Hot Rods Should I re build a DeSoto 291 HEMI?

That is most definitely a 'hemi' configuration..........I assume that is the DeSoto 291 that has been under discussion.......correct?

Ray

p.s. going to bed now........see you tomorrow

 

First off click on the Hemi Tech Index & start reading! I've seen that photo before, has a home made 2X1(or 2X2) attempt @ a long ram bolted on the stock 2 bl intake.

 

...nasty...


As to whether or not the 291 will do the job for you, yes, in all likelyhood, it will do just fine. If you were to compare the hp and tq numbers between the 251 and the 291 you would see that the 291 has slightly more available power but at different rpms. No big deal, just gear it accordingly after you decide on a transmission.

As Ray notes, the 331 extended block may create firewall/floor issues, but since it has the PowerFlite attached it may be worth considering. You will just have to do a trial fit and see what conflicts exist. I would certainly be looking at this option.


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Yes that is the engine I have that is in question in the original post.

 

That engine pictured with the Long ram tubes on the trailer is advertised as a 354 Hemi motor. Also when you say "gear it accordingly" you mean the rear end, right. So how do I determine that gear ratio? Also I have not decided on a rear end yet.

I want to go with a Fat Man front suspension or stub for my project.

 

Most think early hemis are 392s. That is a long tail 331, probably a '54 from the one yr only flatened bell on the PF. Wonder if he actually has the engine, like I said, I've seen pics of that long ram contraption posted somewhere in the past. The comp ratio & cam, tranny & rear gears all have an effect on where you're making power, low speed/grunt or in the middle or high range.

 

My Son has a 291 Desoto hemi that he bought to use in his future 30 Tudor project. He bought it just because it was a hemi and when we called Hot Heads to ask about if it was a good choice they said "There are no bad hemis to build, they are all good."

We have found out that parts availability is a little sparse compared to some other versions, and consequently a little more expensive. However, anytime you play with a hemi you are going to spend money, it comes with the turf. If you want cheap go sbc, but if you want cool you lay out some extra dough and do the hemi. Cool costs money.

Vintage Speed now has tripower intakes for these BTW. Here is the one my Son bought for $400.00

Don

 

If you go the automatic adapter route, I would suggest finding a non-electronic OD from a Dakota or Ram. '95 or older, to hook to your Desoto. Same adapter as a 727. Put a low geared rear behind it and have the best of both worlds, low end dig and good cruise.

 

The DeSotos are shorter & narrower than the Chr & would be an easier fit. As far as 291 vs 354, if we were talking modern engines, would you be happy with a 273/283/289 or feel better with a 340/350/351 under the hood?

 

The 331 engine in the pic may have been bored out to 354 (bad idea in my book...) and thus advertised as a 354 but it definately started life as a 331.
R Pope is spot on regarding the gearing. If you adapt an A518 then you can also use a a fairly deep rear gear, in the 4.1-4.5 range and have a very nice daily driver. The od ratio is right at .7 so just multipy the final gear by .7 to get the actual that the OD provides. 4.1 x .7 = 2.87
The danger at this point is using a gear that is too 'tall' and then not having enough torque to pull the dead weight effectively. I would never use an OD with anything taller than a 3.9 unless I was at Bonneville or had at least 450 inches...
For the rear axle, I have Mopar axle dimensional data on my web site so you can measure your drum face to drum face and make a comparison. This also allows you to select a slightly narowwer assembly if you plan on wide wheels/big rubber.

For the cost of some of the aftermarket front suspension packages I would probably just update the existing. If I was planning any front suspension swap on an early Mopar I would use a Jag IFS. Others will have differing opinions, I just like the Jag and the low costs.

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The O.D. only helps on the road, around town the milage with a 4.11 will be as bad as with a 727. I had a Crown Vic Police Interceptor with 351W/AOD/3.08 posi. Evidently it was fast enough to fill the Cops needs. Of course it would depend on if he uses the 291 or a Chr as to the gearing, I'd think.

 

I agree with deuce roadster. If you want a 354, or a 331 I have two complete units. I need to thin out my hemi stuff.

 

Quite correct on the OD issue. I was only suggesting that the OD would be good in cruise mode and the 'fun' quotient of the TF backed by a 4.1 is really hard to beat around town.
If economy is a concern then a different approach is needed and I would use a non-OD 727 and a 2.9-3.2 rear gear. The 3.2, depending on other factors, will result in cruise rpm in the 2600 range.

As with so many build projects there is rarely a one-size-fits-all answer.

