Hi,
there are some not too expensive kit to upgrade the power of 403, and keep realiability?

I'm looking for some HP and Nm, to have more compression and efficiency about fuel consumption, not to have a drag car with high HP.
Wich number of HP is necessary for that?
Thanks

 

If the bottom end is in good shape, go throw those 4A heads in the bush. They have huge 84+cc chambers and a horrible exhaust port. Early 330 and 350 heads with 2" or 2.07" intake and 1.625" valves with the bowls opened and a better cam swap with dual exhaust will act like a different car. Those heads will boost from high 7 to 1 compression to around 9 to 1 compression. Add about 20 degrees more duration on the cam and replace the nylon timing set with a double roller and degree it.

 

I've to submit your suggestion to my mechanics: for me this is like greek language!

But its cool to read from people who put their hands inside the engine, directly!

Thank you so much

 

Although I understand apprehension of trusting sources on the internet, unless your mechanic is well versed in Oldsmobile speak, he may try to tell you to port the factory heads when in reality, they're not ideal.

Your heads have "4A" on them, lower left hand corner when looking from the top. You want a set that has 3, 4, 5, 6, 7, or 7a (not to be confused with the 7A from the 80s, half the port size).
Something else to consider is the head gasket. You're adding .023" to the deck with a replacement Felpro head gasket. Probably wise to grab a set of thinner MLS head gaskets from Smitty (found on Facebook).

 

All people i ask about 403, talk that's a bad motor.
He drink a lot of fuel, efficiency is not good: i put a GPL implants, now i spent few money, exactly half then before.
Heads are "trash", camshaft dumb.
Anyway i need to 220/250hp, no more: i use with a 1969 4speed muncie, probably i will go around for hundreds miles trip, i don't know...
My way is not run, not track, i like touring/cruising, probably a new camshaft, and a refresh of the engine can give a nice benefits.
Not 220/250hp, but nu heads are too expensive, machine the old, can be a risk, or find a not significant improvement, i don't know...
probably i will trip

 

The 403 is a great motor below 5500rpm...ha. Swap the heads with some big valve earlier versions, put a mild cam in it, a performer RPM intake, some headers, and it'll put down 250hp to the wheels easily. The heads are your biggest holdup in this.

 

Thanks Brwonbomber77
i'm checking some parts to upgrade the motor, not heads, too expensive to buy complete, ship to Italy, and pay fees+camshaft and all other parts.
I'm moving to basic way: camshaft,lifters ecc, forged pistons and headers Hedman Hedders i bought some months ago to lower the car must be enough to empty my wallet...

 

What pistons did you buy? Depending on the dish of the piston that could negate the need for the older heads somewhat because you could already be increasing compression.
Check what rear gears you have. If you have something numerically low like a 2.73 nothing will wake it up like a change to a higher numerical gear

 

Actually the "problem" is on the hands of the mechanic, i'm not able to understand about motor (sincerely), i hope the choice of th eparts for the upgrade will be good!
Thanks

 

 

The location certainly put a wrench in things.... Yep, what pistons did you buy? Do you have a part number? There's a wealth of information just on this forum that might not be in Italy just because the number of Olds there is limited.

 

https://www.summitracing.com/parts/u...ake/oldsmobile
You want the pistons above for you goals. Upgrade the springs and retainers along with 1.625" exhaust valves over the factory 1.5" valves with a bowl cutter under the valves to help flow.

 

Thanks to all you very polyte guys!

I think to leave my car to mechanics next autumn...before of that season i must decide the way, or what i MUST do about modifications (right parts i need).
Really i reading different way to reach my goal: efficiency of 403, not esasperate HP, no drag race or track, but a reliable car who can run around the country and beat the corner because i've a serious kit suspensions. The motor need to be a pearl on the streets: some HP, good Nm, right LPG consumption (yes, my firebird drink LPG!).
So i wanna trip and look the places around, play around ther corner...
Ok, many people talking about KB forged pistons, someone talking about other ways...Hard to decide for a unexpert man.
I can only kep tu listen, try to ask, hope to dont fail, because i spend double of money that a US resident spent on his car, a cause of fees, ship, more fees, tax, other fees, other tax, and agai and again.
..

 

Running on LPG changes things, and I doubt there are many people here that have a lot of experience with that. Be aware that older technology LPG systems that use converter and mixer technology (fuel is vaporized and added to the intake air) likely result in a loss of power compared with gasoline. More modern liquid LPG injection systems may be on par with gasoline. I hope you have a competent shop that can advise you and look at your engine project as a whole and considers the fuel and fuel system you are intending to run.
In theory LPG allows higher compression ratios since the octane rating is somewhere north of 100. However, if the compression ratio were optimized for LPG operation you couldn't run pump gasoline anymore and would need to run expensive race fuel should you ever have to run on gasoline again.

 

Jacksolds never revealed he was planning to use LPG before. That is a recent major point. He is also in ITALY (the country).

Bremer, thanks for the info.

 

Actually the LPG system work really fine: its a modern part, no problem till now.
My goal is keep reliability with a better efficiency on 403. Change pistons, roller and camshaft seem the best way: as Raph said, i'm in Italy, shipping cost and fees are heavy when i buy parts from USA. But, ok, its a work i think to do next autumn, now i'm studyng the way to reach this goal.