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Dome pistons


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Currently i have a stock 1994 SBC 350 block and rotating assm. The pistons a Dish pistons with 4 valve relief cut into them. I think that gives me a compression of 8.75:1.

 

Since my goal is to get 300hp at the wheels would it be a good idea to switch out the pistons with a set of Dome 0.125 pistons which would bring my compression to somewhere between 10.5 to 11:1. The cost of the new pistons is only $170 and seem like they would provide a good jump in HP.

 

I will be running a set of Vortec heads, and Holly 600cfm carb, and a Comp cam Xtreme Energy 268 cam. (Duration @ 0.050":224° / 230°; Max Lift w/ 1.5RR: .477" / .480")

 

 

The pistons i want to buy:

 

http://www.ebay.com/itm/STD-125-Dome-Pistons-350-sb-Chevy-5-7-Rod-Coated-Skirt-sbc-Speed-Pro-H618CP-/170739946851?_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D5%26po%3DLVI%26ps%3D63%26clkid%3D5515721386079550418

Edited by logan1
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i cant see the add but as long as the CH, pin dia and weight are roughly the same you will be good. You will have to get the motor re balanced tho but that isnt bad. 11:1 is almost in the range of haveing to use a higher octane gas just keep your ears open for ping.

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from what i have been reading online over the last few hours; i dont this the dome pistons will work with my vortec heads. I think the best i can hope for is flat tops with 2 VR's.

 

below is a picture of my current pistons.

 

IMG_0348.jpg

 

 

Since i pulled my motor from 1994 chevy shortwide i looked up the spec for the 5.7L 350 that came with the 94 truck found that it had a compression 8.75:1 and was rated for 190hp and 300ft.lb of tq.

Edited by logan1
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Suggest going to 18cc dish piston such as KB-142 crown configuration. Deck the block to piston in the hole at .005". Use .030" thick MLS head gasket. This yields good squish. Machine down the Vortec Head valve guides for higher lift camshaft. Use good springs in the heads. Will need 360 HP at flywheel to get 300HP at rear wheels.

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ok so i made an excel sheet to see how much it would cost to build a sbc 350 that would give me 300hp and the wheels and i'm shocked at the price. I was heading into this think it was going to be a budget build. This so called budget build is gonna cost me a fortune. I wrote down all the numbers and it looks like its going to be way more expensive than i had expected. The expected cost is price of parts off ebay and other internet sites and the actual cost is what i have bought so far.

 

enginebuild.jpg

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1+

 

I wish the T5 I bought was only 300!

 

I would go with a world class if pushing 360 HP. The normal ones are for 305s pushing only like 220 ft/lbs. (Non world classes still very hard to get for 300...)

 

I'm thinking this is a little on the conservative side as well only 200 at the machine shop? An all the Mis stuff is going to be more than 200

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Flat tops would be the best for a 350. However flat tops with 64cc chambers (vortec heads) could make the compression too high for a 268 degree cam (depending on deck height of the piston).

 

Do you know the piston deck height that you have now? (how far the piston is below the deck at tdc).

 

I would shoot for 9.5:1 cr with that cam and those heads. But 8.75 isn't bad. 9.5:1 would be worth about 3% in extra power over 8.75:1. That will be 9hp on a 300hp engine.

 

The good news is 8.75:1 should allow the use of 87 octane fuel which is a plus. Furthermore, you could more safely add a little shot of NO2 with the lower compression.

 

If it was my build, I would use.......

Hyper 4 relief flat top pistons (cheap),

Vortec heads with proper springs and the typical machine work on vortec heads required for extra lift,

280H compcam, not a fan of xtreme cams due to noise and prone to go flat.

RPM intake with a square bore, not airgap rpm due to slow carb warmup on the street

3310 holley 750 cfm

Long tube headers would be best but block huggers will work,

Dual 2-1/4" from the headers, H-pipe, then dual 12" dynomax bullets, then a Y-pipe, to a single 3 or 3.5 pipe, then a turbo muffler on end.

3000 rpm stall if you have an automatic, 10 inch converter

3.90 gear would be best for acceleration, but almost any stock Z gear would work due the the light weight of the z.

20 degrees initial timing, 36 degree total. Then get an adjustable vacuum advance and add another 10.

Finally, use ZDDP oil additive to make the cam live a long life. www.zddplus.com

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  • 4 weeks later...

avoid those cheap pistons.

 

If your fuel quality is not par with your cylinder pressure and timing lead,

then these cheap pistons will over heat the rings til the ring binds up in the bore.

the ring lands fail,

eventually to the point of ripping the head off the piston. :banghead:

 

Buy a Mahle Motorsports piston or maybe a J&E.

Both companies also have quality rings.

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Replacing the pistons likely means rebalancing the rotating assembly, and buying new rings. You'll need to confirm piston-valve clearance using a mockup installation with clay. Even if everything fits mechanically without interference, as Pyro and others have mentioned, the performance gain is incremental at best. And if you currently have a fairly well sorted combination, changing one component tends to trigger a cascade of requisite changes to keep the overall combination consistent. That of course raises costs and promotes risk.

 

My recommendation would be to do nothing, assuming that you have a reasonably well-running engine, until you are ready for a significant upgrade in power. Then get the latest fancy aluminum heads, mechanical roller cam, forged pistons with the right compression ratio, rods, and so forth. The cost advantage of a Chevy small-block is in the low price of the as-is combo. Adding individual components to any engine, no matter how common, quickly gets to be expensive.

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Some really decent advice above.

The flat top piston would be a sensible choice.

A small aftermarket head would be nice, just not a priority if 300- 400 hp is the goal.

Stay with a hydraulic lifter. I expect you're completely sold on a larger cam profile. Yet it does not take much duration over stock to make over 300 hp.

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