350 Pistons

OK I'm in the process of rebuilding my 1970 Buick Skylark 350 4bbl. The machine shop called and stated that the skirts on the pistons were damaged due to over carburation at some point. I'm in the process of trying to find a new set of 9:1 compression pistons without much success. The ones I'm finding are 8.5 or 10:1. I was advised NOT to install the 10:1 pistons due to the octane being so low. Anyone have any ideas or suggestions on where I can locate 9:1 pistons?

 

These are whatever you want them to be;

http://www.buyracingparts.com/pisto...totec-forged-350-buick-dished-piston-kit.html


Customizable to whatever you need;

"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."


GL



Derek

 

Go for the 10:1, they wont actually be that ratio in your engine, more like 9 to 1
Damaged skirts from "over-carburation"o No:
Never heard of that one:laugh:

 

Mark is very close. The 10 to 1 Pistons at .060 depth and 10 cc dish , fel pro .045 gaskets and 58 cc head is about 9.2 actual. There a set of Keith black Pistons that have 1.835 compression height would be the closest to 8.5 with an actual 8.25. Most Pistons are 1.801 compression height which could be .090 down hole with an actual compression of 7.7.
Silvolite hyperitectic are about 9.8 with a 1.855 compression height .
Go with the 340p piston .
S1749h are the Keith black Pistons . With .030 off block should be 8.74 compression. Those would be the most inexpensive choices.

 

I think the shop meant that fuel wash past the rings led to the oil film breaking down, etc...

 

Yes that's it. Thanks for clarifying that. Thus far I've been unable to locate any 9:1 pistons for my 1970 350, only 10:1 pistons. I find that a bit odd.

 

So I'm leaning towards the S1749H pistons mainly because they get me closer to the 8:1 compression mark and what I believe to be stock. The 340P according to the information above average to around 9:2 which is above stock. My main reason in selecting around the 8:1 compression is the unavailability of a higher octane needed for the 9:1 and my concerns it will through off all the other stock components on my 350 Buick. Am I over concerned here?

 

What octane fuel is available? 9 to 1 will work fine with most fuels if cam design, timing and fuel metering are used properly. You would have to measure your dynamic compression to fit withing your fuel requirements. I assume you have a 89 equivalent so a stockish cam would work fine. I think Gary goes with the cs647 sealed power replacement. At 9 to one you should make more power then the stock 350-2 since compression was about 8.4 on the steel shim gasket engine. Or use the keiyh black pistons with .030 shaved off block for about 8.75 like I mentioned. I think the Crower level 3 cam with 4 degrees of advance would make great power there and still be safe for lower octane fuel.
To get that you would need a piston depth of about .028 with a 24 cc dish,58 cc head, .045 gasket and .030 over piston. That would be around .5 more then stock. Just with piston closer to top of cylinder will make it more efficient. Less burn dwell. If you had the 70 4 barrel motor its a good chance you had an SP code engine or the high compression engine anyway. Check your block . and yes you may be overler concerned

 

The car was originally a 2bbl but someone changed it to a 4bbl. I'm installing a stock Melling cam and all stock parts except a stage1 TA intake and 9.5 2500 stall converter with a rebuilt 350 trans. I'm at 5,000 ft above sea level as well. The head gasket will be a fel-pro gasket which came in the overhauling kit.

 

I suggest a 3 series gear in rear . 2500 stall is quite high for a stock cam depending on which cam grind. But doable as I ran a tci 2800 on a low comp 350. It stalled just over 2400 on the wimpy engine. I would still shoot for the 8.75 at least on compression, otherwise your still leaving a lot of power on the table. Altitude can create an issue for lack of power so porting and/or big valves for better volumetric efficiency will help you stuff more of the thinner air into the cylinder..

 

Ok well I'm convinced to go with the 340p pistons. Got the stall converter from Jim Weiss who assured me it should be ok in my Buick. Fingers crossed and thanks for the advice.

 

That should work well with the stock type cam and the 9.5 convertor. A 3.08 or better would round off the combo well. Buy extra tires. They will easily burn up. A quadrajet power rebuilt quad would work very well there. I'm sure mark will adjust for altitude .

 

You live in New Mexico
With the D/A regularly over 5000ft I don't see how anyone can recommend an thing less than 9.5-1 comp and realistically 10-10.25 would be even better!

