3900 headgasket on 3400 head and other lz9 info

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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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

I am thinking about moving a tooth because I am was thinking of keeping the vvt cam, keeping the vvt assembly intact, just have it disconnected with a 7730 ecu. If this works, along with another bolt in mod, it will allow a very easy install into a fiero or other obd1 ecu setup. Which of course gives people way more options and a reason to install this engine over a 3400 or lx9 3.5

So if the cam is advanced in the default position by 7-9 degrees, I was curious if that is crank degrees or cam degrees. If its cam, then that means the crank is advanced 14-18 degrees when vvt is in default mode(no ecu signal)

If true, which I have read different thoughts on this, then by moving one cam tooth retard, that equates to 7 cam degrees or 14 crank degrees. Which will make the cam straight up, or nearly straight up, which will help with more top end power.

So what I want to know is if in order to do this, I turn the crank clockwise while leaving the cam where it is, or do I turn the crank counterclockwise to retard the cam position in relation to the crank. I believe I have to go clockwise with the crank, but want to make sure
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

when using a non 3900 timing cover and water manifold, something needs to be done. had this machined up. might get more. Also looking at 1.8 rockers from an ls7. Sources say the 3900 rocker is a 1.7 but I measured mine at a 1.6. If the ls7 rockers work, it can get more lift while keeping the stock cam.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

in reference to piston to valve clearence at TDC. putting this here so its easy to find later on.

http://60degreev6.com/forum/showthread. ... post309856
Perhaps I didn't state it the correct way but at TDC the intake valve had .260 clearance and the exhaust was .405. Much more clearance on the exhaust valve. Is that what you are looking for? I took the measurements at the valve stem with the piston at TDC.
Of course this is with the cam in the default position. I am assuming retarding the cam will lessen the exh clearence and give more to the intake?
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by The Dark Side of Will »

Shaun41178(2) wrote:I am thinking about moving a tooth because I am was thinking of keeping the vvt cam, keeping the vvt assembly intact, just have it disconnected with a 7730 ecu. If this works, along with another bolt in mod, it will allow a very easy install into a fiero or other obd1 ecu setup. Which of course gives people way more options and a reason to install this engine over a 3400 or lx9 3.5
I dunno about that... think about the way people do 3800 swaps. They buy the engine, they buy brackets, they buy wiring harnesses, they buy PCM's and then bolt everything together and swap it out completely in a couple of weekends with iminimal downtime. The only machining required is the flywheel for a stickshift car and the only fabrication is the exhaust. They still run OBDII computers and still have all the original engine wiring, typically. The only gaskets replaced are valve covers because they leak profusely.

Approach that level of simplicity and you'll give people a reason to pick 3900's. (When did you change from a misanthrope to an altruist anyway?)

Dumbing down the engine management and the accessories to Fiero standards doesn't appeal to the simplistic market. That's self defeating and only appeals to people like Lou Dias who are basically anti-technology

That's asking people to:
1- Disassemble the donor engine that was running fine (Maybe they've never taken an engine apart before...)

2- HOPE:
2a- That your directions were accurate
2b- That they followed your directions accurately
2c- That they get the engine back together right

3- Pull the engine out of the recipient chassis well before installing the donor engine, thereby increasing downtime of the car

4- Transfer parts from the original engine to the new, while:
4a- Replacing gaskets that aren't leaking
4b- Making the accessory drive run worse, reduce belt reliability and increase belt maintenance requirements
4c- Losing the VVT that gives the engine its broad torque curve.
4d- Transitioning to an outdated, LESS popular, LESS capable ECM for which they're LESS likely to be able to get tuning support locally

I don't think any of these things are good ideas.

*I* think that the things the late 60 degree engines need to be more popular are:
1- Low mount alternator bracket that incorporates a mount for a dogbone to use the stock Fiero dogbone location
2- Plug/play harnesses
3- Alternate pulley end engine mount bracket

*ALMOST* everything else bolts up.
Shaun41178(2) wrote: So what I want to know is if in order to do this, I turn the crank clockwise while leaving the cam where it is,
Correct. This retards the cam.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

you make good points. Ill try to address each one.

the cam timing is for myself only. I am not expecting anyone else to perform this mod. I was looking for confirmation that my math was correct, if the info I was given is in fact correct. If others want to do it thats fine. The engine will run with vvt disconnected and still make decent power and still have a good tq curve. Josh Riedl made 206 whp through the auto tranny with a stock 3900 and no vvt. He might have had headers and a cable operated tb on it however as I am sure he didn't use the factory computer for the drive by wire tb. His peak tq was at about 4900 rpm

When swapping the engine, the factory timing cover, and coolant manifod don't need to be removed. This makes installation easy just new coolant hoses are needed. Alternator mounts high like on a 3400 so decklid trimming might be necessary. Its just small things like any swap. Joseph upson covered a lot of it with his swap.

