Can't decide. stock 350 or 403! help

[CHRIS.O]

If the intake has a spreadbore carb flange you shouldn't have any problems. The 403 is a solid base for a good street thumper or just fine as is.

 

[Minion1186]

Both are good choices, both blocks are also windowed mains, a lot weaker than a typical late 60's early 70's blocks, but they can handle a few ponies but I personally wouldnt try revving it to the sky.

I would go with a 403, more torque than the 350. Putting 350 heads on the 403 is also a good choice.

 

[brian_wms]

i've been reading about an RV cam? 350 heads are hard to find in my area.

 

[CHRIS.O]

I thought you wanted a stock rebuild? You are going to be very impressed at the improvement of just dropping a stock 403 in over your 307. If you want to sauce it up a little thats fine but don't go overboard. If you want a cam for it call a cam company and tell them exactly what you want and what your set up is going to be, stall, gear ration, compression, etc. With a fresh rebuild, stock heads, intake, mild street cam, headers you will probably put out around 250hp/350 torque. That is nothing to sneeze at. Stock lt1 f bodies run real close to those numbers and run low 14's. I have also seen them in high 13's with good tires. With the engine I described, a gear ratio of 3.23 or around there and traction you would be in the 14's easy. Have fun frying the drive tire at 30 mph haha.

 

[beeterolds]

If you had the opportunity to grab a complete stock 68-70 350...that would be the way to go.. while the later thin blocks motors make good street motors it remains obvious that the 403 is the way to go..

I had one in my Cutlass..bone stock I was able to run 14.40 with it.. Early 350 heads and a nice comp cam allowed me to go 13.30s..

403's make killer street motors... as long as you dont plan on spraying it or run 10s-11 with them 😉

 

[brian_wms]

Well ill just keep it stock. Just want some more than 307 and keep the stock look, plus be able to keep up with my buddies with chevy 350.

 

[RITTER]

If you implant a 350 or 403 in place of that 307 it will look completely stock, but have a lot more power :!:

 

[bill]

If you implant a 350 or 403 in place of that 307 it will look completely stock, but have a lot more power :!:

 

[brian_wms]

Will my current exhaust system form the 307 hook up and my a/c? I think the a/c is ran through the CCC system how to bypass this?

 

[olds307 and 403]

Yes, the stock exhaust will work but seriously look at getting dual exhaust. I had single stock exhaust WITHOUT a catalytic converter and a glass pack muffler. Ran hard off the line then fell hard on It's face after that. Added a Cat back dual outlet exhaust, ran much better. I would run the stock early 307 HO cam or smog 455 cam, 197/204 .440/.440 vs 194/198 .400/.402 stock, lament. You only have around 7.8 to 1 compression, stay small on the cam. The Lunati high efficiency series 207/207 .461/.461 would also work, wouldn't go much bigger.