'51 218 Rebuild suggestions

[Mortimer452]

Now that the weather's getting warmer here in Kansas, getting my workshop ready for another season of wrenching . . .

 

Planning on pulling the motor out of my P15 this summer for a rebuild.  It runs pretty well, but it overheats occasionally, burns a little oil, leaks a LOT of oil, and being in unknown condition/age (car was supposedly sitting for 20+ years when I got it) I figure it's time.  Called a local machine shop I've used in the past with great results, says he does a couple of these old Mopar flatheads every year so his comfort level is pretty high on these motors.

 

Any suggestions?  Not trying to create a rally car or anything but would definitely like to squeeze a few more HP out of it.  Edgy does custom camshafts, the old carter BB carb is shot and definitely needs replacing and I figure why not get two along with an Offy intake?  Engine has factory dual exhaust.

Edited March 19, 2018 by Mortimer452

[Reg Evans]

A 218 with factory dual exhaust ????

[Mortimer452]

12 minutes ago, Reg Evans said:

A 218 with factory dual exhaust ????

 

Well, I guess maybe not "factory" but when I got the car ('47 Plymouth Deluxe) the engine serial# is P22 (1951) and it has a split exhaust manifold

[greg g]

Usually your machinist will make recommendations after the engine is pulled down based on what condition things are in. But an over bore for a little more displacement, a decking of the block and milling of the head will give you an appreciable bump in power. Working the intake and exhaust ports to match the gasket openings will help things flow a bit better. With the offy intake I would call George Asche and get a matched pair of his redone Carters.  With the camshaft a bit more duration can't hurt but you don't want anything that moves the power peak way up the rpm band because being much over 4000 is mostly more noise and friction loss with the long stroke design.   You don't want to build a race engine for cruising around to the ice cream stand. My modifications pretty much as above but with stock camshaft, and I have no issues, and have had 40000 trouble free miles since the rebuild.

[Lloyd]

I’ve done a lot of searches on here and can say that Greg pretty much stated the general consensus when it comes to squeezing a few more hp. 

One other thing you might look at is swapping in a 230 crankshaft.

[Andydodge]

If you can afford it I'd suggest getting the crank, rods & pistons balanced as well but Gregs suggestions will get the old girl up and dancing............lol...........andyd 

[Frank Elder]

On 3/19/2018 at 8:00 PM, Lloyd said:

I’ve done a lot of searches on here and can say that Greg pretty much stated the general consensus when it comes to squeezing a few more hp. 

One other thing you might look at is swapping in a 230 crankshaft.

Must swap the 230 piston rods also, not just the crankshaft or things will get crunchy.

[Adam H P15 D30]

I've mentioned this before and got poo-pooed but custom pistons are cheap!

Have a modern piston made with a modern ring pack.

Use the 218 rods with the 230 crank.

Measure appropriately to get the pin height correct on your custom pistons for 0 deck.

Balance assembly (any good shop should do this regardless).

Probably cost a few hundred more in the end but its done right.

[motterso]

230 crank + 218 rods + custom pistons = flathead 6 stroker. measure carefully.

[Adam H P15 D30]

14 minutes ago, motterso said:

230 crank + 218 rods + custom pistons = flathead 6 stroker. measure carefully.

I would think any crankshaft change to increase displacement would be a stroker.  The measurement is not difficult and would increase compression in a much better way than head milling.  But with head milling you could get to a reasonable compression without risking valve clearance or hurting flow.

From what I have heard, the stock 230 rotating assembly is around .020 to .030 below deck at TDC but I have never measured mine to be sure.

Then you get the benefit of a longer rod and shorter piston.  

Also get the benefit of a modern ring pack.  This is huge in a long stroke engine with high piston speeds.

[motterso]

 

6 minutes ago, Adam H P15 D30 said:

I would think any crankshaft change to increase displacement would be a stroker.  The measurement is not difficult and would increase compression in a much better way than head milling.  But with head milling you could get to a reasonable compression without risking valve clearance or hurting flow.