Noone is tuning a 3900 that I know of. I think hptuners might have something however. Lets remember though these engines go in cars where people are the do it yourself type. So tuning themselves is a big part of it. I think the 7730 is very popular because of its easyness to find and software for self tuning.

Finding someone familiar with the 3900 and tuning it is going to be few and far between. Does the 3800 have a bcm and other electronics that need to be bypassed? I am not sure of that part. I know the 3900 has more electronics, and many people using a obd1 can use self tuning software. Megasquirt for someone wanting to spend extra will control the vvt just fine too.

essentially, its almost like a 3400 swap or lx9 swap, just more displacement.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by ericjon262 »

Shaun41178(2) wrote:you make good points. Ill try to address each one.

the cam timing is for myself only. I am not expecting anyone else to perform this mod. I was looking for confirmation that my math was correct, if the info I was given is in fact correct. If others want to do it thats fine. The engine will run with vvt disconnected and still make decent power and still have a good tq curve. Josh Riedl made 206 whp through the auto tranny with a stock 3900 and no vvt. He might have had headers and a cable operated tb on it however as I am sure he didn't use the factory computer for the drive by wire tb. His peak tq was at about 4900 rpm

When swapping the engine, the factory timing cover, and coolant manifod don't need to be removed. This makes installation easy just new coolant hoses are needed. Alternator mounts high like on a 3400 so decklid trimming might be necessary. Its just small things like any swap. Joseph upson covered a lot of it with his swap.

Noone is tuning a 3900 that I know of. I think hptuners might have something however. Lets remember though these engines go in cars where people are the do it yourself type. So tuning themselves is a big part of it. I think the 7730 is very popular because of its easyness to find and software for self tuning.

Finding someone familiar with the 3900 and tuning it is going to be few and far between. Does the 3800 have a bcm and other electronics that need to be bypassed? I am not sure of that part. I know the 3900 has more electronics, and many people using a obd1 can use self tuning software. Megasquirt for someone wanting to spend extra will control the vvt just fine too.

essentially, its almost like a 3400 swap or lx9 swap, just more displacement.
obd2 3800 swaps don't require a BCM, and if you're not into looks, you might even be able to get away with a mostly stock wiring harness. personally, I don't see the 3900 replacing the 3800 ever. not saying I dislike the 3900, but the 3800 is easy, it's abundant, and it's proven. by the time there aren't 3800's to swap, there won't be fieros on the road either. I prefer the 3900, but remember, the vast majority of fiero owners are total knuckle draggers like lou dias who barely know which end of the wrench to hold...
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

itb intake for gen 2 and a 3900 intake gasket. The floor was raised in the 3900 as well as the roof obviously. The roof was raised considerably more than the floor was raised.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

hmmm I don't know why the software is rotating my pics. in the preview they look correct. anyways. some are going to punch me, but dizzy clears the 3900 intake.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by ericjon262 »

why run a distributor on a 3900? DIS is a more efficient and flexible system, that has been thoroughly proven as well. why are you so obsessed with distributors?
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by The Dark Side of Will »

Shaun41178(2) wrote:itb intake for gen 2 and a 3900 intake gasket. The floor was raised in the 3900 as well as the roof obviously. The roof was raised considerably more than the floor was raised.
IMG_0492.JPG
Thanks for posting this! I'd been extremely curious about how well those intakes matched the LZx intake ports. Looks like it would take a lot of welding to get it to work.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

yea it would be a rediculous amount of work to get the itb onto 3900 heads. Better off using the gen 2 heads it was designed for.. A comparo pic of the lz4 upper intake to the 3400. The lz4 has a 75mm opening at the TB whereas the 3400 is something like 56. Word is that the 3400 intake flows so much better than the fiero and it does, but next to the 3900 intake the 3400 looks like a stock iron head one in terms of runner size and plenum size. The 3900 can do 300 hp with ease with the right cam and tuning.
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I also took apart the variable vane in the upper intake in case anyone wanted to see its guts.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

comparo pic of large port 3400 intake to the 3900 intake gasket.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

interesting detail on the block. you can see at the oil pan mating surface that there are notches in the LZ block to clear the big end of the rod and the bolts. I am curious if on a 3.5 lz4 crank(76mm stroke) in a lx9 block if notching of the lx9 block would be necessary. Purely based on using the forged steel crank from the lz4 in case your lx9 does not have a steel crank. This of course would make like a destroked 3.5 or what maybe a 3.1 or 3.2? I am guessing it would be close and probably would need to be notched.

