6 inch rod 406 on Street - Team Camaro Tech
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post #1 of 19 (permalink) Old Aug 11th, 16, 04:28 PM Thread Starter
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6 inch rod 406 on Street

I'm considering using a 6-inch rod in my 406 but I am concerned about short piston skirt and the Piston pin intruding upon the oil ring.

Is a forged piston 2618 material and a 6 inch rod a bad combination for Street use in terms of oil consumption and piston slap?

I'm not necessarily talking not about a daily driver, but it will be Street driven with

intended uses of: Street, track, and auto-x.

The benefits appear to be lighter-weight Pistons and easier crank throw clearance for internal balance for 6" rod.

Do the cons outweigh the benefits?

Any comments are appreciated, thanks C68.
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post #2 of 19 (permalink) Old Aug 11th, 16, 06:06 PM
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Re: 6 inch rod 406 on Street

I thought so.

I don't recommend 2618 for the street as that is for blown or power adder combinations that need the added ability to withstand the added heat. You want a 4032 alloy with it's higher silicone content to hold the skirt's shape on the street. Pistons catch fire at about the combustion temp of gasoline.

It is only the brief amount of time that the cooler piston is exposed to the heat that allows them to live in an internal combustion engine. Run a hot enough power level long enough and you will see green flames (caused by the spark plug electrode burning due to the intense heat generated by burning aluminum). Aluminum burns white hot and looks like an arc lamp. Tell tale is silver particles of aluminum oxide coming out the pipes.

Like I said I built a 406 with six inch rods and ran my SRP pistons on the street for seven years before I broke the stock block into three pieces.







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post #3 of 19 (permalink) Old Aug 11th, 16, 06:24 PM
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Re: 6 inch rod 406 on Street

My old combo was a 406ci w/ 5.7" rods....worked well, spun hard. 7500rpm shifts were the normal

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #4 of 19 (permalink) Old Aug 11th, 16, 06:36 PM
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Re: 6 inch rod 406 on Street

I also ran a 406 with 5.7" street car

The guy I sold it to beat the crap out of for years with no issues. Speed pro forged Pistons
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post #5 of 19 (permalink) Old Aug 11th, 16, 07:02 PM
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Re: 6 inch rod 406 on Street

Quote:
Originally Posted by Vega$69 View Post
Speed pro forged Pistons
TRW's here (now speed pro I believe)
If I remember...they were for a 377", but worked great.

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #6 of 19 (permalink) Old Aug 11th, 16, 07:05 PM
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Re: 6 inch rod 406 on Street

I have run 6.0" rods in the last motors I have built , using light weight pins thru the ring glands. I have done this with bbc and my last sbc motors. The most proven is my 383 with srp pistons on Compstar rods on a Scat Profiled crank. .

They may be a little hard for some guys to accept or install or remove pins, but I have not had issues in the last 30k miles over long Power tour cruises. Yes , there is some unsupported oil rails but the rings have proven themselves.

Don
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Last edited by zdld17; Aug 11th, 16 at 07:20 PM.
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post #7 of 19 (permalink) Old Aug 20th, 16, 10:29 AM Thread Starter
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Is an 817 2 Bolt block using main studs worth putting the money into?

Does keeping the Piston the in the hole add any significant strength to the deck?
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post #8 of 19 (permalink) Old Aug 20th, 16, 02:35 PM
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Re: 6 inch rod 406 on Street

2-bolts are "said" to be stronger and a little hard-block can only help with the strength.

I had the same block once upon a time with a little fill too.

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #9 of 19 (permalink) Old Aug 20th, 16, 03:04 PM
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Re: 6 inch rod 406 on Street

Back to the rod length issue, if you are not familiar with the issue, Read this.

Connecting Rod vs. Stroke Analysis: panic Tech Paper No. 1

As for the two bolt block issue, I am not familiar with the one is question having two bolt mains. But I will mention I ran a 468 bbc with two blot mains in an automatic car with a 8" converter , the car weighed 3150 an ran in the high 9's. I never had issues with this combo at every tear down, but I am sure much of the racing public will opt for the 4 bolt blocks. If you set on 4 bolt mains, your two bolt block can be "splayed" drilled but If your going to that expense, consider an after market block. You may be going bigger , sooner or later.
I realize your question was concerning a sbc block but just thought I would mention this. Hope it helps thinking.
As for main cap studs or even head studs, I would recommend them in what ever motor you want to build unless is a grocery getter.

Don
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post #10 of 19 (permalink) Old Aug 20th, 16, 03:38 PM
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Re: 6 inch rod 406 on Street

Yes the two bolt block is the stronger of the two. The older four bolt blok has thiner main webs which promote cracks that were thickened up on the newer two bolt blocks. My '509 block was converted over to a four bolt with half studs and bolts that where threaded into the sides of the block instead of the main webs for additional strength (you can see the 509 block casting number in big letters on the side of the 1978 block out of a one ton Suburban).

