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Upgrading a 230 engine and transmission

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I have a 1951 230 engine (out of I think a generator set or something) fitted to a 1933 Dodge DB, with a 1936 3 speed manual transmission. I would like to fit the following in order to get more power and better gear changing:-

A. The head, carburetor, manifold and whatever else from presumably something like a 56 Dodge Coronet 6 to produce about 130 bhp.

B. A 3 speed manual transmission also perhaps from a 1956 Coronet, which I assume must be a better transmission than a 1936 one.

Can anyone tell me if these Coronet parts will fit a standard 230 engine, should I consider some other way of upgrading, is there a better 3 speed transmission, where can I get the parts from (either old unused, or used)?

This trusty 33 Dodge has recently successfully completed Paris Peking Rally and could use some upgrading for its next rally. I live in England, but am used to shipping parts.

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The 230 cu in engine up to 1959 (passenger cars) is alike and interchangeable with your engine.

The one part that would be of value to you might be the cylinder head. The newest heads had a different design of combustion chamber and higher compression.

There is a lot that can be done to improve performance of your engine.

As you live in England I will try to suggest things that can be sourced locally.

One thing that is often done in the US is to change the stock intake manifold to take 2 or 3 carburetors by welding on 2 pipe stubs and flanges. For 2 carbs you block off the original intake, for 3 you use all 3 but normally with a progressive linkage.

2 carbs is plenty for street use, 3 is more for racing.

If you don't want to do this you can get nearly as much power using a Holley-Weber progressive 2 barrel carb on an adapter to your stock manifold. The progressive carb is good on drivability and mileage but not as "trad".

Another popular mod is to split the exhaust manifold. This means to weld on a second outlet pipe and flange then weld a divider inside. The divider should have a hole in it. Then install dual exhausts.

You can mill the head .060 for more compression.

A reground cam is practically a necessity. You should be able to get your cam reground in England if you can find someone who has a pattern for a "hot" flathead. If not, an Edgy cam costs $165 in the US.

With the hot cam use new valve springs shimmed .060.

While we are on the subject a good 3 angle valve job can't hurt.

You could get into porting and polishing but frankly the stock Dodge intake arrangement is rather hopeless. I would settle for cleaning up any roughness and matching the ports. Don't polish the intakes too smooth, they need to have a coarse finish to vaporise any stray gas droplets.

Electronic ignition conversions are available.

One of the most important things is to make sure the oiling system is in tip top working order with an A1 oil pump, and shim he relief valve for extra pressure. 10 pounds pressure per 1000 RPM is a good rule of thumb.

The downfall of the old long stroke engines is high RPM. It causes fast wear to the crankshaft and rod bearings and can lead to a thrown rod. Pistons also suffer and can even break up under the strain.

The solution is a good oiling system with synthetic oil, special attention to the bottom end and balancing and keep the revs down.

For your engine 4000 or 4500 would make a good limit for sustained use. Although I know a guy who uses basically the same engine for competitive tractor pulling and he redlines his 230 at 6000 RPM.

An old school mod now forgotten, is to shave the flywheel for whippier acceleration. This means to have a machinist put the flywheel on a lathe and take off a few pounds of excess metal.

Your bellhousing can be modified to fit a modern 5 speed manual trans. This will cure your gearing woes and allow a cruising speed of 70MPH or more without straining the engine.

A guy named Don Coatney drives a 1947 Plymouth all over the USA. His car has an engine modified along the lines indicated above, and he also installed the 5 speed in his car.

He has published complete details and photographs on the net. It may be on this web site.


I've looked into this subject quite a bit for my own project (1951 DeSoto flathead 6). There is a lot of info on the web but it takes a while to track it down. Unfortunately I did not bookmark all the good websites.

Here is another good website, Inliners International


Look around for the Chrysler boys, there is some good info to be had.

Suffice to say you can get some startling performance out of the old flathead 6 provided you work within its limitations. The basic engine itself is rugged and well made and will stand a certain amount of modification without blowing up too soon.

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By the way if your engine came out of a generator set you are lucky.

Chrysler made millions of industrial and marine engines. They had the best heavy duty parts including sleeved cylinders.

One thing to look out for on the industrial engines, they had a choice of gear driven or chain driven camshafts. This has an effect on what cam you use.

If yours is an industrial engine there should be an ID plate low down on the left side of the block, about in the middle.

This is in addition to the serial number stamped on the left side of the block, high up near the front.

Another excellent source of parts and advice is Vintage Powerwagons. They cater to the ex military 4 wheel drive Dodge trucks known as Powerwagons. These all used the 230 Dodge flathead 6.

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Thank you very much for all that info. I am not keen to take out the engine again yet to change the cam shaft, so I might just shave the head, or source a later head, and try the carb you suggested, and maybe mess about with the exhaust manifold. Engine has chain driven cam, and bags of oil pressure.

