Hello Slant 6 forum,

I'm exploring options regarding keeping my truck a slant six. I've looked through the engine build matrix, and like what Agressive Ted has put together...

Most of the conventional advice is that even the L318, and LA318 mid 60's sweptline trucks were underpowered... which does not bode well for the SL6

I've got a 7000LB 67 D300 truck, that will at times be fully loaded.. but not ALL the time, lets say it will be loaded 30% of it's mileage which would put it over 10,000GVW

It has 4.88 Rear gears, and a 35" tall tire. RPM range expected 1500-3000. I may be willing (if needed) switch to a 32" tall tire when loaded to increase brake and engine power at the ground.

Ideally, A slant six in the engine room.

IF so, how do I go about learning enough so I can ask intelligent questions here ? Do those "engine dyno" computer simulations have anything to offer the slant six world, or are they only good or a V8?

I've recently read someone say that picking the correct cam is 50% of the challenge in designing an engine, getting the compression ratio right is another 20-30% and the rest is in the tuning of individual components..

BUT that may be putting the cart before the horse. Can an optimized and well designed 225 be equal to a stock 318 in terms of work done?

I do not expect the finished product to pull freight like a new Cummins diesel. But it would need to be able to run on the interstate at 60-65 when lightly loaded.. It will mostly be used locally, but on occasion I would like the option of driving it 100-200 miles if I want to deliver or pick up something. When loaded, it would be nice to be able to maintain 35-40 MPH

As I said, most seem to believe that a V8 is the realistic option. I hear that, and yet Dodge put the SL6 in D500 trucks... And my slant 6 runs really nice.. so I wanted to ask here as a last resort if there is any chances that I can build a 225 (or a 240 SL 6) and be happy with the end result.

I welcome your thoughts and input, what ever it may be.
Thanks,
J

i think the slant is gonna be a dog in that heavy of a truck no matter what. i love my slant, but in your shoes, i would see if a 5.2 or 5.9 magnum was available near by and go that route, either TBI or put a carb on it.

Heres the thing about the slant six. It is a torgue machine. It has allmost compleatly flat torque curve. So for towing and hauling its a great motor. Now my set up it way different than yours but here is what i see. With 3.55 gears, A-833 OD trans. going 70 MPH I run at 2000RPM. The cam I have is not really ment for cruseing and makes its best power at 2500+. Picking the right cam is key. However the cam you pick should be paired with carb as well. I use a 500cfm because that is what my cam likes when im at the drag strip. I dont know if a 4bbl would be good for you or if a 2bbl would work better. I know Holly makes a 390 4bbl. And its nice to have the secoundarys there if you need them. But again if you are just cruseing a 2bbl might be best. You can also get more power just by doing the simple stuff. Get some headers and a 2" exhaust. Upgrade the ignition system. If you are getting a rebuild have the head shaved to bring up the compression. And have some bigger valves put in. No madder what you do I think you would be happyer with a slant six aver a 318. Again there ment to be work horses not RPM machines unlike the V8s. You could make more power and torque with a 318 but it will cost take more money and time.

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~Nic

Correct tool for the job: a V8 engine for a truck like yours that will actually be loaded down and used. Yes, Dodge offered the Slant-6 in giant vehicles including full-size school buses and D-300s such as yours. No, that doesn't mean it was even close to optimal for the task. Yes, you can substantially improve the torque output of a Slant-6. No, that doesn't mean you'll have anything like an easy time getting or keeping your truck up to speed in a manner safely compatible with today's traffic.

And no, Nicademas, the V8s installed in trucks were not "RPM machines", they were torque machines—with more torque than the 6-cylinder engine. Yes, a Slant-6 can be modified to approach the torque output of a stock 318, but those same kinds of mods likewise boost the torque of the 318 once again out of reach of the 6er. It will definitely NOT be more cost-effective to build the slant-6 than to build a V8 for this kind of heavy-hauling service—that's just a starry-eyed myth that comes from being madly in love with the slant-6. Reality does not accord.

NEVjr's got the most cost-effective idea: transplant a 5.2 or 5.9 Magnum engine, preferably intact with its port fuel injection (though that'll take some fuel supply system upgrading).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yep...the magnum engine's have a really nice torque band due to improved heads and the roller cam... the 5.2 will get better mileage in an empty truck over the 5.9....but both will get better mileage than their carbed previous incarnations...

I had a buddy that had a 1967 D600 Dump Truck he used as an occasional hauler...it was a tank...it was optioned with a 2 barrel 413...I rode with him one day hauling some boulders to a friend's house...even with the big block and the granny gear box, it wasn't the fastest vehicle but it grunted along without any complaints.....

Speaking as a guy who had a lifted W 100 with big mud tires and a slant six, go with a 318 or even a 360. The slant six is a great engine and all, but Mopar made V8 engines for a reason.

Even in a short bed 4X4 pickup the slant six was a gas guzzling dog. I couldn't imagine how horrible it would have been in a heavier package.

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If it was easy, everybody would be doing it.

How reliable is a slant under constant boost?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

(…and if we're talking about Magnum swaps, don't forget the 8.0 Dodge Ram V10!)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

That's cruel Dan!

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1976 Dart Sport
Currently under revision

If I need to have a V8, then I will go find a 318 polysphere, and maybe put a 360 crankshaft in it. I need a front sump oil pan, and I suspect the new magnum engines only have a rear sump set up.

Thanks to everyone for sharing your experience.

That would be great to do, if it would work... Quite sure I do not have the know-how to pull it off in a way that I would be happy with

Having had mid 1990's Dodge work trucks (1995 V10 3500 and 1996 5.9 2500) I prefer the 5.9. With an automatic and mostly highway driving the 5.9 would get 12.5 MPG. The 5-speed and V10 combo, 9.5 MPG. I really don't believe the dual rear tires were the cause of the 3 MPG difference.

Heavy trucks need large engines for reliability. A boosted 225 would likely have heat rejection problems that would run the engine into detonation, preignition and melt down.

Almost all trucks of that era were under powered. If you live in Kansas keep the 225. If the truck will ever see a hill with a load use a 318 at least.

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Joshua

If you are dead set on keeping the slant six, you could play with gearing. Those big dodges in the 60s came with two speed rear axles and four or five speed transmissions. Build a slant six for maximum torque, run small tires, give yourself lots of low gears leading into a slight overdrive for long flat highway trips, and get used to rowing through the gears and never going much faster than 55 mph. I doubt you will get gas mileage with the slant worth keeping it vs. building a v-8. unless yo commit to going 35-45 MPH tops.

Something like this:
http://eugene.craigslist.org/cto/5220477863.html

He's already got 4.88 gears.

I agree with the general consensus - a slant isn't the right tool for this application. This truck will need low end and mid-range torque. That means displacement. The bigger the better.

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I like the creative thinking and it could work if I did not want to be able to drive up to 100 miles on occasion.

Some of the trucks came through with 5.89 or so gears in the rear axle... And I have one of those with a 230 flathead. Great for a cruse speed of 30-35 on the back roads... but not much fun trying to run at 50MPH... so I think the 4.88 geared truck needs some displacement in the form of a v8...