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Discussion Starter · #1 ·
i have a 4 bolt main 350 with a "mild" cam/650 holley 4 barrel carb, 882 heads with a 3 angle vavle job and high rise intake....but it has swimming pool pistons .30 over...i picked this motor up for $75.00 and im debating on is it worth changing the swimming pools to some flat tops i have lying around....
i want the car to be alright but not asking it to be a speed demonwill they'll be that much of a difference ?
 

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Maybe...it all depends on what compression you come out with. I would think with 882 heads (76cc) you may want to go with some small dome pistons to get your compression up.
 

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I just used Pat Kelley's formula, and with flat tops, I would estimate about 9:1 compression with flat top pistons. It may be good for you, if you want to run pump gas !
 

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Discussion Starter · #6 ·
this is whats in the motor now..., my dad said there swimmin pools/dished
http://kb-silvolite.com/images/feature/fhr2.jpg
..... and the flat tops i have lying around look like these execpt there longer
http://www.edelbrock.com/automotive/autopartsphotos/valve_cvrs/4407.jpg

is there a big difference in these pistons for me to change them out or will it run good the way its set up now...id like it to be better than my old motor
350 4 bolt stock bore,., WORN out it beat a stock mustang gt with a spun bearing and rods knockin :)
flat top pistons
882 heads stock
street dominatorintake
650 carb
long tube headers to flows
mild cam "no idea what kind"

my new motor is a
350 4 bolt bored .030 over with dished pistons i guess
same 882 heads with a 3 angle job
same mild cam
street domintator high rise intake
650 carb
long tube headers to flows
 

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Leave the dishes, go to a 64cc head. That's the easiest power plus no rebalancing, etc.
 

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A 4-notch, flat-top pistoned 350 w/ stock, .020" thick shim headgaskets and 64 cc heads will be right at 10 to 1 CR. even tho it's spec'd at 10.25 to 1!!

Excellent for good pump gas and anywhere from a 268 to a 274 cam too! Even the great old L-79, 350hp/327 cam, the old -151 jobber too!!!

You are more than likely about 7.9 to 1 or maybe 8!!

And the 64 cc heads should get you up to about 9.23 to 1 CR., if I remember right??

I haven't ran the numbers..

Try here..

http://www.campbellenterprises.com/Race math calculators.htm

Use -5 cc's for the 4 notch, flat-tops and -12 for the dished ones you have, then 64 and 76 for heads and .020" thick and a piston DITH of a stock, .025"....

Have fun running numbers.... It's a hoot to me!!

pdq67
 

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heads might be easier, but more expensive, if he allready has the pistons, its just time, and getting the pistons installed onto the rods.
I say do the piston swap.
Still looking at a rebalance. put the money in heads instead, 64cc or so and maybe some large intake ports?
 

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Either route you take, its going to snowball into something bigger. As said, change pistons, balance job is required, regardless.

Add onto the list, rings, bearing shells, oil pump, gaskets, heads, it never ends.

The new engine in its present configuration probably runs well as it sets, a good torque engine.
 

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Discussion Starter · #13 ·
thanks for the input, i know the flat tops would give me more compression but would it make my car FASTER as in like a whole car leangth faster ...thats what i was asking .... cause if the flat tops will make my car a car length or so faster id love to change the dished ones out...but if it dosnt make it that much faster im not going to bother
 

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Still looking at a rebalance. put the money in heads instead, 64cc or so and maybe some large intake ports?
Either route you take, its going to snowball into something bigger. As said, change pistons, balance job is required, regardless.

Add onto the list, rings, bearing shells, oil pump, gaskets, heads, it never ends.

The new engine in its present configuration probably runs well as it sets, a good torque engine.
I guess it depends on the present condition of the engine, and how HIGH-END you want to get with it, PLENTY of low buck rebuilds have had new pistons installed WITHOUT rebalancing the assemblyand lived happy lives. Its just not NECESSARY on a budget motor like this imo.
Before complete dissasembly I would find a leakdown tester and get an idea of wether the engine is healthy now or not. If not, plan to freshen it up.
As for the bearings,oil pump, heads, if they work now, just throughtly clean and inspect them and measure bearing clearences with plastiguage(I know not perfect) and re-use them. I might spring for rings if everything else looks good. If things dont look good on the inspection, then you shoulda been taking the engine down ANYWAY! and completely freshening it.
So long as your enbine is in good condition now, and with carefull attention to the details this piston swap will cost you very little since you allready have the pistons.
 

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He, He!!

I like the way 3p thinks here b/c he's just gotta be "shade-tree" like me!!

My old junk 301 sure wasn't balanced and would rpm right up there w/ the best of them!!

NOW, I do have to say that I would balance a cast crank rotating assembly, but, heck a forged crank is tough as nails and will last a LOOOOOONG time street driving her stop light to stop light!!

pdq67
 

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A small combustion chamber and reverse dome makes SLIGHTLY more power than flat top with larger chamber. Leave the dishes, pick up some Vortecs and go to town. That's the best bang for your buck, period.
 

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Do you have a part number for the flat top pistons? Are they cast replacement type pistons?
There are 2 reasons why I ask. For one, the engine I built for my '78 1/2 ton truck (now in my '86 truck) was an original '77 passenger car dished piston engine. When I rebuilt it I changed to stock replacement type flat top pistons and did not rebalance it. It runs fairly smooth...although not as smooth as the balanced 388 in my nova...but it is ok. I have been driving it this way since I built the engine 8-9 years ago.
Second, most cast and some hyper flat tops come with a 1.54" compression height, versus a stock piston at 1.56". What this means is that the piston ends up an extra .020" in the hole, which hurts compression and quench. These type pistons will end up around .045-.055" in the hole on an undecked block. If this is the type of piston you have, then you will only gain about .4 to .5 compression...not worth it in my opinion. You would be better off with milling .020-.030 (assuming they are unmilled now) off the heads and using fel-pro 1094 head gaskets (.015" thick).
 

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I have to add that MOST engine reman outfits DO NOT re-balance an engine when it gets re built with new pistons, what does this tell ya.
the flat tops AND the vortec's would be the best :)
 

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Josh:

I am in process of having my 350 rebuilt.What I am changing is the cam, staying with replacement flat tops. The cam is a 350/350hp OEM. The heads on my 350 are 0462 camel hump 64cc and using the Q-Jet I have. The car will have a little more "attitude" at idle and the lights but because of the 2:73 rear end still will cruise down the highway the way it was meant to.

Good Luck!

Dave
 
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