hi guys i have a 1974 pontiac lemans sport coupe with an olds 455 '396021 Fa' with J heads which i found out to be the worst. I not using this car for pro racing but i just want it for street racing. My question is that is it worth it to do porting and polishing for the smog heads? will i gain remarkable difference or it will be better to swap my heads? i am planing to throw in headers , comp cams 268 , performance intake and do some porting and polishing for my heads.... is it worth it... will i gain much hp?

 

Welcome to the site, I moved you post to your own thread. there is no reason to post the same question hijacking older threads. The J heads are not worth dumping a bunch of money on.

 

it isn't that i am hijacking but it is the first time that i use forums so i am not that good using it. thanks for understanding. someone told me that he do some porting and polishing for my heads in 150$ and he said that i will have gd results if i replaced my stock intake with a hi perfo. aluminium intake , and install headers. I am not so sure about this.the issue is that i can't find c' casting heads in lebanon all i can find is either 4a , 5a ,3a and 7a heads.Nevertheless shipping heads from the states to lebanon would cost a lot and this is out of my budget.

 

I didn't realize your location, I agree shipping would be expensive. All the numerical heads are for a SBO. How are you planning on using your engine, just cruising, racing, ...?

 

I live in Lebanon , olds455 parts are really rare especially the heads.. what i'm seeking for is no more than 300hp..I haven't done any modifications all is stock no after market parts... There is no olds expert here so I'm working hard on researching what modification can be done. I have a th350 trans no shift kits no modifications. No idea about gear ratios .1974 olds455 396021Fa with J casting heads, rochester 4bbl 800cfm carb. stock intake stock exhaust.....I would appreciate ur advice on what modifications can be done to reach 300hp....thanks for your help

 

Welcome. If you are going to port the heads and install larger valves, the J heads are as good a place to start as any (maybe better - the smaller ports give you more flexibility in porting). Normally, I'd say it would be cheaper to just dump the iron heads and bolt on a set of aftermarket aluminum heads, but shipping may be the deciding factor in your case. Good luck.

 

is it necessary to install bigger valves? i won't benefit by porting the intake and exhaust sides of the heads and install an aftermarket intake and headers?

 

HP is a function of mass airflow through the engine. Improving port flow is a waste of time if the valve becomes the choke point in the system. You have to upgrade the entire airflow path to see appropriate gains.

 

i have olds403 4a heads would it be better to install them instead of the j headS?

 

I wouldn't recommend it. Those are small block heads and have smaller ports than the J heads.

 

in conclusion what i have to understand is that with the j heads on without installing bigger valves i won't be able to reach 300 hp

 

Port the J's and be happy. I have seen a Cutlass body car at the race track running in the 11's on J heads. I did not look closely to see if the casting ID was altered though. Many years ago, Detroit Raceway, probably heads by Vance Brady. not all porting jobs are equal.

Or, look into the cost of new aluminum heads, delivered.

 

Honestly 4A heads are very similar to J heads except they have an even larger chamber. Both have a terrible exhaust port that will need a lot of grinding to flow worth a darn. Go 2.07/1.68 or 1.71 for valve sizes and open up the bowls to make use of the bigger valves. You will also need a lot milled off the chamber, your motor has around 8 to 1 compression. To fix that you either need small dish pistons, your current pistons are 40 cc dish pistons or the heads milled to try to get closer to 9 to 1 compression. You need .025" milled just to be back at the factory compression with thicker Felpro head gaskets. If you mill the deck side a lot the intake side of the heads or intake needs cut so it will fit. The center exhaust guides also need extra clearance unless you fill the crossover with zinc or aluminum.