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opinions on engine build 355 sbc
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tirefryin_s10
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Joined: 03 Dec 2003
Posts: 70
Location: edmonton,alberta/canada
1925.12 points


1981 Mazda RX-7

PostPosted: Thu Mar 16, 2006 1:09 am    Post subject: opinions on engine build 355 sbc Reply with quote

ok so for my new rx7 i am planning on a mild motor to start then a big cube nitrous motor later to get me goin as fast as i wanna go .. im gonna give a run down of the engine specs and was wondering if i could get some opinions/rough guesstemates on power-thx neil

gm high nickel 4 bolt block
gm cast crank
moroso main bolts
windage tray
gm "X" rods with mr gasket bolts bolts
full rotating assembly balanced
keith black hyper pistons 10.25-1 w/64cc head
comp xe 274 hyd cam
dyna gear double roller chain
7qt pan
vortec heads decked to 62cc,.550 springs,3 angle valve job, mild porting
1.6 comp roller rockers
electric water pump
victor jr intake
holley 770 street avenger
msd pro billet distributor/coil/ 6al box
1 5/8 primary block hugger headers-2.5" mandrel Y pipe into 3" single with a flowmaster

and then a 100-150 shot of juice

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81 mazda rx7 V8 powered got my 12's too easy so now im hoping for 10's with the new 388 on spray -old combo-
Best et-12.59
best mph-114
on bald 235/60/15 street tires
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jonny_b
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Joined: 28 May 2003
Posts: 175
Location: Rogers, MN
5693.36 points


1979 Chevrolet Camaro

PostPosted: Thu Mar 16, 2006 11:02 am    Post subject: Reply with quote

Sounds like a pretty nice combo. I'd guess it at 420-460 flywheel horsepower. How heavy is the rx7?
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1979 Camaro Z28
355 cu.in. 5-speed man.
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jeep_406
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Joined: 12 Sep 2002
Posts: 1661
Location: Tewksbury, Mass 01876
53123.48 points


1972 Chevrolet Nova

PostPosted: Thu Mar 16, 2006 7:19 pm    Post subject: Reply with quote

Be interesting what others think. If you're going to spray it in the future I go for forged pistons.
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96capriceMGR
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Joined: 23 Aug 2003
Posts: 814
Location: New London Wisconsin
20327.88 points


1996 Chevrolet Caprice

PostPosted: Thu Mar 16, 2006 8:04 pm    Post subject: Reply with quote

If you haven't gotten a block yet consider a '87+ roller cam block. Roller cams are worth power and drivability and this would make using one cheaper. They are also "less desirable" to most uninformed folks so the purchase price can be quite low. Once you got into the 90s the rotating assemblies are VERY stout for OEM parts.
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disturbthepeace1
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Joined: 14 Jun 2003
Posts: 303
Location: Stanton, CA
10195.60 points


1965 Volkswagen Beetle

PostPosted: Fri Mar 17, 2006 2:47 am    Post subject: Reply with quote

I personaly dont have alot of experience with hyper t pistons. but ve herd that they dont like nitrous much and i would not push more then 150hp... basically you should treat them like if they were cast.......
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tirefryin_s10
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Joined: 03 Dec 2003
Posts: 70
Location: edmonton,alberta/canada
1925.12 points


1981 Mazda RX-7

PostPosted: Fri Mar 17, 2006 10:04 am    Post subject: Reply with quote

i mbuying the short block its already built with afr 195s it pushed a 3600 lb chevelle to 12.6 @2800 feet of elevation ... so i wont be changing to a roller block ... i have a 97 vortec 350 i will use for my next build ..... my car should weigh right around 2600 lbs without me so it shuldnt be bad for a full interior street car
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81 mazda rx7 V8 powered got my 12's too easy so now im hoping for 10's with the new 388 on spray -old combo-
Best et-12.59
best mph-114
on bald 235/60/15 street tires
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96capriceMGR
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Joined: 23 Aug 2003
Posts: 814
Location: New London Wisconsin
20327.88 points


1996 Chevrolet Caprice

PostPosted: Fri Mar 17, 2006 7:53 pm    Post subject: Reply with quote

Hyper pistons can be very good. The LT1 came stock with Mahle Hyper pistons guys have no problem as long as they keep it fueled, talking 400+rwhp NA + spray for years 150-200 single stage and some guys going to 280 over 2 stages Shocked . This bottomend should be VERY similar to that Vortec motor.

AFRs are an upgrade on gen1s but for the LT1s they kind of suck especially the smaller ones like the 195s. You said you are buying a shortblock which to me says different heads are in store, you can do a lot better than AFR these days keep that in mind while shopping.
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Smokin71RSSS
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Joined: 11 Jul 2002
Posts: 111
Location: Pasadena, Ca
2020.86 points


1971

PostPosted: Sat Mar 18, 2006 4:09 am    Post subject: Reply with quote

I know of someone on this board thats spraying hypers with something like a 150 shot. That would make me a little nervous but as long as you keep it out of detonation your fine.