Also thinking along the lines of a lz4 crank in the aluminum bow tie block if that block would need to be notched. FieroObsessed had to notch his 3.4 dohc block for the 3.9 lz9 crank.
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Interesting fact about the oil filter adapter. You have to use the lz oil adapter as the block does not have threads like the previous generations. Since the oil filter won't clear the cradle crossmember, you would have to use a remote oil filter adapter to use this swap. This has been documented in other swaps. Just showing a pic here.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by The Dark Side of Will »

The LZ4 and LZ9 rod journals are 2.250 like the 4.3 Chevy V6, and not 2.000 like the older V6/60 engines. The LZ9 stroke of course is the same as the 3100, 3400 & LX9 3500 at 84mm... any difference in clearance is related to the larger rod journals.

I don't see why an LZ4 crank in a Bow tie or older block would need to be clearanced.

However, a short stroke engine doesn't really have a benefit. The engine's power output is limited by the heads no matter what the displacement is. All that the shorter stroke does is require the valvetrain to be far more expensive than the rotating assembly. It's better to have as much displacement as practical to keep the engine's RPM range more reasonable and powerband broader.

I wonder if the Bow Tie block could have offset sleeves installed to become a 3900... (or 4100 by offset grinding the large journal crank like Upson did).
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

the 3900 has larger rod journals so I am guessing that the overall width of the big end is larger too. I will try to get a measurement and maybe I still have an older 3.4 rod around here somewhere to get a comparo pic.

I thought I would show the intake port on the head here. the roof of the intake port has about .1 of an inch which isn't a big deal, since the port on the intake manifold is approximately .15 of an inch smaller than the gasket. thus the intake port on the head is slightly bigger. Then again I am sure each head and intake will be slightly different do to core shifting when being cast.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

Some rod comparisons
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

I did some math on my rods. pending on how I measured I got two different mesaurements. One was 5,835 and the other was 5.786. Since they are both closer to 5.8 then 5.9, I am going to say my 2006 3.9 engine has 5.8 inch rods and not the 5.9 that gm specs says they are. this seems to confirm with others who have measured.

THey do have floating pins though and oil grooves in the bushing in the small end
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by The Dark Side of Will »

Shaun41178(2) wrote:I did some math on my rods. pending on how I measured I got two different mesaurements. One was 5,835 and the other was 5.786. Since they are both closer to 5.8 then 5.9, I am going to say my 2006 3.9 engine has 5.8 inch rods and not the 5.9 that gm specs says they are. this seems to confirm with others who have measured.

THey do have floating pins though and oil grooves in the bushing in the small end
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The LZ9 and LZ4 use the same pistons... they use different rod lengths to make up the difference in compression.

Measure the ID of the big end & divide by 2. This is A.
Measure the ID of the small end and divide by 2. This is B.
Take an "outside" measurement from the "upper" of the big end to the lower of the small end. This is C.

Rod center to center is A + B + C
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

That is the formula I used.

There is a bushing in the small end which is what gave me two different measurements. If I measured the ID of the bushing it gave me one number. If I measured the ID of the opening of the small end itself, it gave me a different number. Either way, its not 5.9

Gm documents lists the lz4 and lz9 as having the same CR. You claim they use the same piston. Lets say you are correct.

lz9 has roughly a 3.31 stroke or 84 mm. lz4 is 2.99 or 76mm. Divide by 2 and you get 1.65 and 1.49. If I had to guess, I would say the 3.5 uses the 5.9 inch rod otherwise the lz4 doesn't have the CR that GM advertises as it will be sitting .16 deeper in the hole compared to the lz9. I don't have a lz4 laying around however to know for sure.
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Re: 3900 headgasket on 3400 head and other lz9 info

Post by Shaun41178(2) »

found this link. on the right hand side there is a preview of this report. click on that, and on page two of the preview there are backpressure ratings as well as intake restriction numbers. maybe someone here can look at those and determine if they are good or bad.

http://standards.sae.org/cpgm2_09lgdlz9b/
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