The true compression of stock 426 street hemi !

[maxracesoftware]

Found some info from a person involved with the 426 street hemis at Chrysler regarding the actual compression of a stock 426 hemi as delivered.
It calculated out to 8.5 to 1 even though the factory rated it at 10.25!
This was due to the large amount of material left on the block deck height and on the cylinder heads. Chrylser always made note of how much to cut from block and heads when blueprinting these engines.

Now when you installed the factory Race Hemi 12.5 pistons without any mill work done you really had 10.5 to 1 compression.
And to think back in the day,for us it was 1970, it was only Sunoco 260 going in the tank of our then stock 1970 Hemicuda!

Imagine how much stronger the average stock Street Hemi may have been with the true 10.25 compression!!!
I wonder how far off the mark other makes were during the 60's -70's?

this is 1970 Street Hemi to NHRA Specs :
439.2cid
NHRA 425HP / 426cid
167.7 CC Chambers
88.3 CC Domes ( Dome Height= .536" )
.018" minimum thickness HeadGasket

11.36:1 to as high as 11.725:1 CR ???

[maxracesoftware]

[maxracesoftware]

[maxracesoftware]

BELLE ROSE, La.
Sun, 09 Apr 2017, 21:38 PM

[wyrmrider]

I bought Ray Crawford's step hydro way back when
as Larry knows the valve job makes a big difference to a stock motor
hope everyone ties the subframes together- we were one of the ones that learned the hard way-
hard to straighten but we put a full cage in

[2.2=8]

Larry, Thanks for posting. Do you have any dyno numbers for that Hemi you could share?

[1989TransAm]

My only questions would be what are the allowed pluses and minuses in the specifications of the components? IMHO there would be a lot of variation in the "stacked" tolerances. Then how close was the quality control held?

[pdq67]

As a side note...

I went in and priced a new '70-1/2 Hemi Challenger, 4-speed, posi, "Taxi-Car", using my '67 SS/RS Camaro as trade and the Salesman offered me $500 for my car and I just got up and left!

I think his car was like $4,000 or so? It's been too long so I may be off.. Fennels MOPAR dealership in Moberly, MO!

pdq67

[statsystems]

As a side note...

I went in and priced a new '70-1/2 Hemi Challenger, 4-speed, posi, "Taxi-Car", using my '67 SS/RS Camaro as trade and the Salesman offered me $500 for my car and I just got up and left!

I think his car was like $4,000 or so? It's been too long so I may be off.. Fennels MOPAR dealership in Moberly, MO!

pdq67

You should have done it. The Hemi car has more value now. It did them too, but I'm partial to Chrysler stuff! LOL.

[maxracesoftware]

Larry, Thanks for posting. Do you have any dyno numbers for that Hemi you could share?

[treyrags]

Look how flat that thing is from 6400 - 7400, and then does not fall on its face after that.

[maxracesoftware]

Look how flat that thing is from 6400 - 7400, and then does not fall on its face after that.

As actually run down the Dragstrip ... i'm pretty sure the TQ and HP were a little flatter + better than this last Dyno test
because of Header gasket leak and Oil Filter stainless steel element was way too restrictive ! ( later Woody changed Oil Filters + fixed Header leaks ... ran 9.965 ET, and was on quicker Runs , but aborted because of Index )

in checking out the Oil Filter element by running Varsol thru it in the parts cleaner
as thin as Varsol was , that filter restricted the Varsol flow a lot

Look at the oil pressure readings + these Header gasket leaks Cylinders 1 and 7

[2.2=8]

Wow!, I guess those engines were under rated.........I am interested in the oil pressure problem, as I am helping a fellow racer diagnose a oiling problem with his Indy Hemi; He is using a system 1 oil filter and loses pressure on the big end of the track. He has had the oil pan off many times looking for the cause, I'm suspecting the oil filter screen? What were the symptoms on the engine in your post?

[statsystems]

Wow!, I guess those engines were under rated.........I am interested in the oil pressure problem, as I am helping a fellow racer diagnose a oiling problem with his Indy Hemi; He is using a system 1 oil filter and loses pressure on the big end of the track. He has had it apart many times looking for the cause, I'm suspecting the oil filter screen? What were the symptoms on the engine in your post?

If you didn't call Systems 1 and get the correct screen for the grade of oil you are ypusing. I've found it very common for guys to run too heavy an oil through too fine a screen.

[wyrmrider]

internal pickup 7/16 or 1/2"?
or external
I'd use a dual external pump feed if legal
those pumps are very sensitive to intake restriction
you don't need heavy oil
are all the oil passages opened up in the block
I have a reamer on a long rod for the main oil galley
and check all the oil feeds- I've found broken drill bits
make sure the mains and the oil feed holes line up
etc etc
drill the front plugs to purge foam and lube the chain drill the thrusts
drill an oil squirter for the pump/ dist drive gerar