308 deck height?

Unknown

Does anyone know the exact deck height for the 308 engine?

Thanks.

[Deleted User]

The ones I've measured and know haven't been previously shaved were 12.376-12.379"







Mark

[Deleted User]

Mark:

Is the measurement from the crank journal to the top of the cylinders? Thanks, Bob

Unknown

Thanks!

That makes the piston 2.014" tall at zero deck, yes?

Geoff

The 308 pistons are 1.969" from centre of pin to top (compression height)

Unknown

That sounds odd?

That places the dome at -.045" @ TDC, with quench distance = this + gaskets thickness.

I though they were tighter than that?

Is the rod 8.115", as I have read elsewhere?

[Deleted User]

The measurement was from the center of the main journal to the top of the deck.



The piston to deck clearance in a stock engine is usually .022-.027"



the rod length is ideally 8.125", although that varies more than I want to admit.



The best way to raise the compression on these engines is to tighten up that deck clearance problem, it is excessive. With the thickness of the head gaskets we can get, zero deck is what you need for the right squish clearance at around .035-.040".



A word of caution about this. You need to measure, or have measured, your own engine and do these calculations for the individual project. Calculating the deck cut is the last thing figured after you've resized your rods, measured your piston's compression height, and matched those to get the most consistent overall length.



It is the cheapest performance upgrade while rebuilding a Hudson that can be done. Generally it will raise the compression up to 8.2-8.5 with a 308 head on a factory relieved block, negating the need for a 262 head while retaining the breathing room of the 308 head.



I have run all the fuel grades in our '49 with a zero deck at a measured 8.2:1 compression ratio with no problems in the 20*total mechanical timing range. Alot of the "pinging" complaints on Hudson stem from either a distributor over advancing beyond 20*mechanical or a tiny coolant leak from the head gasket (been there both times!). In the below picture, we're 0.0015" out of the block.







Mark

Unknown

Thanks, I thought that rod length looked odd - but it was simply the exact length of a particular rod set.

I agree on the quench distance - those are good limits for this type of engine. An engine with really tight skirt clearance and high pin offset to reduce "rockover" might get by with .030", but why be the first to find out where it kisses?



So, the "ideal" (flush deck) piston with stock stroke and nominal length rod is:

12.379

- 8.25

- 2.250 (4.500 ÷ 2)

= 2.004"

which leaves the quench distance entirely to gasket thickness, etc.



For the usual 5.000" stroker:

12.379

- 8.25

- 2.500 (5.000 ÷ 2)

= 1.754"



Has anyone tried to use the stock piston in a 5" motor with a shorter rod?

The DeSoto/Chrysler 251 L6 is about the right length at 7.875" although it does make the rod ratio worse (stock 1.806, 5" stock rod 1.625, Chrysler rod 1.575).

[Deleted User]

There is no reason in the world you'd want to change rods.



A quick analysis will reveal it has the perfect rod ratio for a 5" stroke. Much cheaper and easier to get pistons of the correct compression height than deal with a rod change.



The Hudson rod is a better piece than the mopar. We have experiance in performance pushed flathead mopars winding at 6K. All mopar flathead rods are not the same. There were many changes, although minute, in their rods over the vast number of years they were produced. Finding a matched set is tough to do. You have two major variations from the long block versions (251/265) at 2.125" rod journal and the short (218/230) at 2.00" rod journal.



Most of the Hot 302 Jimmy builders are hunting down the Hudson rods: because of length, easy compatibility, and they are living well in excess of 6,ooo rpm in those engines. If we're blessed with a good piece - I see no reason not to use it.



I'm not surprized at your actual measurements on the rods, I've seen as much as .015" difference in lengths. Its the only criticism I have about them. Weight differences can be rather extreme too. This is nothing the mopars have an advange in either.



I do like the way you are thinking.



Mark

Unknown

Thanks, I hadn't seen a 25" Chrysler SV rod in 30 years.

I have 3 different rods for this series: 7.75" for the 265, 7.875" for the 251, 8.00" for the 237.

However: allow me to suggest that the original rod may have the best ratio you're going to get without a great deal of work and expense, but the ratio isn't what I would want at 1.625:1. Unfortunately, when the rod is already this long there's nowhere to hide any more length even with a really tiny piston!

Unknown

Are the other Hudson L6 rod dims available on this site?

[Deleted User]

Unlike mopar,who kept the same piston compression height and changed rod lenghts; Hudson rods are all the same dimensions. 232, 262, and 308 are all the same from 48-56. Another reason to stick with those.



All the other Hudson engines, except the Jet, were dipper rods - I'm sure you wouldn't want those.



What's your intentions? Several of us Hudson speed fanatics lurk this place.

Unknown

Have seen references to use of Hudson rods in the GMC motors, curious about other possible cross-brand swaps.

oldhudsons

interesting as that was an old Smokey Yunick trick as whenever they tore down Hudson engines after they'd won a race, the officials would check the thickness of the head to make sure it hadn't been "shaved" so Smokey planed/milled the block which they never thought of measuring, or didn't want to take the time to do, or never thought anyone would go to the trouble to do that, LOL!

