Technical Increasing compression on '53 Nash head

Hey guys,

I have a great running '59 Rambler American with the 195.6 L-head motor. I'm looking to add some performance. After some research I decided to track down a 2v head from a '53-'55 Statesman.
The head I found is from a '53, by my research this year was the low compression year, only 7:1

I would like to machine the head to get it up to 8.5:1, the stock '59 1v head is 8:1
Anyone do this? Does anyone have an idea how to calculate how much I would need to take off to go from 7:1 to 8.5:1?
I know I could use clay to make a mold of each head chamber to measure volume and compare between my 8:1 and the 7:1 heads
But I'm hoping to leave my stock head installed until I have the new 2v head machined and ready to install.

Thanks for any information

 

I don't think you'll be able to shave off enough to get you anywhere close to where you want to be. Admittedly I know almost nothing about Nash engine design.

 

Could you shave/mill the head and use a steel shim head gasket to get closer to your desired compression? I figure it probably was built with a metal head gasket so that may not be a solution.

 

This might help.

 

I stand corrected. That's a cool chart!

 

That's a terrific chart! But it doesn't cover his engine.

 

Besides the bore and stroke, you'll need to know cylinder head volume in CCs (this can be measured with a volumetric burette), effective dome volume of the piston (dished vs. domed, usually spec'd by the piston manufacturer), deck clearance (piston deck vs block deck at TDC), and lastly, compressed head gasket thickness (spec'd by gasket manufacturer). With these specs, you can use an online calculator like this one to see where you lay. Playing with these number will also show you what needs to be removed from the equation. For example, if I input numbers for a typical small block Chevy, I can change the deck clearance by 0.100" and gain a point and a half, roughly. In theory, that's what I'd remove from the deck of the block, all other things equal. Now, removing that from the head changes some of the other specs (head volume, etc.), so it's not that simple.

If it were me however, I would stop right here with, "I have a great running '59 Rambler American" and forego the tiny increase in performance that a half or even a full point in compression ratio will yield. You'll never notice it with the butt dyno. I would spend my time dialing in the carb and upgrading to electronic ignition with a decent coil.

 

Ok. I am no nash expert, but a few interesting things to note and clarify here.
The Nash L head has the intake built into the head. So the big reason you want to swap to the earlier head is to upgrade to a 2 barrel carb ( and likely better flow) correct?
Is the head you found off of a 184" or 196"?

If same displacement, dropping from 8 to 7.7 (per the chart) but gaining flow would likely still be worth it.

If head is from the smaller engine, you MAY be able to keep it 8-1 or a touch higher going onto your larger engine.

I also would take a good look at the intake....Manifold?...head ports?...passageways and see if you can clean them up, and make sure they match the ones in the block. Or they are significantly smaller than the block ports/the '59 head ports, you may consider keeping your '59 head instead. Perhaps the carb flange on it could be milled off to bolt an adapter for the carb(s) you want.


Have you split the exhaust manifold and run a dual exhaust yet? Likely as much,or more, to gain there than messing with the cylinder head and carb. Most straight 6 engines dump at the rear, causing the front cylinder or two to see a lot of back pressure. Splitting the exhaust balances them out significantly.

Good luck and keep us updated.

 

Might notice it more at the gas station. Low compression and good fuel economy aren't very good friends at all.
Might as well try to get an improvement when you have the opportunity.

 

I don't think that there's a lot to be done with the exhaust manifold, if you want to call it that. It looks like a piece of round water pipe that's clamped to the side of the block, and the engine only has three exhaust ports.

 

The '53-'55 Nash Statesman used essentially the same engine, 3.125" bore, 4.125" stroke, 195.6cui

You are correct, that my goal is the 2v carb, being the intake is cast into the head. My understanding is all the differences in compression ratios from year to year were accomplished with modifications to the heads. The block, bore, stroke all stayed the same, they all used flat top pistons.
From what I can find for factory spec's
The '53 Statesman with the 2v was rated at 7.45:1 compression and 100hp
The '54 Statesman with the 2v was rated at 8:1 compression and 110hp
The very very rare dual 1v heads were rated at 8.5:1 and 120hp
My '59 Rambler with the 1v is rated at 8:1 and 90hp

So my hopes are to achieve close to 8.5:1 with the 2v head and somewhere around a 20-30% increase in hp over my stock 90hp

Just adapting a 2v carb to my 1v head/manifold would still have to flow through the same restrictive port, and I do not think it would add much.

I have replaced the exhaust with a stock style log manifold and a turbo style muffler. I am considering building a custom 3 into 1 pipe header in the future.