 

I haven't found anything higher than a 10:1 piston and that would be the 340P, which is at least affordable.

 

The hyperitectic silvolite h522p has 1.855 compression height and 9.8 compression It's an ok piston but detonation can damage it more then others . The 340p.030 will net about 9.87 with .030 off block as long as piston is about .030 down hole or less. That will work fine .

 

Well, the pistons I linked in the very first reply you can customize them to get whatever compression ratio for the gas octane you want to run. They even sell a flat top piston for really high compression, but that's not what you want for a street car.

Don't let the cost scare you because they not only come with premium rings, the compression distance can be changed! By changing the compression distance you can save on block machining by ordering the piston to be at zero deck without any machining.

Typically the deck height for a sbb 350 is .030" to .060" taller than the factory blueprint spec. Figure in the cost for having the deck milled, plus buying a set of rings separately then subtract that from the above pistons I gave you a link for vs the crappy cast 340P pistons. You will need a machine shop smart enough to be able to measure what the deck height is though so the correct compression height can be ordered.

$649 - $45(guessing what regular cheap cast rings cost, premium rings would be $100 minimum)= $604 - $150(deck milling)= $454 - $75 head milling= $379 actual piston cost. For that price you get a far superior piston with better rings that are lighter and stronger than a cast piston.

Planning your build with better pistons doesn't mean the total build will necessarily be a whole lot more $$ if you have a game plan for the build so a more expensive part pays for itself by being able to save elsewhere. Seems like everyone is only trying to save $$ on the individual components instead of the total build, which can make the cost higher from the hidden costs of making the cheap parts work towards the total build's goal from the extra machining required to make the inferior parts work for the goals of the total build. o No:




Derek

 

WARNING: this post is longer than 5 or 6 sentences, and may or may not contain some controversial topics subject to debate. It will require some reading effort. My apologies in advance.


First of all, the Sealed Power 340p pistons are not crap...maybe if you have something else to sell they are, but for a stock engine turning less than 6k RPM, they're just fine.

Be sure to try and talk him out of using all the other 'crap' stock parts too, and mix up a myriad of take-out parts ranging from chevy's to honda's so he'll have a truly customized engine that is totally necessary for a bone stock car.

I suggest the OP reads up on the pros and cons of cast pistons somewhere other than this website. Seems everyone has some kind of hidden agenda and if you step on the 'wrong' toes, it can land you in some seriously hot water (I'm being very clandestine and polite with this statement...). Anyone who actually NEEDS better than OEM stuff is going to get it anyway. No need to shove it down their throats.

We've always needed a 'racing' section for the sbb instead of just one forum for all of it, because all the hot-rodders have been trying to take this forum over ever since the beginning, and anyone wanting original equipment parts or restorations of these old engines are bullied off the forums, except me (for now), who has taken so much heat for it from almost every angle.

I have gotten lots of emails and PMs from guys who refuse to post anymore out of fear of being ridiculed for not wanting to build a hot-rod engine, because every time it gets brought up, all you see are suggestions for building anything BUT a stock engine. It is only now (after 3 years of trying to get it more attention), that you see some people suggesting a stock cam or other stock parts, and they are sure to let everyone know that it's not their idea, but mine. lol

Hey I'll take that though. It's better than nothing at all. You won't find anyone telling you the pros of using the stock cam except me (I'm sure there's some old posts on this forum you could find), even though the OEM cam is better than anything else out there (all things considered) outside of a more performance oriented cam with a noticeable lope, and that's only if power is your ultimate goal. Even the Crower level 3 cam only has about a 13 hp edge over the 'crappy' stock cam (which produces similar torque when the DCRs of the two are the same, along with installing it as Crower suggests @4* advance), and isn't as 'user-friendly' to install for a novice engine builder, saying nothing of the extra parts needing to be bought just to install it, tighter springs, and closer attention to proper compression match so it won't go too high and detonate on premium because of its earlier intake valve closing point.

This is flat tappet. A roller cam would be best, but this is outside many people's budget, especially for a stock-mild rebuild, so it won't get my recommendation in this particular scenario.

