lz9 3900 V6 buildup

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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Shaun41178(2)
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lz9 3900 V6 buildup

Post by Shaun41178(2) »

Going to document the buildup of my 3900 build.

3.9L
Bored .007 over
JE forged pistons. P# 321238 21.8cc Dish
stock rods
ARP rod bolts.
Stock crank
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Last edited by Shaun41178(2) on Tue Jun 06, 2017 5:46 pm, edited 2 times in total.
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Re: 3900 buildup

Post by Shaun41178(2) »

I had some cam bearing spacers made up, which allow for the use of factory 2.8 cam bearings, and thus any aftermarket 60 degree cam you want made. Here is the spacers, stock bearings, and stock hyd flat tappet cam mocked up to check clearences. everything specs out.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

Good job with the cam bearing spacers. Did they have to be align-honed in place?

Stock rods are cracked cap, right?

What's your compression ratio?
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

no honing necessary.

stock rods are cracked.

Compression is going to be around 10.2:1 pending on how deep they sit in the hole but it should be around .016ish or so. I won't have an exact number till I measure.
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FieroPhrek working on that ls4 swap for 18 years and counting now. 18 years!!!!! LOL

530 whp is greater than 312
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

test fitting rings. I am not sure where I want them to be yet. They are around .019 gap here in this pic. I am thinking I might do .022 top and .024 second.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

What rings?
Opening stock ones for boost?

Since you share a bore size with the LS1, you should be able to get a Total Seal set with steel gapless top rings for a reasonable price.
That design eliminates the balancing act of setting a ring gap. The individual components can be gapped wide enough to be super safe, yet there's no risk of blow-by, power loss or oil consumption when the assembly is installed correctly.
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

I got the matching JE rings that go with the Pistons. Yea most reading I have done says around .005 per inch of bore for a light street or turbo motor but I have also read as much as .006.

It won't see big boost or a ton of nitrous so I am torn on where I want it to be. I am sure it will make power at .024 gap and .019 and all seem to be right around 19-20 thou right now
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

That's why gapless top rings are great. You could gap each piece of the ring at .030 and be extremely safe, yet when the halves are assembled, there won't be any gap at all.
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Re: lz9 3900 V6 buildup

Post by V8Mikie »

Looking good
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Re: lz9 3900 V6 buildup

Post by Spiess »

Nice, I can't wait to see when it's done.
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

I ended up doing .022 top and .021 second ring gap. After getting a few sets of main bearings, and putting in the best looking of several sets, I got a bit of the engine assembled. Odd cylinders are in. Piston sits about .005 in the hole. I measured deck height, then put piston at tdc and then rocked the piston, measured the difference, then divided by two.
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

so help me out guys. Will do some math?

Thinking of new turbo setup for 3900. Want opinions. There are 2 exhaust options.

1. Route exhaust following the Impala, with the crossover flowing into the trunk manifold. This follows the routing like a 3800. The outlet of this to turbo is only 1.8 inches, but can be ported out to about 2 inches. Thinking this will be huge backpressure. 3.9 liters flowing into a 2 inch opening converging at a single point. Here is a video of what I mean...

https://youtu.be/p0f3I-Q3Z9o

2. Route like in pics below. Use the rear manifold from a G6 which has a 1.8 inch opening, while still using the factory impala crossover which is 1.8 inches ID as well and a 1.9xx OD. Weld on some vband clamps, and have merge the two sides into a Y collector to feed the turbo. This will essentially keep the two sides separate until the reach the turbo. The Y merge on this setup would prob be around 2.25 inches. won't know until turbo is purchased.

Turbo will of course have to go into the trunk area if mounted this way.

Curious as to the backpressure of each setup. The easiest for fabrication would be to use the impala trunk manifold and not the G6.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

I don't think the single outlet will be a big problem. Have you come across anyone changing setups while keeping the same turbo, then making more power?
Didn't GM rate both configurations for the same power?

On a single bank, the pipe gets flow from a cylinder every 240 degrees. That's the entire duration of the exhaust stroke, but the blow down phase in which the majority of the exhaust mass leaves the cylinder is less than 90 degrees. The pump down phase of the exhaust stroke is a trickle by comparison.

The story isn't much different if you collect all 6 into one collector. That collector sees a pulse every 120 degrees, but the duration of blow down flow is still less than 90.

Considering how much easier the turbo plumbing would be with the single outlet and how little I think the single outlet will restrict it I'd go straight for the single outlet.

You doing a 3900 turbo swap on your Evo?
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

I took a measurement of the inlet of my precision turbo and its a 2 inch inlet. The crossover on my old setup is about 1.8 to 2 inches. So jumping .4 in displacement isnt a big issue.

It seems flow out of the turbo is more important.

Ill go with the factory crossover and outlet into one pipe as its easier to plumb.. Thanks Will.

Goal on old 3.5 itb was 500 whp. I made that. Gonna make new goal on 3900 at 600 whp

I might need that twin disk after all Will. What do I need? Help me out mang. Gonna set a tentative goal to have car done by october so I can do the 1/2 mile shootout in Ocala.
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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

Here is how it fits. the TB will not fit as the intake points at the strut tower. So I will have to modify the neck of the plenum.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

Dude, What.The.FUCK.Is.That?

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Re: lz9 3900 V6 buildup

Post by Shaun41178(2) »

That's called a rotor. Its attached to the top of a thingamajig called a distributor
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

I've heard of them on knuckle dragging Chevies, but never thought I'd actually see one on an engine built since 2005.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

Shaun41178(2) wrote: Thu Mar 22, 2018 5:09 pm
I might need that twin disk after all Will. What do I need? Help me out mang. Gonna set a tentative goal to have car done by october so I can do the 1/2 mile shootout in Ocala.
I need to check with QM to see if their setup would be a little easier to work with than a Tilton. I can get you a design for a puck for a Tilton pretty quick, but it'll need to be welded into a flex plate.
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Re: lz9 3900 V6 buildup

Post by The Dark Side of Will »

Besides just fitting it in the bellhousing, the other aspect of a dual disk clutch is that unless you re-engineer the throw out mechanism (which could be done via hydraulics) the pedal load goes way up (like 2x) and the pedal travel goes way down. This will be especially bad if you're using the Isuzu throw out arm on a Getrag, as you've mentioned in the past.

I have a design for a throw out bearing holder for the Tilton that's compatible with the Fiero Getrag... but as mentioned, the pedal load doubles and the pedal travel gets cut in half.
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