Advice for Increasing Horsepower - 318

rt_hawley · Apr 30, 2013

I have a 74 Roadrunner that has a stock 318 in it and I'd like to get a few more ponies out of it. I don't want to be able to run 12 second quarter miles with it, but it would be nice to be able to chirp the tires every now and then. Does anyone have any relatively inexpensive suggestions that would help. I don't mind spending a few bucks, but I can't afford to throw a whole bunch of money into it right now either. I've already added headers and I'm looking at putting in a decent Edelbrock intake, as well as a four barrelled carb and stepping up the cam. Those can be done "relatively cheaply", but I was wondering if anyone had any other suggestions for me that wouldn't break the bank. Any and all advice would be appreciated.

Thanks.

RH

YY1 · Apr 30, 2013

That's pretty much it for the "hundred dollar" upgrades, besides maybe swapping out the (more than likely) 7 1/4, 2.73 rear end for a 8 1/4, 8 3/4 or 9 1/4 with 2.94, 3.23 etc.

Most everything else will be "thousand dollar" upgrades.

pabster · Apr 30, 2013

Great question, rt! I'm looking at doing the same with my 318. Wish I had an answer, but I'm asking the same questions. Did headers make a big difference to your car?

RustyRatRod · Apr 30, 2013

Buy my 318. Problem solved.

ply64post · Apr 30, 2013

318

rt_hawley said:
I have a 74 Roadrunner that has a stock 318 in it and I'd like to get a few more ponies out of it. I don't want to be able to run 12 second quarter miles with it, but it would be nice to be able to chirp the tires every now and then. Does anyone have any relatively inexpensive suggestions that would help. I don't mind spending a few bucks, but I can't afford to throw a whole bunch of money into it right now either. I've already added headers and I'm looking at putting in a decent Edelbrock intake, as well as a four barrelled carb and stepping up the cam. Those can be done "relatively cheaply", but I was wondering if anyone had any other suggestions for me that wouldn't break the bank. Any and all advice would be appreciated.

Thanks.

RH

Take a look at this.

http://www.hotrod.com/howto/113_0304_318_small_block_build/viewall.html

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/viewall.html

rt_hawley · Apr 30, 2013

pabster said:
Great question, rt! I'm looking at doing the same with my 318. Wish I had an answer, but I'm asking the same questions. Did headers make a big difference to your car?

I'm not really sure if the headers made a huge difference in horsepower, but it sure sounds great!! I'm sure once I get the intake, carb, etc on it, the difference should be noticeable.

- - - Updated - - -

RustyRatRod said:
Buy my 318. Problem solved.

Rusty, if only I had the disposal coin at hand, I'd be quick to jump on that rebuilt 318 you have....but unfortunately, the well is quickly running dry, which is why I'm looking at some cheaper options.

rumblefish360 · Apr 30, 2013

Inexpensive HP upgrades are a little tuff to get, in a sense. Price is relative. For tire snapping...

Install a shift kit, stage 2 Trans-Go will do it.
Increase the converters stall speed for a better launch.
Increase the rear gear ratio numerically higher.

Back to the engine. IMO, the best ways to increase the power besides what is listed above, Cam, intake & 4bbl. & headers, is to increase the compression. This is normally done with a piston change but since that requires more than just simple pocket change...... AKA A full rebuilding, a simpler step is needed.

Milling the heads helps. But it also creates another issue to deal with. The misalignment of the intake holes to the heads bolt holes. To a certain extent the head properly milled on the chamber side will have the intake side milled as well. How much is described in the MoPar engines book for YOUR engine. Do read up on it. Excellent book by the way.

If you mill the cylinder head a lot, the intake manifold may have to be milled as well in order to allow it to sit down low enough to be bolted on.

NOW! this is not a big power added but, an approx. 1 pt. of compression is worth probably #5 on a low powered engine. More if the build goes up. But at your level, near stock, 3% is generous and not a lot to add. it'll help as every part add's a little bit. All combined, it add's up.

While the head is off, a back cutting of the valves is an idea. If not a larger exhaust (1.60) for the 318.

old tired rebel · Apr 30, 2013

Drop a Stroker 400 or 440 in your car problem solved.

mosquito13 · Apr 30, 2013

old tired rebel said:
Drop a Stroker 400 or 440 in your car problem solved.

that is a downward spiral . i started that way ,a front end rebuild with disc brakes, then a trans rebuild, then the rear end upgrade,then rear disc's, then the body stiffenin', sold my 74 norton and my 63 f100 for a simple 440 build and drop in cause the perfectly good 318 poly was not hot enough... not that i am minding the ride to dante's lire, but 500 hp may cost me my soul.