(If you want more detailed reasons as to why aftermarket cams with earlier intake valve closing points produce more initial power when used with factory assembled compression ratios, there are posts here on this forum by yours truly explaining why--hint: think dynamic compression ratio)

I could even go on to tell you that the more stress you place upon engine components (i.e., valvetrain components), the shorter the lifespan you can expect out of it, but even THIS is disputed! A basic understanding of science should give you all the answers you need here.

On top of all this, Sealed Power makes a .030 set of lower compression OEM replacement pistons for the Buick 350 (657p), which are way cheaper ($132) than even the 340p set. You start off with lower compression, and can mill your deck and/or heads to raise it up a bit to where you want it for use with regular pump gas and the Federal Mogul cs647 cam. Somewhere between 8:1 and 8.5:1 static compression should get you where you want to be with that cam.

Link for those is here: https://www.summitracing.com/parts/slp-657p30/overview/make/buick

This would put you at 1971+ specs. If you want 1970 specs, use the 340p pistons, Fedeal Mogul cs647 cam, and use premium fuel (depending on where static compression ends up being and your timing tune, you may be able to get away with 89 octane 'mid' grade).

Either way, as long as your tune is good, you'll have plenty of street power. Realize that the '10:1' and '8.5:1' are just labels--generic terminology used as descriptors for pistons with certain deck height and dish size parameters. Your actual compression will vary depending on what all else is done. Use this as a basis for determining your dynamic compression for the camshaft you choose to use and subsequent octane rating of fuel.

I hope this information is helpful.

Let the condescending ridiculing begin.

Signing out.


Gary

 

You post like you're a persecuted(can't say whom), so easy you get but hurt for someone with a different opinion than yours. At risk of Gary being but hurt I have to disagree on the India made cast pistons vs the made in USA forged pistons.(yeah I know, its science and I'm stupid for having a different OPINION than Gary's! He has actually posted that to me in a response before)

Changing the deck height not only incurs the cost of having the deck machined it also incurs the cost of new pushrods because now the deck height is shorter than what it left the factory with which changes the geometry. "Shaving" the heads to bring up compression also has the same hidden cost of now needing new pushrods as well and it all adds up.

A lot of machine shops that have to take off more than .030" off of the deck will charge extra to remove more because tooling doesn't grow on trees and it doesn't last forever. Like I wrote, there will be hidden costs to using cheap parts. Take Gary's $132 pistons for example, $132 + $150(deck machining) + $75(removing the extra material) = $355!! That's $56 MORE than the crappy 340P pistons to get to an anemic 8 to 8.5:1 static compression ratio! There is absolutely NO need to run your compression that low unless you want to boost your engine or want to run it on kitten pee instead of the normal cat pee that is sold at gas stations. 9:1 should be the lowest CR to shoot for with a "stock" cam and will run just fine on 87 if tuned with that grade.

Not trying to make you but hurt and sorry if you feel that way, I'm just sick of the kid gloves with you. Re-read your post, it reads like you're pre-but hurt just to take the time to post! Get the flock over yourself!! If you don't like someone else's OPINION, either ignore it or disagree with it. No need to respond to this post because you ALREADY wrote your OPINION refuting my OPINION. But because you forgot to write down the hidden costs and where the 340P pistons are made I felt it necessary to inform people of them.

The OP can buy whatever pistons he wants to, I just want him to be aware of the hidden costs involved to make them what he wants the engine to be. Either get the customizable pistons or have the block custom machined to fit the pistons, get your machine shop to quote what the machine work will be to get you where you want to get with the lesser expensive pistons then add those machining costs up and see which one is more cost friendly. The link I posted was for the more durable longer lasting 4032 forged pistons not the race type 2618 forged piston material.

Seeing how it was pointed out that running higher compression is a good idea because you live in an high altitude environment using forged pistons is good insurance just incase your engine for some reason has some detonation, which the forged pistons would be more resistant to. Just because you get a good piston doesn't mean its a "race" piston like mentioned. Some people just need to NOT be so argumentative and take disagreeing personal when there is a different path presented, like the same person has written elsewhere "everyone has the right to post here" . Hey Gary I luv yah man, but the but hurt posts need to stop.



Derek

 

Your input is appreciated Derek, but my post wasn't directed solely at anyone.

All info is good info to me. Thanks for laying it out there.


Gary