402 Question? - Team Camaro Tech
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post #1 of 6 (permalink) Old Mar 25th, 10, 09:43 AM Thread Starter
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Clint
 
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Location: NE Ohio
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402 Question?

I have a 402 that that I'm in the process of having the block machine work done and would like to build it so its mostly stock and will run well on pump gas. The heads that come with it are #3964290 closed chamber 101cc heads. Can I use this head if I just want a mild engine or will the compression be too high? Can someone recommend a piston to use?

Thanks,
Clint
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post #2 of 6 (permalink) Old Mar 25th, 10, 11:19 AM
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Ron
 
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Re: 402 Question?

With a 4.125" Bore / 3.76" Stroke, 402ci Closed Chamber 101cc head and OEM Stk .019" Shim Head Gasket, you require a Closed Chamber Piston with a dome between 24 to 28cc's to give you between 10.5 to 11:1 Static Compression Ratio where you can run a Strong Cam and still use Pump Gas. I would lean toward the 10.5:1 side of the equation and choose a cam with a duration to produce between an 8.1 to an 8.2 DCR.

Either use the .019" Shim Head Gasket giving a .044" Quench or 0-Deck the Block and run a .039" Composite Gasket.

Look at the Speed Pro Forged Line of Pistons at Summit. Closet I could find for that 101cc Closed Chamber was this Piston ZL2240NF - 21 cc Dome to give you a 10.1:1 which is a Safe Static compression for Pump Gas. You have to consider that you have to match available Head and Piston Castings to achieve your desired Static Compression. If you are running verily Tall gears like 3.31's or 3.08's, I would recommend the Comp Cams XM270H-12 1600-5800 270-286 Adv [email protected] .544/.547 112 Cam to give you an 8.2 DCR to Maximize Torque in a Small Displacement BBC perhaps the XM278H-12(wicked 10:1 454 Cam) with 3.55 and lower Gears.

Play with P. Kelley's DCR Calculator here: http://www.empirenet.com/pkelley2/DynamicCR.html
and Comp Cams Camquest here: http://www.compcams.com/Camquest/
Checkout Mortec Site for BBC Casting#: http://www.mortec.com/bbc.htm

The 396 and the 396 + .030" 402 are the same engine where all 396's had closed Chamber Heads but 402's had lower Compression and used larger Volume Open Chamber heads. So what you are doing is putting a 396 Head on a 402, which likely had open chamber pistons, and must use Closed Chambered 396 Piston.

You can NOT use the 402 Open Chamber Domed Piston with a 396 Closed Chamber Head but can use Close Chamber Domes in Open Chamber Heads; however, you have to mock the Head Assembly to the Block and Scribe the Bore to the Cylinder Head and Open the Chamber as the Pistons can strike the outer Diameter of the Combustion Chamber, plus I would confirm Clearance using Plumbers Putty.

You will find that most Hi-Perf aftermarket MK IV Piston Dome Volumes are quit large and geared toward the 113, 118 and 122cc Open Chamber Castings; however, you do have a better flame with lower domes. I would say that 10.1:1, ZL2240NF/290, Combination above would be about Ideal with that XM270H-12 Cam on Pump Gas; besides, nothing sounds better then a 112LSA Cam ;o)

Always CC the Heads to Confirm Chamber Volume as they are not always Specked as GM Advertises.

Top her off with a 750 Holley/Edelbrock RPM and Headers - 7/16" Push Rods and I recommend 2" ARP Rocker Studs / Roller Rockers like Pro Mags or Harland Sharp.

Your looking at approx 430 to 445 Hp with a HFT Cam perhaps 460 with a SFT Cam.

Everything depends on what you intend to do with your ride - Tranny/ Gear ratio's... etc and how much you want to spend. I given you a Low Cost Solid Performer solution that should last for Years on Pump gas without much Maintenance.

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Last edited by Z15CAM; Mar 25th, 10 at 07:45 PM.
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post #3 of 6 (permalink) Old Mar 26th, 10, 07:31 AM Thread Starter
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Clint
 
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Re: 402 Question?

Ron,

I cannot thank you enough for taking the time to reply back in such detail. It's people like you who help us new guys out that make this site and hobby great!

I will be looking into those pistons today. Does the negative value for the dome (-21cc) make the piston a flat top or dished to keep the compression lower?

Thanks again,

Clint
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post #4 of 6 (permalink) Old Mar 26th, 10, 09:03 AM
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Tom
 
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Smile Re: 402 Question?

A flat top piston has a 0 value.

I have seen domed pistons listed both ways. + or -

Two ways of thinking. A domed piston with a + can be added material (Dome) to the piston top, or it can be a - to take away volume in the engines combustion chamber !

It usually will say dished, flat top, or domed.

69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1

Last edited by TJS69; Mar 26th, 10 at 09:13 AM.
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post #5 of 6 (permalink) Old Mar 26th, 10, 03:59 PM
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Vall
 
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Re: 402 Question?

I used this engine kit on a friend's 402 when we rebuilt it, and it runs fantastic on mid range pump gas:
http://www.summitracing.com/parts/FEM-CSMHP718-300/

It came with TRW forged pistons too!
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post #6 of 6 (permalink) Old Mar 26th, 10, 05:11 PM
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Ron
 
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Re: 402 Question?

That's a NICE Kit with Forged Pistons to boot.

Here's 2 concerns I would have regarding the KIT:

#1 - If Clint intends to use the Closed Chamber 290 101cc Heads, I would make a phone call to ascertain whether the Pistons in the Kit are for Closed Chamber and the Mfgr's PN plus Dome Volume.

#2 Summit claims the Pistons in the Kit have "Approximate compression ratio 10.58:1 with a 109.44cc head." which means the Kit Pistons have approx a 33.6cc Dome Volume for 109.44cc Chamber Heads which is probably a 402 Open Chamber Design. Providing the Kit Pistons are for a Closed Chamber Head, these Pistons would produce a 11.62 Static Compression in a 101 Closed Chamber and way too much for Pump Gas.

Vall - What Cylinder Heads did you use in that 402 Rebuild?

Definitely get the Pistons Manufacturer and Part # in the Kit, verify Dome Volume and compatibility with the 396 290 Head Castings.

The KIT does seem to indicate the Pistons are for Closed Chamber to accommodate the 109cc Closed Chamber Head and make a 10.58 Static Compression; but, the Dome Volume is BIG and will produce a 11.6 Static Compression in a 101cc Cylinder Head which is too much for Pump Gas. I suspect the Kit Pistons are the ZL2242F with the 37cc dome and yields the 10.58 Static compression because they use the .039" Composite Gasket but this throws the Quench out to lunch.

If Clint is to use the Kit he would require the 109cc Closed Head to hit about a perfect 10.58 Static Compression and run that XM278H-12 Cam and put out 500Hp or request the ZL2240NF - 21 cc Dome Piston in the KIT if he intends to stay with the 290 Heads with a 10.1:1 Static Compression and say the XM270H-12 Cam and put out 450Hp.

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Last edited by Z15CAM; Mar 26th, 10 at 07:19 PM.
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