I live at 10,000' elevation, so any power increase I can squeeze out of this motor will be appreciated.

 

I'm actually really curious how this all works out for you! Please keep us updated.

 

I've seen an add in the back pages of a few 1950s Hot Rod magazines advertising a tubing header for this engine, but I'm sure that they're about as common as cheap gasoline.

 

Pictures are always helpful and fun and entertaining, to those of us, that want to see that exotic exhaust manifold, that resembles a section of a child's swing set leg, that is crimped capped off at the end!


Adventure around every corner, indeed !

 

Here is the new stock “manifold” I installed
Waldron exhaust did a great job, it bolted up and fit great.

 

How about getting a set of custom high compression pistons made up?
So far as I know custom pistons are only available forged, of course cast would be fine for this engine.

 

Would the ports in the head allow for any extra airflow if you made up a header? That pipe / manifold is about as cheap as they could have made it!

 

Make sure that you are jetted and timed properly for 10,000-feet.

I have operated the same car with two different fuel systems, from below-sea-level, to just about 10,000 feet.

While still carbureted, the performance change was stark.

 

For each 0.1:1 increase in compression you want, you need to take off 0.010", if my calculations are correct.

 

Is there any way to check the part numbers of both head gaskets? My thinking is that if they are different, that might be a clue whether it's an easy switch........ same bolt pattern, same passages, etc.
The more the other head costs, the more I would sweat the details.
Finding an early Nash online "community" would be most helpful.

 

This is interesting stuff since I like inline & unusual engines. Good on you for sticking with it!

 

Got the head and carb
The date casting on the head is 3-14-56
So it is not the low compression ‘53 year
I think I will have to pull my existing head and compare before I make any decision on machining the head down. Hopefully its already at 8.5:1…

 

If you need an extra carb, I think that I have one.

 

I totally thought these were OHV.

 

So air goes down the carb, straight down the two holes into the "trough" in the head and maybe in the block, before going into whatever ports that lead to the valves, right?
So when you mill for compression you will also reduce intake volume, unless you mill/grind the intake channel a similar amount that you take from the gasket surface.
The asymmetrical chamber shape is really interesting, i have seen similar on supposedly good running Briggs racing flatheads.
I would put #1 and #2 priority on improving flow- intake, exhaust and in-chamber. Any compression between 7.5 and 8.5 is fine for a flathead,, as long as flow improves. More is of course better, especiallyat your altitude, but it must not restrict flow.
I would: CC your new head. From there you should be able to play with a compression calculator and roughly estimate what your current motor is and how this head stands in comparison. Have the head checked for cracks. Reread the David Vizard book on porting and airflow, and likely heavily radius the edges of the two ports where the air enters. Get a 1" or 2" carb riser, most likely one with two holes that match the holes in the intake and carb(vs an open one). If you are going to have the head milled, talk to the shop and see if they can run an end mill in the channel to remove a similar amount there, and hand blend in the ends.
On the block side of the engine, it looks like there is a factory relief that could be improved. But! You better call Kenny Loggins, because you are in the danger zone if you are grinding on an assembled engine.

I found a post on the AMC forum with a ton of info, I would read through it all.
https://theamcforum.com/forum/flat-head-combustion-chamber_topic109862_page1.html

 

Upper is the 2v '56 head (7.45-1 cr)
Lower is 1v '58 head (8-1 cr)
You can see the big divots around the sparkplug, it must be reduced chamber volume, but didn't want a longer thread spark plug. Quench pad is the flat above the flattop piston. Not likely domed pistons are the answer here, since they would have to fill the transfer area to make an increase, blocking flow.
Carb "ports" go through head so opening it up much might hit water.

 

Can you angle mile the head and open up the bolt holes?

 

I would check to see how far down the bore the pistons are at TDC
Maybe 0 deck the block would be a better route.

 

I couldn't find a picture that shows pistons at tdc. I would expect them to be a bit below deck, but Nash did build their v8 of this period with very tight quench (around .028), so their engineers were aware of the advantages of it.
A few corrections of myself, the thread I got the picture from shows the one barrel head as a '58 so it actually should be 8-1, and Car Nut shows the '56 statesman as 7.45-1 but with 130Hp vs Breck's current 90hp.
I would bet that the '56 also has a different cam, at least.
http://www.carnut.com/specs/gen/nash50.html
Here is a picture of the '58 block, a few people on the AMC thread claim good gains by altering that funky factory relief.

 

It is very surprising to me that my 1921 Nash is OHV and these are flatheads.