360 driver build

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KramerSwinger70

KramerSwinger70

70 Dart Swinger360
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so i read on a different forum, cant remember where, and they were talking about how to build a 360ci for high performance an get in the ballpark of 20mpgs. someone there said to build it to stock specs of a 340 for 70 or 71. they also mentioned getting J heads with a 1.88 intake instead of a 2.02, saying you dont want 2.02 for a street car.

so i was wondering why that is? y would one choose a smaller valve diameter over a larger one for mileage/performance. i want to do the same thing, build my 76 cordoba 360 to get about 20mpgs an 300+hp once installed into my 70 dart.

if anyone knows or has done this build with positive results, please post any numbers or brands i should look into. i know pretty much everyone is, but im on a budget of...well i dont even know yet! so the cheaper the better as long as its still reliable

thanks!
 
Because it's all about velocity, not bigger is better. On a street car that rarely sees over 5500 RPM, you'll never feel the difference in the 1.88 VS 2.02 valves, because there won't be any. In fact, in certain instances, you can actually hurt flow because the head cannot flow enough to match the valve size. The larger valve can actually slow the mixture down resulting in less cylinder filling. In fact, Larry Shepard and the boys in R&D at Mopar Performance did dyno testing on a stock 340. They actually found that low end power and torque picked up when they swapped out the bigger valve heads for the smaller valve. They found that it was because of the difference in velocity with the large valve at low engine speeds. The larger valve actually made the engine less efficient under a certain RPM. Course we all know the 340 likes to rev like a bumble bee, so the 2.02s were in their element. But for a mild 360 or even a 340, I would use the 1.88 heads real quick.
 
In addition to the above;
73charger said:
so i read on a different forum, cant remember where, and they were talking about how to build a 360ci for high performance an get in the ballpark of 20mpgs. someone there said to build it to stock specs of a 340 for 70 or 71. they also mentioned getting J heads with a 1.88 intake instead of a 2.02, saying you dont want 2.02 for a street car.

so i was wondering why that is? y would one choose a smaller valve diameter over a larger one for mileage/performance. i want to do the same thing, build my 76 cordoba 360 to get about 20mpgs an 300+hp once installed into my 70 dart.
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The 1.88 valve will keep the mix (Air and fuel) moving rapidly. This will help atomize the liquid better. Aid in torque production and a cleaner, smoother running engine at all engine speeds.

I don't think rebuilding a 360 with 340 specs will do it. The cars back then didn't get 20 mpg's with that type of build or intended gear ratio designed for it.


if anyone knows or has done this build with positive results, please post any numbers or brands i should look into. i know pretty much everyone is, but im on a budget of...well i dont even know yet! so the cheaper the better as long as its still reliable

thanks!
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Do you plan on useing headers and what is your gear ratio.

I was able to get 20 mpg's from my '79 Magnum w/a 360 & 4bbl. But it was a stock engine with dual exhaust off the manifolds and a 625 Carter. It also had Hwy. gears. 2.76's (The car was emmisions leagal becauseit had to be. The dual exhaust also had twin cats.)
 
OK, at least a 9.0-1 comp ratio
standard 1.88 360 heads
600 cfm 4bbl
headers with a good exhaust system
Comp Cams XE262H

The issue with this is the cam will need (According to Comp) at least a 3.23 gear. Not exactly a 20 mpg freindly gear. A lower duration cam will help mileage but hurt HP. I've seen guys get a cam like this and larger and add Rhoads lifters to try and lower the operating RPM range of the cam/engine with there Hwy. gears.

Add a MSD type like system for a good mileage return over the stock system.
 
I'm wanting to get 3.23 gears for the car. And if I can get it to push 280+ that'd b fine. Its my daily driver. I just want a little pep. Mid 14 quarter wud b nice too but it's basically a cruiser. Need enuff power to blow off ricers round here too haha!
 
Then you need more power for the ricers.
 
Haha well I also gotta keep mileage in mind. I'm hopin to keep my dart as a daily driver for quite some time. N I'm Talkin ballpark 20mpg. Meaning 18-23 is wut I'm aimin for. I'd love 300hp if not more but well see. I'm lookin into dougs headers and true duals all the way back. Idk jack bout x and h pipes. I heard a 4 br thermoquad carb will keep the hp/mileage decent but I really kno nothing haha just a kid
 
I like TQ's. A spreadbore carb is IMO an excellent choice for a stock to dual purpose engine/car set up. But, in truth, any carb well tuned will deliever mileage and power. What is under the carb will have a big effect on mileage 100 times more than style/maker of carb on top. Even if out of tune and miss adjusted.

(I'd look into tti's before Dougs. )

As far as a mileage getter is concerned, a helping hand in this search and in a big way would be a overdrive tranny. Let me give you some mathmatical numbers as how the overdrive works out.

Gear ratio X's overdrive ratio equals new final drive ratio or, with numbers;

4.56 X .69 = 3.1464 or 3.15
4.30 X .69 = 2.967 or 2.97
4.10 X .69 = 2.829 or 2.93
3.91 X .69 = 2.691 ...a bit low in final drive. Though MoPar did offer a 2.45 axle ratio at one time.

With the final drive ratio's as seen above, figure your cam specs and useage to those ratios since your after mileage. You can still use a low duration cam. The smaller cam will produce mad torque that will be whipped out by the low gear set. You'll have great get up and go. But instead of running out of steam early, the OD steps up to bat taking over for the Hwy. duties and conserving gas.

