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383 or 440??? #2974899
10/16/21 09:21 AM
10/16/21 09:21 AM
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8urvette Offline OP
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Long story- I'll shorten it and get to the point.-
383 rebuilt 30 over, cam and stealth heads, sniper Efi. Car put down 300 WHP and around 400 TQ on a chassis dyno. decied to swap the cam to a good one, never been happy with the one in it. Pulled the heads to replace the springs to match and found the STEALTH heads guides are beat, the valves are hurt etc.... So now we are rebuilding the heads.

Mean while we have a 77 440 from a motor home- has been rebuilt and is low miles. But was rebuilt to go back into a motorhome. so it is low compression.

Here is the question

Do we go with the rebuilt 383 we have had in the car, it has hyperutectic pistons stock rods and crank. it is a 67 383. OR should we toss the rebuilt low compression 440 in with the stealth heads and a good cam. Will the additonal cubic inches and longer stroke compensate for the lower compression of the 440?

Re: 383 or 440??? [Re: 8urvette] #2974903
10/16/21 09:42 AM
10/16/21 09:42 AM
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DaveRS23 Offline
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440. If everything was equal the 440 should give you about 60 more Hp than the 383. And there is no way the lower compression would cost that much power. Then there is the better leverage on the crank with the longer stroke 440, a better selection of intakes for the 440, etc, etc.


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Re: 383 or 440??? [Re: DaveRS23] #2974911
10/16/21 10:00 AM
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6PakBee Offline
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It's hard to beat cubic inches. Considering that the rule of thumb is 4% power per one point in compression, if you can stand the additional weight and size of the 440 versus the 383, the 440 would seem to be a good choice.


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Re: 383 or 440??? [Re: 6PakBee] #2974915
10/16/21 10:03 AM
10/16/21 10:03 AM
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I say 440.

Re: 383 or 440??? [Re: gch] #2974923
10/16/21 10:30 AM
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just make sure you calculate the hassle and potential cost of getting the correct pulleys and brackets - depending on how your 2 engines are setup and how complete. Potential exhaust fitment issues to be corrected as well. No show stoppers, just things to plan for ahead of dropping the 440 in.


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Re: 383 or 440??? [Re: gch] #2974925
10/16/21 10:35 AM
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Those choices - that 383 vs that 440 - sound like 2 quite different personalities.
The 383 will likely be more perky, and the 440 a bit lazy in comparison, though with more torque.
So, the better combination will depend on usage, car weight, and gearing.

Re: 383 or 440??? [Re: 8urvette] #2974956
10/16/21 11:36 AM
10/16/21 11:36 AM
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BSB67 Offline
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What exactly are the compression ratios of the two motors? You would have had to do some creative work to acquire a decent compression ratio for the 383 considering historic piston availability.

The car, your build priorities and budget will matter as well.

Without knowing these details, maybe consider head milling and gasket choice to get back some of the 440's CR

Re: 383 or 440??? [Re: BSB67] #2974961
10/16/21 11:42 AM
10/16/21 11:42 AM
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440 and the thinnest head gaskets you can use. Be careful about surface finish when using MLS gaskets though.

Re: 383 or 440??? [Re: Pacnorthcuda] #2974974
10/16/21 12:23 PM
10/16/21 12:23 PM
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DaveRS23 Offline
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I have been in several later model motor home 440s and they all had pistons .080" or more down in the hole. In my opinion, not much is going to help that shy of new pistons. But, by keeping that in mind when choosing the rest of the combo, the low compression won't kill the power. Certainly not enough to go with the 383.

The biggest hurdle I have had with these engines, is trying to get a good timing curve in them without them pinging. They spark knock very easily. Must be because of a lack of squish.


KOS
Re: 383 or 440??? [Re: DaveRS23] #2975007
10/16/21 01:55 PM
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8urvette Offline OP
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the 383 is about 9.5 to 1. we rebuilt the motor years ago and barely ever ran it.
the 440 looks like the pistons are 1/8" down so im guessing it will be low 8 to 1 compression. Im hoping with the stealth heads we would get at least 8.5 to 1 compression.
Regardless of the motor that goes it, new headers will be coming. TTI most likely.

Last edited by 8urvette; 10/16/21 10:19 PM.
Re: 383 or 440??? [Re: 8urvette] #2975013
10/16/21 02:13 PM
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My vote is for the 440. You can't argue with inches. Measure how far in the hole the pistons are and get cam spec'd for what you are doing. Sd or performer intake. I had a 440 that had pistons .074 in the hole steel head gaskets 906 heads 91cc checked. The old 509 cam,Team G intake[junk] 3800 convertor 3.91 in an Abody it ran 11.91 @111. So you can make power with low compression. There are a couple good reads on for A bodies only by IQ 52 about some low compression dyno testing he did.

Re: 383 or 440??? [Re: 8urvette] #2975092
10/16/21 05:20 PM
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I'm a fan of the 383, but there's little reason to not do the 440. Cubes will win this competition. Personally I would run the 383. Have the heads shaved. 440 source says approximately 80 cc but I would have them measured and trimmed for maybe 76cs's or less. Run the .021 factory style head gasket. Pay attention to the head finish for a coated steel shim gasket. You may have to trim the sides of the intake to get it to match if you take a lot off the heads.

