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Old 07-04-2018, 01:47 AM   #1
72K5CSTDarkOlive
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427 SBC & 4L80e build

I'm replacing the engine in trans in my 72 K5 and decided on a 427 Stroker mated to a 4L80e.

I'm using a local shop (Gromm Racing Heads) to build the engine and another local guy to build the 4L80e.

The parts for the build we are going to use are the following:

Block: New Dart SHP 400 Block w/350 Mains. 4.125 Bore, 2 pc rear main
Crankshaft: Dart 4340 Forged for Internal Balance
Pistons: Mahle Forged Pistons
Connecting Rods: SCAT Forged
COMP Custom Camshaft: TBD...I know that it will be around .600 Max lift and the duration will be somewhere in the ball park of 243-258 @ .050. The Lobe separation is 110-111.

COMP Full roller stainless steel 1.6 ratio
AFR 210 CC Eliminator heads, 2.08/1.6, 65 CC
Edelbrock Torker 2 Single Plane
MSD Pro Billet Distributor
FiTech Meanstreet EFI system with Command Center 2
Headers: Kooks 1 7/8" stainless steel

The Command Center will let me use my existing electric fuel pump and I am building a return line that will go back to gas tank through the sending unit.

The 4L80e will be updated with the 32 spline input shaft to connect to the 205 TCASE and he is building a billet tq converter using a 2500 stall.

These arrived this week and my builder is going to get going on this for me.
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Last edited by 72K5CSTDarkOlive; 07-11-2018 at 08:38 AM.
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Old 07-04-2018, 02:32 AM   #2
Blazerowner
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Re: 427 SBC & 4L80e build

I just put a 4l80 in my 72 K5. The output is 32 spline stock but you have to make sure it is the correct shaft. It has to be fully splined so you can cut it to adapt to the np205. I kept mine in the stock location. It put the engine forward a bit as it’s a long transmission.
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Old 07-04-2018, 02:41 AM   #3
72K5CSTDarkOlive
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Re: 427 SBC & 4L80e build

Quote:
Originally Posted by Blazerowner View Post
I just put a 4l80 in my 72 K5. The output is 32 spline stock but you have to make sure it is the correct shaft. It has to be fully splined so you can cut it to adapt to the np205. I kept mine in the stock location. It put the engine forward a bit as itís a long transmission.
How do you like the 4L80e? Did you use a single or triple clutch?

The guy that's building has done this swap many of times on our Blazers. I just couldn't remember all the details he went over with me to make it work and support the TQ my engine is going to put out. I'm going to try my best to document the entire build so others can reference it if needed.

We're going to keep the engine in the stock location and move the tcase back and use a custom driveshaft.
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Old 07-05-2018, 01:30 AM   #4
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Re: 427 SBC & 4L80e build

I've been looking at buying the same Dart block for my Suburban.......... going to follow this build. I know the casting is heavier, but any idea of the amount of bore left with the 4.125 hole?
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Old 07-05-2018, 09:29 AM   #5
72K5CSTDarkOlive
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Re: 427 SBC & 4L80e build

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Originally Posted by kwmech View Post
I've been looking at buying the same Dart block for my Suburban.......... going to follow this build. I know the casting is heavier, but any idea of the amount of bore left with the 4.125 hole?

I'm going over there today and can check.
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Old 07-05-2018, 07:52 PM   #6
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Re: 427 SBC & 4L80e build

The block came in undersized @ 4.110. He's going to bore it .010 and hone the last .005
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Old 07-06-2018, 11:45 AM   #7
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Re: 427 SBC & 4L80e build

My thought was to get the factory GM stroker crank which comes in at a 3.8 and have the block bore at 4.080. This gives you a 392 cu engine with more than enough room for an over bore later if needed. I was thinking about using the Dart heads also. Have you given any thought to the rod length and compression?
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Old 07-08-2018, 02:05 PM   #8
72K5CSTDarkOlive
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Re: 427 SBC & 4L80e build

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Originally Posted by kwmech View Post
My thought was to get the factory GM stroker crank which comes in at a 3.8 and have the block bore at 4.080. This gives you a 392 cu engine with more than enough room for an over bore later if needed. I was thinking about using the Dart heads also. Have you given any thought to the rod length and compression?
We'll be using 6" connecting rods and comp will be around 10.5:1. I believe there is either .030 or .060 left in the bore after taking it to 4.125. A 4.155 would get you to 434.
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Old 07-08-2018, 04:41 PM   #9
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Re: 427 SBC & 4L80e build

An issue I've had with a couple of factory 400 blocks. One block was 30 over and the other was 40. Even after having the block decked and the heads surfaced with compression over 10-1, I've had the head gaskets pop between the cylinders. Removing the cyl head and looking at the block, it looks like somebody took a hacksaw and cut a line down the cylinder walls. So that is why I'm considering the 80 over 350 bore with the 350 gasket. Might give it a bit more meat for sealing between. The 400 gaskets are pretty thin between the cylinders. And with the aluminum heads with the difference in expansion...
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Old 07-08-2018, 11:02 PM   #10
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Re: 427 SBC & 4L80e build

On board for the build...
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Old 07-09-2018, 06:03 PM   #11
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Re: 427 SBC & 4L80e build

So I found out the Dart 400 block can be bored up to 4.200. So the 4.125 will leave us .075 for future rebuilds.

Decking it tonight when the temp drops. It's been really hot these last few days. Tomorrow they'll do the internal balance and finish up the rest of the block work by the end of this week.
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Old 07-09-2018, 06:11 PM   #12
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Re: 427 SBC & 4L80e build

With the big cam I'm going to have to convert to hydroboost. Got a set of brackets for the hydroboost from CaptainFab. The hydro unit came from Power Brake Exchange here in San Jose. pwrbrake.com

This particular unit came off a 90's P30 Chevy Step Van. For the MC I needed to step up to a 1 1/8" bore. Everything looks to line up perfectly.
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Old 07-09-2018, 09:02 PM   #13
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Re: 427 SBC & 4L80e build

Quote:
Originally Posted by kwmech View Post
An issue I've had with a couple of factory 400 blocks. One block was 30 over and the other was 40. Even after having the block decked and the heads surfaced with compression over 10-1, I've had the head gaskets pop between the cylinders. Removing the cyl head and looking at the block, it looks like somebody took a hacksaw and cut a line down the cylinder walls. So that is why I'm considering the 80 over 350 bore with the 350 gasket. Might give it a bit more meat for sealing between. The 400 gaskets are pretty thin between the cylinders. And with the aluminum heads with the difference in expansion...
The wall thickness with a 4.125 will be over .2500"... The specs on Darts webpage says that minimum thickness at 4.165 is .230" so even at 4.200 you're still at .190" and most OEM blocks are around .120 at .060 overbore. We'll be using a multi layer steel head gasket
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Old 07-10-2018, 12:21 AM   #14
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Re: 427 SBC & 4L80e build

Wow, that was quick. I shipped your order on Saturday.
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