Ask The Expert- Built 304, choosing stall converter for an automatic

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CowMoo

Jeep Owner
I have the opportunity to purchase a sweet Jeep CJ-7 with a built 304. This thing has a great sounding motor... BUT... The person who built the motor is dead. The wife knows very little.

The engine has a big cam with a stock looking trans. We believe the trans is stock and that was his next link to complete. The idle on the Jeep is currently at 1,200-1,300 RPM and once in gear it is a touch over 850. If you lower the idle, it will not stay idling, it will just stall.

So...... Will a 2400 to 2600 rpm stall torque converter solve this issue? If so, what will it do to the street drivability?

This would be a show jeep as there is too much money invested to wheel it. It's drop dead sexy.
 
Pthorpe84

Pthorpe84

Moderator
Staff member
In no way am I going to touch this one with advice. But I do want to see a picture of it


Sent from my iPhone using Tapatalk
 
Cloaked Willys

Cloaked Willys

Jeep Fanatic
CowMoo said:
I have the opportunity to purchase a sweet Jeep CJ-7 with a built 304. This thing has a great sounding motor... BUT... The person who built the motor is dead. The wife knows very little.

The engine has a big cam with a stock looking trans. We believe the trans is stock and that was his next link to complete. The idle on the Jeep is currently at 1,200-1,300 RPM and once in gear it is a touch over 850. If you lower the idle, it will not stay idling, it will just stall.

So...... Will a 2400 to 2600 rpm stall torque converter solve this issue? If so, what will it do to the street drivability?

This would be a show jeep as there is too much money invested to wheel it. It's drop dead sexy.
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There are a few things that would really need to be known to tell if a high stall is needed.

Different cam profiles are designed for different stalls. My SBC is running a high torque split duration cam that calls for a 2200-2400 convertor. Since I use this off road I have a tight converter build. This causes it to still roll forward when placed in gear unlike a loose style that a drag car would normally use. Even when I had a stock convertor in it I did not get idle drop like that. It would only drop 100-150 rpm.

Another issues that can be causing the idle to drop is a vacuum leak or vacuum line installed incorrectly.

It sounds like someone would need to spend some time getting it all in order. Could be a great buy but could need a lot of work.
 
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CowMoo

Jeep Owner
We spent a bit of time with her this weekend after reading your post. Seems to have a real lopey idle. Each header tube reads the same reading for temp (trying to figure out if there was a miss). At idle, we are able to get 10.5 inches of vacuum. That was after messing with the idle air flow mixture on the carb.

The engine seems to be fine and we could not find any vacuum leaks, other than maybe the check valve on the power brakes. Not sure if that would cause it.

Seems like a roll of the dice. The Jeep is sexy, price is pretty fair, but if you have to pull the motor and tone it down and redo the trans, it could get expensive.
 
Cloaked Willys

Cloaked Willys

Jeep Fanatic
Were you and to drive it at all? If you did, how did the power feel? Was it dogging then grabbed hard when the RPM's came up? This can help tell if it needs a convertor also but there can be some trial and error.
 
Cloaked Willys

Cloaked Willys

Jeep Fanatic
The motor being even temp across the cylinders is a really good sign and 10.5 inches is not abnormal for a big lopey cam with overlap but it is has vacuum advance may not be advancing as much as it needs to. This is why most hot road guys run mechanical advance.
 
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CowMoo

Jeep Owner
Cannot drive it. . The wife is not sure everything was/is buttoned up. The motor is, so she will let us run it. We tried a few times even when warm to get it in gear and it stalls right away. Timing at 3,000 rpm is spot on. BUT, what is this mechanical advance you are talking about? The once on the spring in the cap? Can you link to one?

What about an msd? Could that be the answer?
 
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lindel

Jeep Owner
MSD, Mallory, and a few others offer a distributor that has only a mechanical advance. I used one on my 64 289, and it made it nice and driveable, after stuffing it with a very radical cam.

A mechanical advance only uses moveable weights under the plate the timing unit sits on.

https://www.youtube.com/watch?v=RcmkbQVPz9E
 
B

Brian

Jeep Fanatic
lindel said:
MSD, Mallory, and a few others offer a distributor that has only a mechanical advance. I used one on my 64 289, and it made it nice and driveable, after stuffing it with a very radical cam.

A mechanical advance only uses moveable weights under the plate the timing unit sits on.

https://www.youtube.com/watch?v=RcmkbQVPz9E
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Don't all distributors have a mechanical advance? The 454 we are working on now has a vacuum advance for better timing at idle and a mechanical advance that increases once the rpm's rise.

At anything over an idle, there is little vacuum, so that advance does next to nothing other than help the car idle. The mechanical advance can be adjusted with bushings and springs.

I know very little about 304's, but here, it sounds like he could use more timing at an idle, but a vacuum advance won't provide it.

Would an MSD box or a computer controlled system be able to work better?
 
Cloaked Willys

Cloaked Willys

Jeep Fanatic
Brian said:
Don't all distributors have a mechanical advance? The 454 we are working on now has a vacuum advance for better timing at idle and a mechanical advance that increases once the rpm's rise.

At anything over an idle, there is little vacuum, so that advance does next to nothing other than help the car idle. The mechanical advance can be adjusted with bushings and springs.

I know very little about 304's, but here, it sounds like he could use more timing at an idle, but a vacuum advance won't provide it.

Would an MSD box or a computer controlled system be able to work better?
Click to expand...

Yes, but if it is set up for vacuum advance the mechanical side will not be tuned aggressively enough to support a big cam. The vacuum also removes timing so because of teh low vacuum may be giving a base timing that is close to the full advance depending on how soft the springs are. Best bet would be to set it up as a full mechanical and tune the curve to advance fast enough to allow the cam work. Adding an MSD box will not change the curve but does change how the spark works. In place of a single spark it will give multiple short ones.
 
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lindel

Jeep Owner
^^^This^^^

Mechanical only distributors are more tunable, and better fitted to engines with large, radical cams. A small block (or mid block, like the last gen AMC blocks) will show the effects of a radical cam, more readily than a big block will, and will benefit from an all mechanical distributor. Not to say that big blocks won't, but it's more noticeable with a small/mid block.

As mentioned, low vacuum has no effect on a mechanical distro, one of the major issues with a big cam.
 
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CowMoo

Jeep Owner
Well, this jeep was given to his grandson. It's where it belongs.

Would have been nice, but I would not take it away from family.
 
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