I was warned by my machinist that these stock blocks are not very reliable beyond 500-550 horsepower.

I drove this engine for seven years and it made more than 500 horsepower, but ultimately it broke the block into three pieces (those cracks in the main webs I was talking about). For the amount of money I spent on just parts ($13,600) I should have gone with a Dart Little M but I was just doing a "stock rebuild" not a another race car engine. But the wife wouldn't believe it was a stock rebuild with a block dropped off the back of a semi as she had seen too many of my other builds start out that way to fall for that lie again.

This motor with 305 decals sat in my 1989 Caprice four door for a long time as a daily driver that I could motor into the elevens. It was basically a bait car that I trolled around before going home to get my slicks (which were attached to a 1985 four door Impala with a 582 BBC under the hood that was painted to look like and had the newer front and rear lights to match the '89 (the old bait and switch tatic).

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post #11 of 19 (permalink) Old Aug 20th, 16, 04:55 PM
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Re: 6 inch rod 406 on Street

Dave, correct me if I'm wrong.
Factory 2-bolts were stronger than factory 4-bolts blocks due to the "meat" between the siamese cylinders and a splayed 4-bolt was also better than the factory 4-bolts due to where the 2 splayed bolts went further out from the inner 2 bolts having more meat between them.

This is what I vaguely remember and why my machinist wanted to do the short fill and stay with the 2-bolt.

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #12 of 19 (permalink) Old Aug 20th, 16, 06:01 PM
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Re: 6 inch rod 406 on Street

The strength improvements were under the cylinders. The cylinder walls were a fraction of an inch thicker than the first blocks poured due to cracking complaints from the warranty department, but the block wasn't cracking the heads were (I occasionally fail to understand the thought processes of some GM engineers). The factory four bolt block used main caps that looked the same as the four bolt main 350 block (only super sized for the larger crank journal) which is to say all four bolts going straight down.

My block used steel main caps that were line honed to fit the block. They utilized an angled outer bolt to grab more meat in the casting and to spread out the forces that want to make a cap walk in it's saddles. This is a better approach than just adding two more bolts straight down into the webbing. Though the extra bolts provide for more even clamping they are still secured by the webbing under the cylinders so the forces are concentrated there. That area has proven to be weak long after the block went out of production. Putting more bolts into the block webbing isn't doing anything to alleviate the problem.

With a stock block I might even consider a main bolt girdle ( commonly used on SBF as a an aide to prevent the block from splitting down the middle the way a few 307 LV2 Olds engine do as well as Windsor blocks when pushed too hard. Though had I torn down the motor for periodic inspection I probably would have discovered the cracks before a catastrophic failure, but it wasn't a race engine

You have to keep in mind this is a basically a 396 (402) BBC that utilizes SBC heads. The stresses are the same in the SBC 400 as they are in the BBC 402 and you really can not compare the two short blocks. The engineers saw what was needed to swing that long of a stroke in the 396 and built the bottom end of the Mark IV stronger than the previous 409 or the SBC for a reason (and it wasn't because they were trying to hide 46 pounds of cast iron). The engineers also were aware of main webbing failures in high reving 409 engines (which is why there are so few 409 car blocks surviving until today).

It was only because the Impala had grown so heavy that Chevy was forced to introduce a two barrel 400 cube SBC that didn't offer a manual variant from the factory for that line as well as light pick-ups. It was never intended as a race engine.

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post #13 of 19 (permalink) Old Aug 22nd, 16, 05:20 PM
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Re: 6 inch rod 406 on Street

Mahle with a 1.125 comp height don't have pin holes protruding into the oil ring land. IF that's a big concern, I wouldn't be though.

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post #14 of 19 (permalink) Old Aug 22nd, 16, 06:15 PM
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Re: 6 inch rod 406 on Street

Cowabunga Chief, most of us don't run .043 rings on street but those pistons offer an option here in the states.

Don
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post #15 of 19 (permalink) Old Aug 23rd, 16, 04:25 AM
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Re: 6 inch rod 406 on Street

They are 1.5,1.5,3mm rings. That would be ~.059 rings imperial. Only a few bits and pieces left like pulleys and brackets before I fire up my 6" rod 400 here. I use a Dart block, forged bottom end with those Mahle pistons. I chose 6" rods mainly because of rod angularity and less cylinder wall thrust than with a 5.7. Look at the stock 350, they have a 1.64 rod ratio and runs forever, a 6" rod 400 will be a 1.6 rod ratio. 1.6 or above is a good place to be IMO.

That's not saying that a 5.7 rod won't work, or would make less power, I just strongly believe that if you would put a 5.7 rod 400 up against a 6 inch rod 400 and let them run ten thousand hours under load, you would see more cylinder wear in the 5.7 rod combo.
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