Moparts
383 pistons in 426 wedge
Posted By: Alexdodge
383 pistons in 426 wedge - 04/29/09 01:38 AM
One of my other engines is a 426 marine block. When I put this motor together I used 383pistons and 440 connecting rods in it being it is the same bore . So now I'm told that the pistons set low in the cylinders and I probably only have about an 8 to 1 compression. I don't remember how low they sit low compared to the originial 426 pistons. Is it possible to use a very thin set of head gaskets to make up for some of the difference in the piston height to get the compression higher? I don't want to get into shaving the heads. Just an idea.
Thanks, Alex
Posted By: AndyF
Re: 383 pistons in 426 wedge - 04/29/09 01:48 AM
Yeah those pistons are probably 0.200 down in the hole if not more. Unless it is a tow truck motor you might want to pull it down and buy some pistons that are designed to work in that combination.
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 01:51 AM
the tallest 383 piston has a CH of 1.932 , a sixpak piston has a CH of 2.061 and that puts it .020 in the hole. It's going to cost you almost as much to deck the head on to surfaces as it will to get a correct CH piston .
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 01:51 AM
With these pistons the car is a real dog. Don't know where to go from here. Its only a touring and cruiser but I still would like it to run better than this. Any one have any ideas?
Alex
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 01:53 AM
Quote:
Thats where the problem comes in, just can't find anyone that sales them anymore. Alex
call Bob Mazzolini or you can have Diamond make you a set .
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 01:57 AM
Would anyone have a address for these people?
Thanks, Alex
Posted By: OzHemi
Re: 383 pistons in 426 wedge - 04/29/09 02:02 AM
http://www.bobmazzoliniracing.com/I went and got a Hemi block from him a few years ago, great to deal with
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 02:06 AM
I'll check them out, thanks, Alex
Posted By: CH3NO2
Re: 383 pistons in 426 wedge - 04/29/09 02:30 AM
show us your 383 pistons, you can always put in a longer rod. Steve
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 03:15 AM
A longer rod? I already have 440 rods in there now.
Alex
Posted By: AndyF
Re: 383 pistons in 426 wedge - 04/29/09 05:18 AM
A Hemi rod is longer than a 440 rod but might not be set up for the same pin. Only good solution is to get the right pistons so you can get the compression back up to 9.5 or 10:1 or whatever it is that you want to run.
Posted By: 340SHORTY
Re: 383 pistons in 426 wedge - 04/29/09 07:24 AM
put a blower on it or turbo it. that compression is perfict for either...
Posted By: lewtot184
Re: 383 pistons in 426 wedge - 04/29/09 12:13 PM
hughe's has oem 426 street wedge pistons.
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 01:44 PM
Yes!!! Hughs Engines has an assortment of 426 wedge pistons in stock. Thanks, Alex
Posted By: 6PakBee
Re: 383 pistons in 426 wedge - 04/29/09 02:41 PM
Quote:
One of my other engines is a 426 marine block. When I put this motor together I used 383pistons and 440 connecting rods in it being it is the same bore . So now I'm told that the pistons set low in the cylinders and I probably only have about an 8 to 1 compression. I don't remember how low they sit low compared to the originial 426 pistons. Is it possible to use a very thin set of head gaskets to make up for some of the difference in the piston height to get the compression higher? I don't want to get into shaving the heads. Just an idea.
Thanks, Alex
8:1 with what heads? If you are running the stock 516's I doubt it would be that low. With 906's I'm guessing it would be close. I would think a set of 915's would be a good option. Again not running the numbers, just guessing.
Posted By: patrick
Re: 383 pistons in 426 wedge - 04/29/09 03:27 PM
a cheaper alternative might be to get a 4.15" cast stroker crank.
kb-silvolte.com shows the #1271 piston (for a 383) as a 1.848" comp height.
1.848+6.76+(4.15/2)= 10.683", or .042" in the hole based on the blueprint height of 10.725" for an RB block.
based on my calculations assuming a .040" head gasket and 88cc heads, you're looking at about 9.96:1 compression
use a largish cam or a wide LSA to make the intake closing point late to bleed cyl pressure, and it should run on pump premium.
Posted By: Fury Fan
Re: 383 pistons in 426 wedge - 04/29/09 03:36 PM
Quote:
With these pistons the car is a real dog. Don't know where to go from here. Its only a touring and cruiser but I still would like it to run better than this. Any one have any ideas?
Alex
If you want some easier-than-pistons ideas, I'd recommend:
1. Install -516 heads for the closed chambers and smaller valves/ports (higher velocity).
2. Advance the cam a few degrees. If you have a 'big' cam, consider a swap to an RV or stock cam.
3. Put a fast advance curve in the distributor. Due to your total lack of quench, you still might have detonation issues even though your compression is low, you'll just have to see.
