Can anyone tell if these are stock?

[bandit]

Can anyone tell if these pistons are stock? The previous owner changed some things on the car to race it (4 speed, Dana 60 with 410's, hd leafs in back) and started me wondering if he bored out the cylinders and replaced the pistons. I do know the 383 engine was rebuilt some time in the past. I had the heads off last year but it never dawned on me to measure to see if the cylinders were bored. I did take a pic while the head was off though. Can anyone tell if these are stock pistons by this pic?

 

[Redhorse719]

They don't look stock to me.

 

[Mopars & Missiles]

Here's a set of stock '69 pistons in a 383HP engine.

 

[Seax440Dodge]

not stock

 

[bandit]

Thanks for the pic. Good to know. Can anyone tell anything from seeing the tops? What brand or type these possibly are and if these are made in certain sizes(as in was my 383 possibly bored over)? I know I am stretching for info with this simple pic. Just curious. Not worth pulling the head again to measure it or look for markings but would be nice to know.

 

[Seax440Dodge]

looks like a dome w/ a trough to me

 

[bandit]

looks like a dome w/ a trough to me

What is the point of having these type? I can assume more power but any other reason? Trying to learn. I haven't done much deep engine work besides pulling heads.

I am surprised the previous owner did not swap for a 440 with all the work he did to race this.

 

[Meep-Meep]

As pointed out above - NOT STOCK. If those are in a 383 then you have at least 11:1 compression with an open chamber head; more if in a 440. And you do not want to run those on the street. The other engine with flat tops is what you want.

 

[Seax440Dodge]

What is the point of having these type? I can assume more power but any other reason? Trying to learn. I haven't done much deep engine work besides pulling heads.

I am surprised the previous owner did not swap for a 440 with all the work he did to race this.

like what Meep said: it's to raise the compression ratio w/o swapping the heads, the dome on the piston is meant to take up the room in the combustion chamber, these look to be some higher domed pistons

with these pistons in this engine, later on if you want to swap to a set of closed chambered heads, you don't be able to w/o swapping out the pistons, sure, it might raise the cr now, but it'll bite you in the *** later on in life

 

[bandit]

Why should I not use these on the streets?

Seax, are you saying the higher cr is what will cause me issues down the road or just trying to swap the heads with those pistons in it? Why would I want to go to a closed head vs open? I have no plans on changing anything unless I need to.

 

[Meep-Meep]

Way too much compression for the available pump gas in the older engines. There is a minimum octane required for given compression ratio so to play it safe, and without going into a lot of detail, you want to end up with about 9.5:1 for a street engine.

- - - Updated - - -

Oh, and before you go pulling pistons off rods and replacing them with a stock type flat top, you need to be aware that the entire rotating assembly will have to be rebalanced due to the weight difference of the forged piston vs. cast.

 

[69Bee]

Way too much compression for the available pump gas in the older engines. There is a minimum octane required for given compression ratio so to play it safe, and without going into a lot of detail, you want to end up with about 9.5:1 for a street engine.

- - - Updated - - -

Oh, and before you go pulling pistons off rods and replacing them with a stock type flat top, you need to be aware that the entire rotating assembly will have to be rebalanced due to the weight difference of the forged piston vs. cast.

Only if the rotating assy was balanced when those pistons were put in, otherwise, stock flat tops will go right back in.

 

[bandit]

Thanks for the info! Because I know the older engines want the higher octane, I actually drive up north and mix in racing fuel with non ethanol 91 or 92 to bring it up to approx 96 octane. Not sure if that is enough to make up for these pistons. I could actually take the octane higher by mixing a larger proportion of the racing fuel in but it runs well with the current mix at about 96. What do you think? Go higher???

Am I basically just trying to avoid detonation? I had that issue (not bad, just on stomps) before adding in the racing fuel but is ok now.

 

[Sweet5ltr]

Anything above 9.75:1 on a standard wedge head (non-aluminum) and you are risking detonation with 93 octane. It isn't worth it, drop the compression down as you don't have a prayer at 11:1 compression unless you are running 110+ octane with iron cylinder heads. 9.25-9.5:1 (with 84-88cc heads) are great, street friendly compression ratios with or without the quench effect. In the old racers glory days, bumping the compression ratio was a positive for power as no timing adjustments were necessary as the standard pump 100+ octane fuel was very capable at 10.5:1. With modern fuel/ethanol blend you are lucky to have 9.5:1 and keep a 36* total timing. Local ford guru engine builder states you want no more than 9.75:1 and 32* total timing with pump fuel for the maximum amount of power. Detonation is what kills engines, when going forced induction you see this ten fold. It is better to run rich with safe timing, than be running lean with timing on the limit. Your compression ratio with those pistons will be well above what even your 96 octane blend could handle (more than likely) and if not, you would be near the verge of detonation every time you got into the throttle. Trust us, it isn't worth it.

