Projects Chrysler Flathead 6 or V8 Swap Discussion

Hi All, thought I would start this thread for some experienced debate on engine swapping.
In particular a Chrysler Flathead 6 (in my case a stock 251) to a SB Chrysler (in my case a LA 318) engine swap.
I am not looking for advice on the actual swap, but feel free to throw it in, think I have it covered, fabrication, welding tools and such are not a problem either in my case
Hopping up a flattie 6 can be done, not always cheap for dual/tri carb intakes, split exhaust, the finned aluminum higher compression head etc. At the end of the day, they are cool, look great but do not make huge hp and the long stroke engines do not like high RPMs without some trick work to the mains, cross drilling.
My current recipeient is a 55 Dodge Fargo 108 wb truck, with an 80s Mopar 8 1/4 diff 3.23 gears, it is a 12 volt vehicle too.
Rusty Toole, not looking for a speech on staying stock either.....LOL
I do like the old flatties, but going with a 318/904 combo, would make a nice cruiser in this light truck too.
I built this truck from parts from several old Dodge trucks, so a frankenstein sort of beast, so being original is not a concern in the least.
Post your thoughts ,ideas and experience, thanx.......F S F

 

It's a lot easier swapping a pickup truck because the engine compartment is roomier than a car and they usually did not have a lot of extras like power steering, power brakes and air.

Your 55 was offered with a V8 so you don't have to worry about steering interference. The engine compartment was designed for a V8. Old ladies and grannies should be able to pull off a swap in one of those. I don't even know why you bother asking, the job is so easy you should be done by now.

Is that better? By the way every word is true. If you asked about a 1950 or earlier car, I might have a different opinion.

 

PS be sure you sell that nasty flathead six for scrap, and smash the hell out of it so no one can use it. We have to keep dangerous junk like that off the roads.

 

Well Gee Rusty thanx for the advice. Yup they did come with V8s, deep down like the old 6s , so kinda got attached to the ole mill.
Might have to go and drive her till she blows up then.
My main point of the thread is what others may have done, or what some others may be doing or have already done. Just chewin on the gas rag is all....

 

Ha ha ha good luck blowing up the old engine. Better drain the oil and water first or it will take forever.

 

I think Rusty is trying reverse psychology on this one....

Ray

 

No I'm not. A 55 pickup has a completely different engine compartment from a 50 or earlier car and should be a cinch to do a swap on, for an experienced mechanic. He has already successfully rebuilt the truck, converted to 12V and swapped the rear axle which practically makes him Smokey Yunick compared to the noobs we get on here.

By the way flat six fix don't forget to write down part numbers and take a few happy snaps so you can answer this question with authority next time it comes up.

And a couple of shots of the rods sticking thru the block for laughs.

 

My neighbor put a 400 (I think, maybe a 440) in one. Went very well. He welded in the K member from the car the Big Block came out of. I think the six would be a satisfying engine to play with in a light car. Maybe not so much fun in something heavy.

 

Ray I totally agree, he is the official Mopar Stay Stock Six Man on this forum, this could either be voltage, cylinders or in the case of a trans an M6 semi-auto....He is solid about it all though

440, yup it'll fit, but have a nice 318/904, was/is dirt cheap, well so far. My truck is fairly light, empty a little over 3000 lbs

 

If you find a Poly 318 water pump housing from a 1960 Dodge truck, you can use that on the LA engine(273,318,340&360). Combined with the V-8 A frame front mount, and the engine is in. You will have to fab for the 904 TF.... The benefit of using that water pump housing, other than the obvious to mount your 318, is it will raise your fan to the center of the radiator.

I put a 360 in my 1959 D series, and had to use an electric fan because I did not swap in the pump housing....

Happy motoring, please let us know which road you take.

 

If you cannot find the water pump housing, let me know, I may know where I can get my hands on one.... You may have to use the earlier cast Iron Water pump. I am not 100% certain if the alumninum pump will fit.... It's been about 12 years since I have done this conversion... Sorry for not being more clear

 

Good point on the height of the fan/wp as it can be quite low in some swaps and not be as efficient as it could be.

