wondering about mopar '75 slant 6

Hey all,
so I"m running the stock 270 poly 8 in my 56 dodge pickup, it's got the stock 3 speed column shift transmission. someone on craigslist has a running 75 dodge/plymouth 225 slant six for $100. I'm wondering if the motor would work as a "plug and play" with the trans I have now. He also has a 3 speed bell housing and A body 3 speed manual transmission for it, didn't disclose the price in the ad for those..
I've loved having the poly motor but honestly parts availability as well as rising gas price tempts me. would rather have something usual on the road than something unusual in the garage...
thanks for your input. I really appreciate it.

 

Do not believe it will bolt up, Chrysler changed some things in the early 60s, but with a slant six manual bell and so on it may work.

But if you want to improve fuel economy the first thing I'd look at is what gear is in it, if you have like a 4.11 truck gear just changing that out for a newer rearend with a 2.73 or 3.08 will increase fuel economy on the highway.

 

If the poly is running, keep running it, that's a cool motor.

"........ parts availability as well as rising gas price tempts me......."

Buy a Honda........ oh wait, gas prices are falling !!

 

I have a 78 dodge d 100 6 cylinder / 3 speed and it gets 18 mpg. I dont know what kind of mileage the 270 gets but would it be a big enough difference to warrant the swap. The 225 6 is a good bullet proof engine but I don't think it would be a plug and play. It is not easy to adapt later o/d transmissions to if you decide to go that route at a later date. You might check on a slant six forum to check on transmission options.

 

Is your three speed on the column, or does the stick go into the top of the trans case? If yours is a three-on-the-tree, the 225 /6 and newer three speed should work O.K. Going to a higher gear ratio will also help with the fuel economy. A dual carb intake and tube headers would probably get that six pretty close to the power output of the 270 when it was new. I had a 225 in a '73 duster w/ a 3 speed stick; I don't remember what rear ratio it had, but it had good low end power.

Later, *****6

 

That's an idea, though. I wonder if one of the '80's truck trans, the 3 speed + O.D. stick shift models would go behind either engine. That way you could leave the low ratio stock rear end in.

*****6

 

Not very likely that you could swap just the engine into the truck. And it would be a step back as far as performance goes. Also a $100 37 year old engine is probably worn out. if you can't see it run first, you might be buying a pig in a poke. And then there's the fun issue of the parking brake.

If you can find a complete drivetrain from a running/driving 318 car from the 60s-80s, it might be a better swap candidate.

 

it's the "three on the tree". I don't know what gear ratio it has currently but it's geared low enough to prolly pull a train if I needed to.. about 55mph is it's top end. the poly's started giving a pretty loud ticking noise from the (hydraulic) valves, smoking abit and it's getting about 9-10 mpg. basically I think I'm looking at a rebuild on the poly (at least the top end) or seeing how to make the 100 dollar slant work. I do love the poly though...

 

Eh, it's a slant six. I had a line on an aluminum block one and couldn't find anyone with any interest in it, so I p***ed. $100 for one that runs is probably about what the market will bear.


That's another reason for the rearend swap, though - eliminate the tapered axles, change it to a normal parking brake setup, and get better fuel economy in the bargain.

 

I guess performance is relative to condition in this case. seems like unless I switch over to a hemi top end (read $$$) there's not a lot that can be done performance wise to the polly, while the slant has more possibilities. I could be wrong though (usually). parking break wouldn't be an issue as the wood block in the bed of the truck would transfer over w/ the new(er) motor easy enough . i hear ya on the pig in a poke thing though...

 

I've had problems getting the block of wood under the tires, when the brake pedal goes to the floor, and the truck is going 30 mph

 

I hear ya on the tapered axle thing! got to do the rear breaks today, third F'n time I've had to rent a 12 inch puller. might as well buy one..

 

so you saw me the other day..

 

so far what I'm getting is that it'd be a shame to swap out to the 6. Is that because the poly's older, cooler and more interesting or the six just isn't as good of a motor?

 

just for reference..


http://portland.craigslist.org/clc/pts/3109881974.html

 

mainly because the swap will be a lot of work, you'll run into things that don't fit together, and you'll end up with 45 fewer cubic inches, and a lame 70s engine.

 

The 3 speed w/OD trans came behind many slant 6's so that's not a problem.I have two of those transmissions myself. They have a lower 1st gear than the 8 cyl. trans... and a .75 OD IIRC.

The 6 may be a good fit while you rethink your love for the poly... maybe a rebuild is in the future?

Or put that OD trans behind the poly....

 

damn, sounds like the story of my life...

