Hey guys, doing some research here. A fellow wants to put together a nice strong towing rig. He has a 3.2? 8-1/4 rear and 10 inch drums in the back with discs up front. The engine is a well worn slant. He wants to freshen the walls up, do some gentle porting, improve compression to something in the neighborhood of 9:1. The intention is to leave as much stock as possible, crank, valves, probably a supersix setup. Here is the question: what sort of catalog profiles give the absolute best torque? I think the 791 from Oregon Cams looks useful. He stipulates that he would like to be able to pull a 7,000 lb trailer up a 6% grade without difficulty. He is not interested in spinning faster than about 4,000 rpms. To give you an idea of the fellow: "I'd like to be able to chain up to a loaded semitruck on a dry road and pull it away," essentially what i think he means is that he wants to have as much torque between 1500 and 4000 to " drag the Queen Mary up on the beach."

Obviously, he is using poetic license with his physics references, but he wants to pull hard. The reason he would like to use a catalog cam if he can is so that he doesn't have to explain himself to the manufacturer. Any thoughts? The rv 10 and rv 15 look good to me too (especially after reading the recent camshaft threads)but he really really wants torque. Thanks for humoring us.

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-Christopher

"Gray Ghost"-1970 Dart.
"Frederick II"-1994 Geo Metro.

With a really mild overhaul, 7000# is a lot of weight to pull. It is even more difficult to pull it up a 6% grade.

"without difficulty" May be your definition of difficult is different than some folks but it is going to be very difficult with a 3.21 gear.

In my opinion, your going to need more power than your going to get out of the engine you want to build.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

We used to haul up to 10,000 pounds with a 1978 3/4 ton truck. It had a Super Six and 4 speed with 3.9 gears. It would do pretty good over the mountain passes if we kept in the torque band between 2,500 to 3000 rpm. Anything below that, the power output really dropped off. We ran 94 octane when loaded/hauling and some octane booster.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

THe motor has plenty of power to pull, but 3.2 rear gears won't let the motor operate where it will make the power to pull. To pull a 7,000 pound trailer up a 6% grade I second the recommendation for 3.9:1 or numerically higher rear gears. He may want to put those behind an overdrive transmission to help with fuel economy on the flat bits of road.

Not spinning faster than 4,000 RPM might also be a tall order, but doable, so long as he doesn't expect to be going 75-80 on the highway, especially without an overdrive transmission.

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Casually looking for a Clifford hyperpak intake for cheap.

Subjectively using the desktop dyno with the stock head flow numbers, sizes, and exhaust:

The MP-244, Com Cam 252, and RV10 all have a nice fat flat low torque band if you keep a slightly modified stock SCR (I used 8.6:1 as a just in case). If going a bit more the RV15 would be nicer).

If going mid-9's on CR the 791 works great from about 2500-4000 rpm...but is 'dumpy' in the under 2500 rpm range compared to the
others, if towing I might be worried about timing and pinging...DCR if set at +4 is about 7.96...so you may need Mid-range gas if heavy towing...

-D.Idiot

Exactly.

If you're set on the 3.2? gears, you're going to need a great deal of patience or a different prime mover. A 360 magnum yanked out of a Ram sounds like a good start. Otherwise, I'd first commit to 4:10 gears, a good cylinder head, premium fuel and then I'd think about the cam.

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1966 Coronet Deluxe

I talked to him and by "without difficulty" he means second gear. He was also planning to use premium fuel, so probably a higher compression than stock. He is stuck with the 3.23 though. So as much torque as he can get in that range, he is running a 904, planning on putting v8 904 guts into it. Does that make it easier? I know he's asking perhaps too much, i think he's doing that for emphasis. But he did seem pretty serious about the 7000 lbs. I did suspect the rv15 would be on the table, especially judging by the other cam thread. Is there something else that might work better?

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-Christopher

"Gray Ghost"-1970 Dart.
"Frederick II"-1994 Geo Metro.

Some don't like them, but for that much towing he may wish to install the wide ratio gearset out of a post 1980 904T. Single barrel carb would be a wise choice if he wants to maximize torque. Basically he needs to follow AggressiveTed's recipe.

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Casually looking for a Clifford hyperpak intake for cheap.

The wide ratio will give him a lower 1st and lower 2nd gearing, will not help.

Richard

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Part of Tyrde-Browne Racing

I'm not sure that the 904 would last long yarding the queen mary around...
even with auxlilary tranny coolers in place.

-D.Idiot

I would think the lower first and second gear ratios would help get the truck and trailer moving with the 3.2 rear axle. Pre 1980 904 gears are 2,45, 1.45, 1.00. The wide ratio gears are 2.74, 1.54, 1.00. Not much of a difference, but every little bit helps.

DI does bring up a good point that a 904 likely wouldn't last long in this application. He would be better off getting a 727 if he wants to stick with an auto, and some BIG coolers.

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Casually looking for a Clifford hyperpak intake for cheap.

I agree with the comments being made. I believe your friend needs to focus on the rear end ratio more than on his engine. 3.2 gears are for a lighter setup.

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Slant power!!!
At least I try...

That's an excellent point. I will speak to him about the transmission issue as if that is the weak point it should be addressed first. Assuming he has to stay with the 904 and 3.23 what is a more realistic towing weight? It sounds like the engine is not the weak point here. Thanks again.

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-Christopher

"Gray Ghost"-1970 Dart.
"Frederick II"-1994 Geo Metro.

Well, as far as the engine not being the weak point that is a gray area. In one sense, the engine is plenty durable enough to power a towing vehicle. In another sense, the engine does not make enough power in the RPM range it will be turning in your friends rig to pull a 7,000 pound trailer with 3.2 rear gears. It isn't a question of durability, it is a question of the applicable operating RPM range.

With the proper modifications AND GEARING, a slant six will make more than enough power to move a truck and a 7,000 pound trailer. However, to shift that much weight a rear axle gear ratio at at least 3.9:1 (and preferably numerically higher) gear ratio must be used. Using a 3.2 rear gear ratio will "lug" the engine, or keep it from turning enough RPMs to get to the power band it needs to operate in to effectively power the rig.

If your friend insists on keeping the 904, he needs to build the strongest 904 possible- V-8 guts, kevlar bands, alto clutches etc... and pack as many clutches as possible in there. He should really get a junked late 80s v-8 transmission and just swap all the guts into the slant six case and do a rebuild with heavy duty components at the same time. Better still would be to step up to the 727 which is really designed to take that much abuse. He will definitely need a big transmission fluid cooler or two.

The true "weak point" that needs to be addressed first is the rear axle gear ratio. This will be the most beneficial and effective modification he can make to get his rig able to tow that much weight. If he is dead set on keeping the 3.2 gears, he really should be considering a swap to a 360 or at least a built 318.

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Casually looking for a Clifford hyperpak intake for cheap.

rear gears!!!
cheaper, faster, and better results.

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Slant power!!!
At least I try...