Olds 403 STREET performance builds?

[techg8]

403 guys chime in

Ive got an Olds 403 out of a 1979 transAm, and am curious what can be done with it.

From what I have found online, Its got the same problem lots of engines from that smogger era have....low compression and small cam

But its got a huge Bore and a comparatively short stroke, so it should have some good potential

I have read that swapping Olds 350 heads on can bump the compression up, and obviously swapping to a less-dished piston would do so as well. If I swap on 350 heads, is it a must that I add larger intake valves to the heads?

But what I am really interested in is what can be done with this 403 WITHOUT those specific mods?
I mean how far can one go with a cam before losing low end because of the poor compression?
Assuming a mild camshaft was installed, how much might some head porting help?
Would an edelbrock 3711 intake help with more than just weight savings?

Is the engine such a dog without the headswap/piston compression bump that it just wouldnt be worth it to go thru it without doing them?
Would it be better (or maybe more cost effective) to just nitrous it 50 or 100 shot?

It needs a regasket at a minimum so I am considering this very basic build - tell me if there would be any benefit to it....

Edelbrock performer cam and intake
Headers
2.5" dual exhaust
TH350 w/ B&M kit, 1800 stall saturday night special torque converter
3.08 or 3.23 posi rear

The goal is to build/have a good reliable street engine that can break the tires free from a stop without brakes, and is sporty/responsive to the throttle. Would rev to, but not over, 5000rpm

So what can be done to wake this engine up? Any thoughts/opinions appreciated.

 

[olds307 and 403]

KB pistons make Hyper pistons that raise the compression to 9.5 to 1 with stock heads. The stock heads flow less than early 350 heads, exhaust side especially. You can just swap on early heads, just by enlarging the head bolt and one dowel hole. That brings you from 7.8 to 1 to around 9 to 1. If you can find the. 028" Corteco head gaskets, that will give you a little bump too. I ran a stock 403 with .028" Detroit head gaskets, someone ground the rods .010" and used their gaskets, right around 8 to 1 compression. I added the Performer intake and Melling cam, indentical to the Performer cam and the basic Melling timing set. I also added 2000-2600 stall convertor which flashed at 2400. I had the awful single exhaust which someone necked down to repair, no cat but that joke of a cross over Olds put on nearly everything. I tightened up the air door,to get rid of the huge bog and then did 1/4 block burn outs. I had the 2004R trans with a better first gear but awful 2.56 gears. Without decent exhaust it spun the tires hard but then went flat. That stall will do OK but 2000 would be better and go with a better cam. I am currently running the Performer intake and cam in my low compression 350. I put the cam in the advanced postion on the Cloyes street roller timing set. Seems stronger and my stall is aound the 1800 mark. If I didn't already have that cam, I would have got a different one. I recommend the Cloyes Street roller timing set, very good quality. Cutlassefi on classic olds does custom grinds for low compression engines. Biggest problems with that cam are the bigger exhaust duration and wide lobe separtion. I couldn't break 15 flat with my 403 at the track, due to many problems, fuel stavation, convertor exploding, traction issues etc. Once I added 3.42 gears, 1/2 throttle tire spin was easy though. Make sure your cooling system is up to snuff, good rad, water pump, 7 blade fan with a good clutch and all the air directors and shroud are in place. No under drive pulleys and get the Robert Shaw high flow thermostat. I bought the Stewart Warner modified version which allow some coolant flow, even when closed.

 

[DRIVEN]

First off, I'm not a "403 guy"...yet. Most basic engine theory still applies though. While it is tempting to just keep the 403 heads and try to cover up the negatives with just a cam swap and/or nitrous, I think you're selling yourself short. I don't think I'd spend the effort to do a cam swap without a head upgrade. Adding compression will not only add power but will likely add MPG too. When building or improving an engine it's always important to match parts. Bump the compression and then be sure that the cam, intake, converter and gearing all compliment each other. Don't let HP numbers distract you. When it comes to street engines, making 400lbs of torque from 2000-4000rpms is always more fun than making 4000 peak horsepower at 6500rpm. John Lingenfelter used to say, "build for torque and the horsepower takes care of itself."

 

[1bad79]

check out real olds power forum and ask some questions,lots of guys running 403's they can help you out

 

[84dragcutlass]

Just make sure and change the pistons if you are going to be turning any rpm or pushing any hp or nitrous through it. If i remember right those are cast aluminum pistons that will come apart. I know the ones in my 455 are cast as well as the ones in he olds 350s ive seen. Absolute junk. Also watch the bottom end as the webbing in the bottom end of the block where the mains are is very thin and if you are pushing a lot of hp though it without a girdle you could end up digging your crank out of the road. If your not planning on turning more then 5000 you shouldnt have to worry about this but i would definetly change the pistons out at the very least

 

[olds307 and 403]

All Olds V8's had cast pistons from the factory, even the W30 and W31. Biggest problem is there weight in the 403, the KB, Diamond and Arias pistons shave weight over stock pistons. Honestly heads like Procomp heads make more sense for the 403. With small chamber 350 heads and any decent pistons equals 11 to 1 or better compression, way to much.

 

[L92 OLDS]

403 guys chime in

Ive got an Olds 403 out of a 1979 transAm, and am curious what can be done with it.
So what can be done to wake this engine up? Any thoughts/opinions appreciated.

I thought of pooper when I read your post. He runs a stock reciprocating assembly but he bolted on small chamber heads and has been running nitrous successfully for a long time in his 79 Trans Am. Great performance for a relatively low investment.

Are the cast pistons absolute junk? Not in my opinion....It depends on what your goals are. I run forged TRW's in my 403 but could have used the factory bottom end. Here are some links to poopers build and video. He hasn't posted on Oldspower in a while but that is where he hangs out. 7.5 in the 1/8th means he's running mid to high 11 seconds in the 1/4 mile. Not bad for a mildly built small block Olds.

https://www.youtube.com/watch?v=TBWmsX8M_zw

http://www.oldspower.com/vb/showthread. ... ght=pooper