Cjs1969

I decided to to keep my olds 403 in my 1969 cutlass, but everywhere I look the 403 gets a bad name. I heard that different heads and an intake can go a long way, just looking for some tips to make the most out of the engine!

-CJ

394olds

Joe Mondello didn't think this was a bad engine and neither do I (I have a Mechanical Engineering degree from UVa). Joe wrote an excellent summary in JWO (Journey With Olds) in the late 90s as to how to build an excellent street 403 that developed a true 350 hp.

It essentially replicated many of the attributes of a 1967 442 400 CID engine, which (what a surprise - was rated at 350 HP!)

There are two paths to follow: I built mine with "C" heads, W-34 cam (JM 16-20), Comp roller-tip rockers, Edelbrock Performer "RPM" intake for small-block (high rise), and Arias forged flat-tops giving 9.5:1 compression. I used a 1970 N-code 350 crank and stock rods. I used a Stage II re-jetted Q-jet from a 70 98. I used an Pertronics III ignition. Essentially what I wound up with was the equivalent a 67 442 automatic 400 CID.

The other path is to use 1968-70 350 CID heads (#5 or #6) and stock 403 pistons - still yields about 9.5:1 comp. Cheaper and you don't have to listen to the Arias Forged units rattle like a diesel when cold. I hate the noise BUT the "C" heads are light years ahead of a 350 "5" or #6. Use all the other pieces above. Saves about $500 as Arias is real proud of those forged slugs.

A note on the crankshaft - if you lay a stock 403 crank alongside a 350 N crank the decision does not take long to make. The 403 unit is a lightened unit with every pound removed anywhere they could. It's fine at 180 HP pulling a 98 down the freeway at 70 mph to the end of time. In a street only car that only occasionally is stressed to 4800-5000 rpm it would likely survive in the above application but the 350 N crank is only a $150 or so item.

This is a quick baseline for you to have some fun with a very light large displacement engine!

Good day

PS - Joe would have encouraged your project - RIP

Cjs1969

I plan to check out mondello after work but what's your car running hp and torque anything you would change about you 403?

Doug Blake

For a stronger 403
Cylinder Heads:
If your running stock (8.5:1) pistons, switch to a 350 #5 - #7 head, and install W-31 valves. Otherwise fully port/polish the 403 heads, and install 2.072/1.71 valves.

Block: Use ARP main studs rather than the stock bolts, as the studs will be less prone to damaging the main web area, also install a Halo Support Girdle. Should only be overbored to clean up the bores, to reduce the chance of cylinder wall flex; suggest a maximum of 0.030", with a 0.020" as better. TRW forged pistons #L2230F, will make 10.2:1 if the heads are milled 0.040". KB forged #KB-405 also make 10.2:1 compression with a 0.040" head mill. Forged pistons are available from Aries #16100100, Venolia #403V.

Camshaft: For the street, go with Mondello's JM-18-20 or the factory 409759 294*/296*cam with a 2800 stall and at least 3.42 gears

Exhaust: 1-7/8" x 3" MJ Proformance/American Racing Headers, and "X" pipe

Intake and Carb: Replace the stock intake with an Edelbrock Performer 3711, if running ported heads go with the Edelbrock Performer RPM 7111.

Cjs1969

How do you feel about edelbrock heads? Bang for buck? Polish and Mill 403 heads or pay for the edelbrock heads?

394olds

The Edelbrock heads are a very good move. You will spend a significant part of their cost (~$1500) simply rebuilding and modifying any of the above mentioned Olds heads and wind up with an inferior head to the Edelbrock. They flow superior to a "C" and more important you can raise your compression ratio to a true 10:1 - a big deal. With the weight savings they will make the most of your 403! Money well spent.

I replaced the stock "E" heads on my 70 XS with the Edelbrocks and walked away with a big smile on my face. Very noticeable thrust increase over the E.
Probably 50 HP out of the box with a compression hike.

You asked about what I would change on my 403 above. I did my 403 for well less than $2000 so from that perspective - nothing. Very happy with it - smooth, responsive and powerful. First a correction - the cam I used was a JM16-18 (correction) - 210 intake 216 exhaust, which closely approximates the W-34. It idles pretty smooth. Anything above that (like the 18-20) your idle will begin to deteriorate.

A very commonly used street grind for the 455 is a 214 intake 224 exhaust .480 lift spec. Multiple cam manufacturers offer it including Mondello and Schneider. Idles with a little shake but pulls hard past 5200 rpm.

A block girdle at 350 HP is unnecessary.

I did not bore my 403 but agree that this is a light unit and care should be taken in boring even to .030.

Intragration

I've seen some good things done with 403s. They may be slightly harder to cool, and they don't have the displacement of a 455, this is probably what you've been seeing them ripped for. Still a good motor IMO, and a healthy displacement bump over a 350.

Run to Rund

If you use Edelbrock heads on a small block, the mechanical fuel pump won't fit. If you want to build it for higher HP, consider a J&S halo girdle for the mains.

Cjs1969

Which fuel pumps would fit?

Doug Blake

None, you will have to go with an elec one

copper128

I'd recommend calling Jim Lapikas at J&S Machine. He knows very well what works in a 403 and he is one of the few Olds engine builders who not only will build a 403, but races one in his own car.
Jim's # is 309-361-0907

Cjs1969

Sorry for all the questions im completely new to cars. What size and strength elec pump should I be looking at?

Dave Siltman

I have some news for you----my builder will recommend using 403 rods in a high-horsepower 350. He and his father (both very hard-core Oldsmobile drag racers) have had some very good luck with this combo. He (the son) attended Mondello's courses and I respect his knowledge and advice.

oddball

So there is already a 403 in your '69? First thing's first - what heads are on it, and has it been bored already?
If it's already bored and there's any wall damage, then the block is pretty much useless. If the engine is untouched, then you can build on it. But being swapped into a '69, I bet whoever did that rebuilt it.
Building a 403 takes a little more detail than the 350 or 455, so you might want to enlist a local to help or turn it over to a good shop. Where are you located?

I posted quite a bit about my build - although it isn't assembled yet! - on my site at cutlass.oddworld.org

Vega

The windowed mains are the main weak spot on the 403s. However ive heard a heard a late 60s/early 70s small block head swap, headers, and cam will make this a completely different motor with all else remaining stock. Honestly if it wasnt for the durability issues id be more into one of these than a 455, they are over-square motors unlike the 455s which are under-square. Typically over-square are better for revving and thus better for racing applications. Im sure someone will argue that but thats what most get out of it. My uncle built the 403 in his Trans Am and loved it. I think theres a carcraft or similar magazine article where they did a few simple things to a 403 to make good power, might try to google that up sometime

http://www.popularhotrodding.com/eng...e/viewall.html

lol, there ya go, the numbers speak for themselves. In my oppinion these are awesome motors to build, nobody wants them so theyre cheap cheap cheap

decl1ned

Reply to : 394olds
Can you inform me of this build more. The 403 with 400 crank. My dad built his 68 cutlass with the 403. He followed a mondello write up to the t. Rocket heads, 400 crank, 30 over (I believe) I truly think what your speaking of is the exact build to the car.

svnt442

He didn't use a 400 crank. Not sure where you got that notion from.

boese1978

The heads can be machined / clearanced for the mechanical fuel pump.

svnt442

This thread is 8 years old. I'm sure the build is done by now.