4. Make sure you have a dual-plane intake and a smaller-size carb (or maybe a smallblock Thermoquad?). If not, try to find a 413 or 1966 440 intake, they have smaller flatter runners and might give more velocity than a performance intake. They are easily identified because they kinda look like they've been stepped on.
Posted By: Dodgem
Re: 383 pistons in 426 wedge - 04/29/09 04:54 PM
Quote:
a cheaper alternative might be to get a 4.15" cast stroker crank.
kb-silvolte.com shows the #1271 piston (for a 383) as a 1.848" comp height.
1.848+6.76+(4.15/2)= 10.683", or .042" in the hole based on the blueprint height of 10.725" for an RB block.
based on my calculations assuming a .040" head gasket and 88cc heads, you're looking at about 9.96:1 compression
use a largish cam or a wide LSA to make the intake closing point late to bleed cyl pressure, and it should run on pump premium.
better check your math
1.848 + 6.76 + (3.75/2= 1.875) = 10.483 - 10.725 = -.243
About 7 to 1 compression give or take
Posted By: 71 FJ6 Charger
Re: 383 pistons in 426 wedge - 04/29/09 04:56 PM
Dont mean to hi-jack the post,but can you use 426 wedge pistons in a 383 with stock heads,crank and rods?
Posted By: Dodgem
Re: 383 pistons in 426 wedge - 04/29/09 05:20 PM
Quote:
Dont mean to hi-jack the post,but can you use 426 wedge pistons in a 383 with stock heads,crank and rods?
Piston part number please??
I think you will find a 426 W piston will stick out of a 383 a couple hundered thou.
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 05:57 PM
Quote:
Quote:
a cheaper alternative might be to get a 4.15" cast stroker crank.
kb-silvolte.com shows the #1271 piston (for a 383) as a 1.848" comp height.
1.848+6.76+(4.15/2)= 10.683", or .042" in the hole based on the blueprint height of 10.725" for an RB block.
based on my calculations assuming a .040" head gasket and 88cc heads, you're looking at about 9.96:1 compression
use a largish cam or a wide LSA to make the intake closing point late to bleed cyl pressure, and it should run on pump premium.
better check your math
1.848 + 6.76 + (3.75/2= 1.875) = 10.483 - 10.725 = -.243
About 7 to 1 compression give or take
his math was using a stroker crank , 4.15 stroke . 3.75 stroke and the piston he has currently has a 1.932 CH , assuming it's a factory std bore 383 piston from 68-69 , the OP didn't state what the piston ACTUALLY is .
Posted By: AndyF
Re: 383 pistons in 426 wedge - 04/29/09 06:10 PM
Yeah, a 383 piston with a 4.150 stroke crank comes close to working in a 426 block. Just depends on the details and what the engine builder is trying to accomplish.
Semi-custom pistons don't cost that much these days. I think Diamond only charges $15 per piston to change the CH on a standard part number piston. So you just call them up and order a 383 piston and ask them to make the CH a little higher and you end up with exactly what you want. As long as the change can be handled in the shelf stock forging blank the cost is minor.
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 07:00 PM
The 383 pistons in the 426 that are in there now are about .200 in the hole. I spoke with Dave at Hughs Engines and he figured the correct flat top pistons that they sell at .030 over would come in at about .060 in the hole. With the 452 heads it should be about 9.1 to 1 compression. This is by his figures. This would be great for me being that the car is strictly a cruiser and for touring with the car club. He said I could do better by using a thinner head gasket.
I wonder if it would be better to use the 516 heads that I have on the shelf?
Thanks all, Alex
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 07:12 PM
Quote:
The 383 pistons in the 426 that are in there now are about .200 in the hole. I spoke with Dave at Hughs Engines and he figured the correct flat top pistons that they sell at .030 over would come in at about .060 in the hole. With the 452 heads it should be about 9.1 to 1 compression. This is by his figures. This would be great for me being that the car is strictly a cruiser and for touring with the car club. He said I could do better by using a thinner head gasket.
I wonder if it would be better to use the 516 heads that I have on the shelf?
Thanks all, Alex
Either way you have no quench , the 452's will flow better than the 516's .
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 09:30 PM
Either way you have no quench , the 452's will flow better than the 516's .
This is where I get totally lost. This "quench" thing everyone keeps bringing up. So what happens when there is no quench and how do I get it. How can I not have it if I'm using just stock type parts??? Is there somewhere that I can read about to get an understanding?
Does not having quench lead to pinging in the motor? Thanks, Alex
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 09:45 PM
Quote:
Quote:
Either way you have no quench , the 452's will flow better than the 516's .
This is where I get totally lost. This "quench" thing everyone keeps bringing up. So what happens when there is no quench and how do I get it. How can I not have it if I'm using just stock type parts??? Is there somewhere that I can read about to get an understanding?