Now, your armed with "Food for thought!" and the probabl need for wider tires to hook up.
 
I'd run the 2.02s. Mainly because you can drop them on fresh seats without sinking the valves. That is worth low lift flow, and the stroke is much more of an effect on port velocity than the valve size. You should have no trouble getting 20mpg on a 360 in an A body, but, you will need a high rear axle ratio, 2.76 or 3.23 with a decent hieght tire, and a tight, lower rpm stall convertor. As a comparison... I built a 422" 340 based stroker, with ported iron heads, 2.05 int, 1.65 exh, open chamber, 9.5:1 static. With a hydraulic cam around 242°@.050 and a Holley 870 Street Avenger, it pulls 17mpg when he drives it from NH to Carlise PA. That's in a 3800lbs e body w/3.23s and a 2200 convertor. It also runs 12.80s at 109+, on pump gas. It's a mild stroker but it's a very efficient package. So make the engine work in the right rpm range, gear and stall it to keep it in that range and efficient, and I dont see where 20+ would be not reachable in a car that weighs 500-600lbs lighter.
 
Screw gear vendors. A regular A-500 will do great.

In addition to what moper was saying. In my 1st Dodge Magnum I had a 360 that got 20 mpg's. Stock engine with a factory 4bbl. intake and a Carter 625, dual exhaust off the manifolds, it also had twin cats, needed for the time, (dang laws!) A 340 trap door air cleaner w/K&N filter. An MSD fired it all off on a stock junk yard distributor.

the rear gears were 2.76's w/235/60/15's on all 4 corners. The car weighed in @ 3700 since it was loaded with everything except a moon roof. Carpet in the trunk even.
 
I'm willin to sarcifise I lil for 3.23 gears since I understand I'll have better off the line power

also, what kinda of stall converter should i get? i really know nothing about them
 
4.56 X .69 = 3.1464 or 3.15
4.30 X .69 = 2.967 or 2.97
4.10 X .69 = 2.829 or 2.93
3.91 X .69 = 2.691 ...a bit low in final drive. Though MoPar did offer a 2.45 axle ratio at one time.
Click to expand...

I think Gear Vendors ratio is .78:1. So 3.91 is more like 3.05.
 
The thing between a Gear Vendors OD and a OE O.D. unit is cost. Did anybody do the math?
 
73charger said:
I'm willin to sarcifise I lil for 3.23 gears since I understand I'll have better off the line power

also, what kinda of stall converter should i get? i really know nothing about them
Click to expand...

I'll skip this one since theres to many questions and unknowns about your build to properly answer it. However, once the build is finalized to exactly what your doing, then this can be answered and answered well.

Otherwise, I consult a pro about it.
 
rumblefish360 said:
Screw gear vendors. A regular A-500 will do great.

In addition to what moper was saying. In my 1st Dodge Magnum I had a 360 that got 20 mpg's. Stock engine with a factory 4bbl. intake and a Carter 625, dual exhaust off the manifolds, it also had twin cats, needed for the time, (dang laws!) A 340 trap door air cleaner w/K&N filter. An MSD fired it all off on a stock junk yard distributor.

the rear gears were 2.76's w/235/60/15's on all 4 corners. The car weighed in @ 3700 since it was loaded with everything except a moon roof. Carpet in the trunk even.
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I second this. The A500 is a marvel in itself since it's a 904 variant. They are lighter and built properly stronger than any other automatic their size and probably several other larger units as well. They will take less HP to drive because of the light internals, too. Most all of the same upgrades to the 904 can be applied to the A500. In other words, you can have a nasty *** overdrive unit that's ALL Mopar. Ya can't beat it.
 
rumblefish360 said:
The thing between a Gear Vendors OD and a OE O.D. unit is cost. Did anybody do the math?
Click to expand...

wouldnt i have to do a bunch of modification to the tranny tunnel and crossmember to install an A500 though? and gear vendors doesnt need more than a few hammer dings in the floor pan and gives you a 6 speed. i was figuring id do gear vendors waaay down the road though since i already have a 904 that came with the 360 i bought
 
smartly built carbed 360 with a thermoquad and a conservative right foot=20 plus MPG.
 
73charger said:
wouldnt i have to do a bunch of modification to the tranny tunnel and crossmember to install an A500 though? and gear vendors doesnt need more than a few hammer dings in the floor pan and gives you a 6 speed. i was figuring id do gear vendors waaay down the road though since i already have a 904 that came with the 360 i bought
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Well you bit off an old car. Did you think you could throw a couple bolts at it and it would be done? Something worthwhile requires hard work. Yes, the trans tunnel has to be modded. Yes, the crossmember has to be modded. How bad do you want a cool Mopar? Bad enough to maybe work hard and learn a little bit?
 
strokerscamp said:
well you bit off an old car. Did you think you could throw a couple bolts at it and it would be done? Something worthwhile requires hard work. Yes, the trans tunnel has to be modded. Yes, the crossmember has to be modded. How bad do you want a cool mopar? Bad enough to maybe work hard and learn a little bit?
Click to expand...

lol
 
If I can get 15-16 mpg with a warmed up 340 w/head work/.528 cam/750 dp/3.73/4spd

then you can get 20 mpg.

I bet I could stick a 600 on it, squeeze 2-4* degrees more with a vac adv can, stick 3.55's in it and 20 mpg, as long as I could get about 2800-3k cruise, no problem, right now I'm cruising 3200-3400.

jUst an example
 
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