ClubRoadster.net banner

building a motor

1K views 10 replies 5 participants last post by  TURBOKID 
#1 ·
Well, maybe one of you noticed that I am selling my miata, I am also selling my dodge intrepid and plan on buying a 350z after the first of the year. This will leave me with the Z and my 1978 Pontiac Trans Am.

Cosmetically the T/A is beautiful. Dumped at least 10k into and looks marvelous, however needs a new transmission and will probably just pull the motor and tranny together. So far, nothing I haven't done before.

However, since the car was produced during the gas crunch of the 70's horsepower is around 200... for a 400 ci motor and I would love to take this opportunity to do a mild build on the motor. Problem is, I have never come close to taking a motor apart. I have a pretty good understanding of how a motor works, but not necessarily how to increase horsepower.

I know by visiting forums such as transamcountry.com and firebirdnation.com (I know how more ******* could you get hahah) that guys have no problem getting 400 hp out of these blocks naturally aspirated. To get specifics I either need to do some reading or asking on those forums but I am just trying to get a grasp on how exactly I go about a mild build.

Several of my question, for instance I have no idea what porting and polishing is, I have no idea how heads will increase performance, etc, I can get answered on google.

Anyone care to give a rundown of the main bits of building a motor?
I'd really appreciate it!
 
See less See more
#5 ·
Re: Probably the wrong forum... (building a motor)

Pics of T/A or it didn't happen.




Wow I have a 78 Electra that has a 403 in it and it put out way more HP than than 200 and its all stock. You should be putting a little more than that out of the engine.

However, if I were you I would do the following:

1) Pick out how much you wanna spend.
2) How much HP are you looking for?
3) Call or email Summit Racing Supplies and they will put together a great combo for you.

The problem with the 400 block is that there not all that populer (Im a Chevy/GM guy by the way) compared to a 350, 383, 327, 427, 454, and 455. But there are parts out there to fit you needs. The pure basics are drop some headers on there, upgrade to a Holly 750 carb (or Edelbrocks) and you might wanna put a spacer in between. Some times they offer a nice combo like intake manifold and carb (sometimes even headers are thrown in there) all for under $1000. A lot of times you can even pick up a set of heads that come complete for about $800 and usualy come with roller rockers and stiffer springs. After all of that you can throw in a miled cam and not have to worry about getting your crank turned or replaced (Summit will help addvise what to role with). I wouldent worry about replacing pistons or crank (unless you plan on running higher compression or get a wild ass cam in there. If so look into a voodoo cam). After all that look into MSD and a nice little thing called a flame thrower to go with it.

That sould be a good start and will cost somewhere around $1500-$2500, alot of people also sell aftermarket parts on CL.com and you might be able to save a few bucks.
Thanks for that! Unfortunately the 400 ci for 1978 is rated anywhere from 180-220 depending on which citation they are using. It was later determined that Pontiac falsely advertised the HP to seem lower. I already have plans for bolt ons concerning full exhaust as well as intake. And I rebuilt the qjet in their right now, and while it can be a pita to tune, many guys drag with it so I'll keep it for now.

I am trying to get a more insightful look into a motor internals rather than bolts on at this point. A cam definitley will help out. I've never replaced one before but might give it a go.

Maybe if I ask some specifics this will help out:

-Why do stiffer valve springs increase performance? I guess their job is it push down on the rod, so this probably increases the efficiency of combustion?
-Porting and polishing heads? What does that do? Smoother air flow, less friction, again increasing efficiency?
-Concerning cams: degress measure the lob, how does one figure out what application wikll work best?
-if I leave my pistons alone does this render modifications to the head, cam useless? I hear you should always replace head polts and piston rods for forged when increasing performance. Or if you do leave it, don't go crazy.

the problem is you said you have a good understanding of how a motor works.
k thanks. If you're not going to help out, go raise your post count somewhere els.e
 
#3 · (Edited)
Re: Probably the wrong forum... (building a motor)

Wow I have a 78 Electra that has a 403 in it and it put out way more HP than than 200 and its all stock. You should be putting a little more than that out of the engine.

However, if I were you I would do the following:

1) Pick out how much you wanna spend.
2) How much HP are you looking for?
3) Call or email Summit Racing Supplies and they will put together a great combo for you.

The problem with the 400 block is that there not all that populer (Im a Chevy/GM guy by the way) compared to a 350, 383, 327, 427, 454, and 455. But there are parts out there to fit you needs. The pure basics are drop some headers on there, upgrade to a Holly 750 carb (or Edelbrocks) and you might wanna put a spacer in between. Some times they offer a nice combo like intake manifold and carb (sometimes even headers are thrown in there) all for under $1000. A lot of times you can even pick up a set of heads that come complete for about $800 and usualy come with roller rockers and stiffer springs. After all of that you can throw in a miled cam and not have to worry about getting your crank turned or replaced (Summit will help addvise what to role with). I wouldent worry about replacing pistons or crank (unless you plan on running higher compression or get a wild ass cam in there. If so look into a voodoo cam). After all that look into MSD and a nice little thing called a flame thrower to go with it.

That sould be a good start and will cost somewhere around $1500-$2500, alot of people also sell aftermarket parts on CL.com and you might be able to save a few bucks.
 
#8 ·
Re: Probably the wrong forum... (building a motor)

^ what Hank says (Hank I love your sig, what are you running and what kind of car?)

if your looking to swap in new pistons (im guessing your going high compression) get some butterflys, you can also look into a bore and stroke maybe .30+ (thats a nice safe bet), but you will have to get a new crank or get the one you have turned. Since your talking port and pollish, most of the machine shops/speed shops will also do a bore and some will even turn the crank. And if your looking for some extra boost you can always get a fogger system for cheap.
 
#9 ·
Re: Probably the wrong forum... (building a motor)

Oh ya, depending on how much HP your spitting out you may want to look into beefing up the trans and rear end.
 
#11 ·
^hahahaha nice

Thats one of my dream cars (the other one I already own) but a 72 SS w/ a 454, red w/ black stripes and black vinal top.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top