.

 

Thanx, very interesting, hmmm, but what about the engine angle downwards, or is my thinking about this convoluted.
So the poly 318 water pump housing has the front engine mount, plus the fan pulley is higher on this pump, thus the fan is higher up, yes or no?
Anybody have pics of this conversion and swap?
How about if a later 360 is wanting to be used at a later date, same-same idea....

 

Well you got the swap covered so a discussion on how easy or not easy it is. So just general discussion on the MOPAR 6 or 318 LA.

The LA is easy to get pieces for even speed pieces and there are options down the road if you decide that it is not enough motor for you. it can be made to look really nice but there is a draw back when it comes to dressing one. they are hard to find anything but hokey assed dress up pieces for, like rocker covers and the like. So the dressed for the prom dept may override the hot rod parts availability on them.

Transmission wise I prefer a 727 but the 904 is lighter and can be beefed if the need arises. I do have a young friend who races a 10 second Challenger with a 904 and has for a very long time. So strength is not a problem if you are after that.

So for the 6 I like them real well too as far as a drivin' around motor. Even souped up it will never be the motor that the 318 is but they are good enough if you recognize that they are what they are. With your gear you shouldn't have a problem with the motor @ highway speed. For example if you are running a 28" tire ( which is common) and a 1:1 final transmission ratio (no OD) @ 70 you are only turning around 2700 RPM that six should run all day at that speed. If you jump to a 30" tire you can drop it about 200 RPM.

Speed parts you can do yourself just like the old timers did, an intake would be easy to build and your split is just a split or build yourself a set of headers if you think you really need them but a split would be more traditional. An aluminum head is not entirely necessary other then just for looks just mill the original and pin strip it for looks, just like the old timers did.

The real down side to the 6 is rebuild cost and the fact that like I said it will never make the zot that the 318 makes.

I guess it comes down to likes or dislikes and cost doesn't it.

 

Thanx Beaner,
yes the flathead 6 will never be a 318, lots of those that say a souped up 251/265 will make HP of stock LA 318, not sure about that, and the 318 will be much cheaper to warm up.

Your right, can drive all day at higher speeds, mind you these trucks are not necessarily built for too high speed handling/braking wise.
I have just corrected the pinion angle of the rear diff to match align to engine/trans, engine down 3 degrees, diff pinion up 3 degrees.
My current driveshaft is stock, except has a modern yolk welded onto the back end for my more modern 8 1/4 rear end. This job was done by someone on the cheap, and is not balanced.
I am chasing some road vibration accelerating and at highway speeds. I have not had time to road test since the angle change to my diff, before it was up 10 degrees to engine down 3 degrees, not a good combo.
I can live with the 6, I do find these 6s, in the heat of summer, have the gas boiled out of the carbs easy, nature of the design I suspect. Being a 12 volt, she starts easy though, even when hot.
So I have the LA 318, and the 904 trans is getting new seals and shift kit, it will be used in this truck, or some other project.
The idea of getting a poly block water pump housing,so I can mount the sengine to front mounts is interesting.
I have also just recently built a Mopar electronic ignition for this 6, using a Slant 6 distributor and a flathead dizzy shaft and weights, turned out great worked great, better idle, but failed to start one day, so popped in points dizzy until I can find out what went wrong, the coil checked okay as did the ballast resistor, power to the module, pickup coil in the right ohm range, air gap set at .006 to .008 spec.
Anyways, thanx Guys for the help...

 

If you ditch the stock exhaust and run a header with a dual carb intake the carb boiling problem goes away.

And the stock 251 cam shaft is lousy it has a very close lobe separation. Great for a stationary engine not so much for a vehicle.

 

I don't live in Manitoba so I never run manifold heat. It seldom gets much below the teens here and if it does it just takes me longer to warm up, LOL

One thing that could be done for summer driving is the build some stainless heat shields for the exhaust. I am not sure how effective it will be but it would help a bit. We ever had much problem boiling the fuel out of the carb before we started running alcohol. I don't know about fuel up there, but here we not only have to deal with gasohol but also summer additives. it is a pain but you just learn a few new tricks to deal with the problem I guess.

