Author Topic: 1970 440 Real World CR  (Read 573 times)

Offline Mc MOPAR

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1970 440 Real World CR
« on: November 23, 2016 - 09:09:19 am »
Does anyone know the real world compression ratio for a 1970 440 engine?  From the research I've done on the topic, it looks like Chrysler rated them at 10.2:1.  But I've been told enough times by multiple people that this number was not accurate, and that those CR's could be in fact off by 1 putting my engine at 9.2:1.  Any truth to this?




Offline 1 Wild R/T

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Re: 1970 440 Real World CR
« Reply #1 on: November 23, 2016 - 10:24:28 am »
Absolutely... 9.2 is optimistic.... I just plugged the numbers into a compression calculator & got 8.7...

4.32    Stock Bore
3.75    Stock Stroke
90cc   906 Chamber volume  (Typically between 88 & 92 cc originally)
0cc     piston volume    The stock piston is a flat top with no notches... Except the 440-6 which 4cc has notches
.020   stock head gasket thickness... If it's been changed to a composition gasket this number goes up & compression goes down...
4.41   stock head gasket bore diameter
.090   deck height... How far the pistons are down the hole.... & the number that hurts most...

Plug this into a compression calculator & 8.7 is the number...

Bolt on a set of 84 cc heads & you get 9.14 but aluminum which has pluses & minuses...

Bolt on 80 cc heads & you get 9.45

Bolt on a set of 75 cc heads & get 9.86......... Now we're talking...

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Offline Mc MOPAR

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Re: 1970 440 Real World CR
« Reply #2 on: November 23, 2016 - 12:27:11 pm »
That's great news, because I really want to run the Whiplash cam in my 70 440 but there is a warning on there website to only install them in low comp engines 8.9:1 or less...

Whiplash cams are designed for the very low compression Mopar O.E.M.  engines such as all the 318's, 360, 400 and all 383 & 440's built after 1971.

 The factory built these engines with a combination of low compression and cams that produced very low cylinder pressure and low power (see this tech article CLICK HERE). Normally, to increase the cylinder pressure in these engines you would have to disassemble the engine, buy new pistons & rings (at a minimum), re-bore & hone, rebalance and reassemble. And then you would still need cam & lifters. The cost of this build-up could easily be $2,000.00 or more and take 2-3 weeks.

  The unique design of the Whiplash cam will accomplish all of the same results for as little as $340.00 (cam, springs & lifters) and take about one Saturday afternoon to complete. The Whiplash cams are designed, like all of our "real" Mopar cams to take advantage of the .904" lifter diameter which increases the area-under-the-curve, for more breathing time. However, with low lifts (yes we consider .520" low lift) so that you do not need to remove the heads and machine the valve guides.

   These Whiplash cams have become one of our top selling items and we have customer that want to put them in engines that are not low compression. The problem is that the cam will still raise the cylinder pressure and your engine may then require race gasoline or a mix of pump and race gas. As a general rule of thumb engine with a true measured compression ratio more than 8.9:1 with iron heads or 10:1 with aluminum heads should not expect to be able to run on just premium gas. And, whatever you do, DO NOT retard the timing to "make it work". That will "work" and also reduce your power & torque considerably. You'll be sorry!

So I should be ok, and if not I could change the head gaskets to composition which would bring my CR down to 8.2:1 as per the calculator.


Offline Mc MOPAR

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Re: 1970 440 Real World CR
« Reply #3 on: November 28, 2016 - 07:49:48 am »
I think I'm going to leave the engine the way it is for now with the mopar 557 cam and mopar m1 intake.  Try it out and see how it works before changing things on it.  Previous owner said it worked amazing, and that I would be crazy to change anything on it.  I will have to get a larger carb for it though, I thinking a Eddy AVS 800...