Getting the most out of my 360

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kevindahle

kevindahle

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I have 73 Duster I have had for 23 years and it has been though alot of changes, about 18 years ago I bought a 1971 360 with J heads, bored it .030 over, had the heads rebuilt, stock comp. ratio, basic stock rebuild. Soon after I added edelbrock RPM performance package, intake, cam, carb, added Mopar Performance electronic ignition. Had headers but later on switched back to exhaust manifolds. I swaped it to manual trans, 833 od, rear is 8 3/4 sure grip with 3.23 ratio. The car runs well and strong, but am looking to improve the performance some, thinking about doing some 1/8 mile racing and was wondering where I could get my best bang for my buck!!
 

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Port the heads, better cam, maybe better carb (what size/type is yours, performer or AVS?) and consider saving up for some nice headers (I'm assuming your previous ones were not lol). Also swap rear gears to 3.91 or so your overdrive is just asking for it...

If you can't afford all that at once I'd definitely do gears first, then cam and port heads. Did your top-end kit come with a .488/.512" lift cam or the small .420"? I personally like the Lunati Voodoo line their mid-range 268/276 cam has a great rep here on FABO and would work great with your setup, I run the small 256/262 in my 360 and it's a torque monster.

Nice car BTW and I'm jealous of your workspace, currently I'm having to make do with an apartment parking lot and unhappy neighbors LOL
 
Nice car Kevin! My thinking is will, the low gear 4spd with your existing combo and gear work well. There's a pretty severe drop in rpm between 1 & 2. Gearing in the 1/8th becomes really important. Sorry I just found this thread as it's 1am on my coast. If no one else chimes in, i'll run some rpm/shift point and finish line numbers for you in the morning. Glad to see you wanting to hit the track, it will be a lot of fun.
 
OldmanRick said:
Nice car Kevin! My thinking is will, the low gear 4spd with your existing combo and gear work well. There's a pretty severe drop in rpm between 1 & 2. Gearing in the 1/8th becomes really important. Sorry I just found this thread as it's 1am on my coast. If no one else chimes in, i'll run some rpm/shift point and finish line numbers for you in the morning. Glad to see you wanting to hit the track, it will be a lot of fun.
Click to expand...
most bang for the buck
?change the 323s to 391s and put in a close ratio 4spd....:cheese:
 
Well, thanks. The cam I can't remember the specs but it is the cam thats the "mate" to Edelbrock RPM intake and I think the 650 Edelbrock carb. It has a nice rumble to it. Over the years I've allways thought I screwed up in the rebuild in the compression, at the time I just ordered a kit from summit and didn't think about the compression until I was assembling the engine and it was to late to change. How much of a gain could I get from an increase to say 10-1 compression vs the dished stock ratio piston? As far as the o/d trans it does for sure have a big jump between 1 and 2, but not sure I can do anything about it. the exhaust on the other hand I hated the cheap headers I had on it they smashed the road all the time and needed constant leak repairs but when I changed back to exhaust manifold I don't know if it was all in my head or not, but could feel by the seat of my pants that I lost performance.Lol As a driver its a great car but lately there has been a insurge of first gen camaros, Chevelles and other brand X cars invaded my little town, we are trying to organize some airport racing and I don't want to be on the bottom of the pile!! The only Mopar are my Duster, a Scamp with a mild 340, a Cuda with a hot 340, and a new Hemi Challenger.
 
The extremely low comp is not helping at all,no reason to put a cam upgrade in an 8 to 1 (or less) engine. More gear,904 with a good converter,ditch the edelbrock carb,the list goes on and on. The good thing is you have an easy combo to help.
 
It would seem best to start with gears and headers at this point and see if that gives you what you want.

Should you want more engine wise, cylinder heads, cylinder heads and cylinder heads to start.
 
Just for grins, I ran some numbers.........Total speculation of course, a timed baseline would go a long way. :smile:

Looking at your combo, i used a 5500 shift point, 26" tire and trap speeds of 75 & 80mph.

The 1-2 shift drops to 3000 and the 2-3 drops to 3300 rpm's.

With the 3.23's, trap rpm's are.......
5200 @ 75mph
5600 @ 80mph.......both in 2nd gear.

With the 3.91's,.........
3800 @ 75mph
4100 @ 80mph.......both in 3rd gear.

The big advantage I see with the 3.91's is that it will help pull you up out of that 1-2 shift......although it may feel a little softer at the line in the bottom of 3rd gear?

Sticking with the basics you have right now, future engine mods should be looking toward maximizing mid range torque. Long tube headers will really help along with a aggressive timing curve.
 
Stroke it and send your heads to IQ52, then add gears.

Oh and I'll tell you something I bet you didn't know. Most people do not. 1971 is a ONE year only for the 360. The 71 pistons had a higher compression distance giving them m ore compression than any other year. I bet dollars to doughnuts when you bought "stock replacement pistons" you got 72 and up. In fact, I don't think anybody offers the 71 style piston anymore. I think the only way to raise compression now is to go with KB pistons or some forged units.....and head work of course.
 
I'd get a set of TTI headers, closed chamber 62cc RHS heads from Brian @ IMM, hughes 1.5 roller rockers and ditch the overdrive trans for a real 4 speed.
 
Toss in some KB-107's too, 10.6:1, you gain somewhere around 30 hp/tq. You can get them and a set of moly rings on ebay for around $300.

Set ring gap to largest forced induction spec in case you ever want to juice it, no you don't have to buy file fit to file them down, set up a square file in a vice with some tape to guard the edges and file towards the inside of the ring, never back and forth.


Balance and square decking is highly recommended and should run fairly cheaply.



Also check dynamic compression ratio by adding your cam's ADBC, intake closing, to the rest of your information here:

http://www.wallaceracing.com/dynamic-cr.php

Folks say if you keep at or below 9.0 on those modern, fast burn closed chamber heads and good quench, you can run 89 all day, 87 in a pinch.
 
Lots of great feed back, thanks everyone. The headers are doable as are a gear change, and I think changing to a better piston would be the most gain the only draw back to the pistons is the domino effect a engine tear down will most likely cause, Lots to think about.
 
Another thing to keep in mind. Pistons are about the same price. Stroker or not. You can get a good 4" crank for 400 bucks. Maybe less. You could have 408 cubes pretty reasonably.
 
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