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An A500 will NOT work. It will bolt up using an adpter just fine but when you go to put the starter on you will be SOL. The A500 starter location compared to a Mopar 518/ 46rh is moved and clocked slightly different compared to the 518. The body of the starter hits the block even the smaller newer style starters will not work. How do I know this? I tried it and had to go back to a 518 tranny. I did like the better first gear ratio of the A500.

 

Who suggested using the A500?

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Post #40 the name escapes me.

 

Bwahahaha betcha didn't know I failed my typing class in junior high school.
Dope slap accepted and correction made....geesh, pretty bad when I can't proof read my own crap.
And you are correct. The starter sits about ½" higher on the 904-500 than on the 727-518. It is possible to make it work, IIRC TRWaters has a fix, and I have (once) rotated the trans bolt pattern to accomodate a customer, but not worth the effort.

...maybe a quiet pm next time?

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That's kind of what I was thinking. Plus Chrysler in Chrysler seems more appropriate.

 

Thanks I did go to your web site and there is a lot of information in there for sure, Thanks.

When you say about the front suspension to "update the existing" do you mean ......New bushings and tie rod ends and like that.

I do know 2 guys the installed V/8's in their Chrysler's..One has a 1948 New Yorker Coupe and he installed a 345 Hemi with existing front suspension.
The other has a 1948 Windsor with original suspension and a SBC in that one.

Don

 

The oem front suspension is a pretty good design, especially for the day. If you were to ask the folks over at www.p15-d24.com you would hear alot of good comments. Other than the usual replacement parts, new springs and better shocks would be a big improvement.
Keep in mind that the Inline 6 is not a light-weight package, so swapping to an EarlyHemi will not add weight.

One of the big reasons (excuse?) some folks use to do a swap is the interference with the steering box so you might do a trial fit before spending money on anything related to the suspension. If you use a 727/518 then you can actually bolt the trans to the block without an adapter (and no converter) for trial fitting. There are four common bolts that will suffice for this exploration. Adapter thicknesses vary but you can also add a spacer, about ¾", between the trans and the block if you want to get close. A stack of washers will suffice.

You can also get a general idea of the starter interference by looking at the pics I have showing the 904 trans attached to the L-6 and then look at your car and see where the new starter will sit and what is in the way.
Keep in mind that it is very common to shift the engine to the pass side, sometimes as much as 2", to get clearance and with a v-8 you have some fore-aft movement available since the v-8 is shorter than the inline.

I'm sure that others will opine.

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anyone have a link to the vintage speed 3x2 for a low deck desoto, i do not see it on their site.

 

Do some research on Vintage Speed before you throw your money away and raise your blood pressure.

 

Generally speaking, on 46-8 Mopars a shock relocation & disc conversion is the typical front end update. No idea who thought running shocks from the lower to upper a arms was a good idea. Rack-n-pinion steering can be done, but is more involved.

 

I have decided to bring the bare block in to the machine shop to get it washed and cleaned with their machine. Then magnafluxed and go from there.
I was told by a local builder that they could shave the block and possibly the heads or both to get the compression to 9 or 10-1.
Use pistons for whatever the bore will end up to be.

OR?

 

http://hamiltonintakes.com/products/desoto-291-4v-intake-manifold

4 barrell intake for 291.

 

I do not think "shaving" the block and/or heads to raise the compression on this engine is agood way to go. Get the pistons needed to do the job'

The push rods/rockers arms on these engine are comlicated enough with their geometry...changing the block deck height and head thickness can only make things worse, imo.

Ray

 

I'm with Ray, DO NOT DECK THE BLOCK! get pistons!!!! It's the only right way to bump the compression. You can deck the heads a tiny bit for straightness but this motor is not a Small block chevy. It will not tolerate having the block or heads cut down in a major way. You will have intake sealing and valve train issues.

I repeat, get pistons.

 

Guys,
I agree with you. I think the proper pistons is the right way to go especially since I need pistons anyway.
Thanks,

 

Here is a link for Desoto intakes both low and hi deck.
http://vintagev8s.com/ I think he is in Bradenton Florida also I think he supplies intakes to Hot Heads.
I had my Hi deck Desoto cam reground by Racer Brown. Reground cams require either adjustable rockers or adjustable pushrods. BTW cams are NOT interchangeable between hi and low deck engines.

 

Glad you came to the right conclusion! You might have them check that the decks are square to the crank centerline, both front to back & top to bottom, and check that the 2 decks are equal height.