 

Yup we are staright north what about 800-900 miles, that sure makes a difference in winter weather and the change of the seasons, when you guys may get down to 0 on cold January nights, it's -30 here with a -45 windhcill on occasion, think Grand forks ND, you know what I mean.....LOL
Premium here is alcohol free, mid grade is 5%, regular is 10% corn squeezins.
Any thoughts on road vibrations, on the higway, driveline? Wheels? any other suggestions?

 

Comes down to money IMHO. 318s are great solid motors but of course don't come close to 340s or 360s, but Man oh Man how cool would it be to have a solid cruiser with that flatty?

I vote flatty and a manual box.

 

So many variables. There are probably a dozen things that can set up a harmonic at speed.

if your tires are balanced and not old radials then the next step is to see if they are true. no real side wobble or out of round true.

Toe correction can also set up a vibration at speed, so you will want to be sure that it is good and set to spec. King pins loose or bad spring bushing should also be taken into account. or a cracked or broken leaf.

The drive shaft for me might be suspect if you changed the yolk, it needs to be clocked right and the yolk needs to be true, cocked a little bit can be a problem aside from balance itself. Sometimes even the rolled up cardboard in the drive shaft can be a problem if it has come apart or been burned up or dumped out. Drive shaft diameter also plays a role in highway vibration, but on a stock (ish) vehicle I wouldn't think it would be an issue.

The transmission being a little loose can set you up for a little vibration too as well as the clutch and flywheel combo. Even engine balance can cause problems. On a light car I have seen an out of balance engine actually set up a death wobble.

I usually do the easy stuff first and work toward the hard stuff. LOL

 

Yah I hear yah Brother, lots of people see this engine and think its so cool, just stock looking, split exhaust tri or dual carb intakes.
Here is the beast, she runs pretty good, doesn't burn oil, has decent compression and oil pressure. It is a long block 251, 4 spd T98 Acme B&W trans.

 

Hey there Dumprat, like your thinkin. I wasn't ware of the cam profile for a 251, I do know it seems a bit different from old 218 long blocks.I do know there were a lot of cam profiles for various applications, sure a lot for industrial/farm work types too.
Hey the " Hop Up" stuff, seen a lot online, but have experienced a drive in 1, a 251 or 265, shaved head, hotter cam, dual intake and exhaust, wonder how that would feel seat in the pants driving compared a stock a bit tired engine.....watching your build with interest, read your posts on P15 D24 too....

 

Too bad the P15 is such a goof show....

I did a bunch of little mods to my m37 that made a big difference in power. Ditch the stock fan for a flex fan, bumped the point gap to .025, indexed the plugs. All before I did the intake and exhaust. It all made a difference. The stock intake leans out the front cylinder and 3-4 run rich. A dual intake and better carbs made a huge difference. I ran Autolite 1100s. If you are still running a stock style muffler get rid of it. Run the longest thrush straight through you can get. Makes a world of difference and won't be too loud.

A water box on the intake is enough heat and won't boil things in the summer. A cast iron intake with cast exhaust is hot enough to fry eggs on.

 

Yup those stock intakes, can get wicked hot here in summer, resulting in wicked underhood heat.
You know I custom made a slant 6 electronic dizzy and box, just last week, worked great, but something failed, so back to the pints, mine are gapped at .020, I find the dwell reall goes down on mine with more gap.
What your saying about the stock intake is absolutely correct, plus these engines need everything they can get to breath.
Even hopped up they are quite reliable, and good engines for long cruises.
I would like to hear from someone, witha hopped up version, explain how much more power you actually feel, once hopped up.
The spring you mentioned, try Norm in Winnipeg @ Mid Canada Parts 1-204-475-3399

 

Are you familiar with Salmon arm bc? I got mine tuned to the point I could pull tank hill in fourth gear. It couldnt do third in stock form.

