340 Piston Selection

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yellow rose said:
If that part where the dome should be (the bottom of the piston when it's installed) is higher than the flat above the valve notches then yes, it needs to come out of the hole.

I never EVER deck the piss out of a head to get compression. One, it can be a flow killer. Two, it's a waste of heads. The engine is DESIGNED to have the piston positive out of the deck. That's the way it should be done.

You are running enough cam that I'd be damn sure (and the ONLY way to be damn sure is to measure the volume by doing the 1/2 inch downfill and then doing the math) I had at least a measured 11:1 and if you get to 11.25:1 I damn sure wouldn't worry about it.
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Thank you Hoss
Im taking in all u saying believe that
 
yellow rose said:
If that part where the dome should be (the bottom of the piston when it's installed) is higher than the flat above the valve notches then yes, it needs to come out of the hole.

I never EVER deck the piss out of a head to get compression. One, it can be a flow killer. Two, it's a waste of heads. The engine is DESIGNED to have the piston positive out of the deck. That's the way it should be done.

You are running enough cam that I'd be damn sure (and the ONLY way to be damn sure is to measure the volume by doing the 1/2 inch downfill and then doing the math) I had at least a measured 11:1 and if you get to 11.25:1 I damn sure wouldn't worry about it.
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How would cutting a RPM 340 head kill any flow? Have you actulay seen one of those heads?
Im not saying that im perfectly confident that those heads will take it without problems but that option should atleast be taken a good look at before taking any more steps.

My opinion is that positive deck engines are stupid,unless we are talking about an engine that requires a domepiston then they are just alitle less stupid and its quite obvious that theRPM340 heads are an aftertought.
 
1Fast340 said:
How would cutting a RPM 340 head kill any flow? Have you actulay seen one of those heads?
Im not saying that im perfectly confident that those heads will take it without problems but that option should atleast be taken a good look at before taking any more steps.

My opinion is that positive deck engines are stupid,unless we are talking about an engine that requires a domepiston then they are just alitle less stupid and its quite obvious that theRPM340 heads are an aftertought.
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If his heads have a .060 recess cut in them, the piston needs to be out of the deck.

As for killing flow, you'd have to spend some time on a flow bench. It damn sure does affect flow. Think about how important a top cut is. Then you move the deck closer to the top cut? Bad idea. You can mill a head within reason. To run a zero deck and then deck the piss out of the heads to get the CR you want is *** backwards.
 
1Fast340 said:
Ok i will admit that i have not done the whole math thing on this ,but we are both in kind of the same boat and i did some research on this years ago before i took along break from this so my math is not great on this and i have not figured out if the valvepockets would end up being a problem in this case,the only real difference here is that i havre fresh.030 bore and a somewhat similar cam bit mine is a roller.

Your heads will probably not be 65CC anymore when the headportingshop is done with them,they will probably be alitle bigger.

I would not go with a popuppiston that sits above the deck for a whole bunch of reasons.

I would do a zero deck flattoppiston and cut the heads until i get the desired compresion.

I have read in the past that RPM340 heads are supposed to be possible to cut until they are closedchamber without isues and at that point they will be closer to 55CC but i have not done the math on this,and at that point you will have ended up needing to cut the intakeface of the head aswell a bunch to make any intake fit again,this is just what i have read,i have not measured or calculated this and can not say for sure if this is correct.

Another problem that may show up at this point after cutting the heads 0.060" or so is that the valvepockets in the pistons may not be deep enough anymore but i cant say for sure.

Sure you could get there with either a set of those heavy TRW/Speedpro/SealedPower #L2316 whatever they may be named nowadays pistons or a custom popup piston but at that point if you want to upgrade your heads at any point in time in the future you are screwed again and need to change pistons or go for a ridicilusly thick headgasket.

The other option is some kind of domepiston and at that point you have either ancient TRWL2322 pistons with huge domes (if you can find a set,they show up from time to time for sale brand new )that fits a stock head but will not fit a edelbrock chamber im sure those domes can be reshaped to fit a Edelbrock head since they can be cut down to flattops but i bet its a ton of work to get right and you are once again stuck with a popuppiston that wont fit any other heads except open chamber garbage. Ross makes an of the shelf dome piston aswell(atleast in .030 over)but once again its made for a stock head and the dome wont fit an edelbrock chamber,they may be possible to cut and reshape to fit your heads but who knows. They TRW L2322 piston is quite heavy but not as heavy as a L2316 piston,the ross domepistons are a bunch lighter

I think i have read that Diamond might have done domepistons for RPM340 heads but i have not seen them in the catalog.

