Custom 3900 (LX9)

[thatscustom]

The plan is to build a high performance motor from this engine that is a little more extreme internally than we mite see from this starting point. (60*V6)

Some of what is in the plan:
modify or replace every thing!

OK a little more detail;
start with new engine,
lighten crank as much as possible,
6.125” long very light H beam rods,
forged high comp. Pistons,
solid roller cam and lifters,
steal full roller rockers (1.6:1???)not 1.7
titanium LS valves.
Long tube headers,
customized 3500 plenum,
ported heads,
6 coils, sequential injection, knock censer, broad band AFR,

9000 max rpm
475 hp na (Desktop Dyno estimate)

no vvt.,
no variable plenum.


The Michigan dismantler I bought this 06 motor from for a good price said it was new. That GM dropped it off the test stand. This was the last of 8 he bought years ago. I got it over two years ago.
You can see no staining of the pickup screen or windage tray. The witness marks are still on the pump. Every thing inside and out says it's new

[thatscustom]

lately I've been working on the crank. Knife edging the counter weights leading edge, radius the trailing end, drilling the rod journals, milling of excess materiel, and polishing. When I'm done with this I can finely get the journals ground down from 2.250 to 2.000 for the new rods. The pistons must be notched, polished and balanced before I can have the crank balanced, and the heads must be done before I can do the pistons.

[thatscustom]

OK so I just put up a lot of crankshaft photos. If you have a question I will try to answer them.

[thatscustom]

I have Scat rods. They look real good I think. But will need the big end narrowed and chamfered on both sides to fit the 3.9 crank. Even custom parts always need to be modified.
With the stock rod siting on top of the new Scat rod you can see the difference in sizes ( 2 1/4” V 2”)
The stock rod is siting on top of the new Scat rod you can see the difference in heft. The Scat rod is more refined, more detailed, with all unnecessary weight removed.
The new rod dose not look much longer. You can see where mass has been removed on this end too.

[thatscustom]

This is one of the 6 1/8” long rods I'm using. The big end I narrowed in a lathe to fit the 3.9 crank. Here I am cutting the chamfers on the bearing to clear the radius on the crank. It needs to be done on both sides of each one. I only did one rod and one bearing as it is a learning effort for me and I may change the way I do some of it for the six I will use in the motor.

[Guest]

That crank looks like it might be ruined. You drilled through the journals?

Making things lighter does usually mean you have the ability to rev highwe but the crank weights are so close to the centerline that the moment of inertia is different then if you removed weight from the piston and small end of the rod.

Its like a tire. The less weight furthwr out from the centerline of the axle the more improvement you will see. The crank in this instance would be your axle.

The balancing of your rotating assembly if even possible now is gonna cost a good amount of money

I kept my crank stock in my 3.9 build. Its forged from the factory and will rev to 8k as is without breaking

[thatscustom]

http://www.speedwaymotors.com/Callie...383,24477.html

Thanks for your comment Bigcheese

In the link above you can see a SB Chevy crank. The journals are drilled tho they look like bigger holes than in my crank. Mine are drilled 5/8inch. There counterweights are undercut, but much more than I did. Looking closely you will see the mains are drilled in this SB crank, but not in mine. (yet! Too difficult?)

My crank will not be as extreme as this commonly available small black Chevy cranks.

The balance shop I talked to before I started this thought I may need to turn the o.d. of the counterweights to reduce drilling for balance. That will mean check the balance to calculate how much I can turn off safely. Then do the balance again and drill as needed. 1 ½ hours drive each way, and $190 each time I go there.

No this kind of crank work is not needed. Fun and educational yes. Needed no.

Yes this crank could be junk before I'm done with it, but not yet. That would be an expense I can't really afford. But you need to exceed your limits before you can define them. Or...um...ya...a...that...and-its shiny

[thatscustom]

oops I didn't address all of you comment.

My pistons are a lot lighter than the stock ones. See pics below. 523.4g V 571.2g

The longer, lighter rods also change the balance calculation as do the smaller rod journals on the crank. Long rods reduce piston acceleration at a given RPM. That reduces strain on parts and allows a higher rev. And the small end of the rod is a lot lighter. That photo is in entry #4 the stock rod is on top of the new rod. Big difference. I have not built a rig yet to weigh the separate ends of the rods. It is on my to do list.