 

[dryheat]

You've received some outstanding support and advise in this thread. I'll assume that the motor has some git up and go so ... If you like the way the car is running today then drive it like you stole it until she lets loose and then rebuild it.

 

[Seax440Dodge]

Why should I not use these on the streets?

Seax, are you saying the higher cr is what will cause me issues down the road or just trying to swap the heads with those pistons in it? Why would I want to go to a closed head vs open? I have no plans on changing anything unless I need to.

Back when I was in high school I saved my little McD's checks and slapped together my first 440 (ported 452 heads, .509 cam, single plane m1.. 3.23's and a 2400 stall) and I was impatient, and didn't do enough research before I started throwing money left and right (but more on that later)... anyway, both of the major mail order companies were out of stock on the pistons that I wanted that would put me pretty close to zero deck w/ a flat top, they did, however, have a different set in stock that was the same price, and advertised a little more compression.. they looked a little something like this:




Now these worked fine with my 452's (they're open chambered, so the step had a place to go), and the engine was fun to play with (sounded like a dragster, but was doggy on the bottom end though for what it was, I didn't have enough gear or enough stall for what it really needed). Fast forward 16 years. I'm a little smarter now (though some people will argue on that one), and I'm at a stage in my life where I can go out and get the nice things for my car, so I went on a little shopping spree: new cam, set of gears + new suregrip unit, a fancy schmancy aluminum water pump + housing, and to top it all off, I score a fancy set of aluminum heads for a screamin' price. Remember those nasty stepped pistons from earlier in the story? Well these fancy aluminum heads I score are closed chambered... meaning there's nowhere for that step to go to w/o trying to punch the head off of the block, so I can't use them.



Long story short: some day years down the road a stepped/domed piston might limit your choices on head selection

 

[lewtot184]

those look like the old TRW 12:1's. i ran them once, back in the day. very heavy power robbers. the slot is to clear the spark plug, which ought to tell you something. the plug is heavily shrouded creating poor flame travel and a power loss. as said there is no way those pistons will run on pump gas. if i remember correctly the domes are solid and can be machined off, but why jump thru those hoops.

 

[Cranky]

What cam is in the engine? You can run 11-1 on the street but you need to know what you are doing. A lumpy cam usually bleeds off a lot of cylinder pressure in the lower rpm ranges and can keep the engine out of detonation but the whole combination is very important to do that. Also, if you clean off the top of a piston on the quench side (flat part), there should be a number and/or even a name like TRW or Speed Pro etc. There will also be a .030 on stamped in them if the engine is .030 over. If it's a standard bore, there won't be an over size stamp. Those looks like TRW/Speed Pro to me.

 

[bandit]

Thanks for all the advice guys. I really have no intentions of rebuilding the engine unless I have to. aka something fails or I lose major performance. Not in my skill set nor do I have the tools or room to do it. I would probably send it out or better yet, upgrade to a 440. Cash is limiting that dream right now though.

Yeah the engine has some good power. I have a Dana 60 with 410's in back so it is really nice off of the line.

I can always put pure racing gas in(110 octane around here) but is about double normal gas prices. Around $8.00/gallon.

I have no idea what cam is in this. Never pulled it.

Not to oversimplify all the good advice but it sounds like the main issue keeps coming around to detonation(pinging). Can I safely assume that if I have no pinging, I am ok or am I missing the point here. My car runs fine and I do not notice anything wrong. I opened this question mainly to see if others could tell if my cylinders were bored out and if the pistons were stock or not.

 

[Mopars & Missiles]

Not to oversimplify all the good advice but it sounds like the main issue keeps coming around to detonation(pinging). Can I safely assume that if I have no pinging, I am ok or am I missing the point here. My car runs fine and I do not notice anything wrong. I opened this question mainly to see if others could tell if my cylinders were bored out and if the pistons were stock or not.

Yeah, keep running it and enjoy it until there is a real problem that pops up, and not a theoretical one.

Keep the wheels a spinnin' and the girls a grinnin'.