Hey guys, switching my engine in few months...got a 91 RS with 305 TBI, gonna switch to 350 with 305 heads. At the same time I wanna redo the exhaust and put in a dual system with headers. Was thinking of shorty 1 5/8 headers and whats the best sizes of pipes etc. all the way back? 2 1/2 inch? Im thinking of doing a dual in dual out cat then out to two seperate mufflers. ANyone have any reccomendations or what sizes are good all the way back? thanks.

 

Just stick with a regular single 3" system. A dual system can be done but it is expensive and you give up a lot of ground clearance. Any 1 5/8" headers will be fine. Your motor won't make that much power and that size will suffice.

 

Well at the same time we are porting the heads to add about 20 hp, we're adding a new camshaft, TBI unit and intake manifold....so all told it'll prolly be about 300 hp. Wouldnt a dual system be better with a single duel in duel out cat? Or that would not fit in the area I have? How much difference between a standard 3'' system and true dual? Should I do long tube headers or shortys? Thanks.

 

Yup, stay with 1 5/8's, if single no more than 3", if dual no more than 2 1/2. I don't think I see that combination putting out 300HP though.

 

Well I believe a 350 is about least 220 HP, heads will add 20 or so from the work I'll get done bringing it to 240...cam should add 40 or so and the intake will help a little...then the 305 heads on the 350 will raise compression...plus the headers and complete new exhaust so I dont see why it wouldnt be around or touching 300.

 

It depends on your 350 to get that power rating. Porting the 305 LO3 heads will not give you 20hp. Adding a cam with those heads also won't gain you 40. The heads are so bad that porting will igbve you only a fw more hp and will restrict the cam to about 10 or 15 hp gain. Anyways, it is smart that you are going the 350 route. It is not smart to use 305 heads and port them.

 

I am not using the heads off my 305, they are I believe heads off a truck and Im buying them because the person bought them brand new then only used them a few thousand miles at most. So, are all the 305 heads bad or just my stock ones? Maybe I should get casting numbers if I can and then find out if their worth using. THe thing was I could get the 305 heads for only 50 bucks and their almost new. What would you suggest doing? I mean I could just leave the 350 heads on but thought Id gain more HP from the increased compression from the 305 ones.

 

Don't worry about the compression. You are dealing weith a low power motor to begin with. Both the 305 and 350 heads are junk. I would look for a set of L98 heads (350TPI heads). If you can't do that I would keep the 350 heads. Try to get some casting numbers. The 305 TPI are heads are nice but I don't think many people use them on a 350. Just wait until you start to port them. Then you will see what I mean. You will have no idea where to start. There is material everywhere and various parts of the casting that shroud and get in the way.

 

Might wanna go with some Corvette L98 heads at that.

 

Well I wont be bashful in telling you everything is news to me. Im new to the world of modification and Im jumping in because the car burns about a quart every 200 miles and not powerful enough anymore. Im having a mechanic friend help me and he thought it was a good idea. Thing with the 305 heads is they were only gonna cost me 50 bucks and were basically new. Doubt Im gonna find decent heads in that price range. The motor's from a 79 Impala, so should I just keep the 350 heads? What will I get out of the mods I listed if I do? All this information is appreciated, this is why Im doing research now.

 

Ok now it is coming into focus. What year 305 heads are they? That 350 motor is a non-roller motor and you need a non roller cam. I think but am not positive if you can use self alligning valvetrain stuff on a non roller cam. You also need to make sure that the cam is EFI freindly. Do you have a list of what you wanted to use? That may help us determine if you can or can't use it and if you are going to have problems.

 

Well I dont know about the heads, I will have to somehow get the casting number from the guys house. He's a truck driver and is a way a lot so I really have to go check myself. I was planning on keeping it TBI and using something like this :
Crane Powermax emmision legal cam:
2000-5000 210/216 duration .440/.454 lift

I do know I need a non roller cam. Im trying to find out from a friend what the heads came off of right now, will message again if I can. I was hoping to retain the serpentine system to but thats another subject. Basically what Im aiming for is a great runability car with injection and around 300 hp as cheap as I can. I dont really wanna take apart the bottom of the motor either, with exception of doing cam while its out. ANy more info you need just ask me I appreciate the help. Thanks.