My 33 Plymouth 189ci rebuild

[Reg Evans]

I am planning on rebuilding the stock 189ci engine in my 33 Plymouth PD.  I am wondering if the only way to get more cubic inches is to bore it out.  I am wanting to increase the anemic 70 hp rating as I am spoiled by all my other MoPar flatties with 230, 241, and 251 engines.  My poor little PD just struggles so much to go up the hills where I live but I don't want to remove it's original 189ci engine.

 

[keiser31]

You could find a split manifold setup like this Fenton....adds a little more oomph....someone on the H.A.M.B. site may have one....

Edited September 28, 2017 by keiser31 (see edit history)

[Reg Evans]

I do have the repops from Langdons ready to go and I will mill maybe 60 off the head.  So,maybe with the headers, a milled head and a 40 overbore it'll have enough oomph to not struggle so much on the hills around here.  

 

[ply33]

It is my understanding that the 1933 and 34 blocks are the same. Well the late 33 blocks are the same as 34 (there were running changes on at least the oil pressure relief valve during 1933). Anyway, the main difference between '33 and '34 is they stroked the engine to 201 cu.in. Same bearings, same pistons, etc. Just different crank and rods.

 

And it is my understanding that the crank and rods were the same from 34 until they came out with the 218 in '42.

 

So, it ought to be possible to put the crank and rods from any '34 through '41 Plymouth engine into your '33. Outward appearance would be stock but your power would go up by about 10% based on the 1934 advertising.

[Reg Evans]

Thanks Keiser31 and Tod,

The standard compression ratio is 5.5 to 1 and then there was an optional 6.5 to 1 ratio engine rated at 7 more hp available. 

Was this higher rating achieved with the different head only ?

Shortly after I purchased my car I did a warm compression test on the engine.  These were the readings starting from #1.... 80, 82, 85, 85, 74, and 76. 

What reading should I expect from a freshly rebuilt engine ? 

What might removing .060 off the head do to those readings ? 

Could I go more than .060 ?

[Spinneyhill]

With 5.5:1 compression ratio and say 80% volumetric efficiency, your compression pressure (gauge) would be about

 

14.7 * 0.8 * 5.5^1.3 - 14.7 = 93 p.s.i.

 

If you bump compression up to 6.5:1, the compression pressure (gauge) would be about

 

14.7 * 0.8 * 6.5^1.3 - 14.7 = 119 p.s.i.

 

If you want to take more off, you could put the head on with gasket and some blue tack or something on the valves, then turn the engine over two revolutions, then remove the head. Now you want to measure the thickness of the blue tack to obtain valve clearance to the head. There are probably better materials than blue tack to use here. I am sure I have seen it on these fora somewhere.

Edited September 28, 2017 by Spinneyhill
typo (see edit history)

[Reg Evans]

Thanks Spinneyhill,

I only got as far a bone head math in High School so I'm not sure what the * and the 1.3 mean but 119 p.s.i. sounds real good. 

Can you express that formula so a cave man would understand ?

Reg

[Spinneyhill]

* = times. The superscript 1.3 = to the power of 1.3. On my Windows calculater there is a y^x button. Use that one.

 

Roughly, the formula is

 

(air pressure) times (volumetric efficiency) times (nominal compression ratio) to the power of about 1.3 minus (air pressure).

 

You have to subtract the air pressure at the end because your gauge reads zero under atmospheric pressure.

 

I posted the paper from which this came a while ago. Here it is again....

 

Nominal compression pressure.pdf

Edited September 28, 2017 by Spinneyhill
more information (see edit history)

[Spinneyhill]

Compression pressure is not the full story though.

 

If you are running oversize tires you will be sluggish on the hills and faster on the flat. I have just reduced mine from 6.00 to 5.50 and the car goes like a rocket in comparison but burns a lot more fuel (it is such fun it invites lead footedness) and should be slower on the flat.

 

BTW, I seem to remember carbking saying the second carb won't make much difference.

 

You might be better to look at the valve timing to improve volumetric efficiency?

 

I would expect using a downdraft rather than an updraft might make more difference, as would improved manifold design to reduce drag in the manifold and improve evenness of fuel delivery to the cylinders (i.e. they all get the same charge of fuel and air each stroke).

Edited September 28, 2017 by Spinneyhill (see edit history)

[Reg Evans]

I am running stock size tires 17 x 5.25.    The stock engine has a carter 1 bbl downdraft....small bore.   I wonder....will a later model intake manifold with the larger bore carb fit my 33 to go along with my cast iron dual exhaust headers ?

 

[Spinneyhill]

I found this interesting web site. It relates the carb. capacity in cubic feet /minute (CFM) to the engine size and max. RPM. I expect your engine has VE of about 80%.

http://www.gtsparkplugs.com/CarbCFMCalc.html

 

How you might use it for your situation is still to be determined! I wonder if carb's of the '30s had CFM ratings?

