Blown Desoto Hemi tech (porting heads)

Hey Rat! What is this bad boy eventually going in? Just curious....

 

Hemi 35....havent decided which ride it will go into yet, as I mentioned, this engine project will be a bit of a longer term project.

DW...sounds like that guy was advocating oil restriction so that more oil goes to the mains. Dunno how that would prevent spun bearings unless he was resticting oil to the top end to enable the rods/mains to get more. Care to elaborate which oil p***ages were drilled, tapped and plugged and then redrilled and to what size ?

But if hes was spiining bearings that easily, could the machining have been of poor quality?

As far as I can ascertsin, the oiling system is pretty much good (very similar to SB MoPar) unless youre turning the engine HARD or over 7K consistently. Which wont be the case for me.

There are a few little mods I will underatke but plugging and resriction of oil is not one of them.

 

Is this going to be a race only application or street and strip?? Stay away from the REV valves. I have a number of friends that have been supercharging the new 6.1 Hemi and their builder used Rev valves. Long story short a lot of valve failures. If I read your post correctly you mentioned Arias billet rods. I'm not sure why you would want to run aluminum rods..IMHO I feel steel rods are more reliable but, if you already have them than this is a mute point. Looking at your pics you've got some very nice pieces and am looking forward to seeing your progress.

 

Just saw this so following up with an answer.

It will be mostly street with a little strip action when I get the urge.

I mean Arias Pistons, the rods I will be using are BB Pontiac H beams which use the same rod bearing/journal size as the Desoto, are the same C to C length and only need a few thou off each side of the big end for proper rod side clearance.

You can also use the BB Poncho rod bearing and save some $$$ on the same Hemi bearing that is overpriced b/c it says "Hemi" on the box.

Thanx for the REV valves tip too !!

HAHA.....

Rat

 

Short on time here, haven't read the entire post, but can add this:

1-Definitely skip the "REV" valves, go with the "Ferrea's"! They are by far the best valves in the arena, and the ONLY ones we use! They are almost unbreakable, they will "bend" like pretzels, but they WILL NOT break! These valves have saved us a few builds in the past! (Have had "Manley's" snap also in the dyno room!)

2-Pay attention the advice about the adapter to use the "LA" pumps in these early Hemi's, they are sometimes a real "headache" to install, what we've learned in the past is every block is different. This is where the problem lies! Don't care what the vendor's tell you, been there and done it!

Thanks, Gary in N.Y.

P.S. Have one 341" Desoto (maybe 2) in here now for build!

 

You sound smarter than the average Joe. I my opinion the biggest blockage in the Desoto ports is the area around the stem guide. I ported mine out in that area until going through the pushrod tunnel. Then I J*B Welded br*** tubing inside the tunnel as a seal. The br*** wall is just over .014" so there is very little interference with the pushrod-none actually as there is still plenty of room. I then ported the heads to match a set of Hilborn injectors. This involved moving the walls out about 1/8" on the top and sides. The floor was very close. If you go tuned headers, a neat trick is to put masking tape on the insides of the 2 middle exhaust ports where they connect together to feed the manifold exhaust crossover. Then fill those 2 exhaust ports with plaster of paris. After about a week in the hot sun to cure the plaster, fill the exhaust crossover with molted aluminum on the intake side of the head-an old piston will work fine. Then break out the plaster and tape and blend the fill with a die grinder. My engine uses 2.02' Chevy intakes and 1.77" Pontiac exhast valves and Pontiac hardened seats. The valves are cut down from 1.77" to 1.73" for a litle better valve to valve clearance. The Pontiac seats work better than the 440 seats since the walls are thinner and match the inside of the port better. Bill

 

Nice work Bill.

I was trying to figger out how to block the exh heat riser ad added heat aint desired with a blown combo and it aint a daily driver so I dont care if she takes a bit longer to warm up.

But Im not sure I follow how you did it - well at least I can't picture it in my head.
Do you have any pix to share on how you did it?

Also, did you use/fit a 2.02 11/32" Chevy valves without any mods to the valve? What was the total height of the valve? Same with the Poncho vlave, what was it overall height?

