that, please? The smaller chamber increases compression, and most older 350 heads flow better than the 403 #4 heads, IMO.

 

What do you mean by "stronger"?

The dimensions and architecture of the two motors are the same, but the 403 uses a unique block casting since the cylinders are siamesed to fit that large bore in the block. Other Olds small blocks have coolant passages between the cylinders. Also the 403 obviously uses different pistons as well as beefier rods and different crank balancing. It does use the same 3.385" stroke as all SBOs.

All 1977-up gasoline Olds blocks have windowed main webs. All use the larger 1/2" head bolts.

Um, you're both right. Reread Redog's post, where he said that putting the large chamber 403 heads on a 350 that originally had small chamber heads would cost power. He's correct, however the original question was about putting early 350 heads on a 403.

 

i have the rebuilt 200 miles ago 400 turbo trans with this motor, seems to run very smoothly, cant hardly tell when it shifts, is this a good trans for my motor setup, and also would these two be original to my 77 cutlass supreme?

 

My bad, I read it backwards, as you said I was thinking in terms of 350 heads on a 403. Sorry.