 

Yup Salmon Arm, Vernon, Okanokgan and Kalamalka Lakes, yup been there before, camped through the area with parents 1st time summer of 1969

 

Are you still running the original front drum brakes, or have they been updated to something else? The flathead 6 (especially the 251) is pushing the original brakes. Adding more power without a brake upgrade is probably not a great idea.

Have you figured out what you want the truck to do yet? If you just doing joy rides around the countryside or making the trip to the ice cream shop in the summer, with a rare highway trip, the flathead will probably do just great. Split intake and exhaust manifolds will increast the zut a bit. Lots of people have split manifolds, both intake and exhaust. Its not difficult, there are probably U Tube videos on how to do it. You don't need a store bought one to have the extra power.
You have a great running flathead, mill the head, split the intake & exhaust manifolds, and if you really want to go nuts, have the cam reground to a better profile, then, drive the thing.

However, if you intend on doing a lot of highway, or if want quick throttle response, swap in the 318/904. You can chase down all the original stuff to mount the motor the old fashioned way, but then you will have to figure out how to mount the trans at the bell housing, and leave the rest of it hanging! Motor and transmission mounts need to form a triangle, two either at the front or at the back, and one at the other location.
Old motors (like your truck) are mounted with a single mount in the center, at the front, and one on each side at the bell housing. The small, light weight trans hung off the bell housing, and the drive shaft had a carrier bearing in the center. The bell housing mounts kept the motor from twisting or rotating. The center bearing on the drive shaft handled the up and down movement of the rear suspension. This engine/transmission mounting system was a carry over from very early in automobile construction.

Modern engine mounting systems (like the 318/904) use a mount on each side of the motor, and they moved the single mount to the rear of the transmission. Doing this allowed the removal of the center bearing on the drive shaft in most cases, and made for a more stable mounting system, by spreading to mount pattern out more, and putting the torque control on the motor that was creating the torque in the first place.

You have to have side mounting of either the motor or the transmission to keep the motor from rolling over when under torque. The only place wide enough to add side mounts to a transmission is at the bell housing (unless your turning the trans sideways like the front drive cars). Then the entire weight of the trans has to be carried by the bell mounts, or I suppose you can add another mount at the end of the trans, some race cars do. Short of a plate between the engine and the trans, I don't know how you could add side mounts to the 904 bell. It would be much, much, easier to add brackets to the frame side rails to attach to the 318 engine mounts on the side of the block. Then you can add a crossmember at the rear of the trans for the trans mount. Then it would be safe to remove the center driveshaft bearing and use a 1 piece driveshaft. It would give you better u joint angles.

By using the modern engine mounting system, you can position your motor/trans in better positions to take advantages of engine cooling fans, exhaust clearance, drive shaft angles, and other things.

Engine cooling was listed as a problem area concerning the V8 conversion. There is ample room under the hood to adjust the height of a modern radiator to position the motor driven fan in line with the radiator. Sheet metal ducting, and closing off areas other then the front of the radiator will redirect the air flow through the radiator enough to cool any properly running 318 (or any other motor).

As far as the vibration issue with you truck, 6 degrees difference in pinion angle is still to much, 4 should be the max, unless your doing heavy duty drag racing. Do you still have a carrier bearing in the driveshaft? What shape is it and its rubber bushing in? If there is no carrier bearing in the drive shaft, are the trans mounting bolts tight? That trans was never designed to deal with rear suspension movement. Gene

 

What's the difference in 60 MPH with a L6, vs 60 MPH with a 318 as it pertains to stopping?

 

The water pump housing that I referred to is the same as used on the industrial 318. When I put a 360 in my 1959, I had big issues with the fan being too low, so one of these housings raises not the engine, but the water pump higher, allowing you to run a mechanical fan.

 

My brakes are really good, modern drum on back, stock up front, so far not bad. I may convert the fronts to disc, but not immediately. I would add sway bars and links to front axles and rear diff beofre brake changes.