The quick and ez is change the gearing in the rear, the 318 with headers and a 600cfm carb will do a burnout.

RustyRatRod · Apr 30, 2013

My grandfather's stone stock 71 318 Dart would smoke the right rear tire for literally as long as you held your foot in it.......right into high gear.

David · Apr 30, 2013

I think the headers made a difference in performance on the upper end. Sounds like you have a good plan upgrading intake/carb. Like Rumble said you may want to look into a shift kit, it gives you a nice firm shift. If you are looking to upgrade cam I would recommend the Hughes Whiplash cam and springs. I have a similar setup as you are describing with headers, 2.5" exhaust, Weiand Action Plus intake and Holley 600 cfm carb with the Hughes cam and shift kit. It has a good amount of power at the bottom end and can easily chirp the tires.

YY1 · Apr 30, 2013

Your next step, other than a rear end change, is likely head work or piston work.

Plan on near 1000 bucks counting parts and labor.

If your cam selection is too much more than stock (about .450 lift) you will need head work as well (at least springs).

I'd skip the converter unless your going with a cam over .480 lift or gears higher than 3.55.

As you can see, we're well into the thousands at this point.

***buying a junk yard 5.9 magnum for $500 (or a running, driving Ram or van) is like getting a used 300 HP crate motor.

There are a few other issues involved (namely intake, fuel pump, converter), but it's in the neighborhood on total cost.

rumblefish360 · Apr 30, 2013

"LIKE" YY1's post!

rt_hawley · May 1, 2013

Thanks VERY much for the input fellas...gives me lots to think about!!!

RH

kb67mopar · May 1, 2013

Anybody think to mention depending on which year he is running he can switch to a stock head with a lower combustion chamber volume to increase the compression ratio? I am not a guru but depending on year some heads can make a big difference in compression. I know the magnums have pretty small chamber volumes but they are a little harder to drop on but still doable.

Might be worth some research.

dvw · May 1, 2013

rt_hawley said:
I have a 74 Roadrunner that has a stock 318 in it and I'd like to get a few more ponies out of it. I don't want to be able to run 12 second quarter miles with it, but it would be nice to be able to chirp the tires every now and then. Does anyone have any relatively inexpensive suggestions that would help. I don't mind spending a few bucks, but I can't afford to throw a whole bunch of money into it right now either. I've already added headers and I'm looking at putting in a decent Edelbrock intake, as well as a four barrelled carb and stepping up the cam. Those can be done "relatively cheaply", but I was wondering if anyone had any other suggestions for me that wouldn't break the bank. Any and all advice would be appreciated.

Thanks.

RH

Ok lets start here. I ran my dads brand new 318 73 Road Runner at Milan. It ran 15.90s. The car is heavy, 3900 at least. It needs gear,small cam, proper carb. I'm assuming 904 trans so the convertor will fly for now. Start with at least a 3.91/4.10 gear. I would recomend the Comp cams 268H. Good grind for a heavy small motor car. Stock 360 intake and Thermo Quad. I know the ports don't match, not a big issue at your level. Stop there and go no further. Beter route. Find a used 360. Plenty of mild builds around cheap. Even a junk yard one with the above mods. I've built 12 second 318s that would run easy 13.5s in your car. Find someone local who has a clue that will help you. Read enough about motors to become confident in your own abilitys. Then go for it. Any other questions ask.
Doug

rumblefish360 · May 1, 2013

The head swap is a good idea but a little pricey. This is why I did t mention it.

daredevil · May 1, 2013

thought everyone ran the swirl port 302s with a 1.88 intake valve.Cheap enough.

Coronet 14 · May 3, 2013

I got a 4 barrel intake and carb with electric choke on my 72 Coronet. What a difference in power. Ordered from Summit Racing. You can see some of my pictures on here. Checkout post 72 Coronet running good You will be able to spin some rubber. If you want I will give you a list of what I ordered to get it done.

pabster · May 3, 2013

Coronet 14 said:
I got a 4 barrel intake and carb with electric choke on my 72 Coronet. What a difference in power. Ordered from Summit Racing. You can see some of my pictures on here. Checkout post 72 Coronet running good You will be able to spin some rubber. If you want I will give you a list of what I ordered to get it done.

Please put up the list. I'm totally interested in doing this.

Advice for Increasing Horsepower - 318

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