I have fitted a separate overdrive which has passed the ultimate test, so a later 3 speed box would be OK. Would one from a Coronet be easier to source and would it actually be any better than my original?


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The unspoken assumption in all the above was that the mods would be part of an engine rebuild.

Unless your engine has recently been rebuilt and you know the bearings pistons etc are in good condition I suggest you leave it alone.

I have seen several older cars that the owners modified for more speed that blew up within a couple of months. If they had left them alone they would have gone on for thousands of trouble free miles.

So now my rule is do not modify an engine with over 50,000 miles on it unless you give it an overhaul at the same time.

You do not have to take out the engine to change the camshaft. If you remove the radiator, front pulley and timing chain cover you can withdraw the camshaft wtih the engine in situ.

If you don't want to go overboard or change the cam may I suggest a milder hop up?

Get the Holley-Weber progressive carb (it may go by a different name in England, such as plain Weber). They are a very common aftermarket carb and were also used as factory equipment on many 4 cylinder and 6 cylinder cars up until the 80s. The carb and adapter should be available locally. I know in the US the carb costs $85 and the adapter $15 or $20.

Have a muffler shop make up a new exhaust for your car 1/2 inch larger than stock. I think your stock system is 1 3/4 so that would mean going to 2 1/4 or thereabouts. This will give you a more open exhaust with the minimum expense and work.

Run the exhaust all the way to the back of the car and use a straight thru muffler if you don't mind the noise.

Shave the head, and get the Pertronix electronic ignition (if you are on 12 volts).

These mods alone will give you a noticable improvement in performance. But you need the cam to really wake it up.

Overdrive transmissions are very rare for these 50s models. Most American cars in those days were bought with automatics. The six cylinder, manual transmission models were bought by the tightwads. Very few ordered overdrive transmissions.

I'm not saying they don't exist but one would be rare, expensive, and probably no better than what you have now.

If you have an overdrive, stick with it. If you want a more modern slick shifting transmission install a late model 5 speed.

But if you like the 3 speed plus overdrive I suggest you have an expert rebuild the one you have now. They do get worn over the years especially the synchros.

If it was put in good condition it should be quiet, easy to shift and fairly fast shifting but not up to the newest standards. One from the 50s would be pretty much the same thing and not work any better.

Incidentally while the transmission is out it would be a good time to take the flywheel to the machine shop.

Everything I have told you is more or less standard practice in speed circles. I'm sure there are old time racing mechanics in your area who would know exactly what I am talking about even if they never saw a flathead Dodge in their lives.

If you know anyone like that ask around for an old bald headed or gray haired racing mechanic.He will know what to do, how to do it and where to get things.

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Thank you for all that most useful info.

The engine was completely rebuilt 9000 miles ago, but I take your point about over doing it.

If I do not use a modern looking Holly-Webber, which would be the best 'period' carb? The one that is currently fitted is a 1933 Stromberg with the main jet enlarged to 1.6 mm. There must be something better than that, a carb which would look reasonably in keeping with the rest of the car and one which would give more power.

Actually the existing gearbox is OK, I renewed everything inside with a complete set of parts from North West Transmission. Its only problem is that it is difficult to shift it out of 1st gear! Any idea why that would be?

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The real vintage solution is 2 of the stock carbs on a modified manifold.

But if you want to use a larger single carb I don't have any specific suggestions.

If it was mine I would measure the bolt spacing and start looking for a larger carb to fit the stock manifold. In England I suspect you would end up with a Zenith off an older model commercial vehicle. Everything else used SU's or was too small.

I've seen a Hudson hop up where the owner made his own "vintage" air filters. He used saucepans topped with his original air filter lids. Inside, a modern paper air filter. But a vintage look unless you look very very close.

On the gearbox it sounds just like a bad 1st-2nd synchro which is usually the first thing to go. But you say it has been renewed.

Does double clutching help? If so there may be something wrong with that synchro after all.

It's not easy to quantify this. But a stock American 3 speed will never shift as easily or as fast as the gearboxes you are used to. Simply because they are bigger and heavier with heavier components.

Think of the Moss gearbox used on old Jaguars. They got a lot of criticism for slow shifting, yet given the torque, horsepower and weight they had to deal with a smaller trans simply wouldn't have been up to the job. They were the best trans available for the job at the time.

Your gearbox will be rather slower and clunkier than that.

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Here are 2 web sites that show the modified intake and exhaust manifolds.

I am showing you this in case you wish to modify yours. Headers are available from Langdon's Stovebolts and Offenhauser still makes dual carb intakes for your engine. But I am keeping in mind that it may be more convenient for you to avoid sending to the US for parts.



