H855cp

You will not get the advertised compression ratio unless the piston is set at zero deck height and you use a .020" thick head gasket.

Find out what cc the piston dishes are and the pin height.

Keep in mind these are cheap stock replacement parts, don't spin them over 5200 RPM for very long.

 

If he uses these;

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AutoTec Forged 350 Buick Dished Piston and Ring Kit:
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• 
  [*=left]3.830 Bore (.030 Over)
  [*=left]-13.5 CC Dish
  [*=left].945 Pins (.005 oversized)
  [*=left]1.850 Compression Height
  [*=left]9.75 to 1 Compression
  [*=left]Includes Premium Ring Set
  [*=left]Valve pockets for oversized valves and big cams

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[TD]Part #: 29734

Price: <meta content="USD" itemprop="priceCurrency">$719.00
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He can have them customized at no extra cost, here's what the company says about their pistons.

"AutoTec is a High Quality, Precision Manufactured piston option. That comes at a very respectable price. Our Design Specific Forging allows us to manufacture our parts with less machining time, thus allowing us to keep production cost down. Then pass that savings on to you, the customer. Made out of 4032 High Silicone Aluminum Alloy, it has great wear resistance, a low expansion rate, is very durable, and is very low in friction. These pistons accommodate multiple uses including. Your local auto shop, muscle car restorations, performance street rods, as well as many spec racing classes. They can also withstand mild nitrous kits and small turbo or super chargers. Just about everyone can benefit from the excellent value the AutoTec line carries. Keeping in mind these pistons were originally designed for about 600 Horsepower. In Small Block applications, we have customers that frequently fine tune engines that yield 850+ Horsepower with a bit of Super Charger boost. Bore, Ring Pack, and Compression Distance changes can be made to any shelf part at no extra charge. Meaning that if you do not see your application listed in the guide, we can make what you need without charging a custom price. Every part is made with same high quality machines and tools as our RaceTec line including diamond turned ring grooves, and skirts. Not to mention our parts are 100% made in the USA."

These will work for a 340 as well because the bore size can be customized as well as the dish cc and compression height to get whatever compression ratio is desired. These are also available as flat tops but would be way to high a compression ratio for the street for pump gas because the compression distance can be controlled to a zero deck height with minimum machining. The rings are included in price. GL

Derek

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Even though the 350 heads are an "open chamber" design with the piston at zero deck there would still be a slight benefit with a higher compression application with a quench ring instead of a quench pad with a closed chamber head.

Also these pistons are forged so they are capable of revving over 5200 safely even as high as 10,000 PRM if someone can get one of these to rev that high. The 4032 forged pistons are great for the street because they can run tighter clearances in the bore than the 2618 forged pistons and would be a more durable for a street app. The 2618 is more for the high end race pistons app like very high boost and big shots of N02. The 4032 material can still handle 200 HP shot of N02 or 10 PSI of boost.

 

Steel shim head gaskets only work with early heads without scallop coolant passages. I suggest milling block .030 -.035 and using felpros. With 340p pistons that nets about 9.78 if piston is in hole around .030. Hyperutectic h522p pistons have a comp height of 1.855. 10.2 340p pistons have a height of 1.830 (10cc dish)and stockers(28 cc dish) and 3.0 flattops have a height of 1.805. Also I always drill out oil screen passage in block to 1/2 in minimum and add melling 5/8tube screen S20i its about 12 bucks.

 

I was told the the bores are not perfect but could be run, this is before I ventured down the road of replacing Pistons. Is it true that when replacing pistons a good bore will yield best results?
Ta told me that the cam will run with stock compression @ 8:1??

Seems Like I'm going to replace the Pistons (why not improve it while it's apart) so the given options in my budget are the 340p30 or the silvolite 1734-20 flat tops. they both equate to the same $$. Why would I use one over the other??

 

It looks to me as the 340-30 is the easiest way to go with the lowest potential for issues. The other option may cause too much compression for a pump gas weekend cruiser with a possible valve issue.

 

I've found you can run 9.5 to 1 compression MAX with 94 octane without detonation. Depends on you cam. I'd say +/- .2 for street cam variations.

And when I say 9.5 I mean actual measured number not a guess. You have to CC everything and do the math, it's not that hard.

 

The 284 cam wants at least 9.5:1 and would prefer over 10:1... Other people have been Very disappointed in the 284 with low compression. The 212 is a better cam for low comp.

