Swap A833 for Auto - 71 Duster 340

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AJ/FormS said:
the compression test will tell a lot.
According to Wiki, Iowa has elevations ranging from 480 to 1670.. On an 8/1 340 that change is worth 6psi.
If you are starting with an 8/1 engine, with a factory 340 cam, your pressure at 1000ft is predicted to be 120psi or less, making it feel pretty soft, I mean really soft down low, especially with a 2000 or less stall TC. There is no cure for this, except more pressure.
You can bandaid it with more stall or a mote rear gear, or a clutch, but those only help you get moving. The low pressure is just a sad thing thru out the rpm range.
There are a couple of ways to get more pressure, but the best is to get the pistons closer to zero-deck.

But hang on; this is 2020 and that engine is nearly 50 years old. There is no telling what pistons are already in there as they are not likely to be the original... so
the compression test will tell a lot.
Click to expand...
I really appreciate all the info. I've got it in storage now but may be able to get at it later and check it out.
 
AJ/FormS said:
the compression test will tell a lot.
According to Wiki, Iowa has elevations ranging from 480 to 1670.. On an 8/1 340 that change is worth 6psi.
If you are starting with an 8/1 engine, with a factory 340 cam, your pressure at 1000ft is predicted to be 120psi or less, making it feel pretty soft, I mean really soft down low, especially with a 2000 or less stall TC. There is no cure for this, except more pressure.
You can bandaid it with more stall or a mote rear gear, or a clutch, but those only help you get moving. The low pressure is just a sad thing thru out the rpm range.
There are a couple of ways to get more pressure, but the best is to get the pistons closer to zero-deck.

But hang on; this is 2020 and that engine is nearly 50 years old. There is no telling what pistons are already in there as they are not likely to be the original... so
the compression test will tell a lot.
Click to expand...

OK....did the compression test today on a warm engine, spark and fuel supply disconnected and here are the results. The first number is at 4 cranks and the second is with 3 additional, so 7 cranks.....
1- 143 150
2- 150 165
3- 147 150
4- 149 152
5- 150 165
6- 137 150
7- 145 157
8- 140 163

I believe they all fall in the 10% range, but that's all I can say about them. So, low compression?
 
twstd340 said:
OK....did the compression test today on a warm engine, spark and fuel supply disconnected and here are the results. The first number is at 4 cranks and the second is with 3 additional, so 7 cranks.....
1- 143 150
2- 150 165
3- 147 150
4- 149 152
5- 150 165
6- 137 150
7- 145 157
8- 140 163

I believe they all fall in the 10% range, but that's all I can say about them. So, low compression?
Click to expand...

Did you block the throttle wide open ?
 
twstd340 said:
What I do know is that it is a '72 340 bored 30 over with Edelbrock aluminum heads, Air Gap intake, Comp cam, and Demon 750 carb. 8 3/4 rear with 3:23 gears (wanting to go 3:91 or 4:10) Running 275/60 street radials and it will not by any stretch of the imagination smoke those tires with 3:23. Hell it won't even scratch them!
Click to expand...
twstd340 said:
So, low compression?
Click to expand...
heck no; that is very noice!
I get an average of 156.5 and you are somewhere around 1000 ft elevation, so that's looking like about 9.9 Scr with the factory 268 cam in at 64* Ica. That's looking mighty good. With headers, a free-flowing exhaust and the rest of your combo, Ima guessing that should be hitting better than 320hp, if the tune is good.
So, you got a very good baseline there; we'll have to work on the tune to see where it's choking. I think the tune has been talked to death already, so you'll have to sift thru the thread to come up to speed.
The 3.23s are a good gear and the 275s are what I would run.

So, if the tune comes up good,and don't forget that cam-timing is part of the tune; altho with your pressure, I don't suspect a problem.
So then, I would be testing the trans to make sure it ain't slipping, and
then testing thechit out of the TC cuz Ima thinking unless you got a ton of cement in the trunk, she's either a very low stall, or the stator is hooped.
But before you do anything,
verify that your rearend really is a 3.23.
A 2.76 for instance will kill about 15% of your torque at zero mph, which could be more than 40 ftlbs at 2000rpm. If the TC is simultaneously hooped, that would make for a super lazy take-off
 
Last edited:
twstd340 said:
I have heard that the a518 overdrive might be an option. What are your thoughts on that? Gear ration to far apart?
Click to expand...
Go talk to Les at Redline in Clarksville. He does all sorts of transmission swaps. Tell him I sent you.
 
AJ/FormS said:
heck no; that is very noice!
I get an average of 156.5 and you are somewhere around 1000 ft elevation, so that's looking like about 9.9 Scr with the factory 268 cam in at 64* Ica. That's looking mighty good. With headers, a free-flowing exhaust and the rest of your combo, Ima guessing that should be hitting better than 320hp, if the tune is good.
So, you got a very good baseline there; we'll have to work on the tune to see where it's choking. I think the tune has been talked to death already, so you'll have to sift thru the thread to come up to speed.
The 3.23s are a good gear and the 275s are what I would run.

So, if the tune comes up good,and don't forget that cam-timing is part of the tune; altho with your pressure, I don't suspect a problem.
So then, I would be testing the trans to make sure it ain't slipping, and
then testing thechit out of the TC cuz Ima thinking unless you got a ton of cement in the trunk, she's either a very low stall, or the stator is hooped.
But before you do anything,
verify that your rearend really is a 3.23.
Click to expand...

That's good to know. I know the tune is not right because it seems to load up...plugs 2 and 6 were pretty fowled for sure and I believe 5 if I remember right. I did switch wheels and am now running 255/60-15 non sticky. Noticed at 60 I'm now running 2500rpm.
 
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