Another trick I heard he did, which I thought clever, was in a later era when they'd weigh the cars, he would do whatever to lighten the car (so it weighed less than the allowed weight), but when time to weigh in for the race put water in the tires enough to meet specs then remove it before car put on the track!

SuperDave

At some time during production Hudson did make some changes in the 48-54 rods . Sometime in 1950. Maybe a diferent vendor? Anyway the weights are a lot different. the newer ones are lighter. The parts book cautions the rebuilder to not interchage part numbers. Early heavier rod and cap PN #302601 forgeing number 302609 Later lighter PN# 303904 Forgeing number 305906. I discovered this while overhauling a '52 308 and a '49 narrow block 262.at the same time.

[Deleted User]

SuperDave wrote:

At some time during production Hudson did make some changes in the 48-54 rods . Sometime in 1950. Maybe a diferent vendor? Anyway the weights are a lot different. the newer ones are lighter. The parts book cautions the rebuilder to not interchage part numbers. Early heavier rod and cap PN #302601 forgeing number 302609 Later lighter PN# 303904 Forgeing number 305906. I discovered this while overhauling a '52 308 and a '49 narrow block 262.at the same time.

Thank you for this tidbit of information I did not know. Which rods would you think were best, the early or later?



I have run into later rods with the same forging number, some stamped "Atlas" and some not. Atlas also made the rods for Allis Chalmers, and no telling who else.



The rods stamped Atlas will weigh differently from the non-Atlas stamped rods. Not by a great deal, but more than you can correct by safely grinding on the rod or drilling a piston. I do not have the weights recorded to pass along. I need to do that when I mess with those rods again.



Mark

53jetman

Atlas of Fostoria OH also produced the cranks for the 202 engine, so I'd tend to beleive they also produced some cranks for the big block engines also. Just a tidbit of info I happened to run into in the past.



Jerry

53jetman

SuperDave

`Hudsonator wrote:

Thank you for this tidbit of information I did not know. Which rods would you think were best, the early or later?



I have run into later rods with the same forging number, some stamped "Atlas" and some not. Atlas also made the rods for Allis Chalmers, and no telling who else.



The rods stamped Atlas will weigh differently from the non-Atlas stamped rods. Not by a great deal, but more than you can correct by safely grinding on the rod or drilling a piston. I do not have the weights recorded to pass along. I need to do that when I mess with those rods again.



Mark

mark,

As to which are better?I really don't know, but since Hudson lightened them in time for the 308. As I recall, the difference was in the slightly larger beam section. I would assume they felt that the early heavy rods were over engineered? I don't know the actual weights but they are easily recognized by just handeling them. must be a significant amount......

[Deleted User]

Guys,

I have only seen two different types and both were radically different.



The early rods had wrist pin oiling holes that run from the rod journal up threw the center of the beam to the wrist pin. all of the pre 51 rods I have seen (which is not many) were like this.



the later rods did not have that oiling passage threw the beam but a small hole

at the top of the rod to oil the wrist pin. This type of rod is what I am running

my 56-308 engine. I believe they are original to this engine.



It would not surprise me if there were two additional types as Mark brought up. not uncommon to update the weak links when found during racing and

I know that's what Hudson was doing. After all look at the change to 1/2"

head diameter, better cooling with the wide block, different flywheel bolt

clamping method and so on.

any more information on the rods and Hudson internal engine parts would be cool to hear.

thanks,

PaceRacer50

[Deleted User]

The narrow blocks have the pressurized wrist pin oiling?



Very interesting stuff.

[Deleted User]

i bought a box of three sets of NOS rods off of ebay that were all labeled.

Doug and I checked them all out after I compared them to the rods in my

56-308.



there was 6 rods with the oil hole threw the beam to oil the

wrist pins. the part number was for the 48-50 narrow block engines.



the other rods all had a solid beam with the oil hole in the very top of the

wrist pin boss. these all had part numbers for the 51-up engines. these

rods matched what my 56-308 had so I kept all of these as spares for

racing.



I did not see the name of ATLAS forged into any of these.

Mark can you post the part numbers of the four different rods you have?

any idea which ones you think are the strongest for racing?



on another note the 50 is back together and running. the blower belt is

not on it at this time as I still need the right crank pulley for the water

pump and alternator. soon it will be complete again.

thanks,

PaceRacer50

[Deleted User]

Ralph,



Glad to hear you're back together and running.



On the rods, I don't have a good opinion as to which rod is better for racing - Atlas or not. They both have the same later forging number. The numbering style is different between the two, but same numbers.



To really be able to comment - I'll have to find out the hard way.



I would like to know the final analysis on your broken crank? What do you think about it since you have it out.

[Deleted User]

Flaw in the forging. In the center of the rod arm, the metal was "smeared" in a rough jagged shape. I have seen this before in a pinion to a 9" ford I snapped in half from a 63 Ford truck. it appears there was a air pocket or something form inside this arm during the forging process. It finally broke out threw the

good material on the edges.

I would take a picture of it to post but the camera is not working right and its hard for me to get enough light on it.

all I know is I was lucky it never let loose before under really hard punishment at the drag strip. I did notice that the outside edge of the arm looks different from the new crank that went in. there is a rough lip present on the broken one that is not on the new crank.

she will be finished next weekend and ready to go back to the strip in the spring.

later,

PaceRacer50