73 roadrunner

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im new to the muscle car scene. I was recently out looking for a car and i spotted a 73 roadrunner. The body is in decent shap but everything has been stripped. My dad and I are going to buy it and slowly build it up over a couple years. My question is; there was no motor or tranny on the car and it was a 340 to start but i want to but somthing bigger in it, is it possible to fit a 440 (off a71' GTX) on the stock mounts, or will i have to do a lot of modifications to get it fitting right? Any help would be great


posted by  RoadRunner73

You need to find yourself a big block k-member, motor supports, and possibly move/change your trans crossmember. Good luck finding the parts in a junkyard, you'll most likely have to go the aftermarket.

posted by  vwhobo

Ok, ill see what i can do but i might just put in a 383 or another kind a crate motor cuase the scrap yard we have here is not that good, mostly for people you have ricers uggg i hate ricers but thank you for your help


posted by  RoadRunner73

A 383 is still a big block, same mods will be required.

posted by  vwhobo

ugg :x all i know is i want somthing bigger than a 340 it only has 275 (approx) hp and i want to be able to kick the sh%t out of ricers. The modifications that i need to do would require welding expertise right? And if you could tell me a couple sites or a site that might sell bigger k-members and some information that would be a big help. Is it possible though i doubt it to take the parts needed from the gtx (k-member) and somehow graft it to the fram of the 73 or is it best to find one from another 73 or buy a new one. Im fairly new at this so i might be asking really stupid questions :oops:


posted by  RoadRunner73

1. Are you sure you need something bigger?

2. Maybe.

3. I could but you'll learn more researching for yourself.

4. Yes, depending on the year GTX and if it had a big block.

5. There are no stupid questions. Only questions asked by stupid people, so far you're not in that category.

Let me give you an opinion. I think you may be putting the cart in front of the horse. The first step in any build-up is realistically determining what you need and what you can afford. I'm not so sure you've done both of those yet. Once those are accomplished you'll know where to go and it will be much easier to help you.

posted by  vwhobo

well my goal is to have the project finsihed with in 5-6 years. money is not an issue becuase the motor i want comes from a 440 gtx (1971) so money is not an issue. I really need to find a motor and 340 i find is to small and there isnt a car around where i live that has one. I find i rather have an engine that i can work on would be more fun that putting in a crate engine though it will cost more money in the long run i believe it will give me some experience building an old one up. My dad has all sorts of connections with welders and people with mopars so im sure they could help me out with finding parts i need. The first thing i really need to do with the car is to get it powered with a new old motor and new 4 spd tranny. The second thing i want to do, is do the interior (new everything since there was nothing in it to begin with) then get the body finished and painted. Money wont be a problem cuase ive been saving for awhile and just the length of the project.

posted by  RoadRunner73

Alrighty then. You need to read my last post more carefully. Unless you're Bill Gates, money is always an issue. Good luck.

posted by  vwhobo

True, so what do you think i should start out with? Its just this 440 is readily available and its gonna cost around $300 cdn and ive checked specs on it and it sounds like a nice engine that i would like to put in my car. All in all the 340 doesn't appeal to me as much as a big nasty Big Block. If i can get the motor would you suggest getting it or stick with 340 (Buy a rebuilt one). Ive also checked the internet you can get conversion parts to make the stock K-member able to go with a big block.

posted by  RoadRunner73

I agree, I love a big block but..... They're more expensive to build, operate and also the conversion costs. Plus with the substantial extra weight they take a poor handling car and make it worse ( I have a '73 Satellite).

I would go with a 360. Relatively cheap to build, capable of good power, and the junkyards are full of them. If you can get a 440 cheap enough save it for when you have more experience.

If you look in "SUV and Trucks" you'll find a link I gave a dude for his small block build up.

posted by  vwhobo

You've lost me wouldnt more weight in the front give better turning?What i can see as a problem is maybe id need to buy new shocks or somthing. Its just i help my friend with his olds 455 and he spent about $1500 rebuilding his engine (acid bath,gaskets etc). Plus his dad is good with engines, and my dad used to work on them so im sure we can work it out. Its just that i was watching horse power T.V and they put a 572 in a nova and i was thinkin that would be sweet to have a big engine in a small car. But i can see your point a 440 would get like 7-10 mpg, but gas prices up in alberta are still cheaper than anywhere else. Your imput is greatly appreciate. We will see how things pan out and ill keep you posted. ;)

posted by  RoadRunner73

1. Do you have any idea how much additional fabrication you would have to do to install a SBC?

2. Don't even joke about bastardizing a Road Runner. Live and love Mother Mopar. Otherwise you might as well run a ricemobile.

posted by  vwhobo

i realized that read my post again i edited it.

posted by  RoadRunner73

1. No, a heavier front end will certainly not help the handling. Even if you use big block torsion bars it'll still be pretty much a pig.

2. If he only spent $1500 to rebuild an Olds 455 his idea of a rebuild may be a little bit different from mine.

3. They're not paying for their parts on that Nova. I've caught bits and pieces and can tell you it will cost near 40k by the time they're done.

