1971 360 question

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Wicked4659

Wicked4659

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I just picked up a 1973 Duster 340, with a 1971 360, 904 trans and 8.25 rear. I haven't checked yet, but I think the gears are 3.91's or 4.10's. The engine at some point had a fairly beefy cam installed and I'm not sure about the stall speed on the converter. My question is, the engine has an older Holley 600 cfm carb. It needs a rebuild, but I have a practically brand new Holley 4160 750 vacuum secondary laying around. Will the 750 be too much carb? Should I think about a new 650?

Second question, I have been thinking of upgrading to an MSD billet distributor with a 6AL box and coil. Is the change to a new ignition system, worth the investment?
 
750 will work fine when tuned up.

Set initial timing in the 12-16 range to start (maybe more depending on cam), limit total it to about 36 with iron heads and go have some fun.
 
I think the vacuum secondaries will make it a great fit. Mystery cam is the big question. Ignition, how much strip time? You will give up gas mileage for wot performance
 
69conv said:
I think the vacuum secondaries will make it a great fit. Mystery cam is the big question. Ignition, how much strip time? You will give up gas mileage for wot performance
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I might take it to the strip once or twice. It will mostly be a weekend cruiser. Gas mileage is not a concern.
 
nutz said:
unless your running high rpm /big cam 750 is big
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Not necessarily at all. I run a 750 double pumper on my stock stroke 340. I tried everything from 670’s to 870’s on it, the 750 double pumper with mechanical secondaries is by far the best fit, confirmed with an afr gauge as well. Just a street car, moderately sized cam but by no means “big”.

750’s on a 360 with a decent cam/build is very common.
 
Wicked4659 said:
I just picked up a 1973 Duster 340, with a 1971 360, 904 trans and 8.25 rear. I haven't checked yet, but I think the gears are 3.91's or 4.10's. The engine at some point had a fairly beefy cam installed and I'm not sure about the stall speed on the converter. My question is, the engine has an older Holley 600 cfm carb. It needs a rebuild, but I have a practically brand new Holley 4160 750 vacuum secondary laying around. Will the 750 be too much carb? Should I think about a new 650?

Second question, I have been thinking of upgrading to an MSD billet distributor with a 6AL box and coil. Is the change to a new ignition system, worth the investment?
Click to expand...
The 4160 will be fine once tuned to your combo.
If you have the factory electronic ignition, just get the curve dialed in and you'll be fine. You'll have to do that no matter what ignition you run, and the change in ignitions (I won't say "upgrade" in this case) won't necessarily be worthwhile for your use.
 
Wicked4659 said:
I just picked up a 1973 Duster 340, with a 1971 360, 904 trans and 8.25 rear. I haven't checked yet, but I think the gears are 3.91's or 4.10's. The engine at some point had a fairly beefy cam installed and I'm not sure about the stall speed on the converter. My question is, the engine has an older Holley 600 cfm carb. It needs a rebuild, but I have a practically brand new Holley 4160 750 vacuum secondary laying around. Will the 750 be too much carb? Should I think about a new 650?
Click to expand...

A 750 will be fine. Tune that thing well. Take your time with it and dial it in good.
Wicked4659 said:
Second question, I have been thinking of upgrading to an MSD billet distributor with a 6AL box and coil. Is the change to a new ignition system, worth the investment?
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I’m not a fan of the MSD. For me, they fail way too often.
IMO, the only advantage is 3K rpm and below. After that, a Chrysler Chrome box or equal box is all you’ll need.

There are a few aftermarket manufacturers that make knock off like boxes, like FBO.com which will perform great.
That’s the only step up in ignition boxes I’d do. Unless your getting serious, Daytona electronics (I Think the name is) in Daytona Florida has some serious bad *** material.

nutz said:
unless your running high rpm /big cam 750 is big
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Don’t take this to offensively but - BULLSHIT!

I happen to ru. A 750 Edelbrock on my 5.9/727-2500 stall-3.55 geared set up in a ‘79 Dodge Magnum. The engine only has added on bolt on parts, no cam yet, a RPM intake, hooker super comp headers at 1-3/4 into dyno max mufflers at 2-1/2 to the rear bumper, fired by a Chrysler Chrome box and a MP distributor.