Thanx,

Rat

 

The length of both valves were so close to the original Desotos as to be negligable. Within about .030" I think. Slightly longer so it made up for the extra lift. Another route is to use the older 340 intakes and 440 exhausts, but they arer heavier. By putting masking tape inside the 2 middle exhaust ports, you basically make the plaster conform to the inside of the ports themselves. The tape basically just covers the tunnel that crosses over to the other port. That one gets taped too. Then fill both exhaust ports with plaster and let cure for about a week in a warm environment. Hot aluminum can cause the plaster to shatter if not completely free of moisture. When you fill the crossover with molten aluminum on the intake side, the metal now conforms to the inside wall of the port itself. Break out the plaster and the aluminum should now be the part of the port that was the hole leading to the other port. If you want I can send a couple of photos of putting on the tape an adding the plaster on a piece of a head I use for patterns. Bill

 

Rat-
That's my old motor! I pulled it out of a '51 White COE (!) Glad to see that it made it safe all the way to Oz and that you're working on it. Also glad to see that it is in as good condition as I thought it was. Good luck with your project.
--Bob

 

Seems like a lot of mucking about to block the exhaust crossover. We have successfully used a stainless shim under the gasket to cover the port and we have also machined a small step into the port at the face of the manifold and fitted a stainless plug at that point. Both seem to work equally well, however the shim only works with fat composition gaskets.


.

 

Thanx for the info guys !! IMO machining a small step into the intake for a S/S plug sounds easier. Qun is, will filling the crossover help the two center exh ports flow better? If so then it might be a mod worth doing instead of the S/S plug method.

To my mind filling and contouring might reduce exhaust turbluence b/w both centre ports. What say you?

WOW !! Small world !!

Bob are you SURE its your old motor?

You have a PM !!

Rat

 

They're not really trying to block the heat to the manifold, but block the p***age that is between the two center exhaust ports (same as on a Chrysler Hemi). When you had a set of race heads done by the likes of Mondello, they would weld up the cross-overs between the ports and rework them into two separate ports. I've always heard that it was something important to do on blown race motors (but never ran these types of heads???)

I've never heard of the 'poured aluminum' method . . . kind of reminds me of the early methods of using aluminum to 'hard block' the lower parts of a hemi-block . . . before what we now know as 'hard block' existed.

 

What exactly is mol***es soup? Bill

 

great thread rat, any progress ?
iv used mol***es a couple times bill, it eats up some rust, damn, but its nasty **** for sure.

 

Mark...in the process of nutting out my piston/rod combo for the build.

Will be a custom Ross or Venolia slug and a BB Pontiac H beam rod to replace the factory rod.

Rat

 

Those are some nice looking heads. Can't wait to see the completed engine. I did a set for my 341. Was hoping for some real flow improvement. Fortunately I had a bad head to dissect so I cut it in half right through the middle of the ports and went to work figuring it out. The smallest cross section of course is in the throat between the pushrod tunnels. I drilled through the walls in various places and found there wasn't much in the way of core shift. The roof of the port is plenty thick but you have to be careful under the spring seat. An average of 1/8" material was removed. The sidewalls were different. About 3/32" was taken out and I went ahead through the walls at the pushrod tunnels. Since the sharpest turn in the port is through this area, and it has the smallest cross section, it will have the highest velocity and therefore should have the greatest cross section if possible. Reducing the valve guide boss to it's minimun cross section and streamlining it will help. On mine I cut through the walls at the pushrod tunnel, cleaned the tunnels with stainless brushes with soap and water. Then cut some thin wall br*** tubing and JB Welded them in the tunnel. K&S tubing from the local hobby shop was used. It has a wall thickness of about .015" and will work just fine. This will give the most cross section possible in the right area of the port. Even though the diameter of the tunnels were reduced by 1/32", it offered no problem with the larger pushrods.
As far as the exhaust ports, I left mine stock size, but streamlined the valve guide boss to a nice teardrop shape.

 

Just found this thread, and its a good one. I asked this on another thread, never really got an answer. Does anyone have the relative dimensions of the intake port at the face on the short deck and tall deck desoto heads?

Another thought. I wonder if the CSA between the pushrods is the same on the tall deck and low deck heads?? If it were, and you were going to do considerable porting, it wouldnt make a hell of a lot of difference which head you started with.

 

Another bit of info I am looking for that seems to missing from the so-called "Complete Chrysler Hemi Engine Manual" and the HAMB tech archive, anyone know what the nominal rocker ratio is? I seem to recall 1.52, but I'm not sure.

 

I can give a measurement..but I'm using a chevy water pump....should be good enough for a reference...

 

according to info I dug up last night, rocker ratio is same as late hemis, 1.57 intake, 1.52 exhaust.

 

What source did you find?

Hmmmm...I believe that all of the early engines are a nominal 1.5 but have found them as much as 1.52. I have not seen a 1.57 but they might exist.

.

 

Magazine article, so I would take it for what its worth.

Thanks Gary, I will go with the 1.5