From what I have heard, the stock 230 rotating assembly is around .020 to .030 below deck at TDC but I have never measured mine to be sure.

Then you get the benefit of a longer rod and shorter piston.  

Also get the benefit of a modern ring pack.  This is huge in a long stroke engine with high piston speeds.

Yes, absolutely the best way to go to improve performance - and easy, too! 

[JD luxury liner]

well look close.

this is a 218 with a  230 crankshaft, but we removed a small bit of the top of the pistons in the lathe.{ about 3 years ago}

you can still see the center divot in the pistons. I needed the 8 bolt flange crankshaft to couple the fluid drive in my d19 after original block & crankshaft were scrapped by mistake.

This engine runs great. 

[Frank Elder]

14 hours ago, Adam H P15 D30 said:

I've mentioned this before and got poo-pooed but custom pistons are cheap!

Have a modern piston made with a modern ring pack.

Use the 218 rods with the 230 crank.

Measure appropriately to get the pin height correct on your custom pistons for 0 deck.

Balance assembly (any good shop should do this regardless).

Probably cost a few hundred more in the end but its done right.

Also a good way to get some ooomph, custom pistons never crossed my mind when I posted earlier in the thread, Thank you Adam.

[Dartgame]

Something to remember about “strokers”. The only thing that controls the stroke is the crank throw. Longer rods just move the piston up closer to the deck, the stroke does not change. I’m not saying its bad to move the piston up just that if you use 218 rods (which are longer than 230’s) and a 230 crank the piston travel is the same as a 230 and you gain no increase in displacement. You do potentially gain compression ratio. 218 and 230 pistons are the same and can interchange ....

[Plymouthy Adams]

1 minute ago, Dartgame said:

Something to remember about “strokers”. The only thing that controls the stroke is the crank throw. Longer rods just move the piston up closer to the deck, the stroke does not change. I’m not saying its bad to move the piston up just that if you use 218 rods (which are longer than 230’s) and a 230 crank the piston travel is the same as a 230 and you gain no increase in displacement. You do potentially gain compression ratio. 218 and 230 pistons are the same and can interchange ....

I think you need to reevaluate your posting a bit...you seen to be forgetting an important part of the lower portion of the crank throw...

[Dartgame]

Tim - in what way ? the crank throw determines the stroke not the rod nor the piston.

[Adam H P15 D30]

16 minutes ago, Dartgame said:

Something to remember about “strokers”. The only thing that controls the stroke is the crank throw. Longer rods just move the piston up closer to the deck, the stroke does not change. I’m not saying its bad to move the piston up just that if you use 218 rods (which are longer than 230’s) and a 230 crank the piston travel is the same as a 230 and you gain no increase in displacement. You do potentially gain compression ratio. 218 and 230 pistons are the same and can interchange ....

There are benefits to a longer rod, a slightly higher piston pin and a shorter piston with a better ring pack.  You have the piston made so you get the correct total height, preferably close to zero deck.  There’s a lot more to it than stroke and displacement. 

 

[Plymouthy Adams]

you said that the rods move the piston closer to the deck and the stroke does not change....throw changes stroke...stroke changes CID etc etc..

[Plymouthy Adams]

Just now, Adam H P15 D30 said:

There are benefits to a longer rod, a slightly higher piston pin and a shorter piston with a better ring pack.  You have the piston made so you get the correct total height, preferably close to zero deck.  There’s a lot more to it than stroke and displacement. 

 

take our beloved 218 when using the 230 crank and rods you get a stroked engine...yielding an extra 12 cubes and uses the same exact piston, nothing fancy or special made...

[Adam H P15 D30]

Yeah but there are better ways that really don’t break the bank in the scheme of things. If I ever have to go through my 230 I would never use the archaic stock pistons with 4 rings. A longer rod has its benefits, it is not all about displacement. 

[Plymouthy Adams]

yes to that end I agree, better piston forging are made today for this application but the relative boss to deck remains unchanged with stock rods and crank