 

First of all, the Slant Six might just be a bit too long to fit your engine bay....I had a GMC inline six in my 56 Dodge 1/2 ton w/Muncie SM420 granny gear trans....Had to modify the firewall to get it in keeping the radiator in the stock location...Had to lose the trans crossmember too...not for the feint of heart....take out your tape measure and use it....My truck was purchased by me for $500.00 with a 270 Hemi instead of a poly....Hemis were only available in 2 1/2ton or larger trucks...The previous owner swapped it in years before they were sought after...I took it out and put it in my 52 F1 pickup...sweet!...I had the bell housing hole bored out on my hemi 1/8" to use a 77 Dodge all synchro A230 three speed trans...the mounting holes I just redrilled and tapped and the trans bolted right in!...Now you can modify your bell to use any later Mopar trans and get rid of that hokey non-synchro first gear trans like I did...On the Dodge I have an 8 3/4" rear from a 72 Challenger and 3:23 Sure grip center section....this rear has parking brake cables and no tapered axles....If I were you, I definately would rebuild the 270 poly...I think the slant six would be very close to not fitting al all.(too long)...just locate a suitable rear axle with a highway gear...swap it in...you'll be happy with it....BTW...I love Slant Sixes !!

 

It's a work truck that does your hauling, or is it going to become a truck for the local shows?


If working truck, I might just try the slant six, and consider options there later, for the 4 speed OD. Or swap rears, or both, but later. I don't know what the 6/stick driveshaft front yoke is like, but some other yokes can be modded for a disc E-brake

I can't see feeding a poly on a go getter work truck, but that depends on loads, terrain, speed, etc.

Let's face it, the economy, if that's what it's called now, is not getting better and a choice between gas and food?

 

definitely see a rear end swap in the future. was hoping to find one at the PIR swap this year. ford and chevy stuff all day long but not much for pickin as far as the dodge stuff went. thought about the fit up (length), wanted to get some input from folks who had more experience before driving all the way out there to measure it. I kinda want to pick up the slant/trans combo just because but thats how I ended up with a garage full of old motorcycle parts. lord knows i'd be tripping over the thing for a couple years before using it or selling it for less than I paid.

 

As was already said, I don't think the slant six will do much better gas-wise if it has like a 4.56 rear gear and the motor's screaming at 4000 RPM at 55 mph.

 

mostly a work truck, hauling bikes, hay and dirt shortish distances and low speeds. occasionally work commuting when I'm sick of riding my motorbike in the rain. I'd like to clean it up a bit and set it up like my grandfather had his. he ran the same truck every weekend as a push truck at the portland speedway in the late 50's early 60's. -paint some graphics from the speedway on the side and an in memory of.. sort of thing.

for the authenticity def would like to keep the poly but at the same time he was such a pragmatist it wouldn't be out of spirit to put something in that's more "sensible"...

 

your prolly right gas wise. was thinking long term maintenance though also, (parts availability, etc..)

 

I think the slant 6 is a bit shorter than the 6's offered by GM and Ford.
Part of the reason for the slant was to place the water pump on the side of the engine and not have it bolted to the front.
They wanted it short and slanted to give a lower profile for the small Valiant.

 

The slant and shortness of the engine are due to it being a long stroke, small bore, 4 main bearing engine. The other makers went to a short stroke large bore 7 main design with their new engines in the early 60s.

 

Yes,I believe it was slanted over for the low hood line.The length is as Squirrel says above...
A slant 6 in a PU or van will get the job done,but they are doggy ...

 

Swapping to a 3.55 or 3.23 Dakota or Cherokee rear axle would require less surgery than swapping to a slant 6. The slant 6 could fit in an engine compartment that was designed for a flathead 6, but usually the radiator area would have to be modified for firewall clearance. Modern rear brakes and highway-friendly gearing would make for a happier driving experience. I've read several examples where the original flathead 6 + 3spd was kept and a 3.55 axle was installed that resulted in 60mph+ highway cruising and better mpg; swapping to OD transmissions have improved performance even more.

 

First, forget about mating the stock trans to anything else.

There is nothing wrong with a Poly engine as compared to a /6 or even the Hemi. If properly rebuilt with more compression it will certainly surprise most folks who dismiss small cubes.
If you intend to put alot of miles on the truck then a tired engine won't be helpful. Yes, a fresh top-end could be a good bandaid...how tight are the rings?
If you need something dead reliable then use a 318. Plenty of donor cars/vans that can be had and you can use alot of the bits and pieces.
Keep in mind that you will be switching to 12 volt if you swap a newer engine.

.

 

I have a 3.9 V6 with the 5 speed and 3:55 sure grip drive train out of a 90 Dodge Dakota in my coupe. It gets a regular 18-20 mpg at 65-70 mph and has decent power. The V6 fits nicely under the hood with plenty of room in all directions. If you don't open the hood, who will know what's under it?

I have a slant 6, a 360, and a 318 all laying here that are all in good condition and went with the 3.9 for the fit and mileage. I have driven my coupe about 2,000 miles since April 2nd and intend on driving the wheels off the car. Don't dismiss a 3.9 V6 without at least checking it as an option. I bought the whole Dakota truck for (way) under $500, and many parts from a Dakota will work well on your truck. Gene