This is the reality of pistons for the 340RPM heads its nothing wrong with the head itself its a rpm head but the whole option of that openchambercut makes them a damn headache to anyone who wants to do something hotter with them than bolting them to a stock shortblock and have fun. I have a very well ported set ontop of a 345cui shortblock in my garage and i regret not getting the closedchamber version everytime i look at them it was a damn stupid mistake.
The thing is that you will end up having to cut quite alot to make them closed chamber and get some kind of squish/quench or whatever you like to call it.

There are other opinions in this thread and i think more people could have more and better opinions and possibly options,but i would not go for another popup piston build,i would certainly go for a zerodeck flattop and cut the heads until compression is where it needs to be,and possibly cut deaper valvenotches,im not sure about that part.

Darn it,i was wrong on Mahle,found the place where i saw .040 over pistons for a stockstroke 340 and they where made by SRP
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What he said X’s 2!
 
yellow rose said:
I never EVER deck the piss out of a head to get compression. One, it can be a flow killer. Two, it's a waste of heads. The engine is DESIGNED to have the piston positive out of the deck. That's the way it should be done.
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Disagree. Just because the engine was designed from the factory that way doesn’t mean it has to be copied in the same way. Even with the Edelbrock head designed to be used with a stock piston.

You are running enough cam that I'd be damn sure (and the ONLY way to be damn sure is to measure the volume by doing the 1/2 inch downfill and then doing the math) I had at least a measured 11:1 and if you get to 11.25:1 I damn sure wouldn't worry about it.
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This X’s 2!
 
yellow rose said:
If his heads have a .060 recess cut in them, the piston needs to be out of the deck.
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While that is the best method, what to do if you can’t? Not build the engine or make concessions?

As for killing flow, you'd have to spend some time on a flow bench. It damn sure does affect flow. Think about how important a top cut is. Then you move the deck closer to the top cut? Bad idea. You can mill a head within reason. To run a zero deck and then deck the piss out of the heads to get the CR you want is *** backwards.
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I agree with the second half of this paragraph. With the first half, I do not necessarily disagree but, it would be closer to working with a closed chambered W head. W5, W2. Power still made with these engines. You just have to take a different approach to how things are done. It is not a huge step. It’s a minor thing that most Average Joe’s would never ever notice.
MAre you trying to squeeze every last ounce of power out of this engine? If not, then do not worry about it. What yellow Rose is saying makes sense if you’re going to start racing for the money. Then again, that would not be the cam I’d use, that would not be the head I’d would use, that would not be the displacement I’d use, ( unless forced to buy the rules!) that would not be the piston that I’d use, those would not be the rings I’d use, etc...

If you can indeed find the proper piston for the job designed with a dome to be used with those Edelbrock heads, then for Shirley, go for it!
 
1Badcolt said:
I - 250
E -254
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What do you come up with when your cylinder head is used for a compression ratio with a zero deck piston with a 6cc valve relief used & a .039 x 4.1 gasket?
 
Do you have all the information needed to plug-in?
 
yellow rose said:
If his heads have a .060 recess cut in them, the piston needs to be out of the deck.

As for killing flow, you'd have to spend some time on a flow bench. It damn sure does affect flow. Think about how important a top cut is. Then you move the deck closer to the top cut? Bad idea. You can mill a head within reason. To run a zero deck and then deck the piss out of the heads to get the CR you want is *** backwards.
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That recess is assbackwards,its a solution offered to people who already have those tall pistons in an asembled shortblock,its pretty much an extension of the cylinderbore.

Im out of this now,i have given my opinion on this and hope 1Badcolt will find a good solution to his build,i bet it will run great once done nomather what solution is chosen.:)
 
1Fast340 said:
That recess is assbackwards,its a solution offered to people who already have those tall pistons in an asembled shortblock,its pretty much an extension of the cylinderbore.

Im out of this now,i have given my opinion on this and hope 1Badcolt will find a good solution to his build,i bet it will run great once done nomather what solution is chosen.:)
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Thank you all for the valuable info , I will have something to look at in about a month .

20180629_171412.jpg
 
1Fast340 said:
That recess is assbackwards,its a solution offered to people who already have those tall pistons in an asembled shortblock,its pretty much an extension of the cylinderbore.

Im out of this now,i have given my opinion on this and hope 1Badcolt will find a good solution to his build,i bet it will run great once done nomather what solution is chosen.:)
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I know what it's for. So you'd tell someone to mill .060 or more off a head and waster a casting rather than fix it right by d caking the block? That's just stupid. I say it over and over and over since 1980, if you are running a 340 and the heads are the open chamber type the piston MUST be out of the bore to get the compression up.

If your engine builder doesn't understand that, kick him to the curb.
 
yellow rose said:
I know what it's for. So you'd tell someone to mill .060 or more off a head and waster a casting rather than fix it right by d caking the block? That's just stupid. I say it over and over and over since 1980, if you are running a 340 and the heads are the open chamber type the piston MUST be out of the bore to get the compression up.