 

Valve issue would depend on how much you mill deck and if you decided to go with bigger valves. There are a few recent builds with same piston/cam setup and the flattops sit .090 down bore of an unmilled block.. But as I mentioned .030 off deck with 340 piston should put you at 9.77 which would be good with that cam. Although that cam has been proven to like higher compression and still work on pump gas . or go E85 fuel and go as high as compression as you want. Some porting of heads would be something to consider at this time also.

 

I'm sure an 8 to 1 engine will run with that cam but you will be dissatisfied with it. A lot of parts have to work well together that just putting a big cam in your engine. If its an auto trans you will need a higher stall ,somewhere around 2500 minimum (do not expect advertised stall to be that stall on your engine as that's more of what if rating is what if you had a big block with lots of torque) and a 3 series rear end gear.
But the bottom line is many guys on here have done made the mistakes on engine build that did not live up to expectations so take their advice so you can get this right with little if any mistakes and expense.
If you want to go back to stock compression just freshing up your original stuff. Throw a 212 cam in it and spend some money on porting. I would still deck block at this level as the 350 likes compression.
If you decide to go for higher compression then figure the pistons and deck block .035 with the 284 cam. Again porting has shown to wake up this engine ,even more so with bigger valves.
J.Staged and Taulbee both I think run the 310 cam and with alot of head milling and porting with big valve have gotten low 13 second 1/4 mile times and is still street driven. Mark Demko is still learning but his street driver is in 14s with hi mph that shows he can be in 13s.
So the combos are proven street able and these guys on here will help you get there too.

 

or ask the guys who run 11's in nhra stock class with the 350's. they run the apollos and one guy southwest runs a 73 century.

 

So I'm going with the 10:1 advertised 340-30 Pistons and I already have the ta 284 cam. I'm about at the top of my budjet for a cam swap:laugh: my crank is .010 under the only bearings summit sells in that size is king engine? Then as far as more milling goes, does it have to come off the block or can the heads be done to achieve the same results. I ask because I could get my block back now and do the heads later but I'm guessing no. Is it going to make a substantial difference? I guessing headers and intake are going to have to wait till next year

 

You need to take more metal off heads then off block . and that could cause intake fittment problems where you will need to mill intake or intake side of head. The block is taller than blueprint and more than likely not square either. Mill block then have them square up decks.

 

The issue is that the machining has all been done as of now except for now boring .030 over. Yes I know it can go back on the mill but......$$$$

 

Summit only lists what they have previously sold recently on bearing stuff. Call and see if they can look up federal mogul. Or check with machine shop. Jeg and northern auto might have it listed. Falcon on eBay. Although king is supposed to be a good bearing

 

That is why the flat tops are good, no need to mill to get over 10:1....

 

This is my Ross piston. 33cc dish. Will be at .005 above deck with only 8.9 compression. Will still create quench with open chamber head .there is more force against piston this way vs cylinder wall as combustion happens. More efficient design than flat tops when piston is below deck .090 . there is a reason they zero deck Chevy's and fords and its not just to get compression up. That's why I believe you should stick to 340 piston and deck block. And then square block. I have used the flat tops and the hyperutectic pistons and have made decent power but never reached my goal of 400 HP with any setup . learn from mistakes and trying to build a better engine this time. If 280-300 is your goal then you are close. If your going to want more then you have to go farther.

 

Marc is not building a race engine. He wants basically a stock one with a little more power. A small cam and later down the road, bolt-ons such as headers and intake manifold.

We are trying to get the cr to about 9.4. I will be cc'ing the pistons, heads and checking the deck height once we get the parts back from the machine shop. New 340 pistons will be used. We will most likely attain the 9.4 by milling the heads .020" (good for .5 point according to info found here) or by using steel head gaskets.

I haven't worked on a 350 Buick in so long that I don't remember a lot of things.

Can someone post a picture or a block and or head that shows the difference between the scalluped and non-scalluped versions? The steel head gaskets can be only used with which version? Seems to be conflicting info here on whether 72 350's might have come with steel head gaskets or not. Marc seems to think that his did but can't find the old ones and doesn't remember for certain. If steel head gaskets can't be used, I will have the machine shop take .020 off the heads. It isn't in the budget to square-deck. For Marc's goals, that will be just fine.

Second question, is the TA cam Marc chose (284) compatible with stock rockers and springs? TA says that it is, so it should be, just want to be certain. Would the 212 be a better choice?

 

It does seem to me when there has been any questions on this, it looks like the 212 cam is the best choice. The 284 cam has a little more on the duration and a little more lift. Exhaust side is same as 212. The 294 looks to be a nice cam but you probably need 10.0 comp for that one.