383 Build Questions - Chevelle Tech
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post #1 of 14 (permalink) Old Jan 30th, 18, 1:21 PM Thread Starter
 
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383 Build Questions

Hey everyone, I have questions about this 383 I知 building and the compression ratio I知 trying to achieve. Here痴 what I have:
-350 bored out to 30 over
-400 crank turned down to fit the 350 block
-I知 probably going to use a CompCam .425-.440 valve lift @206-212 duration @.050
-30 over pistons
-5.7 Rods
-.040 Head gasket
-062 cast iron vortec heads
My questions are, I知 looking to get between 9.5:1 or 10:1 compression ratio. I think i listed all of the info, should I use dished pistons or flat tops? The dishes are floating wrist pins, the flat tops I would have to have the wrist pins pressed in. I think the flat tops would put me well over 10:1 with the 062 65cc chambers. What do you guys think? Also, this cam CompCam 12-388-4) stares that it痴 for flat tappet lifters. Can I use roller lifters with it?


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post #2 of 14 (permalink) Old Jan 30th, 18, 2:04 PM
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Re: 383 Build Questions

A flat top piston is going to put you closer to 11 to 1 depending on the exact deck height.

Unless you already have a 400 crank that has been machined for the 350 block you will be way ahead of the game buying a complete balanced rotating assembly from someone like Eagle.

As far as the camshaft goes I would pick a cam manufacturer and call them. Tell them what you are trying to accomplish and have them recommend a camshaft for your combination. There are way too many variables involved to picking a camshaft. The cam companies want you to be happy with their product so they try very hard to give you a cam that will work well. I have been doing this for over 40 years and still will not try to pick a camshaft for a performance engine. I have a couple of manufacturers I use and they have yet to steer me wrong.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


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post #3 of 14 (permalink) Old Jan 30th, 18, 2:08 PM
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Re: 383 Build Questions

You'll have to use a dish, a 4VR flat top on a zero decked 350 gets 10.1:1.
You'll also have to use a rod with a pin height that matches the 5.7" rod you're going to use. If you end up buying rods, get 6" and the appropriate pistons, your bearings will appreciate less weight swinging around.
Can't use roller lifters on a flat tappet cam.
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post #4 of 14 (permalink) Old Jan 30th, 18, 2:10 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by Busted Knuckles View Post
You'll have to use a dish, a 4VR flat top on a zero decked 350 gets 10.1:1.

You'll also have to use a rod with a pin height that matches the 5.7" rod you're going to use. If you end up buying rods, get 6" and the appropriate pistons, your bearings will appreciate less weight swinging around.

Can't use roller lifters on a flat tappet cam.


Ok thank you for the reply.


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post #5 of 14 (permalink) Old Jan 30th, 18, 2:11 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by BillK View Post
A flat top piston is going to put you closer to 11 to 1 depending on the exact deck height.

Unless you already have a 400 crank that has been machined for the 350 block you will be way ahead of the game buying a complete balanced rotating assembly from someone like Eagle.

As far as the camshaft goes I would pick a cam manufacturer and call them. Tell them what you are trying to accomplish and have them recommend a camshaft for your combination. There are way too many variables involved to picking a camshaft. The cam companies want you to be happy with their product so they try very hard to give you a cam that will work well. I have been doing this for over 40 years and still will not try to pick a camshaft for a performance engine. I have a couple of manufacturers I use and they have yet to steer me wrong.


I already have a Camshaft though. I don稚 want to buy another one if I don稚 have to. With the heads I just bought, the valve lift with this cam is within specs of the valves on the heads.


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post #6 of 14 (permalink) Old Jan 30th, 18, 2:13 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by surfridermoflo View Post
I already have a Camshaft though. I don稚 want to buy another one if I don稚 have to. With the heads I just bought, the valve lift with this cam is within specs of the valves on the heads.


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The crank has already been machined to fit in the 350.


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post #7 of 14 (permalink) Old Jan 30th, 18, 4:23 PM
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John
 
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Re: 383 Build Questions

Overall rotating assy height, head gasket thickness and block deck height need to be considered.

Example with Keith Black 18cc dished pistons (1.433 c.h.) yields a compression around 9.7:1.

1.875 (1/2 stroke of 400 sbc crank)
+ 5.7 (rod length)
+ 1.433 (KB18cc dished) (compression height of piston)
= 9.008 overall height from the crankshaft center line to top of piston.

Ballpark factory block deck height is typically around 9.025 from deck to crank centerline.

So 9.025-9.008 = piston .017 down in the block

You can try and find a head gasket this will give about .035-.040 quench. Find a .018 to .023 compressed thickness value of a head gasket would be desired.

Has the blocked been decked? Yes, what amount as you will need to find the right head gasket thickness or change piston selection as there are dishes that are more optimized.

John

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post #8 of 14 (permalink) Old Jan 30th, 18, 4:47 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by Enganeer View Post
Overall rotating assy height, head gasket thickness and block deck height need to be considered.



