Gen 5 LT1 L83 L86 heads

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A_VAS
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Re: Gen 5 LT1 L83 L86 heads

Postby A_VAS » Fri Jul 21, 2017 9:33 am

In February I built a Gen5 short block with stock crank, forged rods, and forged Wiseco piston.
numbers work out same as earlier stuff...6.125 rod, 3.622 stroke, 1.304 CH
pistons were ~.004-.006 out of the hole using this new GM, undecked Gen5 block
so yes the 9.240 nominal is correct

I also just put a set of Diamond pistons in a LT1, reusing the stock rods and crank.
stock rod length in the Gen5 is 6.125 btw, just use a weird pin dia.
too lazy to make power w/o boost

In-Tech
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Re: Gen 5 LT1 L83 L86 heads

Postby In-Tech » Sun Jul 23, 2017 1:34 am

Thanks A_VAS,
I wasn't sure which head I have here but it does appear it is a L83 and not a L86. It appears the L83 has a 1.928" In valve and 1.556" ex valve. The L86 is 2.13" and 1.59" respectively. I haven't measured it completely yet but it looks like a 2" valve is all the L83 will handle in stock form. The casting does appear to have enough meat for me to install a larger seat so as time allows I will do that.

A_VAS, besides the 8 bolt flexplate/flywheel, is the Gen5 the same crank otherwise as a Gen3/4? Thanks again for all the feedback.
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

A_VAS
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Re: Gen 5 LT1 L83 L86 heads

Postby A_VAS » Mon Jul 24, 2017 9:19 am

on the crank, yes as far as I could tell it is the same as say a LS9 crank.
journal sizes and width are same as previous...it is a forging..I did not measure the snout length to see if it was the same as earlier versions.

the main line is a bit different in that they use the same #3 cap as the rest 1/2/4/5. There is no machined surface on the cap for a thrust bearing...they only put a flange bearing in the block side of #3 and not the cap. The cap uses the same bearing as the other positions.
so it has a 1/2 thrust bearing so to speak, with flange only on 180*
too lazy to make power w/o boost

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Re: Gen 5 LT1 L83 L86 heads

Postby In-Tech » Mon Sep 11, 2017 12:49 am

midnightbluS10 wrote:
tt 383 wrote:L83 has a 248cc intake and 107cc exhaust 57/58 combustion chamber. That's from LPE. Can't find the L86 port volumes but supposedly they are about 50cfm better than the L83 head... I feel like the L86 was 26x cc volume in some literature I read.



According to a post on their forum from Tim@Lingenfelter,

L86 LT1 General Motors Cylinder Head Runner Volumes and Chamber Volumes

The factory L86 LT1 cylinder heads runner volumes and chamber sizes are as follows.

Stock L86 LT1 cylinder heads -

297 CC intake runner volume / 107 cc exhaust , 56.5 cc chambers


Lingenfelter CNC ported L86 LT1 cylinder heads -

308 CC intake runner volume / 110 cc exhaust . 61 cc chambers before surfacing.

With a camshaft change you would require better valve springs.

We offer the following camshafts for the LT1 engine & the related spring kits are included on the item pages

http://www.lingenfelter.com/mm5/merc...gory_Code=C606

I would suggest checking the pushrod length during assembly. In most cases the stock pushrods can be reused (LT1)


And the LT1/L86's flow somewhere around 320/210 estimating from a quick glance at the graphs

http://www.lingenfelter.com/forum_linge ... -flow-data


Hello Folks,
I apologize for the delay, I've had some health issues and this all got back burner'd :| Somehow I missed that the L86 had such a larger port(noted in above quote), to me that means it must be a different casting so I'll be on the hunt for one and if anyone knows the casting number I should be looking for, it would be appreciated. I might even put a new blade on the band saw for this one. :mrgreen:

A-VAS, thanks for the half thrust bearing knowledge. Maybe I missed it in one of your posts, do these all have piston oilers like the LSA and LS9?
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

A_VAS
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Re: Gen 5 LT1 L83 L86 heads

Postby A_VAS » Mon Sep 11, 2017 10:02 am

the car engines LT series have the squirters yes.
I have not personally seen a LT truck engine to verify if the squirters are in all of them.
too lazy to make power w/o boost

cuisinartvette
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Re: Gen 5 LT1 L83 L86 heads

Postby cuisinartvette » Mon Sep 11, 2017 10:18 am

nothing technical to add just gotta admire what gm has done
back in the 80s or 90s guys woulda cut their toes off for something similar
Todays stock engines are the "race" engines of those days in a sense.


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