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Old 12-13-2006, 10:13 PM
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Blower pistons

Im getting ready to buy myself my xmas gift, im getting my pistons for my 671 blower build.
i have been reading is my street supercharging book that stated that when you have forged aluminum pistons they require more clearence because of the diferent expanding rates of the block and pistons.
the questions i pose is i have a 350 bored 40 over, and i plan on gettin 64cc aluminum heads from white performance, and i need help with pistons selection.
i want to achieve a low compression ratio something on the lower end of 8 to 1 and i dont really know about what to order keeping in mind that i need extra clearence from the aluminum pistons and i have a 40 overbore.
i really like summit racing because of the amazing customer service i have had with their tech department so i have pretty much been looking exclusivly with them.
does anyone have pistons with a good dish they have had alot of luck with?
THanks alot
Marc

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Old 12-14-2006, 07:30 AM
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Marc,
If your block is good at .040 over, then you just need to order pistons for an .040 over nore. The clearance is built into the piston. What I mean is a cast .040 piston will be slighlty larger in diameter than a forged .040 piston.

As far as piston brands and types go, much of it is personal choice. Do you already have the 64cc heads? If so you have to work around them. If not it might be easier to use 72cc heads. Since it is a 350 there are pistons out there that will work fine with 64cc heads. That can be a problem with large cube engines.

Depending on the boost level and use of the engine/car that will determine if you need a dedicated blower piston. It is a good idea in either case. Check with SRP, J&E, Probe, I think you can get SRP through Summit. I will do a little looking for you and come up with a SRP part number to get your compression where you want/need it (8.5:1 or lower).
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Old 12-14-2006, 07:48 AM
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SRP Piston Compression Ratio
P/N ci bore stroke rod 58cc 64cc 70cc dish oversize
139633 357 4.040 3.480 5.700 9.0 8.5 8.0 -24cc 0.040

Fits 3.480 and 3.500 stroke. The pistons weigh 503 grams

These pistons will work fine for you, they are excellent quality as well. I would shop around to see who has the best deal. Check with Doug Herbert Racing, they have some good sales sometimes.

I hope that helps.
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Old 12-14-2006, 08:10 AM
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I just built a blown 350 chevy. I did not come across any forged blower pistons in .040" over. I have this motor built but do not have running. I also bought the heads from Whites. I took the heads completely apart and checked them all out. I found they were just perfect. All the valeves lapped in fine and all the spring heights were correct.
If it was me I would find another block, because I don't think you will find an inexpensive blower piston .040" over. I am sure that Venolia or Aris will be happy to make a set for you. But finding TRW, Speedpro won't happen.

Are you going to run a double key on the crank snout? Every one I talked to reccomended it. I bought the Eagle forged crank with a double key and a BDS blower hub for mine to be safe.
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Old 12-14-2006, 08:41 AM
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RPMs,
Wait a second. I just listed a .040 blower piston, I'm not sure why you couldn't find one. There are plenty of them out there. My blown engine is .060 over.

Here is a direct link to SRP blower pistons for an .040 350 http://store.summitracing.com/partde...0&autoview=sku Only $530

Double keyway is another point that can't be agreed on in many cases. If you have a big block snout then go for it. Personally I went with an extended single heyway and a crank hub.
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Old 12-14-2006, 09:32 AM
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Those pistons will work, but I thought of those as expensive pistons. I bought some TRW-Cleveites forged for about $320 for the set.

On the double key thing I talked to several who had a single key fail and it ruined the crank. With what I saved on the pistons, I spent on a better crank and hub.
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Old 12-14-2006, 10:57 AM
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There are two ways to look at it. There is nothing wrong with a double keyway, the issue is you are taking more material from an already small snout. When I say I use a single keyway, I don't mean a stock key way. I had the snout cut to accept one long key, this kept the loss of material to a minimum. Both ways will get the job done. Running a hub eliminates much of the stress anyway. Do you remember how much your TRW's weigh? While $520 isn't cheap, it is not expensive when it comes to an excellent quality piston. I don't remember what I paid for my Wisecos but, I know it was more than $320
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Old 12-14-2006, 02:01 PM
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another question i was thinking about is i am getting a crank and if i need a new crank would it be beneficial to get one with a 3.750 in. stroke and have my block made with extra clearence?,
just a thought i had in my head
let me know what you think
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Old 12-14-2006, 02:20 PM
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and is forged aluminum really the only way to go? is there seriouse drawback to cast aluminum?
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Old 12-14-2006, 02:23 PM
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Keith Black Hypereutectic Pistons: these have 28+ cc http://store.summitracing.com/partde...5&autoview=sku
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Old 12-14-2006, 03:04 PM
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I would stick with forged. Even though they are heavier than cast they arent brittle like cast and hyper. But I guess it depends on what kind of boost you will be pushing in. I would go forged for insurance. Im sure some will agree/disagree with this statement though.
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Old 12-14-2006, 03:22 PM
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Quote:
Originally Posted by DeathRattle
I would stick with forged. Even though they are heavier than cast they arent brittle like cast and hyper. But I guess it depends on what kind of boost you will be pushing in. I would go forged for insurance. Im sure some will agree/disagree with this statement though.
Most performance forged pistons are much lighter that cast or hyper pistons.

tom
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Old 12-14-2006, 04:12 PM
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If you are building it and dont have the pistons yet it is crazy not to get forged.
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Old 12-14-2006, 04:30 PM
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kb pistons

keith black -22 dish piston 230 for set
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Old 12-14-2006, 08:28 PM
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Forged pistons are a MUST for a blown engine. If you plan to make any decent power with it don't even think about non-forged pistons. If you detonate it one time without forged pistons the motor will be history. For street rods and VERY mild blown engines you can get away with less than forged pistons. I am talking about 4lbs of boost and less. It's not worth saving $200 and having a time bomb for an engine. How much will you save if/when the cast or hyper pistons shatter?

As far as going with a longer stroke (building a 383), yes it is worth it but, only if you don't have 64cc heads. If you already have the heads you will have problems finding a deep enough dish to get the compression down with teh added stroke. I had to open up my 72cc heads to 75cc's to get my compression down with a 3.75" stroke. I was working with 6" rods, if I had 5.7" rods I could have gotten by with 72cc's.

You have been reading up on blown engines. Go back and see what they say about forged pistons.
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