Example with Keith Black 18cc dished pistons (1.433 c.h.) yields a compression around 9.7:1.



1.875 (1/2 stroke of 400 sbc crank)

+ 5.7 (rod length)

+ 1.433 (KB18cc dished) (compression height of piston)

= 9.008 overall height from the crankshaft center line to top of piston.



Ballpark factory block deck height is typically around 9.025 from deck to crank centerline.



So 9.025-9.008 = piston .017 down in the block



You can try and find a head gasket this will give about .035-.040 quench. Find a .018 to .023 compressed thickness value of a head gasket would be desired.



Has the blocked been decked? Yes, what amount as you will need to find the right head gasket thickness or change piston selection as there are dishes that are more optimized.


Ok, copy that. I do have a head gasket thickness of .040, don稚 know if the block has been decked, I pick it up from the machine shop on Thursday. But all of the other numbers match what you池e saying. So I can pretty much expect around 9.8:1 compression. Thanks for the expertise!!


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post #9 of 14 (permalink) Old Feb 3rd, 18, 7:42 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by surfridermoflo View Post
Ok, copy that. I do have a head gasket thickness of .040, don稚 know if the block has been decked, I pick it up from the machine shop on Thursday. But all of the other numbers match what you池e saying. So I can pretty much expect around 9.8:1 compression. Thanks for the expertise!!


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I have another question, will a 12 torque converter with a 1500 stall work well with my setup?


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post #10 of 14 (permalink) Old Feb 4th, 18, 7:47 PM
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Re: 383 Build Questions

I ran a 280H magnum [email protected] .050 in a 385" with 11+ compression and the stock very tight 1500 stall worked just fine.
On another note FIL had a 355" with 624 heads 76cc and his converter stalled at 1200-1400 in that car.

I built him a 383 with those same 624 heads but milled them to 72cc and used 400 rods and his 350 pistons.
I ported the heads.
He picked a 214-224 on a 112 LSA generic cam and his same converter and trans were used.
That converter now stalled to 2500rpm.

Use what you have and if ya do not like it then change it.. it may surprise you how well it will work behind some cubes.
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post #11 of 14 (permalink) Old Feb 4th, 18, 7:54 PM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by jeff swisher View Post
I ran a 280H magnum [email protected] .050 in a 385" with 11+ compression and the stock very tight 1500 stall worked just fine.

On another note FIL had a 355" with 624 heads 76cc and his converter stalled at 1200-1400 in that car.



I built him a 383 with those same 624 heads but milled them to 72cc and used 400 rods and his 350 pistons.

I ported the heads.

He picked a 214-224 on a 112 LSA generic cam and his same converter and trans were used.

That converter now stalled to 2500rpm.



Use what you have and if ya do not like it then change it.. it may surprise you how well it will work behind some cubes.


Ok, I will. Do you know what a stock 84 K5 Blazer with a 700r4 and whatever stock gears has as far as what stahl converter it came with?


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post #12 of 14 (permalink) Old Feb 4th, 18, 8:08 PM
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Mr Bill
 
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Re: 383 Build Questions

One more thing to keep in mind. You will need to grind some of the tops of the rod bolts to keep them from hitting the camshaft if you use a stock 5.7 rod. Most of the newer aftermarket rods are already clearanced.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


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post #13 of 14 (permalink) Old Feb 5th, 18, 8:46 AM
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jeff
 
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Re: 383 Build Questions

No idea on gears and converter.
Jack up the rearend.
Spin one tire and if the other tire spins the opposite direction then put one tire back onto the ground.
SO out of gear one rear tire in the air and one on the ground.

Spin that 1 tire in the air 2 revolutions make sure it is exactly 2.
At the same time count how many revolutions the driveshaft makes.

If it makes just under 3.5 turns it is probably 3.45:1 if it makes just a tick over 4 revolutions it is probably 4.11:1 gears.

If it is a posi track and both tires spin the same way when in the air then both tires need to be off the ground. make 1 revolution spin of the tire and count driveshaft revolutions to get gear ratio.
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post #14 of 14 (permalink) Old Feb 13th, 18, 12:10 AM Thread Starter
 
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Re: 383 Build Questions

Quote:
Originally Posted by jeff swisher View Post
I ran a 280H magnum [email protected] .050 in a 385" with 11+ compression and the stock very tight 1500 stall worked just fine.

On another note FIL had a 355" with 624 heads 76cc and his converter stalled at 1200-1400 in that car.



I built him a 383 with those same 624 heads but milled them to 72cc and used 400 rods and his 350 pistons.

I ported the heads.

He picked a 214-224 on a 112 LSA generic cam and his same converter and trans were used.

That converter now stalled to 2500rpm.



Use what you have and if ya do not like it then change it.. it may surprise you how well it will work behind some cubes.


I will try the stock tc and see if it works. Thanks for the different point of view!


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