 

Looks like they did not.

http://thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

 

This may also be useful to you.

http://www.thecarburetorshop.com/Carbshop_carbs.htm

Edited September 28, 2017 by Spinneyhill (see edit history)

[maok]

I'd imagine those VE figures are for a OHV engine with better cam profiles, the flathead would be less than 80% if not less than 75%.

 

Unless you are willing to do a fair bit of valve and porting work, and cam re-profiling then I would stick with increasing your CR to gain the extra oomph you are chasing.

[Spinneyhill]

1 hour ago, maok said:

I'd imagine those VE figures are for a OHV engine with better cam profiles, the flathead would be less than 80% if not less than 75%.

 

Agreed. I worked out VE based on compression pressures and ratios given quoted in MoToR's Manual 1947. Here are a few results:

MoToR 1947 starts at 1935. It is interesting the VE is 10+ % higher  at 1000 RPM than at Cr. (cranking) speed! The Chrysler '40 and '41 comparison is the same size engine with raised compression (and whatever else they did) but the compression pressures are given at 1000 RPM in 1940. Similar for Plymouth '41 vs '42 & '46.

 

For Reg's Plymouth at 74% VE, the compression pressures would be 85 & 109p.s.i. for 5.5 and 6.5:1 compression ratios.

 

 

[Spinneyhill]

Just found this. It was probably from these fora before. It shows the 1932 Plymouth compression pressure is 73.5 p.s.i.! So either your head is already planed or you have a high carbon load!

[maok]

Doh! No listing for a '28 Chrysler...:(

 

 

 

 

[C Carl]

Hi Reg , what octane gasoline are you running ? It is best to use the lowest octane gasoline available. You may also advance the timing a few degrees. Octane when your car was built was probably 60 or so. Even the lowest grade gasoline today is made for much higher compression , and higher volumetric efficiency.    - Carl

[Reg Evans]

4 hours ago, C Carl said:

Hi Reg , what octane gasoline are you running ? It is best to use the lowest octane gasoline available. You may also advance the timing a few degrees. Octane when your car was built was probably 60 or so. Even the lowest grade gasoline today is made for much higher compression , and higher volumetric efficiency.    - Carl

Carl,  I run regular in all my cars including my 05 Ram 1500 w/a hemi.  I will try advancing the timing a little.

 

Spinneyhill,  Can you send me that page listing the nominal compression values.   I can't read it on this forum...too blurry.  email to rego@hughes.net.   Many Thanks !

 

[dep5]

You could swap in a 1934 Dodge DR passenger car engine. Outward appearance the same, google for specs,  later Ply-Dodge speed equip fits including cyl head

[Spinneyhill]

7 hours ago, Reg Evans said:

Spinneyhill,  Can you send me that page listing the nominal compression values.   I can't read it on this forum

 

You can get it from the post. Right click on the image. Select Save Image As. Save (edit name first!) in a location of your choice. Find the file in File Explorer and open it with your favourite photo viewer. Done.

[ply33]

20 hours ago, Spinneyhill said:

Just found this. It was probably from these fora before. It shows the 1932 Plymouth compression pressure is 73.5 p.s.i.! So either your head is already planed or you have a high carbon load!

FWIW, the 6 cylinder '33 Plymouth engine with modern thin shell bearing inserts, cam ground aluminum pistons, etc. is quite a bit different beast than the '32 Plymouth 4 cylinder engine with poured babbitt rod bearings.

 

The expected pressure at cranking speeds for a '33 Plymouth with the stock 5.5:1 compression ratio is 90 psi. I am not sure what the pressure would be with the optional 6.5:1 aluminum head. Specifications along with references from whence they came are at http://www.ply33.com/Models/PD/specs.html

 

I still think Reg should consider dropping in '34-'41 rods and crank as an easy way to boost displacement and compression ratio. Basically just doing what the factory did in '34.

[Reg Evans]

Okay Tod. or anyone else........  Any ideas where I can find a good '34-'41 ? 

[Reg Evans]

3 hours ago, Spinneyhill said:

 

You can get it from the post. Right click on the image. Select Save Image As. Save (edit name first!) in a location of your choice. Find the file in File Explorer and open it with your favourite photo viewer. Done.

I tried that a couple of ways and it is still blurry but a little clearer.  Does the 33 say 88psi or 83 ?

[Spinneyhill]

1 minute ago, Reg Evans said:

I tried that a couple of ways and it is still blurry but a little clearer.  Does the 33 say 88psi or 83 ?

Indeed it is blurry. I think it says 88. That would make your VE about 76%.

 

Assuming the same VE with 6.5:1 CR, you would get 112 p.s.i. gauge pressure.