4. Trust me, no matter what the price of gas a well built, low budget 360 will be plenty fast for you. There's a learning curve with fast cars and nobody should try to start too near the top.

posted by  vwhobo

a pig eh? thats funny, i was just checkign through my hot rod magazine and theres a 360 magnum here that produces almost 400hp and 420lb-ft of torque thats more than the 440 and it will probably fit on the stock mounts right?

posted by  RoadRunner73

It's a small block. If the car originally came with a small block it will drop right in.

posted by  vwhobo

well the car was a 340 small block im guessing and a 360 is a small block its got a lot of hp and torque im just hopin it isnt like $5000 american lol cuase we in canada gte bad exchange rates tobad it wasnt like 20 or so years ago when the canadian dollar was stonger than the american


P5249499 Magnum 380 hp 360 Engine Assembly $ 3,799.00

1.925" Intake/1.625 Exhaust Valves .501"/.513" lift 288-2920 Hydraulic Roller Camshaft
M1 Single Plane Intake Manifold Special Valve Springs Dbl Roller Timing Chain
Electronic Distributor Package MP Cast Valve Covers Oil Pan

should this be suffcient i would hope so its pretty expensive

and another question i have is how do you increase torque?

posted by  RoadRunner73

73340RR,All mopar small blocks are not the same. The motor mounts are a little different. There is a place where you can get the right ones. And you can get them for a big block you dont need to change the k-member. I own a 73rr with a 340. vwman doesn't now what he is talking about. He may know chevy but he doesn't now mopar.

posted by  73340rr

actually mopar engines like the 318, 340, and 360 are the same things really, same mounts and size, just bored differently and with different parts. i got a 69 dart, came with a 273, right now its got a 318 fits perfectly, if i wanted to i could put in a 360, which i will most likely do when i have the cash. thats why mopars are so great, you can drop pretty much any of their engines into your car without much trouble. i think i got a link for you road runner, let me find it here... http://www.mopartsracing.com/parts/blocks.html check that stuff out if you wanna see some american prices for engines. i really want that 380 hp 360 there, i think thats the same one that you were talking about in a few post back. hope it helps you.

posted by  Vaspier

All small block Mopars are easily interchangable... Except the 318 poly-block and the later Magnum engines have slightly different bosses on the block. And as you already know you can get conversion mounts. In my book that makes them interchangable.

As for the SB to BB conversion, yes you can do it without changing the k-member but... You have to do substantial fabrication, so why not just swap the k-member? Yes sweetie, I do know Mopar.

posted by  vwhobo


Did a swap in my 74 Runner years ago, 318 to 440. At that time, I had to sawzall the frame brackets and relocate them to stick the big block in.
Now I believe YearOne has direct mounts for that purpose, no k-frame swap
required. Check it out!

posted by  aerodynamic

RoadRunner73, after reading the replies from vwhobo I must say that I agree with him 100%. If you don't think that money will be an issue, than perhaps you should go to the Barret Jackson Auto Auction and buy a 1971 Plymouth Hemi Cuda convertible. In fact, if money isn't an issue pick one up for me too! I found myself in a very similar position to yours a few years ago. I purchased a solid '73 Road Runner from a local junkyard. The car required a complete restoration. The body looked rough, but was not rusted through the quarters or floorboards, making it an extremely solid car and good resto candidate. The car had a 318/727 combo which I felt needed to be exchanged for something a bit bigger. At the time I was 15 and was working 3 part time jobs just to get money to buy parts for my car (I had been saving since I was 12). In today’s twisted Mopar society, it seems that if you don't have a big block, your car isn't worth anything. I looked at some early Hemi's and a 400 CID big block all of which would have required a rebuild, plus the major suspension mods that you have already inquired about. I ended up with a 340 CID small block (that's what the car originally had). I felt that with the right combination of parts a lightweight 340 with big block horsepower would be the best option. I was not fortunate enough to obtain a 340 with X heads (something that deserves consideration for your build), but the J heads with lower compression ratios were fine for my build. For approximately $5000, much more than I wanted/expected to spend on the engine, I had my engine completely rebuilt, magnfluxxed, bored .030 over, new pistons installed, new external parts installed, rebuilt heads, a custom built low profile aluminum intake manifold, B&M 144 roots type supercharger, and 650 cfm Demon Race Carburetor. According to the engine dyno the setup is worth 425 hp on pump gas. The engine can use racing fuel, which I prefer, and if the belts are adjusted on the blower the hp can be increased. The monster 340 just barely fits underneath the road runner hood bulge, but from the outside of the car it appears strictly stock. Don't just blow off the idea of a small block yet, you can do a lot more for a lot less $$$ if you use a 340 or 360. Below is a picture of my engine after I got it back from the race shop. By the way, I'm now 20 and still working to finish the car. Money and time are the two biggest issues that you have to overcome in any restoration, so keep these in mind when you consider what kind of build you are going to do.


posted by  MoparMedic

...damn near 2 years later...

here is a slight clarification on some points, though. in case someone reads this looking for info...

318 polys have the same motor mount bosses as the wedge 318, the blocks are very similar

iirc, 360's have a slightly different bracket between the block and the motor mount on the passenger side. i think it's a matter of one bolt hole that isn't present on the 318/340 mount...

if switching from a 273/318/340 to a 360, you will need to add weights to the converter (providing someone didn't internally balance the 360)

schumacher makes (and made in '03 and '04, i'm sure) conversion mounts that they could facilitate putting a b or rb motor in damn near anything w/o changing the k-frame. trans location shouldn't change...

posted by  dodger65

sweet pics dodger65

posted by  ryth2692

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