brewcity

Hello all,

A newbie here, so please do not hate me for posting another questions about heads...I have searched and searched, and need some real answers from the Olds experts and the 403...I have read about adding some power to the 403 by swapping the heads out for 72 7a's, which is what I am going to do.
But what do the heads really need besides drilling the bolt holes to match the 403? Do they need any work done to them to help the flow of the 403, or can I just clean them up, and bolt them on without worrying about anything?
What type of intake manifold will compliment it the best, and does anything need to be done to that to make sure everything is working effectively? I heard that the heads need extra holes drilled to avoid overheating...is this true? Do I need to do anything to the cam or pistons to balance the heads with the rest of the engine? Should I be replacing the springs and rockers? If so...what are the specs of what I need? I am a total novice, and need some real advice from people who know the 403 engine inside and out.
As you can see...I am a bit overwhelmed. The car (79 Trans Am) does have the cats removed, and has dual exhaust, but stock manifolds. It will be a street performer, and see some highways as well...about 65/35.
I am looking to just get some more performance and torque (mainly) out of the 403, but nothing to overboard.
Any help would be greatly appreciated. Thank you so much for helping us new guys out...you have no idea how much it means to us.

Pete

Warhead

I can understand what you are looking for, here. You did not state what differential gears you have, or what gear you are planning to go to, nor camshaft, nor induction. All that will matter, too.

First off, this is not like a Chevy 400 where you drill steam holes in the head deck surface. You will have to open the head bolt holes to 17/32nds, AND open the extra locating pin hole to 5/16ths--neglecting that will cause the head to not be able to bolt to the block. Use the 403 head gasket.

NOT doing a valve job is like throwing away half of your expected power gains. New guides. Valve job. Viton seals. While you are doing the valve job, have 2 inch intake valves installed in the 350 heads--that's what 403's had from the factory. Your heads have 1.88 intakes, stock.
The Performer RPM manifold. Headers, yes. I have yet to get my 403 fired up, but I went with an A4 intake (later fact alum) and stock exhaust manifolds for more of a factory look on my car.
You will be shocked how much a boost in compression, from FRESH heads will give you in a 403. You will be going from a 7.8:1 compression ratio, to around a 9:1 with stock pistons, and a Fel-pro gasket.
Mark (cutlassefi) can give a good camshaft/valve spring recommendation, once you tell him what gears your car has.
Jim

joe_padavano

The stock valves in the 7A heads are small for a 403. I would suggest that at a minimum, install the 2.000/1.625 valves in these heads. Everyone is worried about compression ratio without looking at other factors like valve size and port size. Again, the 400 big block motors used C heads with larger ports and even bigger valves. A 403 should be able to use the same heads. Of course, the 7A heads are an good compromise if you aren't planning to change the pistons.

brewcity

Thank you guys sooooooo much.
The engine is all stock right now, and the gears are as well...if I remember correctly, they are the 2.73 (?) gears with the 10 bolt.

brewcity

Thanks so much Jim for all the help...so when you say "have 2 inch intake valves installed in the 350 heads--that's what 403's had from the factory. Your heads have 1.88 intakes, stock."...does that mean the stock 350 heads only had 1.88, and I need to open them to 2.00? Just want to make sure.
Also...I take it I need to get rid of the original exhaust manifolds, and throw on some headers? If so...any recommendations on which ones work the best on a 403 with power steering and air, along with the 7a heads?
Thanks again for the help on this...I really appreciate it.

cutlassefi

Just sent you a pm.
Are you staying with the 2.73? Yes I would recommend headers and true duals with an h-pipe, helps low end.
Also I would go to the bigger 2.00 intakes, yes your 403 heads came with 2.00, the 7a's come with 1.88. Filling the crossover and welding the divider helps as well with headers.
This combination of upgrades is the most common. You can find dozens of posts on various Olds forums on the same. When your final combo is done I'll be happy to address your camshaft configuration.

Keep us posted.

Oldsmaniac

Do you already have the heads? I have a pair.

brewcity

Thanks for the help...I think I will be keeping the 2.73 gears...but just not sure about the future. For now, yes, they will stay stock.

brewcity

Sent you a PM. Thanks!