If your engine builder doesn't understand that, kick him to the curb.
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Yellow Rose - im running the Rpm 340 heads this is my first LA engine so educate me on my heads they are basically a performance version of stock head with a little better flow ?
 
yellow rose said:
I know what it's for. So you'd tell someone to mill .060 or more off a head and waster a casting rather than fix it right by d caking the block? That's just stupid. I say it over and over and over since 1980, if you are running a 340 and the heads are the open chamber type the piston MUST be out of the bore to get the compression up.

If your engine builder doesn't understand that, kick him to the curb.
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Ok i said i was out and you want more answers?
The correct solution is to not buy those heads in the first place,the ones with closed chambers are a better starting point then mill them or fill the chambers to the size required to create the desired compression with a flattop,but 1Badcolt is past that option now.
Seriously doubt the heads will be wasted my milling them to closed chamber,but i would confirm the deckthicknes with Edelbrock first or someone who has done the same in the past,i know it has been done.
Decking the block until the piston is .060 out of the bore or whatever is required seam incredibly inteligent to make sure that the block,head,intake and rotating assembly combination has no chance to ever be used again with a different set of heads in the future if plans change as they often do but hell in 1980 there where still plenty of unmolested 340s around to waste.


Thanks for the advice,i will kick myself to the curb or in the *** or whatever when i get my heads cut just that much to get my **** done less wrong than it was in the first place,after making damn sure the heads have enough meat to cut that much,but i doubt it will be a problem.
 
1Badcolt said:
Yellow Rose - im running the Rpm 340 heads this is my first LA engine so educate me on my heads they are basically a performance version of stock head with a little better flow ?
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Since i was dragged back in here by Rose,yes they are a performance head that fits most stock parts.

They are good heads,its just that recess in the 340 version that is stupid since its made for a piston that no one that builds a new engine wants to use if it can be avoided. The regular RPM head is a better option in the first place for anyone that gets new pistons anyway,however those will have to end up being cut aswell or get pistons with some oddball dome to make the compression you desire with a little 340 cube engine its just part of the nature of these small engines.

It takes alot of confirmning specs on parts,thinking,measuring and matching parts to build an engine right in the first place,dont feel intimidated by it,it might seem alitle overwellming at first but you will figure it out.

Im out for now :)
 
1Fast340 said:
Since i was dragged back in here by Rose,yes they are a performance head that fits most stock parts.

They are good heads,its just that recess in the 340 version that is stupid since its made for a piston that no one that builds a new engine wants to use if it can be avoided. The regular RPM head is a better option in the first place for anyone that gets new pistons anyway,however those will have to end up being cut aswell or get pistons with some oddball dome to make the compression you desire with a little 340 cube engine its just part of the nature of these small engines.

It takes alot of confirmning specs on parts,thinking,measuring and matching parts to build an engine right in the first place,dont feel intimidated by it,it might seem alitle overwellming at first but you will figure it out.

Im out for now :)
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Ten 4 thank you Hoss
 
Found another option,some dome pistons has solid domes that can be cut down to fit different chambers or even be made into flattops with a popup,might be worth looking into,there is two partnumbres for a 4.08 bore 340.
340
 
1Fast340 said:
Found another option,some dome pistons has solid domes that can be cut down to fit different chambers or even be made into flattops with a popup,might be worth looking into,there is two partnumbres for a 4.08 bore 340.
340
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Thank you for your help obviously I messed up by purchasing the 340 Rpm head I should have just purchased the reg 340 head .
Im ordering custom pistons next week and will need some guidance from u veterans within the forum . Machine shop said that mycontent://media/external/file/91436.block
1Fast340 said:
Found another option,some dome pistons has solid domes that can be cut down to fit different chambers or even be made into flattops with a popup,might be worth looking into,there is two partnumbres for a 4.08 bore 340.
340
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Thanks for your input Im ordering custom pistons for my project and will of course need some guidance.
Machine shop said my block needs decking so other than that my components are cut and dry
Im running stock stroke with factory steel crank and Scat 6.123 H beam rods and would like to have around 11.5.1 or just under 12.1 compression I found a nice piston with the specs close to what I want but of course its offered for the 4.0 stroke engine.
 
1Fast340 said:
Found another option,some dome pistons has solid domes that can be cut down to fit different chambers or even be made into flattops with a popup,might be worth looking into,there is two partnumbres for a 4.08 bore 340.
340
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Check these out if u get the compression ratio is where I want to be !
These are nice but of course made for 4.0 stroke set up versus what I have stock stroke Im going to get a custom set made but hopefully the tech guy can achieve that with my odd heads the 340 Rpm !
 
I wouldn't order the pistons untill the block has been square decked, and you know the actual finished deck height.
 
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