I thought i'd start a new thread for this so it's easier to find

OK, to recap I have just bought a 1975 455ci (396021Fa) with the following serial: 35R110516, J Heads, low compression pistons, cast iron intake and a 4bbl Q-Jet.

I want to build this into a nice respectable street engine, but not go too over the top since the car is a 4 door sleeper and not a muscle car. Ideally i'm looking for torque but if this engine can deliver a bit more HP than my current 425ci then I would be happy. Current 425ci setup is: Edelbrock Performer Intake, 4bbl Q-jet and Pertronix ignition. (I'm guessing currently somewhere above 330hp due to the intake and carb??)

For the 455ci, so far i have been advised:

1. Swap out the pistons for high compression
2. Port the valves
3. Use the Ed Performer intake and HEI distributor

I have a couple of questions:

What compression pistons should I use (95-97 RON Fuel)?

Is it just the intake valves that get enlarged or is it advisable or even possible to get the exhaust valves done too?

Would there be worthwhile benefit of installing a different cam at this point?

I have an engine shop here that can undertake the above work for me but they are recommending that i completely rebuild the whole thing but I'm not sure that the combination of type of car and size of budget really warrants that much outlay to be honest.

My dilemma now is to decide whether the just porting etc will be enough to get me where i want to be?

Will the piston change even be necessary??

I can see how easy it is to get carried away

 

What is wrong with the 425? It should already be a higher compression than the 455. The 425 has a steel crank and better heads also. I just got a 455 myself and would have gladly taken any good 425. If you are upgrading the 455 I would at least do rings and bearings, cam and lifters and rebuild the heads. I feel you would be leaving quite a bit of power on the table if you don't go to higher compression pistons.

 

The biggest improvement you'll feel would be compression increase with a corresponding cam - 9 to 9 1/2 to 1 shoud be safe - cam around .500 lift, and 285 duration will work well.
Larger intakes wil help, as long as you blend the pockets, and make everything flows their best. Teardrop the vave guides on both intake and exhaust, and you can port/polish the exhaust all the way out.
I've always 'match ported' the intake side of the head and the manifold to the gasket, going in about 2".
If your shop has the expertise to 'lap' the valves before assemby, and 'back-cut' them to the seat surface, that'll also free up some horsepower.
Also check the combustion chamber for sharp edges or casting flash - just knock them down!

 

nothing wrong with it at all.
The 455 came up for a song and due to it's rarity over here I had to buy it.
I figured it would save me time and money to build the engine that's already on a stand and if it takes longer than anticipated at least i could still drive the car.

 

Do you think it would be better to just get the 455 up and running as it is, swap them over and rebuild the 425 instead?

 

The 455, you can get "KB" pistons with the 14cc cup. you should deck the block for straightness and up the compression. The "J" head will work for what you want to do. You can clean up the intake port and port match, but there is a lot of work to be done on the exhaust side. The valve size is very good. For the amount of work to increase the valves you would not see it on the street. Up grade to the Edelbrock cam and be sure to degree it as per the cam card. The "Cloyes" true roller timing set is the best way to go. You can also get "Comp Cams roller tip rockers to convert to adjustable rockers.
The 425 is a great engine,there is just no forged pistons of a good price, cast is the only ones available. Cast pistons are good, and for the street, will be fine. After market cams will have to be ordered for it is a 45* block. You will need to make sure what lifter size you have also. If yours are "A" heads you can order 3/8 X 3/8's rocker studs and guide plates and convert to roller rockers.

Gene

 

I would be tempted to get the 455 running and rebuild the 425. I would love to have a good 425 but mine needs an overhaul so I am going with a 455. Swap in your 455 and rebuild the 425.