For power it looks pretty stout. Vortecs are all the rage right now and they do make good power for a factory GM head. I'd guess your into the low 400's in HP. If you want I can run the combo through Engine Analyzer Pro.
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coppergmc
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Joined: 19 Dec 2005
Posts: 278
Location: Georgia
5857.30 points



PostPosted: Sat Mar 18, 2006 10:48 am    Post subject: Reply with quote

CHP or Carcraft did an article on a 350 w/vortec heads and the XE274 cam. I had the article printed to show a customer that wanted about the same engine. The magazine claimed something like 450hp. Of course, the magazines are in the business to sell parts. Copper
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clay
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Joined: 24 Nov 2002
Posts: 3209
Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Sat Mar 18, 2006 10:54 am    Post subject: Reply with quote

My take on hypers is that withstanding the cylinder pressure from a nitrous shot like up to 200 h.p. isn't a big deal, BUT they can't withstand detonation like a forged piston can. I think the difference is a forged piston can "flow" or basically bend under a detonation condition, but a hyper is a harder, more brittle material that basically shatters under the extreme pressure spikes of an improper tuneup. That's probably why OEM's like them, longer engine life due to a longer wearing piston. The only other thing I have read about is the top ring gap may need to be opened up more than a forged piston due to the higher ring location on the piston, but that may be on the larger nitrous shots. 96capriceMGR has seen a lot of evidence of the strength of hypers and I don't think you'll have any problems with the 100-150 shot you are talking about as long as you follow the manufacturers recommendations on fuel pressure and timing retard. Clay
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tirefryin_s10
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Joined: 03 Dec 2003
Posts: 70
Location: edmonton,alberta/canada
1925.12 points


1981 Mazda RX-7

PostPosted: Sat Mar 18, 2006 5:20 pm    Post subject: Reply with quote

well last year i had the exact same set up with a little bit less ocmpression and only 1.5 rockers and a performer rpm intake and it ran 114 mph i nthe 1/4 so i know it was making over 400 crank hp so im hoping with this set up it should make closer to 450 off the motor and then hit it with a 100-125 shot and hope for the best
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81 mazda rx7 V8 powered got my 12's too easy so now im hoping for 10's with the new 388 on spray -old combo-
Best et-12.59
best mph-114
on bald 235/60/15 street tires
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af2
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Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Sun Mar 19, 2006 1:40 am    Post subject: Reply with quote

My concept is. Put the best parts in and hope it wins!!!! The Hyper pistons are a step above stock. They have high silicone to make them able to withstand high temp and that is it. For $150 more you get forged pistons that are WAY better and don't have the breakage you will see in a hyper piston. I have been waiting 2 months to get my pistons and that sucks!!! But when I get them it will bee all good. Adam
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Big Dave
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Joined: 04 Dec 2005
Posts: 2646
Location: Tampa Florida
119973.02 points



PostPosted: Sun Mar 19, 2006 8:20 am    Post subject: Reply with quote

Hypereutetic pistons are used in GMPP crate engines (and others) because they seal the hole better than a straight cast piston and are quieter than forged pistons (cheaper too). The reason I use only forged is because all pistons that are pushed to the extreme will fail.

Once you accept that, you then go on and plan on how you want them to fail. My problem with Hypers is that they are still a cast piston, and as such shatter when they fail. A forged piston goes soft and flows rather than shattering like a piece of dropped ceramic.

I would rather have a hole in the top of a piston, which keeps the rod from going through the block than being the guy every body talks about saying, "Wow did you see that! It just exploded in a big fireball. Lets go get a beer while they clean up that mess."


Larger Dave
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96capriceMGR
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Joined: 23 Aug 2003
Posts: 814
Location: New London Wisconsin
20327.88 points


1996 Chevrolet Caprice

PostPosted: Sun Mar 19, 2006 2:08 pm    Post subject: Reply with quote

If I were going to push a motor then yeah forged would be the way to go, but for most of us hyper works. If "have the have the best" is applied to everything then jump right to a Bowtie or Dart block and some SB2.2 heads, silly right?

Yes hyper are cast and yes they will crack if detonated under spray, but treat them well and they will return the favor.
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osmiumfoot
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Joined: 11 Jun 2002
Posts: 299

2387.84 points



PostPosted: Tue Mar 21, 2006 6:48 pm    Post subject: Reply with quote

I vote for forged for the extra $150, and my choice would have nothing to do with the spray you're planning on. I think hypers are fine with the levels you're talking about. However, when a valvespring decides to slit its wrists, you definitely want forged. I put an outhouse symbol in a piston that you wouldn't believe and the engine lived. If it had been cast or hyper there would have been carnage.
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