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  • 2 years later...

Rusty, thank you for all your advice, all very useful. I have not upgraded my 230 because I think the transmission of my 33 Dodge DP is not up to much more power, having broken a half shaft recently. I think I have an industrial 230, on the dynometer I get 87 bhp at 3800 revs and 185 ft lb torque at 1200 revs.

Am soon going to drive the car across Europe to Syria; about 3000 miles. What max revs could I cruise at without causing too much wear do you think?

With what torque should I tighten down the cylinder head?

Many thanks, Robert

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Cylinder head torque, 65-70 foot pounds

Tighten in stages, go over all the bolts 3 times before final tightening.

Start from the center and work your way out as follows

17 11 5 2 8 14 20

16 10 4 1 7 13 19

18 12 6 3 9 15 21

If you want to know what a Chrysler built flathead is capable of, read this. You won't believe it until you read it for yourself. I know I wouldn't.


The author is the original owner of a 1951 DeSoto Suburban 8 passenger sedan. He writes of cruising at 70 MPH towing a caravan. 75 MPH in a 5000 pound car, with 4:11 gears = 3600 RPM. I find this hair raising for a flathead six with a 4 3/4" stroke but he says, "at high altitudes it smooths out like a turbine".

Personally I would be happier if I could keep it down to 2200 RPM or so. Your 33 Dodge if it has stock gearing and stock size tires would probably be happy cruising at 50 to 60 MPH

Edited by Rusty_OToole (see edit history)
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Here's how i get more out of my 230.


Has everything you need.

Very nice, have you had this engine running yet, what does the Dyno register for HP.

This is quite an expensive touch, at about 6 grand, for the f head conversion.

I am glad you are on e Guy whao believes inthese old flathead 6s....

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  • 8 years later...

I did not see anyone answer the question on how to upgrade the transmission to work with a 53 230 flat Head 6. I am looking for a similar item. 


would like to do all the upgrades to my 1933 Dodge that has a 53 230ci engine, but I need to get the transmission upgraded for speed on the freeway. may also change rear end and drive line also. 


any help appreciated. 

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The only way to "upgrade" the transmission is to install something where the top gear ratio is not 1:1 or direct drive. Thus an overdrive or a later 5 speed where 5th gear is effectively an overdrive.


Just observe that you will be dead meat if you have a crash at freeway speeds in that car and seriously injured at relatively low speeds. At least fit appropriate lap and diagonal seat belts before you drive at those speeds.

Edited by Spinneyhill (see edit history)
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X3 with Spinney. Any speed over 40mph (60kph) will be a challenge to control these vehicles that have vintage suspension systems and very tall side wall cross ply tyres in the event of an 'incident'.The high centre of gravity is not helping either.


Yes, the engine and drive train maybe capable of doing over 50mph in a straight line but how will the control systems perform when you have to deviate?



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1 hour ago, maok said:

Yes, the engine and drive train maybe capable of doing over 50 mph in a straight line but how will the control systems perform when you have to deviate?

At 65 mph, indicated on the speedometer, when my Pontiac's inside wheels started to lift I just eased off on the throttle. Real scary the first time and almost as scary the second time, never has been a third time. Remember brake before entering a turn, not during the turn.

Edited by Guest (see edit history)
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23 minutes ago, Tinindian said:

At 65 mph, indicated on the speedometer, when my Pontiac's inside wheels started to lift I just eased off on the throttle. Real scary the first time and almost as scary the second time, never has been a third time. Remember brake before entering a turn, not during the turn.


What if a Koala jumps in front of you??

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If you want to change transmissions might as well adapt a modern 5 speed such as the one out of a Chevrolet S10 or S15 pickup truck 1983 - 87. The model used in pickup trucks and vans is preferred because the gearshift lever is better positioned for old cars compared to the same trans used in Mustang and Camaro.


I did give Don Coatney's adaptation of this trans to the Plymouth and Dodge engine. For our English and European readers I am sure you are spoiled for choice given the number of European cars with manual 5 speed transmissions.


It is a good idea to install a modern rear axle at the same time because the new trans has no handbrake on it.

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  • 3 months later...

Ive been racing a 38 Plymouth for the past 14 years at historic meetings in Australia and do reasonably well.Just cant get in front of most of the Ford V8's.I have been running a 217 cu in Plymouth with triple Stromberb BXOV1.Not bad .does 14.9 sec 1/4 mile and 200 Kpa at Phillip island (120 MPH)

I am building another car using 38 230 cu in Plymouth running gear again.I would like to know if someone has any evidence of triple SU's being used on a Dodge or Plymouth side valve pre war. To log book the new build I have to present CAMS the governing body with hard evidence that it was done in period.

Any help greatly appreciated

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