Does not having quench lead to pinging in the motor? Thanks, Alex
Quench wasn't a big deal when you could buy hi octane fuel at the pump on any street corner for pennies a gallon , now it's what you need to achieve if you wnat optimum performance to run on the piss available on every street corner.
Yes it can lead to detonation (pinging) especially with higher compression ratios .
What you want is .040-.045 between the piston and the head on the side of the chamber away from the valves , to achieve it with open chambers leads to aggressive head milling or step dome pistons , with closed chamber you want the piston no more than .020 below the deck with a steel shim gasket or zero deck with a composite gasket and a closed chamber head.
I have 2 friends with almost identical built 440's both using the same cam and 906's, one with KB step domes and .060-.065 quench distance , his compression ratio was 9.3 and it would ping with anything less than 93 octane , other was a motor I did a lot of machining to achieve .040-.043 with the same step dome pistons. The heads were something I had bought from another member with big valves and milled about .050 initially and compression ended up about 10.3, this one ran with no pinging on 93 octane with 38 degrees total timing.
As far as why you don't have it using stock type parts , mopar didn't do anything to really achieve it so it's a mix and match to get it if possible , unfortunatley you are working with something you can't mix and match with .
I don't know what hughes has for pistons but to get it with your 452's will be impossible without a custom piston , which is easily doable. I'm getting ready to have a set made up by diamond and it's not as pricey as you would expect for a 440 build I'm doing using 452's. Or you need a flat top with about 2.060 CH , that'll be .020 in the hole on a 10.725 deck , steel shim gasket and a closed chamber head of your chosing .
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 09:52 PM
Quote:
The 383 pistons in the 426 that are in there now are about .200 in the hole. I spoke with Dave at Hughs Engines and he figured the correct flat top pistons that they sell at .030 over would come in at about .060 in the hole. With the 452 heads it should be about 9.1 to 1 compression. This is by his figures. This would be great for me being that the car is strictly a cruiser and for touring with the car club. He said I could do better by using a thinner head gasket.
I wonder if it would be better to use the 516 heads that I have on the shelf?
Thanks all, Alex
I just ran this setup with the hughes engine piston thru a calculator , Dave is correct , you'll have 9.1ish compression , no quench , you can run that and with the right tune it won't be a pinging pig , this is using the 452's , the 516's will bump the compression closer to 10.0 , you may have issues but with a custom ground cam and the right tune you should be ok , but you'll give up a little because of the lack of quench , to get it would require cutting .040 off the block which I highly do not recommend as the machining cost will get you up to having Diamond make you a better suited piston .
Posted By: Alexdodge
Re: 383 pistons in 426 wedge - 04/29/09 10:18 PM
John, In my other car I have a 440 block that I put in sixpack pistons and sixpack rods. I'm using 452 heads on this motor and I do have pinging at higher rpms. More noticable when I get on it. Would a different set of heads do better on this motor?Like 915s? I always hated hearing the pinging!!!
Going back to the 426, can you tell me what specs I would need to order custom pistons for this engine to make it right? Thanks, Alex
Posted By: JohnRR
Re: 383 pistons in 426 wedge - 04/29/09 11:42 PM
Quote:
John, In my other car I have a 440 block that I put in sixpack pistons and sixpack rods. I'm using 452 heads on this motor and I do have pinging at higher rpms. More noticable when I get on it. Would a different set of heads do better on this motor?Like 915s? I always hated hearing the pinging!!!
Going back to the 426, can you tell me what specs I would need to order custom pistons for this engine to make it right? Thanks, Alex
the 440 you can tune that out somewhat , rool back the timing some , if vac advance is connected disconnect or limitthe amount of advance , putting on the 915's would help it alot , the open part of the chambe on a 452 can be as much as .120 deep and I'll assume you are using composite gaskets .
As far as the 426 , no because I can't tell if your block is square as it is and what the ACTUAL deck height is from where I live anything would be a complete guess and that's not a good way to measure for customs .
Posted By: Dodgem
Re: 383 pistons in 426 wedge - 04/29/09 11:48 PM
did not see it was 4.15
Posted By: max_maniac
Re: 383 pistons in 426 wedge - 05/04/09 02:16 AM
Quote:
John, In my other car I have a 440 block that I put in sixpack pistons and sixpack rods. I'm using 452 heads on this motor and I do have pinging at higher rpms. More noticable when I get on it. Would a different set of heads do better on this motor?Like 915s? I always hated hearing the pinging!!!
Going back to the 426, can you tell me what specs I would need to order custom pistons for this engine to make it right? Thanks, Alex
Are you looking for a set of old standard bore pistons, flat tops? 
I also know where there is a set of 70 over hi comp pistons. Or even some real old TRW 60 over 13.5 pistons.