It’s nothing fancy, very simple bolt on parts. Makes 300hp. Is an excellent cruiser and out out around town. The carb OOTB performed really really good and can use some trimming on the tune. That’s it.

Runs and drives the way it should, the way you’d want it to be.

Now I will say the larger carb only shows a few hp gain up top.
I haven’t tested it against a smaller 600 yet or my modified 600.
That day will come soon if all goes well.
 
If that 71 360 still sports the original ONE YEAR ONLY pistons, then it has higher compression than ANY other year LA 360 and probably DANG CLOSE to the 5.9 Magnum, because they had one year only pistons with a taller compression height and that gave those engines around a true 9:1 "or so" compression. So yeah, it'll suck that 750 down and blow it out the tail pipes.
 
If you are running a dual plane manifold, you could go with a bigger carb than a 750.

Like said previously, Halifax hops on this forum is the man. He will set you up by selling you a total ignition system or dial your existing one in.

Stay away from the later years Chrysler electronic ignition distributor made by Accel that was sold through direct connection. The earlier years distributors made by Chrysler are the ones to have.
 
It's basically a 375cfm 2 barrel with additional engine activated, on demand, CFM via the spring.
 
Not a fan of the new MSD at all high priced failure in waiting. Tons of ways to do what you want. Recurve tune what you have, a 510 kit which is similar to the 6al but 1/3 the cost etc etc.
 
We all know the 340 was the highest performing SBM. The 360 came on the scene in 71 to replace the 340. When the 360 was put in Dusters did it now become better then the motor the 340 was? So would a 72 340, lower compression and what ever detuning was done, beat a 73 360 Duster? I had a 71 340 duster and it was a great motor, but never really saw a side by side comparison of 340 vs 360 back then.
 
Some stock small blocks came with 850 cfm thermal quads. 340 Six packs were 1350 cfm. with 444 lift cam same as 4bbl cam and same ports and valves
 
750 will run great on that. may have to tune it some but it will be fine.


as far as the ignition how about putting HEI on it.
 
Your engine gonna basically flow the similar amounts of air no matter what carb, it's the pumping loss that's the concern, you only need enough restriction for the carb to function properly for the application.
 
273 said:
Based on what ?
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On the few engines I played with
As said here depends on a lot of things
I was thinking stock engine small cam
Driving on the street
Unless you have enough cam and exhaust and gearing
They will bog down on quick acceleration
If you snap the throttle open quickly
But tuned right ...it will be fine
 
Does the OP need a 750 ? probably not, will a 650 perform much different ? probably not.
750 is probably the most versatile size, people have successfully ran them from mild to wild.

Bet most of the horror stories come down to poor tuning.
 
tonysrt said:
We all know the 340 was the highest performing SBM. The 360 came on the scene in 71 to replace the 340. When the 360 was put in Dusters did it now become better then the motor the 340 was? So would a 72 340, lower compression and what ever detuning was done, beat a 73 360 Duster? I had a 71 340 duster and it was a great motor, but never really saw a side by side comparison of 340 vs 360 back then.
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I have often wished someone would build a 340 & a 360 at both having a 10-1 compression and swap top ends and camshaft over to the other using the same exhaust manifolds or headers for the best possible A to B dyno test just to see where the cards fall.

IMO, I think it would be a fun testing.

Oldmanmopar said:
Some stock small blocks came with 850 cfm thermal quads. 340 Six packs were 1350 cfm. with 444 lift cam same as 4bbl cam and same ports and valves
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IIRC, the 6 pack works out to be 955 cfm when converted to the 4bbl measurements.

I think the TQ’s, big or small, work great for what they are due to the small primaries. It’s also my opinion that for a OEM stock carb offering they perform realllllly well.

I miss the days of $20 TQ’s. Crazy cheap to get and rebuild kits were 20/25 bucks. Add in a few tricks and off to the races with a cheap *** kick *** carb bowling the song of my people at WOT!


Ahhhhhh, that soooooogning howling sound.
Mmmmmmmmmmm
Warm fuzzy feelings abound…
Mmmmmmmmmmmmm
 
halifaxhops said:
Not a fan of the new MSD at all high priced failure in waiting. Tons of ways to do what you want. Recurve tune what you have, a 510 kit which is similar to the 6al but 1/3 the cost etc etc.
Click to expand...

Who does recurving now? When I was a kid, there was a Sun distributor machine at the local tech school.
 
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