Why use lighter pistons and rods and not lighten the crank as well. If I was building a SB or LS I could just buy one. But for this motor you must do it yourself. No other option for a 3900 60*V6. None. Stock or diy that's it.

[Guest]

Yeah, I've seen plenty of V8 cranks that are lightened that way, drilled through the rod journals.

However, they typically use larger journals than you're going to be using and with the way that the 60 degree V6 rod journals are aid out, the larger journals are for strength, at the slight expense of increased bearing surface speed and small weight penalty. This is one reason why I'm keeping my LZ9 journals large. The old small journal cranks before 1985.5 were notorious for breaking in completely stock engines. Then in 1985.5 the journals were increased in size and far, far fewer cranks have been known to break, only the only ones I've heard of sounded like they were abused and or pushed to limits with power adders, sometimes both. Granted these were cast iron cranks and the forged steel should still be far better, I just don't believe the slight weight loss and slower bearing surface speed is worth the risk.

I'd be interested to see how that pans out though.

[thatscustom]

Raven, I find your comment somehow, exciting. I never expected to see "increased bearing surface speed" cited. Wow. And rod journal overlap, or lack of, is a concern.

I know in some big blocks (fords I think) bearing surface speed was a problem, but not a part of my decision here.

Unlike that of a 90 degree there is a lot of materiel between adjacent journals in the 60 degree, so I hope to be OK there.

On the journal size, some NASCAR builders are using 1 7/8inch rod journals. They make more than 100 HP per cylinder, two cylinder rods on each journal. I "hope" to to make about 80 HP per cylinder, one rod on each journal.

I can't fined my paper right now but I think I'm reducing the stroke by .027inch so I can use "off the shelf" pistons and rods.

At this stag I do not plan to use a power adder. All motor all the time.

Thank you for not saying "you can't do that"!

George

[thatscustom]

In this picture you can see the water cross over has had all the extra stuff cut off then smoothed. And the timing cover is being customized for a remote water pump as well as vvt removal.

[Guest]

You get the ti valves yet?

[thatscustom]

Bigchees;
Yes.

The Dell West titanium LS intake valves are larger, 2.000 in OD, and more than 31 grams lighter. The distance from the seat to the lock groove is the same. The margin is thicker and the tip is .050 longer from the lock groove to the end on both, in. and ex..

I got the titanium valves for less then stainless steel valves and they have never been run. The exhaust were installed. Then at the end of the season removed and sold. Two of the intakes have what looks like water spots on the stems, however I can't feel them or measure a difference. Besides I only need 6. And they have an anti ware coating.

Valves are a critical place to increase rpm's safely.

[Guest]

hmmm you bought them used. I was hoping you had a part number or something. Curious if a 2.0 valve is worth it I think someone else tried it and flow results didn't reflect the amount of work to put in larger valves. I was looking to run stock sized intake valves but ti. I lost a couple of vlaves and saw some aftermarkets but I don't know their weight and I don't want something heavier than stock

[thatscustom]

Bigchees;

Yes they are secant hand but not exactly "used" and not listed by part number but by description. Sorry. When I can I will get a number(s) from the manufacture(s) for the part I want and then do a search for that number at the big parts houses. With a known low price I then search Google. Race shops tend to buy more than they need then sell the extra when no longer needed. Specialty houses sell the over stock as well as used race parts. It takes time but can be worth it.

Manufactures will have more info than the stores some times. So it can be good to look to them first. But I agree with you it can be hard to find all the info you may want. Especially for these 60*V6s.

That said Dell West dose not list LS valves or valves of the size I have. They charge $7.00 to $12.00 additional for each custom valve.


The titanium LS exhaust valves are 1.550, stock 1.525. I need a new 9V battery to tell you the wights though.

Stainless steel is only a little heavier than steel so a pro flow valve with the undercut stem may be less than a stock one.


http://www.ebay.com/itm/5-16-Del-Wes...dZFKLD&vxp=mtr

these guys have two sets of used ti. ex. valves that look close. This one for $150.00 and another for $225.00, 5/16" - 4.965" - 1.550". I don't see intakes here or on google today.
Check your valves and keep searching until you find a good deal on good parts.