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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> TH350 vs. 7004R? Also, gears?
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Topic Review (Newest First)
10-18-2007 08:05 PM
307malibu
hmmm . . .

Ok, so looks like I'll need to swap gears. I gotta say though that I've seen cars with 2.73s and a TH350 (in car mag's "reader rides") that claim mid-13s with a built 350--and can't be toooo much more than 375-400 horse out of the combos they claim. I'm fine with a 3.08 or 3.36, but I do want to take some trips with the car so I don't want to get too steep out back.

I talked to a guy at a tranny shop in town today--one with a real good reputation--and he claimed he'd need $1200 to build the 7004r to a decent level and $600 for a TH350. The price for the TH350, mind you, was for a complete performance run through, not just a rebuild. Does this sound like a reasonable ballpark?

How hard is it to do a performance rebuild on a TH350 myself? Anyone out there done it?

Thanks!
10-17-2007 11:53 PM
westfaliaguy
Auto Trans/Ratio Problems

You say that you have one "issue", but I see at least three. A plain TH350 won't run 14 second quarters with 2:73 gears even if you have 375hp. Your best choice would be 3:73 gears with a modified TH350C trans. This transmission has the ability to lock-up in top gear and return decent milage on the highway. You could "build" a 700-4R trans for this application but you would have to install an upgraded clutch pack and sprage kit from a 350C/R trans to make it reliable. You can buy this upgrade-kit from most suppliers for about $300-$350. If you take a 700R4 trans out of an Astro Van, it is set-up for a 4.3 liter V6 and can't handle the power from a V-8 engine! At some point in time, you will have to decide if you want good milage or to run 14's in the quarter! Speed costs money! How much "speed" do you need? Good milage requires good sense. The choice is your's! Your's, Westfaliaguy
10-17-2007 07:04 PM
307malibu
TH350 vs. 7004R? Also, gears?

I found a good deal on a 1997 vortec truck block and heads and figured I'm sick of the 307 anyway. The block has about 25k on it and is super clean, and the heads are nicely reworked by Competition Products out of Oshkosh w/ 2.02 / 1.6 valves and are set up for a .550 lift roller cam (see pics if the attachment worked). Are those titanium retainers? I have a set of Comp roller tipped 1.52s for self-aligning heads, too.

Here's my issue. I've got a '71 Malibu with 40k original on it, a TH350 and 2.73s. 25 inch BFGs, not super sticky drag tires. I'm planning on 350-375 hp out of this motor and I'd like to go sub-14s in the quarter (which I will probably only get to do once a summer). I'd also like good all around driveability with close to 20 mpg on the highway.

SO . . . .

Will the original TH350 hold up to this with a cooler and deep pan?

Should I get a TH350 built for this application? I have an older one I could use.

Should I stick with the 2.73s (again, I want to do some highway driving)? I'd be okay with 3.08s or 3.23s even.

OR

I do have a 7004R with real low miles on it, out of a 1990 Astro Van. Will this handle that kind of power? I understand this will involve 3.55s or 3.73s in the rear, a shortened driveshaft, TV cable adjustment issues, and a lock-up controller.

OR

Should I keep the motor mild and slap it in with the TH350, then maybe later upgrade gears if I want more performance?


A big thing to consider is that as soon as this project is done, I have a '47 Ford street rod in the works, so I will probably plan on reusing my original 307 and overall price is an object. If I'd be better served using the 7004r in that, then fine.

Also, I want to get rolling. So if a 7004r will take forever to set up, then screw it.

Thanks for all your help.

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