Assuming moving from an .039" to an .021" gasket and cutting the head to 76cc from 80cc on a .030" over 440 gets you .7 increase in compression. If the pistons are .08" in the hole and flat top you move from 9.38:1 to 10.08:1


The change of compression, with these mods, in the 383 would be lesser.

Last edited by Moparteacher; 10/17/21 02:28 AM.
Re: 383 or 440??? [Re: Moparteacher] #2975105
10/16/21 05:53 PM
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The 440 piston will be way down in the hole (.080 if stock). Shaving the heads (which might be a problem if they are used on future builds) and using a thin head gaskets are not going to have much, if any, impact. 4 CCs less in the chamber and .020 less in gasket thickness can be calculated. With the pistons that far down the hole, the difference will be small enough to probably not be worth the trouble since the OP will probably be starting with no more than 8:1 with the motor home engine.


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Re: 383 or 440??? [Re: Moparteacher] #2975126
10/16/21 06:22 PM
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BSB67 Offline
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I agree.

The pistons are probably 0.160" in the hole and and a CR of 8:1-ish. I think head milling and thin gasket to add about 0.5-ish to the CR would be worth it.

Re: 383 or 440??? [Re: carnut68] #2975129
10/16/21 06:27 PM
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Originally Posted by carnut68
The old 509 cam,Team G intake[junk] 3800 convertor 3.91 in an Abody it ran 11.91 @111. .


Personally, this is not the example I would use to make the case that you can make power with low compression.

Re: 383 or 440??? [Re: BSB67] #2975162
10/16/21 08:31 PM
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This might help you, I don't know.
I am rebuilding a 383 right now. The pistons are some kind of forging, the only marking is an "80" on the underside of the crown.
Anyway, the compression height is pretty close to 1.781. Well guess what, if I use a 440 crank and the 383 rods, the pistons
will stick out of the deck about .034". With a composition gasket and 906 heads, I think I can bring it in around 9.5 ~~ 10.0 compression.
The pistons are a flattop with a small trough valve relief.
With the 3.38 crank the compression would be around 8.2.
Almost 440 inches in a low deck block.

Re: 383 or 440??? [Re: hemienvy] #2975195
10/16/21 10:36 PM
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Originally Posted by hemienvy
This might help you, I don't know.
I am rebuilding a 383 right now. The pistons are some kind of forging, the only marking is an "80" on the underside of the crown.
Anyway, the compression height is pretty close to 1.781. Well guess what, if I use a 440 crank and the 383 rods, the pistons
will stick out of the deck about .034". With a composition gasket and 906 heads, I think I can bring it in around 9.5 ~~ 10.0 compression.
The pistons are a flattop with a small trough valve relief.
With the 3.38 crank the compression would be around 8.2.
Almost 440 inches in a low deck block.


Low deck 426 wedge.

Re: 383 or 440??? [Re: justinp61] #2975204
10/17/21 12:16 AM
10/17/21 12:16 AM
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Run which ever engine will be the most reliable while you build/rebuild the other.
I have a 440 in the car now, good motor, starts, runs, drives.
I have a 383 stroked to 438 on the stand. Big rumpty bumpty cam. Its the Road Race engine. makes all its power from 3500-6500rpms
as bad as I want the speed and power that comes with the "big motor" (the 383), I sure like the hassle free operation of the 440. But its a dog and peps out at 5000

Last edited by 68rrunner; 10/17/21 12:17 AM.
Re: 383 or 440??? [Re: hemienvy] #2975214
10/17/21 02:17 AM
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Originally Posted by hemienvy
This might help you, I don't know.
I am rebuilding a 383 right now. The pistons are some kind of forging, the only marking is an "80" on the underside of the crown.
Anyway, the compression height is pretty close to 1.781. Well guess what, if I use a 440 crank and the 383 rods, the pistons
will stick out of the deck about .034". With a composition gasket and 906 heads, I think I can bring it in around 9.5 ~~ 10.0 compression.
The pistons are a flattop with a small trough valve relief.
With the 3.38 crank the compression would be around 8.2.
Almost 440 inches in a low deck block.


The counter weights will need to be cut significantly to clear the pistons with 383 rods, and the piston pin bosses may need some trimming if you use 383 rods and 440 crank. Additionally, if the piston rises into the combustion chamber of a 906 you'll want clay for clearance around the edges of the chamber. I have a 383 that is .020 positive deck and a .021 gasket. I had a chamfer cut on the piston head for clearance on stock 906s. It was too close for a .06" over 383. Combustion chambers are not round, but oval. They hang over the cylinder front and rear.

The other option is to simply cut the tops of the pistons. Most forged 383 and 440 pistons have plenty of material. I've cut .170"+ off the top of TRWs and Speed Pros.

Last edited by Moparteacher; 10/17/21 02:18 AM.
Re: 383 or 440??? [Re: BSB67] #2975216
10/17/21 05:09 AM
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Originally Posted by BSB67
Originally Posted by carnut68
The old 509 cam,Team G intake[junk] 3800 convertor 3.91 in an Abody it ran 11.91 @111. .


Personally, this is not the example I would use to make the case that you can make power with low compression.
I know what you are saying. I didn't build i, but it made power. Mismatched parts and all.

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